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首页> 外文期刊>International Journal of Heat and Mass Transfer >Aspect ratio and boundary conditions effects on laminar natural convection of power-law fluids in a rectangular enclosure with differentially heated side walls
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Aspect ratio and boundary conditions effects on laminar natural convection of power-law fluids in a rectangular enclosure with differentially heated side walls

机译：长宽比和边界条件对幂律流体在具有不同加热侧壁的矩形外壳中的层流自然对流的影响

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摘要

Two-dimensional steady-state simulations of laminar natural convection in rectangular enclosures with differentially heated vertical sidewalls subjected to both constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions have been carried out where the enclosures are considered to be completely filled with non-Newtonian power-law fluids. The influences of the CWT and CWHF boundary conditions on the effects of aspect ratio (AR = H/L where H is the enclosure height and L is the enclosure length), in the range 0.125 ≤ AR ≤ 8, on the heat transfer characteristics have been investigated numerically for power-law index n in the range 0.6 ≤ n ≤ 1.8 for nominal values of Rayleigh number {Ra) ranging from 10~4 to 10~6 and at a nominal Prandtl number (Pr) of 10~3. A scaling analysis is performed to elucidate the anticipated effects of aspect ratio, Rayleigh number, Prandtl number and power-law index on the mean Nusselt number for power-law fluids. It is found that the mean Nusselt number Nu follows a non-monotonic trend with aspect ratio AR for a given set of values of the Rayleigh number and Prandtl number for shear-thinning (n< 1), Newtonian (n = l) and shear-thickening (n>l) fluids for the CWT boundary condition whereas a monotonic increase in (Nu) was obtained for increasing values of aspect ratio AR in the case of CWHF boundary condition irrespective of the value of n. This non-monotonic trend for the CWT boundary condition is caused by the competing effects of thermal convective and diffusive transports with increasing AR. New correlations are proposed for the mean Nusselt number Nu for power-law fluids in both the CWT and CWHF boundary conditions, which are shown to satisfactorily capture the correct qualitative and quantitative behaviour of Nu in response to the changes in Rayleigh number, aspect ratio and power-law index.
机译：在矩形壁罩中对层流自然对流进行二维稳态模拟，在矩形壁罩中，垂直侧壁受到不同的加热，同时受到恒定的壁温（CWT）和恒定的壁热通量（CWHF）边界条件的影响，在这种情况下，壁垒被认为是完全的充满非牛顿幂律流体。在0.125≤AR≤8的范围内，CWT和CWHF边界条件对纵横比的影响（AR = H / L，其中H为外壳高度，L为外壳长度）对传热特性的影响为对于瑞利数（Ra）的标称值介于10〜4至10〜6且标称普朗特数（Pr）为10〜3的幂律指数n在0.6≤n≤1.8范围内进行了数值研究。进行了定标分析，以阐明纵横比，瑞利数，普朗特数和幂律指数对幂律流体的平均Nusselt数的预期影响。对于剪切稀化（n <1），牛顿（n = l）和剪切的给定值的瑞利数和普朗特数的给定值集合，发现平均努塞尔数Nu遵循非单调趋势，纵横比为AR在CWT边界条件下增稠（n> l）的流体，而在CWHF边界条件下，不管n的值如何，对于纵横比AR的值增加（Nu）单调增加。 CWT边界条件的这种非单调趋势是由于热对流和扩散输运随AR的增加而产生的竞争效应引起的。针对CWT和CWHF边界条件下幂律流体的平均Nusselt数Nu，提出了新的相关性，这些相关性被证明可以令人满意地捕获Nu的正确定性和定量行为，以响应Rayleigh数，纵横比和幂律指数。

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