Refrigeration & Air-conditioning Lab EME-654

Experiment No. 6

Objective: Study of Single stage Air compressor and find out:

The volumetric efficiency Isothermal Efficiency And calculate compression ratio.

Apparatus: Single stage Air compressor. Introduction: Air compressor is a device, which sucks the air from atmosphere and compresses it and delivers in reservoir tank. It compresses the air by means of a reciprocating piston. Which reciprocates in a stationary cylinder? It can be single stage or multi stage. It can be single acting or double acting. Theory: In a single cylinder air compressor, piston reciprocates in the cylinder. It is driven by crankshaft through a connecting rod. There are two valves mounted in the head of cylinder. These valves are the inlet and delivery valves. Both the valves usually operate as a result of pressure difference across them.

The compressed air is used in a wide range in industrial, domestic, aeronautics fields etc. so compressors are applied in wide range. Compressors are used where the air is required at high pressure.

Description:

Single stage air compressor test rig consists of single cylinder, piston & a reservoir tank. Driven by A.C. motor, Temperature sensors are provided at inlet and outlet. To find out the inlet volume of air, an orifice meter is provided, pressure gauges is provided at reservoir tank. Safety valve and auto power out switch is provide for the safety factor.

Experimental procedure:

1. Close the outlet valve of tank and start the compressor.2. Let the reservoir pressure rise up to around 2 kg/ cm2. Now open the delivery valve so that constant delivery pressure is achieved.3. Wait for some time and see that delivery pressure remain constant. Now note down the pressure.4. Record the time for 10 pulses of energy meter.5. Record the manometer readings.6. Record the temperature of air at inlet.7. Find out the rpm of compressor with the help of tachometer.8. Find out the volumetric efficiency and isothermal efficiency by given formula.9. Repeat the same procedure for different delivery pressures.Observations & calculations: Data:

d =L =

d0 =

dp =

m =

a =

Cd =

E.M.C =

Patm =

R =

m =

m =

Observation Table:S.No. NRPMPdKg/cm2H1cmH2cm

T K tp

Calculation:

, m = mH = x h, m of air = m

Experiment No. 4

Objective: Study of different types of compressors used in Refrigeration and Air-conditioning Systems.

Apparatus: Models of Different types of compressors.

Introduction: The compressor is the most critical component of a mechanical vapor compression refrigeration system. Air compressor is a device, which sucks the air from atmosphere and compresses it and delivers in reservoir tank. It compresses the air by means of a reciprocating piston, which reciprocates in a stationary cylinder. It can be single stage or multi stage. It can be single acting or double acting. There are four types of compressors commonly used in refrigeration and air conditioning applications are: Reciprocating, Vane, Centrifugal and Screw type. Recently scroll type compressors have been introduced into the market.

Semi sealed Compressor:When the compressor and motor operate on the same shaft and are enclosed in a common casing, they are known as semi sealed compressors. These types of compressors eliminate the use of crankshaft seal, which is necessary in ordinary compressors in order to prevent leakage of refrigerant. These compressors may operate on either reciprocating or rotary principle land may be mounted with the shaft in either vertical or horizontal position. The hermetic units are widely used for small capacity refrigerating system such as domestic refrigerators, home freezers and window air conditioners.

A semi-hermetic compressor has an electric motor and a compressor built into an integral housing, similar to those in home refrigerators. The motor and compressor have a common shaft and bearings. The motor is generally cooled by suction gas (refrigerant) passing through the windings of the electric motor, but it may be water cooled. These units eliminates the problems of motor mountings, couplings alignment , motor lubrication and refrigerant leakage at shaft seals , since the entire unit is hermetically seals into one housing.Hermetic compressors may be sealed (requiring factory service for repairs) or accessible (permitting service on the job. be sure you know which type you have before attempting repairs.

Hermetic sealed compressor:A hermetic sealed compressor is a factory-sealed unit in which the compressor, either reciprocating or rotary, and motor is direct connected and enclosed in a gastight housing, true hermetic compressors are factory sealed and cannot be disassembled for repair in the field. They are limited to fractional horse power units and up to 7 hp. larger units, some to several hundred horse power, are being built and have been very successful operation. These units have the same advantage as hermetic compressors but should be classified as semi hermetic, since they can be disassembled in the field.

