Experimental Study on Behavior of Frost Crystal Formation

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

“…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 (C1→D1), gas-solid process (C2→D2) and occurring simultaneously (C1→D1 and C2→D2) [22,55]. The results provided by Xu [56] also confirmed it. The process C1→D1 revealed that when Pv > Ptp, Tdp > Tcs and Tcs < Ttp, the condensation water firstly appeared on the cold surface, followed by being frozen and finally the frost formation occurred with decreasing Pv on the surface of the frozen water droplets.…”

“…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 Pv of water vapor is greater than the triple point pressure Ptp (Pv > Ptp) and the cold surface temperature Tcs was higher than the triple point temperature Ttp but lower than the wet air dew point Tdp (Ttp < Tcs < Tdp) [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 (C1→D1), gas-solid process (C2→D2) and occurring simultaneously (C1→D1 and C2→D2) [22,55]. The results provided by Xu [56] also confirmed it.…”

“…And a probability model (Pro.) related to time was proposed, as expressed in Equation (1) [55]. (1) where, a is the delay time of occurring transformation, s; and b is the speed of phase change, m/s.…”

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

“…After the appearance of frost on frozen droplet, there exists the crystal growth, frost layer growth and frost layer full growth [4] on the cold surface. From the viewpoint of phase change, the frost formation may go through the processes of vapor-liquid-solid, direct vapor-solid or occurring simultaneously [6].…”

Observation of surface crystal sublimation during frosting

“…However, a comprehensive recognition about frost formation from a macroscale viewpoint is still absent because of the complexity of frosting. In recent years, researchers have begun to investigate the details and dynamic behaviors of frost formation, including visualization and theoretical analysis on its initial stage [3][4][5][6] as well as observation and brief discussion on the local details of a frost layer [7][8][9]. Nevertheless, insufficient investigation has been conducted on exploring the formation mechanism of frost crystals, which may be significant to a profound understanding of frosting.…”