利用微/纳米结构分级强化微通道流动沸腾换热机理研究

Using micro/nano structures to enhance the flow boiling heat transfer in microchannels is becoming one of the research focus all over the world, but the heat transfer mechanisms of flow boiling and the strengthening reasons of surface structures are still not clear. Generally, only single form of surface structure is used in whole microchannel to enhance the flow boiling heat transfer, which in fact cannot fully and effectively improve the heat transfer capability due to the changing heat transfer modes along the flow direction, and may lead to the increased pressure drop. An hierarchical strengthening strategy using multistage micro/nano structures is proposed in this project, which can enhance the flow boiling heat transfer based on the heat transfer modes at different regions along flow direction. There are two key scientific problems: the influences of surface structures on the bubble behavior and the heat transfer in microscale space and the heat transfer mechanisms of flow boiling in the microchannel with multistage micro/nano structures. The mechanical model and heat transfer model of bubbles on the micro/nano structures in microscale space will be established by analyzing the bubble behavior characteristics. The strengthening mechanisms of surface structures on the flow boiling and the heat transfer mechanisms in microchannel will be studied based on the flow patterns transition and heat transfer characteristics. The results of the project can perfect the knowledge on the flow boiling heat transfer at structured surface in microscale and improve the strengthening technology of microchannel flow boiling, which have not only the theoretical but also the practical significance.

微通道流动沸腾换热模式的沿程变化导致采用单一形式微/纳米结构不能充分有效强化整个通道的沸腾换热过程，并可能带来压降的显著增加。本项目提出分级强化策略，即沿程分区域采用不同形式的微/纳米结构及其复合结构以强化微通道流动沸腾换热。本项目的关键科学问题是微尺度空间中微/纳米结构表面发生流动沸腾时的气泡行为特征和气泡热质传递规律以及多级微/纳米结构微通道中流动沸腾的换热机理。项目拟通过研究多级微/纳米结构微通道中的气泡行为特征，建立微尺度空间微/纳米及其复合结构表面沸腾过程中气泡的动力学模型和热质传递模型；基于流型转换规律和换热特性研究，分析微尺度空间中微/纳米结构强化沸腾换热的机制，揭示多级微/纳米结构微通道中发生流动沸腾的换热机理。预期研究成果可完善微尺度空间微/纳米结构表面沸腾换热理论，推动强化微通道流动沸腾换热技术的发展。

越来越多的高热流密度装置其散热要求已逐渐逼近甚至超过现有微通道流动沸腾的换热极限，进一步提高微通道流动沸腾的换热能力已经迫在眉睫。利用微纳米结构进一步强化微通道流动沸腾换热能力是解决高热流密度装置冷却难题的重要途径，本项目提出分级强化策略，即沿程分区域采用不同形式的微纳结构多级强化微通道流动沸腾换热，研究微尺度空间中分区域的微纳结构影响流动沸腾气泡行为特征和流型转变规律的机制以及强化两相热质传递的机理。项目搭建了微通道流动沸腾实验平台，利用矩形截面微槽修饰狭缝通道换热表面，提高了两相流动稳定性并强化了流动沸腾换热性能。提出了下游局部修饰截断微针肋的狭缝微通道结构和粗糙表面与三角形截面微柱分区域修饰表面的渐扩狭缝通道结构，有效抑制下游局部蒸干并进一步强化微通道流动沸腾换热能力提升CHF。建立了多级强化结构微通道流动沸腾的气泡动力学模型和热质传递机理模型，构造出新的具有高两相换热能力的泡毯流型，揭示了分区域局部修饰微结构多级强化流动沸腾换热内在机制，将微通道流动沸腾换热系数提升至183.4 kW/m2K，达到国际先进水平，验证了采用沿程分区域多级微米结构强化微通道流动沸腾换热效果。研究结果对于进一步完善利用微纳米结构强化流动沸腾换热基础理论具有重要的科学意义，为利用微纳结构分级强化流动沸腾换热方案的研制与设计优化提供理论依据，并为高热流密度装置高效冷却技术的研发提供关键技术支撑。