Reciprocating compressor:

The reciprocating compressors suck the low pressure and low temperature refrigerant during its suction stroke and deliver it at high pressure and high temperature. A reciprocating compressor consists of one or more piston and cylinder combinations. The piston moves in reciprocating motion to draw the suction gas into the cylinder on one stroke and to compress and discharge it to the condenser on the return stroke.

Rotary compressors:

In rotary compressor the vapor refrigerant from the evaporator is compressed due to the movement of blades. The rotary compressors are positive displacement types compressors type. Since, the clearance in rotary compressors is negligible; therefore they have high volumetric efficiency. This compressor may use R-22, R-12 and R-114. There are two basic types of compressors:

Single stationary blade type rotary compressor. Rotating blade type rotary compressor.

Single stationary Blade type Rotary compressor:

A single stationary blade type rotary compressor consists of a stationary cylinder, a roller (or impeller) and a shaft. The shaft has an eccentric on which the roller is mounted. A blade is set into the slot of a cylinder in such a manner that it always maintains contacts with the roller by means of a spring. This blade moves in and out of the slot to follow the rotor when it rotates. Since the blade separates the suction and discharge ports, therefore it is often called a sealing blade. When the shaft rotates, the roller also rotates so that it always touches the cylinder wall.

The completion of intake stroke and the beginning of compression stroke. When the roller rotates, the vapor refrigerant ahead of the roller is being compressed and the new intake from the evaporator is drawn into the cylinder. As the roller turns towards mid position, more vapor refrigerant is drawn into the cylinder while the compressed refrigerant is discharged to the condenser. At the end of compression stroke, a new charge of refrigerant is drawn into the cylinder. This, in turn, is compressed and discharge to the condenser. In this way, the low pressure and temperature vapor refrigerant is compressed gradually to a high pressure and temperature.

Experiment No. 9

Objective: Study of different types of condensers.

Apparatus: Models of Different types of condensers.

Shell and tube type condenser:

The shell and tube condenser consists of a cylindrical steel shell containing a number of straight water tubes. The tubes are expanded into grooves in the tube sheet holes to form a vapor-tight fit. The tube sheets are welded to the shell at both the ends. The removable water boxes are bolted to the tube sheet at each end to facilitate cleaning of the condenser. The intermediate supports are provided in the shell to avoid sagging of the tubes. The condenser tubes are made either from steel or copper, with or without fins. The steel tubes without fins are usually used in ammonia refrigerating corrode copper tubing. In this type of condenser, the both vapor refrigerant enters at the top of the shell and condensers as it comes in contact with water tubes. The condensed liquid refrigerant drops to the bottom of the shell which often serves as a receiver. However , if the maximum storage capacity for the liquid refrigerant is less than the total charge of the system, then a receiver of adequate capacity has to be added in case the pump down facility is to be provided as in ice plant, cold storage etc. In some condensers, extra rows of water tubes are provided at the lower end of the condenser for sub cooling of the liquid refrigerant below the condensing temperature.

Shell and coil type condenser:

These are usually on smaller tonnage low pressure units. They cannot of a shell that contains a coil for circulating the water. They do not have removable heads and the water side of the coil may be cleaned only with chemicals. In case of a coil leakage the entire coil bank must be replaced.

Fins and Tube type Condenser:

The condenser must have enough heat transfer surface to condenser the delivered vapor into a liquid state. This must be done at a reasonable operating pressure and temperature. The condenser must also have enough volume to store the vapor pumped by the compressor. Before condensing, the vapor occupies a definite volume: this volume can be decreased by increasing the pressure, but an increase in pressure causes an increase in the horse power required to operate the system. If a condenser has sufficient surface, it usually has enough volume. Care should be taken when selecting finned surface condensers. Finned surface may indicate sufficient area for heat rejection without providing enough volume. The condenser must also allow enough space for the condensed liquid to separate from the vapor and drain to the liquid receiver.

Experiment No. 3

Objective: Study of different types of Evaporators.

