Empirical method for selecting working pairs for sorption heat pumps and for estimating isobaric bubble temperatures

Abstract

By the use of the integral enthalpy of evaporation of binary mixtures obtained from the linearized Clapeyron diagram (In P against 1/T plot) an expression was derived which may be useful for screening purposes when new working pairs are to be selected. For the construction of the Clapeyron diagram, the knowledge of isobaric bubble temperatures of binary mixtures is required. Suitable mixtures for heat pumping consist of polar components and exhibit normally strong negative deviations from Raoult's law. A method for the estimation of isobaric bubble temperatures of binary organic and organic/water mixtures was derived and tested. The method was based on an empirical generalization of Clapeyron's and Raoult's law for dilute solutions, certain symmetry properties of the linearized Clapeyron diagram and the knowledge of pure component properties. For 35 test mixtures, a total average deviation of 1·42% of estimated thermodynamic bubble temperatures was calculated.