Research On Condensation Heat Transfer Of R32/R290 In Horizontal Channels

Today the refrigerants used in air conditioning systems not only damage the ozone layer but also create the greenhouse effect. So it is important to choose an alternative refrigerant to protect environment. From the environmental point of view, combine the advantage of R32 and R290 as well as offset their shortcomings. By using the minimum temperature glide principle I chose a near-azeotropic mixed refrigerant R32/R290 with the 68/32 mass content ratio. R32/R290 is a new mixed refrigerant with excellent environmental properties. But the number of studies of R32/R290 condensation heat transfer characteristics in the tube is very small, so it is necessary to use experimental methods to study R32/R290 condensation heat transfer characteristics in a horizontal pipe and it can provide theoretical support for the rational and efficient operation of the heat exchanger.Basic properties and thermal properties of R32/R290, R410 A and R32 during condensation were comparative analyzed firstly. Then characteristics of R32/R290 and R410 A were compared in home air conditioning by the theoretical cycle calculation method. Experimental system, content and method were described in detail. Condensation heat transfer characteristics of R32/R290 in different sizes of light tubes and micro-ribbed tubes were experimentally investigated with different conditions. Then condensation heat transfer characteristics of R32/R290 and R410 A were compared in a 5×9.52 mm micro-ribbed tube. Experimental study on condensation heat transfer characteristic was conducted at mass flux of 100~250 kg/(2? ), saturation temperature of 40~55°C and Average dryness of 0.6.The results show the shear stress between gas and liquid refrigerant increases with mass flux, then the liquid film thickness on the wall can be reduced by the increasing shear stress. The thermal resistance is reduced which enhance R32/R290 condensation heat transfer characteristic. The physical property of the refrigerant changes with the decrease of the saturation temperature, it reduces the density of gas refrigerant and increases the density of liquid refrigerant. The shear stress increases with speed difference between the gas and liquid refrigerant under the constant mass flux which can enhance the heat transfer coefficient. With the diameter of tube decrease, compared with gravity, shear stress occupy a dominant position which enhance the condensation heat transfer. Micro-fin can not only increase the inner tube surface area but also enhances the disturbance to the liquid refrigerant, it can reduce the liquid film and the thermal resistance which enhance the condensation heat transfer characteristic. So condensation heat transfer coefficients of the mixed refrigerant R32/R290 increase with mass flux while decrease with the saturation temperature and the diameter of tube. Then condensation heat transfer characteristics of R32/R290 in micro-ribbed tube is better than it in light tube under the case of equal diameter. Experimental data of R32/R290 and R410 A were compared with the same conditions. Because the gas-liquid density of R32/R290 is less than R410 A, under the constant mass flux, the flow velocity of R32/R290 is greater than R410 A as well as the thermal coefficient and the latent heat of vaporization are greater than R410 A. So the condensation heat transfer coefficient of R32/R290 in the same level of micro-fin tube is greater than R410 A. As an alternative refrigerant of R410 A, excellent heat transfer characteristics of R32/R290 make it has many potential advantages.