160a lab manual-student s2014

5/28/2018 160A Lab Manual-Student S2014

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CHEMICAL ENGINEERING 160AENVIRONMENTAL ENGINEERING 160A

Chemical & Environmental Engineering Laboratory I

Laboratory Manual

Edition

2014

DEPARTMENT OF CHEMICAL &

ENVIRONMENTAL ENGINEERING"#$%&' (#))*+* #, *&+-&**%-&+

$&-.*%'-/0 #, (1)-,#%&-12 %-.*%'-3*


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C H E M I C A L A N D E N V I R O N M E N T A L E N G I N E E R I N G L A B O R A T O R Y I

Laboratory Manual

!UC Riverside, 2014Bourns College of Engineering

Department of Chemical and Environmental EngineeringRiverside, CA 92521


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Table of Contents

C H A P T E R 1

Introduction 1

Laboratory Exercises, Organization,

and Scheduling 2

Laboratory Preparation 3

Personnel 4

C H A P T E R 2

Laboratory Conduct 5

General Rules 6

Care and Use of Laboratory Equipment 7

Care and Use of Chemical Reagents 9

C H A P T E R 3

Data Analysis, General Considerations 11

Sources of Errors 12

Uncertainty Analysis 13

Statistical Analysis of Data 14

Graphical Analysis 15

C H A P T E R 4

Experiment #1 Drag Coefficient 18

Experiment #2 - Gas Diffusion 20

Experiment #3 - Aeration 24

Experiment #4 Ion diffusion 26

Experiment #5 - Wetted Wall 29


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I N T R O D U C T I O N

1

INTRODUCTION

What is the purpose of Chemical and Environmental EngineeringLaboratory I?

he course, Chemical and Environmental Engineering Laboratory I, CHE &ENVE 160A, is the first in a series of three laboratory courses required of all

Chemical Engineering and Environmental Engineering majors. The goals ofthese courses are to: 1) reinforce concepts learned in previously taken lecture

courses, 2) provide students with hands-on experience in collecting design andoperating data from engineering systems, 3) begin to challenge students in planningand conducting experiments to obtain relevant data needed for proper design andoperation of chemical and environmental engineering systems, and 4) give students anopportunity to practice and improve their technical writing and oral presentation skills.

To avoid crowded lab conditions and give each student as much hands-on experienceas possible, each lab section is limited to 25 students. Students will work in groups offour or five. Groups will stay together throughout the quarter. It is important that the

members of the group work together to develop laboratory protocols, complete thelaboratory exercises, and submit written reports in a time efficient manner. Each groupMUST review the laboratory manual and develop a laboratory protocol together priorto doing the lab work, and determine work tasks before conducting the lab. Duringeach session each student should record the experimental data in her/his laboratorynotebook.

There are six scheduled hours per week for this class. However, for the weeks yourgroup is in laboratory, only two to three hours will actually be spent in the laboratorycollecting data. The additional time each week is provided for lab groups to meettogether to discuss upcoming laboratory exercises, visit the laboratory to becomeacquainted with each laboratory module, to work on pre-labs and protocol

development and/or to work on data analysis and lab write-ups. EXTREMELYIMPORTANT SUGGESTION: TAKE ADVANTAGE OF THIS

ADDITIONAL TIME - DO NOT WASTE IT!

For the Spring 2014 Quarter, there are two lab sections. Section 1 labs will beconducted Monday and Wednesday, 9:10 am to 12:00 pm. Section 2 labs will be

Chapter

1

T


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conducted Wednesday and Friday, 12:10 pm to 3:00 pm. The lab period for whichyour group is not scheduled will be used for your regular lab group meeting.Laboratory exercises will begin on the week of April 7th.

Laboratory Exercises, Organization, and

Scheduling

There are a total of five different laboratory exercises for CHE/ENVE 160A. Thefour labs will be conducted over 10 weeks. There are extra weeks available for oralpresentations and lectures.

The four laboratory exercises are:Lab no. Topic

1 Drag coefficient

2 Arnold Cell/Gas

diffusion3 Aeration

4 Ion diffusion

5 Wetted Wall

As noted previously, there will be four or five students per lab group. Unless a studentwithdraws from the class, the composition of each lab group will remain fixed for theentire quarter. During the first week of the quarter, groups will be determined andassigned a number.

If difficulties arise within a group, please communicate them to Prof. Wheeldon orProf. Yan. REMEMBER, HOWEVER, AN IMPORTANT CHARACTERISTIC

THAT EMPLOYERS ASK ABOUT IS HOW WELL A PROSPECTIVEEMPLOYEE CAN WORK AS A MEMBER OF A TEAM. In a company you willnot be able to pick the people you work with. You must be able to overcome personalidiosyncrasies to get the job done - period.

The general laboratory schedule will be:

Week No. Task

1 Introduction, Lab Training

2 Laboratory Rotation #1



5 Oral Presentation #1

6 Statistical Analysis Lecture



9 Make-up week

10 Oral Presentation #2


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The specific schedule for each lab group is as follows:

Session 1

Rotation

Module 1

Drag coeff.

Module 2

Arnold Cell

Module 3

Aeration kLa

Module 4

Ion diffusion

Module 5

Wetted Wall

1 1A, 1F 1B, 1G 1C, 1H 1D, 1I 1E, 1J2 1E, 1J 1A, 1F 1B, 1G 1C, 1H 1D, 1I

3 1D, 1I 1E, 1J 1A, 1F 1B, 1G 1C, 1H

4 1C, 1H 1D, 1I 1E, 1J 1A, 1F 1B, 1G

5 1B, 1G 1C, 1H 1D, 1I 1E, 1J 1A, 1F

Session 2

Rotation

Module 1

Drag coeff.

Module 2

Arnold Cell

Module 3

Aeration kLa

Module 4

Ion diffusion

Module 5

Wetted Wall

1 2A, 2F 2B, 2G 2C, 2H 2D, 2I 2E, 2J

2 2E, 2J 2A, 2F 2B, 2G 2C, 2H 2D, 2I

3 2D, 2I 2E, 2J 2A, 2F 2B, 2G 2C, 2H

4 2C, 2H 2D, 2I 2E, 2J 2A, 2F 2B, 2G

5 2B, 2G 2C, 2H 2D, 2I 2E, 2J 2A, 2F

When you find out what your lab group number is - write it down here.