Apparatus: Models of different evaporators:

Finned evaporators:The finned evaporators consists of bare tubes or coils over which the metal plates or fins are fastened. The metal fins are constructed of thin sheets of metal having good thermal conductivity. The shape, size or spacing of the fins can be adapted to provide best rate of heat transfer for a given application, since the fins greatly increases the contact surfaces for heat transfer, therefore, the finned evaporators are also called extended surface evaporators. The finned evaporators are primarily designed for air conditioning applications where the refrigerator temperature is above 00c, because of the rapid heat transfer of the finned evaporator, it will defrost itself on the off cycle when the temperature of the coil is near 00c. A finned coil should never be allowed to frost because the accumulation of frost between the fins reduces the capacity. The air-conditioning coils which operate at suction temperatures which are high enough so that frosting never occurs, have fin spacing as small as 3mm. the finned coils which frost on the on cycle and defrost on the off cycle have wider fin spacing.

Plate evaporator/ chest evaporator / skin evaporator:

In this type of evaporator, the coils are either welded on one side of a plate or between the two plates which are welded together at the edges. The plate evaporators are generally used in house hold refrigerators, home freezers, beverage coolers, ice cream cabins, locker plants etc.

Shell and tube evaporators:

The shell and tube evaporator is similar to a shell and tube condenser. It consists of number of horizontal tubes enclosed in a cylindrical shell. The inlet and outlet headers with perforated metal tube sheets are connected at each end of the tubes.

These evaporators are generally used to chill water or brine solutions. When it is operated as a dry expansion evaporator, the refrigerant circulates through the tubes and the liquid to be cooled fills the space around the tubes within the shell. The dry expansion shell and tube evaporators are used for refrigerating nits of 2 to 259TR capacities. When it is operated as a flooded evaporator, the water or brine flows through the tubes and the refrigerant circulates around the tubes. The flooded shell and tube evaporates are used for refrigerating units of 10 to 5000 TR capacities.

Shell and coil evaporators/ immersed type evaporators:

The shell and coil evaporators are generally dry expansion evaporators to chill water. The cooling coil is a continuous tube that can be in the form, of a single or double spiral. The shell may be sealed or open. The sealed shells are usually found in shell and coil evaporators used to cool drinking water. The evaporators having flanged shells are often used to chill water in secondary refrigeration system.Both types evaporators are usually used where small capacity (2 to 10TR) liquid cooling is required. It may be noted that the shell and coil evaporator is restricted to operation above 50c in order to prevent the freezing problems.

Tube in tube or double tube evaporators:

The tube in tube or evaporators (or double tube evaporator), consists of one tube inside another tube. The liquid to be cooled flows through the inner tube while the primary refrigerant or secondary refrigerant (i.e. water, air or brine) circulates in the space between the two tubes. The tube in tube evaporator provides high heat transfer rates. However, they require more space than shell and tube evaporators of the same capacity. These evaporators are used for wine cooling and in petroleum industry for chilling of oil.

Experiment No -5

Object: To study the vapor compression air conditioning cycle and to calculate coefficient of performance (COP) by the use of P-H diagram.

Introduction: Air conditioning is the simultaneous control of the temperature, humidity, motion and purity of the atmosphere in a confined space. Air conditioning applies in the heating season as well as in the cold season. The air conditioning has wide applications in submarine ship, aircraft and rockets. Air conditioning is associated with the human comforts and controlling the humidity ratio.

Theory: Air conditioning may be defined as the process of removing heat from a substance under controlled conditions. It also includes the process of reducing and maintaining the temperature of a body below the general temperature of its surroundings. This is widely used for cooling of storage chambers in which perishable foods, drinks and medicines are stored. Figure shows the schematic of the unit with complete description.

Compressor: The main function of compressor is to raise the pressure and temperature of the refrigerant by the compression of the refrigerant vapor and then pump it into the condenser.

Condenser:Condense the high pressure vapor refrigerant into the high pressure liquid by condenser fan and passes it into the receiver tank for recirculation.

Capillary tube:Expands the liquid refrigerant at high pressure to the sub cooled liquid refrigerant at low pressure so that a measured quantity of liquid refrigerant is passed into the evaporator.

Evaporator:Evaporates the sub cooled liquid refrigerant by absorbing the sensible heat into vapor refrigerant and sends back into the compressor.

