The frosting characteristics on the surface of the fin-tube evaporator of an air source heat pump(ASHP)were experimentally investigated. The effects of the outdoor air temperature and humidity on the frost morphology and the average density
total average density
and dynamic density of the frost layer were analyzed. The experimental results indicate that the decrease in the outdoor air temperature or the increase in the relative humidity results in the formation of the acerose-shaped ice crystals
even of the fluffy frost layer on the evaporator surface of the ASHP. At higher air temperature and humidity
the average frost density rises clearly due to the existence of the water droplet on the frost layer surface. In the deceleration stage of the frost growth
the average frost density increases with the frosting time. In the acceleration stage of the frost growth
the average frost density decreases rapidly with the increase in the frosting time and the dynamic frost density is much lower than the average density of the frost layer. The comparison between the average frost densities at the same frost layer thickness under different environmental conditions shows that the average frost density increases with the increase in the ambient temperature and the decrease in the relative humidity
and the influence of the relative humidity under the low humidity condition is more significant.
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