On the thermodynamic stability of the generalized Chaplygin gas

The main purpose of this Letter is to discuss the temperature behavior and the thermodynamic stability of an exotic fluid known as generalized Chaplygin gas considering only general thermodynamics. This fluid is considered a perfect fluid which obeys an adiabatic equation of state like P = -A/rho(alpha), where P and rho are respectively the pressure and energy density; the parameter A is a positive universal constant and alpha > 0. It is remarked that if the energy density of the fluid is a function of volume only, the temperature of the fluid remains zero at any pressure or volume, violating the third law of thermodynamics. We have determined a scenario where its thermal equation of state depends on temperature only and the fluid presents thermodynamic stability during any expansion process. Such a scenario also reveals that the fluid cools down through the expansion without facing any critical point or phase transition. (C) 2006 Elsevier B.V. All rights reserved.