脉冲管制冷机新进展直流现象

简述了脉冲管制冷机研究现状和存在的问题 ,介绍了低温中心建立的脉冲管制冷机动态参数实验系统。通过对一典型脉冲管制冷机的动态参数的实验数据测量 ,分析了动态压力和质量流量之间的振幅和相位关系 ,首次在实验中发现了存在于脉冲管制冷机内部的直流现象 (DC-Flow)。指出该直流分量是脉冲管制冷机的一种损失 ,揭示了多路旁通进气方式可减小直流损失 ,提高脉冲管制冷机的效率。并从理论上分析了产生直流现象的根本原因 ,给出了直流分量的具体数值和大小。     

脉冲管制冷机第三种直流敏感性实验研究

直流是脉冲管制冷机中重要的机理性问题。本文介绍了脉冲管制冷机第三种直流效应的最新理论研究结果,深入分析了第三种直流效应的产生机理和影响因素。结合制冷机系统的流动和热力学非对称性,通过实验研究了脉冲管制冷机第三种直流效应对几何结构、冷头温度、频率、压力等参数的敏感性。     

脉冲管制冷机机理研究新进展

脉冲管制冷机是近年来空间微型机械式制冷机研究的前沿课题，作者通过精确的实验测量和分析，首次发现了双向进气型脉中管制冷机存在直流分量，该直流分量是脉冲管制冷机的一种损失，并指出多种旁能流程可以减小直汉损失，提高脉冲和制冷机的制冷性能。     

一种新结构U型脉冲管制冷机

在U型脉冲管制冷机结构基础上,研制了一台带有一个蓄冷器和两个相同脉管的新结构U型脉冲管制冷机,并进行了实验研究和分析。制冷机采用惯性管调相,在压缩机输入电功率80 W,运行频率52 Hz下,获得了120 K@6 W的制冷量。重点对两种惯性管调相方法进行研究和分析,得出了对新结构U型脉冲管制冷机调相有益的结论,并对惯性管调相过程中产生的直流现象进行了验证分析。     

热端温度对高频微型非金属脉冲管制冷机性能影响的实验研究

热端温度对小制冷量的微型脉冲管制冷机的性能有着较为显著的影响.本文针对所设计的两台高频微型同轴非金属脉冲管制冷机,实验研究了制冷机冷端无负荷最低温度和轴向导热损失随热端温度的变化规律.实验对其影响幅度进行了量化分析,并发现通过降低热端温度的方法可以对样机制冷机性能起到很好的促进作用.     

单级高频脉冲管制冷机研究

采用单级高频脉冲管制冷机获得低于30 K的制冷温度是脉冲管应用的一个新方向.本文介绍了一套获得了26 K最低制冷温度的单级高频脉冲管制冷机,这是无多路旁通的单级高频脉冲管制冷机获得的最低温度.实验表明,即使对于惯性管作为主要调相结构的高频情况,双向进气方案在进一步调相和降低温度方面仍有很大作用.该工作为单级高频脉冲管制冷机在30～40 K温区的应用奠定了基础.该实验结果和模拟分析结果基本相符.通过和二级制冷机的比较说明了单级制冷机的优势,即较大的制冷量斜率.     

单级高频脉冲管制冷机耦合特性研究

线性压缩机、回热器、脉冲管以及惯性管的耦合特性对高频脉冲管制冷机的整机性能有很大的影响.本文对高频脉冲管制冷机的各部件及整机的耦合特性进行了理论分析和实验研究.研究表明,当脉冲管制冷机运行频率越接近压缩机的谐振频率时,脉冲管制冷机的效率会越高,压缩机效率受冷头温度影响就较小;而改变惯性管的尺寸是改善脉冲管制冷机耦合特性的最有效的手段.     

改进冷端换热器的大功率脉冲管制冷机

依据热力学非对称理论对脉冲管制冷机冷端的热力学过程进行分析 ,对脉冲管制冷机制冷功率的提高提出了改进方案 ,搭建了单级低频大功率脉冲管制冷机的实验台 ,在实验中首次采用新型的填料烧结型换热器作为脉冲管的冷头 ,对这种换热器的效率在不同实验条件下进行了计算 ,并通过实验验证了这种新型换热器在脉冲管制冷机中应用的可行性。实验表明 :改进冷端换热器是提高脉冲管制冷机制冷效率的关键问题。在使用烧结换热器的单级脉冲管制冷机实验台上 ,采用输出功率 3k W的压缩机在 80 K时得到了 35W的制冷量 ,在效率上属国内领先水平。     

