Determination of Heat Capacity Ratio

Extract

[...] Furthermore, valve V5 may not have been adjusted correctly; this may have caused the airflow to be slightly too fast causing a change in the temperatures of both vessels effecting the results. Other external environmental factors also may have affected the pressure and temperature of the system. Finally, to improve the experiment for more accurate results a data logger can be used to help prevent human error and repeating the experiment would have helped attain more reproducible results. [...]

[...] The experiment is to determine the heat capacity ratio of air, by emulating an adiabatic expansion of air. Objective for experiment The objective is to calculate the volume ratio of two vessels for air. This calculated by using an isothermal expansion. Background The 1st law of Thermodynamics is the conservation of energy for thermodynamic systems, meaning that heat cannot be created or destroyed. Thermal energy can therefore be converted into various forms of energy. To calculate the change of internal energy of a given system the formula shown in figure 1 is used: Q represents the amount of heat added to a system and W represents the Work done. [...]

[...] This means that the change of internal energy is the work done. An adiabatic process would be when gas expands at such a fast rate that no heat can actually be transferred, for example a Carbon dioxide fire extinguisher; the gas leaves the extinguisher at a high pressure and the temperature drops with it expanding at atmospheric pressure. Figure 2 shows a Pressure-Volume graph for an adiabatic process. Adiabatic and Isothermal graphs follow a similar trend. An isothermal process is one where the temperature is a constant throughout. [...]

[...] Due to the rate of expansion, occurring so quickly the heat transfer would not have occurred in time. Furthermore, we recorded the instantaneous value of the pressure Pi after opening and closing valve V1 quickly. By taking Pi immediately after, the value had not been affected by heat transfer meaning that the initial expansion could be considered adiabatic. However, the result obtained was not quite the same as the expected result; we obtained a value of 1.34 for air although the expected result was The results may have been affected from reading the Pressure Pi, as we needed the instantaneous value once the valve was closed. [...]

[...] Alternatively, to further improve the accuracy, the pressure Pi could have been obtained by reading off the data logger instead, giving the pressure at instantaneously. Unless an automatic method of opening and closing the valve the experiment could have only given results that are more reliable by repeating the experiment. Method for experiment 2 Before carrying out the experiment both vessels needed to be at atmospheric pressure and this was achieved by opening valves V1 and V3 whilst keeping the other valves closed; the atmospheric pressure was measured using a barometer. [...]