Study On Pulse Tube Refrigerator And Refrigeration Performance With Helium & Hydrogen Mixture

Without moving parts at the cold head, pulse tube refrigerators have considerable advantages over other types of refrigerators in terms of reliability, lifetime, vibration, and cost. Furthermore, pulse tube refrigerators are suitable to carry out experimental study on refrigeration performance with gas mixture. Great progress has been made on improving COP of pulse tube refrigeration with gas mixture. The works done in this thesis are as follow:1. Firstly, the theoretical analysis on the regenerator performance and the thermodynamic performance prediction are presented in Chapter 2. During the process of experimental study, we found that magnetic material, Er3Ni, has the ability to adsorb hydrogen fraction in the mixture. The theoretical analysis on this phenomenon shows that the specific heat of this magnetic material increased very much after adsorbing hydrogen, which is the instinct mechanism to improve the performance of refrigeration.2. Based on the improvement of the single-stage pulse tube refrigerator, two parallel-placed needle valves with opposite flow direction referred as two-valved configuration instead of traditional single-vlaved configuration as double-inlet are introduced in experiments to eliminate the DC flow, which proves to be a successful way to improve the performance in this system. The lowest cooling temperature 22.4K and the cooling power 5.65W at 80K has been reached. This results show that the single-stage pulse tube could be fit for the experiment with mixture. And the optimized operating parameters of valve timing and frequency are established.3. When the refrigeration temperature reaches the liquefaction point of hydrogen, the hydrogen will be liquefied in pulse tube refrigeration system used helium and hydrogen mixture. Experiments using a number of helium and hydrogen mixtures in a G-M type two-stage pulse tube refrigerator have been carried out. The experimental results show that both COP and cooling power of helium-hydrogen mixture can be increased to some extent at hydrogen vapor-liquid transitiontemperature when the pulse tube refrigerator works with hydrogen fraction from 7% to 70%. The excess of cooling power and COP is 30.6% and 45.8% respectively at 20K when hydrogen fraction is 70%.