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首页> 美国卫生研究院文献>Nanoscale Research Letters >Enhancements of thermal conductivities with Cu CuO and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system
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Enhancements of thermal conductivities with Cu CuO and carbon nanotube nanofluids and application of MWNT/water nanofluid on a water chiller system

机译：CuCuO和碳纳米管纳米流体的导热性增强以及MWNT /水纳米流体在冷水机系统上的应用

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In this study, enhancements of thermal conductivities of ethylene glycol, water, and synthetic engine oil in the presence of copper (Cu), copper oxide (CuO), and multi-walled carbon nanotube (MWNT) are investigated using both physical mixing method (two-step method) and chemical reduction method (one-step method). The chemical reduction method is, however, used only for nanofluid containing Cu nanoparticle in water. The thermal conductivities of the nanofluids are measured by a modified transient hot wire method. Experimental results show that nanofluids with low concentration of Cu, CuO, or carbon nanotube (CNT) have considerably higher thermal conductivity than identical base liquids. For CuO-ethylene glycol suspensions at 5 vol.%, MWNT-ethylene glycol at 1 vol.%, MWNT-water at 1.5 vol.%, and MWNT-synthetic engine oil at 2 vol.%, thermal conductivity is enhanced by 22.4, 12.4, 17, and 30%, respectively. For Cu-water at 0.1 vol.%, thermal conductivity is increased by 23.8%. The thermal conductivity improvement for CuO and CNT nanofluids is approximately linear with the volume fraction. On the other hand, a strong dependence of thermal conductivity on the measured time is observed for Cu-water nanofluid. The system performance of a 10-RT water chiller (air conditioner) subject to MWNT/water nanofluid is experimentally investigated. The system is tested at the standard water chiller rating condition in the range of the flow rate from 60 to 140 L/min. In spite of the static measurement of thermal conductivity of nanofluid shows only 1.3% increase at room temperature relative to the base fluid at volume fraction of 0.001 (0.1 vol.%), it is observed that a 4.2% increase of cooling capacity and a small decrease of power consumption about 0.8% occur for the nanofluid system at a flow rate of 100 L/min. This result clearly indicates that the enhancement of cooling capacity is not just related to thermal conductivity alone. Dynamic effect, such as nanoparticle dispersion may effectively augment the system performance. It is also found that the dynamic dispersion is comparatively effective at lower flow rate regime, e.g., transition or laminar flow and becomes less effective at higher flow rate regime. Test results show that the coefficient of performance of the water chiller is increased by 5.15% relative to that without nanofluid.
机译：在这项研究中，使用两种物理混合方法研究了在存在铜（Cu），氧化铜（CuO）和多壁碳纳米管（MWNT）的情况下提高乙二醇，水和合成机油的导热率的方法（两步法）和化学还原法（一步法）。但是，化学还原法仅用于水中含有Cu纳米粒子的纳米流体。通过改进的瞬态热线法测量纳米流体的热导率。实验结果表明，与相同的基础液体相比，具有低浓度的Cu，CuO或碳纳米管（CNT）的纳米流体具有更高的导热系数。对于5％（体积）的CuO-乙二醇悬浮液，1％（体积）的MWNT-乙二醇，1.5％（体积）的MWNT-水和2％（体积）的MWNT合成机油，导热系数提高了22.4，分别为12.4％，17％和30％。对于0.1％（体积）的铜水，导热系数提高了23.8％。 CuO和CNT纳米流体的导热系数与体积分数呈线性关系。另一方面，对于铜水纳米流体，观察到热导率对测量时间的强烈依赖性。实验研究了受MWNT /水纳米流体作用的10-RT冷水机组（空调）的系统性能。该系统在标准冷水机组额定条件下进行测试，流量范围为60至140 L / min。尽管静态测量了纳米流体的导热系数，但在室温下相对于体积分数为0.001（0.1 vol。％）的基础流体仅增加了1.3％，观察到的是冷却能力增加了4.2％，并且制冷量很小对于纳米流体系统，在100 L / min的流速下功耗降低约0.8％。该结果清楚地表明，冷却能力的提高不仅与导热系数有关。诸如纳米颗粒分散的动态效果可以有效地增强系统性能。还发现动态分散在较低流速状态下，例如过渡或层流中比较有效，而在较高流速状态下则较不起作用。测试结果表明，与没有纳米流体的冷水机相比，冷水机的性能系数提高了5.15％。

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