近临界流体微通道热声不稳定的理论优化与实验探索

在气液（拟）临界点附近，流体的强可压缩性使得传热总是伴随着压力波动，称为热声耦合。在热声耦合的影响下，微通道内的近临界流体在温度梯度的作用下会激发热声不稳定，最终演化为稳定压力振荡。近年来，基于这一原理实现热功转换成为前沿新兴领域。目前，已有研究利用制冷工质搭建了实际热声装置，取得了很好的实验结果，但相关研究仍有较大潜力。结合申请人研究基础，本项目独辟蹊径：提出变截面微通道设计，通过理论优化，实现复杂交变流动传热与剧烈物性变化的最佳匹配；提出在理论优化的基础上以近临界CO2为工质试制热声装置。为此，本项目将综合利用线性稳定性分析、直接数值模拟和实验，探究变截面微通道的最佳设计参数，总结经验设计准则，探索实际CO2热声装置的性能及变工况运行特性。本项目将实现关键部件和系统层面对近临界CO2热声装置的理论优化和实验，在近临界流体热声耦合的主动应用上迈出重要一步。

Near the liquid-gas (pseudo-) critical point, the strong compressibility of fluid makes heat transfer always coupled with pressure oscillations, reflecting the nature of thermoacoustic coupling. For a supercritical fluid in microchannels subjected to a streamwise temperature gradient, the thermoacoustic coupling leads to thermoacoustic instability especially under near-critical conditions, manifested as self-amplified oscillations. Recently, exploiting thermoacoustic instability in energy conversion has become an emerging field. Researchers successfully built a thermoacoustic prototype using R218 as working fluid and excellent performance was confirmed. The applicant proposes there are still many potentials in this field. Based on the applicant’s previous experiences, this project innovatively proposes to develop variable-section microchannels to achieve the best matching between heat transfer and drastic variations in physical properties. Then, a thermoacoustic prototype using near-critical CO2 as working fluid will be built. Technically, this project involves linear stability analyses, direct numerical simulations, and experiments. The goals are to achieve the best design of the variable-section microchannel, summarize design criteria, and explore the actual performance of the prototype. This project will realize the theoretical optimization and experiment of the near-critical CO2 thermoacoustic device at both key-component and system levels, and will take an important step forward in the active application of the thermoacoustic instability of near-critical fluids.