Lab Reports

Rectifying Common Mistakes

Sections (Revised)

• Title Page (separate page)• Abstract• Background and Theory• Materials and Methods• Results and Discussion• Conclusion• Literature Cited (References)• Appendix: Sample Calculations

Title Page

• Title of lab• Name• Names of partners • Date(s) performed• Date submitted

Abstract

• Write the purpose of the experiment• What effects and conclusions you observed• Include some numerical data that you found

(the variables that you observed)

• Note: I always write the abstract LAST

The purpose of this experiment is to observe pressure drops and determine flooding points of a packed column using various combinations of water and air flow rates. The effect of packing properties and liquid and gas velocities on the magnitude of the pressure drop in the column is investigated. For dry air runs, the experimental pressure drop across the column is compared to a theoretical value calculated by the Ergun equation. This equation depends on two packing characteristics: fractional void volume and specific surface area, found to be 0.898 and 240 ft-1, respectively. For liquid and gas counterflow runs, visual flooding points are observed and compared to a theoretical flooding line calculated by Wankat’s equation. The flooding line accounts for the packing characteristics by the packing factor, which is found to be 986. The pressure drop increases with high gas velocities, low fractional void volumes, and high packing factors.

Background and Theory• Give background on the chemistry involved in the

experiment– Explain the topic. Give any definitions. – Give chemical reactions and explain them– Write equations used and explain them– What are the chemicals used? What are their uses? Any

distinctive properties?– Any unique pieces of equipment used? Why? How do they

work?– Any applications in industry or everyday life?

• Do NOT give procedure here.

Background and Theory• Pictures/Diagrams can and should be entered into

background and theory– Structural formulas of compounds used– Pictures of actual samples of the compounds– Pictures of equipment used– Pictures of technology that use the theory

• Pictures should be pasted below the paragraph where they are mentioned (every picture should be mentioned).

• Pictures should be centered (one per line) with a title under or above the picture

Methylene chloride

This experiment involves the use of a packed tower, which is a vertical column filled with selected packing material. A liquid stream is fed to the top of the column, where it is evenly distributed over the packing material by nozzles or distributor plates. A gas stream is fed to the bottom of the column and travels upward, where it meets the downward-flowing liquid, as illustrated in Figure 1. The gas runs in the void space between pieces of packing while the liquid flows over the packing surface [1]. Hence, the packing in the tower provides a surface for vapor-liquid contact.

FIGURE 1: General Schematic of a Packed Tower [2]

Background and TheoryEntering Equations

• Don’t write equations in the body of a paragraph• Each equation gets it’s own line and it’s own number• Use an equation editor or write them in• They should most likely be entered in background and theory• Specify what each symbol means and its units

Through measuring the mass and volume of the metals, the density can be experimentally determined:

(1)

Where: d = density, g/mL v = volume, mL m = mass, g

v

md

The pressure drop of a single-phase fluid flowing through a packed column can be calculated by the Ergun equation: (1)

Where: ΔP = Pressure drop across the column, lbf / ft2

Z = Packed bed height, ft μg = Absolute fluid (air) viscosity, lb/ft-s ε= Fractional void volume, dimensionless gc = Newton’s law proportionality factor, 32.174 ft-lbm /

lbm-s2

ρg = fluid (air) density lbm/ft3

φsDp= Effective particle diameter for the packing, ft vo = Superficial air volumetric velocity, ft/s

This equation can be used to determine the expected pressure drop per unit height of packing for the dry air run. The first term on the right hand side of the equation accounts for viscous losses in laminar flow, while the second term accounts for kinetic losses in turbulent flow. Therefore, the flooding curves in Figure 3 should be curved lines with a slope approaching 1.0 for laminar flow and a slope approaching 2.0 for turbulent flow.

3

2

3

2

2

)1(

)(

75.1)1(

)(

150

psc

og

psc

go

Dg

V

Dg

V

Z

P

Materials and Methods

• If you were to create your own procedure, you would write your step-by-step recipe-type procedure– Be specific about what equipment is used

• Ex: 10 mL graduated cylinder

– Look at the procedures of other labs to see the level of detail needed

Materials and Methods

• When given the procedure, describe any changes from the procedure

Some changes made to the experiment include changing the solvents used for the separation of carotenoids in the annatto extract. The solvents used in the experiment were methylene chloride, acetone, 1% ethanol in methylene chloride, 2% ethanol in methylene chloride, and 4% ethanol in methylene chloride. In addition, less than 15 fractions were collected, and the column was stopped running after the orange bixin had eluted. Finally, the weight of the bixin isolated was not measured in the lab. No other deviations from procedure were undertaken.

