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%.