For improving the coefficient of performance of carbon-dioxide water-water heat pump effectively, this paper focuses on the study of the performance of evaporator. Models of the shell tube type evaporator were established. The performance of the evaporator was studied when carbon-dioxide was in the tube side and the shell side respectively. The steady imitation of the model corresponding to the real heat pumps was carried out. The calculated results show that the performance of the single-tube pass of the evaporator is better than that of the double-tube pass one. The calculated coefficient of the evaporator was low at the given parameters of the evaporator when the CO2 is inside the tube due to small mass flow rate of fluid. The increased length of the tube and the decreased number of the tube can help to increase the mass flow and benefit to heat exchanging of evaporator with CO2 inside the tube. The multi-shell pass and single-tube pass type of evaporator is proposed in order to improve the performance of heat exchanger.
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