基于两相流EWF模型蒸发式空冷器数值模拟

Numerical Simulation of Evaporative Air Cooler Based on Eulerian Wall Film Model of Two-Phase Flow

建立了8排蒸发式空冷器管束三维模型,在恒壁温边界条件下,在管束表面施加质量源项模拟喷淋液膜,采用Eulerian Wall Film (EWF)模型与Mixture Species Transport模型耦合来研究蒸发式空冷液膜与空气间热质传递。数值模拟得到的空气出口温度、含湿量的数据与试验数据的误差分别为-0.67%～-0.98%、-4.95%～2.29%。比较了不同喷淋流量下管束表面液膜质量分布,小喷淋流量下液膜主要分布在管壁下半部分,随着喷淋水流量增加,管壁液膜分布趋于均匀,管排水膜温度由上至下先增加后减小。由于空气在管束背风面的流速较低,形成较高含湿量与温度三角区域。数值模拟得到的水膜与空气间的传质系数比试验值小,误差为-8.00%～-9.30%。揭示了蒸发式空冷器热质传递机理,为蒸发式空冷器设计改造提供了理论基础。

Based on the experiments of eight plain tube bundle wet air cooling,a three-dimensional physical model of plain tube bundle was established.Hexahedral mesh generation and symmetric boundary were applied to the model.A mass source was applied to the tube surface to form liquid film based on the tube boundary condition of constant temperature.The Eulerian Wall Film(EWF)model was coupled with the mixture species transport model to study the heat and mass transfer between liquid film and air in wet air cooling.Six sets of different numbers of grids were divided,and grid independence test was done.The final division grid number was793152.The outlet temperature and moisture content of air passing through the tube bundle were obtained by numerical simulation.Compared with the experimental data,the simulated error of outlet air temperature was from-0.67%to-0.98%,while the simulated moisture content error is from-4.95%to2.29%.The mass distribution of liquid film on the surface of tubes under different spray flow rates is compared.Under the condition of small spray flow,the liquid film is mainly distributed in the lower half of the tube wall.With the increase of spray water flow,the liquid film distribution in the tube wall tends to be uniform.Water film temperature increases firstly and then decreases from upper to lower tube bundle.Air in the leeward side of the tube bundle,due to the low flow rate,forms a triangular region with higher humidity and higher temperature.The simulated mass transfer coefficient between water film and air is lower than that of experiments,and the error is from-8.00%to-9.30%.The heat and mass transfer mechanism of wet air cooling is revealed by numerical simulation,which provides a theoretical basis for the design and transformation of air cooler.