Influence Of Nanofluid And Cavity Structure On Heat Transfer Characteristics Of Helical Mini-channels

With the development of micro-electrical-mechanical and micro-electronic technology,higher heat flux requires more efficient and smaller heat exchanger.The helical mini-channels with the secondary flow produced by centrifugal effect and the small size effect are favored,the addition of vaporization and nanofluid can improve the degree of flow turbulence and improve the efficiency of mass transfer and heat transfer.This paper established a three-dimensional physical model of jacket heat device of ordinary helical mini-channels and different cavity structure parameters of helical mini-channels,the numerical simulation of the heat transfer characteristics of the fluid in the physical model has been studied.The heat transfer and flow characteristics between the helical mini-channels and the helical mini-channels of cavity structure have been compared,the nusselt number,flow friction coefficient,thermal resistance and comprehensive performance evaluation factor of the research object have been analyzed,the optimum dimension of the cavity structure within the scope of the study has been explored.The results show that,except for d=3.6 mm and d/l=1:1,the comprehensive performance evaluation factor of the cavity structure decreases with the increase of Reynolds number,and in other cases increases with the increase of Reynolds number and then decreases.And by contrast,when d=3.0 mm and d/l=1:2,the evaluation factor of the helical mini-channels of the cavity structure is the highest.Finally,according to the optimum parameters of the cavity structure and the actual processing conditions,two different structures of helical mini-channels jacket have been obtained by machining.Then,Using nanofluid and deionized water as heat exchanger,heat transfer characteristics of two kinds of helical mini-channels have been studied,and the nusselt number of different locations of the helical mini-channels have been analyzed.The results show that,whenReynolds number is greater than 5000,the nusselt number of the helical mini-channels with cavity is greater than the ordinary helical mini-channels,when water based Al2O3 nanofluid in the mass fraction of 0.1%and 0.2%,the heat transfer characteristics of helical mini-channels are suppressed,the nusselt number of water based Al2O3 nanofluids with mass fraction of 1%is recovered.