空间预冷型J-T节流制冷机热力学流程优化研究

预冷型J-T节流制冷机是深空探测普遍采用的制冷机,本文针对本实验室研制的三级脉冲管预冷J-T节流循环的复合式制冷机,对液氦温区J-T节流制冷机进行了系统的热力学分析。通过对理想节流循环的T—s图的分析发现,预冷温度和节流前氦气状态参数是影响节流制冷机性能的关键因素。通过合理选择预冷温度和节流前氦气的温度和压力,可以提高节流循环的制冷量和整机效率。在理论分析基础上,开展了相关的实验研究,实验结果验证了理论分析的正确性。     

超高频脉冲管的气体微团位移分析

本文通过建立绝热模型,理论上分析了小孔型脉冲管制冷机内部气体微团的运动过程,定性地推导出了小孔型脉冲管制冷机冷端的相位差,以及冷端和热端的最大位移量。同时分析了频率、温度和小孔阻力对相位角和最大位移量的影响以及超高频下脉冲管制冷机冷头温度比一般高频制冷机高的原因。     

Experimental investigation of a thermoacoustic-Stirling refrigerator driven by a thermoacoustic-Stirling heat engine

In this paper, a thermally-driven thermoacoustic refrigerator system without any moving part is reported. This refrigeration system consists of a thermoacoustic-Stirling heat engine and a thermoacoustic-Stirling refrigerator; that is, the former is the driving source for the latter. Both the subsystems are designed to operate on traveling-wave mode. In the experiment, it was found that the DC-flows had significant negative effect on the heat engine and the refrigerator. To suppress these DC-flows, two flexible membranes were inserted into the two subsystems and worked very well. Then extensive experiments were made to test the influence of different parameters on refrigeration performance of the whole system. The system has so far achieved a no-load temperature of -65 degrees C, a cooling capacity of about 270 W at -20 degrees C and 405 W at 0 degrees C; in fact, the result showed a good prospect of the refrigeration system in room-temperature cooling such as food refrigeration and air-conditioning.     

一种无磁低振微型同轴脉冲管制冷机

脉冲管制冷机与超导量子干涉仪耦合进行微弱磁场测量是脉冲管制冷机的一个主要应用方向。本文系统分析了脉冲管制冷机的主要干扰源并给出其相应的解决办法,并据此设计制造了一台无磁低振微型同轴脉冲管制冷机。以实现同轴脉冲管制冷机的低振动、低电磁干扰化,并最终实现利用脉冲管制冷机有效冷却包括高温超导量子干涉仪在内的对电磁干扰要求极严格的高温超导器件。     

30m~2槽式太阳能集热器性能模拟研究

本文针对30 m~2槽式太阳能集热试验装置,对太阳能集热器的性能进行了模拟。分析了太阳能集热器光热转化过程,建立了太阳能能量转换与传递模型,并开发了模拟计算程序,研究了集热器关键结构参数和运行参数对集热性能的影响规律。具体考察了太阳辐照强度、工质流量、环境风速、吸热管管径等对集热效率的影响。结果表明:太阳能集热器的集热效率随太阳辐照强度的增加而增大,随工质流量的增加而增大,存在最佳的吸热管管径使得集热效率最大。研究结果将为太阳能集热器的设计提供参考依据。     

Comparisons of frequency selectivity in simultaneous and forward masking for subjects with unilateral cochlear impairments

Two experiments are described in which frequency selectivity was estimated, in simultaneous and forward masking, for each ear of subjects with moderate (25-60 dB HL) unilateral cochlear hearing losses. In both experiments, the signal level was fixed for a given ear and type of masking (simultaneous or forward), and the masker level was varied to determine threshold, using an adaptive, two-alternative forced-choice procedure. In experiment I, the masker was a noise with a spectral notch centered at the signal frequency (either 1.0 or 1.5 kHz); threshold was determined as a function of notch width. Signal levels were chosen so that the noise level required at threshold for a notch width of zero was similar for the normal and impaired ear of each subject in both simultaneous and forward masking. The function relating threshold to notch width had a steeper slope for the normal ear than for the impaired ear of each subject. For the normal ears, these functions were steeper in forward masking than in simultaneous masking. This difference was interpreted as resulting from suppression. For the impaired ears, significant differences in the same direction were observed for three of the five subjects, but the differences were smaller. In experiment II, psychophysical tuning curves (PTCs) were determined in the presence of a fixed notched noise centered at the signal frequency (1.0 kHz). For the normal ears, the PTCs were sharper in forward masking than in simultaneous masking. For the impaired ears, the PTCs were similar in simultaneous and forward masking, but those in forward masking tended to be sharper at masker frequencies far removed from the signal frequency. Overall, the results suggest that suppression is reduced, but not completely absent in cases of moderate cochlear hearing loss.     

