Effects of Temperature-Dependent Viscosity Variation on Entropy Generation,Heat,and Fluid Flow Through a Porous-Saturated Duct of Rectangular Cross-Section
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摘要: 研究了充填流体-饱和多孔介质的矩形管中,随温度变化的粘性对充分发展强迫对流的影响.采用Darcy流动模型并假设粘性-温度为倒线性关系.管壁视为均匀热通量,即Kays和Crawford称为的H边界条件.当流体粘性随温度升高而降低时,管壁的Nusselt数增大.求解速度和温度分布时,利用热力学第二定律求解了局部平均熵产率.根据Brinkman数、Péclet数、粘性变化数、无量纲管壁热通量和管道截面宽高比,给出了熵产率、Bejan数、传热不可逆性和流体流动不可逆性的表达式.这些表达式是该类问题参数研究的基础.可以看出,当管道截面宽高比的增大使熵产率减小时,方形管中流动产生的熵大于矩形管,这类似于Ratts和Raut研究的明流(clear flow)情况.Abstract: Effect of temperature-dependent viscosity on fully developed forced convection in a duct of rectangular cross-section occupied by a fluid-saturated porous medium is investigated analytically. The Darcy flow model was applied and the viscosity-temperature relation was assumed to be an inverse-linear one. The case of uniform heat flux on the walls, i. e. the H boundary condition in the terminology of Kays and Crawford, was treated. For the case of a fluid whose viscosity decreases with temperature, it is found that the effect of the variation is to increase the Nusselt number for heated walls. Having found the velocity and the temperature distribution, the second law of thermodynamics was invoked to find the local and average entropy generation rate. Expressions for the entropy generation rate, the Bejan number, the heat transfer irreversibility, and the fluid flow irreversibility were presented in terms of the Brinkman number, the P clet number, the viscosity variation number, the dimensionless wall heat flux, and the aspect ratio (width to height ratio). These expressions let a parametric study of the problem based on which it is observed that the entropy generated due to flow in a duct of square cross-section is more than those of rectangular counterparts while increasing the aspect ratio decreases the entropy generation rate similar to what previously reported for the clear flow case by Ratts and Raut.
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