Theoretical Analysis And Experimental Verification On Cooling Performance Of A New Type Evapor Ative Air Cooler

The limit temperature of the traditional evaporative air cooler is the wet bulb temperature of the inlet air. There are many restrictions due to the climate and geographical conditions such as high humidity in the air conditioning area, limited temperature drop. So it can’t meet the higher requirements. As evaporative cooling air conditioning technology becomes more sophisticated, the separate direct evaporative cooling system has developed into two-stage evaporative cooling air conditioner combined the indirect with direct evaporative cooler, even three or four stage evaporative cooler combined two or three levels of indirect evaporation with the direct one. They have achieved good application effect, while many problems completely expose. These are the reasons for the advantage of the indirect evaporative cooling section not to be fully utilized. Therefore, how to make the tube type indirect and direct multistage evaporation cooling air conditioning more efficient and stable in practical application should be solved urgently.In this paper a new kind of two-stage evaporative cooler was designed, which usded the finned tube to precool the air before the process of the traditional direct evaporative cooling to make up for the disadvantage that the heat transfer coefficient between air and air is small. The temperature of air is firstly reduced with humidity unchanged and then flow through the packing in progress of heat and mass transfer with the spray water,, which can reach secondary cooling. So it can be a good solution to the above problems. This research is rarely involved at home and abroad. This paper verified the system the feasibility of its application in China, but also enriched the research category of evaporative cooling technology. In addition, bassed on the method of combining theoretical analysis with experimental research, various factors affecting the performance are found and verified, with a view to providing theoretical support for improving traditional air coolers and guiding the practical application.By contrasting the experimental results based on the traditional direct evaporative air cooler and this new evaporation air cooler with finned tube, the heat transfer advantage of the latter has been shown visually. Supply air temperature after the latter can be low to 22.23℃, but only 84.63% relative humidity, corresponding to 24.31℃ and 86.7% by the traditional direct evaporative air cooler in the velocity of 2.5m/s and spraying density of 16.87 m3/(m2?h). The air conditioned by the new evaporative air conditioner has a higher degree of air unsaturation, illustrating a better effect of air conditioning. In this heat and moisture transfer process, fresh air is precooled first in the finned tube and subsequently gains secondary cooling in the water drenching fillers due to water evaporation and heat absorption. So this new type air cooler can make air temperature and humidity lower by two-stage evaporative cooling principle.The total circulating water of this new type evaporation air cooler keeps about 3m3/h. Experimental results show that under the operation conditions with the finned pipe and the packing quantity ratio of 2:1 and 4.93:1, the cooling efficiency and pressure loss of both do not vary much. Considering wind captain running time, the 2:1 proportional flow can be chosen in order to ensure that the water spray on the packing has better wetting effect. Due to the use of finned pipe, air by this new type evaporative cooler has higher pressure loss under the same condition. As the air outlet temperature of the cooler is more concerned in the project, and the general fans can fully reach the pressure loss requirements, so the relatively little loss of air resistance is often not particularly important. Therefore, only the air outlet temperature in the experimental test is compared.Meanwhile, the heat transfer and flow characteristics of the two section based on the assumed model below were analyzed in the numerical calculation with finned tube rows increasing from 3 to 6. Results show that the cooler with 6-row tube has the highest pressure loss for 153 Pa grows exponentially with the air velocity. So their balance should be considered in engineering practice. When the air velocity is 3~ 5m/ s, the air cooler with five rows has reached a higher cooling efficiency of 82.5% and relative humidity of 82.2% which also has a higher degree of air unsaturation. The pressure loss is 110 Pa, the comprehensive effect is the best.With the air wet bulb temperature gradually increases, the outlet temperature of the air in these conditions gradually increases. It is lower than the wet bulb temperature of the air after the wet bulb temperature is greater than 25℃, which also reflects the good performance of this new type evaporative cooler in moist area of southern China. Because the maximum difference of each value is more than 3℃, this results show that the air wet bulb temperature has a great influence on the air side heat transfer.