Sample Laboratory Handout




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This web page presents a sample lab handout [Dancey and others, 1999] written for a thermal fluids course at Virginia Tech. Accompanying the experiment discussed in this handout is a laboratory report.





Lab Assignment: The Ideal Gas Equation of State


Orientation

The ideal gas equation of state (pV = mRT) provides a simple relationship between pressure, temperature, mass, and volume for gases at relatively low pressures and high temperatures. This experiment illustrates the application of the ideal gas equation of state to relate the properties of air contained in a rigid vessel with heat addition.


Assignment

A pressure vessel with a volume of 1 liter has been instrumented with a pressure transducer and thermocouple to measure the gage pressure and temperature, respectively, of the air inside the vessel. The pressure transducer produces a voltage signal that can be related to the gage pressure in the cylinder by a calibration curve that is supplied with the instrument. Note that atmospheric pressure in Blacksburg is approximately 13.6 psia. The calibration curve for the pressure transducer is given by the following equation:

p = 4.3087(V·V) - 13.1176V + 10.7276

where V equals the voltage output (volts) from pressure transducer, and p equals the absolute pressure (kPa).

The thermocouple in the pressure vessel is connected in series with a second thermocouple that is located in an ice bath that provides a reference temperature. The thermocouple pair produces a voltage signal that is related to the temperature (T) of the air in the pressure vessel by the following expression:

T = Tref + V/S

where Tref equals the ice bath reference temperature (0°C), V equals the voltage (volts) measured across the thermocouple pair, and S equals the thermocouple constant, 42.4 µV/°C.

A signal processor displays and records the voltage signals from both the pressure transducer and the thermocouple during the course of an experimental trial. In addition, the signal processor records the data in a data file that can be downloaded to other programs for data analysis and plotting.

The steps you should follow to carry out the experiment are as follows:
  1. Turn on the signal analyzer. Identify the location of the "start" and "pause" buttons.
  2. Make sure the voltage ranges are appropriate. The signal analyzer should display two different plots of voltage versus time. The first should show the voltage coming from the pressure transducer; the second should show the voltage coming from the thermocouple pair.
  3. Check to verify that the hot plate is operating.
  4. Press "start" to begin reading data, and then heat the pressure vessel by placing it on the hot plate. Continue heating the vessel until the pressure reaches approximately 400 kPa.
  5. Save the data appearing on the display onto a disk (ask the T.A. for help). Choose a meaningful name such as "LabTemp.dat" for the files. You will have to save two sets of data--one for temperature and another for pressure.
  6. Using the two equations above, and appropriate software, determine values for pressure and temperature from the recorded voltage data.

Analysis

Using the initial values of the measured pressure and temperature, the volume of the vessel, calculate, from the ideal equation of state, the mass of air in the vessel. Assuming the volume and mass are constant during the heating process, calculate the temperature of the air (from the ideal gas equation) for each of the pressure values--remember that the recorded values of the pressure are absolute. Plot the experimental and calculated temperatures as a function of the measured pressure. Clearly label the graphs. Compare the experimental results with the theoretical results. What might be responsible for the differences?
Report

Prepare a brief report (1 - 1.5 pages, plus the graph and appendices) that summarizes your work. Your report should include the following items:

Title
Introduction
Procedures
Results and Discussion
Conclusions
Appendices

Prepare the report with a word processor and the plots with plotting software.


Last updated 8/04
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