纳米流体导热系数影响因素分析

为了将复合纳米流体应用于微道通，以水为基液，以聚乙烯吡咯烷酮为表面活性剂，采用两步法制备了体积分数为0.1%~0.4%且稳定性好的Al₂O₃-TiO₂复合纳米流体，用热物性分析仪（Hot-Disk 2500S）测试了其导热系数.将其应用于直线型和折线型微通道散热器，实验研究了体积浓度、入口温度、Re以及微通道结构对微散热器流动换热性能的影响.结果表明：较于直通道，复合纳米流体在折线通道内的强化换热效果更为显著；提高入口温度、Re和纳米颗粒的体积分数都能增加复合纳米流体的换热能力.当入口温度为30℃、体积流量为30 mL/min时，相较于去离子水，体积分数为0.4%的复合纳米流体在折线形微通道内的对流换热系数提高30.9%，综合性能提高了18.7%，压降提高了6.86%.

Enhancing thermal conductivity of fluids with nanoparticles

Al₂O₃-TiO₂ hybrid nanofluids based on DI-water with particle volume fraction from 0.1% to 0.4% were prepared by the two-step methods. The appropriate surfactant was added to ensure the stability of hybrid nanofluids, and a thermal property analyzer (Hot-Disk 2500S) was used to measure the thermal conductivity of hybrid nanofluids. The prepared hybrid nanofluids were used to flow through straight-line and broken-line microchannel heat sinks, and the effects of concentration, inlet temperature, Re and microchannel structure on the heat transfer performance of microchannels were studied. Results show that compared with the straight-line microchannels, the heat transfer performance of hybrid nanofluids in the broken line is more strengthened; the heat transfer coefficients of hybrid nanofluids increase with the increase of the inlet temperature, Re and nanoparticle volume fraction; when the inlet temperature is 30℃, and the volume flow is 30 mL/min, compared with deionized water, the convective heat transfer coefficient, comprehensive performance and pressure drop of the hybrid nanofluids with a volume fraction of 0.4% in the broken-line microchannel increase by 30.90%, 18.70%, and 6.48%, respectively.