Research On Micro-channel Evaporator With CO₂ Binary Mixtures In The Heat Pump System

With the development of science and technology, the micro mechanical systems gradually applied in the engineering and social life. In order to ensure smoot h running of the micro mechanical system, reduce the volume of heat exchanger, rational and efficient use of energy, the micro heat exchanger is widely applied in all kinds of micro mechanical systems. The increasingly serious environmental problems, such as greenhouse effect and ozeone depletion, allow investigators to study on refrigerants which are friendly to environment. CO₂ is the only natural refrigerant which can be widely used in automobiles, household, commercial and industrial systems. But CO 2 system operation pressure is higher so there is a hidden danger and throttling loss is bigger so the energy efficiency is lower. To solve environmental problems and improve energy utilization efficiency, the application of nonazeotropic mixtures containing CO₂ refrigerant has a profound effect on refrigeration industry.Adopted a laminated micro-channel heat exchanger as evaporator of heat hump system. The micro-channel evaporator‘s volume is 1.1856?10-4 m³ and heat transfer area is 7.9456?10^-2 m², the ratio of volume and heat transfer area is 670.18. The size of refrigerant circular channel is 0.2?0.2 mm, the water circulation channel is 0.5?0.4 mm. The refrigerant of the hump system were pure R744 and R744/R32,R744/R161, R744/R41 binary nonazeotropic mixture which mass fraction were 80%/20% and 60%/40%, respectively. Studied on micro-channel evaporator‘s heat transfer and flow characteristics, compared the experimental results with model prediction results.The experimental results showed that the water inlet temperature had little effect on heat transfer properties and flow characteristics of micro-channel evaporator. The bigger water volume flow was, the greater heat transfer coefficient of refrigerant heat transfer coefficient was. But the pressure drop of refrigerant didn‘t change with volme flow of water. The refrigeration capacity of micro-channel evaporator could be 4.52 kW. It showed that micro-channel evaporator‘s compact structure and excellent heat transfer performance.The experimental results of different binary nonazeotropic mixture showed that as the mass fraction of R744 was 80%, the laminated micro-channel evaporator‘s heat transfer coefficient was higher and the number of heat transfer unit was bigger than those of the mass fraction of R744 was 60%. As the mass fraction of R32 was 20%, the evaporating temperature of refrigeration system was highest and the heat transfer coefficient?HTC? was maximum. As the mass fraction of R161 was 20%, the HTC was smallest.As the mass fraction of R161 was 20%, the pressure drop of laminated micro-channel evaporator was maximum, the pressure drop of 20% R32 mixture was smallest. Compared the experimental results of three binary mixtures, as the mass fraction of R744/R32 was 80%/20%, the laminated micro-channel evaporator heat transfer property and flow performance was best.