Numerical Study On The Characteristics Of A Tube Indirect Evaporative Cooling Air-Conditioning

The evaporative cooling air-conditioning cools the air flow by evaporation cooling effect of water in the unsaturated air, and it is more energy-saving and environmental-friendly compared to the traditional air-conditioning. It is prospective to take the evaporative cooling air-conditioning as an alternative to the traditional air-conditioning, especially in those dry regions.According to the principle of cooling, the evaporative cooling air-conditioning can be divided into the direct evaporative cooling air-conditioning and the indirect evaporative cooling air-conditioning. The direct evaporative cooling air-conditioning cools the air flow by direct evaporating of water in the air. Although the cooling efficiency of the direct evaporative cooling air-conditioning is higher, the air humidity at the exit is usually high, even more than 90%, which will lead to an uncomfortable environment. The indirect evaporative cooling air-conditioning usually includes both types of plate and horizontal-tube, of which the horizontal-tube type is more common. It is hard to strengthen the effect of heat transfer of the horizontal-tube indirect evaporative cooling air-conditioning due to the limitation from its structure. Although the horizontal-tube indirect evaporative cooling air-conditioning does not change the humidity of the air flow, its cooling efficiency is low and its volume is huge.Because the cooling effect of the evaporative cooling air-conditioning is closely related to climatic conditions, the studies are mainly focus on its application. The fruits on improving the cooling efficiency of the horizontal-tube evaporative cooling air-conditioning are bits and pieces due to the limitation from its structure. Based on the above, firstly, this article deeply analyzed the cooling mechanism of various kinds of the evaporation cooling air-conditioning, and concluded the advantages and disadvantages of the evaporation cooling air-conditioning, particularly the defects of horizontal-tube indirect evaporative cooling air-conditioning. Secondly, the horizontal-tube type indirect evaporative cooling air-conditioning in Lanzhou was tested, and its cooling efficiency was obtained. Thirdly, this paper presented a vertical tube indirect evaporative cooling air-conditioning. With the help of FLUENT software, the performance of the vertical-tube indirect evaporative cooling air-conditioning was studied by numerical method, including the introduction of the physical model, numerical model and the numerical method, the verification of the grid independence and the numerical method, and the study of the relationship between the cooling efficiency and tube diameter and spacing. The better combination of the vertical-tube diameter and spacing was obtained. Finally, under the same conditions, the comparison of the cooling effect between the experimental results of the traditional horizontal-tube indirect evaporative cooling air-conditioning and the numerical results of the vertical-tube type indirect evaporative cooling air-conditioning.Based on the analysis and studies of this paper, the following conclusions can be drawn:(1) The average cooling efficiency of the horizontal-tube type indirect evaporative cooling air-conditioning is 33.2%, and it is suitable for Lanzhou area.(2) The numerical model and the numerical method in this paper can be effectively applied to study the performance of the tube indirect evaporative cooling air-conditioning.(3) The tube diameter and the tube spacing are the important factors on the performance of the vertical-tube type indirect evaporative cooling air-conditioning. Under the condition of 5000m3/h, the cooling effect of the vertical-tube type indirect evaporative cooling air-conditioning is best when the tube length is 1 m, the tube diameter is 30 mm and the tube spacing is 50 mm.(4) Compared with that of the traditional horizontal-tube indirect evaporative cooling air-conditioning, the cooling efficiency of the vertical-tube type indirect evaporative cooling air-conditioning presented by this paper can be improved by 10% under the same conditions.