Wong Kau-Fui Vincent, Kurma Tarun
Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33124, USA.
Nanotechnology. 2008 Aug 27;19(34):345702. doi: 10.1088/0957-4484/19/34/345702. Epub 2008 Jul 16.
Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this paper all three transport properties, namely thermal conductivity, electrical conductivity and viscosity, were studied for alumina nanofluid (aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3-8%) and temperature (2-50 °C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. The effect of particle size was not studied. The transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inch diameter was used. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W m(-1) K(-1) was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6 °C. The effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor-based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meter's glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a small 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity, 314 µS cm(-1), was recorded for a volumetric concentration of 8.47%. In the determination of the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid, 2.901 42 mm(2) s(-1), was obtained at 0 °C for an 8.47% volumetric concentration of alumina nanoparticles. The experimental results of the present work will help researchers arrive at better theoretical models.
最近的研究表明，与基础流体相比，纳米流体具有显著更高的热导率。较大的表面积与体积之比以及纳米颗粒布朗运动的某些效应被认为是纳米流体热导率显著增加的主要因素。在本文中，对氧化铝纳米流体（水中的氧化铝纳米颗粒）的三种传输特性，即热导率、电导率和粘度进行了研究。实验分别作为体积浓度（3 - 8%）和温度（2 - 50°C）的函数进行。平均直径为36纳米的氧化铝纳米颗粒分散在水中。未研究粒径的影响。采用长谷川和长岛描述的用于导电流体的瞬态热线法来测试热导率。在这项工作中，使用了直径为0.003英寸的绝缘铂丝。使用去离子水进行初始校准，所得数据在水的标准热导率值的2.5%以内。氧化铝纳米流体的热导率随温度和浓度的增加而增加。在46.6°C下，氧化铝纳米颗粒体积浓度为8.47%时，记录到的最大热导率为0.7351 W m⁻¹ K⁻¹。在该浓度和温度下的有效热导率为1.1501，与室温下水相比，热导率提高了22%。氧化铝是良好的电导体，氧化铝纳米流体的电导率随体积浓度的增加呈上升趋势。使用基于微处理器的电导率/TDS计进行电导率实验。在用标准氯化钾溶液仔细校准了带有铂尖端的电导率计的玻璃探头后，在不同体积浓度下进行读数。对于水中体积浓度仅为1.44%的少量氧化铝纳米颗粒，测得电导率增加了3457.1%。体积浓度为8.47%时，记录到的最高电导率值为314 μS cm⁻¹。在测定氧化铝纳米流体的运动粘度时，使用了带有恒温浴的标准运动粘度计。使用校准后的毛细管粘度计在精确控制的温度下测量重力作用下的流动。毛细管粘度计在不同温度下用去离子水校准，所得运动粘度值在已发表标准值的3%以内。对于水中体积浓度为8.47%的氧化铝纳米颗粒，观察到运动粘度增加了35.5%。氧化铝纳米流体的最大运动粘度为2.90142 mm² s⁻¹，是在0°C下氧化铝纳米颗粒体积浓度为8.47%时获得的。本工作的实验结果将有助于研究人员得出更好的理论模型。
