Experimental Study On The Boiling Heat Transfer Characteristics Of R32/R290 In Horizontal Tubes

The research of alternative refrigerants has become a hot topic within the industry as the ozone depletion and global warming worsening currently, which deteriorate the environment. In this paper, due to higher GWP of R407 C and R410 A which are widely used as alternatives for R22 at present, a new mixture of R290 and R32 is brought forward to replace R22. The ODP of R32 and R290 are zero, their GWP values are much lower than R410 A, which means good environmental performance, but they all have some flaws when used alone. Mixed refrigerant is expected to solve the usage limit of R290 because of its high flammability and the problem that the exhaust gas temperature of R32 is too high.In this paper, R32 / R290 mixed refrigerant is treated as object of study. Firstly, according to the minimum temperature slip principle, compositional ratio of R32/ R290 is determine as 68/32(mass fraction) by the physical properties software REFPROP.v9.0. The thermal properties and thermal cycling performance of the new working fluid are discussed, and analyze its strengths and weaknesses as alternative refrigerants in theory. When determining alternative refrigerants, their performance should be appraised and researched as fully as possible. For any alternative refrigerant, the in-tube boiling heat transfer characteristic is an important application parameter, and it is rather necessary for comprehensively analyzing its actual performance and the application potential. At present, there was not report about the boiling heat transfer performance of R32/R290 mixture refrigerants in the domestic and abroad yet, this research will fill in this blank and supply reference for the engineering design and optimization of R32 / R290 evaporation.On the basis of setting up the experimental system which can meet the requirements, the boiling heat transfer coefficient of working fluid in the optical tube and micro-fin tube was obtained by experimental methods. The influence of the mass flow rate, the saturation temperature, the diameter and type of tube were analyzed from the experimental and theoretical aspects, and the boil heat transfer coefficient of R32/R290 were compared with that of R410 A. The main contents and conclusions are as follows:1. For the limited heat transfer area, in the case of the same evaporation temperature and heat flux, along with the mass flow rate increases, the average boiling heat transfer coefficient of the refrigerant at first increases, after reaching a peak and followed by a decline. 2. For a limited heat transfer area, at the same mass flow rate, the average boiling heat transfer coefficient presents an increasing trend with the evaporation temperature increasing; 3. Micro-fin tubes can effectively enhance the boiling heat transfer performance of the mixed refrigerant; 4. The influent of diameter on the average heat transfer coefficient of R32/R290 is greater than the impact of the tube type, heat transfer coefficient decrease with the hydraulic diameter. 5. The heat transfer performance of R32/R290 is significantly superior to R410 A.