Analogy in the processes of heat exchange of capillary-porous coatings in energy installations

¹ Almaty University of Power Engineering & Telecommunications, Almaty, Republic of Kazakhstan
² Dept. of Thermotechnics, Hydraulic and Ecology, University of Ruse, Ruse, Bulgaria
³ Dept. of Power Engineering and Power Machines, Technical University of Sofia, Sofia, Bulgaria

^* Corresponding author: aterziev@tu-sofia.bg

Abstract

A model of the dynamics of steam bubbles generating on a solid surface in porous structures and a steam-generating wall (substrate) is developed. The model is based on the filming and photography with speed camera SKS-1M. The removal of high heat fluxes (up to 2х10⁶ W/m²) is provided by the combined action of capillary and mass forces with application of intensifiers. An analytical model is developed based on the theory of thermoelasticity. The limiting state of a poorly heat-conducting porous coating and a metal substrate has been determined. The heat fluxes were calculated from the time of spontaneous appearance of the steam nucleation (10^-8) up to the time of material destruction (10² ÷ 10³ s). The destruction of the coating under the action of compression forces occurs in much earlier time than the tension forces. The intervals of the heat flux within which such destruction occurs are different for the quartz coating q_max ≈ 7х10⁷ W/m², q_min ≈ 8х10⁴ W/m² and for granite coating q_max ≈ 1х10⁷ W/m², q_min ≈ 21х10⁴ W/m². Experimental units, experimental conditions, the results of the heat exchange crisis and the limiting state of the surface are presented, and critical heat fluxes are calculated. The investigated capillary-porous system, operating under the combined action of capillary and mass forces, has the advantage over pool boiling, thin-film evaporators and heat pipes.