Te Florida State UniversityDigiNole CommonsElectronic Teses, Treatises and Dissertations Te Graduate School7-2-2004Design, Analysis, and Testing of a Low PressureCryogenic ValveAnthony James GleatonFlorida State UniversityFollow this and additional works at: htp://diginole.lib.fsu.edu/etdTis Tesis - Open Access is brought to you for free and open access by the Te Graduate School at DigiNole Commons. It has been accepted forinclusion in Electronic Teses, Treatises and Dissertations by an authorized administrator of DigiNole Commons. For more information, please contactlib-ir@fsu.edu.Recommended CitationGleaton, Anthony James, "Design, Analysis, and Testing of a Low Pressure Cryogenic Valve" (2004). Electronic Teses, Treatises andDissertations. Paper 4255.THE FLORIDA STATE UNIVERSITY COLLEGE OF ENGINEERING DESIGN, ANALYSIS, AND TESTING OF ALOW PRESSURE CRYOGENIC VALVE By ANTHONY JAMES GLEATON A Thesis submitted to the Department of Mechanical Engineering in partial fulfillment of the requirements for the degree of Master of Science Degree Awarded: Summer Semester, 2004 The members of the Committee approve the thesis of Anthony James Gleaton defended on July 2, 2004. __________________________ Cesar Luongo Professor Directing Thesis __________________________ Steven Van Sciver Committee Member __________________________ David Cartes Committee Member Approved: ______________________________________ Chiang Shih, Chair, Mechanical Engineering ______________________________________ Ching-Jen Chen, Dean, College of Engineering The Office of Graduate Studies has verified and approved the above named committee members. ii ACKNOWLEDGMENTS First, I thank God for His wisdom and His perfect plan for my life.I firmly believe that He is always with me, constantly providing encouragement and fresh ideas when I need them most. Thank you Dr. Luongo and the Center for Advanced Power Systems for providing the opportunity, both financially and academically, for me to pursue my Masters degree. Many thanks to Bill Kottke at Air Products and Chemicals for his vision, experience, and insight during the critical, initial stages of this project.Without his assistance, my journey would have been much rockier. Thank you Danny Crook and Cliff Loughmiller for providing practical knowledge and experience throughout this project.Thank you for rarely criticizing but rather teaching a young engineer the tricks of the trade. Thank you Ed Hill and Tim Gamble for your machining and welding work at the FAMU-FSU College of Engineering.You taught me that transferring computer design to an actual working part may not always be a simple task. Thank you Dr. Steve Woodruff for you many hours of discussion on fluid mechanics.Many days I felt like you were the only person I could talk to.Thanks for listening to my problems. Finally, thanks to my family and especially my girlfriend, Cassidy, who stood by me throughout these two years.Cassidy, you dealt with me when I was grumpy, frustrated, or so excited that I could talk to you for an hour about a project you knew little about.Thanks to you all for encouraging me to stay and get another degree.My experiences during this time have been unforgettable. iii TABLE OF CONTENTS List of Tables ................................................................................................................................ vii List of Figures.............................................................................................................................. viii List of Abbreviations ..................................................................................................................... xi Abstract ......................................................................................................................................... xii CHAPTER 1:INTRODUCTION.................................................................................................. 1 1-1The Center for Advanced Power Systems .......................................................................... 1 1-2Superconducting Magnetic Energy Storage........................................................................ 1 1-2.1Superconductivity ....................................................................................................... 1 1-2.2Cryogenics .................................................................................................................. 2 1-2.3Thermal Radiation and the Liquid Nitrogen Shield.................................................... 3 1-3Liquid Nitrogen Reconditioning and Transfer Station ....................................................... 4 1-3.1Linear Cryogenic Pump.............................................................................................. 5 1-3.2300-Gallon Liquid Nitrogen Tank .............................................................................. 5 1-3.3LN2 Cycle in the LN2 RTS.......................................................................................... 6 CHAPTER 2:CRYOGENIC NITROGEN VALVE..................................................................... 8 2-1Introduction......................................................................................................................... 8 2-1.1Pressure Relief Valves ................................................................................................ 8 2-1.2Floating Valves ........................................................................................................... 9 2-2Valve Design..................................................................................................................... 10 2-2.1LN2 RTS Nitrogen Requirements ............................................................................. 10 2-2.2Specifications for a New Valve ................................................................................ 12 2-2.3LN2 RTS Floating Valve........................................................................................... 13 2-2.4Valve Supporting Structure....................................................................................... 14 CHAPTER 3:FLOATING VALVE ANALYSIS....................................................................... 15 3-1Introduction....................................................................................................................... 15 3-2Valve Set Pressure ............................................................................................................ 15 3-3Pressure Drop with Bernoullis Equation ......................................................................... 16 3-3.1Flow Assumptions .................................................................................................... 17 3-3.2Basic Equations......................................................................................................... 17 3-3.3Temperature Influences on Nitrogen ........................................................................ 18 3-4Modeling the Floating Valve ............................................................................................ 18 3-4.1Flow Regimes ........................................................................................................... 18 3-4.2Flow Geometries....................................................................................................... 19 3-4.3Floating Valve Entrance ........................................................................................... 20 3-4.4Regime A.................................................................................................................. 21 3-4.5Regime B .................................................................................................................. 21 3-4.6Regime C .................................................................................................................. 21 3-4.7Regime D.................................................................................................................. 21 3-4.8Regime E................................................................................................................... 21 3-4.9Flow Efficiencies ...................................................................................................... 21 iv 3-4.10Modeling Setup in EXCEL....................................................................................... 22 3-4.10.1 Divisions 3-4.10.2 Flow Point and Flow Section Calculations 3-4.10.3 Boundary Conditions 3-4.10.4 Iteration Cycle 3-5EXCEL Model Results for Three Piston Weights ............................................................ 25 3-5.1Floating Piston Weight:4.641 lb ............................................................................. 26 3-5.2Floating Piston Weight:6.111 lb ............................................................................. 27 3-5.3Floating Piston Weight:8.252 lb ............................................................................. 28 3-5.4Remarks on the EXCEL Model Results ................................................................... 29 3-5.4.1First Graph:Tank Pressure vs. Floating Piston Height 3-5.4.2Second Graph:Tank Pressure vs. Nitrogen Mass Flow Rate 3-5.5Nitrogen Flow Velocities.......................................................................................... 31 CHAPTER 4:VALVE TESTING............................................................................................... 39 4-1Introduction....................................................................................................................... 39 4-2Testing Apparatus ............................................................................................................. 39 4-2.1Instrument Selection and Placement ......................................................................... 39 4-2.1.1Pressure Measuremen 4-2.1.2Position Measurement 4-2.1.3Temperature Measurement 4-2.2Nitrogen Interface ..................................................................................................... 40 4-2.2.1Compressed Nitrogen Gas 4-2.2.2Liquid Nitrogen 4-3Testing Goals & Procedures ............................................................................................. 41 4-3.1Set Pressure............................................................................................................... 41 4-3.1.1Goal 4-3.1.2Procedure 4-3.2Simmering Effect ...................................................................................................... 41 4-3.2.1Goal 4-3.2.2Procedure 4-3.3Pressure Drop............................................................................................................ 41 4-3.3.1Goal 4-3.3.2Procedure CHAPTER 5:VALVE TESTING RESULTS............................................................................. 43 5-1Introduction....................................................................................................................... 43 5-2Set Pressure Results .......................................................................................................... 