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Abstract
The paper presents the results of an experimental study of the effect of hydrophobic fluoropolymer coating on the multiscale characteristics of heat transfer at water boiling. New experimental data on dynamics of vapor bubble growth and detachment, evolution of contact line, nucleation site density, heat transfer coefficient were obtained using high-speed imaging techniques, including infrared thermography and video recording from the bottom side of transparent ITO heater. It was shown, that the using of hydrophobic fluoropolymer coating leads to heat transfer enhancement, to decrease of the superheat temperature at the onset of boiling, to increase of the active nucleation site density and to significant change in the dynamics of growth and departure of vapor bubbles and the evolution of the triple contact line.
Highlights
It is well-known that the properties of heat exchange surfaces have a significant influence on dynamics of phase transition, in particular on liquid boiling [1]
Experimental data on the heating surface temperature obtained by IR thermography were averaged over the recording time and surface area at different heat flux densities
Analysis of data shows that the heat transfer intensity at water boiling on the hydrophobic surface are more than 3 times higher than on the uncoated sapphire surface at heat flux density up to q = 45 kW/m2
Summary
It is well-known that the properties of heat exchange surfaces have a significant influence on dynamics of phase transition, in particular on liquid boiling [1]. Despite the prospects of the above-described high-speed measurement techniques, there are practically no studies in literature that would allow one to study the effect of nanocoatings with different wetting properties on the local and integral characteristics of heat transfer at liquid boiling using these methods. This would make it possible to achieve a significant progress in understanding the fundamental laws governing the influence of wetting properties on the most important parameters characterizing the boiling process. Data were obtained with the use of simultaneous high-speed video and infrared recordings with high temporal and spatial resolution, and special construction of on a transparent heater
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