To compare and understand the laminar thermal-hydraulic performance of plate-fin channel with rectangle plain fin by using variable thermophysical properties of the most commonly used nanofluids (Al_2O_3-water), a three-dimensional numerical study is investigated by using the single-phase approach at a constant wall temperature boundary condition. Different models published in literatures are considered for the thermal conductivity and viscosity. On this basis, a parametric analysis is conducted to evaluate the effects of various pertinent parameters including nanoparticle volume fraction (0%-4%), Brownian motion of nanoparticle and Reynolds number (800-1500) on the heat transfer and flow characteristics of plain fin channel in detail. All the numerical results demonstrate that the addition of Al_2O_3 nanoparticle can enhance the heat transfer and flow pressure loss of base fluid because of the higher thermal conductivity and viscosity for nanofluids. And these enhancements are more obvious by increasing the volume fraction of nanoparticle, increasing Reynolds number, and considering the effects of nanoparticle Brownian motion. In addition, there are significantly differences in the thermal and flow fields for different nanofluids models at a fixed Reynolds number, which means that the effective theoretical formulas and empiric corrections for the nanofluids thrmophysical properties need to be studied extensively in the future.
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