43 5-3Simmering Effect Results ................................................................................................. 44 5-3.1Low Mass Flow Rates............................................................................................... 44 5-3.2High Mass Flow Rates.............................................................................................. 44 5-3.3Flow Regimes and the Simmering Effect ................................................................. 44 5-4Pressure Drop Results....................................................................................................... 45 5-4.1Low Mass Flow Rates............................................................................................... 47 5-4.2High Mass Flow Rates.............................................................................................. 47 5-4.2.1Results 5-4.2.2Drag Influences on the Floating Piston 5-4.2.3Remarks 5-5Liquid Nitrogen Results.................................................................................................... 50 v CHAPTER 6:CONCLUSIONS .................................................................................................. 52 6-1Introduction....................................................................................................................... 52 6-2300-Gallon Tank Pressure Relief...................................................................................... 52 6-3The Simmering Effect of the Floating Valve.................................................................... 52 6-4EXCEL Modeling vs. the Actual Valve Performance...................................................... 53 6-5Final Remarks ................................................................................................................... 53 APPENDIX A:Regime A EXCEL Model Results for 4.641 lb Floating Piston ........................ 55 APPENDIX B:Regime B EXCEL Model Results for 4.641 lb Floating Piston......................... 71 APPENDIX C:Regime C EXCEL Model Results for 4.641 lb Floating Piston......................... 86 APPENDIX D:Regime D EXCEL Model Results for 4.641 lb Floating Piston ...................... 100 APPENDIX E:Regime E EXCEL Model Results for 4.641 lb Floating Piston....................... 112 APPENDIX F:Nitrogen ............................................................................................................ 122 References................................................................................................................................... 124 Bibliography ............................................................................................................................... 125 Biographical Sketch.................................................................................................................... 126 vi LIST OF TABLES Table 2.1Enthalpy comparisons for subcooled liquid nitrogen ..........................10 Table 2.2N2 mass flow rates (kg/s) calculated at 200 psi ...................................11 Table 2.3Percentage of LCP pumping capacity required (200 psi) ....................12 Table 3.1Internal tank pressure vs. piston weight...............................................16 Table 3.2Calculation matrix for regime divisions ..............................................22 Table 3.3Maximum mass flow rate through Ledge C before set pressure is exceeded.............................................................................30 Table 3.4Mach numbers for critical flow areas in floating valve .......................32 Table 5.1Measured set pressure for each floating piston weight ........................43 Table 5.2Comparison between calculated and measured set pressure................43 Table 5.3Modeled and experimental pressure drop differences for low mass flow rates..............................................................................45 vii LIST OF FIGURES Figure 1.1SMES Superconducting coil (A), with coil splices and LHe vents (B) inside vacuum vessel (C) ............................................2 Figure 1.2Temperature scale displaying absolute zero (0 K), nitrogen boiling point (77 K), and atmospheric conditions (298 K) ................................................................................................3 Figure 1.3SMES without LN2 shield (left) and with LN2 shield (right) ..................................................................................................4 Figure 1.4Cylindrical air gap linear motor, by California Linear Devices................................................................................................5 Figure 1.5LN2 system layout of major components............................................6 Figure 1.6Heating effect on saturated liquid nitrogen.........................................7 Figure 1.7Heating effect of SMES cycle on liquid nitrogen...............................7 Figure 2.1Simple schematic of a spring-operated pressure relief valve....................................................................................................8 Figure 2.2Simple schematic of a floating relief valve.........................................9 Figure 2.3Nitrogen mass flow rate for temperature change vs. heat load....................................................................................................11 Figure 2.4Cross-section of actual RTS floating valve ......................................13 Figure 2.5Cross-section of valve and supporting structure...............................14 Figure 3.1Free body diagram of floating piston................................................17 Figure 3.2Regions of the floating valve ............................................................18 Figure 3.3Loss coefficients for sudden flow area changes ...............................19 Figure 3.4Coefficient of fluid resistance for discharge from a tube onto a baffle ......................................................................................19 Figure 3.5Bottom view of the actual valve base ...............................................20 Figure 3.6Regime calculation breakdown.........................................................23 Figure 3.7Flow point/section communication diagram.....................................24 Figure 3.8Diagram of iteration cycle performed in EXCEL.Gray boxes indicate values changed during cycle .....................................25 Figure 3.9EXCEL model analysis graph of tank pressure vs. floating piston height for 4.641 lb floating piston ............................26 Figure 3.10EXCEL model analysis graph of tank pressure vs. nitrogen mass flow rate for 4.641 lb floating piston.........................26 Figure 3.11EXCEL model analysis graph of tank pressure vs. floating piston height for 6.111 lb floating piston ............................27 viii Figure 3.12EXCEL model analysis graph of tank pressure vs. nitrogen mass flow rate for 6.111 lb floating piston.........................27 Figure 3.13EXCEL model analysis graph of tank pressure vs. floating piston height for 8.252 lb floating piston ............................28 Figure 3.14EXCEL model analysis graph of tank pressure vs. nitrogen mass flow rate for 8.252 lb floating piston.........................28 Figure 3.15Modified Regime E EXCEL model analysis graph of tank pressure vs. nitrogen mass flow rate for 4.641 lb floating piston.................................................................................................31 Figure 3.16Floating valve entrance for all regimes.............................................32 Figure 3.17Beginning of Regime A.dZ = 0.000..............................................33 Figure 3.18Regime A modeling diagram............................................................33 Figure 3.19Beginning of Regime B & end of Regime A.dZ= 0.047Ledge A of floating piston clears Ledge A of valve base..........................................................................................34 Figure 3.20Regime B modeling diagram............................................................34 Figure 3.21Beginning of Regime C & end of Regime B.dZ = 0.0895Ledge B of floating piston clears Ledge B of valve base..........................................................................................35 Figure 3.22Regime C modeling diagram............................................................35 Figure 3.23Beginning of Regime D & end of Regime C.dZ = 0.188Flow area of Ledge B gap equals flow area of Ledge C gap......................................................................................36 Figure 3.24Regime D modeling diagram............................................................36 Figure 3.25Beginning of Regime E & end of Regime D.dZ = 0.323Ledge A of floating piston clears Ledge B of valve base.................37 Figure 3.26Regime E modeling diagram............................................................37 Figure 3.27Pressure drop for rectangular section elbows ...................................38 Figure 4.1Hand-held digital manometer ...........................................................40 Figure 4.2Static pressure port(top) and gas/liquid input port (bottom) on base assembly pipe........................................................40 Figure 4.3Position indicator fixed above small tube which extends down to the floating piston ...............................................................40 Figure 4.4500 psig pressure regulator ...............................................................41 Figure 5.14.641 lb floating piston Low nitrogen mass flow rate test result averages ............................................................................45 ix Figure 5.26.111 lb floating piston Low nitrogen mass flow rate test result averages ............................................................................46 Figure 5.38.252 lb floating piston Low nitrogen mass flow rate test result averages ............................................................................46 Figure 5.44.641 lb floating piston High nitrogen mass flow rate test results..........................................................................................47 Figure 5.5Flow past a flat plate.........................................................................49 Figure 5.6Drag coefficients for different objects ..............................................49 Figure 5.7Warm vs. cold nitrogen gas experimental results for 8.252 lb floating piston .....................................................................50 x LIST OF ABBREVIATIONS CAPSCenter for Advanced Power Systems LCPLinear Cryogenic Pump LHeLiquid Helium LN2Liquid Nitrogen LN2 RTSLiquid Nitrogen Reconditioning and Transfer Station MLIMulti-Layer Insulation SMESSuperconducting Magnetic Energy Storage xi ABSTRACT The design of a unique liquid nitrogen pumping station requires a unique pressure relief valve.This new relief valve must operate at low pressure differentials, work effectively at low cryogenic temperatures, and release a wide range of nitrogen vapor mass flow rates.A floating valve design was selected, one that requires no springs and relieves pressure based upon the