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The paper presents results of an experimental study of the effect of pin microstructures on the wetting front propagation and its structure under adiabatic conditions and on strongly pre-heated surfaces, as well as the heat transfer and critical heat fluxes under steady-state heat release with liquid nitrogen film flowing. The surface structuring was created by the deformational cutting method (DCM). Comparison with data obtained on a smooth heater is presented. It is shown that the microstructures created by the DCM may have a significant effect on the nature of the temperature curves, reducing the total time of plate cooling at rewetting up to 2 times, and significantly change the structure and dynamics of the wetting front under adiabatic conditions. At the same time, such microstructuring with preset parameters of microfinning has weak influence on the heat transfer under steady-state heat release. High-speed video data of the processes are presented.

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.

The effect of structured plasma-sprayed capillary-porous coatings on transient processes and the development of crisis phenomena at boiling under pulsed heat release was studied. The working fluid was liquid nitrogen on the saturation line at atmospheric pressure. It is shown that under unsteady heat release, there is a degeneration of the development of the boiling crisis on heaters with structured capillary-porous coatings at q < qCHF (critical heat flux at steady heat release). Under unsteady pulsed heat release, no rapid transition to the film boiling regime (without passing through the nucleate boiling stage) is observed on heaters with such coatings until the thermal load is more than two times higher than the critical heat flux for steady heat release. This significantly increases the times of transition to post-critical heat transfer. Analysis of synchronized measurements of surface temperature of heaters and high-speed video recording of transient processes shows that the degeneration of the heat transfer crisis at q < qCHF on samples with coatings occurs due to significantly lower liquid boiling temperature differences and specific features of the dynamics of propagation of self-sustaining evaporation fronts in comparison with a smooth heater.