论文总字数：25720字

摘 要

重力热管是一种高效传热元件，目前在可再生能源开发利用、余热回收等领域得到了广泛应用。国内外许多学者对热管进行了理论和实验研究，但由于热管是一个复杂的传热元件，其内部包括沸腾、冷凝和气液两相流，传热机理仍有待深入研究。CFD数值模拟方法具有高效迅速等特点，目前已开发用于两相流传热过程模拟。本文通过建立重力热管数值仿真模型，研究加热功率、倾角和加热高度等操作参数对其传热性能的影响规律，主要研究内容和结论如下：

（1）基于VOF多相流模型，建立了重力热管二维CFD仿真模型，对网格进行独立性验证，并对模型结果进行了实验验证，误差在3%以内，验证了模型的可靠性。

（2）从两相流流型可以看出加热功率增加，管内气泡产生的频率、平均直径也增加，管内气泡扰动明显加剧，促进了传热。当加热功率由50W增加至100W，重力热管的总热阻由0.21K/W降至0.16K/W，减小了22％。

（3）重力热管倾角（重力热管轴线与水平方向的夹角）对其传热性能影响也较大：当倾角为70°时，重力热管总热阻最小，为0.12 K/W，分别比90°倾角时小31％，比30°倾角时降低了48%。另外，从两相云图可以看出，倾角会影响两侧壁面气泡的形成、合并和脱离。在有倾角的情况下气泡一般从下侧壁面产生，在浮力作用下上升，并与上方的气泡合并，然后脱离壁面。

（4）加热段高度对重力热管传热性能的影响较小。加热功率为100W条件下，加热高度由50mm增加到100mm，总热阻下降了6.2％。热管工质沸腾后，液池会上升，当加热高度等于充液高度（50mm）时，有效加热高度小于液池高度，热管的热阻较高；随着加热段高度增加，有效加热高度也增大，促进了热管的传热。

关键词：重力热管 数值模拟 沸腾冷凝 两相流 操作参数

Numerical simulation of the heat transfer characteristics of the gravitational heat pipe

Abstract

Gravity heat pipe is a kind of high efficiency heat transfer element, which has been widely used in renewable energy development and utilization, waste heat recovery and other fields. Many scholars at home and abroad have made theoretical and experimental studies on heat pipes, but because heat pipes are complex heat transfer elements, including boiling, condensation and gas-liquid two-phase flow, the heat transfer mechanism still needs to be further studied. CFD numerical simulation method has the characteristics of high efficiency and rapidity, and has been developed for two-phase heat transfer process simulation. In this paper, a numerical simulation model of gravity heat pipe is established to study the influence of operation parameters such as heating power, inclination and heating height on its heat transfer performance. The main contents and conclusions are as follows:

(1) Based on VOF multi-phase flow model, a two-dimensional CFD simulation model of gravity heat pipe is established, and the grid is independently verified. The experimental results show that the error of the model is less than 3%, which verifies the reliability of the model.

(2) It can be seen from the two-phase flow pattern that the heating power increases, the frequency and average diameter of bubbles in the tube also increase, and the disturbance of bubbles in the tube increases obviously, which promotes heat transfer. When the heating power increases from 50W to 100W, the total thermal resistance of gravity heat pipe decreases from 0.21K/W to 0.16K/W, which decreases by 22%.

(3) The inclination angle of gravity heat pipe (the angle between the axis of gravity heat pipe and the horizontal direction) also has a great influence on its heat transfer performance. When the inclination angle is 70 degrees, the total thermal resistance of gravity heat pipe is the smallest, which is 0.12 K/W, 31% smaller than that of 90 degrees, and 48% lower than that of 30 degrees. In addition, it can be seen from the two-phase cloud images that the dip angle will affect the formation, merging and detachment of bubbles on both sides of the wall. In the case of obliquity, bubbles generally arise from the lower wall, rise under buoyancy, merge with the bubbles above, and then break away from the wall.

(4) The height of heating section has little influence on the heat transfer performance of gravity heat pipe. When the heating power is 100W, the heating height increases from 50mm to 100mm, and the total thermal resistance decreases by 6.2%. After boiling, the liquid pool will rise. When the heating height is equal to the height of filling liquid (50mm), the effective heating height is less than the height of the liquid pool, and the heat resistance of the heat pipe is higher. With the increase of the height of the heating section, the effective heating height also increases, which promotes the heat transfer of the heat pipe.

Key Words: gravity assisted heat pipe; Numerical simulation; boiling and condensation; Two-phase flow; operating parameter

目录

重力热管相变传热特性数值模拟 I

摘 要 I

Abstract II

第一章 绪 论 1

1.1 课题研究背景及意义 1

1.2 重力热管概述 1

1.3重力热管数值模拟的研究现状 2

1.4 本文研究内容 6

第二章 重力热管数学模型的建立及求解过程 7

2.1 引言 7

2.2 CFD模型介绍 7

2.3.1 VOF模型 7

2.3.2 控制方程 7

2.3.3 相变模型 8

2.3.4 CSF模型 9

2.3 网格划分以及独立性验证 9

2.3.1 几何模型及网格划分 9

2.3.2 模型设置步骤 10

2.3.3 求解策略 11

2.3.4 网格独立性验证 11

2.3.5 模型可靠性验证方法 13

2.4 本章小结 14

第三章 重力热管数值模拟的求解结果及分析 15

3.1 引言 15

3.2 加热功率对热管内部流动及传热性能的影响 15

3.2.1 基本参数 15

3.2.2 管壁温度 15

3.2.3 两相云图 16

3.2.4 热阻 16

3.2.5 数值模拟可靠性分析 17

3.3 倾角对热管内部流动及传热性能的影响 18

3.3.1 基本参数 18

3.3.2 管壁温度 18

3.3.3 两相云图 19

3.3.4 热阻 20

3.3.5 数值模拟可靠性分析 21

3.4 加热段长度对热管内部流动及传热性能的影响 21

3.4.1 基本参数 21

3.4.2 壁面温度 22

3.4.3 两相云图 22

3.4.4 热阻 23

3.4.5 数值模拟可靠性验证 23

3-5 本章小结 24

第四章 结论与展望 25

4.1 本文结论 25

4.2 展望 25

参考文献 27

致谢 30

第一章 绪 论

1.1 课题研究背景及意义

经济的发展导致资源的消耗量在逐渐增加。所以，我们更有必要践行节约资源保护环境的基本国策^[1]。例如在汽车、化工、电力等行业领域资源消耗巨大的同时也伴随着大量低品位能源的排放，所以我们可以回收大量的低品位能源，其中能够回收的约占总排放量的60％^[2]。因此对低品位能源的回收利用能够更好地节约资源保护环境。

热管作为一种有效传输热量的元件，具有能够传输大功率，导热性高、等温性优良、工作温度范围广、可靠性高及环境适应性好等优点，这使得热管得到众多学者的青睐并为此开展了多种研究。现如今热管得到了广泛的使用，应用于许多领域，包括空气调节，制冷及低温工程^[3-5]，蓄热装置^[6]，换热与节能装置^[7-10]，冻土保护^[11]，余热利用^[12-15]等。与有吸液芯热管相比，重力热管不需要吸液芯。重力热管的蒸发段普遍在热管的下部，冷凝段在上部，中部是绝热段，这样冷凝段液态工质能够依靠重力作用完成回流^[16]。这就使得重力热管具有操作简单、使用方便、可靠性好、操作极限比较高的优势。在强调结构简单的工程应用领域重力热管的这一优势显得格外重要。

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