斯特林制冷机回热器热损研究

讨论了回热器的各种损失对斯特林制冷机的影响,对斯特林制冷机回热器的结构和丝网填料进行了分析,并模拟分析各种损失的影响.研究表明,回热器的结构、丝网填料对制冷机的性能有重大影响.     

20K以下温区斯特林型脉管制冷机的最新研究进展与损失机理分析

系统介绍了20 K以下温区斯特林型脉管制冷机的最新研究进展,指出了多级斯特林型脉管制冷机的应用前景与发展趋势.深入分析了多级斯特林型脉管制冷机20 K以下温区的主要损失特性,以及其难以达到更低制冷温度和更高制冷效率的内在原因,着重说明进一步提高高频回热器效率、发展高效线性压缩机技术是实现突破的关键.     

微型回热器等效直径与振荡频率的理论研究

通过对微通道中影响振荡流体的粘性损失的两个准则数的论述,得出实际的微型热声制冷机微通道回热器的等效直径、驱动膜片的振幅以及对应的辐射声功等参数的对应关系,即是:回热器通道直径或通道等效水力直径必须满足高频下的沃姆斯莱数小于5的限制;同时还必须满足在高频下的马赫数小于0.1;频率的上限也必须满足马赫数、沃姆斯莱数、回热器微孔直径以及膜振动平均位移计算前提(ka＜0.5).     

微型斯特林制冷机可靠性现状及趋势

制冷机的可靠性一直是军用微型斯特林制冷机最重要的性能指标。首先阐述了可靠性的一些基本知识,之后介绍了RICOR、Thales Cryogenics和BAE等几家公司的斯特林制冷机可靠性预测方法。同时还详细介绍了从上个世纪50年代至今国内外军用微型制冷机可靠性水平的增长情况及其发展趋势,最后介绍了一些制冷机常用的可靠性加速方法。     

斯特林制冷机混合填料回热器性能优化及试验研究

针对旋转整体式斯特林制冷机的回热器性能优化,讨论了回热器丝网填料选型的原则,分析了不同温区采用不同丝网参数的回热器模型,并利用REGEN软件对混合丝网模型进行了优化分析。通过实验数据对模拟优化的结果进行了分析和讨论,验证了混合丝网模型优化结果的正确性,为旋转整体式斯特林制冷机回热器性能优化提供依据。     

20 K低温制冷机回热器结构设计

20 K温区高效制冷是目前空间探测任务制冷的关键需求之一,斯特林/脉管复合制冷机是实现20 K温区高效制冷的重要技术手段.回热器作为复合制冷机的核心部件,其性能对制冷机的整机性能有决定性的影响.合理的设计方法和流程可以保证回热器的性能.20 K温区时回热器工质氦气和填料的物性与较高温区,如80 K温区,相比有很大区别,...     

高频脉冲管制冷机特性分析

通过相位理论分析了提高频率可以减小制冷机体积的原理,通过脉冲管制冷机内部损失影响分析了实现微型高效脉冲管制冷机的方法.研究表明:在现有的50 Hz高频下,减小制冷机体积会导致效率降低,提高运行频率,提高充气压力并采用更小水力直径的回热器填料,可以在减小体积的同时获得高效的制冷机.     

斯特林制冷机分层回热器优化设计与实验

为了提高斯特林制冷机在低温下的性能,把分层填充回热器结构应用于低温斯特林制冷机中。利用REGEN3.3对自行研制的斯特林制冷机用分层回热器进行了优化设计,并对此进行了实验研究。研究结果表明,回热器采用恰当的分层方式能大幅度提高制冷机的性能。该斯特林制冷机与优化前相比,其膨胀机效率提高了52.8%,整机效率提高了79.8%。     

斯特林制冷机污染失效研究进展

斯特林制冷机内部放气造成的失效严重影响制冷机寿命。制冷机内部放气气体会在回热器冷端及膨胀腔低温表面凝结,降低回热器的回热效率和冷头换热面传热能力,并加大制冷工质流动阻力。主要介绍了斯特林制冷机加速寿命试验和污染放气模拟数值计算方法等,提出了制冷机污染失效研究发展方向。对今后主要研究方向进行了展望。     

工质和回热器参数对斯特林制冷机性能影响的研究

针对斯特林制冷机在环保、节能、结构紧凑等方面的优点,建立了一种应用于制冷温区(即:家用和商用冰箱领域,温度在173K～283K的范围)的整体式斯特林制冷机.并对其进行了不同工质(分别采用的氮气和氦气)和四种不同的回热器结构参数(文中表2)对整机性能影响的研究.研究结果表明:整体式斯特林循环制冷机应用于制冷温区时,各种结构间存在着最优匹配.四种回热器结构中结构3的系统整机性能最优.在最优匹配的结构中,不同工质氮气和氦气的最佳充气压力和制冷性能有所不同,在结构3中以氮气和氦气为工质的最佳充气压力分别为IMPa和1.3MPa,而制冷量和COP与转速的最优关系区域分别是:氮气为500～700r/min,氦气为800～1000r/min.     

