Experimental evaluation of the effects of bubble nucleation under confined conditions on two-phase flow distribution among the microchannels of heatsinks

Abstract

Heat sinks/heat exchangers composed of multi-microchannels (dh <3 mm) applied to heat pumps,energy cells, and micro-reactors in chemical processes, for example, presents several advantages when compared to those composed of conventional channels (dh> 3 mm). Among them, thefollowing are highlight: the possibility of operating under high pressures, largest contact area per unit of refrigerant volume and higher heat transfer coefficient, especially for phase-change heat transfer processes. Due to these characteristics microchannels associated with convective boiling seems a promising solution to remove high heat fluxes in restricted spaces. However, thermal instabilities associated to bubble growth under confined conditions can lead to irreversible damages of the cooled component. In this context, the present research proposal deals with the study of the effect of the nucleation of bubbles on the flow distribution in multi-microchannel heatsinks. Initially, an experimental apparatus will be build that allows to emulate the nucleation and growth of bubbles through the injection of air in the liquid water flow along the microchannels. Particles of silicon carbide will be dispersed in the liquid flow in order to characterize the effect of bubbles nucleation and growth on the liquid velocity field inside the microchannels. Images of the particles illuminated through a laser sheet will be obtained with a high speed camera. An in-house software developed in MATLAB will be updated in order to obtain the flow field in microchannels. Tests will be carried out for two heatsink geometries manufactured in ABS using 3D printing. Both configurations will be composed of parallel channels, however, one of them will contain flows restrictions in the inlet of the microchannels in order to reduce thermal instabilities associated to bubble growth under confined conditions.