Investigation On Single-Stage Ge-Type Pulse Tube Cooler With He-H₂ Mixtures

The history and recent development of pulse tube cryocooler are introduced. After the performance optimization of single-stage pulse tube cryocooler with pure helium, experiments about gas mixture -helium and hydrogen in the same pulse tube cryocooler are carried out, as follows:1. The DC flow appears when the pulse tube cryocooler works as double-inlet mode, which results in the deterioration of cool capacity and temperature instability. It's pretty meaningful for us to look for an efficient way to adjust DC flow. Two kinds of theories about DC flow are introduced here.2. The theoretical analysis on how He-Hi mixture to influence the performance of pulse tube cryocooler is done. The specific heat of Er₃Ni increases a lot after adsorbing hydrogen, which is one of possible reasons to improve the performance of pulse tube cryocooler.3. Two parallel-placed needle valves with opposite flow direction referred as two-valved configuration instead of traditional single-valved configuration as double-inlet are adopted in experiments to control DC flow and are proved to be a successful way to decrease the refrigeration temperature of a single-stage pulse tube below 20K. After the optimization of such parameters as orifice valve, two-valved double-inlet, frequency and so on, with the input power 4KW, no load temperature 15.1K has been reached, and the cooling power 30W at 40.6K could be obtained. It was the first time in our country to reach the temperature below 20K, which did great help to the experiment of two-stage split pulse tube cryocooler.4. The performance of single-stage pulse tube cryocooler with He-H₂ mixtures is experimentally studied. The results show that the performance of pulse tube cryocooler is improved while using He-H₂ mixtures as working fluids. The cooling power and COP increase by 3.6% and 4.7% respectively at 32.9K when hydrogen fraction is 10%. However, the results in a two- stage pulse tube cooler show that the performance could be greatly improved at 30K with He-H₂ mixture and its positive effect is much larger than that of the single-stage cooler.