回热循环燃气轮机中回热器的动态特性研究

采用多段集中参数模型对具有分布参数特性的回热器建模，简化了由偏微分方程带来的大量计算，应用Matlab／Simlink软件作为仿真平台，采取数值方法求解，对具体回热燃气轮机中的回热器进行了仿真，结果表明，回热器时间常数较大，在回热循环燃气轮机仿真中回热器的热惯性不能忽略，而且是影响系统平衡稳定性的重要因素．     

Phase shifting method for retroreflective grating analysis

A phase shifted retroreflective grating system has been presented for measuring the derivative and contour of quasi flat specular surfaces. The system has been tested with a small indent of maximum depth less than 10 microns. The experiment shows that the system can tell the defect size, shape and polarity (indent/outdent). The method can be developed for industrial application in nondestructive testing and evaluation(NDTE).     

小型制冷系统中吸气管-毛细管回热器特性实验研究

由吸气管与毛细管热交换形成的回热器对小型制冷装置的制冷性能有着重要影响。目前,回热器主要有以下四种类型:毛细管外穿式、铝箔覆盖式、铜锡焊式、毛细管内穿式。结合理论分析,实验研究了制冷装置采用不同类型回热器时毛细管进出口温度、吸气管进出口温度、蒸发器温度以及压缩机吸排气温度对其工作性能的影响。结果表明,从换热性能上看,毛细管内穿式回热器与铜锡焊式回热器的性能基本相同,从制冷装置总体制冷性能上看,毛细管内穿式回热器优于铜锡焊式,且比毛细管外穿式及铝箔覆盖式回热器同等条件下单位容积制冷量提高17.4%,采用毛细管内穿式回热器有利于提高系统的制冷性能。     

Forced convection adsorption cycle with packed bed heat regeneration: Cycle à adsorption à convection forcée avec régénération thermique du lit fixe

The convective thermal wave is part of a patented cycle which uses heat transfer intensification to achieve both high efficiency and small size from a solid adsorption cycle. Such cycles normally suffer from low power density because of poor heat transfer through the adsorbent bed. Rather than attempting to heat the bed directly, it is possible to heat the refrigerant gas outside the bed and to circulate it through the bed in order to heat the sorbent. The high surface area of the grains leads to very effective heat transfer with only low levels of parasitic power needed for pumping. The new cycle presented here also utilises a packed bed of inert material to store heat between the adsorption and desorption phases of the cycle. The high degree of regeneration possible leads to good coefficients of performance (COPs). Thermodynamic modelling, based on measured heat transfer data, predicts a COP (for a specific carbon) of 0.90 when evaporating at 5°C and condensing at 40°C, with a generating temperature of 200°C and a modest system regenerator effectiveness of 0.8. Further improvement is possible. Experimental heat transfer measurements and cycle simulations are presented which show the potential of the concept to provide the basis of a gas-fired air conditioner in the range 10–100 kW cooling. A research project to build a 10-kW water chiller is underway. The laboratory system, which should be operational by June 1997, is described.     

The frequency dependent regenerator cold section and hot section positional reversal in a coaxial type thermoacoustic Stirling heat pump

We have constructed and tested two travelling wave thermoacoustic heat pumps using a coaxial configuration with the regenerator positioned in the annulus. We discovered a frequency dependent positional reversal of the cold section and hot section of the regenerator within the test frequency range. By decomposing the measured pressure wave within the annulus, we obtained the positive (w₊) and negative (w₋) propagating travelling waves. It has been revealed the change of frequency is accompanied by a change in magnitudes of w₊ and w₋ which is in part influenced by the presence of travelling wave attenuation through the regenerator. The resulting change of dominant travelling wave on a given end of the regenerator will then change the direction of thermoacoustic heat pumping at that end. This will alter the regenerator temperature distribution and may reverse the cold and hot sections of the regenerator. As the reversal does not require additional moving parts, merely a change in frequency, this feature in coaxial travelling wave devices has tremendous potential for applications which require both heating and cooling operation.     

