Development of a simulation program for high-temperature and high-performance heat pumps.

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In comparison with conventional single-component refrigerants, the application of refrigerant mixtures in high temperature heat pumps may result in a higher coefficient of performance, lower condensing pressure, and higher reliability. But it is well known that the boiling and condensation heat transfer coefficients of binary mixtures are reduced due to the mass transfer effects compared with single-component refrigerants. Main purpose of this study is to develop a computer program for simulating refrigeration cycles of mixed refrigerants.Simple models for evaluating the mass transfer effects on boiling heat transfer and condensation heat transfer were developed. In both boiling and condensation heat transfer, mass diffusion layer near the gas-liquid interface causes the increase in heat transfer resistance. To investigate the feasibility of high temperature heat pumps with mixed refrigerants, the simulation program was used.In order to confirm the simulation program including heat transfer models, a heat pumptest rig was constructed, which consisted of water-cooled or -heated counterflow heat exchangers and an open-type-compressor. The COP and the heat transfer performance for the pure refrigerants R12 and R22 and the mixtures R22 with R114 in different compositions were measured. The comparisons between the simulated and experinental results of heat transfer coefficients and the COP were satisfactorily good. When the heat transfer area of heat exchangers is large enough and the temperature increase of the heat sink fluid at the condenser is large, the COP can increase.