Results and DiscussionThis is where you will tabulate or graph your data and FULLY DISCUSS it•The WHY (in terms of chemistry)•Interpret your results. What do they mean? Do they make sense? What’s the chemistry reason for it? •Compare your results to literature values. •Include percent error/ percent discrepancy. Explain possible reasons for error.•Include % yield if possible•Explain ways to eliminate error in the future or things you could have done differently. •The answers to all prelab/postlab questions should be found here in paragraph form

Tables and Figures• Give a bold title and number either above or

below the table/figure• Include units and symbols

TABLE 1. Physical Properties for PRO-PAK Protruded PackingPhysical Properties Values

Calculated from Data

Values Found in Literature

[6]Bulk Density, ρB [lbm/ft3] 16.2 21.0Fractional Void Volume, ε 0.898 0.96Specific Surface Area, aP [ft2/ft3]

240 372

Packing Factor, Fp 331 420

Tables and Figures

• Place the table or figure centered below the first paragraph that you discuss it

• After showing the table or figure, you may continue to discuss it in following paragraphs.

• Always keep a chart together on one page

The physical properties for the protruded PRO-PAK packing used in the column is shown in Table 1. The second column of the table lists the values that were calculated from measurements taken during the lab. The third column shows values for the same physical properties that are found in literature. The calculated bulk density of 16.2 lbm/ft3 is 22.8% less than the expected value of 21.0 lbm/ft3. This discrepancy may be due to human error when measuring the total volume occupied by the packing. Another reason may be that since the packing is randomly dumped into the column, the bulk density can vary each time according to the random arrangement into which the packing falls. In a large column, the arrangement of packing has a negligible effect on the calculated value. However, with a smaller control volume such as the graduated cylinder, the arrangement will have a greater effect on the calculation and can foster greater deviation from the expected value. The calculated void fraction of 0.898 is only 6.5% less than the expected value of 0.96, and its discrepancy may be due to the same reasons as the bulk density.

TABLE 1. Physical Properties for PRO-PAK Protruded PackingPhysical Properties Values Calculated

from DataValues Found in

Literature [6]Bulk Density, ρB [lbm/ft3] 16.2 21.0

Fractional Void Volume, ε 0.898 0.96Specific Surface Area, aP [ft2/ft3] 240 372

Packing Factor, Fp 331 420

Literature Cited1. P.C. Wankat, Equilibrium Staged Separations, Elsevier Science Publishing Co., New York, NY, 1988, Chapter 13

2. W.L. McCabe, J.C. Smith, and P. Harriott, Unit Operations of Chemical Engineering, 7th ed., McGraw-Hill, New York, 2005, Chapter 7, Chapter 18

3.C.J. King, “Separation Processes”, Chemical Engineering Series, 2nd ed., McGraw Hill, New York, 1980, Chapter 4

4.Fractional Distillation, Wikipedia, 2006, < http://en.wikipedia.org/wiki/Fractional_distillation>

5.P.A. Schweitzer, Handbook of Separation Techniques for Chemical Engineers, 2nd edition, McGraw Hill, NewYork, 1988, Section 1.7

6.PRO-PACK Protruded Metal Packing, Bulletin No. 23, Scientific Development Co., State College, PA.

How to use your references

The packed column is an apparatus that is commonly utilized in gas absorption, an operation in which one or more components of a gas stream are removed or absorbed by a liquid solvent. There are several industrial applications of packed columns for the purpose of gas absorption. One such application is the removal of CO2 and H2S from natural gas or synthesis gas by absorption in solutions of amines or alkaline salts [2]. Another application includes the washing of ammonia from a mixture of ammonia and air by means of liquid water [2].

Sample Calculations• In this section, you are to show all calculations (except % error) done in

the experiment. • If there are several trials, you only have to show your work for one trial• Explain what you are doing. • Show the formula, then numbers plugged into the formula, and then

your final answer. • Carry correct units throughout the calculation• Define any variables

Sample CalculationsConvert Inlet Temperature and Pressure to Absolute English UnitsFor the experimental data, inlet temperature must be converted from °F to °R, and inlet pressure must be converted from psig to psia. These values are to be used in subsequent equations. Using data from Run #6, where Po = 55 psig and To = 73 °F:

Po [psia] = Po [psig] + 14.7 [lb/in2] (2.1)

Po = 55 [psig] + 14.7 [lb/in2] = 69.7 psia

To [°R] = To [°F] + 460 (2.2)

To = 73 [°F] + 460 = 533 °R

Calculate the Air Density, ρg.The air density any at any point in the column for a given run, i, can be found by

the ideal gas law: (2.11)

Where: Ti = Temperature in ˚R at point for given run Pi = Pressure in lbf/ft2 = Pressure in lbf/in2

multiplied by 144 in2/ft2

R = Universal Gas constant in English Units = 1545.4 [ft-lbf / lbmol-˚R] Mair = Molecular Weight of Air = 29.0 lbm / lbmol

Take Dry Air Run #6 data and calculate the air density at the top of the column: = 0.0745 lbm/ft3

i

airii RT

MP

RRlbmollbft

lbmollbftlb

f

mfTop 533/4.1545

/0.29/)1447.14( 2

NOTE