Characteristics of the double inlet pulse tube

The performance of the double inlet pulse tube (DIPT) is analyzed using a linearized model that takes account of the void volume of the regenerator. The maximum rate of refrigeration obtainable with the regenerator is determined as a function of frequency and void volume. This rate can be achieved by a DIPT with infinitely large reservoir volume. Corrections resulting from a finite reservoir volume are important only at low frequency. The coefficient of performance of a DIPT with optimized rate of refrigeration is less than half of the thermodynamic maximum. The results obtained for the DIPT are compared with corresponding results for the optimized orifice pulse tube refrigerator (OPTR). The large improvements in performance obtained with the DIPT over the OPTR are due primarily to an increase in the pulse tube pressure. The maximum rate of refrigeration decreases as the temperature at the cold side decreases. This is caused primarily from the resulting decrease in cold side flow rate. At given temperature ratio, addition of the second inlet reduces the flow rate through the regenerator over a range of intermediate frequencies.     

Ion channel sensors for glutamic acid.

Coulometric biosensors using glutamate receptor (GluR) ion channel protein as a signal-amplifying sensory element that exploit the glutamate-triggered Na+ ion current through bilayer lipid membranes have been fabricated. The formation of stable planar bilayer lipid membranes was achieved by applying the folding method across a small circular aperture bored through a thin polyimide film. The multichannel type sensing membranes, formed across an aperture of ca. 120 microns diameter, contained more than 10 GluR proteins and showed L-glutamate-triggered response as a composite of individual single-channel currents. The single-channel type sensing membranes, formed across an aperture of ca. 20 microns diameter, contained a sufficiently small number of GluR proteins so that the response was observed as a series of single-channel pulse currents. Dependence of the integrated channel current on the glutamate concentration was examined. A sharp concentration dependence of up to ca. 1.5 x 10(-7) M and 3 x 10(-6) M for the multichannel and single-channel type sensors, respectively, was observed. A high selectivity for L-glutamate compared with D-glutamate for inducing the channel current was observed. A detection limit as low as ca. 3 x 10(-8) M was attained for the multichannel type sensor. This remarkable sensitivity is discussed in terms of the potential use of GluR ion channel protein for a new type of sensing system.     

Performance of vapor compression systems with compressor oil flooding and regeneration

Vapor compression refrigeration technology has seen great improvement over the last several decades in terms of cycle efficiency through a concerted effort of manufacturers, regulators, and research engineers. As the standard vapor compression systems approach practical limits, cycle modifications should be investigated to increase system efficiency and capacity. One possible means of increasing cycle efficiency is to flood the compressor with a large quantity of oil to achieve a quasi-isothermal compression process, in addition to using a regenerator to increase refrigerant subcooling.In theory, compressor flooding and regeneration can provide a significant increase in system efficiency over the standard vapor compression system. The effectiveness of compressor flooding and regeneration increases as the temperature lift of the system increases. Therefore, this technology is particularly well suited towards lower evaporating temperatures and high ambient temperatures as seen in supermarket refrigeration applications. While predicted increases in cycle efficiency are over 40% for supermarket refrigeration applications, this technology is still very beneficial for typical air-conditioning applications, for which improvements in cycle efficiency greater than 5% are predicted. It has to be noted though that the beneficial effects of compressor flooding can only be realized if a regenerator is used to exchange heat between the refrigerant vapor exiting the evaporator and the liquid exiting the condenser.     

A small helium-3 pulse-tube refrigerator

A new three-stage pulse-tube refrigerator (PTR) is developed by scaling down a previous PTR by 50%. The new system is small in size and weight, capable of operating using little input power, and uses a small amount of working gas and regenerator material. In addition to that the system is flexible and convenient for modifications. The volume of the low-temperature part of the new PTR (pulse tubes + regenerator) is as small as 0.28 l. With ³He as a working fluid a no-load temperature of 1.73 K is reached and a cooling power of 124 mW at 4.2 K is realized.     

PARTICLES AND POWER GENERATION BY FUSION REACTIONS*

Particles, particle generation, and particle control have become critically important to power generation by fusion reactions. Generation of power by energy released from fusion reactions in a gaseous plasma contained and heated in a magnetic “bottle” has provided research problems for two generations of physicists and engineers. One of the problems has been that of fueling the reactor through the magnetic containment field. Relatively large (micrometers to millimeters diameter) particles of frozen fuel material traveling at moderate speeds (a few kilometers per second) may provide a solution to the fueling problem.

In the inertial confinement fusion program, particle generation and control have also played an important role. Some of the fuel containing spheres have been glass and polymer shells which have started their existence as particles tens to hundreds of microns in diameter. The production of the particles, their control, and the detailed characterization of the particles have all presented some very difficult but interesting problems and some very interesting solutions to the problems have been developed.

It is highly likely that for any fusion reactor operating on a continuous basis, generation and control of fuel particles will play an extremely Important role.