THE CONCEPT OF HEAT PIPE(S)

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THE CONCEPT OF HEAT PIPE(S)

Heat pipe (HP) (Fig. 1) is one of the most remarkable achievements in the field of thermal physics and heat transfer engineering in recent century because of its unique ability to transfer heat over considerable distances with minimal or without considerable heat losses. It is a highly passive device that can quickly transfer heat from one point to another. They are often referred to as the ‘‘superconductors’’ of heat as they possess an extraordinary heat transfer capacity and rate with almost no heat loss [1, 2]

热管(HP)(图1)是近百年来热物理和传热工程领域最显著的成就之一,因为它能够在相当长的距离内以最小或不太大的热损失传递热量。它是一种高度被动的装置,可以快速地将热量从一点传递到另一点。它们通常被称为热的“超导体”,因为它们具有非凡的传热能力和速率,几乎没有热损失[1,2]。



Heat pipe working cycle[7]

Heat pipe was first coined by Gaugler [3] in 1994 of the General Motors Corporation in the U.S. Patent No. 2350348. In 1962, Trefethen [3] revived the idea of a heat pipe in connection with the space program. However, serious development started in 1964 when the heat pipe was independently reinvented and a patent application was filed by Grover at Los Alamos National Laboratory in New Mexico. After the work of Grover, the heat transfer community started usage of heat pipe in different applications [4, 5]D.A. Reay and P. Dunn [6] described different applications of heat pipes in the areas of space craft, chemical reactors etc. The main applications of HPs are to protect the environment and as well to save energy. The utilisation of heat pipes in a nuclear application improves the heat transfer coefficient, which is higher than in conventional heat exchanger systems.

热管最早由通用汽车公司的Gaugler[3]于1994年发明,专利号为2350348。1962年,Trefethen[3]在太空计划中重新提出了热管的概念。然而,真正的发展始于1964年,当时热管被独立改造,Grover在新墨西哥州的洛斯阿拉莫斯国家实验室提出了专利申请。在Grover的工作之后,传热界开始在不同的应用中使用热管[4,5]。D.A.Reay和P.Dunn[6]描述了热管在航天器、化学反应器等领域的不同应用。热管的主要应用是保护环境和节约能源。在核能领域中使用热管可以提高传热系数,这比传统的热交换器系统要高。

The operation of a heat pipe [7] is easily understood by using a cylindrical geometry. Though, it can be of any size or shape. Working fluids such as water, methane, etc can be used with respect to its operating temperature. HP length is divided into three sections: The evaporator, adiabatic and condenser sections. Heat applied externally to the evaporator section is conducted through the pipe wall and wick structure, where it vaporizes the working fluid. The resulting vapor pressure drives the vapor through the adiabatic section to the condenser, where the vapor condenses, releasing its latent heat of vaporization to the provided heat sink. The capillary pressure created by the menisci in the wick pumps (or drives) the condensed fluid back to the evaporator section. Therefore, the heat pipe can continuously transport the latent heat of vaporization from the evaporator to the condenser section. This process will continue as long as there is a sufficient capillary pressure to drive the condensate back to the evaporator. During the condensation process, the menisci in the condenser section are nearly flat. A capillary pressure exists at the liquid-vapor interface due to the surface tension of the working fluid and the curved structure of the interface. The difference in the curvature of the menisci along the liquid-vapor interface causes the capillary pressure to change along the pipe. This capillary pressure gradient circulates the fluid against the liquid and vapor pressure losses, and adverse body forces such as gravity or acceleration.

热管[7]的工作原理很容易用圆柱形几何体来理解。不过,它可以是任何大小和形状。工质,如水、甲烷等,可根据其工作温度使用。热管可分为三个区域:蒸发器区域、绝热区域和冷凝器区域。外部施加到蒸发器部分的热量通过管壁和芯结构传导,使工作流体蒸发。由此产生的蒸汽压驱动蒸汽通过绝热段到达冷凝器,在那里蒸汽冷凝,将其汽化潜热释放到所提供的散热器。芯部弯月面产生的毛细压力将冷凝液泵(或驱动)回蒸发器部分。因此,热管可以将汽化潜热从蒸发器持续输送到冷凝器部分。只要有足够的毛细管压力将冷凝液送回蒸发器,该过程将继续进行。在冷凝过程中,冷凝段的弯月面几乎是平坦的。由于工作流体的表面张力和界面的弯曲结构,在液-气界面处存在毛细压力。弯月面在液-汽界面上曲率的差异导致毛细压力沿管道变化。这种毛细压力梯度使液体循环,以抵抗液体和蒸汽压力的损失,以及不利的身体力,如重力或加速度

References

1.Zohuri, B., Heat Pipe Design and Technology Modern Applications for Practical (z-lib.org).pdf. second ed. 2016: Springer International Publishing.
2.Zohuri, B., Heat Pipe Design and Technology. 2016.
3.Wang, P., et al., A laboratory scale heat pipe condenser with sweating boosted air cooling. Applied Thermal Engineering, 2020. 170.
4.Mochizuki, M., et al., Heat pipe based passive emergency core cooling system for safe shutdown of nuclear power reactor. Applied Thermal Engineering, 2014. 73(1): p. 699-706.
5.Kuang, Y., C. Yi, and W. Wang, Heat transfer performance analysis of a large-scale separate heat pipe with a built-in tube. Applied Thermal Engineering, 2020. 167.
6.Faghri, A., Heat Pipes: Review, Opportunities and Challenges. Frontiers in Heat Pipes, 2014. 5(1).
7.Faghri, A., Heat Pipes: Review, Opportunities and Challenges. Frontiers in Heat Pipes, 2014: p. 48.

Writer: Emmanuel Osei Tutu (Harbin Engineering University)
Editor: Priscilla Oforiwaa
Designers: Zhang Jing & Zhang Chao
Translation : Zhang Chao

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