ANALYSIS OF THE PRESSURE EFFECT ON THE CRYSTALLIZATION KINETICS OF POLYPROPYLENE: DILATOMETRIC MEASUREMENTS AND THERMAL GRADIENT MODELING

Dilatometric measurements in isobaric cooling mode were performed to study the pressure effects on the crystallization kinetics of polypropylene (PP) up to 100 MPa. The experimental specific volume curves were analyzed by taking into account the thermal gradient that appears in the sample even for relatively low cooling rates. The Tait equation was used to describe the specific volume of the purely amorphous phase, and linear variations of the purely crystalline phase specific volume are considered. The relative crystal linity was modeled using the Nakamura equation, which is relevant for non-constant cooling rates. Considering an Avrami exponent of 3, the Nakamura rate constant was obtained first at atmospheric pressure and then generalized for higher pressures considering the equilibrium melting temperature variation. The obtained intrinsic specific volume was validated by computing the thermal gradient in the sample and comparing the calculated average specific volume to the experimental one.     

Temporal effects in masking and their influence on psychophysical tuning curves

Psychophysical tuning curves (PTCs) were obtained in simultaneous and forward masking for a 20-ms, 1000-Hz signal presented at 10 dB SL. The signal was presented at the beginning of, at the temporal center of, at the end of, or immediately following a 400-ms masker. The first experiment was done in quiet; the second experiment was done in the presence of two bands of noise on either side of 1000 Hz. The results were similar in quiet and in noise. In simultaneous masking, the PTCs were broadest for the signal at masker onset, and generally sharpest for the signal at temporal center; the differences were largest on the high-frequency side. In most cases, there was virtually no difference in Q10 between the forward-masking PTC and the simultaneous-masking PTC with the signal temporally centered, although the high-frequency slope was always steeper in forward masking. These results indicate that, at least for brief signals, frequency selectivity measured with simultaneous-masking PTCs and the degree of sharpening revealed in forward-masking PTCs depend upon the temporal position of the signal within the simultaneous masker.     

Psychophysical estimates of level-dependent best-frequency shifts in the apical region of the human basilar membrane

It is now undisputed that the best frequency (BF) of basal basilar-membrane (BM) sites shifts downwards as the stimulus level increases. The direction of the shift for apical sites is, by contrast, less well established. Auditory nerve studies suggest that the BF shifts in opposite directions for apical and basal BM sites with increasing stimulus level. This study attempts to determine if this is the case in humans. Psychophysical tuning curves (PTCs) were measured using forward masking for probe frequencies of 125, 250, 500, and 6000 Hz. The level of a masker tone required to just mask a fixed low-level probe tone was measured for different masker-probe time intervals. The duration of the intervals was adjusted as necessary to obtain PTCs for the widest possible range of masker levels. The BF was identified from function fits to the measured PTCs and it almost always decreased with increasing level. This result is inconsistent with most auditory-nerve observations obtained from other mammals. Several explanations are discussed, including that it may be erroneous to assume that low-frequency PTCs reflect the tuning of apical BM sites exclusively and that the inherent frequency response of the inner hair cell may account for the discrepancy.     

蓄冷器内部气体微团的热力过程分析

从脉冲管制冷机中的核心部件蓄冷器入手,考虑不同情况下气体微团的具体热力过程,循序渐进的分析等温和有温度梯度情况下蓄冷器内部不同相位关系的气体微团的压缩和膨胀过程,得出蓄冷器的泵热效应;并通过一定程度的近似假设,给出蓄冷器内部气体微团的理论制冷量的近似公式,得到影响脉冲管制冷机理论制冷量的关键因素。     

减少光学元件亚表面缺陷的方法研究

针对强激光光学元件的应用要求,对光学材料在研磨和抛光过程中形成的亚表面缺陷进行了分析,并借鉴小工具数控抛光和Marangoni界面效应,提出采用数控化学刻蚀技术来实现光学表面面形和微结构形貌的高准确度加工.通过实验对亚表面缺陷的分布位置和特性进行了分析,实验验证了在静止和移动条件下Marangoni界面效应的存在.对材料的定量去除进行了实验,提出了亚表面缺陷的去除方法.