Evaporative Condenser Heat Transfer And Mass Transfer Theory Analysis And Experimental Research

In modern society, the refrigeration system has been widely used in all departments of national economy and people's daily life. In recent years, under the pressure of shortage of water and power resources in our country, higher demands for energy conversation of the refrigeration system are required, which hasten the attention and the usage of the evaporative condenser. Evaporative condenser has many advantages, such as energy conversation, water-saved, compact structure and small usage of ground area. But the design of the evaporative condenser in the refrigeration system is lack of enough experimental datum and theoretical guidance. The heat and mass transfer process that takes place in evaporative condenser is quite complex. The air and water which flow outside the horizontal tube coil are studied, and the mathematical model of heat and mass transfer in the evaporative condenser is presented with their boundary conditions and some associated algebraic equations. Based on the theoretical analysis on the heat and mass transfer in the evaporative condenser, the experimental apparatus of the refrigeration system with evaporative condenser were built up, by which not only the refrigeration performance of the system but the heat and mass transfer performance of the evaporative condenser could be tested and visually studied. Many factors can affect the water film distributions outside the horizontal tubes. Visualization experimental results indicate that, the largest non-clog water diffuser B with 360 degree spray angel, twisted tube and hydrophilic coating on the tube surface can get better effects of water film distributions respectively, so as to reduce the heat resistance between the tube surface and the water film and increase the area on the water-air interface. In addition, the water film temperature profile was studied; Results indicate that, the spray water flow rate has a best value, the heat transfer processes include the sensible heat transfer and the latent heat transfer, the water temperature in the laver can keep constant under steady operation conditions. The study on the heat transfer performance of the evaporative condenser and the refrigeration performance of the refrigeration system is the emphasis of the paper. Results indicate that, the minimum spray density is 0.043kg·m^-1·s^-1, the experimental minimum spray density is 0.047kg·m^-1·s^-1 for safety; the best faced air velocity is 2.9 ～3.1m ·s-1, and the energy efficiency ratio(EER) can reach 4.5 ～5; The calculation correlations for heat and mass transfer coefficients of water film and air flow are given by the experimental datum regression analysis. The deviation between the calculation value and the experimental value is within 10%. What is more, the correlations are compared with other relative correlations; results indicate that, the experimental correlations have better correctness. The heat transfer coefficients indicate that the main heat resistance is on the water-air interface area. To enhance the heat transfer performance, the packing was installed between the tube coil and the air inlet louver. The experiment was carried out, results indicate that, overall heat transfer coefficient, air heat and mass transfer coefficient are 7.2%～16.9%, 29.6%～66.3%,34.5%～63.4% higher than that of the evaporative condenser without packing respectively, but it reduces the cooling capacity by 3.5%～9.1%.