Study On Flow And Heat Transfer Characteristics Of Nanofluids In Fractal Miricrochannels

With the rapid development of microelectronic technology,the power and integration of electronic chips are increasing rapidly,and the heat flux in the micro components system is very large.The traditional cooling method has been unable to meet the heat dissipation requirement of electronic devices with high heat flux.In order to keep the working temperature of electronic devices within the allowable range,it is an urgent problem to design a new and efficient cooling device.Fractal microchannel is a new type of heat sink structure inspired by bionic principle,which has strong heat and mass transfer capability.Compared with the traditional parallel microchannel heat sink,the cooling of the electronic chip has the advantages of small pressure drop,small thermal resistance and relatively uniform temperature distribution.The new type of heat exchanger nanofluid has high thermal conductivity under certain conditions.And the Combination nanofluid and fractal microchannel provides a good way to solve the cooling problem of high heat flux desity chips.In order to study the flow and heat transfer characteristics of nanofluids in fractal microchannels,a fractal microchannel heat sink with initial channel length of 7.11 mm and hydraulic diameter of 360 ?m has been designed and processed.The experiment was conducted in fractal microchannel heat sink with TiO2,Al2O3 nanofluids and deionized water respectively in the range of Reynolds number of 80~700.The flow and convection heat transfer characteristics of TiO2 and Al2O3 nanofluids in fractal tree like microchannels at mass fraction of 0.01%~0.15% were investigated from the aspects of nusselt number,pressure drop,thermal resistance,frictional resistance coefficient and enhanced heat transfer factor,and so on.The research results show that the temperature distribution of the bottom surface of the fractal microchannel heat sink is uniform and has good homogeneity,and the nanofluid can effectively reduce the bottom surface temperature in the fractal microchannel heat sink and improve its homogeneity,the bottom surface temperature decreased compared to deionized 3~5.4 ?;The nusselt number of Al2O3-deionized water nanofluids in fractal microchannels is 1.32~1.67 times of deionized water,and the nusselt number of TiO2-deionized water nanofluids is 1.56~1.99 times of deionized water.The improvement of mass fraction can enhance the convective heat transfer effect of nanofluids,but also increase the flow resistance of nanofluids,resulting in the increase of pressure drop of nanofluids.In addition,the thermal resistance of the nanofluid in the fractal microchannel is less than the deionized water.The heat transfer enhancement factors of two kinds of nanofluids in TiO2 and Al2O3 in fractal microchannels are all greater than 1,and the heat transfer enhancement effect of them is remarkable.The enhanced heat transfer factor increases with the increase of Reynolds number and concentration.With the increase of particle concentration,heat transfer enhancement factor increase significantly.The research result of nanofluid in fractal microchannel heat sink is of great significance for the design of new efficient radiator.