Abstract
Organization of a cloud of micro-droplets of condensate into an ordered hexagonal structure levitating over a heated layer of liquid (the so called micro-droplet cluster) has been observed in several recent experimental works, however the nature of this phenomenon is still not completely understood. In the present paper the micro-droplet cluster is studied on a test section with relatively large heating area, under the condition when the liquid layer ruptures and dry spots form on the heater. It has been found, that the micro-droplets can levitate not only over the heated liquid surface, but also over a dry surface of the heater, following the rupture of the liquid layer. The micro-droplets can move over the dry surface as far as 3 mm away from the contact line, and can exist for up to 3.5 seconds after the rupture.
Highlights
A micro-droplet cluster is a spatially ordered structure of micro-droplets, discovered in [1] over the surface of liquid layer spot-heated from below
The drop diameter is on the order of 10 microns; the distance between the drops is of several drop diameters, while the drops levitation height above the liquid surface is comparable to the drop diameter
The heater surface temperature, Tw, and surface temperature of stainless steel plate are measured at several points by thermocouples
Summary
A micro-droplet cluster is a spatially ordered structure of micro-droplets, discovered in [1] over the surface of liquid layer spot-heated from below. Among the effective solutions for removing high heat fluxes, there are systems of spray cooling [4] as well as the systems using stratified two-phase flows in microchannels [5,6]. Heat in these systems is removed due to evaporation of liquid microdroplets that are in contact with the surface [7,8]. The phenomenon of droplet levitation above a heated surface may have a significant effect on operation efficiency of the two-phase cooling systems, since the evaporation rate of levitated droplets is much lower than that of droplets in contact with the heated surface
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