Self-jumping Mechanism of Melting Frost on Superhydrophobic Surfaces

Abstract

Frost accretion on surfaces may cause severe problems and the high-efficiency defrosting methods are still urgently needed in many application fields like heat transfer, optical and electric power system, etc. In this study, a nano-needle superhydrophobic surface is prepared and the frosting/defrosting experiments are conducted on it. Three steps are found in the defrosting process: melting frost shrinking and splitting, instantaneous self-triggered deforming followed by deformation-induced movements (namely, in-situ shaking, rotating, rolling, and self-jumping). The self-jumping performance of the melting frost is extremely fascinating and worth studying due to its capability of evidently shortening the defrosting process and reducing (even avoiding) residual droplets after defrosting. The study on the melting frost self-jumping phenomena demonstrates that the kinetic energy transformed from instantaneous superficial area change in self-triggered deforming step is the intrinsic reason for various melting frost self-propelled movements, and when the transformed energy reaches a certain amount, the self-jumping phenomena occur. And some facilitating conditions for melting frost self-jumping phenomena are also discussed. This work will provide an efficient way for defrosting or an inspiration for further research on defrosting.

Theoretical and Experimental Studies on the Controllable Pancake Bouncing Behavior of Droplets

“…Research related to the dynamic wettability of solid material surfaces has attracted much attention, especially for the investigation concerning the reduction of liquid–solid contact time. − The ability of droplets to rapidly bounce on the surface is of great importance to industrial applications, particularly with regards to the surface with self-cleaning, anti-corrosion, and icing resistance. − When a droplet impacts on a superhydrophobic surface, it will first spread to a maximum diameter on the solid surface, then retract, and finally leave the substrate or stick to it through heterogeneous surface wettability regulation. − It has been reported that the contact time in the spreading stage is independent of the substrate’s microstructure or droplet’s impact velocity. − In order to reduce the contact time of the droplets with the surface, shortening the contact time of droplets in the retracting stage is the key.…”

Frost Self-Removal Mechanism during Defrosting on Vertical Superhydrophobic Surfaces: Peeling Off or Jumping Off

“…As reported in literature which contains our own work, large amounts of surface energy can be released during the shrinking of melting frost with irregular shape, which easily triggers a self-propelled movement such as jumping. [22][23][24] As seen in Fig.3(a), the self-propelled jumping of melting frost indeed occurs very frequently (the solid circles represent original frost, the dashed circles show clean surfaces after jumping, and the white arrows indicate shadows of jumping paths). These jumping movements are able to selfremove most frost pieces, leaving an almost clean surface.…”

“…[18][19] Like that occurred during condensation, [20][21] self-propelled jumping, rotating and sliding movements during defrosting also take place frequently, making the defrosting process very dynamic and generating very low surface coverages on superhydrophobic surfaces. [22][23][24] On vertical superhydrophobic surfaces, the defrosting process is more efficient that the melting frost departs from the superhydrophobic surface directly at the early stage of defrosting. [25][26][27] Compared with conventional surfaces such as bare Aluminum surfaces and hydrophobic surfaces, the retention water mass or fraction presents a much lower value.…”

“…On horizontal superhydrophobic surfaces, our previous work showed that the frost meltwater films (ice–water mixtures) first dewet by edge curling and then by shrinking or coalescence, and finally dewet into isolated droplets . These droplets, which have been demonstrated to be in the highly mobile Cassie–Baxter state, are able to roll down at very small titled angles. , Similar to that during condensation, , self-propelled jumping, rotating, and sliding movements during defrosting also take place frequently, making the defrosting process very dynamic and generating very low surface coverage on superhydrophobic surfaces. − On vertical superhydrophobic surfaces, the defrosting process is more effective, because the melting frost usually departs from the superhydrophobic surface directly at the early stage of defrosting. − Compared with conventional surfaces such as bare aluminum surfaces and hydrophobic surfaces, the retention water mass or fraction presents a much lower value. − …”

Delayed Frost Growth on Nanoporous Microstructured Surfaces Utilizing Jumping and Sweeping Condensates

“…Hence, the small gaps (spacings) between the microstructures not only enable dewetting transitions of droplets, but also promote Cassie–Baxter state frost formation, enhancing the defrosting efficiency similar to what has been observed previously. The defrosting phenomenon on nanotextured-superhydrophobic surfaces has been widely investigated, ,,− concluding that the uniform nanoscale roughness promoted the Cassie–Baxter frost state, enhancing the defrosting efficiency. However, patterned square-shaped microstructures considered as hierarchical superhydrophobic surfaces cannot have confined regions.…”