weight of the actuating piston.Before testing began, an analytical flow model of pressure loss through the valve was completed and valve set pressures were calculated.The purpose of the valve testing was to both prove the concept of the valve and verify results from the modeling.Experimental results revealed accurate agreement between the model and the test for low mass flow rates.However, at high mass flow rates, the model and test results did not agree, as the effects of vortices above the valve were not included within the model.While the basic concept and operation of the floating valve were established, further and more precise testing are required to develop a complete understanding of the valves operation.xii CHAPTER 1 INTRODUCTION 1-1The Center for Advanced Power Systems In 2000, The Center for Advanced Power Systems (CAPS) was established by Florida State University and the FAMU-FSU College of Engineering, in cooperation with the National High Magnetic Field Laboratory (NHMFL), in Tallahassee, FL.The Center for Advanced Power Systems focuses on advanced power technologies with particular emphasis on transportation systems, as well as traditional utility systems [CAPS].CAPS is also interested in the application of recent advances in power semiconductors, materials, advanced controls, and superconductivity to advanced power system technologies [CAPS]. CAPS moved into a new facility in 2003, establishing one of the premier power research facilities in the country.Because of CAPS early affiliation with the NHMFL, a portion of the Office of Naval Research (ONR) funding was earmarked for research in superconductivity.Eventually, specific programs in superconducting materials, motors, transformers, and magnetic energy storage devices were developed.The latter of this list, superconducting magnetic energy storage, and its supporting systems, created the basic need for the project described in this thesis. 1-2Superconducting Magnetic Energy Storage The need for a superconducting magnetic energy storage (SMES) system started with the implementation of sensitive power electronics in the machinery used by different sectors of industry (Figure 1.1).Equipment like variable speed drives and induction motors require uninterruptible, high quality power. Currently, any industry requiring continuous processing while using these machines is subject to potential problems caused by voltage instabilities.Therefore, companies need a reliable method to ensure a constant source of power.Large banks of batteries and capacitors may work for smaller applications, but a SMES unit is designed for applications that require megawatts of supplemental power within fractions of a second. 1-2.1Superconductivity The advantages of a SMES system are based on the properties of superconducting materials, or superconductors.When an electrical current is induced through a normal material like copper, some energy is dissipated due to resistive heating, which represents lost electrical energy (lost work).With superconductors, once they are cooled below a critical temperature, 1 their electrical resistance becomes zero1; hence, they become perfect conductors of electricity.In a superconducting loop, direct electrical current can theoretically flow forever, as long as the superconductor is kept below its critical temperature, which varies for each superconducting material.In addition to offering little or no resistance to electrical flow, the current density of superconducting wires is many times greater than traditional copper wire [American Superconductor]. One popular application of metal wire is the electromagnet.When an electrical current flows through a metal wire, the wire generates a magnetic field.Coiling the wire around a common center can increase this magnetic field.The more wrappings of wire around the coil, the more powerful the electromagnet.Common examples of electromagnets are electric motors, speakers, and solenoids.Another important use of the electromagnet is its ability to store energy.However, because of the electrical resistance of the wire in the coil, electromagnets are neither highly efficient nor effective at storing energy.With the discovery of superconductivity, a traditional electromagnet can now become a superconducting magnet by using a superconductor as the coil material.Now, all the benefits of superconductivity can be transferred and applied to make an even more powerful and efficient magnet. FIGURE 1.1SMES SUPERCONDUCTING COIL (A), WITH COIL SPLICES AND LHE VENTS (B) INSIDEVACUUM VESSEL (C) CBA1-2.2Cryogenics Without the science of cryogenics, superconducting technology would not exist.Cryogenics is the branch of physics that deals with the production and effects of very low temperatures [Merriam-Webster].In order to reach the critical temperatures of a superconductor, cryogenic systems comprised of fluids like liquid helium (LHe) and liquid nitrogen (LN2) are necessary.Early superconductor critical temperatures were below 10 K.The only element that does not freeze at this temperature is helium, which liquefies at 4.2 K, at 1 atm (Figure 1.2).Because of this uniqueness, LHe became the choice fluid for cooling superconductors with critical temperatures above 4.2 K.However, in order to produce LHe, an intense refrigeration process must occur.Huge amounts of energy are spent to cool helium from room temperature (298 K, 77 F) to liquid temperature (4.2 K, -452 F).This is a difference of over 500 F!As technology improves, the efficiency of this process increases.But, it still remains very costly.Currently, the CAPS SMES uses a niobium-titanium (NbTi) superconductor, with critical temperature of 9 K, and is designed to operate at LHe temperatures. In addition to cooling the superconductors below their critical temperatures, in a system like the SMES, cryogens are relied upon to transfer heat away from the magnetic coil (typically its non-superconducting components) and provide a shield that intercepts thermal radiation from the outside environment. To accomplish this, the superconducting loops are enclosed in baths of 2 1 A superconductor carries direct current (DC) with near-100% efficiency, but still exhibits a slight dissipation of energy with alternating current (AC). cryogenic fluids, which may be either flowing or (in a few cases) stationary.As long as the cryogens successfully transfer heat away from the superconducting coils, thus keeping the superconductors below their critical temperature, the magnetic field will remain active. 1-2.3Thermal Radiation and the Liquid Nitrogen Shield There are three basic modes of heat transfer: conduction, convection, and radiation.Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles [engel], and can occur in solids, liquid, or gases.Conduction is typically greater in solids because they are much more dense, thus their particles are closer together.Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas which is in motion, and it involves the combined effects of conduction and fluid motion.The faster the fluid motion, the greater the convective heat transfer [engel].If the fluid becomes motionless, conduction between the solid surface and the fluid becomes the primary heat transfer mode.Radiation is the energy emitted by matter in the form of electromagnetic waves [engel].There are many types of radiation (i.e. X-rays, gamma rays, radio waves) but thermal radiation, or radiation emitted by objects because of their temperature, is the most important for heat transfer problems.Radiation does not require a medium (such as a solid, liquid, or gas) in which to travel.For example, the energy from the sun reaches Earth through the vacuum of space by means of radiation. Several steps are taken to minimize heat transfer input into the SMES superconducting coil.For conduction, contact points between metals are reduced and materials with low thermal conductivities are chosen.For convection, a vacuum is produced inside the SMES vessel.For radiation, shields are installed between the hot and cold surfaces.These shields may consist of a multilayer insulation (MLI) of highly reflective material (similar to aluminum foil, and seen on many spacecraft or satellites orbiting the earth) or a single layer containing a moving fluid of either liquid or vapor (as designed for the CAPS SMES).MLI is the new technology for radiation insulation and is very lightweight and effective.However, MLI requires 30-80 layers to be effective, and is very expensive to purchase and install.The second method uses liquid or vapor shields to surround the primary (inner) cryogen.A secondary cryogen (most commonly LN2) is circulated through the shield to absorb incoming radiation.Studies have shown that by using a liquid nitrogen shield, approximately 99.6% of the total radiant heat influx can be intercepted by the less expensive liquid [Timmerhaus & Flynn].Because of the low cost of LN2 relative to LHe, this design may save costs in the long term.In contrast, thistechnique increases the weight of the entire system, anhas the constant need for the secondary liquid cryogen.Vapor shields typically use the cold gas from the primary liquid cryogen to absorb incoming radiation. d FIGURE 1.2TEMPERATURE SCALE DISPLAYING ABSOLUTE ZERO (0K), NITROGEN BOILING POINT (77K), AND ATMOSPHERIC CONDITIONS (298K) 3 This set-up eliminates the need for an additional cryogenic liquid, but the radiant heat intercept ability is less when compared to the liquid shield. FIGURE 1.3SMES WITHOUT LN2 SHIELD (LEFT) AND WITH LN2 SHIELD (RIGHT) The selection of a thermal radiation shield for the CAPS SMES depended upon two factors: availability of LN2 and cost.A future goal of CAPS is to provide LN2 onsite for the different users within CAPS.The SMES will be just one of these users.The impending availability of LN2 was a driving factor for incorporating a LN2 shield, as opposed to a simple He vapor shield, into the SMES design.MLI was eliminated because of the costs associated with wrapping the relatively large surface of the SMES with 30-80 layers.Without a shielding device like the LN2 shield, the inner LHe of the superconducting coil at 4K (-452F) absorbs thermal radiation from the SMES vessel at 298K (77F) (Figure 1.3, left).When a LN2 shield is installed, the inner LHe at 4K only absorbs thermal radiation from the LN2 at 77K (-321F) (Figure 1.3, right).The radiation surface temperature difference for the superconducting coil is reduced from over 290K (500F) to merely 73K (131F).From the thermal radiation equation (Eq. 1.1), it is evident that reducing the temperature difference can greatly reduce the overall radiation energy. of CAPS is to provide LN2 onsite for the different users within CAPS.The SMES will be just one of these users.The impending availability of LN2 was a driving factor for incorporating a LN2 shield, as opposed to a simple He vapor shield, into the SMES design.MLI was eliminated because of the costs associated with wrapping the relatively large surface of the SMES with 30-80 layers.Without a shielding device like the LN2 shield, the inner LHe of the superconducting coil at 4K (-452F) absorbs thermal