MY LAB GROUP NUMBER IS ________.

Laboratory Preparation

Laboratory notebook. Prelabs, notes and data should be recorded with an ink pen

in a permanently bound laboratory notebook. The most useful notebook is one

that has pages that makes graphing easy. Students should purchase one before

the beginning of the first exercise and use the same notebook for each

experiment. You must have a lab notebook that creates carbon copies of each

page. Record pre-experiment notes and protocols, changes from standard

procedures made during the course of the experiment, data, preliminary data

analysis and plots (for example, checks of a calibration curve to make sure an

instrument is operating correctly), and any other observations that you may feel

are interesting and noteworthy.

Why is it important to record information in a permanently bound notebook?

Loose papers and pages in spiral bound notebooks are easily lost. Further, a

permanently bound notebook is a journal of your in the laboratory. Journals are

extremely important when legal issues such as patents and lawsuits come about.

The time and activities associated with the experiment are entered sequentially.

Thus, there can be no question of whether information was added at a time

other than when the experiment was conducted and that the information was

indeed collected from the experiment and not another source.


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Each laboratory session requires considerable preparation.Students are required to develop their own protocols for conducting experiments inCHE/ENVE 160A. The information about each module in Chapter 4 of this manualis intended only to introduce the students to the apparatus they will use to collect data

necessary to complete experimental objectives. EXPERIMENTAL PROTOCOLSARE NOT PROVIDED. It is each groups responsibility to visit the lab during anappropriate class session prior to conducting each laboratory in order to inspect theapparatus and become acquainted with its operation. Each group will then be requiredto draft a protocol that must be approved by the TAs or Prof. Wheeldon/Prof. Yanbefore conducting the laboratory at the scheduled time.

Thus, students are required to be very familiar with the instrumentation and havedeveloped all procedures before coming to the lab session and should have her/hislaboratory notebook ready to enter data at the start of each lab period. LABPROTOCOLS AND ALL COLLECTED DATA SHOULD BE RECORDED IN

A BOUND LABORATORY NOTEBOOOK WITH SEQUENTIALLYNUMBERED PAGES. Never use loose or scrap pieces of paper. Note, the TAs willnot be responsible for providing data for the experiments or making sure students havecollected all of the necessary data.

Prior to each laboratory session, the laboratory manager (Kathy Cocker) and TAs willgenerally check that all of the equipment is in good working order and they will makesure that all necessary gases and/or solutions are available for the labs. However, otherthan ensuring that the students carrying out the lab exercises in a safe manner, the TAswill be there primarily to answer questions, not run the instruments for the lab exercise.

PersonnelClass Instructor: The professor for the class are:

Session 1: Dr. Ian Wheeldon. His office is in B319, his phone is (951) 827-2471, andhis email address is [email protected].

Session 2: Dr. Ruoxue Yan. Her office is in A247, her phone is (951) 827-2242, and heremail address is [email protected].

Laboratory Manager

The Chemical & Environmental Engineering Laboratory Manager is Kathy Cocker.His office is in B307 Bourns Hall and the phone number is (951) 827-2097.

Laboratory Instructors

The TAs for Spring 2013 are to be determined. Contact info. will be provided as soonas possible.


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E N G I N E E R I N G C A S E # 1

5

LABORATORY SAFETY AND PROTOCOL

What to do and what not to doabove all use common sense!

The Chemical and Environmental Engineering Programs are privileged to haveexcellent teaching and research laboratories in Bourns Hall. Rooms B108, B121, andB134 are the principal wet-lab teaching laboratories. B314, B316, B318, B328, B328A,B350 and B334 are the research laboratories areas. The general research topics and

faculty responsible for the research labs are as follows:

B312 Bourns - General biochemical engineering support and analyticalinstrumentation

B314 Bourns - Biosensors - Dr. Ashok Mulchandani

B318 Bourns Biological Processes in Environmental Engineering - Dr.Mark Matsumoto

B328 Bourns - Soil/hazardous organic contaminant interaction - Dr. MarkMatsumoto; Bacterial adhesion laboratory - Dr. Sharon Walter;

B350 Bourns-Nano electrochemical system laboratory Dr. Nosang V.Myung

B334 Bourns - Cold room (general support)

If you are interested in working in any of these areas or with any of these facultymembers, students are encouraged to contact the various faculty members.

LABORATORY CONDUCT

Proper conduct of everyone in the laboratories is important not only for the efficientand congenial operation of the labs, but also for the safety of all involved. Thisconduct applies to ALL STUDENTS - undergraduate, graduate, and postdoctoral. Inaddition to these guidelines, STUDENTS WORKING AS AN EMPLOYEE IN ARESEARCH LAB MUST ATTEND A GENERAL SAFETY ORIENTATIONFOR LABORATORY PERSONNEL GIVEN BY THE CAMPUS

Chapter

2


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L A B O R A T O R Y S A F E T Y A N D P R O T O C O L

6

ENVIRONMENTAL HEALTH AND SAFETY GROUP! This is a state andfederal regulation. A faculty supervisor or the Laboratory Manager (Kathy Cocker) cansign you up for one of these regularly offered sessions.

General Rules

Clothing and shoes: Always wear closed shoes in the laboratory. Open toe sandalsare not adequate protection from chemical spills. Spills and accidents can (and do)happen. Students should wear clothes that they are worried about damaging and/orpurchase a lab coat when working in the labs. Clothing is readily damaged as a resultof chemical spillage and splashing, particularly from strong acids, bases, and redoxchemicals. As an added precaution students should wear a chemical resistant apronwhen handling strong acid/base/solvent chemicals.

Safety Goggles: CHEMICAL SAFETY GLASSES OR GOGGLES MUST BE

WORN AT ALL TIMES IN THE LABORATORY. If you wear eyeglasses, theyshould have splash shields to protect against chemical splashing. Regular eyeglasses, bythemselves, are not adequate protection against chemical splashing. Also, certainchemicals may ruin plastic lenses. It is recommended that students purchase a pair ofchemical safety glasses/goggles from the bookstore and reserve them for their personaluse when working in the laboratories.

