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PULSE TUBE CRYOCOOLERS


In a time span of about 15 years the orifice pulse tube refrigerator and its variations have become the most efficient of all cryocoolers for a given size, even exceeding that of Stirling refrigerators in some cases for temperatures between about 60 and 120 K. Efficiencies of 24% of Carnot have been achieved at 80 K. They have no moving parts at the cold end, and for large systems can be driven with thermoacoustic drivers that also have no moving parts. The lack of moving parts in the cold end gives them the advantage of less vibration, higher reliability, and lower cost than all other cryocoolers, except for Joule-Thomson refrigerators, which also have no cold moving parts. However, the Joule-Thomson refrigerators currently have lower efficiencies than pulse tube refrigerators, at least for temperatures below about 100 K. The use of flexure-bearing linear-resonant compressors to drive the pulse tube refrigerator results in lifetimes of at least three years and possibly even ten years or more. As a result of their high efficiency and high reliability they are being designed into many future space missions. Commercial and industrial applications of pulse tube refrigerators are slower to develop because of the need to reduce cost while maintaining high reliability. Nevertheless, at least four companies now sell pulse tube refrigerators for commercial applications. In most cases the compressors are Gifford-McMahon type compressors, and rotary valves are used to switch between the high-and low-pressure lines. Thus, these commercial systems do not have the high efficiency of the space systems where valveless compressors are used. In a few cases Stirling-type pulse tube refrigerators are being sold commercially for high efficiency applications. So far most of the development of pulse tube refrigerators has been for rather small systems with less than a few watts of cooling at 80 K or lower. Recently there has been much more interest in pulse tube refrigerators for industrial applications in gas liquefaction and in power applications of superconductors. In many of these cases refrigeration powers of kilowatts or even tens of kilowatts are required. These are intermediate-size applications and are smaller than the large air and gas liquefaction plants where megawatts of refrigeration power are needed. At present there is not a clear upper limit to the useful size of pulse tube refrigerators. There are three disadvantages of pulse tube refrigerators compared with some other cryocoolers. One is the sensitivity to gravitationally induced convection in the pulse tube, even during operation, whenever the pulse tube diameter is larger than about 10 mm. In the off state, convection can occur in even smaller pulse tubes. Thus, pulse tubes need to be operated with the cold end down except in zero gravity. This convection can limit some terrestrial applications where the refrigerator is to be moved about in various orientations. The second disadvantage is the extra space required for the pulse tube. Most military tactical applications for cooling infrared sensors have very well defined envelopes into which the cooler cold finger must fit. These specifications were developed many years ago when the Joule-Thomson and Stirling refrigerators were the only options. At present it is difficult to achieve the same refrigeration power in a pulse tube refrigerator with the same diameter cold finger as that of a Stirling refrigerator. The third disadvantage is that the pulse tube refrigerator is a regenerative system that utilizes oscillating pressures. Such pressure oscillations can cause the envelope of the cold finger to move due to stretching. Such vibrations are about an order of magnitude less than those generated with a moving displaces Nevertheless, for some applications that are very vibration sensitive, even that small vibration may be too large. An example is certain space telescope applications, where turbo-Brayton cryocoolers must be used. Th......

【作者名称】: RAY RADEBAUGH
【作者单位】: Physical and Chemical Properties Division National Institute of Standards and Technology Boulder, Colorado 80303, USA
【关 键 词】: PULSE TUBE CRYOCOOLERS
【会议名称】: NATO Advanced Study Institute on Low- Temperature and Cryogenic Refrigeration Jun 23-Jul 5, 2002 Izmir, Turkey
【期刊论文数据库】: [DBS_Articles_01]
【期刊论文编号】: 101,723,198
【摘要长度】: 4,000
【会议地点】: Izmir(TR)
【会议组织】: Physical and Chemical Properties Division National Institute of Standards and Technology Boulder, Colorado 80303, USA
【会议时间】: 2002
【上篇论文】: 外文会议 - EXPERIMENTS ON DEPOSITION OF NANO-STRUCTURED ALUMINA-TITANIA COATINGS BY NORMAL DETONATION WAVES
【下篇论文】: 外文会议 - FINITE ELEMENT MODELS FOR LINEAR ELECTROELASTIC DYNAMICS

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