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首页> 外文期刊>International Journal of Heat and Mass Transfer >Unexpected natural convection heat transfer for small Rayleigh numbers in external geometry
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Unexpected natural convection heat transfer for small Rayleigh numbers in external geometry

机译：外部几何中较小的瑞利数时发生了意外的自然对流换热

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摘要

Recently, analysis of experimental data of heat transfer from submillimeter heaters at different levels of gravitational acceleration revealed a peculiar behavior of the natural convection Nusselt number (Kostoglou et al. (2011) [4]). In particular, it was found that no natural convection heat transfer appears for Rayleigh numbers smaller than a threshold value in external geometry which contradicts the common belief that this is possible only in internal (confined) geometry. This issue is studied further herein. Additional experiments are performed with higher resolution in the parameters' range and also with other liquids of varying thermophysical properties to clarify the situation. The analysis of the present data confirms the findings of the previous work and leads to a more detailed picture for the relation between Nusselt number and Rayleigh number. The relation found is against existing correlations and existing experimental evidence in literature (acquired at terrestrial conditions). Numerical simulations of natural convection in the employed external geometry are performed in order to explain the discrepancy between the behavior of the present measurements and existing correlations. It seems that the effect of varying gravitational acceleration is rather complex and cannot be accounted simply by a change in the Rayleigh number.
机译：最近，对在不同重力加速度下从亚毫米加热器传热的实验数据的分析揭示了自然对流努塞尔数的特殊行为（Kostoglou等人（2011）[4]）。特别地，发现对于小于外部几何形状中的阈值的瑞利数，没有自然对流传热出现，这与通常认为仅在内部（有限）几何形状中是可能的矛盾。本文将对此问题进行进一步研究。可以在参数范围内以更高的分辨率以及其他具有不同热物理特性的液体进行其他实验，以弄清情况。对当前数据的分析证实了先前工作的发现，并为Nusselt数与Rayleigh数之间的关系提供了更详细的描述。发现的关系与文献中现有的相关性和现有的实验证据相反（在陆地条件下获得）。为了解释当前测量值的行为与现有相关性之间的差异，对所采用的外部几何形状中的自然对流进行了数值模拟。看来，重力加速度变化的影响相当复杂，不能仅通过瑞利数的变化来解释。

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