Abstract:To further reveal the heat/mass transfer and pressure drop characteristics of evaporative cooling between staggered tube bundles, considering the formation of water film on the tube bundle wall and the mass transfer process between wet air and spray water, an analytical model was established by using the Euler-Lagrange method based on the coupling of discrete phase model (DPM) and wall film. First, the reliability of the model was verified by the experimental data from literature, and the error was within 1%. Then, the characteristics of heat/mass transfer and pressure drop between staggered tube bundles along the vertical direction were studied by simulation method. Results show that the mass transfer coefficient fluctuated along the coil height due to the variation of the enthalpy differences of wet air and saturated air, but the overall trend was decreasing. Under the same working condition, the influence of the enthalpy difference of wet air was greater on the mass transfer coefficient, and the fluctuation of mass transfer coefficient was mainly caused by the enthalpy variationof wet air. The temperature of the spray water film between staggered tube bundles was not constant, but it decreased with the decrease in the coil height, that is, the temperature of the liquid film gradually decreased along the falling direction. The spray water evaporation in the bottom area of the staggered tube bundle was the largest, and it decreased along the height of the coil. The spraying process mainly occurred on the surface of the tube bundle and the wake area of the tube bundle. By adding baffles or reducing the distance between the tube bundles, the turbulence of the flow field on the surface and the wake area of the tube bundles was strengthened, and the evaporative cooling effect of the spray water was enhanced.The heat transfer coefficient between the staggered tube bundles had little changes in the middle stable region of the heat exchange coil, and it was less affected by the inlet air temperature, spray water temperature, and relative humidity. The pressure loss between the staggered tube bundles had little changes along the coil height, and it was the largest in the air inlet transition area of the heat exchange coil. The above research results provide theoretical basis for the design of heat/mass transfer and pressure drop performance of air-water evaporative cooling between staggered tube bundles.
