Abstract This study investigates the influence of nanoparticle size on the heat transfer and pressure drop characteristics of nanofluids for laminar forced convection in a microchannel subjected to constant heat flux. Aqueous nanofluids containing spherical shaped particle dispersions of Al 2 O 3 and TiO 2 , have been simulated by employing discrete phase model (DPM) for a range of ten particle sizes 20–200 nm. Analysis has been carried out by considering two particle weight concentrations (0.1% and 2%) at Reynolds number of 1000, 1200 and 2000. Results demonstrate that for constant nanofluid compositions and flow conditions, convective heat transfer and friction factor are in inverse association with the particle diameter. With the reduction in particle size, the heat transfer coefficient of nanofluids escalates because of particles’ enhanced effective particle surface area and uniform distribution along the channel radial direction. However, this improvement in heat transfer coefficient is compensated by undesirable increase in pressure drop as a consequence of higher viscosity. The variation in hydrothermal characteristics of nanofluids with particle diameter is more significant at higher particle concentration. The maximum heat transfer and friction factor difference of 11% and 20% respectively has been observed between particle sizes 20 nm and 200 nm for the particle concentration of 2%.

中文翻译：

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不同粒径对微通道中纳米流体水热特性的影响

摘要 本研究研究了纳米颗粒尺寸对纳米流体在恒定热通量下层流强制对流的传热和压降特性的影响。含有 Al 2 O 3 和 TiO 2 的球形颗粒分散体的水性纳米流体已通过采用离散相模型 (DPM) 对 20-200 nm 的十种粒径范围进行了模拟。通过考虑雷诺数为 1000、1200 和 2000 时的两种粒子重量浓度（0.1% 和 2%）进行分析。结果表明，对于恒定的纳米流体成分和流动条件，对流热传递和摩擦系数与粒径。随着粒径的减小，由于颗粒有效表面积的增加和沿通道径向方向的均匀分布，纳米流体的传热系数逐渐升高。然而，传热系数的这种改进被由于较高粘度而导致的不希望的压降增加所补偿。纳米流体的水热特性随粒径的变化在较高的颗粒浓度下更为显着。对于 2% 的颗粒浓度，在 20 nm 和 200 nm 的粒径之间观察到的最大传热和摩擦系数差异分别为 11% 和 20%。传热系数的这种改进被由于较高粘度而导致的不希望的压降增加所补偿。纳米流体的水热特性随粒径的变化在较高的颗粒浓度下更为显着。对于 2% 的颗粒浓度，在 20 nm 和 200 nm 的粒径之间观察到的最大传热和摩擦系数差异分别为 11% 和 20%。传热系数的这种改进被由于较高粘度而导致的不希望的压降增加所补偿。纳米流体的水热特性随粒径的变化在较高的颗粒浓度下更为显着。对于 2% 的颗粒浓度，在粒径 20 nm 和 200 nm 之间观察到的最大传热和摩擦因数差异分别为 11% 和 20%。