The Heat-Transfer And Pressure Drop For Bubbling Evaporative Cooling

At present in the cooling mode of condenser in refrigeration devices, the cooling water needs to be cooled in cooling tower. Not only this takes more energy but also the settings are so large. This paper brought forward a new cooling mode-bubbling evaporative cooling. This mode makes the condensation and the cooling of cooling water becoming one process. And experimental study on the heat transfer performance and pressure drop characteristic of the process of bubbling evaporative cooling are carried.As there are so little attention and studies on the process bubbling evaporative cooling about heat transfer in the world at present, this paper mainly deals with the effects of the different bare tower velocity, weir height, heat flux density and plate perforation geometries on the heat transfer coefficient and the pressure drop of the process of air flowing. It summarized heat transfer and pressure drop experimental relating equation on these experimental conditions.The plate dimensions were 400×160mm by 5mm thick. The apertures of the four plates are 4mm,4mm,3mm and 6mm,and the aperture ratios are 7.13％,3.61％,4.37％ and 8.13％;the weir height changes in 30mm,60mm,80mm and 100mm;The bare tower velocity ranges from 0.299m/s to 1.056m/s; the total heat tubes are ten and four lines; the heat flux density changes from several hundred w/m2 to over two thousand w/m2.The experiment validates several kind of transformation of two-phase flow on the perforated plate. And the influence factors of leakage were discussed in this paper. The result indicates that with the decreasing of perforated plate aperture,aperture ratio and weir height and increasing of bare tower velocity, the leakage is hardly to appear. The pressure drop of airflow consisting of pressure drop of the perforated plate and liquid-layer is mainly influenced by the plate dimension and bare tower velocity, with the increasing of bare tower velocity, pressure drop of the perforated plate increases. The experimental data are used to develop a correlation as follows: ΔpD＝1.04×10－8(WA/Sβ)2gThis correlation should be used whenβ＜5％,0.299m/s＜u＜1.056m/s.And the pressure drop of liquid-layer is mainly influenced by weir height. With the increasing of weir height, the pressure drop increases. And it is independent of bare tower velocity and plate dimension. The correlation before was corrected as follows:ΔpL＝3911ZThis paper analyzed the heat transfer coefficient between the outer wall of heat tubes and cooling water. And it was considered that plate geometries,weir height,bare tower velocity and heat flux density would affect the heat transfer coefficient. With the increasing of weir height, the heat transfer coefficient increases; in the range of bubbling, with the bare tower velocity increasing, the coefficient increases; at these experimental conditions, the coefficient gets maximum when the heat flux velocity gets 10kw/m2. The experimental data are used to develop two heat transfer correlations of No.1 and No.2 tubes as follows: Nu＝8.8562Re0.14 Nu＝20.066Re0.2These correlations should be used when 0.299m/s＜u＜1.056m/s,3.61%＜β＜8.13％。...