radiation from the SMES vessel at 298K (77F) (Figure 1.3, left).When a LN2 shield is installed, the inner LHe at 4K only absorbs thermal radiation from the LN2 at 77K (-321F) (Figure 1.3, right).The radiation surface temperature difference for the superconducting coil is reduced from over 290K (500F) to merely 73K (131F).From the thermal radiation equation (Eq. 1.1), it is evident that reducing the temperature difference can greatly reduce the overall radiation energy. ) (4 4surr s radT T A Q = &) (4 4surr s radT T A Q = &(EQ. 1.1)(EQ. 1.1) wherewhere e temperatur g surroundine temperatur surfacearea surfaceconstant Boltzmann- Stefanemissivity surface====e temperatur g surroundine temperatur surfacearea surfaceconstant Boltzmann- Stefanemissivity surface=====surrsTTA With implementation of a LN2 shield, the inner LHe enclosure absorbs less radiation energy and thus uses less overall LHe, which results in a more cost effective solution for CAPS in the long term. 1-3Liquid Nitrogen Reconditioning and Transfer Station The design of the liquid nitrogen (LN2) shield for the SMES requires a method by which to circulate the LN2.Current methods simply rely upon differential pressure as the driving forcehigh pressure LN2 at the inlet flows to a lower pressure at the outlet.Consequently, only by changing the differential pressure can the mass flow rate of the LN2 be changed, and this action may either be slow or not even available to the user.In the event of a critical heat flux 4 into the LN2 shield, the mass flow rate must be able to increase immediately to carry away the additional heat load.Hence, engineers at Air Products and Chemicals have developed a specpump for cryogenic fluids that allows the mass flowrate and pressure of a cryogenic fluid system to be modified instantly.And, for its particular application at CAPS for the SMES unit, a supporting system, or reconditioning and transfer station, was designed for this pump at Air Products and Chemicals.This section describes the basic layout and function of the LN2 reconditioning and transfer station (LN2 RTS), and outlines the areawhere this thesStatorArmatureFIGURE 1.4CYLINDRICAL AIR GAP LINEAR MOTOR, BY CALIFORNIA LINEAR DEVICESial is is concentrated. 1-3.1Linear Cryogenic Pump The design of the LN2 RTS is primarily based around the linear cryogenic pump (LCP).The LCP was designed, patented, and built by Air Products and Chemicals, based in Allentown, PA.Cryogenic refers to the LCPs application to the extreme operating conditions of the cryogenic world.Its special design considerations help reduce heat leak into the LN2 flow and ensure that its materials will withstand the low operating temperatures.Linear corresponds to the action of the LCPs cylindrical air gap linear motor, designed by California Linear Devices, based in Carlsbad, CA.The motor is actually an electro-magnetic motor that converts electrical energy into the mechanical linear motion.The motors center armature (Figure 1.4) behaves similarly to that of a car engines pistonmotion is uniaxial (side-to-side in Figure 1.4).This linear, reciprocating armature is controlled by a fully programmable microprocessor, which can vary the armatures stroke, speed, acceleration, and motion delay.Pump describes the basic purpose of the LCPcirculating a fluid at a specific pressure and mass flow rate around a fluid circuit.The pumping action of the LCP is produced as the armature applies force onto the fluid.The faster the armature movement, the higher the pressure and mass flow rate.The designed discharge pressure for the LCP is 250 psi, and the maximum volumetric flow rate is 3.5 gpm at a speed of 100 cpm. 1-3.2300-Gallon Liquid Nitrogen Tank The second major component of the LN2 RTS is the 300-gallon LN2 tank.This tank was originally built by Air Products and Chemicals in 1962 as a storage dewar for liquid oxygen.Several modifications are planned to retrofit this tank to the desired needs and specifications of CAPS and the LN2 RTS. The primary purpose of the 300-gallon tank is to act as an interface between the LN2 main supply, the LCP, and the equipment requiring LN2.The basic system is shown in Figure 1.5.This system represents a closed-loop system, where the outputs from the SMES and multiple end-users at CAPS are returned to the 300-gallon tank.By recycling the LN2, CAPS is conserving LN2 (and consequently money).However, the design of such a closed-loop system demands an interface or buffer volume, like the 300-gallon tank, that can both equalize various incoming pressures and exchange heat absorbed by the LN2. The 300-gallon tanks inner operating pressure is uniqueless than 1 psi above atmospheric pressure.This specification is explained further in the following section.One 5 FIGURE 1.5LN2 SYSTEM LAYOUT OF MAJOR COMPONENTS. LP = LOW PRESSURE; MP = MEDIUM PRESSURE; HP = HIGH PRESSURE problem associated with the low operating pressure is the design of a suitable nitrogen (N2) gas vent.In consideration of safety, all pressure vessels must have an inherent method to relieve internal pressure.These relief devices differ depending upon the application.For cryogenic vessels, the extreme temperature difference between the cryogen and the atmosphere complicates the solution.In cooperation with engineers at Air Products and Chemicals, this thesis project focuses on the design, analysis, and testing of a relief valve for the 300-gallon tank. 1-3.3LN2 Cycle in the LN2 RTS The primary purpose of the LN2 RTS is to pump liquid nitrogen through the shield of the SMES.During this process, it is important that the LN2 remain liquid throughout the shield and all system piping.If the pressure drop or energy influx is too large, vapor will form within the flow.Vapor introduction causes flow instabilities and pressure fluctuations, which are undesirable.When LN2 is on the saturated liquid curve (Figure 1.6, #1), any additional energy (enthalpy) begins producing vapor (#2).To prevent any vapor production in the shield and piping, the pressure of LN2 must be increased.Figure 1.7 shows the simplified steady-state cycle of LN2 through the SMES system: #1-2:LN2 pressure is increased by LCP to a set pressure; small energy influx from LCP. #2-3:Large energy influx from SMES shield; small pressure drop from piping. #3-4:Large pressure drop as LN2 returns to 300-gallon tank; energy absorbed in LN2 by cycle is released as vapor. 6 #4-1: LN2 remaining after vapor boil-off is reused by LCP; N2 vapor accumulates inside top of 300-gallon tank and is released by N2 valve. As mentioned earlier, point 3 in Figure 1.7 is the critical point for the cycle.At the end of the SMES cycle, if point 3 is located left of the saturated liquid curve, the LN2 flow will remain liquid.However, if the LN2 begins absorbing too much energy, the LCP can increase the pressure of the LN2 to counter the production of vapor within the cycle.This effect is shown by points 2*, 3*, and 4* in Figure 1.7.Sensors and instruments are used to monitor LN2 flow and relay information to the LCP.Because of the various pumping pressures and flow rates, the vapor produced within the 300-gallon tank is not constant, which is an important factor in the design of a relief valve for the 300-gallon tank. FIGURE 1.7HEATING EFFECT OF SMES CYCLE ONLIQUID NITROGEN FIGURE 1.6HEATING EFFECT ON SATURATED LIQUID NITROGEN 7 CHAPTER 2 CRYOGENIC NITROGEN VALVE 2-1Introduction To ensure a constant operating pressure inside the 300-gallon tank, a pressure relief valve must be installed to release the nitrogen vapor accumulating in the top of the tank.This valve is the basic component of a larger vent system, and is the focus of this thesis project.This chapter explains the difference between standard pressure relief valves and the CAPS liquid nitrogen reconditioning and transfer station (LN2 RTS) cryogenic valve.Also, highlights of the design process for the cryogenic nitrogen valve are discussed. 2-1.1Pressure Relief Valves Typical pressure relief valves are actuated by a spring (Figure 2.1), which is adjusted to allow the valve piston to open at a specific pressure.Hookes Law defines the linear relationship of springs as: kx F = (EQ. 2.1) where,constant springm equilibriu from ntdisplacemeforce applied===kxFFIGURE 2.1SIMPLE SCHEMATIC OF A SPRING-OPERATED PRESSURE RELIEF VALVEBecause most springs have a fixed spring constant, engineers know the force needed to stretch or compress the spring a specific distance.In the simple valve example shown in Figure 2.1, the high-pressure fluid applies a force upon the lower piston.As pressure builds, the spring is compressed as the piston is pushed upwards.Eventually, the lower pistons bottom surface will reach the vent hole, and flow movement will occur.The initial pressure at which this occurs is the valves set pressure, and depends upon both the type of spring and its initial state of compression (which can be adjusted).To increase the flow rate through the valve, the lower piston must continue to rise in order to increase the vent hole opening.Raising the lower piston is accomplished by a pressure increase inside the tank.For most systems this is acceptable; for the 300-gallon tank, pressure must be maintained near the set pressure, and not deviate above it.Therefore, a spring valve 8 FIGURE 2.2SIMPLE SCHEMATIC OF A FLOATING RELIEF VALVE;P = PRESSURE, T = TIME, PS = SET PRESSURE is not desired for use within the 300-gallon tank. 2-1.2Floating Valves Valves that rely upon their weight to regulate pressure are not new.Some flapper valves use the same technique and most float valves rely upon buoyancy to actuate.The floating valve design is very similar to Figure 2.1, but without a spring and adjustment screw.The set pressure for the floating valve can be increased or decreased by adding or subtracting weight from the floating piston, respectively.Figure 2.2 demonstrates the basic operation of the LN2 RTS floating valve.In Figure 2.2a, pressure steadily increases with time with the build-up of nitrogen vapor.During this phase, the weight of the piston is greater than the force applied by the pressure.There is no nitrogen vapor flow movement.In Figure 2.2b, the force of the pressure balances the weight of the piston, and the piston is free to move.Eventually, pressure is released as nitrogen vapor escapes through the vent hole.The vent hole may never be fully open for low-flow cases.Also, a sinusoidal or simmering effect is expected as pressure builds and is subsequently released.In Figure 2.2c, increased flows of nitrogen vapor will force the vent hole completely open.The simmering effect is gone, and ideally, the pressure inside the tank will stabilize around the set pressure (PS).However, the valve will have a critical flow rate, where pressure inside the tank will begin rising due to the fixed vent hole area. 9 2-2Valve Design Several factors must be evaluated before a final valve design and its dimensions are produced.This section discusses the requirements and expected performance of a valve for the LN2 RTS. 2-2.1LN2 RTS Nitrogen Requirements The primary sizing factor for the valve is the nitrogen mass flow rate.Throughout the operation