Research On The Water Film Characteristics Outside The Tube Of Evaporative Cooler

At present,the construction of the subway in China is in the period of rapid development.However,the subway construction scope covers the prosperous areas and main roads of the city,it is difficult to find the location on the ground of the underground station that not only meets the requirements for cooling tower,but also coordinates with the surrounding environment to install cooling tower.Therefore,many subway engineering have to adopt the centralized freezing or centralized cooling,which not only occupy valuable underground tunnel space,greatly increase engineering costs,but also greatly increase operating costs.If the evaporative cooler installed in the underground exhaust tunnel,it will replace the cooling tower installed on the ground of the platform can effectively solve the above-mentioned engineering problems.However,the air flow velocity in the exhaust tunnel of underground station is far greater than the design conditions of existing evaporative cooler which leads to the assumption that the water film is uniform and complete in the calculation model and the conditions that ignore the influence of water film thickness and velocity are no longer valid.Therefore,it is urgent to solve the problem of water film distribution characteristics on the surface of evaporative cooler to optimize the calculation model of evaporative cooler for guide its engineering application.In this paper,ANSYS-ICEM was used to establish a model to study the influence of wind velocity,wall contact angle,water distributor spacing and tube type on the water film distribution on the surface of evaporative cooler.The results show that the fluctuation of water film thickness in vertical direction increases with the increase of wind velocity,the variation trend is first stability and then fluctuation.In the vertical direction,the water film velocity first decreases,then increases and finally fluctuates at the center angles 30°、60°and 90°.at the center angles 120° and 150°,the water film velocity first increases and then stabilizes.The fluctuation of water film thickness in the circumferential direction starts at the center angle of 20°,reaches the peak value near the center angle of 60°～120° and tends to be stable after the center angle 120°.The thickness at the peak value of water film can reach 3～4 times than the water film thickness in the stationary area.With the increase of contact angle,the area of uniform water film formed becomes smaller and the maximum wetting length increase,the water film velocity increases with the increase of water film thickness and decreases with the decrease of water film thickness.The water film thickness and water film velocity increased with the distance between water distributors increase,In this paper,the wetting rate and wetting length under different wind velocity and wall contact angle are given,the relationship between wetting rate and wetting length is also obtained.In view of the above factors that affect the distribution of water film outside the tube of evaporative cooler,a special-shaped tube with a central angle of 60°～120° as a straight line was tentatively proposed to improve the distribution of water film outside the tube.The distribution of water film outside the special-shaped tube was simulated,when the contact angle is 105° and the different wind velocity.The results show that at the positions 60° and 120° of the special-shaped tube,due to the geometric structure of the special-shaped tube,the thickness of water film still fluctuate sharply.Thus,the special-shaped tube can not optimize the distribution of water film.Based on the research results of the water film characteristics,a secondary water distribution strategy proposed to reconstruct water film outside tube and the reconstructed water film also studied,when contact angle is 105° and wind velocity is 8m/s,6m/s,4m/s,respectively.The characteristics of water film which may be applied in practical engineering with a wind velocity is 7m/s and contact angle is 15° also simulated.The results show that the secondary water distribution can improve the maximum wetting length and wetting rate.However,because the disturbance between the water distributors,the leeward surface is easy to form dry spots.In order to solve the disturbance between the water distributors,this paper simulates secondary water distribution half water filling and secondary water distribution without water when the wind speed is 8m/s and the contact angle is 105°.It revealed that the water distribution half water filling neither improve the water film distribution nor reduce the disturbance between the water distributors.The secondary water distribution without water can reduce the disturbance between the water distributors,but it can not optimize the water film distribution outside the tube.