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

Water film evaporation air cooler is widely used due to its characteristics of high heat transfer efficiency, energy saving, water saving and so on. However, it is always a difficulty for designing that obtaining the heat and mass transfer coefficient outside of the tube by reason of the coupling of water and air.On the basis of experimental rig of the water film evaporation air cooler, three evaporative tube bundles were set up, the sensors such as flow meter, anemograph, psychrometer and so on were configured, the measurement method for water film temperature of outside tube was designed independently which included 72 thermocouples. Through 125 experimental cases including 5 hot water temperatures, 5 hot water flows and 5 wind speeds, the hot water temperature, the air temperature and humidity, the pressure distribution along tube pass were measured. And the water film temperature distribution of outside tube was measured along tube pass, bundle width, and bundle height. According to experiment data, the influence of operating conditions on the air state parameters distribution, on the difference of air specific enthalpy at import and at export, on the spraying water average temperature, on the device overall pressure drop and on the average heat transfer coefficient of inner and outside of tube were analyzed in detail. The water film temperature field and the heat and mass transfer coefficient field of outside tube are described here, the influence of operating conditions on water film temperature field is discussed, and the calculation method of the heat transfer coefficient of tube wall-water are researched through the procedure from hot water temperature distribution and water film temperature distribution to the heat flux.The experiment data and analysis indicate that, on the surface of tube, the temperature distribution of water film is zigzag, with distribution curve changing great in top bundle, changing gently in bottom bundle. The heat transfer coefficient of tube wall-water and mass transfer coefficient of air-water are bigger in top bundle, the heat transfer coefficient of air-water are bigger in bottom bundle. In water film evaporation air cooler, the latent heat accounts for about 85% of the total heat air absorbed, the majority of heat absorbed by the air is latent heat in top and middle bundle, and the sensible heat approximately equals to the latent heat among the air absorbed heat in the bottom bundle. The bigger the wind velocity is, the closer to top of bundle the peak of water film temperature is. The hot water temperature plays a more important role on the water film temperature than the hot water flow rate. The heat transfer coefficient of tube wal-water-hw(x,z) can be acquired by water film temperature field.