Eyewash stations and showers: There is a flexible eyewash/shower hose located atall sinks in the teaching and research laboratories. In addition, drench showers arelocated in several of the research labs. Familiarize yourself with the location and use ofthese safety items.

Eating and Smoking: Eating, drinking or smoking is not permitted in any of thelaboratories.

Animals and Pets: Animals and pets are not permitted in any of the laboratories.

Refrigerator and Ovens: Refrigerators, incubators, and ovens located in thelaboratories are not to be used for storing or preparing food.

Flames: Open flames should be placed in a fume hood if possible and always on anon-flammable surface away from combustible material. Never leave open flamesunattended in the lab.

Chemical Spills: Small spills should first be neutralized: sodium borate for base spillsand sodium bicarbonate for acid spills. After neutralizing mop or sponge up spillsimmediately. Large spills should first be contained with an absorbent material such asvermiculite and then neutralized. Additional absorbent may then be added to take upthe neutralized liquid and picked up. A faculty member or the Laboratory Manager,

Please read these

rules thoroughly.

They are very

important in

ensuring that

students have a

safe lab

experience.


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7

and Environmental Health and Safety (25528) should be notified when a large spilloccurs.

Volatile Organics: A fume hood should be used when using or dispensing a volatile

organic reagent. If the reagent is to be regularly used or dispensed for a project, asadditional protection, an appropriate respirator should be purchased, fitted, used, andregularly maintained. Respirators should not be shared; they are to be purchased,fitted, used, and maintained by one person. Environmental Health and Safety will fitand test respirators free of charge.

Pipetting: NEVER pipet any solutions by mouth. Pipet with a pipet bulb or apipettor. After using any pipet, please place it in a pipet storer for subsequent washingin a pipet washer.

Gas cylinders: Pressurized gas cylinders should be strapped or chained to a benchtop or wall. Before moving cylinders always remove regulators and screw on the cap.

DO NOT attempt to change regulators without prior training. Depending on the gastype, regulator threading and connections vary to prevent mixing of incompatiblematerials. Empty gas cylinders should be returned to the supplier as soon as possible.

Chemical waste disposal: Chemical wastes, spent and old reagents, and effluentsfrom bench-scale reactor systems SHOULD NOT BE DISPOSED INTO THEFLOOR DRAINS OR SINKS! Before beginning your laboratory experiment, checkwith a faculty member of the Laboratory Manager regarding proper disposal ofexpected wastes. Environmental Health and Safety will collect and dispose ofhazardous wastes upon request.

Daily departure: Check your work area when you leave for the day to be sureeverything is clean and neat. If you are the last person in the room, check all sinks inthe room to make sure the tap water is turned off. Make a cursory glance around theremainder of the laboratory to see if there are any major problems. If you are the lastone to leave for the day, please check each lab to see that all tap water is off, that thereare no major problems, and that all doors are locked. As you leave the laboratoryTURN OFF THE LIGHTS AND LOCK THE DOORS.

CARE AND USE OF LABORATORY EQUIPMENT

Many of the analytical instruments and much of the laboratory equipment in the

Chemical and Environmental Engineering Laboratories are commonly used for bothteaching and research. Therefore, it is imperative that each student use and maintaininstruments and equipment properly.


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8

BEFORE USING ANY ANALYTICAL INSTRUMENTRead the instruction manual or obtain training by qualified personnel on the use, care,

and maintenance of the instrument. Please contact the Laboratory Managerregarding instruction manuals or training.

Failure to use and maintain instruments properly will lead to poor laboratory resultsand jeopardize the progress of important research projects. Students who use andmaintain of laboratory instruments and equipment improperly may be subject todisciplinary action.

From time to time, students may experience problems when using some of theanalytical instruments. When problems occur, they should be discussed with theLaboratory Manager. DO NOT ATTEMPT TO "FIX" THE INSTRUMENTS

WITHOUT CONSULTING WITH A FACULTY MEMBER OR THELABORATORY MANAGER.

Balances: Balances and their surrounding areas should be cleaned using a brush aftereach use. Residual traces of reagents, liquids, etc. should not be evident. Theexperiment of the next person using the balance may be ruined by your laziness andlack of consideration.

pH Meters: pH meters are available in various laboratory rooms. They are not to bemoved from the room without permission from the Laboratory Manager or facultymember. The pH probes should not be used in harsh solutions or solutions that may

foul the probe. After use, the probes should be rinsed and placed in a neutral buffersolution for storage; pH meters should be placed in a stand-by mode.

Ovens and Furnaces: Convection ovens are primarily for reagent desiccating andsolids/moisture analyses, and are typically set at around 100 to 110oC. Muffle furnacesare primarily used for volatile solids analyses and are set at around 550oC. Do notadjust the temperatures of ovens or furnaces without consulting with the other users.

Autoclaves: In addition to small autoclaves located in several of the researchlaboratories, a large autoclave for sterilizing glassware and culture media is located inB358 Bourns Hall. Students needing to use this autoclave should consult with theLaboratory Manager before use.

Fume hoods: The Chemical and Environmental Engineering Laboratories containtwo types of fume hoods: canopy (elephant trunk) and sash. Sash-type fume hoodsare to be used for making up strong acid/base reagents, dispensing volatile chemicals,and performing digestions and extractions. When using sash-type fume hoods, theglass screen should be lowered at all times, except when placing equipment and or


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chemicals inside. Always prepare reagents with the glass screen lowered, wearinggoggles at all times. DO NOT STORE EQUIPMENT, CHEMICALS ORREAGENTS IN SASH-TYPE FUME HOODS. Canopy fume hoods are to be usedwhen hazardous volatile vapors may be emitted from a bench-scale laboratory

experiments that runs for long periods of time.

Dishwashers: There are various laboratory dishwashers located in the labs to be usedfor glassware cleaning. Instructions for their use can be obtained from the LaboratoryManager. Often, however, glassware will need to be washed by hand. When washingglassware, etc. by hand always wear goggles and gloves. You may not know whatresidual chemicals may be present in dirty glassware. Do not store dirty glasswarearound the sinks. Wash them first before leaving them to dry around the sink. Thiswill prevent an accident occurring when someone else picks up the glassware.

