chem eng practs

8/13/2019 chem eng practs

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Chemical Engineering Laboratory I, i.e., ChE 302, aims to familiarize the students with some of

the basic concepts of chemical engineering and concentrates mostly on fluid flow, heat and mass

transfer experiments, some basic separation operations and behavior of chemical reactors.

Another major aim of the course is to familiarize the students with the concepts of accuracy and

precision as well as the fundamentals of the application of statistics in engineering

experimentation as it is related to model building, model parameter estimation and experimentaldesign. This part of the course is introduced mostly in the one hour lecture period held each

week.

The course is not intended to be parallel to one or more theoretical courses present in the

Chemical Engineering curriculum. It is felt that to do an experiment before one is formally

introduced to the theory relevant to the experiment has as many advantages as the reverse

procedure. To have done the experiment prior to a formal introduction to theory will definitely

help a faster and firmer understanding of the theory when it is introduced. On the other hand, if

the formal introduction to theory has preceded the experimentation it should help the

experimenter to grasp and perform the experiment easier and also help re-inforce the available

theoretical background. All students taking ChE 302 will have a chance to do at least a few

experiments in to which they have not yet been formally introduced as well as doing some otherexperiments about which they already have been introduced to the theoretical fundamentals

concerning the experiment.

The purpose of any of our chemical engineering laboratory courses is to serve several important

functions in a student's program of development that reflect clearly expectations of abilities of a

technical professional.

Among the most important are:

1. To teach students to communicate results obtained from experimentation through a writtendocument in a clear and concise fashion2. To put theory into practice in a realistic sense, through a set of instructions, which willrequire independent logical thinking (the intent here is to compare the idealistic

(theoretical) teachings in the classroom with the real-world operations (experimental

equipment)and to realize the limitations of each)

3. To acquaint the student with the availability and use of published data and the varioussources for obtaining these references

1. To illustrate the difficulties associated with leadership and group effort approaches insolving particular problems. In essence, these difficulties include the complexities of people

working together and contributing to a common goal

Four projects (four experiments) will be carried out during the semester. Students willwork in groups of 3-4. There will be a project leader for each project. This position will

rotate throughout the semester. Each project will require either an individual or group

report (written or oral).

It is fairly easy to obtain copies of previous experimental reports. But please do your

own work as an individual and on your team. No plagiarism of laboratory data or reports

will be tolerated. Such actions will result in academic misconduct charges being brought

against the student.


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Modeling

A very important component of your Analysis is Modeling. As shown in the figure, the interaction

between your experimental data and your model is a two-way path that will lead to the truth behind

what

you've done. You must have confidence in both your data and your model in order to be successful.

Experiment

Model

Truth

The choice of model is not a trivial one. Consider the following model classification:

Fully Predictive

Based onfundamental principles and assumptions

Might include parameters determined by previous researchers

User-input of experimental independent variables (e.g. flow rate set by you)

No adjustable parameters; predict dependent variables

Direct comparison of model predictions with observed data (e.g. outlet temperatures)

If comparison poor, review applicability of the model and/or data quality

Partially Predictive

Based onfundamental principles and assumptions

User-input of experimental independent and dependent variables

Key parameter(s) determined by regression of observed data as applied through the model

equation(s) (e.g. heat transfer coefficient)

If regression not statistically acceptable, review applicability of the model and/or data quality

If regression acceptable, compare values of fitted (regressed) parameters with published or

reasonable values

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4

Simple Correlation

* Basis in fundamental principles and assumptions not needed


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* User-input of experimental independent and dependent variables into simple regression

(correlation)

* If regression not statistically acceptable, correlation not valid

* Acceptable regression suggests a relationship might exit, but is no guarantee

During data analysis, often there is confusion in applying which model type. We will not be using any

simple correlations. The Fully Predictive model is always preferred. Many of the experiments have

multiple parts, however, where you will require the Fully Predictive model for one part and the

Partially

Predictive model for another part. The choice depends on the availability of key modeling

information.

Example

Consider the "Continuous Heat Transfer" Experiment. For the shell & tube steam condenser, you

record

condensate and coolant exit temperatures as functions of coolant rate for a given steam rate. Below,

the

various models are considered.

Simple Correlation

For a given steam flow rate, you observe that the exit coolant temperature changes as you vary its

flow

rate. You plot up this exit temperature vs. flow rate. By itself, this says little; you proceed to next

level

of complexity.

Partially Predictive

Your model includes the following components:

* Overall exchanger heat balance in terms of log-mean temperature driving force and overall

heat transfer coefficient.

