Experimental study on frost formation on a cold surface in low atmospheric pressure

Frosting Phenomenon and Frost-Free Technology of Outdoor Air Heat Exchanger for an Air-Source Heat Pump System in China: An Analysis and Review

“…The results are In addition, as shown in Figure 2, the only condensation phenomenon (C→D) occurred on the cold surface under ideal condition, when the partial pressure P v of water vapor is greater than the triple point pressure P tp (P v > P tp ) and the cold surface temperature T cs was higher than the triple point temperature T tp but lower than the wet air dew point T dp (T tp < T cs < T dp ) [55]. Meanwhile, we can also see from Figure 2 that there are three kinds of different pathways to form frost layer, and that is gas-liquid-solid process (C 1 →D 1 ), gas-solid process (C 2 →D 2 ) and occurring simultaneously (C 1 →D 1 and C 2 →D 2 ) [22,55]. The results provided by Xu [56] also confirmed it.…”

“…Kwak and Bai [19] found that the heating capacity and COP of the system increased significantly by In addition, from the viewpoint of phase change kinetics, the phase change driving force leads to the freezing of the water droplets [61]. Chen et al [22] showed that a smaller phase change driving force will be obtained if the partial pressure of water vapor or atmospheric pressure decreases under keeping other conditions constant. This will contribute to keeping the cooling state of ambient air and the supercooling state of the water droplets without being frozen.…”

“…To promote the rapid development of ASHP technology and the successful implementation of Coal to Electricity policy in China, the anti-frosting and defrosting technologies are focused by researchers worldwide in recent years [14]. According to the references, the anti-frosting technologies include changing the characteristics (temperature, velocity [20], humidity [21], pressure [22] and purified air [23]) of inlet ambient air, changing the cold surface temperature [24], surface treatment [25], changing the structure of air heat exchanger (fin-tube geometry [26][27][28], fin spacing [29,30], fin type [31,32]), changing the interaction between air or frost layer and cold surface (electric field [33], ultrasonic wave [34], magnetic field [35] and low frequency mechanical oscillation [36]). And the defrosting technologies mainly have reverse cycle [37], hot gas bypass [38], electrical heating [19,39,40], warm-air defrosting [41], compressor shutdown [42], hot water spray [43], phase change heat storage, electric field [44], ultrasonic wave [45], magnetic field [46], air-particle jet [47], control strategy [48] and waste heat recovery [49,50].…”