WHEN USING CHROMIC ACID OR OTHER DILUTE ACID SOLUTIONSTO WASH GLASSWARE, BE SURE TO CLEAN THE SINKS, FLOORS, ANDSURROUNDING AREAS THOROUGHLY. YOU MAY CAUSE THE NEXTPERSON TO HAVE SERIOUS BURNS AS A RESULT OF YOURNEGLIGENCE!

Borrowing: Environmental Engineering laboratory instruments and large equipmentshould not be moved from room to room. If there is a need to do so for yourresearch, obtain permission from a faculty member or the Laboratory Manager.EQUIPMENT OR SUPPLIES OF ANY KIND MAY NOT BE BORROWED ORREMOVED FROM THE LABORATORIES FOR USE BY OTHERDEPARTMENTS WITHOUT FIRST FILLING OUT A DEPARTMENTALEQUIPMENT LOAN FORM. SEE THE LABORATORY MANAGER FOR

PERMISSION AND THE NECESSARY FORMS. DO NOT LOANEQUIPMENT OR SUPPLIES TO NON-CHEMICAL/ENVIRONMENTALENGINEERING FACULTY OR STUDENTS WITHOUT CONSULTINGWITH THE LABORATORY MANAGER.

CARE AND USE OF CHEMICAL REAGENTS

Dry chemicals are separated generally into two categories: organic chemicals andinorganic chemicals. Strong liquid acids and bases are stored separately in cabinetsunder fume hoods. Volatile liquids are stored in cabinets which have exhaust vent builtin to carry away any off-gases.

Labeling: When new reagents are received, either for general lab use or for a specificproject, mark each bottle or jar of chemical with the month and year received, and yourinitials (e.g. Rec'd 10/96 MRM). Also mark the bottle or jar when the chemical is firstopened (e.g. Open 12/96 MRM). Use labeling tape (not masking tape) or adhesive


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label. Grease pencil, or other non-permanent marker, is not acceptable; labelinginformation is easily erased.

Dispensing: When weighing reagents, use an intermediate container. Carefully

dispense the approximate amount of reagent you'll need into the intermediatecontainer first, then transfer the reagent onto the weighing vessel or paper in thebalance. Do not return excess chemical (in the intermediate container) back into thereagent bottles.

Strong Acids and Bases: Liquid acids and bases should be dispensed in a sash-typefume hood. Carry acid/base bottles in the rubber acid/base carrier, or use a cart.Never carry acid/base bottles by the handle or neck. When holding an acid/basebottle, always have one hand under the base of the bottle. Wear goggles, apron andgloves when dispensing and mixing strong acids or bases. Mix strong acids or bases ina Pyrex or Kimax flask or beaker. Ordinary flint glass reagent bottles will crack fromthe heat. Add the acid or base to water in small incremental amounts over time.

ALWAYS add concentrated acids or bases to water. NEVER add water toconcentration acids or strong bases !!

Storage and Labeling of Reagent Solutions: Reagent solutions should be preparedusing volumetric flasks or graduated cylinders. However, solutions should NOT bestored in them. After a reagent solution is made, it should be placed in a clean,appropriately sized reagent bottle. The reagent bottle should then be labeled with thefollowing information: contents, date of preparation, preparer's initials, project,disposal date (date beyond which reagent should be discarded), and other specialwarnings (e.g. flammable, volatile, extremely caustic, etc.). An example is: 0.1 MNaOH, MRM, Prep. 11/1/96, Dis. after 2/1/97. Improperly marked reagents mustbe assumed to be old and will be discarded.

Water: There are three kinds of water available in our laboratories:

Tap water: Water at the sinks is regular water from the municipal water supply.However, because there are many chemicals in use and the possibility of backflushingexists, all of the taps are marked, Industrial Water - Do Not Drink. If you wantdrinking water, please use the drinking fountains near the lavatories.

Reverse osmosis (RO) water - This water is available from the special taps markedDI at each sink. This water is very high quality and is adequate for most reagentpurposes.

Nanopure water - This water is made by taking RO water and passing it through

activated carbon, two mixed bed ion exchange columns, and a 0.2 micron filter. Thiswater is the highest quality water available in the Chemical and EnvironmentalEngineering laboratories, and should be used sparingly, for mixing high purity reagentsand standards, and for final rinsing of special glassware.


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D A T A A N A L Y S I S B A S I C S

11

DATA ANALYSIS BASICS

Some form of analysis is required on experimental data. The analysis may be avery simple qualitative assessment about an observed trend or it may involvecomplex error analysis coupled with a statistical analysis to determine the

probability of true differences between experimental data sets.

While the ability to carry out experiments and collect data is important, the usefulnessof conducting experiments depends on careful analysis of the collected data. Withoutanalysis, an experiment is merely a work task. Data analysis can be used for a variety ofpurpose such as determining 1) whether collected data are reasonable, 2) theuncertainty associated with the measurements, 3) coefficients for theoretical modelssuch as KLa, 4) whether significant differences in data sets exist as a result of changedoperating conditions, and 4) empirical mathematical models for relationships betweendifferent parameters. However, the analysis of experimental data is an acquired skillthat improves (hopefully) with experience. One of the purposes for this course is thatstudents begin to develop these skills.

General ConsiderationsA good outline that can be used for experimental data analysis has been developed byHolman1(1994).

1. Examine data for consistency. Are the measurements reasonable? This basic questionis the common sense approach to experiments. A simple example is when you fillup your car with gasoline, you expect your gas gage to read Full right after. If itdoesnt, you suspect something is wrong like the gage is broken, your gasoline tankleaked, or the pump wasnt working correctly.

This same logic applies to engineering experiments. When you bubble pure

oxygen gas through water that is not saturated with oxygen, you would expect thatdissolved oxygen concentration to increase, not decrease or stay the same. Why doyou know this? Based on mass transfer considerations (of course!).

1Holman, J.P. Experimental Methods for Engineers, 6thed., McGraw-Hill, Inc., San Francisco, 1994.

