Abstract For non-axisymmetric conditions, the traditional fluid mean (bulk) temperature at a tube cross section, subjected to constant heat flux, can be higher than the temperature of a point on the wall. This results in a mismatch between the direction of applied heat flux and the temperature difference resulting in (misleading) negative peripheral heat transfer coefficient and Nusselt number (Nu). The resulting cross-sectional Nu (average of peripheral Nu values) differs from that calculated from average surface temperature and mean temperature. To address this gap in the literature, a detailed procedure is investigated based on a radial mean temperature of individual lines calculated from the lowest temperature spot in the cross-section to wall points, physically satisfying the mechanism of actual heat transfer from hot to cold spots. Each radial line’s mean temperature is used to calculate a peripheral Nu. These peripheral and average Nu are always positive and matches with the cross-sectional Nu that is calculated using the traditional method – single average cross-sectional temperature. This method is verified for different duct geometries including circular, square, and rectangular. The method also succeeds in the estimation of the peripheral and cross-sectional Nu values for eccentric annular ducts that are inherently non-axisymmetric and have negative Nu values according to the published literature.

中文翻译：

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解决非轴对称流动条件下外围和局部努塞尔数之间的不匹配问题：重新定义平均温度

摘要 对于非轴对称条件，在恒定热通量作用下，管横截面的传统流体平均（体积）温度可能高于壁上一点的温度。这会导致施加的热通量方向与温差不匹配，从而导致（误导）负的外围传热系数和努塞尔数 (Nu)。由此产生的横截面 Nu（周边 Nu 值的平均值）与根据平均表面温度和平均温度计算得出的不同。为了解决文献中的这一空白，基于从横截面中的最低温度点到壁点计算的各个线的径向平均温度，研究了详细的程序，在物理上满足从热点到冷点的实际热传递机制. 每条径向线的平均温度用于计算外围 Nu。这些外围和平均 Nu 始终为正值，并与使用传统方法计算的横截面 Nu 相匹配 - 单个平均横截面温度。该方法已针对不同的管道几何形状进行了验证，包括圆形、方形和矩形。根据已发表的文献，该方法还成功地估计了偏心环形管道的外围和横截面 Nu 值，这些管道本质上是非轴对称的并且具有负 Nu 值。该方法已针对不同的管道几何形状进行了验证，包括圆形、方形和矩形。根据已发表的文献，该方法还成功地估计了偏心环形管道的外围和横截面 Nu 值，这些管道本质上是非轴对称的并且具有负 Nu 值。该方法已针对不同的管道几何形状进行了验证，包括圆形、方形和矩形。根据已发表的文献，该方法还成功地估计了偏心环形管道的外围和横截面 Nu 值，这些管道本质上是非轴对称的并且具有负 Nu 值。