Frost on a solid surface is known to spread through the buildup of bridges between condensed droplets. For this reason, modulation of condensate droplet distributions is an efficient method to tune frost spreading.
Condensate frosting is one of the most pervasive forms of ice, which is related to several industrial applications including refrigeration, heat pump, air conditioning, and cryogenic units. However, several detrimental effects may be referenced to frost accretion. Specifically, heat exchanger performance of these systems is found to deteriorate considerably owing to additional thermal resistance induced by the frost layer. Reference to the highly unsteady nature of the condensation processes, droplet interaction and ice nucleation mechanisms, condensate frost formation as well as its dependence on substrate attributes, thermal history and other environmental aspects remain unclear. For this reason, effective methods are necessary to limit condensate frost accretion.
Deicing methods designed to solve condensate-frosting issues have been the center of research in the last few decades. Researchers have indeed focused on super hydrophobic surfaces. However, despite super hydrophobic surfaces being good candidates for icehobic surfaces as identified by many researchers, contradictory reports have been advanced identifying superhydrophobic surfaces not always possessing superior icehobicity. Therefore, a rational surface design to resist condensate frosting should consider the effects of roughness and wettability.
Yugang Zhao and Chun Yang at Nanyang Technological University in Singapore investigated frost spreading on a number of substrate surfaces, which included a surface with wettability patterns, a smooth hydrophilic surface, a surface with morphological patterns, a smooth hydrophobic surface, and a surface with dual patterns. The authors investigated the frost spreading on these surfaces for an array of substrate temperatures ranging from -5 °C to -30 °C. They focused on the relationship between the condensate droplet distribution and frost spreading velocity. Their research work is published in Applied Thermal Engineering.
The authors studied the effects of wettability and surface morphology together with substrate temperature on the frost spreading velocity. The authors found that the morphology-patterned surfaces retarded effectively the frost spreading by providing a controlled droplet distribution pattern. On the other hand, the wettability patterned surface indicated identical performance as the smooth hydrophobic surface. The researchers also studied the frost spreading on the selected surfaces at varying substrate temperatures. They also observed that the frost spreading velocity increased drastically with decreasing substrate temperature on both wettability patterned and smooth surfaces owing to the large number of condensate droplet nucleation sites, implying that the ice bridges become smaller.
The researchers achieved a stable frost spreading velocity on the morphology-patterned surface as well as the dual patterned surface. These results indicated that surfaces with morphology patterns were promising building blocks for anti-icing applications over a range of substrate temperature. Zhao and Yang therefore developed an analytical model in a bid to describe the building of ice bridges that takes into account the effects of wettability, temperature, and morphology on the frost spreading. The predictions of the proposed model agreed well with experimental results.
Yugang Zhao and Chun Yang. Frost spreading on microscale wettability/morphology patterned surfaces. Applied Thermal Engineering, volume 121 (2017), pages 136–145.Go To Applied Thermal Engineering