Chapter

#


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To use this common sense approach it is important that the experimenter befamiliar with the expected trends/readings based on theory and/or pastexperience. You dont want to continue doing an experiment if you are collectingbad data. If you know beforehand what to expect, this type of situation can be

avoided. The more thorough the understanding of what is expected based ontheory and/or experience prior to the start of an experiment, the more likely it isthat the experiment will be successful.

2. Perform a statistical analysis of data where appropriate. When measurements are repeatedseveral times, statistical parameters such as mean, median, and standard deviationare useful in evaluating the level of precision for a particular measurement, andlevel of confidence for a given data set.

3. Estimate uncertainties in the results. All instruments that measure something have anuncertainty associated with them. For example, when a thermometer reads 100oC,is it accurate to 1oC or 0.1oC. If the temperature reading is used in conjunction foranother parameter such as heat content, then the temperature uncertainty carriesover to heat content as well. Generally, these types of uncertainties can beestimated beforethe experiment is conducted.

4. Anticipate results from theory. The theory or theories relevant to the experimentsubject should be carefully reviewed to determine what trends may be expectedbefore the experiment takes place. This step is particularly important indetermining an appropriate graphical presentation of the experimental data. Forexample, if a first-order system is subjected to a step input, a semilog plot of thedata should result in a linear plot. Use of dimensionless parameters (e.g. Reynoldsnumber, Peclet number) may also provide important insights.

5. Correlate the data. The experimental data should be interpreted in terms of physicaltheories or the basis of previous experimental work (done by others). The resultsshould be examined to see if they conform to or differ from previousinvestigations or standards.

Sources of Errors

Errors occur in all experiments. Some of the errors can be avoided while otherscannot. Most of the errors that can be avoided are due to uncontrollable variables,and/or lack of experience or carelessness on the part of the experimenter. These types

of errors can be avoided by carefully reviewing each step and condition (variable) in anexperiment and assessing whether they can significantly affect the outcome of theexperiment. If so, then the experimenter should alter the experiment, or pay particularattention to certain aspects of the experiment, to ensure that a gross error does notoccur. As the saying goes, An ounce of prevention is worth a pound of cure. This


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13

means that time spent preparing an experiment is well worth the effort. A great deal oftime and money can be wasted as the result of poor planning.

Beyond these controllable errors, there are errors of uncertainty. These are errors

that are beyond the control of the experimenter. There are two principal uncertaintyerrors, fixed and random. Fixed, systematic,or bias errors are errors that are generatedrepeatedly by the same amount for an unknown reason. For example, a ruler used tomeasure length indicates a length of 1 m. However, the ruler actually measures 0.99 mwhen compared to the actual standardized 1 m length. Thus, the ruler always measures1 cm short per m measurement. These types of errors are often unknown. Calibrationof an instrument to an absolute standard, such as National Bureau of Standards (NBS)standards, is the best way to detect and/or avoid systematic errors.

The second type of uncertainty errors is random errors. These errors are caused by avariety of reasons that cannot be avoided such as experimentalist bias, fluctuations ininstrument readings, minor temporal variations in variables, etc. Every measurementhas a random uncertainty associated with it. This uncertainty is often related to theaccuracy of the instrument. For example, a pH probe may have an accuracy of 0.01pH units within the pH range between 2 and 12. This means that, properly calibrated,that this particular pH probe is accurate to within 0.01 pH unit between pH 2 and pH12. Outside of those pH ranges, the pH probes accuracy may or may not fall withinthat specification.

Uncertainty (Error) Analysis

Whenever a measurement is made there always is some uncertainty. The instrumentmanufacturer may define this uncertainty, or may be estimated by the experimenter

(based on experience). Whatever the case, these measurement uncertainties are carriedon when a calculated result is generated. Many measurement uncertainties may beassociated with a single calculated result. The overall uncertainty for the calculatedresult is a function of the error associated with each measurement. In general, thisoverall uncertainty can be calculated as:

where R = function of the independent (measured) variables, xi = independent(measured) variable i, ei = uncertainty in measured variable i, and ET = overalluncertainty in calculated function R.

As a simple example, consider the volume of a rectangular box that is determined bymeasuring its dimensions with a ruler that has an accuracy of 0.2 cm. The measured


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dimensions are L = 45 cm, W = 60 cm, and H = 20 cm. Based on thesemeasurements, volume would be 54,000 cm3.

To determine the uncertainty of the volume:

Statistical Analysis of Data

The purpose of this section is to not to provide a comprehensive overview of statisticaldata analysis, but rather to review important concepts and outline appropriateapplication of statistics to experimental data. Most of this information has beencovered in previous courses. More in depth coverage of statistical data analysis can beobtained from course work or various textbooks.

Population StatisticsWhen a set of repeated measurements is made, the individual readings will vary fromeach other. Most often statistical measures are used to describe the entire set ofmeasurements in terms of a centralized number, the spread of the data, and frequencyof distribution. Typical parameters include:

Arithmetic mean(or average) -

Median - middle data point of a sequentially ordered data set. The datum for which halfof the data points in the set are higher and half are lower in value is the median.


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Standard deviation - descriptor of the spread of the data compared to the mean =

Confidence interval - the probability that the actual mean value lies within a certainnumber of "values around an experimental mean. As an example, if a measured flowreading has a mean of 100 and a standard deviation of 5, the 95% confidence intervalwould be 100 1.96(5) = 100 9.8. In other words, there is a 95% probability thatthe actual mean value is between 90.2 and 109.8.

Chauvenets criterion - sometimes one or two data points seem to be very differentcompared to all of the other data points in a population. While it is logical to throw

out these types of data points, it is possible to apply a statistical test, Chauvenetscriterion, to determine whether data may be discarded. To apply this criterion, thedeviation of each data point from the mean must be calculated and divided by the

standard deviation: . The calculated value is compared to Chauvenets

criterion, which is a function of the number of readings in the population.

Number oftotal readings

3 4 5 6 7 10 15 25 50 100

Max.deviation,

1.38 1.54 1.65 1.73 1.80 1.96 2.13 2.33 2.57 2.81

Graphical Analysis

Experimental scientists and engineers are well known for the use of graphs to highlightcertain data trends and insights. However, random graphing of data usually generatesan excess of charts that are useless. Considerable thought must be given to thephysical phenomena involved in each experiment before preparing a plot. The personwho understands the physical processes (the theory) is usually the person who canmost successfully present experimental data graphically.

