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U of U CHEN 3453 - Chemical Engineering 3453 Heat Transfer

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Chemical Engineering 3453 Heat Transfer University of Utah Fall 2007 Project Assignment Prof. Geoff Silcox Due Friday, November 30 by 17:00 Introduction Welcome to Red Iguana Controls (RIC). We have an opportunity to steal a big client from our rival company to the south (YBU Controls). A large processing company is having difficulty controlling a batch reactor cooling process that is important to their profit margin. They have given us the opportunity to solve their problems by showing results on a bench-scale process that we have set up in our lab. We are counting on your project team to develop a model of the process that can be used to design a control system for the reactor. The model should accurately predict the temperature of the reactor as a function of time. Detailed Instructions 1. Prepare a schematic of the process. 2. Record the air temperature. 3. Bring a pot of tap water to a boil and pour 500 ml into the beaker. Note that the volume markings on the beaker are ± 5 % (95 % confidence level). 4. Set the magnetic stirrer at 5. The hot plate should be off. 5. Insert the thermometer and cover the beaker with the watch glass. Note that the uncertainty in the temperature readings is ± 1 °C (95 % confidence level). 6. Record the time and temperature over a period that is long enough to capture the behavior of the process. 7. Fit the data using one or two models that are based on what you have learned in Heat Transfer. For each model, state your assumptions, give the values you obtain for its parameters, and state their uncertainty at the 95% confidence level. Our client is particularly interested in the time scale of the process. 8. For each model, plot the data and the model on the same graph. On a second graph plot the residuals. 9. Prepare a short memo report using the format of the sample in the appendix. Please number the pages of your memo. Grading You are working on the reports as part of a team and each team will produce a single written report. The reports will be assessed using the attached rubric. Your participation as a team member will be evaluated by your colleagues using the attached rating form.Appendices The appendices include (1) a sample memo report, (2) a grading rubric, and (3) a rating form for team citizenship.1 Memorandum To: Prof. Noel de Nevers From: Mr. David Fikstad Date: 6 February 2006 Subject: Calibration and Evaluation of an Omega Model HX93V Relative-Humidity and Temperature Transmitter cc: Sarah Read Summary During the period from January 6 to January 27, 2006, the members of Group F calibrated and evaluated the performance of an Omega Model HX93V relative-humidity and temperature transmitter (Omega Engineering, Stamford Connecticut). The transmitter was calibrated with an Omega HX92-CAL relative-humidity calibration kit, and its accuracy was tested with various solutions of ethylene glycol and water ranging from 10% to 100% relative humidity (RH)1. The transmitter was accurate to within 5% RH at higher relative humidities (>50%) but was not accurate to within 5% RH at humidities lower than 50%. The transmitter's performance in a moving airstream at temperatures greater than room temperature was also investigated. A cardboard tube and an air blower containing a heating element supplied a suitable stream of heated air. A brief summary of the calibration and the results of our performance evaluation follow. Apparatus and Procedure The relative-humidity sensor uses a capacitor containing a water-absorbing polymer as its detector. The water absorbed in the polymer alters the dielectric constant of the capacitor which causes a change in output current. In the HX93V model, this current output is converted to a voltage from 0 to 1 volt. The voltage output of the transmitter was monitored with a Hewlett-Packard (HP) on-line data-collection system and two digital multimeters. The on-line data-collection system operated at sampling intervals of 20 seconds. The HP system also served as the power source for the RH transmitter; the entire system was disconnected daily between experimental runs. The transmitter was calibrated by attenuating the voltage output by adjusting the two potentiometers built into the transmitter. The procedure follows. a) Potentiometer A, the RH-zero value, was adjusted to give an output of 0.00 volts in a low-humidity environment (air above a saturated LiCl solution from the HX92-CAL RH Calibration Kit, 11.3% RH at 82°F). 1 Seader, J. D., Jeffrey J. Siirola, and Scott D. Barnicki, "Distillation" in Perry's Chemical Engineers’ Handbook, 7th Edition, D. W. Green and J. O. Maloney, eds., p 13-12, McGraw-Hill, New York (1997).2 b) Potentiometer B, the RH gain, was then adjusted in a high-humidity environment (air above saturated NaCl solution, also from the HX92-CAL, 75.3% RH at 82°F) to give a voltage reading equal to the RH difference between the two solutions. c) Potentiometer A was adjusted to give a voltage output of 0.753 V while the sensor was in the high-humidity environment. An unfortunate problem with the transmitter was that, when it was disconnected from its power supply (currently, its power supply is the HP data-collection system) the calibration was not maintained. Repeated calibrations were required each time the system was shut down and restarted. Results and Discussion The accuracy of the transmitter was tested by measuring the RH in air above solutions of ethylene glycol (EG) and de-ionized water. Also, its repeatability was checked with a measurement of the LiCl solution used for calibration after several measurements of EG/water solutions. The upper range of the transmitter was determined by placing it above pure water. The results from these experiments are shown in Figure 1. The transmitter was noticeably less accurate over the lower humidity EG/water solutions and was reproducible only to within 5% RH for the measurement of the air above the LiCl solution. The maximum measurable relative humidity was found to be about 97%. This value is slightly higher than the maximum value reported in the transmitter literature. 100806040200020406080100Line of perfect agreement Ethylene Glycol-H20 solutionsLiCl solution and dist H20% Relative Humidity of standard solutions, based on published (handbook) valuesMeasured %RH Figure 1. Measurements taken by the Omega transmitter in the air space over solutions of known relative

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