Vapor compressor cycle:The refrigerant starts at some initial state or condition, passes through a series of processes in a definite sequence and returns to the initial condition. This series of processes is called a cycle.

The standard vapor compressor cycle (SVCC) consists of the following process: Reversible adiabatic compression from the saturated vapor to a super heated condition. Reversible heat rejection at constant pressure (sub cooling liquid and condensation of the refrigerant). Irreversible enthalpy expansion from saturated liquid to a low pressure sub cool liquid. Reversible heat addition at constant pressure.

Coefficient of performance (COP): The coefficient of performance (C.O.P) of a refrigerating cycle is defined as the ratio between net refrigeration (output) and compressor work (input).

C.O.P= RE CW

RE = H1-H4 CW= H2-H1 C.O.P=

Experimental Procedure: 1. Clean the apparatus and make it free from dust.2. Ensure that all ON/OFF switches given on the panel are at OFF position.3. Now switch ON the main power supply.4. After 2 minutes switch ON compressor.5. After the gap of 10 or 15 minutes take the reading of pressure gauges, voltmeter, ampere meter and T1, T2, T3,T4,T5 and T6 by digital indicator.Observation & calculations: OBSERVATION TABLE S.No.P1P2T1T2T3T4T5T6VI

Calculation :

Mark point 1, 2, 3 using (P1,T1), (P2,T2), and (P2,T3) respectively on P-H diagram for (R-22) and read H1, H2 and H3 (where H3=H4) to calculate COP.

Experiment No -7

Object: To study the working of Ice plant and to study the vapor compression refrigeration cycle and its performance. And to find out: Theoretical C.O.P of the unit. Actual C.O.P of the Unit. Relative C.O.P of the unit.Introduction: Natural ice was used for preservation purpose for a very long time. But it has been replaced to a large extend by manufactured ice since the beginning of twentieth century because of the uncertainty of the natural supply and also because of the cost of transportation to the retail trade. The manufacture of ice is one of the principal needs of refrigeration and it will continue, as ice is the cheapest means for short time preservations of food. Theory: The vapor compression refrigeration cycle is based on a circulating fluid media viz , a refrigerant having special properties of vaporizing at temperatures lower than the ambient and condensing back to the liquid form, at slightly higher than ambient conditions by controlling the saturation temperature and pressure . When the refrigerant evaporates or boils at temperatures lower than ambient it extracts or removes heat from the load and lowers the temperature consequently providing cooling. The superheated vapor is increased to a level by the compressor to reach a saturation pressure so that heat added to vapor is rejected into the atmosphere, using operational ambient conditions with cooling medias such as air or water. The vapor is condensed to the liquid form and recycled again to form the refrigeration cycle.

The main components used in refrigeration cycle are 1. Compressor 2. Condenser 3. Throttling Device4. Evaporator.

Coefficient of performance: The coefficient of performance (c.o.p) of a refrigerating cycle is defined as the ratio between net refrigeration (output) and compressor work (input).

RE= H1-H4 CW= H2-H1

Procedure: 1. Ensure that ON/Off switches given on the panel are at OFF position.2. Switch On the condenser fan switch.3. After 2 minutes, switch ON the compressor.4. Check the compound and pressure gauge and note the readings.5. Note down the readings of pressure and temperature.6. Put brine solution in the tank.7. Note down the temperature of brine tank from digital temperature indicator.8. At the time of starting the apparatus note down the ammeter & voltmeter reading.9. Note down the reading of gauges, temperatures, ampere meter & voltmeter after running of the rig at least 20 to 30 minutes .take 2 or 3 readings.10. Start the agitator motor for 5 minutes only, after the gap of every 15 minutes. 11. Run the unit continuous and note down the brine solution temperature, if the brine temperature reaches up to 40c then put water in the ice cans for freezing. 12. Now check the temperature of suction pressure and discharge pressure.Observation & calculation:Data:Cos = 0.8Cph = 3.20 kJ/kg0Ch = ..kg/m3

Observation Table: S.No. tP1P2T1T2T3T4T5T6 V I

Calculations: COPthCOPactCOPrel

Mark points 1, 2, 3 using (P1, T2), (P2, T2) and (P3, T3) respectively on P-H Diagram for (R-134a) and read H1, H2 and H3 (where H3=H4) to calculate theoretical COP.