The most common graphical technique is the correlative graph in which the

relationship between two variables is plotted in a linear manner. To do this, theexperimenter must know what type of function will best describe the data. Thisknowledge is based on theoretical understanding of physical phenomena.

A summary of plotting methods for various functions to obtain straight lines.


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Function Plotting Method Slope Y-intercept

yvs.x on linear paper A b

log y vs. log x on log-log paper B log a

log y vs. x on semilog paper b log e log a

vs. on linear paper A b

vs. x on linear paper C b + cx1

vs. x on linear paper a + bx1

vs. x on semilog

paper

c log e b + cx1log e

vs. x on semilog

paper

B

y vs. 1/x on linear paper B a

y vs on linear paper B a

The best method to determine the slope and y-intercepts for these various plots is theuse of the least squares method of linear regression, which is found in many standardplotting software packages such as Excel.


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L A B O R A T O R Y E X E R C I S E S

17

LABORATORY EXERCISES

This chapter provides an introduction for the laboratory exercises thatCHE/ENVE 160A students will be conducting during this course.

As noted previously, there are a total of four different laboratory exercises forCHE/ENVE 160A. The four labs will be conducted by each group over the durationof the 10 week quarter. The four laboratory exercises are:

Lab No. Topic

1 Drag coefficient

2 Arnold Cell/Gasdiffusion

3 Aeration kLa

4 Ion diffusion

5 Wetted wall column

To reiterate there will be four or five students per lab group. Groups are required toreview the relevant sections in this chapter prior to conducting each laboratory

exercise. This information is intended to assist each group in generating an appropriatepre-lab and experimental protocol that they can use during their assigned laboratorysession to achieve all experimental objectives.

Chapter

4


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L A B O R A T O R Y E X P E R I M E N T

8

Exercise 1 Drag Coefficients ofParticlesExperimental Objectives

Please design and conduct experiments to achieve both of the following objectives

1) Determine the relationship between drag coefficient and Reynolds number forspherical particles. Compare you results to Stokes Law where CD= 24/Re.

2) Demonstrate the effect of particle shape on the velocity of a sphere and astreamlined shape in a viscous fluid.

Experimental Apparatus

Experimental apparatus consists of two liquid filled tubes shown Figure 4.1 below. Theparticle of interest is dropped into one of the columns and the time required travel apredefined distance is recorded. It is suggested that glycerol and castor oil are used. Thespheres and variously shaped particles are to be dropped ONE AT A TIME from thetop of the tubes. When each particles arrives at the recess in the base of the tubes, it isremoved by turning the valve through 180. It is importantly to remove each sphere asit reaches the valve, as two or more spheres will prevent the valve from operating.

Figure 4.1 Schematic of drag coefficient apparatus.

Background

The drag force exerted on a solid object moving through a fluid is commonlyconsidered as being made up of two components Surface Drag and Form Drag.The total drag force can be expressed as,


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Stokes Law can be used to determine the viscosity of a fluid using the followingequation.

In the case of surface drag around a sphere, it has been shown that the drag coefficientis related to the Reynolds number (Re) as follows:

And, that the drag coefficient of spherical particles can be determined experimentallyby,

Notation:

F, drag force (N); CD, drag coefficient; A, cross-sectional area of solid object (m2); #,fluid density (kg m3); V, relative velocity of sphere through fluid (m s-1); , coefficientof dynamic viscosity (N s m-2); $s, specific weight of solid object (N m

-3); $f specificweight of fluid (N m-3); r, radius of sphere (m); D, diameter of sphere (m); Re,Reynolds number of a solid object; g, gravitational acceleration; M, mass of solid object

$glycerol=1.046 g cm-3;$Caster oil=0.95 g cm-3;$water=1 g cm-3

$= Mg/Volume

Suggested Discussion Questions to Address in the Laboratory Report

Discuss the relative contributions of surface and from drag when particles of various shapes are

dropped in a viscous fluid. In this case, which is dominant? When would you expect a

streamlined shape to travel faster than the spheres?


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Exercise #2 - Gas Diffusion

Experimental Objectives

The design and operation of process plants to achieve the desired changes in materialsdepends upon the properties of the materials (or contaminants) in a flowing medium(gas or liquid). One of the most important properties of materials in fluids under suchcircumstances is diffusivity. Fluid flow and mass transfer operations depend to someextent on this property and such data are always needed in plant design.

The objective for this laboratory exercise is to determine the diffusivity of a volatilefluid in air using an Arnold cell. Please design and conduct experiment to achieve thefollowing objectives

1) determine the gas phase diffusion coefficient of acetone in air at 40 C.

2) compare the diffusion coefficient obtained from experimental data withpublished data from a handbook.

Theory

The diffusivity of the vapor of acetone in air can be determined by Winklemannsmethod in which liquid is contained at constant temperature in a narrow diametervertical tube, which an air stream is passed over the top of the tube. This techniqueensures that the partial pressure of the vapor is transferred from the surface of theliquid to the air stream by molecular diffusion.

As outlined in the text:

where constant molar flux of A ( ), = diffusivity of acetone in air (

), c=total molar concentration in the gas phase ( ), = change of the mole

fraction of A along the diffusion path,yA = mole fraction of component A in the vapor

phase, = molar flux of B

However, the net flux of B is zero throughout the diffusion path. Therefore,


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The above equation may be integrated from z= z1to z= z2and fromyA=yA1toyA=yA2which yields:

where = log-mean average concentration of component B and L= length of the

diffusion path (m).

Under pseudo-steady-state conditions, the molar flux may also be described by:

where = molar density of A in the liquid phase ( ).

Again, under pseudo-steady-state conditions, these two equations may be equated:

The above equation may be integrated from t= 0 to t = tand from z= L0to z= Land yields

Arnold Cell Apparatus

The Arnold cell apparatus consists of an acrylic assembly sub-divided into twocompartments (see next page). One compartment is used as a constant temperaturewater bath. The other compartment incorporates an air pump and necessary electricalcontrols for the equipment.