* Overall exchanger heat balances in terms of sensible heat gained by the cooling water

* Overall heat transfer coefficient as sum of resistances - incorporating both film coefficients

* Use both heat balances to estimate the overall heat transfer coefficient

* Apply Wilson method to estimate the lumped quantity of tube metal resistance and shell-side


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resistance

* From sum of resistances, estimate tube-side heat transfer coefficient

* Compare this tube-side coefficient to that predicted by literature correlation of Nusselt

numbers vs. Reynolds and Prantdl numbers

Fully Predictive

Your model includes the following components:

* Overall exchanger heat balance in terms of log-mean temperature difference and overall heat

transfer coefficient

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* Overall exchanger heat balances in terms of sensible heat gained by the cooling water

* Overall heat transfer coefficient as sum of all resistances - (shell-side, metal, tube-side)

* Predictive (literature) correlations for tube-side and shell-side heat transfer coefficients

(Nusselt numbers vs. Reynolds and Prantdl numbers); thermal properties of metal

* Estimate the overall coefficient; combine with log-mean temperature difference; predict heat

transfer rate; apply this to sensible heat increase of coolant and the enthalpy loss of the steam;

predict observed coolant and condensate exit temperatures

Rule-of-Thumb

Consistent with your requirements and the available information, always apply a model that is as

heavily

based in first principles as possible. In this way, your model becomes more truly predictive, and,

hence,

more instructive to you in its revelations about the truth of what you've studied. In addition,

recognize

that the Fully Predictive approach is, in effect, a design calculation. So, in the example above, you

have

effectively designed a steam condenser!

SUCCESSFUL PLANNING FOR EXPERIMENTS

Notebooks


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Each group should have a designated lab notebook.

You can use fresh pages in your old P-Chem lab notebook.

You should each have your own copies of raw data.

Feel free to do you analysis / data work-up in the notebook.

Make sure you have the "Pre-Experiment Plan" in the notebook before starting each new

experiment.

Pre-Experiment Plan

1) Provide a clear statement of the research objectives of your upcoming experiment. How

will each be met?

2) What is your experimental plan? Identify:

+ Personnel assignments (including group leader)

+ Experimental tasks to be executed

+ Experimental parameters to be adjusted

+ Data to be collected

+ Working plot(s) to be drawn into lab notebook

3) Show the appropriate theoretical relationships that you expect to use in modeling your

data.

4) Clearly illustrate how data obtained from your experiment will be used with the theoretical

relationships identified in Step 3.

5) What are the likely sources of experimental uncertainty in your case?


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The report should be bound. The final bound size of the report should conform to A4 size

(210 x 297 mm).

As a character font, use Times New Roman. The font size must be 12 point in the text and 8

point in subscripts and superscripts. Main headings should be in 12 point and bold typeface.

Spacing of the text material should be 1.

Margins of pages should conform to the following specifications:

a. Left margin - 2.5 cm from the edge of paper

b. Right margin - 2.0 cm from the edge of paper

c. Top margin - 2.0 cm from the edge of paper

d. Bottom margin - 2.0 cm from the edge of paper

Pagination: Each page in the report is expected to bear a number : The preliminary section,

i.e., Title Page, Abstract, Table Of Contents, List of Figures, List of Tables, should be

numbered using lower case Roman Numerals, e.g., i, ii, iii, etc. The title page counts as Page

i, but the number does not appear. For the remainder of the report Arabic numbers are used.

Page numbers should be placed at right top edge of the page. The numbering in the main

body of the report should begin with Page 1 and run consecutively to the last page


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Error Analysis of Experimental Data (4, 6, 7, 8, 9, 10, 11)

All measurements are subject to errors. Hence, it is very

important that following the measurement of data and the

development of derived quantities from the data for

presentation in a report, a careful statistical analysis be made of

the measured results.Some important points to consider in measuring data are:

1. Even if you are careful, inaccuracies can occur

There are:

1. Mistakes

2. Errors

A mistake is the recording of a wrong reading (236

recorded as 263 lbs.)

An error is of two forms:

1. consistent

2. random

A consistent error is a defect in the measuring

device or the improper use of an instrument, for

example, the use of a burette calibrated for 20C

but used at 30C

A wrong scale is an incorrect reading of a wet test meter.

One can usually remedy consistent error by correction or

a calibration.

Random errors are caused by fluctuations and sensitivity

of the instrument or the poor judgment of theexperimenter. An example would be a fluctuating

rotameter.

2.Associated with random error is the most probable

value

The more readings you take the more likely the average

will be the most probable value. The analysis begins

with the normal distribution curve or, as it is commonly

called, the bell-shaped curve.

7. Regression AnalysisRegression analysis is used to determine the

constants in a relationship between variables. It can be

simple regression analysis of y versus x, multivariable

regression analysis of y versus x1, x2, x3, . . . xn or

curvilinear regression analysis using any mathematical

equation which is desired to curve fit the measured data.

