Heat transformation with the ternary working fluid TFE-H 2O-E181 : Transformation de chaleur avec le fluide de travail ternaire TFE-H 2O-E181

Abstract

As shown in previous papers, the binary mixture of trifluoroethanol (TFE) and tetraethylene-glycoldimethylether (E181) seems to be advantageous for absorption heat pumps and absorption heat transformers. Both substances are completely miscible and applicable in a wide temperature range from below 0 up to 160°C. The density of TFE vapour is much higher than that of water, so that condenser and evaporator become smaller than in processes with water as a working substance. Because of the fairly low thermal conductivity and the low enthalpy of evaporation of TFE it is, however, advantageous to use TFE-water instead of pure TFE with E181 as working substances. The present paper deals with the thermophysical properties of this ternary mixture. The thermal stability, vapour-liquid equilibrium, density and viscosity were measured. The enthalpy of the ternary mixture was predicted from data for the three binary subsystems. As a study of the single-stage absorption heat transformer shows, up to 15 mass% or almost 50 mol% of TFE in the mixture TFE-E181 can be replaced by water. The COP of a process working with the ternary mixture is slightly higher than that of a process working with the binary mixture TFE-E181. Because of the higher thermal conductivity and enthalpy of evaporation of TFE-water compared with pure TFE, the heat transfer is improved. Also, the costs for the mixture are reduced.