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首页> 外文期刊>International Journal of Heat and Mass Transfer >Natural convection heat transfer in a power-law fluid from a heated rotating cylinder in a square duct
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Natural convection heat transfer in a power-law fluid from a heated rotating cylinder in a square duct

机译：幂律流体在方管中从加热的旋转圆柱体中自然对流传热

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摘要

Laminar natural convection heat transfer in a power-law fluid from an isothermal rotating cylinder placed coaxially in a square duct has been studied numerically over the following ranges of conditions: Grashof number (10 = Gr = 10(3)); Prandtl number (0.72 = Pr = 100); power-law index (0.2 = n = 1.5) and non-dimensional rotational velocity (0 = S = 4). The spatial variation of the velocity and temperature fields are visualised in terms of the streamline and isotherm patterns, and temperature and vertical velocity at a few locations, respectively. Indeed, a range of flow patterns including twin-celled and single-celled recirculating regions can be observed depending upon the relative strengths of the buoyancy-induced and forced flow. The rate of heat transfer is described in terms of the distribution of the local Nusselt number over the surface of the cylinder together with its surface averaged value. As expected, the mean Nusselt number shows a positive dependence on the both Grashof and Prandtl numbers irrespective of the values of the power-law index and rotational velocity. For a non-rotating cylinder (S = 0), shear-thinning fluid behaviour promotes heat transfer, whereas shear-thickening viscosity impedes it with reference to that in Newtonian fluids otherwise under identical conditions. For the case of a rotating cylinder (S not equal 0), the rotation has positive influence on the rate of heat transfer at low values of the Grashof or Rayleigh number (Ra 500) irrespective of the type of fluid behaviour, i.e., shear-thinning or shear-thickening or Newtonian. However, at high values of the Grashof or Rayleigh numbers, the gradual increase of rotation of the cylinder first lowers the rate of heat transfer, and then increases it for shear-thickening (n 1) and Newtonian fluids (n = 1). On the other hand, a reverse trend is seen for shear-thinning fluids. These non-monotonous trends in the overall heat transfer stem from the interactions between the rate of variation of the fluid viscosity and the temperature gradient on the surface of the cylinder. Therefore, a prudent choice of the operating conditions and the fluid behaviour can be used to regulate the rate of heating or cooling from a rotating cylinder. Finally, the present values of the average Nusselt number are correlated in order to facilitate the interpolation of the present results for the intermediate values of Gr, Pr, S and nand/or the estimation of heat transfer duty in a new application. (C) 2018 Elsevier Ltd. All rights reserved.
机译：在以下条件范围内，对来自同轴放置在方管中的等温旋转圆柱体的幂律流体中的层流自然对流传热进行了数值研究：格拉斯霍夫数（10 <= Gr <= 10（3））；普朗特数（0.72 <= Pr <= 100）;幂律指数（0.2 <= n <= 1.5）和无量纲旋转速度（0 <= S <= 4）。速度和温度场的空间变化分别以流线和等温线图以及在几个位置的温度和垂直速度表示。实际上，取决于浮力引起的和强制流动的相对强度，可以观察到包括双细胞和单细胞再循环区域在内的一系列流动模式。传热速率是根据圆柱体表面上的局部Nusselt数及其表面平均值的分布来描述的。不出所料，平均Nusselt数对Grashof和Prandtl数均呈正相关，而与幂律指数和旋转速度的值无关。对于不旋转的圆柱体（S = 0），稀化流体的行为会促进传热，而黏稠化的粘度会阻碍牛顿流体的传热，否则在相同条件下。对于旋转圆柱体（S不等于0）的情况，无论流体行为的类型（即剪切力）如何，在低Grashof或瑞利数（Ra <500）时，旋转都会对传热速率产生积极影响。 -变薄或剪切变厚或牛顿。但是，在高Grashof数或Rayleigh数的情况下，圆柱体旋转的逐渐增加首先会降低传热速率，然后在剪切增稠（n> 1）和牛顿流体（n = 1）时增加传热速率。另一方面，剪切稀化流体的趋势相反。整体传热中的这些非单调趋势源于流体粘度的变化率与气缸表面温度梯度之间的相互作用。因此，可以谨慎选择操作条件和流体性能来调节旋转气缸的加热或冷却速率。最后，将平均努塞尔数的当前值进行关联，以便于在新应用中对Gr，Pr，S和nand的中间值和/或传热负荷的估计进行当前结果的插值。 （C）2018 Elsevier Ltd.保留所有权利。

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