Simulation And Experiment Research Of Heat And Mass Transfer Of Water Film Evaporative Air Cooler

The water film evaporative air cooler is being used more and more widely in engineering design due to its high efficiency of heat transfer and low consumption of energy and water. The heat and mass transfer coefficient out of the tube has been a research hotspot all along, and numerical simulation of heat and mass transfer has been a problem to be solved yet.In this paper, 30 groups of experiments(5 kinds of wind speed ×6 kinds of tube pass number) were carried out on the experimental platform of water film evaporative air cooler. Through measuring the air temperature, air humidity and flow pressure drop outside the tube and hot water temperature distribution inside the tube, the effect of operating conditions on heat and mass transfer was obtained, the heat transfer coefficient of each tube was calculated, and the law of heat transfer coefficient of water film along the flow direction was analyzed. Based on physical model of the cooler, a mathematical model of heat and mass transfer of the cooler was developed. The simulation software of the cooler was programmed by using Visual Studio 2010. The coefficients developed from the experiment were input into simulation program to calculate heat and mass transfer of air cooler, and its comparing result with experiment data verified the correction of the model and program and showed that the simulating program reflects the performance of different water film evaporative air cooler, so the program can be used to predict the representation of the cooler and provide a reliable simulation support to the optimal design of the cooler.The experiments indicate that: the average heat transfer coefficient of the cooler along the tube passes increases first and then decreases. The average heat transfer coefficient of the cooler is at the top when the number of tube rows is 4 to 8. There is an obvious low efficiency zone in the middle of the cooler when the tube pass number is large. Uneven distribution of inlet air causes the heat release amount of bottom tube pass to be the minimum. Along the water film flow direction, the heat transfer coefficient of each tube from tube wall to the water film go up at first and then go down, and water-air convection heat transfer coefficient get to the largest in the last tube pass. The water-air mass transfer coefficient is the largest in the first tube pass, then change smoothly in the midd le, and reaches the smallest value in the last tube pass. Heat transfer coefficient calculating formula along the circumferential angle of the tube is theoretically analyzed and corrected by experiment, and then got heat transfer coefficient field in the tube bundle of the cooler.Simulation calculation indicates that: the water film temperature increases at first and then decreases along the circumferential angle of the tube, but if tube pass number is very large, the water film temperature decreased monotonically at the latter half of the tube row. The overall temperature change of water film is smaller while the tube passes number is small. If the tube row number of more pass bundle is equal to the the tube row number of less pass bundle, the effect of heat transfer of more pass is better than less pass. If total tube length remain unchanged, the heat transfer effect of longer tube is better than shorter tube.