Abstract
An experimental investigation has been carried out regarding the effect of microstructural parameters of capillary porous coatings produced by directed plasma spraying on the heat transfer and critical heat fluxes during boiling of nitrogen at steady-state heat generation on horizontally-oriented tubular heaters of 3 and 16 mm in diameter. For both the tube diameters, the highest increase in the critical heat flux by a factor of 1.8 as compared with smooth heaters is observed for coatings with the highest porosity. The maximum heat transfer coefficients were observed in three-dimensional capillary-porous (TCP) coatings with large channel widths. Those were more than 3.5 times as high as the heat transfer coefficients on a smooth heater at low heat fluxes. The influence of the thickness of residual layer of microstructured capillary-porous coatings on the heat transfer during nucleate boiling has been shown. Based on the data of high-speed video recording, it has been shown that enhancement of heat transfer during boiling on structured capillary-porous surfaces is not associated with increase in the nucleation site density, but is caused by enhancement of liquid inlet and vapor phase removal in the macrolayer between the ridges of the coating.
Published Version
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