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Figure 4.2 Schematic of Arnold cell.

Water in the water bath is heated by an immersion heater which is controlled to atolerance of 1C.

The capillary tube utilized for the determination of the diffusivity coefficients ismounted on top of the constant temperature water bath. The total capillary length is

10.5 cm. Air can be supplied to the capillary tube by a flexible tube connected to theair pump. The height of the liquid in the capillary can measured using a travelingmicroscope mounted on a removable support stand that incorporates a vernier heightgage.

Procedures

1. Partially fill the capillary tube with acetone to a depth of approximately 35 mm.Remove the top nut from the metal Swage-lok fitting. Carefully insert thecapillary tube through the rubber ring inside of the metal nut until the top ofthe tube rests on the top of the nut. Gently screw this assembly into the topplate stopping with the T piece normal to the microscope. GENTLY

connect the air tube to one end of the T piece and adjust the object lens towithin 20-30 mm of the tank.

2. Adjust the vertical height of the microscope until the capillary tube becomesvisible. To improve initial visibility of the tube, first adjust the object lens(closest to the tank) until the tube becomes clearer. Finer adjustment of the


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3

focus on the meniscus is accomplished with the eyepiece lens. (The capillarytube the image will be upside down.) When the meniscus has beendetermined, align the sliding vernier scale with a suitable graduation on thefixed scale.

3.Turn on the air pump, and record the level inside of the capillary. Turn on thetemperature controlled water bath and wait for the temperature to reach thedesired temperature . Read the level and from this determine L0.

4. Record Land t, and repeat at regular time intervals.

References:Welty, J.R., Wicks, C.E., and Wilson, R.E. Fundamentals of Momentum Heat andMass Transfer. 3rded., John Wiley & Sons, Inc., 1984.Suggested Topics to Address in the Discussion of results.

1. Both your results and those from handbooks were determined fromexperimentation. Why wouldnt your data be just as valid as that found in anengineering handbook? What were the most likely sources of error for theexperiment?

2. Propose a method by which the aqueous phase diffusion coefficient of acetonecould be measured simply in a laboratory. This need not be sophisticated, butthink of principles and problem solving strategies developed in CHE 120 thatcould be used to determine Dacetone/H2Ofrom easily measurable parameters in alaboratory. Do you expect the aqueous phase diffusion coefficient to be biggeror smaller than the value you measured here? Why?


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4

Exercise #3 - Aeration KLa values


A commonly used parameter in gas-liquid mass transfer systems is the overall gas

transfer coefficient, KLa, which combines several physicochemical parameters. In thismodule please address two or more of the following objectives:

1) to determine the value of the overall mass transfer coefficient, KLa, in a batchmechanical aerator using a dynamic measurement technique

2) to determine the effect of stirrer speed and paddle size on KLa,

3) determine the effect of salinity on KLa.

Background

Gas-liquid mass transfer is often accomplished in well-mixed tank systems. Inparticular, aeration of water typically involves the introduction of compressed air intothe bottom of a well mixed tank through dispersers such as perforated pipes, poroussparger tubes, or porous plates. These dispersers introduce air as small bubbles thatrise through the overlying water, allowing air-water transfer of oxygen to occur acrossthe cumulative interface of the bubbles within the system. The rate of mass transferwill control the rate of aeration (i.e., the rate at which the oxygen concentration in thewater increases over time). Thus, variables that influence the rate of mass transfer canbe used as variables for process optimization. In this laboratory, you will be examiningseveral potential process variables that may or may not influence aeration rates.

Experimental Apparatus

Equipment and supplies provided for this laboratory exercise include:

1. Armfield fluid mixing apparatus and accessories. The reactor vessel holds up toX liters of water, and is connected to a variable speed motor that allows foragitation of the fluid via a paddle mixer. Note that several sizes of paddles areprovided for mixing. At the bottom of the vessel are several gas dispersionstones that can be used to deoxygenate the water supply (when nitrogen is fedthrough the dispersion stones) or aerate the water supply (when air is suppliedthrough the dispersion stones). The feed gas composition can be controlledby regulators connected to the nitrogen and air tanks. A flow valve is also

provided so that the rate of gas flow delivered into the system can becontrolled.

2. Dissolved oxygen meter and probe

3. Salt (NaCl)


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5

4. Pan balance

5. Ruler, stop watch, thermometer and barometer

6. Nitrogen and air cylinders

Procedures

The general procedure for each KLameasurement is outlined below.

Fill the reactor with the appropriate solution and determine its volume. Measure andrecord the temperature of the solution and the atmospheric pressure.

1. Deoxygenate the solution by first introducing nitrogen gas into the bottom ofthe tank. The flow of nitrogen should be the same as the air rate that will beused for the desired test.

2. Monitor the dissolved oxygen concentration. When the dissolved oxygenconcentration is zero or very close to zero, switch the gas flow from nitrogen

to air.3. Record dissolved oxygen concentration as a function of time.

References

Welty, J.R., Wicks, C.E., and Wilson, R.E. Fundamentals of Momentum Heat andMass Transfer. 3rded., John Wiley & Sons, Inc., 1984.Suggested Discussion Questions to Address in the Laboratory Report

Aeration is a common process in wastewater treatment, in which air is introducedinto secondary effluent (i.e., effluent that has already undergone biologicaltreatment during which oxygen can be consumed) to increase the dissolvedoxygen (DO) concentration prior to effluent discharge into the environment. Forwastewater treatment, can you think of other potential variables that mightinfluence air-water exchange? Please be sure to provide an explanation for yoursuggestion of each variable.


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6

Exercise #4 - Liquid DiffusionThe design and operation of process plants to achieve the desired changes in materialsdepends upon the properties of the materials (or contaminants) in a flowing medium

(gas or liquid). One of the most important properties of materials in fluids under suchcircumstances is diffusivity. Fluid flow and mass transfer operations depend to someextent on this property and such data are always needed in plant design.


Design and conduct the experiment to determine the diffusivity of a dissolved sodiumchloride in water and compare the experimental data with published data from ahandbook using one-dimensional diffusion cell.

