Joule-Thomson coefficients of quantum ideal-gases

The temperature drop of a gas divided by its pressure drop under constant e nthalpy conditions is called the Joule-Thomson coefficient (JTC) of the gas . The JTC of an ideal gas is equal to zero since its enthalpy depends on on ly temperature. On the other hand, this is only true for classical ideal ga s which obeys the classical ideal gas equation of state, pV= mRT. Under suf ficiently low-temperature or high-pressure conditions, the quantum nature o f gas particles becomes important and an ideal gas behaves like a quantum i deal gas instead of a classical one. In such a case, enthalpy becomes depen dent on both temperature and pressure. Therefore, JTC of a quantum ideal ga s is not equal to zero. In this work, the contribution of purely quantum na ture of gas particles on JTC is examined. JTCs of monatomic Bose and Fermi type quantum ideal gases are derived. Their variations with temperature are examined for different pressure values. It is shown that JTC of a Bose gas is always greater than zero. Minimum value of temperature is limited by th e Bose-Einstein condensation phenomena under the constant enthalpy conditio n. On the other hand, it is seen that JTC of a Fermi gas is always lower th an zero and there is not any limitation on its temperature. For high temper ature values, JTCs of Bose and Fermi gases go to zero since the quantum nat ure of gas particles becomes negligible. Moreover, variation of temperature versus pressure under the constant enthalpy condition is also examined. Co nsequently, it is understood that the quantum nature of a Bose-type gas con tributes to the positive values of JTC while the quantum nature of a Fermi type gas contributes to the negative values of JTC. Therefore, a Bose-type gas is more suitable for cryogenic refrigeration systems. (C) 2001 Publishe d by Elsevier Science Ltd. All rights reserved.