三角形微通道内纳米流体流动与换热特性

Characteristics of convective heat transfer in triangular microchannel heat sink using different nanofluids

以去离子水为基液,通过两步法制备出粒子体积分数为0.1%的Si O2、Al2O3、Ti O2纳米流体,并分别在流体内添加一定量的表面活性剂以提高其稳定性。利用紫外分光光度计和热物性分析仪,对3种纳米流体稳定性和热导率进行测试。此外,为研究纳米流体在三角形微通道内的流动与换热特性,利用红外热像仪观察通道底面温度分布。结果表明,表面活性剂会对纳米流体吸光度产生影响,且粒子会随着时间的增加逐渐团聚。纳米颗粒的添加可有效提高工质的热导率并强化对流换热,微通道底面温度明显降低,且均温性得到改善。3种纳米流体中,Ti O2纳米流体呈现出更加良好的导热和换热性能。

SiO_2, Al_2O_3 and TiO_2 nanofluids based on deionized water with a particle volume fraction of 0.1% were prepared by the two-step dispersion method. Surfactants were added into the nanofluids to reduce particle aggregation and enhance stability. An ultraviolet spectrophotometer was used to test the absorbance of nanofluids as the absorbance decreased with decreasing concentration of nanoparticles suspended in liquid. Based on the principle of transient plane source（TPS） method, the 2500 S thermal constant analyzer was employed to conduct the thermal conductivity of nanofluids. In order to investigate the heat transfer performance in a triangular microchannel heat sink using nanofluids, an Infrared Thermal Camera（Image IR 3350, Germany） was inverted and hanged immediately over the microchannel heat sink to observe the temperature distribution on the substrate. The condition of heat dissipation was imitated by a DC power supply（34420A, Agilent, China）, which would energize to the thin film heater at a heat flux of q = 200 W·cm^（-2）. As different nanofluids were studied, DI-water was used to clean the experimental system after the previous experiment was done to avoid the residues of nanoparticles. The results reflected that the surfactants had effect on the absorbance of nanofluids, and the particles would aggregate with the increase of standing time. The thermal conductivity and convective heat transfer were improved by adding nanoparticles. The average temperature on substrate was cooled down, and the uniformity of temperature was also repaired. As the result, TiO_2 nanofluids had a better behavior than SiO_2 and Al_2O_3 nanofluids.