Thermodynamics and dark energy

Significant observational effort has been directed to unveiling the nature of the so-called dark energy. However, given the large number of theoretical possibilities, it is possible that this a task cannot be based only on observational data. We discuss some thermodynamic properties of this energy component assuming a general time-dependent equation-of-state parameter w(z) = w(0) + w(a)f(z), where w(0) and w(a) are constants and f(z) may assume different forms. We show that very restrictive bounds can be placed on the w(0) - w(a) space when current observational data are combined with the thermodynamic constraints derived.