Study On Two-Phase Flow And Heat Transfer Characteristics Of R407c In Helical Coils

Due to the advantages of coMPact structure and high efficiency, helical coiled tubes has been widely used in the heat exchanger design. When the helical coiled tubes are laid horizontally, the gravitational and centrifugal forces vary continuously. Due to this, the two-phase flow and heat transfer becomes much more complex than that in the vertical helical pipes. By now, most of the research about two-phase flow and heat transfer have been conducted on the water and some one-component refrigeration, not much effort has been devoted to the ternary non-azeotropic mixing refrigerants of R407c(R32/R125/R134a), which is a long-term substitute for R22.Therefore,it is essential to deeply study the mechanism and characteristics of environmentally friendly refrigeration of R407c in the horizontal helical pipes.In this paper, after reestablishing the two-phase flow and heat transfer experimental system, the characteristics of wall temperature, flow boiling heat transfer and resistance in the helical coiled tubes are investigated. Following is the main work of this paper:The wall temperature distribution characteristics of horizontal helical coiled tubes studied on basis of experiment. The results of the experiment are as follows:The wall temperature distribution is closely related to the heat flux, the pressure and the mass flux. The temperature of the inner point is much higher than that of the outer point; The temperature increases with the increasing of heat flux, pressure and decreases with the increasing of mass flux. The temperature curve becomes gentler along the direction of helical tube length with the increasing of quality. CoMPared to the temperature of R 134a increasing clearly along the tube length, the temperature of R407c’Changing is not obvious.The analysis of boiling heat transfer characteristics is as follows:The heat transfer coefficient of helical tube is closely related to heat flux, the pressure, the mass flux and quality. The regular of the boiling heat transfer coefficient in the four points(inner, outer, left, right) is similar to the wall temperature. The influence of pressure on heat transfer coefficient is not very obvious.The coefficient increases with the increasing of the mass flux, heat flux and quality. But, when the quality increases to x=0.5-0.6,it decreases with the increasing of quality.The analysis of flow pressure drops characteristics is as follows:The pressure drops’ characteristic is closely related to the pressure and the mass flux. The pressure drops increase with the increasing of quality and the mass flux. However, with the increasing of pressure, the pressure drops decrease clearly.