低压条件下纳米流体的沸腾换热特性

在不同低压压力和不同纳米流体浓度下对光滑传热面上的水基纳米流体的池内沸腾特性进行了试验研究.纳米流体由平均直径50 nm的氧化铜粒子加入去离子水中组成,没有加入任何添加剂.研究主要针对7.2 kPa到100kPa的压力区间和0.1%到2%的质量浓度区间内压力和颗粒浓度对光滑表面沸腾换热特性的影响,研究结果表明:压力对纳米流体的沸腾换热特性有强烈影响,沸腾换热系数和临界热流密度(CHF)强化率随着压力的降低而大幅度增加.纳米流体浓度对沸腾换热系数和临界热流密度(CHF)有重要影响,并且在质量浓度约1%附近存在一个最佳颗粒浓度.研究结果显示由与去离子水相比,质量分数为1%,压力为7.2 kPa的纳米流体在光滑表面上的沸腾换热系数和临界热流密度都得到了显著提高.

Pool Boiling Heat Transfer of Nanofluids on a Plate Surface under Sub-atmospheric Pressures

Some boiling heat transfer experiments were performed to understand the boiling characteristics of the water-based nanofluids on a smooth plate surface under various sub-atmospheric pressures and concentrations of the nanofluids. The nanofluids consist of CuO nano-particles with average diameter of 50 nm and deionized water without any additional reagent. The study was focused on the influences of the pressure and nano-particle mass concentration of the nanofluid on the boiling heat transfer characteristics; the experimental pressure used is in the range of 7.2 kPa to 100 kPa, and the used nano-particle mass concentration of the nanofluid is between 0.1%(wt) and 2%(wt). The experimental results show that both the heat transfer coefficient and critical heat flux (CHF) of nanofluids increase greatly with the decrease of test pressure. The nano-particle concentration of the nanofluids also has significant effect on the boiling heat transfer and CHF of the nanofluid, and the optimal nano-particle mass concentration with which the nanofluid can have the maximum boiling heat transfer is about 1.0%(wt). It was found that, comparing with deionized water, water-based nanofluid with concentration of 1.0 %(wt) can obviously improve the heat transfer coefficient and CHF under the pressure of 7.2 kPa.