液氦温区斯特林型脉管制冷机回热强化机理研究

The high-efficiency, compact and long-life cryocoolers working at liquid helium temperatures play a crucial role in national defense, space application, superconductor, and medical usages. Recently, the Stirling pulse tube cryocooler (PTC) has become a hot topic in the worldwide cryocooler research field due to its compactness, low vibration and other advantages. However, it is still hard for the Stirling PTC to work efficiently around 4.2 K owing to its severe regenerator losses under high-frequency operation. This project aims to increase the refrigeration efficiency of Stirling PTC through enhancing its regenerator performance and decreasing its consumed power at liquid helium temperatures. A multiple-parameter coupling method based on frequency has been proposed to optimize the regenerator. The effect of different frequencies, pressure ratios, and regenerative material combinations on the regenerator losses will be explored to reveal the optimum operating conditions for the regenerator under liquid helium temperatures. An approach of driving acoustic power through a cold transmission tube is also proposed in order to eliminate the pressure loss in the regenerator at higher temperatures. By utilizing a new acoustic power measurement, the acoustic loss of the cryocooler and the impedance characteristic of the cold transmission tube will be estimated and analyzed, exploring the perfect matching between the cryocooler and the linear compressor. A Stirling PTC based on the above optimizations will be built and tested to realize high-efficiency refrigeration at liquid helium temperature in experiment. This study is benefit to the development of regenerative cryocoolers, and is also of great significance to the development of recent cryogenic application fields.

液氦温区高效、紧凑、长寿命的低温制冷技术是国防、航天、超导、医疗等领域的重要支撑和保障。液氦温区的斯特林脉管制冷机因其具有体积小、振动低等优势，成为低温制冷领域的研究热点。然而深低温下高频运行造成回热损失严重，导致当前斯特林脉管制冷机难以实现液氦温区高效制冷。本项目以显著提高液氦温区斯特林脉管制冷机效率为目标，提出利用基于频率特性的多参数耦合优化方法以及低温传输管声功驱动方式，显著降低回热器换热和阻力损失。探索液氦温区运行频率、压比、不同填料组合对回热器各损失的影响机理，揭示液氦温区回热器的最佳运行工况；提出新的声功测算方法对整机功损进行评估，分析低温传输管的声阻抗特性，探索制冷机与压缩机的高效匹配方式；研制基于最佳设计工况的低温声功驱动型斯特林脉管制冷机，最终实现液氦温区的高效制冷。

本项目基于航天探测设备对4K、20K温区斯特林脉管制冷技术的需求，研究了深低温区斯特林脉管制冷机的回热强化技术。通过理论分析和实验验证得出在6.1K以下，采用比热容更高的GOS填料可以改善回热器温度梯度，减小回热器焓流损失，在5mm GOS填料下，其最低制冷温度相比采用纯HoCu2填料时，可从4.75K降低至4.57K，制冷量也能得到一定提高。提出了斯特林脉管制冷机利用外部冷源预冷传输管和基于DC流方法内部预冷脉管技术，理论和实验验证了预冷传输管技术直接传输声功驱动冷端高效制冷的可行性；验证了DC流在20K脉管制冷机内可通过改善脉管和回热器温度梯度减少其内部热损失，实现制冷性能的提高。当DC流为2.15mg/s时，最低温度可比无DC流时降低6.7K，在22K时制冷量比无DC流时增加约1W，验证了DC流强化20K温区制冷性能的可靠性。基于上述基础研究，本项目进一步研制了基于低温声功传输管技术的两级斯特林脉管制冷机，并与航天五院合作进行后续应用转化，将其用于某卫星探测计划的冷却系统中。