Oxford Pulse Tube Incorporating COaxial Regenerator (OPTICOR)

脉管冷却器是一种小型低温冰箱，可以为红外探测器、超导设备和国土安全系统中的伽马射线探测等电子设备提供冷却。单级充氦脉冲管可以获得低至10 K的温度，但更典型的是30 K，因为更低的温度将使用多级方法。脉冲管可以被认为是一个斯特林循环冷却器，它依赖于一个气柱作为置换器；http://en.wikipedia.org/wiki/Pulse_tube_refrigerator。往复活塞（压缩机）驱动流体通过再生器进入管（“脉冲管”）；热量在压缩机和蓄热器的界面处被排出，热量在蓄热器的另一端被吸收。将脉冲管通过孔板或惰性管连接到缓冲体上，可以大大提高脉冲管的性能。由于这可以非常庞大，并有有限的可能性控制，有一个优势，在暖端膨胀器（实际上是一个振荡活塞）。这可以设计为响应由压缩机产生的压力变化，相位滞后和振幅由系统动力学决定。脉动流可以由具有高压气体供应的阀门系统产生，但由于阀门的操作，这种方法只能在低频（几赫兹）下运行。在最近的应用中，使用的往复活塞可以是机械驱动的，也可以是电磁驱动的，这些活塞的工作频率通常在30到100赫兹之间。由于气体需要无油和其他污染物（以避免再生器和冷端热交换器的污垢），那么使用“牛津式”压缩机是明智的。牛津风格的压缩机是30多年前为斯特林循环冷却器开发的，其主要特点是：*弹簧悬挂系统，径向刚性，提供气缸中活塞的精确线性运动，*活塞和气缸之间的小径向间隙（约8微米），因此泄漏可以忽略不计，没有接触（所以没有磨损）。电磁驱动器（最初类似于扬声器的音圈）。最近，牛津大学研制出了带有活动磁铁的压缩机。在EP/E036899/1“开发用于电子冷却的微型制冷系统”中，一个关键步骤是压缩机的设计，该压缩机使用移动磁铁和固定驱动线圈。这导致了一个更便宜，低移动质量的系统，可以在高频下工作-这不仅增加了比输出，而且还导致了更低的密封泄漏损失和驱动线圈的电阻损耗。本项目将要进行的工作将采用一种由制冷压缩机发展而来的设计。最简单的脉冲管具有线性配置（压缩机，热端热交换器，蓄热器，冷端热交换器，“脉冲管”体积）。但这些有冷端是在中间的缺点，所以一个“U”管的安排是使用。然而，“U”型弯道带来的流动损失可以通过新型径向流和同心管布置来消除。这将与热端膨胀器和单个动态平衡器相结合，以提供脉冲管的完美平衡。斯特林循环冷却器，一般来说，有更好的性能比脉冲管，但脉冲管更简单，更适合于更高频率的操作。最新的动磁压缩机电机，可实现高频运行。此外，高频运行可以降低压缩机间隙密封泄漏损失，因为这种功率损失和欧姆功率损失基本上与频率无关。因此，在高频（比如90赫兹）下工作的脉冲管将比在较低频率下更有效，并且比斯特林循环冷却器更紧凑。

Pulse tube coolers are small low temperature refrigerators that can provide cooling for electronic devices such as infra-red detectors, superconducting devices and gamma ray detection in homeland security systems. Temperatures as low as 10 K can be obtained with a single stage helium-filled pulse tube but 30 K would be more typical, as lower temperatures would use a multi-stage approach.Pulse tubes can be thought of as a Stirling cycle cooler that relies on a gas column to act as a displacer; http://en.wikipedia.org/wiki/Pulse_tube_refrigerator. A reciprocating piston (the compressor) drives a flow through a regenerator into a tube (the 'pulse tube'); heat is rejected at the interface between the compressor and the regenerator, and heat is absorbed at the other end of the regenerator. The performance of the pulse tube can be improved greatly by connecting the pulse tube to a buffer volume through an orifice or inertance tube. As this can very bulky and have limited possibilities for control, there are advantages in having a warm-end expander (in effect an oscillating piston). This can be designed to respond to the pressure variation generated by the compressor, with a phase lag and amplitude determined by the system dynamics. The pulsating flow can be produced by a system of valves with a high pressure gas supply, but this approach can only operate at low frequencies (a few Hz) due to the operation of the valves. In most recent applications a reciprocating piston is used which can be either mechanically or electromagnetically driven, and these typically operate at between 30 and 100 Hz. As the gas needs to be free of oil and other contaminants (to avoid fouling of the regenerator and cold-end heat exchanger), then it is sensible to use an 'Oxford-style' compressor. The Oxford-style compressor was developed over 30 years ago for a Stirling cycle cooler and its key features are:* a spring suspension system that is radially stiff to provide accurate linear motion of a piston in a cylinder,* a small radial clearance between the piston and cylinder (of order 8 micron) so there is negligible leakage and no contact (so no wear).* an electromagnetic drive (originally like the voice-coil of a loudspeaker).More recently compressors with moving magnets have been developed at Oxford. A crucial step was the design of a compressor in EP/E036899/1 'Development of a Miniature Refrigeration System for Electronics Cooling' that used a moving magnet with a stationary drive coil. This leads to a cheaper, low moving mass system that can operate at high frequency - this not only increases the specific output, but also leads to lower seal leakage losses and resistive losses in the drive coils. The work to be undertaken in this project will use a design that has been developed from the refrigeration compressor.The simplest pulse tubes have a linear configuration (compressor, hot-end heat exchanger, regenerator, cold-end heat exchanger, 'pulse tube' volume). But these have the disadvantage of the cold-end being in the middle so a 'U' tube arrangement is used. However, there are flow losses associated with the 'U' bend that can be eliminated by a novel radial flow and concentric tube arrangement. This will be combined with a warm-end expander, and a single dynamic balancer to provide perfect balance of the pulse tube.Stirling cycle coolers, in general, have a better performance than pulse tubes, but pulse tubes are simpler and better suited to higher frequency operation. The latest moving magnet compressor motor is capable of high frequency operation. Furthermore, high frequency operation leads to lower compressor clearance seal leakage losses, since this power loss and the Ohmic power loss are essentially independent of frequency. Therefore a pulse tube operating at high frequency (say 90 Hz) will be more efficient than at lower frequencies and be more compact than a Stirling cycle cooler.