of the LN2 RTS, this mass flow rate may vary significantly, depending mostly on the heat load from the SMES shields.The heat load is estimated to be a minimum 100W for steady-state operation and a maximum 600W for SMES shield cool-down.Intuitively, the nitrogen mass flow rate should increase to maintain effective cooling of the shields during cool-down.However, by pressurizing the liquid nitrogen into a subcooled state, more enthalpy (heat) is required to vaporize the liquid (see the example in section 1-3.3).Therefore, the required increase of nitrogen mass flow rate is not so severe. The linear cryogenic pump (LCP) design discharge pressure is 250 psi (1.737 MPa), but nominally operates at a discharge pressure of 200 psi (1.379 MPa).Table 2.1 shows the enthalpy benefit of subcooling liquid nitrogen within the LN2 RTS circuit.The enthalpy change required to reach the saturated liquid line on Nitrogens Pressure vs. Enthalpy diagram (Figure A.1) is shown in the h vapor column.The corresponding temperature change is shown in the T vapor column. Temp (K)Pressure (psi)h vapor (kJ/kg)T vapor (K) 77.3514.700 77.357535.9617.06 77.3515058.4326.90 77.3520070.0031.59 TABLE 2.1 ENTHALPY COMPARISONS FOR SUBCOOLED LIQUID NITROGEN At a subcooled pressure of 200 psi at 77.35 K, liquid nitrogens temperature can increase over 31 K before it begins to vaporize.The required mass flow rate of nitrogen ( ) can be calculated from the heat load (P2 Nm&heat) and the enthalpy change (hheat) from the temperature increase (Theat): heatheatNhPm=2& (EQ. 2.2) Table 2.2 shows the results from Eq. 2.2, for a range of values for Pheat and Theat, at 200 psi. 10 Theat (K)Theat (K) 2.557.51015202530 6000.11800.05900.0390 0.0290 0.0190 0.0140 0.01100.00915500.10800.05400.0360 0.0270 0.0180 0.0130 0.01000.00845000.09800.04900.0330 0.0240 0.0160 0.0120 0.00930.00764500.08800.04400.0290 0.0220 0.0140 0.0110 0.00840.00684000.07900.03900.0260 0.0190 0.0130 0.0095 0.00750.00613500.06900.03400.0230 0.0170 0.0110 0.0083 0.00650.00533000.05900.02900.0200 0.0150 0.0096 0.0071 0.00560.00462500.04900.02400.0160 0.0120 0.0080 0.0059 0.00470.00382000.03900.02000.0130 0.0097 0.0064 0.0047 0.00370.00301500.02900.01500.0098 0.0073 0.0048 0.0036 0.00280.0023Pheat (W) 1000.02000.00980.0065 0.0049 0.0032 0.0024 0.00190.0015TABLE 2.2 N2 MASS FLOW RATES (KG/S) CALCULATED AT 200 PSI FIGURE 2.3NITROGEN MASS FLOW RATE FOR TEMPERATURE CHANGE VS. HEAT LOAD11 As expected, the nitrogen mass flow rate is lowest for low SMES shield heat load (Pheat) and high liquid nitrogen temperature change (Theat).Table 2.2 and Figure 2.3 help define the operating range of the floating valve.If a maximum Theat of 10 K is desired, the valve must have the ability to release 0.029 kg/s of vapor at 600 W; for a maximum Theat of 5K, a release of 0.059 kg/s of vapor is required. Finally, the required nitrogen mass flow rate to cool the SMES shields must be compared to the mass flow rate available from the LCP.At 100% pump speed (at 100 cycles per minute), the LCP pumps 3.5 gpm of liquid nitrogen.This volumetric flow rate ( v ) is equivalent to 2.208E-4 mLCP&3/s.Liquid nitrogens density (LN2) of 809.94 kg/m3 (77.35 K, 200 psi) and Equation 2.3 yield a maximum LCP nitrogen mass flow rate of 0.1788 kg/s. 2 LN LCP LCPv m & & = (EQ. 2.3) The required nitrogen mass flow rate for the SMES shields is well within the pumping capacity of the LCP, as shown in Table 2.3. Temperature Change (K) 2.557.51015202530 600 65.932.921.816.310.88.06.35.1 550 60.430.120.014.99.97.35.74.7 500 54.927.418.213.69.06.65.24.2 450 49.424.616.412.28.16.04.73.8 400 43.921.914.510.97.25.34.23.4 350 38.519.212.79.56.34.63.73.0 300 33.016.410.98.15.44.03.12.5 250 27.513.79.16.84.53.32.62.1 200 22.011.07.35.43.62.72.11.7 150 16.58.25.54.12.72.01.61.3 Heat load (W) 100 11.05.53.62.71.81.31.00.8 TABLE 2.3 PERCENTAGE OF LCP PUMPING CAPACITY REQUIRED(200 PSI) 2-2.2Specifications for a New Valve While the liquid nitrogen pumped through the LN2 RTS circuit is pressurized to 200 psig, the pressure inside the 300-gallon tank must be maintained at less than 1.0 psig above atmospheric pressure.A pressure relief valve for the 300-gallon tank must meet this specification.The new valve must also allow both low and high mass flow rates of nitrogen vapor to escapeapproximately 0.005 kg/s to 0.18 kg/s (about 0.5 to 24 lb/min).The low mass flow rates represent normal steady-state operation of the LN2 RTS, while cool-down of the SMES LN2 shield is represented by the high mass flow rates.In order to prevent backflow into the 300-gallon tank, the valve must permit only one-directional flow and seal effectively when no-flow cases exist.Finally, the valve must operate at 80K. 12 2-2.3LN2 RTS Floating Valve In an effort to meet the above specifications for a new valve, Air Products and Chemicals proposed a floating valve design.This design does not incorporate a spring to counter the tank inner pressure, but simply relies upon the weight of a floating piston inside the valve.Once the set pressure is reached and the weight of the floating piston is overcome, the floating piston lifts and allows the N2 vapor to escape.When cases of increased N2 flow occur, no additional force is needed to lift the pistonpressure inside the tank does not exceed the operating level.When no-flow cases exist, an o-ring in the floating piston seals to prevent a backflow of gas. Figure 2.2 showed simple examples of floating pressure relief valves.The actual valve for the 300-gallon tank in the LN2 RTS is very similar, with a few modifications.Figure 2.4 shows a section view of the RTS floating valve in Autodesk Inventor, a 3D modeling computer program.This valve is comprised of five pieces, shown as: A)Valve housingstainless steel tube B)Valve basestainless steel C)Valve center pinstainless steel D)Valve floating pistonbrass E)Valve piston o-ringTeflon The valve is symmetric around the center axis.Flow enters the bottom through slots in the valve base (also shown in Fig. 3.5), passes by the o-ring, and finally exits into the space above the piston.The floating piston is limited to vertical motion by the center pin, which is secured to the base.A groove secures the piston o-ring to the piston. When pressure inside the tank is not high enough to lift the piston, the piston o-ring sits on the base, effectively sealing the inner tank region from the outer environment. Most of the parts are made from stainless steel because it has both a low thermal conductivity and a low coefficient of thermal expansion.Brass was chosen for the floating piston to create a dissimilar metal interaction between the piston and the center pin.While the coefficient of thermal expansion for brass is greater than that of stainless steel, the difference is not expected to cause problems.Teflon was chosen above a more common o-ring material like rubber because it has greater survivability in cryogenic environments. FIGURE 2.4CROSS-SECTION OF ACTUAL RTS FLOATING VALVEThe contour of the mating interface between the base and the floating piston was designed to both minimize the expected simmering phenomena described previously and support the transition between low- and high-flow cases.Optimization of this interface was not 13 FIGURE 2.5CROSS-SECTION OF VALVE AND SUPPORTING STRUCTIRE performed, but test results should provide evidence of success or failure of these two goals. The floating valve is only one sub-assembly of the larger vent system for the RTS.While the entire vent system was designed over the course of this project, only the performance of the floating valve was analyzed. 2-2.4Valve Supporting Structure With the exception of one non-critical aluminum piece, the entire valve supporting structure is made of 304/304L stainless steel.The structure is composed of a series of interlocking pipes and flanges that support one another and ultimately the valve.Figure 2.5 shows a section view of the structure in Autodesk Inventor.The base assembly of the supporting structure is colored blue.The entire valve assembly connects to this modified weld-neck flange and pipe.The next assembly is the valve housing assembly, colored green.The valve base and pipe slide into the base assembly, with a modified slip-on flange bolting to the weld-neck flange.Finally, the top assembly, colored red, slides into the valve housing assembly and prevents the floating piston from lifting above the valve center pin.The top assembly is connected to the previous assemblies by two sets of threaded rods and nuts (not shown in Figure 2.5 for clarity of the entire structure).This assembly also contains parts that will be ultimately modified for future installation into the 300-gallon tank.14 CHAPTER 3 FLOATING VALVE ANALYSIS 3-1Introduction In order to verify the design of the liquid nitrogen reconditioning and transfer station (LN2 RTS) floating valve, two values must be calculated.First, the set pressure of the valve must be determined, since the primary function of the floating valve is to relieve pressure inside the 300-gallon tank.Second, the pressure drop across the valve must be calculated because the pressure difference between the 300-gallon tank and the atmosphere is small.Most industrial valves and fittings have a head loss factor associated with them, allowing system designers to anticipate pressure losses.Because the LN2 RTS floating valve is unique, no such data exists for its design.Bernoullis Equation and other loss coefficients are used to calculate the pressure drop across the valve. 3-2Valve Set Pressure The set pressure of the LN2 RTS floating valve is determined by the design of the floating piston.For zero mass flow rate cases, only the downward weight of the piston (Eq. 3.1) counters the upward force applied by the gage pressure in the 300-gallon tank (Figure 3.1).This upward force is calculated from the effective surface area on the piston enclosed by the piston o-ring (Eq. 3.2). g m F Wpiston= = (EQ. 3.1) where,on accelerati nal gravitatiomassForceght Piston Wei====gmFWpiston oring gA P F = (EQ. 3.2) where,area ring - o4 tank of pressure gage2= ==DAPoringg A relationship between the piston weight and the tank pressure is established by: 15 goringpistonPAW= (EQ. 3.3) The results from Eq 3.3 are shown in Table 3.1.From this table, the correct piston weight can be determined from the desired tank inner pressure.From Table 3.1, two general relationships between tank pressure and piston weight can be made: lb psig 0822 . 0andpsig lb 16 . 