Numerical simulation on heat transfer characteristics of a two-phase closed thermosyphon with low filling ratios

IF 5.4 3区工程技术 Q2 ENERGY & FUELS

Thermal Science and Engineering Progress Pub Date : 2025-09-30 DOI:10.1016/j.tsep.2025.104165

Wandong Min , Wei Zhong , Yanping Yuan , Dan Zhao , Xiaoling Cao

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Abstract

The two-phase closed thermosyphon (TPCT), an efficient heat transfer device, relies on the phase change of the working fluid. The distribution of the working fluid, which significantly affects the heat transfer mechanism, is influenced by the filling ratio (FR) along with other factors such as input power and geometry. Under certain conditions, the liquid pool height when the TPCT operates stably can typically be categorized into three scenarios: the liquid pool below the evaporator (often at low FRs), exceeding the evaporator (regular FRs), or reaching the condenser (high FRs). Previous research has shown that under low FRs, heat transfer deterioration occurs in the evaporator wall of TPCT. However, the existing literature has not fully elucidated the boiling mechanism underlying this phenomenon. In this paper, an improved CFD model of the TPCT was established to effectively simulate the flow and boiling process of liquid film in the evaporator section. The calculated data exhibited good consistency with experimental results, with a maximum relative error of 1.43 %. It was observed that the liquid film displays a wave-like pattern, which is attributed to the balance of gravity, surface tension, shear force, and buoyancy force when the TPCT is stable. As wall height decreases, there is an increase in amplitude for liquid film fluctuation above the evaporator wall height. Bubbles generated on the evaporator wall leads to an increase in the frequency of liquid film fluctuation and causes the liquid film to rupture. At low FRs, the distribution of liquid films in the evaporator generally can be distinguished into three scenarios: continuous liquid film, discontinuous liquid film, and dry-out areas. When the heating input is 232.89 W, the overall thermal resistance of methanol-TPCT with a 35 % FR decreased by 33.2 % compared to a 15 % FR, and only increased by 0.4 % compared to a 70 % FR. According to the findings in this paper, a proper FR of the TPCT can be employed for a given heating input, ensuring exceptional heat transfer performance and reducing the quantity of working fluid utilized.

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低填充率两相封闭式热虹吸管传热特性的数值模拟

两相闭式热虹吸（TPCT）是一种依赖于工质相变的高效传热装置。填充比（FR）以及输入功率和几何形状等因素对工质分布的影响显著。在一定条件下，TPCT稳定运行时的液池高度通常分为以下三种情况：低于蒸发器（通常为低FRs）、超过蒸发器（正常FRs）或达到冷凝器（高FRs）。已有研究表明，在低FRs条件下，TPCT蒸发器壁面发生换热恶化。然而，现有文献并未完全阐明这一现象背后的沸腾机制。本文建立了改进的TPCT CFD模型，有效模拟了蒸发器段液膜的流动和沸腾过程。计算结果与实验结果吻合较好，最大相对误差为1.43%。观察到液膜呈波浪状，这是由于TPCT稳定时重力、表面张力、剪切力和浮力平衡的结果。随着壁高的降低，蒸发器壁高以上液膜波动幅度增大。蒸发器壁上产生的气泡导致液膜波动频率增加，导致液膜破裂。在低FRs时，蒸发器内液膜的分布一般可分为连续液膜、不连续液膜和干区三种情况。当加热输入为232.89 W时，35% FR的甲醇-TPCT的总热阻比15% FR降低了33.2%，而与70% FR相比仅增加了0.4%。根据本文的研究结果，在给定的加热输入下，可以采用适当的TPCT FR，以确保卓越的传热性能并减少工质的使用。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

Thermal Science and Engineering Progress Chemical Engineering-Fluid Flow and Transfer Processes

CiteScore

7.20

自引率

10.40%

发文量

327

审稿时长

41 days

期刊介绍： Thermal Science and Engineering Progress (TSEP) publishes original, high-quality research articles that span activities ranging from fundamental scientific research and discussion of the more controversial thermodynamic theories, to developments in thermal engineering that are in many instances examples of the way scientists and engineers are addressing the challenges facing a growing population – smart cities and global warming – maximising thermodynamic efficiencies and minimising all heat losses. It is intended that these will be of current relevance and interest to industry, academia and other practitioners. It is evident that many specialised journals in thermal and, to some extent, in fluid disciplines tend to focus on topics that can be classified as fundamental in nature, or are ‘applied’ and near-market. Thermal Science and Engineering Progress will bridge the gap between these two areas, allowing authors to make an easy choice, should they or a journal editor feel that their papers are ‘out of scope’ when considering other journals. The range of topics covered by Thermal Science and Engineering Progress addresses the rapid rate of development being made in thermal transfer processes as they affect traditional fields, and important growth in the topical research areas of aerospace, thermal biological and medical systems, electronics and nano-technologies, renewable energy systems, food production (including agriculture), and the need to minimise man-made thermal impacts on climate change. Review articles on appropriate topics for TSEP are encouraged, although until TSEP is fully established, these will be limited in number. Before submitting such articles, please contact one of the Editors, or a member of the Editorial Advisory Board with an outline of your proposal and your expertise in the area of your review.