| Unlike the Stirling or Gifford-McMahon refrigerators, the pulse tube cooler (PTC) has no moving parts at the cold end. The lack of cold moving parts has allowed it to solve some of the problems associated with cryocoolers in many different applications, such as vibration and reliability. In the past ten years, great progress has been made on the development of the PTC. However, its efficiency is still lower than that of the traditional cryocoolers, which is one of the barriers to further development of this refrigeration method. To insure a commercial success of the PTC by replacement of conventional GM- or Stirling-coolers in most of their applications, it is of major importance to optimize the PTC and to demonstrate performances and efficiencies as close as possible to those known for the conventional cryocoolers. After a detailed review on the recent development of the pulse tube cooler, the present work focuses on the following objects:1) DC flow and its suppressionThe DC flow will appear for the introduction of the double-inlet in a pulse tube cooler. It greatly deteriorates the cooling capacity as well as leads to temperature instability under high heat load of the cooler. From the fluid network theory, the root of the DC flow in a double-inlet pulse tube cooler is theoretically investigated. Some suppression ways are briefly described.2) Experimental investigation on DC flow suppression and refrigeration characteristicsBased on the detailed analysis and comparisons for all kinds of the suppression methods, two parallel-placed needle valves with opposite flow direction referred as two-valved configuration instead of traditional single-valved configuration as double-inlet are introduced in experiments to eliminate the DC flow and are proved to be a successful way. Driven by RW2 and CP4000, 18.4K and 14.7K no load temperature has been reached respectively and11. 5W and 29. 5W cooling-power at 30K could be obtained. Meanwhile, the effect of the regenerator matrix on the performance of the cooler under different operation modes has been extensively investigated.3) Influence of Regenerator Flow Resistance on Stability of the PTCThe feasibility of an increased regenerator flow resistance to suppress the DC flow is experimentally and theoretically investigated. Results show that an increased flow resistance of the regenerator leads to a reduction and stabilization of the disturbing DC-flow in the cooler under high heat load.4) Experimental Investigation on pulse tube refrigeration with He-H2 mixtureThe excellent heat transfer and flow characteristics of the hydrogen may contribute to a better performance of the PTC. Based on effect of He-Ha mixtures on the regenerator flow resistance, cold heat-exchanger performance, cooling capacity and efficiency (COP) at 3 OK with He-H2 mixtures is experimentally studied. The experimental results show, properly rationing He-H2 mixtures the cooling power and COP could be improved by several percent at a temperature near 30K. Besides, the effect of the He-Hi mixture on the performance of a two-stage pulse tube is also undertaken in order to reveal the operation mechanism of the gas mixture on the cooler. Experimental results in a two- stage pulse tube cooler show that the performance of the PTC could be greatly improved at 3 OK with He-Hj mixture and its positive effect is much larger than that of the single-stage cooler.5) PULSE TUBE NITROGEN LIQUEFIERA small-scale cryogenic liquid is widely used in a number of applications. A high-performance single-stage G-M pulse tube cooler was rebuilt into a nitrogen liquefier. The liquefaction rate, cool-down and warm-up characteristics of the liquefier operating under different modes were experimentally investigated.
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