Study On Heat And Mass Transfer Of Subway Station Plate Evaporative Cooler

For sake of getting more passengers, the subway station is always located at down town. In order to meet setting demand of cooling tower and not to destroy urban landscape, it is very difficult to find an appropriate location to install cooling tower. Hence, there is an impatient need to find an efficient heat exchanger to substitute the cooling tower, move the cooling tower into the subway station and solve the problem that there is no place for installing the cooling tower of the underground buildings. The paper presents a novel subway station plate evaporative cooler as an alternative to cooling tower, and the key technology of it was investigated experimentally and theoretically. The main contents of the present paper include:The working environment, system composition and working principle of subway station plate evaporative cooler were expatiated. Based on the simulated results of concurrent flow counterflow and cross flow and comparative analysis of install location in subway station exhaust airway, it is pointed out that the optimal install location is horizontal segment of subway station exhaust airway, not only from the aspect of installing, but also from the aspect of running attention.The subway station plate evaporative cooler comprises plate evaporative heat exchanger and liquid film distributor at least. Plate evaporative heat exchanger and liquid film distributor in corresponding compose the cooling unit. The number of cooling unit could be increased or decreased according to the heat transfer rate in practical application. Based on relevance analysis of simulated results and experimental results, it is indicated that the uniform liquid film technique and the developing of plate evaporative heat exchanger suitable for subway station exhaust airway are the key technology. It is pointed out that the spacing between heat exchange flat, the angle between reservoir and heat exchanges flat and the spacing between reservoir lower limb and heat exchanges flat are the key parameters.Under the gas stream sweeping condition, the hydrodynamics and heat transfer model of subway station plate evaporative cooler was established. The heat transfer performance of laminar liquid film under nonlinear temperature distribution with interfacial shear stress was discussed. The change of liquid film thickness and heat transfer coefficient along with the flow direction of liquid film was discussed. The effects of interfacial shear stress and the intensity of interfacial convection heat transfer and Reynolds number on hydrodynamics and heat transfer are explained. The results indicate that with a rise in Reynolds number the dimensionless liquid film thickness increases and heat transfer coefficient decreases. The cocurrent shear stress plays the roles on thinning film thickness and enhancing heat transfer, and the countercurrent shear has inverse effect. And the effect of countercurrent is more remarkable than that of cocurrent shear stress. The effects of eddy viscosity, interfacial shear stress and Reynolds number on heat transfer of turbulent liquid film were discussed. The results indicate that eddy viscosity increases with a rise in interfacial shear stress. And the eddy viscosity maximal value gets close to gas-liquid interface gradually as the interfacial shear stress increases. The dimensionless velocity distribution increases with the increasing of distance from wall.Based on volume of fluid (VOF) method, the three-dimensional model of subway station plate evaporative cooler was set up under gas-liquid cross-flow condition. By compiling user-defined functions, the surface tension source and mass transfer source were taken into account. The heat transfer of liquid film under experimental condition and constant heat flux condition was investigated. The effects of surface tension and liquid solid contact angle on heat transfer of liquid film were investigated. The results show that with the increasing of surface tension and liquid solid contact angle the instability of liquid film strengthens and liquid film brim begins to fluctuate. Hence, in practical engineering physical or chemical methods should be taken into account to reduce the surface tension source.By designing and founding the experimental apparatus and collecting the data of liquid film flow rate, inlet and outlet water temperatures and the air velocity, the heat transfer of liquid film was investigated. The experimental results indicate that as the increasing of Reynolds number there was an optimal liquid Reynolds number which minimize thermal resistance and maximize heat transfer coefficient of liquid film. Temperature plays an important role in heat transfer of laminar flow liquid film. Whereas, the heat transfer of turbulence liquid film flow is not sensitive to liquid film inlet temperature.