【作者】 张红；

【导师】 徐斌；

【作者基本信息】 中国科学技术大学 ， 动力工程及工程热物理， 2025， 硕士

【摘要】 在热管理领域,微型电子器件热流密度的持续增长,大型装置热控系统对极端工况适应性需求愈发严格,散热问题日益严峻。平板热管凭借出色的散热均温性能和被动散热的安全性,成为散热技术的重点研究对象。本文基于介观模拟尺度,采用格子玻尔兹曼方法(Lattice Boltzmann Method,LBM)开展研究。运用LBM中的伪势模型求解流场,采用混合方法求解温度场,构建了以厚度方向传热为主的平板热管二维沸腾-冷凝两相流模型。主要研究内容和结论如下:(1)对比典型芯结构的工作优势。对微槽芯、烧结粉末芯、网芯三种典型多孔芯结构建模,分析它们在相同工作条件下对平板热管性能的影响。通过调控加热面过热度、接触角、重力场等参数,探索优化热管传热的规律。研究发现,核态沸腾显著提升热管整体传热性能,其中微槽芯成核性能最优,其热管蒸发面热流密度较其他结构最高提升了1.9倍。优化蒸发表面亲水性可进一步促进成核,增强传热效率。以微槽芯为例,增加壁面亲水性可使蒸发面热流密度提升1.8倍。此外,在无重力环境下,热管冷凝性能因对流缺失而急剧恶化,有重力条件下冷凝换热系数至少是无重力时的五倍。(2)探讨不凝性气体(Non-condensable Gas,NCG)浓度影响。借助LBM多组分模型,向平板热管模型中添加与工作流体混合分布的不凝性气体。在有芯和无芯热管中,系统研究不凝性气体运行不同阶段的作用机制。研究发现,不凝性气体对热管传热性能具有双重效应。适量浓度的不凝性气体可增强流场扰动,提升沸腾与冷凝换热效率。在无芯热管中,低浓度不凝性气体能使蒸发面热流密度最大提升181.6%,冷凝面平均热流密度提升39.0%。然而,不凝性气体会增大热管内部传热热阻,削弱芯结构的毛细能力,导致有芯热管蒸发面热流密度下降20.1%,降低热管综合传热和流动性能,不利于热管长期稳定运行。本文围绕平板热管,系统探究了受限空间内不同因素对其相变与传热特性的影响。研究表明,合理选定芯结构、精确调控不凝性气体浓度,对提升平板热管传热性能至关重要。一方面,为深入认识平板热管工作机制筑牢了理论根基;另一方面,基于研究成果,在优化热管芯体结构、调控表面特性,推动汽液两相高效流动,规避膜态沸腾致使传热效率降低等方面,提供了理论指导,为强化平板热管高效散热提供坚实支撑。更多还原

【Abstract】 The continuous increase in the thermal flux density of microelectronic devices and the increasingly stringent requirements for thermal control systems of large-scale equipment under extreme conditions have highlighted the challenges of heat dissipation.Flat heat pipes,with their excellent thermal uniformity and the safety of passive cooling,have become a key research focus in thermal management technology.Based on mesoscopic simulations,the Lattice Boltzmann Method(LBM)is employed to conduct the research.The pseudo-potential model in LBM is used to solve the flow field,while a hybrid method is applied to solve the temperature field.A two-dimensional boiling-condensation two-phase flow model for flat heat pipes with heat transfer primarily in the thickness direction is established.The main research content and conclusions are as follows:(1)Comparison of the advantages of typical wick structures.Three typical porous wick structures—microgroove wick,sintered powder wick,and mesh wick—are modeled to analyze their impact on flat heat pipe performance under the same working conditions.By adjusting parameters such as the overheating degree of the heating surface,contact angle,and gravity field,the optimization laws of heat transfer in heat pipes are explored.Nucleate boiling is found to significantly enhance the overall heat transfer performance of the heat pipe.Among the structures,the microgroove wick exhibits the best nucleation performance,with the heat flux density at the evaporation surface being 1.9 times higher than that of the other structures.Optimizing the hydrophilicity of the evaporation surface can further enhance nucleation and improve heat transfer efficiency.Taking the microgroove wick as an example,increasing the hydrophilicity of the wall can increase the evaporation surface heat flux density by 1.8 times.In addition,under a zero-gravity environment,the condensation performance of the heat pipe deteriorates drastically due to the lack of convection,with the condensation heat transfer coefficient under gravitational conditions being at least five times that in zero gravity.(2)Investigation of the impact of non-condensable gas(NCG)concentration.Using the multi-component model in LBM,non-condensable gas is added to the heat pipe model in a mixed distribution with the working fluid.The role of non-condensable gas at different stages of operation is studied in both wick and wickless heat pipes.The concentration of non-condensable gases has a dual effect on the heat transfer performance of the heat pipe.A moderate concentration of non-condensable gas can enhance flow field disturbance,improving both boiling and condensation heat transfer efficiency.In wickless heat pipes,low concentrations of non-condensable gas can increase the evaporation surface heat flux density by up to181.6%,and the average heat flux density at the condensation surface is increased by39.0%.However,non-condensable gas increases the thermal resistance inside the heat pipe,weakening the capillary ability of the wick structure,leading to a 20.1%reduction in the evaporation surface heat flux density in wick heat pipes,thereby diminishing the overall heat transfer and flow performance and making long-term stable operation of the heat pipe difficult.This study systematically investigates the effects of various factors on the phase-change and heat transfer characteristics of flat heat pipes in confined spaces.The importance of selecting appropriate wick structures and controlling non-condensable gas concentration is indicated for improving the heat transfer performance of flat heat pipes.On the one hand,a solid theoretical foundation is laid for a deeper understanding of the working mechanisms of flat heat pipes.On the other hand,based on the findings,theoretical guidance is provided for optimizing wick structures,adjusting surface properties,promoting efficient two-phase flow,and preventing the decline in heat transfer efficiency caused by film boiling,thereby offering strong support for enhancing the heat dissipation performance of flat heat pipes.更多还原