Thermodynamic Investigation of the Joule-Thompson Effect and Coefficient Determination for Helium and Carbon Dioxide

Niki Spadaro, Megan Cheney, and Jake Lambeth
University of North Florida, CHM4410C Fall 2010

The Joule-Thomson coefficient explains the behavior of any real gas when changes in intensive properties, such as temperature and pressure, occur. The coefficients for helium and carbon dioxide were determined using a Joule-Thomson apparatus that created constant enthalpy within the system. Using literature values for the coefficients at room temperature, the experimental results allow examination of each gas’s unique nature.

Introduction Enthalpy is a critical study in thermodynamics. It is a measurement of a system’s …show more content…
During the trial runs, the CASSY software system (Leybold Didactic) gathered constant measurements of the temperature change and pressure across the barrier, and recorded time in seconds. These measurements were displayed onto a computer to which the apparatus and sensor were connected. A graph was produced from the data and displayed functions of pressure versus time as well as a temperature change versus time. Adjustments to the temperature change and pressure data allowed creation of a new graph in which the slope equals the Joule-Thomson coefficient, as can be seen in equation 7. Production of the slope required acute hand control in order to release the precise pressure needed during each trial. Initially, the pressure and temperature scales on the CASSY system were calibrated to 0. Three trials were run for each gas at each set system temperature. The system temperatures for carbon dioxide were set at 294 K and 315 K; the temperatures used for helium were 276 K, 294 K, and 315 K. Once all scales read 0, measurements were then recorded. Pressure was carefully released from the gas source until the scale on the computer read 200 hPa for 100 seconds. The pressure was released to 0 hPa,, and time elapsed another 100 seconds to establish equilibrium once more. This process was repeated for pressure measurements of 400, 600, 800, and 1000 hPa. Recordings were terminated once 150 seconds of 0 hPa had passed after the pressure