The effect of porous coatings obtained by various methods on heat transfer and crisis phenomena during nitrogen boiling including non-stationary heating and cooling

Abstract

The paper presents the main results of experimental investigation of the influence of porous coatings obtained by various methods on heat transfer and crisis phenomena during nitrogen boiling, including unsteady heating and cooling regimes. Modification of heater surfaces was carried out by the methods of directed plasma spraying, additive 3D printing and micro-arc oxidation. For all types of porous coatings, a significant intensification of heat transfer at atmospheric pressure relative to smooth heaters was obtained (maximum degree of heat transfer increase up to 6 times). The mechanisms playing a determining role in the process of heat transfer coefficients increase are suggested. The essential influence of structured capillary-porous bronze coatings on the dynamics of transient processes and development of crisis phenomena of non-stationary processes is shown, leading to degeneration of the heat transfer crisis at pulse supply of heat load and significantly reducing the time of complete cooling of the heater in the process of rewetting.