面向低品位热源的多级环路行波热声发动机研究

Low grade thermal energy is one of the potential resources, of which making full use will be the important solution for energy conservation and emission reduction. The aim of the present project is to use the low-grade thermal energy to drive a loop-structured multi-stage thermoacoustic prime mover, taking advantage of its low onset temperature feature, to realize the thermal-acoustical conversion, from which the acoustic power can be used to drive a load, such as electricity generator or refrigeration system. Based on the discussion of the working mechanism of the loop-structured multi-stage traveling wave thermoacoustic system and on the analysis of the regenerator location and phase matching in the loop, our emphasis will be firstly devoted on the optimization of the topological configuration of the loop. Considering the unbalanced acoustic impedance between sound generation (thermoacoustic core section) and sound transmission (resonance tube section) and the required different diameters in the loop, the influence of the component dimensions on the sound field, thermoacoustic conversion efficiency and the acoustic power distribution and transmission will be analyzed and optimized, in order to achieving lower onset temperature, higher thermoacoustic efficiency, and more efficient acoustic power output. Based on the theoretical optimization and prior experimental work, the updating and reconstruction of the experimental apparatus of multi-stage loop-structured thermoacoustic prime mover will be followed by systematic experimental work and further optimization. This study is expected to provide a novel technical choice for the utilization of low-grade thermal energy, and also to extend the space for the application of thermoacoustic technology through the strategy of diversified competition.

低品位热源是能源领域尚未充分利用的重要潜在资源，对其进行有效利用是节能减排的重要举措之一。本项目的研究思路为通过具有低起振温度特征的多级环路行波热声系统，利用低品位热源驱动热致声转换过程，所产声功可用于驱动有效负载。拟探讨多级环路行波热声系统的工作机理，系统分析热声核在环路中的布置方式以及相位匹配情况，提出多级环路系统的拓扑结构优化原则。鉴于环路系统中声功产出单元（热声核部分）和声功传递单元（谐振管部分）的阻抗不平衡特征而需采用非等径结构实现环路中的声阻匹配，拟就热声部件结构尺寸对系统声场、热声转换效应和能量分布与传输的影响进行分析与优化，旨在降低起振温度、提高低温位驱动下的热声转换效率和提升系统的声功输出性能。在理论优化和先期实验研究的基础上，改进原有或者构建新的实验系统，开展更系统的实验研究工作。本项目可望为低品位热能的利用和热声技术实用进程拓展出差异化竞争的空间。

本项目就多级环路行波热声发动机系统开展理论和实验研究工作，旨在进一步降低热声系统的起振温度，提升在低温热源驱动下的热声转换效率，并提高环路中声功的输出性能。首先，分析了多级环路行波热声系统的声阻抗匹配机理并完成了拓扑结构优化。揭示了热声转换效应声场相位的依赖机制，提出依靠阻容协同来精确调控热声核所处声场的相位关系。系统提出单级到四级环路热声发动机，实现具有合理声阻抗分布的拓扑结构。然后，从数值计算和实验两方面研究了回热器对系统起振特性和输出性能的影响, 阐明了回热器几何尺寸对环路行波热声发动机输出特性的作用机理。采用可变阻容负载法对三级热声发动机系统的输出特性进行了实验研究, 揭示了阻容负载对多级环路行波热声发动机输出特性的影响机制。在此基础上，将三级环路热声发动机与一台直线电机耦合，搭建了一台三级环路热声发电系统，探究了热源温度对系统的输出电功和热电转换效率的影响，初步验证了利用低品位热源驱动环路热声发电系统进行发电的可行性。建立三级环路行波热声发电系统模型，通过机理分析和实验验证相结合的方法，进一步对外接电容和电阻、谐振频率以及容腔位置和长度进行了优化，有效提高了三级环路行波热声发电机的热电转换效率。对比分析了一到四级环路行波热声发电机的系统性能，并探究了环路热声系统中的Gedeon声直流对输出性能的影响机制，成功实现低温位热源驱动热声发电。本项目为低品位热源的有效利用提供了一条新思路，这对于拓展热声技术实用进展的差异化竞争空间具有重要意义。