Study On The Heat Transfer Performance Of Evaporative Air Cooler

Evaporative air condensers or coolers combining tube heat exchangerand air cooling tower, using the evaporation of the water film outside tubesand air heat transfer, can significantly improve heat transfer intensity ofoutside the tubes. Compared with the traditional water-cooled and air-cooledheat exchangers, evaporative air condensers or coolers has many advantages,such as compact structure, small usage of ground area,high heat transferefficiency,water-saved and stable operation. They have broad applicationprospects in the petrochemical industry, power plants, metallurgy and otherindustries.At present, evaporative air condensers have been widely used in therefrigeration system. To promote the application of the evaporative air heatexchanger for cooling operation in the petrochemical industry, the researchon heat transfer performance of evaporative air cooler is made in this paper.The experiment research has completed for the influence of the circulatingwater flow rate, air flow rate and process medium flow rate, and otherfactors on the heat transfer performance. The main contents are as follows:(1) The heat transfer principle for evaporative air coolers has beendescribed. The heat transfer area of the experimental device is determinedthrough process design.(2) Effects of tube-inside fluid flow rate on cooling performance beeninvestigated. When the tube-inside fluid flow rate increases, the strongerturbulence and the thinner thermal boundary layer thickness, the tube-insideheat transfer resistance and the total thermal resistance reduce accordingly. So,the tube-inside heat transfer film coefficient and the total heat transfercoefficient increase. The change of tube-inside fluid flow rate has no effect onthe tube-outside heat transfer film coefficient. (3) An investigation that the effects of spray water flow on heat transferis carried. When the spray water flow increases, the water film turbulence isthe stronger to cause the water film thermal resistance is lower. So, thetube-outside heat transfer film coefficient and the overall heat transfercoefficient increase. As spray water flow to a certain extent, the water filmthickness is more thicker, and the water film thermal resistance is larger,thus the tube-outside heat transfer film coefficient and the overall heattransfer coefficient is reduced. At the circulating water pump frequency is80%, the heat transfer performance is the best.(4) Within a certain range, the increase of the tube outside air flow canimprove heat transfer efficiency. With the increase of the tube outside airflow, the air turbulence is the stronger, accelerated heat and mass transferbetween air and water, the heat transfer resistance of the tube outside isreduced. The tube outside heat transfer film coefficient and overall heattransfer coefficient gradually increase. The heat transfer efficiency reachesthe best when the fan frequency up to80%.(5) The experimental results show that the media inlet temperature onheat transfer efficiency has a certain impact. In a certain temperature range,when the inlet temperature increases, the heat transfer driving forceincreases, the heat transfer process of tubes inside and outside is enhanced atthe same time. The heat transfer rate, the overall heat transfer coefficient,the heat transfer film coefficients of tubes inside and outside increaseaccordingly. The heat transfer rate at45℃about medium inlet temperatureis2.6times at30℃, and the overall heat transfer coefficient of1.4times.(6) The heat transfer efficiency has been investigated on the dry aircooling, spray cooling and evaporative air cooling. The heat transferefficiency of the dry air cooling is the worst, and the heat transfer efficiencyof the evaporative air cooler is the best. The heat transfer rate of evaporative air cooler is up to584.6kW, is13times of the dry air cooling heat transfer.The overall heat transfer coefficient of evaporative air cooler is1021.6W/(m~2·K) for more than23times of the dry air cooling.