Investigation Of Heat And Mass Transfer Of Horizontal Oval Tube In Closed Wet Cooling Tower

In industry, due to the fact that the cooling water in cooling towers directly contacts with air, cooling water can easily be polluted. At present, traditional closed wet cooling towers because of its environmentally friendly and energy saving, are widely used in chemical, metallurgy, etc. Based on the computational analysis and CFD simulation and experimental verification, the heat and mass transfer and thermal performance of the new structure closed wet cooling tower with packing are presented as follows:Computational fluid dynamics(CFD), ANSYS FLUENT, was implemented for the numerical solution. By changing ellipticity as a/b=1.5, 2, 3, 4, and changing the liquid spray water density as 0.015,0.019,0.024,0.029,0.033,0.037,0.041,0.045kg/(m·s), numerical stimulation of horizontal oval single tubes are calculated. Numerical results indicated that the water film convection heat transfer coefficient of oval tubes increase with the increase of the spray water flow rate. Under the same liquid Reynolds number, with the increase of ellipticity, the water film convection heat transfer coefficient of oval tubes decrease. The oval tubes of a/b=1.5 has the highest water film convection heat transfer coefficient. According to the numerical results, the water film convection heat transfer coefficients of tubes with different ellipticity are fitted, which provides evidence for closed wet cooling tower design calculation and model prediction.By employing Poppe method, thermal performances of the closed wet cooling tower are analyzed and its numerical differential equation is set up, based on the assumption on the heat and mass transfer of closed cooling towers. With following an approach to discrete finite difference method, analytical models of the closed wet cooling tower under concurrent flow and countercurrent flow were derived. The reliability of numerical results was tested against experimental data, which were obtained from literature. And the analytical results are compared well with experimental data. The comparison between computational analysis and FLUENT simulation showed an acceptable agreement with each other.By the proposed Matlab model was also applied to improve and predict the thermal performance of closed wet cooling tower under different operating conditions and structure perameters. The analytical results shows that the oval tube with a/b=2 has better cooling effect among other investigated ellipticity. The cooling water inlet and outlet temperature difference of the oval tube with a/b=2 is higher than that with 1.5, 3 and 4 of 1.65%~21.9%, 4.40%~36.90% and 2.94%~39.6%. The cooling efficiency of the oval tube with a/b=2 is higher than the that with 1.5, 3 and 4 of 1.01%~22.28%,3.12%~54.06% and 0.39%~55.32%.The effect of cooling water flow direction in the closed wet cooling tower was investigated under normal operationg condition. Results show that, under the same conditions, the cooling efficiency in concurrent flow has higher 8.5% than in countercurrent flow.Oval tubes with a/b=2 in closed wet cooling tower are design by computational model of matlab, and the analytical results are compared with circle tube. The major semi-axis of the oval tube is 8.2mm, and the minor semi-axis is 4.1mm. The circle tube has the same perimeter with the oval tube, which is 12.7mm. It is indicated that under the same operating conditions, the oval tube with a/b=2 has better cooling effect. The cooling water inlet and outlet temperature difference of the oval tube is higher than the circle tube of 1.57%~16.82%, and the cooling efficiency of the oval tube is higher than the circle tube of 0.76%~7.75%. Therefore, under the normal operating conditions, the oval tube with a/b=2 has better cooling effect.