12 .Basically, for every one pound of piston weight, the set pressure increases by 0.0822 psig.Also, for every 1 psig of desired set pressure, 12.16 lb of piston weight is required. While Table 3.1 represents the important initial set pressure for the valve, once the valve is opened, the set pressure changes due to a change in area in Equation 3.3.As the piston lifts, the effective area increases.With the piston weight remaining constant, the tank pressure decreases.If the effective area remains constant at stages during valve operation, the tank pressure will begin to settle upon a new set pressure.This effect is discussed in Section 3-5.4. By using gage pressure for the 300-gallon tank, the additional downward force on the floating piston from atmospheric pressure is disregarded.Initially, it was assumed that the pressure immediately above the floating piston was atmospheric pressure.For the static case of the set pressure and low nitrogen mass flow rates, this assumption is valid.However, once large amounts of nitrogen vapor begin flowing through the valve, the pressure immediately above the floating piston is not atmospheric pressurean additional force from pressure must be added to the calculation. TABLE 3.1 INTERNAL TANK PRESSURE VS. PISTON WEIGHT Tank Press.Piston Weight Piston Weight Tank Press. (psig)(lb)(lb)(psig) 0.22.4322.00.164 0.33.6482.50.206 0.44.8653.00.247 0.56.0813.50.288 0.67.2974.00.329 0.78.5134.50.37 0.89.7295.00.411 0.910.9455.50.452 1.012.1616.00.493 3-3Pressure Drop with Bernoullis Equation The Bernoulli Equation is a powerful and useful equation because it relates pressure changes to velocity and elevation changes along a streamline [Fox & McDonald].By creating a map of fluid velocity through the LN2 RTS floating valve with the continuity equation, changes in pressure are easily calculated with the Bernoulli Equation.However, before the Bernoulli Equation can be used, several assumptions must be made concerning the nitrogen vapor flow through the valve. 16 3-3.1Flow Assumptions In order to develop the Bernoulli Equation from Eulers equations for motion, four assumptions are made: frictionless, steady, incompressible, streamline flow.First, the nitrogen vapor flow is assumed frictionless through the valve because the viscous losses are small compared to the pressure losses associated with the valves internal geometry.Second, the flow is assumed steady because only steady-state conditions will be tested.Third, the flow is assumed incompressible because the nitrogen vapor velocity throughout the valve never exceeds a Mach number of 0.3.Fourth, the flow is calculated along a streamline that represents the average conditions of the flow for a given flow area. Tank PressurePiston Weight FIGURE 3.1FREE BODY DIAGRAM OF FLOATING PISTON 3-3.2Basic Equations With these assumptions, Bernoullis Equation between two points on a streamline reduces to: 222 2121 12 2z gV pz gV p+ + = + + (EQ. 3.4) By stating that z1 = z2, and rearranging Equation 3.4: ) (22122 2 1V V p p = (EQ. 3.5) = pwhere,height zconstant nal gravitatio gvelocitydensitypressure====V Equation 3.5 is important because it shows that the pressure drop between two points on a streamline is directly related to the change in velocity of the moving fluid.The pressure in Bernoullis Equation is commonly referred to as thermodynamic, or static, pressure.By applying the conservation of mass, or the continuity equation (Eq. 3.6), and rearranging it for the same two points on the streamline (Eq. 3.7), velocities inside the valve are calculated from the initial mass flow rate and change of flow area. 0 = A d VCS (EQ. 3.6) m A V A V & = =2 2 2 1 1 1 (EQ. 3.7) where,rate flow massarea==mA& 17 3-3.3Temperature Influences on Nitrogen Whether as a liquid or a vapor, many properties of nitrogen are highly dependent upon temperature.Three of these properties that are important to the floating valve are density, viscosity, and speed of sound.The calculated pressure changes depend upon nitrogens densityas temperature increases, the density decreases.The Reynolds number for each flow point inside the valve depends upon density and viscosityas temperature increases, the viscosity increases.Lastly, the Mach numbers inside the valve depend upon the local speed of sound of nitrogenas temperature increases, the speed of sound increases.The temperature inside the actual valve must be measured to ensure an accurate model of the floating valve. 3-4Modeling the Floating Valve The floating valve must be broken down into smaller divisions before the entire pressure drop across the valve can be calculated.Special applications of Bernoullis Equation are required for many regions inside the floating valve to ensure accurate modeling.This section describes the modeling method used inside the floating valve. 3-4.1Flow Regimes As the floating piston rises and falls above the valve base, the flow streamlines inside the valve change due to the unique profiles of these parts.The modeling technique must be varied to ensure accurate modeling of the entire performance of the floating valve.Flow between the piston and the base can be divided into five sections or regimes, all dependent upon the piston height above the base.Regimes A-E are shown at the end of the chapter (Figures 3.17-3.26), and are described in further detail in this section.These figures are two-dimensional cross-sections of the valve and in each figure, dZ refers to the height of the floating piston above the valve base.FIGURE 3.2REGIONS OF THE FLOATING VALVE 18 3-4.2Flow Geometries FIGURE 3.3LOSS COEFFICIENTS FOR SUDDEN FLOW AREA CHANGES [FOX & MCDONALD] A modeling standard must be developed for each type of geometry contained in the nitrogen flow path of the floating valve.The valve geometries can be classified into six basic categories:contraction, expansion, converging nozzle, diverging nozzle, baffle, and elbow.Each flow regime is further divided into flow sections, which are outlined by specifically chosen flow points. It is these flow sections that are classified as contraction, diverging nozzle, etc.All of the critical valve regions that help define the flow points and sections are shown in Figure 3.2. Contraction and expansion refer to flow sections that contain an abrupt or sudden change in flow area.This flow area change may occur within a channel or describe the entrance or exit to/from a plenum chamber.A plenum is an air-filled space in a structure [Merriam-Webster].The modeling method for contractions and expansions was taken directly from Fox & McDonald.Their insight and graphs (Figure 3.3) provided valuable information for head losses associated with sudden changes of flow area.From Figure 3.3, area ratios (AR) of 0.0 represent flow to/from a plenum chamber.As the graph indicates, the loss coefficient for contractions, KC, is found from the bottom left-hand curve.Accordingly, the loss coefficient for expansions, KE, is found from the top right-hand curve. Also, the velocity used in each head loss equation refers only to the flow through the smaller flow area, and not a difference between flow velocities (a modification from Bernoullis Equation).Finally, pressure drop is calculated by multiplying the head loss by the flow density.Every regime contains contractions and expansions. Converging and diverging nozzles refer to flow sections containing gradual reductions FIGURE 3.4COEFFICIENT OF FLUID RESISTANCE FOR DISCHARGE FROM A TUBE ONTO A BAFFLE [FRIED & IDELCHIK] 19 and enlargements, respectively, in flow area.A converging nozzle modeled the flow between Plenum B and Ledge B for all regimes except Regime E.A diverging nozzle was used to model the nitrogen flow through Channel 1 and the O-ring Gap because the flow area slightly increases due to the radial increase along the flow path.Pressure drop through the nozzle is calculated with the simplified Bernoullis Equation (Eq. 3.2) and a flow efficiency term, as described in Section 3-4.9. Flow entering the floating valve at Channel 1, exiting Plenum A, is modeled in all regimes as flow obstructed by a baffle.A baffle is a device (as a plate, wall, or screen) to deflect, check, or regulate flow (as of a fluid, light, or sound) [Merriam-Webster].This baffle is basically the floating piston, and Fried and Idelchik have a good approximation in their text (Figure 3.4).However, two geometrical assumptions must be made.First, the coefficient of fluid resistance, , for discharge from a tube onto a baffle is a function of the piston height divided by the flow diameter through the valve base.Figure 3.5 shows a bottom view of the actual valve base, with three cutouts for flow to enter Plenum A of the valve.The total flow area through these cutouts is known, and an equivalent flow diameter, D0, must be calculated.Second, as the flow transitions from Plenum A to Channel 1, the valve base is not filleted, but rather chamfered.An equivalent radius must be assumed, which yields an 0D rratio of about 0.1.While this is lower than the approximation allows, for this analysis, a 0.2 ratio was used. FIGURE 3.5BOTTOM VIEW OF THE ACTUAL VALVE BASE Finally, a rectangular-section elbow models nitrogen flow through 90 bends in the floating valve.This technique is used in Regimes A, C, and D.Fried & Idelchik (Figure 3.27) provide a detailed description on determining pressure drop for this type of elbow.Case 1 in Figure 3.27 was not valid due to low Reynolds numbers in the floating valve, which were on the order of 104.Therefore, the modified Case 2, with Equation 3.8, was used. lock k Re =(EQ. 3.8) where t coefficien elbowt coefficien Ret coefficien roughnesst coefficien loss totalRe====lockk The values for loc and kRe were used as described in Figure 3.27.However, since all the surfaces inside the floating valve are smooth, the roughness coefficient was taken to be 1.0. 3-4.3Floating Valve Entrance Entrance into the floating valve is modeled identically for each of the regimes discussed in the following sections, and is shown in Figure 3.16.For all regimes, Point 0 (P-0) describes the conditions inside the base assembly pipe (refer to Figure 2.5) and Point 1 (P-1) describes the conditions inside the valve base (refer to B in Figure 2.4).The transition between P-0 and P-1 is always modeled as a contraction. 20 3-4.4Regime A Regime A (Figures 3.17 and 3.18) begins at 0.000 and ends at a floating piston height of 0.046.Interestingly, the critical flow area is shared between two points.Until a height of 0.019, the highest velocities in Regime A are at Point A5.After this height, and for the remainder of Regime A, the critical flow area is at Point A12. During steady-state operation of the LN2 RTS, it is expected that the valve will remain in Regime A.The mass flow rate of N2 gas leaving the 300-gallon tank should not exceed the mass flow rate calculated for Regime A. 3-4.5Regime B Regime B (Figures 3.19 and 3.20) begins at 0.048, where Ledge A of the piston reaches Ledge A of the base, and ends at a floating piston height of 0.088.For the entirety of Regime B, the critical flow area is located at Ledge B, or Point B11 (which corresponds to Point A12). 3-4.6Regime C Regime C (Figures 3.21 and 3.22) begins at 0.090, where Ledge B of the piston reaches Ledge B of the base, and ends at a floating piston height of 0.186.For the entirety of Regime C, the critical flow area is located at Ledge B, or Point C8. In addition, the expansion from Ledge A (Point C6) into Plenum B has changed.Plenum B now functions as an elbow that directs flow into Ledge B (Point C8). 3-4.7Regime D Regime D (Figures 3.23 and 3.24) begins at 0.188, where the critical flow areas of Ledge B and Ledge C are equal, and ends at a floating piston height of 0.323.For the entirety of Regime D, the critical flow area is located at Ledge C, or Point D8. The modeling of Regime D is not much different than that of Regime C; only two points were eliminated.Nonetheless, the dramatic shift of critical flow areas between these regimes provided a basis for creating this additional regime. 