Study On Performance Of Indirect Evaporative Cooler Considering Surface Wettability Of Wet Channel

The evaporation driving force of traditional indirect evaporative cooler is the difference between dry-bulb temperature and wet-bulb temperature of air,so it is difficult for the cooler to meet the air supply requirements in hot and humid areas.In order to break the regional restrictions,the combined air conditioning system of indirect evaporative cooler and mechanical compression refrigeration unit came into being in recent years.This paper studies the heat and mass transfer process of primary air condensation when the surface wettability of exhaust channel is not 1 and analyzes the main factors affecting the performance of indirect evaporative cooler and the distribution of air temperature and humidity under different surface wettability,so as to provide a theoretical basis for expanding the application scope of this technology.In this paper,based on the consideration of the surface wettability of the exhaust channel and the condensation of primary air,a two-dimensional mathematical model of the plate cross-flow indirect evaporative cooler is established.The distribution law of air temperature and moisture content in each channel of the cooler is obtained through numerical calculation,and the distribution changes of air temperature and humidity under different surface wettability are analyzed.In order to verify the reliability of the model,an experimental platform was built,and the effects of spray water temperature,water flow,primary air temperature,secondary air temperature,relative humidity,and secondary/primary airflow ratio on the refrigeration capacity,dehumidification capacity and water consumption of the cooler were studied.The experimental results show that when the spray water temperature increases from 19 ℃ to 31 ℃,the refrigeration capacity of the cooler decreases rapidly,the wetbulb efficiency decreases from 64.8% to 55.2%,and the total heat transfer of primary air decreases by 15.3%.With the increase of spray water flow from 0.05kg/s to 0.2kg/s,the refrigeration capacity of the cooler is significantly improved,and the wet-bulb efficiency increases from 57.4% to 65.3%.When the secondary/primary airflow ratio increases from 0.2 to 1.4,the average wet-bulb efficiency increases from 35.2% to56.5%.Due to the increase of airflow ratio,the supply air volume of secondary air increases,which will inevitably lead to higher fan energy consumption.In general air conditioning systems,the ratio of exhaust air volume to fresh air volume generally does not exceed 1.1.It is found that the primary air is continuously cooled in the channel,the temperature near the inlet of the exhaust channel is the lowest,and the descent rate of primary air moisture content is the highest.In the exhaust channel,the temperature of the secondary air decreases along the flow direction,while the temperature rises near the outlet.For the surface wettability of the exhaust channel,with the increase of the surface wettability from 0.3 to 1,the average air supply temperature of the heat exchanger decreases from 26.7℃ to 22.8℃,and the average wet-bulb efficiency increases from 35% to 58.2%.The increase of the surface wettability strengthens the degree of condensation of primary air,and the latent heat released by water condensation will reduce the possibility of condensation at the inlet of the fresh air channel.The occurrence of condensation will reduce the wet-bulb efficiency of the heat exchanger,but the water consumption is significantly increased.The water consumption of heat exchanger under complete condensation condition is significantly higher than that under partial condensation and non-condensation conditions.