We will consider only the simplest case or the method of

least squares (10). In this simple case, y is only a

function of x and the relationship is linear.

Student Responsibilities in the Laboratory


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Condition of Working Area. Students are responsible for the condition of their

working area at the end of each laboratory period. All power to the equipment

and instruments should be turned off, and cooling water flows should be shut

off. Glassware used should be cleaned and dried. Any equipment or

instrumentation malfunctions should be reported promptly to the instructor or

the TA.

Checkout before Leaving Laboratory. The students must have their notebooks

initialed by a faculty member or the teaching assistant prior to leaving at the end

of the laboratory period. At that time the faculty member or teaching assistant

will check the working area and take information about any equipment or

instrumentation problems.

higher that the predictions of Poiseuille flow). If the value of a single variable or

a short list of numbers is given, the numbers should give the uncertainty (e.g.,

solubility at 25C was 25 3 moles/liter) and of course units should be included.We recommend that you write the abstract last, when your thoughts are most

clearly in focus (i.e., you know all the answers and thus know what to say!).


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How to Keep a Lab Notebook

One of the most useful skills you will acquire in the laboratory is the proper use of a

laboratory notebook. Notebooks, or other formally kept records, are an essential tool in

many careers, ranging from that of the research scientist to that of the practicing physician.

The effort invested in developing good habits of notebook use will be amply repaid for

students who pursue a future in the basic or applied sciences. Some of the main principles of

sound notebook use are outlined below.

The laboratory notebook is a permanent, documented, and primary record of laboratory

observations. Therefore, your notebook will be a bound journal with pages that should be

numbered in advance and never torn out. All notebook entries must be in ink and clearly

dated. No entry is ever erased or obliterated by pen or "white out". Changes are made bydrawing a single line through an entry in such a way that it can still be read and placing the

new entry nearby. If it is a primary datum that is changed, a brief explanation of the change

should be entered (e.g. "balance drifted" or "reading error"). No explanation is necessary if a

calculation or discussion is changed; the section to be deleted is simply removed by drawing

a neat "x" through it.

In view of the fact that a notebook is a primary record, data are not copied into it from other

sources (such as this manual or a lab partner's notebook, in a joint experiment) without clear

acknowledgment of the source. Observations are never collected on note pads, filter

paper, or other temporary paper for later transfer into a notebook. If you are caught using

the "scrap of paper" technique, your improperly recorded data may be confiscated by your

TA or instructor at any time. It is important to develop a standard approach to using a

notebook routinely as the primary receptacle of observations.

Your notebook should be your primary source of information. Everything you do in the

laboratory should be included in your notebook, from procedure to calculations. When

notebooks are examined, we will look for the following points in almost all cases:

Prelab that shows that you were prepared for lab before beginning the experiment.

Data and associated graphs and calculations that quantitatively gauge how

successful your laboratory technique was.

Enough explanatory information so that someone else with your knowledge of

chemistry could, from your notebook alone, enter the lab and repeat your work.

Your discussion and answers to questions raised from time to time in the laboratory

manual itself.

The majority of the calculations and notebook write up can and should be accomplished in

"real time" -while you are in the lab, recording data and observations, and making


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calculations. Always bring a calculator to lab. It will be invaluable in making preliminary

calculations and even for calculating final results while you wait for other things to finish.

A laboratory notebook should be legible, and data in it should be readily accessible, clearly

labeled with units, and grouped in a logical way.

It is a good habit to start a notebook by leaving a few blank pages at the beginning for

entering Table of Contents later. Make sure every page starts with the title of the

experiment you are recording.

Ref:http://www.dartmouth.edu/~chemlab/info/notebooks/how_to.html

8. Student Responsibilities in the Laboratory

Condition of Working Area. Students are responsible for the condition of their working area

at the end of each laboratory period. All power to the equipment and instruments should

be turned off, and steam and cooling water flows should be shut off. Glassware used should

be cleaned and dried. Any equipment or instrumentation malfunctions should be reported

promptly to the instructor or the TA.

Checkout before Leaving Laboratory. The students must have their notebooks initialed by a

faculty member or the teaching assistant prior to leaving at the end of the laboratory period.

At that time the faculty member or teaching assistant will check the working area and take

information about any equipment or instrumentation problems.
http://www.dartmouth.edu/~chemlab/info/notebooks/how_to.htmlhttp://www.dartmouth.edu/~chemlab/info/notebooks/how_to.htmlhttp://www.dartmouth.edu/~chemlab/info/notebooks/how_to.htmlhttp://www.dartmouth.edu/~chemlab/info/notebooks/how_to.html

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chem eng practs