3-4.8Regime E Regime E (Figures 3.25 and 3.26) begins at 0.325, where Ledge A of the piston reaches Ledge B of the base, and ends at a floating piston height of about 1.0.For the entirety of Regime E, the critical flow area is located at Ledge C, or Point E5. 3-4.9Flow Efficiencies The pressure calculations from Bernoullis Equation rely upon ideal conditionssmooth pipes, uniform flow, exact dimensions, etc.However, ideal conditions are seldom the actual conditions.To account for these actual conditions within the ideal calculations, an efficiency term must be introduced.Efficiency is defined as the ratio of the effective or useful output to the total input in any system [Dictionary.com].The efficiency is always less than one, and is multiplied or divided into the pressure drop calculation, depending upon the situation.Most efficiencies for standard machinery applications are well-known, but fluid flow efficiencies through channels are more abstract.Equation 3.9 shows the efficiency equation for a diverging nozzle (DN), with Equation 3.10 showing the efficiency equation for a converging nozzle (CN): DN ideal DN DN actualP P, , = (EQ. 3.9) 21 CNCN idealCN actualPP,,= (EQ. 3.10) where, change pressure Idealchange pressure Actual= = idealactualPP For diverging nozzles, the pressure change is positive, and the actual pressure gain is less than the ideal pressure gain.For converging nozzles, the pressure change is negative, and the actual pressure loss is greater than the ideal pressure loss. Efficiency modifications for the contraction/expansion, baffle, and rectangular-section elbow pressure changes are not required because the calculations have already accounted for the actual conditions. 3-4.10 Modeling Setup in EXCEL Microsoft EXCEL provides a valuable calculation platform, and the embedded Visual Basic program allows many mathematical processes to be programmed.The modeling layout inside EXCEL is simple.However, before diving into a detailed model explanation, a brief orientation is necessary. 3-4.10.1Divisions There are three main divisions for each regime in the model:flow points, flow sections, and floater height.As mentioned in Flow Regimes, the definition of flow points and flow sections depend upon the flow geometry between the floating valve and valve base interface.While flow points and flow sections are related, each performs a different set of calculations.Further, all calculations for each flow point and section are dependent upon the floater height, or dZ.An example of this calculation matrix (showing only the row/column headers) is shown in Table 3.2.Each regime contains a similar layout, but flow point and flow section names change, as do the dZ values.Flow points and sections are always listed horizontally, and floater height is always listed vertically. 3-4.10.2Flow Point and Flow Section Calculations Within each flow point, there are several values that need to be calculated:radius, flow area, velocity, Reynolds number, and pressure.The flow point radius (rpoint) is required to calculate the flow area (Aflow): G r Apo flow int2 =(EQ. 3.11) where,G = flow gap (height or width) TABLE 3.2CALCULATION MATRIX FOR REGIME DIVISIONS dZ0.140.120.100.080.060.040.02Point 2 Point 0 Section 0-1 Point 1 Section 1-222 The flow area, nitrogen mass flow rate ( ), and nitrogen density (2 Nm&N2) are required to calculate the point flow velocity (Vpoint): flow NNpoAmV22int&=(EQ. 3.12) The point flow velocity, nitrogen density, nitrogen absolute viscosity (N2), and a characteristic length (L) are required to calculate the Reynolds number (Re): 2int 2ReNpo NL V= (EQ. 3.13) Lastly, the flow point pressure (Ppoint2) is calculated from the previous flow point pressure (Ppoint1) and the change in pressure of the previous flow section (P1-2): 2 1 1 int 2 int + = P P Ppo po(EQ. 3.14) Within each flow section, there are also several values that need to be calculated:average pressure, surface area, average force, and change in pressure.The average pressure for a flow section (Pavg1-2) is simply the average of the flow points immediately before (Ppoint1) and after (Ppoint2) the section: 22 int 1 int2 1po poavgP PP+=(EQ. 3.15) FIGURE 3.6REGIME CALCULATION BREAKDOWN 23 The surface area (Asection) is the circular area between the adjacent flow points (rpoint1 and rpoint2) projected onto the floating piston: ) (21 int22 int sec po po tionr r A =(EQ. 3.16) The average pressure and surface area are required to calculate the average force (Favg1-2) the current section applies onto the floating piston: tion avg avgA P Fsec 2 1 2 1 =(EQ. 3.17) Finally, the modified Bernoullis Equation, with all associated efficiencies (), is required to calculate the pressure change within the section (P1-2): ) (221 int22 int22 1 po poNV V p = (EQ. 3.18) Figures 3.6 and 3.7 summarize the relationship between the floater height, flow points, and flow sections, as described in Equations 3.11-3.18.Figure 3.6 displays the basic path of calculations.However, Figure 3.7 reveals the true interconnectivity between the flow points and sections.Each flow point and flow section transfers information before it and after it, much like actual fluid flow communicates upstream and downstream. 3-4.10.3Boundary Conditions After calculating all the values for every flow point and section within a regime, the only remaining task is to define boundary conditions.Two primary boundary conditions exist: the pressure at the last flow point in every regime is assumed to be atmospheric pressure; the total force from each flow section applied up on the floating piston must equal the weight of the floating piston pushing down.These conditions also provide goals for the model to converge upon. 3-4.10.4Iteration Cycle In order to complete the model, two values must be guessed:nitrogen mass flow rate and 300-gallon tank pressure.With these inputs, all other flow point and section values can be calculated.However, most likely, the boundary conditions or goals are not initially met, and an error for both goals is generated.The flow rate and tank pressure must be altered, the calculations reworked, and the errors checked again.An EXCEL program called goalseek simplifies this lengthy iteration cycle.The goalseek function finds a specific result for a cell by changing the value of another celBasically, goalseek is instructed to both reduce the last flow point pressure error to zero by changing the mass flow rate and reduce the force error to zero by changing the tank pressure.With a little l.FIGURE 3.7FLOW POINT/SECTION COMMUNICATION DIAGRAM 24 FIGURE 3.8DIAGRAM OF ITERATION CYCLE PERFORMED IN EXCEL.GRAY BOXES INDICATE VALUES CHANGED DURING CYCLEprogramming, Visual Basic can goalseek all the dZ values within a regime from the touch of a macro button.The iteration cycle is outlined in Figure 3.8. 3-5EXCEL Model Results for Three Piston Weights Three separate floating piston weights were tested for the floating valve:4.641 lb, 6.111 lb, and 8.252 lb.This section describes the set pressure and pressure drop expected for each case.Because of the similarity between the EXCEL models for all three cases, generalized remarks are made at the end of this section. 25 3-5.1Floating Piston Weight:4.641 lb The calculated set pressure for a floating piston weight of 4.641 lb is 0.381 psig.Figures 3.9 and 3.10 display the EXCEL model analysis for this floating valve weight.The tabulated EXCEL model results are in Appendices A-E. FIGURE 3.10EXCEL MODEL ANALYSIS GRAPH OF TANK PRESSURE VS. NITROGEN MASS FLOW RATE FOR 4.641 LB FLOATING PISTON FIGURE 3.9EXCEL MODEL ANALYSIS GRAPH OF TANK PRESSURE VS. FLOATING PISTON HEIGHT FOR 4.641 LB FLOATING PISTON 26 3-5.2Floating Piston Weight:6.111 lb The calculated set pressure for a floating piston weight of 6.111 lb is 0.502 psig.Figures 3.11 and 3.12 display the EXCEL model analysis for this floating valve weight. FIGURE 3.11EXCEL MODEL ANALYSIS GRAPH OF TANK PRESSURE VS. FLOATING PISTON HEIGHT FOR 6.111 LB FLOATING PISTON FIGURE 3.12EXCEL MODEL ANALYSIS GRAPH OF TANK PRESSURE VS. NITROGEN MASS FLOW RATE FOR 6.111 LB FLOATING PISTON 27 3-5.3Floating Piston Weight:8.252 lb The calculated set pressure for a floating piston weight of 8.252 lb is 0.678 psig.Figures 3.13 and 3.14 display the EXCEL model analysis for this floating valve weight. FIGURE 3.13EXCEL MODEL ANALYSIS GRAPH OF TANK PRESSURE VS. FLOATING ON HEIGHT FOR 8.252 LB FLOATING PIST PIST ON FIGURE 3.14EXCEL MODEL ANALYSIS GRAPH OF TANK PRESSURE VS. NITROGEN MASS FLOW RATE FOR 8.252 LB FLOATING PISTON 28 3-5.4Remarks on the EXCEL Model Results Basically, a distinctive trend is noticed across the results:both types of graphs have almost identical profiles for all floating piston weights.Therefore, a general analysis of the two graph types accurately describes the results for all three piston weights.Please refer to Figure 3.2 for descriptions of the valves internal geometry. 3-5.4.1First Graph:Tank Pressure vs. Floating Piston Height This graph shows the calculated tank pressure results for various piston heights, and is shown in Figures 3.9, 3.11, and 3.13.This TP-PH graph can be divided into three regions: beginning, middle, and end. The beginning of all the TP-PH graphs first display a quick pressure drop from the set pressure.At a piston height of 0.020, the pressure drop for each different piston weight is 23%.The built-up nitrogen vapor inside the tank is released as the piston initially rises.Until about 0.020, the o-ring gap is the restricting flow area and every thousandth of an inch increase in piston height allows more nitrogen to flow through the valve, rapidly reducing the tank pressure.Second, the set pressure and Regime A modeling for each piston weight correlate almost perfectly to one another, though both were calculated using a different method.This confirms that the EXCEL model is starting at the correct pressure. In the middle of each TP-PH graph, pressure gradually decreases as the piston rises, but slight differences in this decrease are obvious.After a piston height of about 0.020 in Regime A, the restricting flow area transitions from the o-ring gap to Ledge B, which is a non-varying flow area until Regime C.Therefore, the latter half of Regime A and all of Regime B exhibit very small decreases in pressure.A new set pressure is being established.Using the area up to Ledge B under the piston in Equation 3.3, the new set pressure is 0.265 psig for the 4.641 lb piston.With the transition to Regime C, the flow area at Ledge B begins increasing as the piston rises.With a concave down profile, the pressure steadily decreases.However, the beginning of Regime D signals yet another change in the restricting flow area, from Ledge B to Ledge C.Because the Ledge C flow area does not change, the tank pressure begins to stabilize, as evidenced by the concave up profile. The end of the TP-PH graph is very visible as the tank pressure converges on approximately 52% of the original set pressure, for all piston weights.This stabilization is most evidenced in Regime E.The 52% value represents the lowest pressure inside the tank during valve operationthe additional lifting of the piston caused no change in flow area at Ledge C and subsequently no decrease in tank pressure.A second new set pressure occurs here.Using the area up to Ledge C under the piston in Equation 3.3, the new set pressure is 0.187 psig for the 4.641 lb piston.Although the model calculates pressures for piston heights over 1.0, the TP-PH graphs only show piston heights up to 0.50 for clarity and scaling purposes.However, it is expected that once nitrogen mass flow rates force the velocity through Ledge C to approach the sonic velocity for nitrogen, tank pressure will start to increase.This expectation leads the discussion to the second set of graphs. 