The effect of a heater thin porous coating on the critical heat flux in flat microchannels with intense localized heating

Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, 630090, Russia

Abstract

Experiments were carried out on flow boiling in mini- and microchannels with non-uniform heating (channel width 30 mm, size of centrally located heater 3x3 mm²) with smooth and porous heater surfaces. It has been established that for that surfaces, the dependencies of the critical heat flux and heat transfer coefficients behave similarly, but in the case of porous surface, the critical heat flux increases more strongly with the growth of mass flow, and the heat transfer coefficients are higher due to developed boiling. Instead of a slowly developing boiling crisis with a large bubble constantly sitting on a smooth heater, boiling on porous surface was replaced by intense formation of small bubbles sweeping away large one. As a result, large bubbles either pulsate intensely or do not form at all until the moment of “classical” crisis - the sudden formation of stationary one with a sharp increase in surface temperature. This is true for both types of surfaces. But in the case of a smooth surface, the regime of a pulsating large bubble prevails, and on porous surface it ceases to form until “classical” crisis. The frequency of small bubble formation is significantly greater when boiling on porous surface.