Flow Resistance And Pressure Fluctuation Of Al₂O₃-R141b Nanorefrigerant Through Low Surface Energy Microchannels

Along with the social’s rapid development, the energy problem becomes a global problem. For this instance, developing new technologies to save energy become particularly important. The microchannel heat exchanger is a kind of energy saving products, which gradually used in chemical, metallurgy, cooling, aeronautics, metallurgy, etc. Nanofluids have very good performance on heat transfer, it is one of the most popular issue in heat transfer field. Papers about boiling flow resistance in microchannels is very limited, and the independent investigators got different conclusions. So, this issue needs further study.This paper presented an experimental investigation to flow boiling in microchannels with a cross-section of 1mm×2mm using γ-Al2O3-R141 b and pure refrigerant R141 b as working fluids. This experiment mainly explored the fluctuation characteristics of pressure drop and flow resistance.By measuring contact angle on the inside and outside surface of microchennels, we got the surface energy of microchannels. The result reflects that the experimental microchannels’ surface energy are all less than 35 m J/m2, which meets the criterion of low-surface energy surface.The effect of mass flux, inlet subcooled temperature and heat flux on two-phase frictional pressure drop and total pressure drop were investigated. When nanorefrigerant was the working fluid, nanoparticles adhered to the heat exchanger surface. Higher concentration result in more adherence. The adherence of nanoparticles will decrease the roughness and increase the wettability of heat exchanger surface. Then it will reduce the resistance and pressure fluctuation to a certain extent.After compared the experimental data with other existing pressure drop predictive model, a new two-phase frictional pressure drop correlation is revised based on Qu-Mudawar’s correlation, which improve the predictive ability of models. The average absolute error decreased to 11.3%.With the pure refrigerant and nanorefrigerant(mass fraction=0.2%) as the working fluid, inlet and oulet pressure response characteristics in microchannels were studied. Three kinds of independent variable — heating voltage, cooling water flux and mass flow was used as disturbance and got dynamic response curve, respectively. Finally, we discussed the pressure drop and it’s fluctuate characteristics during the dynamic period briefly.