EXPERIMENTAL INVESTIGATION ON TWO-PHASE HEAT AND FLUID FLOW IN POROUS HEAT SINKS

Abstract

The current paper presents a novel experimental study on flow boiling in heat sinks with rectangular cross-section parallel microchannels fabricated by conventional powder metallurgy process. The dimensions of microchannel heat sinks are 20 mm × 20 mm. Porosities of heat sinks produced by sintering vary between 13.9% and 21.3%. A pure (nonporous) copper heat sink was also produced to compare the experimental data with each other. Channel sizes and numbers of all heat sinks used in the tests are identical. Flow boiling tests were carried out with deionized water at a flow rate of 238.2 kg/m<sup>2</sup> s and 430.32 kg/m<sup>2</sup> s. The fluid enters the heat sink at 80°C, completely liquid. The tests were carried out under constant heat flux conditions and the heat fluxes are 46.5 W/cm<sup>2</sup> and 61.5 W/cm<sup>2</sup>. Experimental studies have shown that the heat transfer coefficients in the heat sink with the highest porosity are from 28% to 33.3% higher than in the pure copper heat sink. Experimental heat transfer coefficients increase with increasing flow rate and decrease with increasing heat flux and vapor quality. On the other hand, the pressure drop values of the heat sink sample with the highest porosity were measured to be one and half times more than that of the pure copper heat sink. The imaging technique was used during the experiments. With the imaging technique, it was determined that the fluctuations in the pressure values were caused by the reverse steam flow. Additionally, the heat transfer coefficient values obtained experimentally were compared with the existing correlations in the literature. Experimental results showed that pure heat sinks are more compatible with the results given in the literature than porous heat sinks.