An experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface

Abstract

The freezing and melting process of a small water droplet on a superhydrophobic cold surface was investigated using the Laser Induced Fluorescence (LIF) technique. The superhydrophobic surface was prepared using a sol-gel method on a red copper test plate. From the obtained fluorescence images, the phase transition characteristics during the freezing and melting process of a water droplet were clearly observed. It was found that, at the beginning of the droplet freezing process, liquid water turned into ice at a very fast rate. Such phase transition process decreased gradually with time and the volume of frozen ice approached a constant value at the end of the icing process. In addition, the freezing time was found to reduce with the decrease of the test plate temperature. Besides, when the test plate temperature is relatively high, the effect of droplet volume on the freezing time is very significant. Over all, we provide some tentative insights into the microphysical process related to the icing and melting process of water droplets. sol-gel, icing, melting, superhydrophobic surface, water droplet PACS number(s): 44.10.+i, 68.08.-p, 68.18.Jk Citation: experimental investigation into the icing and melting process of a water droplet impinging onto a superhydrophobic surface.

The impact, freezing, and melting processes of a water droplet on an inclined cold surface

“…Besides, a large amount of air bubbles appeared and was trapped in the ice bead. Due to the formation of air bubbles, the liquid-solid interface could not be discerned as clearly as our previous studies [49,50,52]. At t = 690.0 s, a cusp point was found to form on the top of the ice bead, which marked the completion of the freezing process.…”

“…In the present study, the time interval between the moment when the circulator was turned off and the moment while the ice bead melt completely was defined as the melting time of the ice bead. Thus, the total melting time of the ice bead for this case was about 700 s. It should be noted that Jin et al [49] obtained the melting process of a water droplet on a horizontal superhydrophobic surface. Their results indicated the solid-liquid interface kept almost parallel to the superhydrophobic surface during the melting process of ice bead.…”

“…The third explanation is that a solid ice shell forms at the droplet surface while the droplet center is still liquid. The change in optical transparency has been used to indicate the beginning of the freezing process of the droplet by many previous studies [44,[49][50][51][52][53]48]. Then, water turned into ice at the bottom of the water droplet and a liquid-solid interface thus formed.…”

Modelling the dynamics of the flow within freezing water droplets

“…on wind turbines, airplane wings, and roads, calls for a better understanding of the freezing process for water droplets on cold surfaces. Previous research has identified a number of factors important to the freezing process such as the temperature of the cooling surface, T p [1], the size of the droplet [2] the impact of free and forced convection [3,4], the roughness and wettability of a surface [5], the freezing on superhydrophobic surfaces, e.g. [6], the effect of an inclined surface [7][8][9], internal heat transfer [10,11] and internal flow [12].…”

Ice-dependent liquid-phase convective cells during the melting of frozen sessile droplets containing water and multiwall carbon nanotubes

“…The thickness of this layer remains relatively constant through the melting process, measuring approximately <0.05 mm. All remaining water converted from solid to liquid accumulates below the floating ice block, and as the ice crystal shrinks it releases contained air volumes and MWCNT clusters into the liquid beneath [42]. The air bubbles either accumulate along the bottom edge of the ice or rise to the top of the droplet through the thin liquid shell.…”