Heat Conductivity in Gases

In this experiment you will study the process of thermal conductivity by gas molecules.

Experimental Procedure

  1. Assemble the electrical circuit.
  2. With the help of your instructor, limit the power supply maximum current to 3A.
  3. Measure the resistance of the resistor. How can we measure the resitance? How accurate the measure will be?
  4. Measure R0:
    1. Make sure the tube is filled with air.
    2. Measure the voltage on the wire and the voltage on the resistor at increasing output voltages. Start at 0.02V, and take 10 measurements at 0.01V intervals.
    3. Use Ohm's law to calculate the resistance of the wire at room temperature, RT.
    4. Use equation (11) from the theoretical background to calculate an experimental value of the wire's resistance at 0°C, R0.
    5. Use equation (12) from the theoretical background to calculate a theoretical value of the wire's resistance at 0°C, R0.
  5. Measure the thermal conductivity coefficient at 760 Torr and at 350 Torr for five gases: air, He, Ar, N2 and CO2.
    1. Pump down the system, and flush it with the gas t be analyzed. Flush several times to be sure all traces of previous gases are gone.
    2. Let the measured gas flow into the tube, until the desired pressure is reached.
      Make sure the safety valve is open when you insert gases into the tube!
    3. Measure the voltage on the wire and the voltage on the resistor at increasing output voltages. Use output voltage range of 0.2V-1.5V, and take 20-25 measurements.
  6. Measure the dependence of the thermal conductivity on pressure. Measure the thermal conductivity of He and N2 at two pressures different from the pressures you used previously.
  7. Data analysis:
    1. Calculate the resistance and temperature at each data point, using Ohm's law and equation (10) from the theoretical background.
    2. Plot VI as a function of T1 - T2, and find the slope. Use equations (9) and (11) from the theoretical background to determine k for each gas at each pressure.
    3. Use equation (13) from the theoretical background to find the viscosities of the gases at different pressures.
    4. Compare your results to the literature.
    5. Plot k for He and N2 at different pressures, and determine the dependence of k on P.