Comparison Investigation On Flow Boiling Heat Transfer Of Non-nanofluid And Nanofluid In Microchannels

Heat transfer and flow in microchannels are of great different with that of in conventional channels as a matter of scale factor. So it is very important to study microscale heat transfer properties in order to promote scientific development. On the other hand, as the equipment toward miniaturization and compaction, new working fluids are necessarily required in heat transfer field. Since 1990s, many scholars have done many efforts to apply nanofluids in heat transfer enhancement, however, it is rarely to make use of it in microscale heat transfer. Experiments on heat transfer performances, two-phase pressure drop are conducted in aluminium rectangular microchannels with 0.5% volume fraction of Al2O3 nanofluid and deionized water as working fluid. All the heights are uniformly 2mm, and the width is 2mm, 1mm and 0.6mm respectively.The experiment results of two-phase heat transfer show that heat transfer coefficient of Al2O3-water is bigger than that of orginal pure fluid under the same conditions. heat transfer coefficient can be increased by 7%-12% for the experiment. Heat transfer coefficient increases slightly, but not significantly, as the mass flux increases, showing that mass flux have little effect on heat transfer coefficient of Al2O3 nanofluid and pure water. Heat transfer coefficient of the two working fluids is increased when heat flux increase. The data fitting of heat transfer coefficient and heat flux had been made. At the different inlet temperature, heat transfer coefficient of the working fluids almost overlap, indicating inlet temperature for the saturated boiling heat transfer coefficient has no significant effect. The size of microchannel has a great impact on the heat transfer coefficient. Heat transfer coefficient was increasing as the size decreased. At last, comparisons of the flow boiling heat transfer coefficient of deionized water obtained by experiment in microchannels and that calculated by five known empirical correlations in the literatures are carried out. It is found that the empirical correlations can't predict the experiment well.Experiments on two-phase frictional pressure drop show that frictional pressure drop of Al2O3-water is slightly going up when put nanoparticles into water. Frictional pressure drop of the two working fluids is increased with the outlet dryness increasing. At the same outlet dryness, higher the mass flux is, Higher the frictional pressure drop is, while the inlet temperature has no substantial impact on frictional pressure drop. The size of microchannel has a great impact on two-phase friction pressure drop. Frictional pressure drop is increasing as the size is decreasing. Irregular cyclical pressure drop fluctuation is observed. It is found that fluctuation range of Al2O3 nanofluid is bigger than that of deionized water and frictional pressure drop of the two working fluids is growing up when heat flux increase.