极低温吸附制冷机多孔介质内稀薄气体吸附过程的模拟与实验研究

Sub-Kelvin sorption refrigeration is a critical technology for a wide range of future astronomy and cosmology missions. As a key component in an adsorption cooling system, adsorbent bed is the main factor to decide cooling temperature, temperature stability and structure design. To the knowledge of the present applicant, the performance of adsorbent bed of sorption cooling has not been analyzed. Owing to the Knudsen(Kn) number of gas flow being in the range 0.01≤Kn≤5.0 during adsorption process of the adsorbent bed, the gas flow in porous media of adsorbent bed is between slip and transition regimes, therefore the rarefied gas effects should be taken into account. Based on the study status of rarefied gas flow in the porous media, this project will set up Navier-Stokes equations and model with second-order slip flow in slip and transition flow regimes.Then the model is applied to investigating the relationship among flow field resistance, Kn number and average field pressure, and the effects of parameters on the adsorption performance. The transient performance of adsorbent bed during the adsorption process will be obtained. In addition, experiments will be carried out to investigate the characteristics of flow field resistance and adsorption process. Experiment results will be applied to design the adsorbent bed and validate the numerical simulation. Results of the project will fulfill the research in relative arts and advance the widely application of sorption cooling technology in space.

极低温（<1K）吸附制冷技术已成为空间应用中极为重要的制冷技术。极低温吸附制冷机最关键部件吸附床的吸附过程是决定制冷温度、温度稳定性和结构设计的主要因素，目前尚未检索到这类吸附床的相关研究文献。鉴于吸附床多孔介质吸附过程中气体流动的Knudsen(Kn)数∈(0.01,5)，属于滑移过渡流区，需考虑稀薄气体效应的影响。本项目针对多孔介质内稀薄气体吸附研究薄弱的现状，拟建立滑移过渡流区二阶滑移边界的Navier-Stokes控制方程及数学物理模型，分析流场阻力、Kn数及平均压力之间的关系，探讨各因素对吸附性能的影响，获得多孔介质的动态吸附特性，并实验研究多孔介质内稀薄气体在不同Kn数、孔隙率和颗粒直径等参数下的流动和吸附过程，实验结果将被用于吸附床的设计和验证模拟计算的有效性。通过这些研究，完善、填补目前极低温吸附制冷技术研究的不足与空缺，为空间极低温吸附制冷技术的应用提供理论和实验支持。

随着空间科学计划的开展，深空探测和载人空间站等领域中的相关研究都需要空间极低温（<1K）温度，相关研究的顺利开展都离不开空间极低温技术的支持。由于极低温吸附制冷机具有长寿命、高可靠、低振动和无干扰等特点，因此极低温吸附制冷技术是空间240mK~4K温区最重要的制冷方式之一。欧洲宇航局和美国NASA都展开了极低温吸附制冷技术的研究，我国在本项目之前几乎空白。极低温吸附制冷机最关键部件吸附床的吸附过程是决定制冷温度、温度稳定性和结构设计的主要因素，本项目重点研究了吸附床内部的传热传质，开展了活性炭的筛选和表征、活性炭的吸附性能测试、活性炭的成型、活性炭流动阻力等实验工作，基于Navier-Stokes控制方程提出了一种吸附床非集总温度动态模拟方法，理论研究了多孔介质内稀薄气体吸附过程等内容，搭建了一套极低温实验系统，研制了一套极低温吸附制冷机样机，样机制冷剂为He-4工质，在样机上开展并验证了上述研究内容，并在1.5W@4.2K G-M制冷机基础上获得了最低0.759K(零下272.391)的制冷温度，达到世界先进水平。通过这些研究，完善、填补目前极低温吸附制冷技术研究的不足与空缺，为空间极低温吸附制冷技术的应用提供理论和实验支持。