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首页> 外文期刊>Energy Conversion & Management >Effects of gravity and variable thermal properties on nanofluid convective heat transfer using connected and unconnected walls
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Effects of gravity and variable thermal properties on nanofluid convective heat transfer using connected and unconnected walls

机译：重力和可变热特性对使用连通壁和非连通壁的纳米流体对流换热的影响

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摘要

In this paper, heat transfer characteristics of natural convection in an enclosure are investigated by considering variable thermal properties. The heated enclosure with an aspect ratio of unity is full of an alumina-water nanofluid. To analyze the effect of different thermal properties on the flow and temperature distributions, many comparisons are conducted for various cases at various Rayleigh numbers and volume fractions of nanoparticles (1-9.5%). The effect of low-gravity conditions on natural convection is investigated by using the gravity values of 0.25 g (2.45 m/s(2)), 0.5 g (4.9 m/s(2)), 0.75 g (7.35 m/s(2)) and 1.0 g (0.98 m/s(2)). It was found that larger temperature gradients near the heated and cold walls can be obtained by increasing the Rayleigh number. By increasing the value of gravity, the flow velocity increased along the y direction. This indicated that gravity has great influence on enhancement of heat transfer. The investigation of the volume fraction of nanoparticles shows that the variation of the Nusselt number for high volume fraction presented a more flat profile than for low volume fraction. The Nusselt number decreased with an increase of the volume fraction. Results for cases with connected and unconnected heated walls are presented. The results showed that heat transfer for the case with the nanoparticle volume fraction of 1% at 1.0 g increased by 89.9% using an unconnected heated wall compared to the connected heated wall.
机译：在本文中，通过考虑可变的热特性来研究箱体内自然对流的传热特性。长宽比为1的加热外壳充满了氧化铝-水纳米流体。为了分析不同热性质对流动和温度分布的影响，针对各种情况在各种瑞利数和纳米粒子的体积分数（1-9.5％）下进行了许多比较。低重力条件对自然对流的影响通过使用0.25 g（2.45 m / s（2）），0.5 g（4.9 m / s（2）），0.75 g（7.35 m / s（ 2））和1.0 g（0.98 m / s（2））。发现通过增加瑞利数可以在加热壁和冷壁附近获得较大的温度梯度。通过增加重力值，流速沿y方向增加。这表明重力对提高传热有很大的影响。对纳米颗粒体积分数的研究表明，高体积分数的Nusselt数变化比低体积分数的Nusselt数呈现出更平坦的轮廓。努塞尔数随着体积分数的增加而降低。给出了连接和不连接加热壁的情况的结果。结果表明，与连接的加热壁相比，使用未连接的加热壁，在1.0 g时纳米颗粒体积分数为1％的情况下的热传递增加了89.9％。

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