Research On Flow Characteristics And Heat Transfer Enhancement Of A1₂O₃-h₂0Nanolfuid In Microchannels

Improvement to make heat transfer equipment more energy efficient wo uld need to focuson miniaturization on the one hand and an increase in heat flux on the other. The flow andheat transfer characteristic in micoscales has been one of the most important field of research.With the priority of compact and high heat flux, microchannels has great prospects fordevelopment espacially in fields which has limited space and ultral high heat flux, such asmicroelectronics, MEMS (Micro-Electro-Mechanic System), refrigeration and aerospace.Over the past decades, researchers have revealed that there has difference between themicrochannels and the conventional’s. The Experimental studies and theoretical analysis offlow characteristic and heat transfer in microchannels has been made in this thesis.Experimental investigation were performed on single-phase and two-phase flow and heattransfer characteristics through the aluminum-based rectangular micochannels with differenthydraulic diameter of0.3636mm,1.0370mm and1.3333mm, using Al2O3-H2O nanofluidswith particle mass fraction of0%,0.2%,0.5%and1%as the working fluids. The effect ofReynolds number, the size of the channel and the nanoparticle concentration on pressure dropand convective heat transfer were investigated. The visualization method was used to analyzethe behavior characteristics of the bubble formation, growth and movement in themicrochannel.Experimental results shows that the nusselt number increased considerably asnanoparticle mass fraction increased slightly and caused little extra pressure drop. The0.2%mass fraction nanofluid enhanced the heat transfer coefficient by8%, Nusselt number by8%than deionized water in1×2mm channel and with25%pressure drop increase; the heatcoefficient in0.7×2mm channel using deionized water as working fluid is enhanced2%thanthat in1×2mm channel and with100%pressure drop increase.Via visualization methods, it is found that the channel downstream was mainlydominated by annular flow. It has been theoretically analyzed the phenomenon of flowunstability and backflow in single microchannel. Finally, the improved structure ofmicrochannel heat sink was given.