Experiment No -1Object: To study refrigeration test rig and to study the vapor compression refrigeration cycle. And to calculate coefficient of performance and draw P-H diagram.Apparatus: Refrigeration Test rig.Introduction: Refrigeration is the branch of science that deals with the process of reducing and maintaining the temperature of a space or material below the temperature of the surroundings. Heat must be removed from the body being refrigerated and transferred to another body whose temperature is below that of the refrigerated body.Theory: Refrigeration may be defined as the process of removing heat from a substance under controlled conditions. It is used for the manufacture of ice and similar products. This is widely used for cooling of storage chamber in which perishable foods, drinks and medicines are stored. The refrigeration has also wide applications in submarines ships, aircrafts.Vapor compression cycle:The refrigerant starts at some initial state or condition, passes through a series of processes in a definite sequence and returns to the initial condition. This series of processes is called a cycle.The standard vapor compressor cycle (SVCC) consists of the following processes: 1-2 reversible adiabatic compression from the saturated vapor to a super heated condition input. 2-3 Reversible heat rejection at constant pressure (de-superheating and condensation of the refrigeration). Irreversible is enthalpy expansion from saturated liquid to a low-pressure vapor. Reversible heat addition at constant pressure.

Compressor: The main function of compressor is to raise the pressure and temperature of the refrigerant by the compression of the refrigerant vapor and then pump it into the condenser.

Condenser: condense the vapor refrigerant into the liquid by condenser fan and passes it into the receiver tank for recirculation.

Capillary tube:It expands the liquid refrigerant at high pressure to the liquid refrigerant at low pressure so that a measured quantity of liquid refrigerant is passed into the evaporator.Evaporator:It evaporates the liquid refrigerant by absorbing the heat into vapor refrigerant and sends back into the compressor.Drier:A drier is used between the condenser and expansion device. The main function of the drier is to absorb the moisture from the liquid refrigerant and filter the dust particles.Accumulator: An accumulator is fitted in between the evaporator and compressor. It prevents the liquid refrigerant from entering the compressor.Coefficient of performance: The coefficient of performance (C.O.P) of a refrigerating cycle is defined as the ratio between net refrigeration (Output) and compressor work (Input).

RE= H1-H4 CW= H2-H1 Utilities required:Electric supply: single phase, 220 volt AC, 5-15 Amp socket with earth connection.

Water supply @ 2 LPM.Drain Required.Experimental procedure:1. For batch operation, fill known amount of water in the evaporator tank and put temperature sensor T6 in the evaporator water.2. Ensure that all ON/OFF switches given on the panel are at OFF position.3. Switch ON mains power supply.4. Switch On the compressor.5. Open the valve for discharge and suction pressure gauges.6. Switch ON the pump for uniform temperature of water in the evaporator.7. Note down the readings as per observation table after every 10 min. interval.8. Experiment can be repeated on load by switch ON the heater.9. Repeat step 2 to 7.Observation & calculation:Data:Cos = 0.7w = 1000kg/m3C p = 4.186 kJ/kg0CArea of evaporator = 30 x 25 cm2

Observation Table:For batch operation T6i = 0CS.No tminP1Kg/cm2P2Kg/cm2T10CT20CT30CT40CT60CVwltrVvoltIamp

Calculation: Mark points 1, 2, 3 using (P1,T1), (P2,T2), (P3,T3) respectively on p-h diagram for R-134 a . Read H1, H2 and H3 (where H3=H4). (

REact.= mXCpx(T6i-T6)kJ/sec.= (CO.P)act

EME-654: REFRIGERATION & AIR CONDITIONING LabMinimum 8 experiments out of following;

1. Experiment on refrigeration test rig and calculation of various performanceParameters.

2. To study different types of expansion devices used in refrigeration system.

3. To study different types of evaporators used in refrigeration systems.

4. To study basic components of air-conditioning system.

5. Experiment on air-conditioning test rig & calculation of various performanceParameters.

6. To study air washers.

7. Study of window air conditioner.

8. Study & determination of volumetric efficiency of compressor.

9. Experiment on Ice-plant.

10. Study of Hermetically sealed compressor.

11. Experiment on Desert coolers.Department of Mechanical Engineering