高充液率封闭回路内压力波产生机理及能量传递过程研究

The heat absorbed into some liquid mediums can be converted into pressure wave under certain conditions, which can be called thermal-pressure conversion effect. According to this feature, a novel closed loop heat transfer device, with the properties of passive, high heat flux, structure simple, diverse shape, antigravity and wide temperature range, can be achieved, which has wide application prospect in the high heat flux transfer field. However, the mechanism of thermal-pressure conversion effect and the process of heat transfer are still not clear. Based on the analyses of the disadvantages of relevant research methods and present experimental studies, the way combined with molecular dynamics (MD) simulation and experimental method is used to study the issues above. By the study on the micro nature of energy conversion and transfer, the microscopic thermophysical mechanism of thermal-pressure conversion effect can be revealed. Combining with the sound and temperature filed, the generating mechanism of thermal-pressure conversion effect can be revealed deeply. On the foundation, the heat transfer modes, contribution of every mode and coordinated action of each mode are investigated by using MD method, visualization and particle image velocimetry experiments from microcosmic and macroscopic, so as to give a better understanding of high heat flux transfer process in the devices. Finally, based on the conclusions of research, the simplified mathematical models about the mechanism of thermal-pressure conversion effect and heat transfer are obtained, respectively, through theoretical deducing, which can establish the theoretical base for the practical application of the device.

利用某些液态工质一定条件下可将输入的热量转换为压力波的特性（暂称为热压转换效应），形成了一种被动式、高热流、结构简单多样、反重力、适应温度范围宽的新型封闭回路传热器件，在高热流密度散热领域展现了较大的应用潜力，但目前对其热压转换效应产生的热物理机制及高强度换热过程尚不清晰。在综合分析了相关研究方法及团队前期研究不足的基础上，课题拟采用分子动力学（MD）模拟与实验研究相结合的方法，从能量转换和输运的微观本质入手，探究热压转换效应的微观热物理机制，并结合热压转换规律的实验研究，对热压转换效应的产生机理进行深层次揭示；在此基础上，采用MD计算以及可视化和PIV定量化实验方法，从微观和宏观两个方面研究器件内存在的热量传递方式，各种方式的贡献度以及多种方式间的协同作用，进而揭示此器件的高强度换热过程；最后通过理论推导分别建立热压转换机理及热量传递的简化数理模型，为此传热器件的实际应用奠定理论基础。

高充液率封闭回路内的热压转换效应（热能转换成压力波）是其具有优异高热流密度散热能力的重要原因，然而现有研究对热压转换过程，以及热压转换效应在热量传递过程中所扮演的角色还不清楚。本项目采用理论、实验和数值计算相结合的方法，研究了液态工质热压转换的微观过程，发现液体态工质在高热流作用下发生热能-压力波转换，压力波以声速传递，在传递过程中还伴随着工质的膨胀和压缩过程，这促使加热面附近液体产生纳米级气化核心，引发爆炸沸腾，在2%的转换效率内，压力波即可起到强化传热的作用。实验研究表明高充液率封闭回路相对中、低充液率具有显著的高热流密度传热优势，随着热流密度的增加，环路内出现流型的周期性变化，并伴随压力波传递，高热流传热状态下，气泡的体积显著降低，通过大量的实验数据总结出封闭回路传热器件的传热规律图谱。将热边界层的热膨胀特性引入气泡受力分析中，同时校核蒸发-冷凝因子、饱和温度-饱和压力的函数关系、以及过冷度对冷凝的影响，建立了能够准确预测封闭回路传热特性的CFD计算模型，计算结果表明压力波使得气泡的脱离直径降低，脱离频率提高，相变换热系数增加，压力波-相变-对流之间的强耦合作用使得高充液率封闭回路表现出优异的高热流密度散热能力。