Study of the effect of three-dimensional capillary-porous coatings with various microstructural parameters on heat transfer and critical heat flux at pool boiling of nitrogen

An experimental study of the effect of capillary-porous coatings obtained by directional plasma spraying on heat transfer and critical heat fluxes during pool boiling of nitrogen under conditions of stationary heat release on copper tubular heaters with a diameter of 16 mm was carried out. It is shown that for the coating with the highest porosity, the maximum increase in the critical heat flux is 1.8 times higher than that for a smooth heater. The maximum heat transfer coefficients were observed on TCP coatings in the region of low heat fluxes, which were up to 3.5 times higher than the heat transfer coefficients on a smooth heater. The effect of the thickness of the residual layer of microstructured capillary-porous coatings on heat transfer during nucleate boiling is shown. Based on the data of high-speed video recording, it was shown that the intensification of heat transfer during boiling on structured capillary-porous surfaces is not associated with an increase in the nucleation site density. Revealed pulsating nature of boiling in the region of high heat fluxes is characterized by the periodic formation and departure of vapor conglomerates along the surface of the heater.