共查询到15条相似文献,搜索用时 92 毫秒
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制备了粒度分布为11~50nm的TiO2-H2O纳米流体,测量了纳米流体的相变潜热、表面张力和过冷度。相对于去离子水,质量分数为1%的纳米流体相变潜热减小了2.4%,表面张力增大了1.6%,过冷度降低了66.2%。纳米流体过冷度随TiO2浓度增大而降低,表面张力随TiO2浓度增大没有明显变化。运用相变动力学原理,对纳米流体过冷度降低的机理进行了分析。 相似文献
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纳米流体黏度与温度的关系研究 总被引:1,自引:0,他引:1
温度变化对纳米流体粘度的影响是很明显的。结果表明:含有表面活性剂的纳米流体的黏度在温度低于60℃时,黏度随温度的升高而降低,超过此温度后,纳米流体的黏度随温度的升高而升高。只含有纳米粒子的纳米流体黏度随温度的升高而降低,高温时黏度随温度升高而减小的幅度减小,而使用表面活性剂后黏度与温度的关系出现异常,高温时黏度随温度的增加而增加。随着温度的升高,纳米粒子的布朗运动加强,粒子的无序运动增加流体流动的阻力,虽然表面活性剂的使用提高了纳米流体的稳定性,但大分子结构的表面活性剂吸附在粒子周围,致使粒子作布朗运动时大大增加液体的粘性,以至高温时纳米流体黏度随温度的升高而升高。本研究还对Cu-water、ZrO2-water纳米流体的黏度与温度的关系式进行拟合,拟合公式与实验数据吻合,误差小于0.5%,拟合公式中纳米流体的黏度与温度、粒子体积分数和基液有关。 相似文献
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DSC法测量低温相变蓄冷纳米流体的比热容 总被引:1,自引:0,他引:1
介绍差示扫描量热仪(DSC)测量液体比热容的原理和方法,并测量4种不同体积分数的TiO2-Ba-Cl2-H2O纳米流体比热容。结果表明,加入纳米粒子后其比热容都有所降低,并随TiO2体积分数的增大而逐渐减小。 相似文献
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纳米流体稳定性和粘度的影响因素分析 总被引:1,自引:0,他引:1
《材料科学与工程学报》2020,(1)
采用"两步法"制备质量分数为0.5wt%~4.0wt%的Cu-乙二醇纳米流体,研究超声时间、浓度和温度对纳米流体稳定性及粘度的影响。研究结果表明,温度为20℃时,分析经过超声15~75min处理的Cu-乙二醇纳米流体(4.0wt%)粘度发现,超声45min时其粘度最大;分析超声45和60min的纳米流体透射电镜(TEM)图像发现,超声45min时其稳定性更优;在乙二醇溶液里添加Cu纳米颗粒会影响流体的粘度,且粘度随粒子质量分数增大而增大,流体稳定性随质量分数增大而减小;Cu-乙二醇纳米流体的粘度随温度的升高而变小。通过分析实验数据,在修正已有的粘度模型基础上,拟合纳米流体粘度与粒子浓度、温度的关系,提出了新的粘度计算公式。根据固溶体的形成机理和能量最低原理对以上现象进行了理论解释。 相似文献
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分别采用瞬态热线法、比较量热法和旋转粘度计测试了不同温度、粒子浓度和粒径下的Al2O3-DW(蒸馏水)纳米流体的导热系数、比热容、粘度等热物性参数。试验结果表明,粒子浓度、粒径和温度都是影响Al2O3-DW纳米流体热物性参数的重要因素。与水相比,纳米流体导热系数和粘度增加,常温4%体积份额下增幅分别为21.5%和52.3%;纳米流体比热容随着粒子体积份额增加而降低,并推导出了常温下低浓度纳米流体比热容的预测公式。 相似文献
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Muhsin M. Ameen K. Prabhul G. Sivakumar Praveen P. Abraham U. B. Jayadeep C. B. Sobhan 《International Journal of Thermophysics》2010,31(6):1131-1144
A discrete computational approach based on molecular dynamics (MD) simulations is proposed for evaluating the latent heat
of vaporization of nanofluids. The computational algorithm, which considers the interaction of the solid and the fluid molecules,
is used for obtaining the enhancement of the latent heat of a base fluid due to the suspension of nanoparticles. The method
is validated by comparing the computed latent heat values of water with standard values at different saturation temperatures.
Simulation of a water–platinum nanofluid system is performed, treating the volume fraction and size of nanoparticles as parameters.
The trends in the variation are found to match well with experimental results on nanofluids. Discussions are also presented
on the limitations of the proposed model, and on methods to overcome them. 相似文献
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《Journal of Experimental Nanoscience》2013,8(5):539-546
The effective specific heat of several types of nanofluids are measured by transient double hot-wire technique. Sample nanofluids are prepared by suspending 1–5 volume percentages of titanium dioxide (TiO2), aluminium oxide (A12O3) and aluminium (Al) nanoparticles in various base fluids, such as deionised water, ethylene glycol and engine oil. The effective specific heats of these nanofluids were found to decrease substantially with increased volume fraction of nanoparticles. Besides particle volume fraction, particle materials and base fluids also have influence on the effective specific heat of nanofluids. Except Al/engine oil-based nanofluid, predictions of the effective specific heat of nanofluids by the volume fraction mixture rule-based model showed reasonably good agreement with the experimental results. Based on the calibration results obtained for the base fluids, the measurement error is estimated to be within 2.77%. 相似文献
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Nanofluids have attracted wide attention because of their promising thermal applications. Compared with the base fluid, numerous experiments have generally indicated increases in effective thermal conductivity and convective heat transfer coefficient for suspensions having only a small amount of nanoparticles. It is also known that with the presence of nanoparticles, the viscosity of a nanofluid is greater than its base fluid and deviates from Einstein's classical prediction. However, only a few groups have reported nanofluid viscosity results to date. Therefore, relative viscosity data for gamma-Al2O3 nanoparticles in DI-water and propylene glycol/H2O mixtures are presented here based on pressure drop measurements of flowing nanofluids. Results indicate that with constant wall heat flux, the relative viscosities of nanofluid decrease with increasing volume flow rate. The results also show, based on Brenner's model, that the nanofluid viscosity can be explained in part by the aspect ratio of the aggregates. 相似文献
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Huaqing XIE Jifen WAN Lifei CHEN 《材料科学技术学报》2008,24(5):742-744
Nanofluids have been demonstrated to have intriguing thermodynamic properties. In this work, we described the investigation of the phase transformation behaviors of nanofluids containing alumina (Al2O3) or titania (TiO2) nanoparticles with different weight fractions. The experimental results indicate that the melting temperatures of nanofluids (in freezing states) are reduced with the increase of the weight fraction of nanoparticles. The reduction is related to nanoparticle species as well as nanoparticle size. 相似文献