有机工质管内相分布调控强化沸腾传热机理研究

Phase change heat transfer of organic fluid is an effective way to utilize low-grade thermal energy. The energy transfer mechanism between the two phases and phase interface is significantly determined by the phase distribution in tube. Due to gravity and inertial force, a mismatch between flow pattern and heat transfer exists, such as the non-uniform liquid film on the wall surface and the vapor entrains small liquid droplets in the tube core, which weakens the heat transfer. However, the previous enhancing heat transfer techniques do not involve the flow pattern modulation in tubes. Inspired by the principle of cactus spine water collection, a bionic structure and multi-scale inhomogeneous surface in the tube wall are constructed to modulate flow pattern. The surface appearance not only accelerates the separation of bubbles form the boiling surface, but also achieves the objectives of self-adsorption and anti-gravity climbing of liquid phase fluids. Thus, the flow pattern is modulated to enhance the heat transfer. The relevant bubble and liquid droplets dynamics behaviors are analyzed and nucleate boiling heat transfer model is established. The dominant mechanism of the dynamic behavior of intergranular liquid droplets is revealed, and the critical transition conditions of anti-gravity climbing of liquid phase fluids are obtained. The effects of surface preparation parameters on boiling heat transfer enhancement are also discussed. The investigation of this project provides theoretical and technical supports for the flow pattern modulation and heat transfer enhancement in boiling tubes.

有机工质相变沸腾传热是实现低温差热能传递的有效手段，管内相分布决定了两相及相界面间能量传递过程机制，但存在管壁面非均匀液膜及汽核夹带液滴这一弱化传热的相分布。现有强化传热技术无法从根本上改善上述相分布，实现流型与传热的协同。受仙人掌锥状刺集液原理的启发，项目通过在换热管中插入仿仙人掌刺型强化锥，并在换热管壁及强化锥表面构建纳-微-毫多尺度非均质结构，促进汽泡快速从换热面脱离，实现液相流体可控吸附及快速再浸润，调控管内相分布强化沸腾传热。并通过制备表面液滴与汽泡动力学研究，建立非均质金属颗粒空间分布及表面核态沸腾汽泡溢出过程模型，获得控制液体运动行为的临界转变条件及揭示表面结构参数对沸腾传热性能的影响机理，掌握制备参数对结构功能的影响规律，形成系统的多尺度非均质表面制备方法。本项目的研究为沸腾管内相分布调控强化传热提供了理论和技术支撑，具有重要的学术及应用价值。

项目围绕“多尺度烧结表面构建与非平衡界面作用力分布的协同关系”以及“沸腾管内相分布调控原理与方法”这两个关键科学问题，开展微纳多尺度沸腾表面制备方法、气液界面分布规律及液体动力学行为规律和强化沸腾传热特性实验三方面研究工作。发展了烧结+电化学沉积耦合技术，构建了微-纳复合多尺度结构表面，其管壁涂层粘附强度达到5.49N，是纯烧结单一尺度表面的2.64倍。开展了多尺度表面浸润性测试及液体动力学行为规律研究，发现多尺度结构具有显著的液体吸收能力，相比单一尺度烧结表面完全铺展时间缩短了3.7倍。揭示了微纳多尺度管内镀层改善相分布调控机理，多尺度管壁结构能够有效增强壁面润湿效果，实现了液相工质反重力快速爬升，减薄了分层流型中管底液膜厚度，促使环形流中的液体被表面涂层快速捕获，加速换热面再浸润。搭建了换热器性能测试平台，创制相分布调控强化蒸发换热管，研究了其强化传热特性及规律，获得不同参数下强化管内沸腾传热特性、规律及机理，明晰了多尺度烧结电镀表面结构调控管内相分布强化传热的有效结构参数范围及运行条件，实现了最大2.28倍的强化倍率。项目的研究成果在低温余热利用、散热等领域具有应用前景，显现出巨大的节能减排和社会环境经济效益前景。