Icke-azeotropa blandningar i värmepumpar - Förstudie för fullskaleprojekt

Report, 1990

In cooperation between STAL Refrigeration AB and the Department of Heat and Power Technology, Chalmers University of Technology, an experimental heat pump with a nonazeotropic mixture as working fluid is being prepared. This will be the first full scale plant in Sweden. This report contains the results from a pre-study to the full scale project. The influence of a non-azeotropic mixture, as compared with a pure fluid on the design of the components in the heat pump, has been analyzed. This study has partly been done with a previously developed computer program, which has been improved. Some supplementary routines have been added to it, and the specific design of the prepared experimental plant has been inserted. The experimental heat pump which is to be used, has a countercurrent evaporator and a crosscurrent condenser. Since the best design for a non-azeotropic mixture is countercurrent, heat exchanger calculations have been done for this type of condenser. Comparisons indicate that a shell and tube heat exchanger with the non-azeotropic mixture on the shell side is highly interesting to investigate practically. The study of the internal heat exchanger shows that the dependence of COP on the degree of superheat before the compressor is slightly larger for a non-azeotropic mixture than for a pure fluid. During this project and also afterwards a dynamic debate on the environmental effect of "CFCs" has been going on. The use of the mixture HCFC22/CFCl14, suggested in this report, will be forbidden in the future. However, it is still interesting to study it, since there are more and better thermodynamic and physical data available for this mixture than for other non-azeotropic mixtures. The experience and knowledge acquired in this project are possible to apply on other mixtures. Accurate calculations can be done for these when more reliable data are available.