Background

Ficks first law defines the diffusion of a dissolved component in an isothermal,isobaric system. In one dimension, the Fick rate equation is:

where constant molar flux of A ( ) in the x-direction, = diffusion

coefficient of A through B ( ), and = concentration gradient of A in the x-

direction.

The total mass transfer rate (in one dimension) due to diffusion can be determined bymultiplying the flux rate times the cross-sectional diffusion area.

where is the total transfer rate ( ).

In dilute solutions, the concentration of an ionic (salt) solution can be monitored bymeasuring the electroconductivity of the solution. The molarity of a solution can be

determined directly.


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whereM= molarity (mole/L), k= conductivity (S cm-1), and CM= proportionalityfactor (S cm-1M-1). CMvaries with salt. For NaCl, CM= 9.67 S cm

-1M-1.

Incorporating this into the previous equation:

where V= volume of reactor into which mass is being transferred.

The diffusion coefficient, DAB, can be determined by:

Reference: Welty, J.R., Wicks, C.E., and Wilson, R.E. Fundamentals of MomentumHeat and Mass Transfer. 3rded., John Wiley & Sons, Inc., 1984.Experimental Apparatus

The liquid diffusion apparatus consists of a variable speed magnetic stirrer and stir barfor agitation of the test solution. A specially designed diffusion cell is mounted to thetop of the stirred vessel and clamped into position using the locking screw. At the baseof the stirred vessel is a connection for the conductivity cell, which is connected to theconductivity meter with data acquisition system.

The apparatus uses vertical capillaries 5 mm long and 1mm bore (inside diameter) torestrict the diffusion to one dimension. Salt concentration will be effectively zero in

the water end and 2M at the concentrated salt solution end.

Procedures

1. Completely fill the diffusion cell with 2M NaCl solution. Wipe of any excess.Clamp cell into position. DO NOT SPILL into the outer vessel. Fill the outervessel with distilled or equivalent water. Record the amount and temperatureof water used to fill the vessel.

2. Check the conductivity meter and make sure the initial reading is below 10-4%-1.

3. Turn on the magnetic stirrer to GENTLY agitate the water. Record theconductivity at regular intervals.

4. Generate a calibration curve to confirm the constant Cm


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Figure 4.3Schematic of one-dimensional diffusion cell.

Suggested Discussion Question to Address in the Laboratory Report

Discussion the relative magnitudes of diffusion coefficients for gases, liquids, andsolids.


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9

Exercise #5 - Wetted Wall Absorber


A wetted wall absorber is commonly used to study gas-liquid mass transfer. Thisdevice provides a well-defined area of contact between the two phases. A thin liquidfilm flows along the wall of the absorption column while in contact with a gas phase.The objectives for this laboratory exercise are

1) to determine the relationship between mass flow rate and the mass transfercoefficient, kL, and to compare the experimental results with other empiricalrelationships reported in engineering textbooks.

2) to prepare an appropriate plot of Sh versus Re for the experimental data.Determine the slope of the resultant best-fit line and compare results to the

Vivian and Peaceman equation

Wetted wall absorption apparatus

The wetted wall absorption apparatus consists of an absorption column connectedto a feed chamber of water. A pump is used to deliver the water to the top of theabsorption column, where it cascades down the sides of the column to develop afalling water film that is ideal for air-water gas exchange. The apparatus allows thewater flow rate to be controlled between ~100 and 300 cc/min. An aircompressor delivers airflow outside the falling film, with the rate of air flowcontrolled by regulator between 1000 and 3000 cc/min.

Adjacent to the absorption column is a deoxygenator column, through whichwater from the supply tank first passes. In the deoxygenator column, nitrogen gascan be used to remove oxygen from the feed water supply, thereby creating a lowdissolved oxygen concentration at the top of the absorption column (check withTA to make sure the water is being degassed properly during operation).Dissolved oxygen probes are provided at the top and bottom of the absorptioncolumn to allow oxygen concentration to be monitored during absorption columnoperation. A thermometer is also available so that the temperature of water can bemeasured during operation.

Procedures

1. Turn on the supply switch and start the deoxygenator vessel feed pump.Admit nitrogen into this vessel and regulate the nitrogen flow until a constantstream of gas bubbles fills the vessel. (NOTE: If a plug flow pattern occurs,the nitrogen flow rate is too high.)


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2. Start the compressor and regulate the air flow rate until it reads 1,000 cc/min.Start the wetted wall column feed pump and set the flow rate to 100 cc/min.

3. After the water overflows the top section of the wetted wall column and runsdown the inside wall, make sure the whole perimeter is wetted by carefullysliding a brush down the inside of the tube.

4. Allow the system to reach steady state, about five minutes, then take oxygenreadings from both the inlet and outlet.5. Increase the water flow rate. Allow the system to reach steady state again.

Take oxygen readings from both the inlet and outlet. Repeat at various waterflow rates of.

6. Repeat the experiment for two other air flow rates.


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1. Absorption column 17. Air compressor2. Bearing and knife-edge gimbal 18. Sintered metal disk3. Feed chamber 19. Not available4. Discharge section 20. Toggle selector switch (not used)

5. Sintered metal disk 21. Deoxygenator vessel feed pump switch6. Discharge line 22. Wetted wall column feed pump switch7. Drain valve 23. Air compressor switch8. Supply tank 24. Main supply switch9. Sensor probe 25. Not available10. Adjustable feet 26. Nitrogen tank11. Dissolved oxygen probe 27. Water flowmeter12. Sensor probe 28. Air flowmeter13. Deoxygenator column 29. Electronics cabinet14. Nitrogen inlet valve 30. Support framework15. Deoxygenator feed pump 31. Support ring16. Absorption column feed pump

Reference:

Welty, J.R., Wicks, C.E., and Wilson, R.E. Fundamentals of Momentum Heat andMass Transfer. 3rded., John Wiley & Sons, Inc., 1984.Suggested Discussion Question to Address in the Laboratory Report

In this experiment, a convective mass transfer coefficient (akLvalue) is used todescribe mass transfer of oxygen between air and water in the wetted wall absorptioncolumn. At a specific point along the columns flow path, derive an expression thatrelates kLto DO2/water, the diffusion coefficient for molecular oxygen in water.

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