Modeling Studies On Performance Of Regenerative Cryocoolers With 3~He And 4~He As Working Substance

Regenerative cryocoolers have been widely used to achieve low temperature environment. With great potential, pulse tube refrigerator (PTR) has drawn wide attention from researchers all over the world. Their research focuses on the following aspects: improving efficiency and reliability, achieving lower temperature or higher refrigeration power in specified temperature region, and minimizing size and input power, etc. Using helium-3 (3He) as working substance in place of the traditional helium-4 (4He) is considered to be an effective way to achieve lower temperature and higher cooling capacity. This thesis intends to investigate the principles and methods of optimizing the performance of the regenerator in a cryocooler using 3He theoretical analytically and numerically. The following work has been done:(1) Qualitative analysis on superiority of using 3He in cryocoolers. Properties of working substance itself are a dominating factor for its application. By investigating and comparing d the expansivity of 3He to that of 4He, qualitative analysis was implemented on the advantages of 3He used in cryocoolers. Besides, the revised reverse Brayton Cycle model was introduced to describe the Stirling-type pulse tube refrigerator. Effort was made to verify the improvement of cryocooler using 3He instead of 4He ideally.(2) Introduction of the regenerator model and the revision of simulation software– REGEN. On the basis of reviewing three classical simulation software for regenerative cryocoolers, the physical model and the mathematical equations of regenerator are discussed. A graphical user interface (GUI) was developed for REGEN3.3a so that functions such as batch-cases calculation, convenient parameters input and modification, analysis, and instantaneous plotting are available. More working substances such as nitrogen, hydrogen were incorporated. This makes REGEN3.3a more powerful for the practical optimization of regenerative cryocoolers.(3) The quantitative calculation of the advantages of regenerative cryocoolers using helium-3 as working substance. Focusing on the demand of 4 K cryocoolers, the dominant operational parameters was selectedand studied, including regenerator matrix (type, shape, and porosity), regenerator diameter, cross-sectional mass flow rate, phase angle between mass and pressure waves, hot-end temperature, average pressure, cold-end pressure ratio, and frequency. A quantitative analysis on cryocoolers for both 3He and 4He was conducted.(4) Design of the 3rd stage pulse tube refrigerator pre-cooled by a G-M cryocooler based on the optimization results. In order to verify the reliability of calculated results of REGEN3.3a, the third-stage Stirling pulse tube refrigerator was designed, pre-cooled by a G-M cryocooler which controls the hot-end temperature of then target refrigerator between 20 and 40 K. The cold-end temperature is controlled by means of heat balance. The regenerator is designed to be an independent part for the sake of easy replacement.Minimization of the internal volume was also considered.