Abstract Heat transfer between two streams of hot and cold fluids separated by a plate is an unavoidable exergy destruction process as a whole, i.e. the exergy gain from the cold fluid cannot fully cover the exergy loss of the hot. However, it is noticed that the amount of exergy destruction can be minimized by introducing the work done by the external gravity force that the natural convection of the third fluid in a closed loop driven by the hot and cold fluids themselves can enhance their heat transfer. Based on this idea, a heat transfer enhancement unit of a closed rectangular loop was constructed, the two parallel legs of which were vertically penetrated through a horizontal plate with one half on the hot side and the remained half on the cold side. In order to clarify the mechanism of heat transfer enhancement for the natural circulation loop (NCL), a numerical simulation was performed for a comparison between the heat transfer rates of the NCL and the copper fin with the same shape and size. The effects of side length, velocities of heating and cooling air, and temperature difference on the heat transfer rate were investigated in detail. The results show that the heat transfer rate of the NCL can be larger than that of the copper fin while the temperature difference is over a critical value.

中文翻译：

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基于单相自然循环回路的传热强化

摘要 由板隔开的两股冷热流体之间的传热是一个整体上不可避免的火用破坏过程，即冷流体的火用增益不能完全弥补热流体的火用损失。然而，值得注意的是，通过引入由外部重力所做的功可以最小化火用破坏的量，即由热流体和冷流体本身驱动的闭合回路中的第三流体的自然对流可以增强它们的热传递。基于这个想法，构建了一个封闭矩形回路的传热增强单元，其两个平行的腿垂直穿过水平板，一半在热侧，另一半在冷侧。为了阐明自然循环回路（NCL）的传热增强机理，进行了数值模拟，比较了自然循环回路与相同形状和尺寸的铜翅片的传热率。详细研究了边长、加热和冷却空气的速度以及温差对传热速率的影响。结果表明，当温差超过临界值时，NCL 的传热率可以大于铜翅片的传热率。