A simple method for the analysis of sub-Kelvin refrigerators that use a dilute superfluid He-3-4 He mixture as a working fluid

The recent development of new types of sub-Kelvin refrigerators that use di lute superfluid He-3-He-4 mixtures has made it apparent that a simple metho d of cycle analysis is needed. General control volume forms of the first an d second laws of thermodynamics appropriate to this working fluid are prese nted. Simple analytic constitutive relations for the internal energy, entro py, enthalpy, osmotic enthalpy and He-4 chemical potential are presented. S everal examples are worked out using these relations. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.