金属翅片冷表面多孔性灰尘内水气透湿过程的实验研究

Research on Water Vapor Permeability in Porous Dust Layer on the Surface of Cold Metal Fin

为了能够开发利用灰尘内部结冰胀脱方法来实现换热器翅片表面自清洁的技术,需要研究翅片表面多孔性灰尘内部水气透湿过程的物理机制及影响规律。本文设计并搭建了金属翅片表面多孔性灰尘水气透湿过程的可视化实验台,研究了金属冷板温度、灰尘样件厚度和入口湿空气相对湿度对多孔性灰尘内水气冷凝量的影响,实验参数范围涵盖金属冷板温度5~7℃、灰尘样件厚度3~8 mm、入口湿空气相对湿度15%~90%。结果表明:湿空气会优先通过由颗粒物团聚体构成的间隙通道渗透至灰尘内部并引起灰尘团聚体形变。低的金属冷板温度会提高灰尘内的水气冷凝速率,当金属冷板温度从7℃降至5℃时,灰尘样件内的水气冷凝速率平均提高约20%;大的灰尘厚度有利于提高水气冷凝量,当灰尘样件的厚度由3 mm增至8 mm时,灰尘样件内的最大水气冷凝量提高约15%;高的相对湿度有利于提高灰尘样件内的水气冷凝速率,但当相对湿度低于30%时,多孔性灰尘内将不会发生水气冷凝现象。

To develop a self-cleaning technique for fin-and-tube heat exchangers by adopting the method of dust layer freezing and expansion,the mechanism of water vapor permeability in porous dust layers on fin surfaces should be investigated.In this study,a visualization experimental rig of water vapor permeability in a porous dust layer on a cold metal fin surface was designed and developed,and the effects of the temperature of the cold plate,thickness of the dust layer,and relative humidity of the inlet moist air on the water vapor permeation mass were studied.The ranges of the experimental parameters cover the temperature of the cold plate ranging from 5℃to 7℃,the thickness of the dust layer ranged from 3 mm to 8 mm,and the relative humidity of the inlet moist air ranged from 15%to 90%.The results show that the water vapor in moist air may preferentially transfer into the inside of the dust layer along the permeability channels constituted by the dust aggregation and cause a morphological change in dust aggregation.The low temperature of the metal plate helps in increasing the water vapor permeation rate by approximately 20%as the metal plate temperature decreased from 7℃to 5℃.The large thickness of the dust layer is beneficial to the water vapor permeation mass,and the maximum water vapor permeation mass increased by approximately 15%as the dust layer thickness increased from 3 mm to 8 mm.The high relative humidity of moist air facilitates the water vapor permeation rate,but the water vapor may not permeate into the porous dust layer if the relative humidity of moist air is lower than 30%.