3-5.4.2Second Graph:Tank Pressure vs. Nitrogen Mass Flow Rate The second set of graphs (Figures 3.10, 3.12, and 3.14) show the dependence of tank pressure on the nitrogen mass flow rate.The TP-MFR graphs display a more realistic view of the EXCEL modelin reality, the nitrogen mass flow rate causes the change in floating piston height and hence the drop in tank pressure.However, due to the unique interface between the floating piston and the valve base, the simplest method to calculate these values was to vary the 29 piston height, hence Regimes A-E were created.Understanding the TP-PH graphs is facilitated through analysis of the TP-MFR graphs, which contain the same beginning, middle, and end regions. The beginning of the TP-MFR graph behaves similarly to the TP-PH graph in that initially, there exists a rapid decrease in pressure due to the increase in both mass flow rate and flow area.As before, the restricting flow area for this case is the o-ring gap.Also, the set pressure at zero mass flow rate fits nicely with the Regime A curve. The middle of the TP-MFR graph is also defined by the location of the restricting flow area.The minimal pressure drops in the TP-PH graphs during the latter part of Regime A and all of Regime B are clearly visible here also.In addition, the tank pressure and mass flow rate do not change during Regime B.Very little increase in mass flow rate lifts the floating piston through Regime B.This is a critical point to understand, because it is evident that a specific range of floating piston heights neither contribute to nor aid the valve design.This range is roughly between 0.030 and 0.096, which basically defines the fixed flow area region at Ledge B.As in the TP-PH graph, the first new set pressure is also seen here.However, once the flow area at Ledge B is allowed to change (Regime C), a gradual decrease in pressure occurs for an increase in mass flow rate.For Regime C, the spacing between the model data points on the TP-MFR graphs remains relatively uniform.However, with the transition to Regime D, and the variable flow area at Ledge B replaced by the fixed flow area at Ledge C, the model data point spacing shrinks.This effect is evidence that the mass flow rate is affecting the piston height much more.Basically, small changes in mass flow rate are creating large changes in piston height. The end of the TP-MFR graph (Regime E) continues the trend started in the middle section:small increases in mass flow rate cause larger increases in piston height, with little decrease in tank pressure.However, above a piston height of about 1.0, the nitrogen mass flow rate and tank pressure change less than 0.02%these properties are no longer affected by the rise in piston height.As in the TP-PH graph, the second new set pressure occurs here also.Though the flow area was fixed during Regime E, below 1 piston height, pressure losses were still obtained from the non-restricting flow areas inside the valve.However, above 1, no additional pressure losses are achieved inside the valve, as the primary pressure losses result from Ledge C and the valve entrance at the base.Because the majority of the pressure losses are centered at Ledge C above a 1 piston height, a tank pressure and mass flow rate relationship was created as if only Ledge C impeded the nitrogen flowthis calculation is labeled Ledge C on the TP-MFR graph.This relationship shows that if the mass flow rate is increased above the calculated levels in Regime E, the tank pressure will begin to rise.Eventually, the tank pressure will exceed the set pressure.From the Ledge C calculations, Table 3.3 shows when this limit is reached for each piston weight.After comparing these maximum mass flow rates with those required by the SMES in Table 2.2, sufficient cooling power is achieved before the set pressures are finally exceeded. TABLE 3.3 MAXIMUM MASS FLOW RATE THROUGH LEDGE C BEFOREVALVE SET PRESSURE IS EXCEEDED30 FIGURE 3.15MODIFIED REGIME E EXCEL MODEL ANALYSIS GRAPH OF TANK SURE VS. NITROGEN MASS FLOW RATE FOR 4.641 LB FLOATING PIS PRES TON The Ledge C calculations demonstrate that the tank pressure eventually increases as a function of the velocity squared.However, the EXCEL model never shows this.It is possible that the EXCEL model begins breaking down in Regime E, where piston height increases do not affect flow area and tank pressure.Because the mass flow rate is dependent upon other factors in the model, it never increases to the Ledge C calculation levels.However, if the model was altered, holding a constant piston height of 0.325 inches while increasing the nitrogen mass flow rate through the valve, a new Regime E would develop (see Figure 3.15).The new Regime E shows a higher tank pressure per mass flow rate than the Ledge C calculations due to its inclusion of the additional pressure losses inside the valve. 3-5.5Nitrogen Flow Velocities One of the assumptions made in Section 3-3.1 for Bernoullis Equation was that the nitrogen flow was incompressible because the local Mach number (M) (Eq. 3.19) throughout the floating valve never exceeds 0.3. cVM = (EQ. 3.19) where,sound of speed local velocity flow==cV Besides validating this assumption, it is also important to check for critical, or choked, flow conditions throughout the valve that would severely limit the mass flow rate.The highest flow velocities in the floating valve occur at the critical flow areas in each regime.By determining the local Mach numbers for these critical flow area, both the incompressible assumption and the choked flow concern can be assessed.Table 3.4 shows the Mach numbers for the greatest local speeds in each original regime in the floating valve.The nitrogen speed of sound was calculated at 1 atm, 70 F (test conditions).These values are well within the required limits.Also shown 31 are the velocities at Ledge C, for the maximum flow cases discussed in Table 3.3.These numbers also effectively describe the conditions of the modified Regime E, shown in Figure 3.15. TABLE 3.4 MACH NUMBERS FOR CRITICAL FLOW AREAS IN FLOATING VALVE 32 FIGURE 3.16FLOATING VALVE ENTRANCE FOR ALL REGIMES FIGURE 3.17BEGINNING OF REGIME A.DZ = 0.000 FIGURE 3.18REGIME A MODELING DIAGRAM 33 FIGURE 3.19BEGINNING OF REGIME B & END OF REGIME A.DZ = 0.047LEDGE A OF FLOATING PISTON CLEARS LEDGE A OF VALVE BASE FIGURE 3.20REGIME B MODELING DIAGRAM34 FIGURE 3.21BEGINNING OF REGIME C & END OF REGIME B.DZ = 0.0895LEDGE B OF FLOATING PISTON CLEARS LEDGE B OF VALVE BASE FIGURE 3.22REGIME C MODELING DIAGRAM 35 FIGURE 3.23BEGINNING OF REGIME D & END OF REGIME C.DZ = 0.188FLOW AREA OF LEDGE B GAP EQUALS FLOW AREA OF LEDGE C GAP FIGURE 3.24REGIME D MODELING DIAGRAM36 FIGURE 3.25BEGINNING OF REGIME E & END OF REGIME D.DZ = 0.323LEDGE A OF FLOATING PISTON CLEARS LEDGE B OF VALVE BASE FIGURE 3.26REGIME E MODELING DIAGRAM37 FIGURE 3.27PRESSURE DROP FOR RECTANGULAR SECTION ELBOWS [FRIED & IDELCHIK] 38 CHAPTER 4 VALVE TESTING 4-1Introduction With flow analysis results from EXCEL, a full-scale test was designed to validate the computational analysis.This test included building and assembling an accurate working model of the valve and its supporting structure.The following chapter describes the testing apparatus, goals, and procedures. 4-2Testing Apparatus The testing apparatus is essentially a full-scale prototype of the floating valve.By creating the actual valve and its supporting structure, little work is necessary to modify the valve to operate and function on the actual 300-gallon tank.Instruments were placed to have minimal impact on the valve assembly. 4-2.1Instrument Selection and Placement In order to achieve the testing goals, three measurements must be taken: pressure, position, and temperature. 4-2.1.1Pressure Measurement A digital handheld manometer from Mannix Testing and Measurement, model DM8215 (Figure 4.1), was chosen to measure pressure for the experiment.A static pressure port (Figure 4.2) was installed on the base assembly pipe to record pressure within the valve.However, the digital manometer cannot operate below 0C.To ensure that the gas in the connection between the static pressure port and digital manometer remains above this temperature, approximately ten feet of coiled copper tubing was installed between them.Periodically during the testing, the connection gas temperature was checked. The digital manometer has two pressure taps: positive and negative.The positive tap was connected to the static pressure port and the negative tap was left open to the atmosphere, resulting in the manometer reading a gage pressure.Because atmospheric pressure constantly changes, updated pressure readings from the internet were obtained before each test. 4-2.1.2Position Measurement A position indicator with 0.001 increments from Starrett, model #25-441, was chosen to measure the vertical displacement of the floating piston.The position indicator was connected to the valve assembly, as shown in Figure 4.3.A long, thin-walled tube was placed on top of the 39 FIGURE 4.2STATIC PRESSURE PORT (TOP) AND GAS/LIQUID INPUT PORT (BOTTOM) ON BASE ASSEMBLY PIPE FIGURE 4.1HAND-HELD DIGITAL MANOMETER FIGURE 4.3POSITION INDICATOR FIXED ABOVE SMALL TUBE WHICH EXTENDS DOWN TO THE FLOATING PISTON floating piston and extended vertically up to the position indicator.The extra weight of the tube was added to the weight of the floating piston. 4-2.1.3Temperature Measurement A handheld Fluke thermometer with a type K thermocouple lead was used to measure the temperature of the nitrogen gas inside the valve assembly.This measurement was required to calculate the nitrogen density and also helped ensure that the digital manometer was reading accurately. 4-2.2Nitrogen Interface Both compressed nitrogen gas and liquid nitrogen were supplied to the valve at different stages of the test.The compressed gas was used for most of the testing while the liquid was used to validate the valve operation at low temperatures.Both gas and liquid flows were connected to the bottom port on the side of the base assembly pipe (Figure 4.2).This connection was made normal to the pipe axis in an effort to disperse the incoming flow.4-2.2.1Compressed Nitrogen Gas 3000 psi cylinders of compressed nitrogen gas supplied most of the gas used during the testing o