导流结构对脉管制冷机性能影响的研究

提出了一种用于脉管制冷机的导流方法:在射流正前方引入挡片,消除射流对导流丝网的冲击作用,减小丝网对气体进行导流所需的阻力和产生的流动损失,从而提高制冷机性能。通过CFD模拟对挡片的作用机理进行了研究,表明导流挡片可以有效抑制脉管中涡流的出现,减少冷热气流的混合。进一步的实验研究验证了导流结构的积极作用,为脉管制冷机导流结构的设计提供了一种新的参考方式。     

热声发动机热缓冲管损失的实验研究

热缓冲管是热声发动机的关键部件之一,位于高温换热器和次室温换热器之间,理想情况下可避免在高温换热器附近往复运动的气体接触室温环境,造成热量损失。不过由于换热器流道的特殊结构,使热缓冲管两端会产生射流等现象,带来流动紊乱、热量损失等问题。本文设计并搭建了研究热缓冲管损失的实验平台,主要考查在热缓冲管两端分别添加不同层流化丝网对系统性能的影响。实验结果表明,未添加层流化丝网会使热量损失急剧增大,热声效率大幅下降;而过多添加层流化丝网会使阻力损失增大,同样降低热声效率;当两端分别添加3片层流化丝网时,所需加热量最少,热声转换效率最高。     

脉管制冷机层叠丝网填充回热器导热特性数值分析及优化

回热器为回热式低温制冷装置的关键部件,其性能直接影响到整机性能。对层叠丝网回热器的轴向导热损失进行了理论分析和数学建模,采用单一及不同目数金属丝网混填了单级脉管回热器,基于80K,50Hz的工况下,理论分析了不同目数层叠丝网混合填充时,配比组合参数对回热器轴向导热损失的影响。结果显示:层叠丝网所引起的轴向导热损失为回热器轴向导热损失的主要形式。研究表明,恰当的混填形式可以提高回热器性能。在此基础上提出了层叠丝网回热器填充配比优化方法。     

脉管制冷机回热器流动阻力系数测量和模拟研究

针对脉管制冷机CFD模拟时,回热器的粘性阻力系数和惯性阻力系数的选取至关重要。为研究回热器的粘性阻力系数和惯性阻力系数,搭建了实验测量平台,实验研究了粘性阻力系数和惯性阻力系数与制冷温度、充气压力和丝网目数的变化关系,利用所测得的粘性阻力系数和惯性阻力系数作为输入参数进行仿真计算,建立了回热器二维数值仿真模型。结果表明:粘性阻力系数随充气压力和制冷温度的增加而减小,随丝网目数的增加而变大;惯性阻力系数随充气压力和丝网目数的增加而减小,随制冷温度的增加而变大。     

脉管制冷机室温换热器强化辐射换热研究

脉管制冷机是目前最常用的高效小型低温制冷机之一。相对于主动散热，采用被动散热的室温换热器具有可靠性高与使用便捷等优点。辐射换热强化是提高室温换热器性能的一种方法。本文选取了一种小型脉管制冷机，研究在其主肋片换热器表面涂覆高发射率涂层对整机散热性能的影响。在自然对流条件下实验，对比涂覆高发射率涂层前后制冷机的运行温度。结果表明，喷涂高发射率涂层后，制冷机电机温度基本不变，冷指下方的辅助肋片换热器温度下降了约1～2℃，而主肋片换热器温度下降了约3～4℃。通过理论推算得，改变发射率前后主肋片换热器的辐射换热占比从8.6%提升至29.7%。结果证明强化辐射换热降低了制冷机室温换热器的工作温度，是一种改善小型制冷机散热的可行方法。     

双向进气脉管制冷过程的实验研究

一、本文的目的 脉管制冷法发明于六十年代,称为基本脉管。七十年代末出现了改进型,称为小孔脉管,后来又经不断改进,制冷温度达到实用要求,从而把这种新颖的制冷方法推进到实甩化的研究阶段,引起高技术和军工部门的很大兴趣。1989年西安交大热工教研室脉管研究组进一步提出了双向进气脉管制冷方案,并获得专利。试验表明,双向进气小孔脉管比之当今国内外常规的单向进气小孔脉管可以达到更低的制冷温度,而且方法简便可行。然而,脉管制冷内部过程复杂,详尽的理论和试验工作尚很缺乏。本文的目的是由实验探索阀门开度、脉动频率、充气压力等对脉管内部压力波形的调相调幅作用。因为文献[1]已分析表明,脉管内部动态参数幅值和相位的变化对其制冷过程有着直接的影响。     

脉管制冷机中复杂DC流的影响机理

为了进一步研究系统非对称性对DC流现象和脉管制冷机中直流分量对制冷性能的影响,采用数值模拟方法,引入了描述系统阻力元件的非对称性的几何参数—不对称率,详细研究了系统不对称性对脉管制冷机DC流、制冷性能的影响规律,并且在分析和比较不同流向和幅值大小的条件下,详细研究了DC流的流向和幅值对脉管制冷机的关键部件脉管和回热器的壁面温度分布特性的影响规律。数值验证了将壁面温度分布作为描述脉管制冷机中DC流的流动方向和大小的判定准则的正确性,且回热器和脉管的壁面温度分布的非线性越强烈,预示着系统内DC流的流向和幅值越大,对制冷性能的影响越剧烈,并间接指出系统热力不对称性是造成DC流的主要原因,为进一步发现和抑制直流现象提供了可靠的理论依据。     

惯性管对热声驱动脉管制冷机性能的影响

为了考察惯性管对热声驱动脉管制冷性能的影响,利用驻波型热声驱动脉管制冷实验装置,开展了惯性管结构参数对系统性能影响的实验研究.实验中所采用的惯性管由直径分别为2 mm和4 mm的两段铜管串联而成,重点研究2 mm直径管段的长度对压比和制冷温度的影响.通过实验优化,当惯性管结构参数为内径2 mm的铜管长度2.5 m,内径4 mm的铜管3 m长时,在加热功率1.8 kW条件下,脉管制冷机的无负荷制冷温度达到63.0 K.     

大冷量脉管制冷机回热器温度不均匀性的实验研究

本文对一台设计目标为液氮温区千瓦级冷量的脉管制冷机展开了实验研究。在回热器中填充纯不锈钢丝网时,观测到了巨大的温度不均匀现象,当入口压比为1.25时回热器中部最大温差高达163.3 K,并且回热器中的温度场难以发展稳定。在向回热器中填充了一定数量的紫铜丝网后,回热器内的温度不均匀现象得到了有效的抑制,制冷机的制冷量也有了明显的提升。最后通过对充气压力和工作频率的优化,在入口声功9.08 kW、制冷温度77 K时获得了647 W的制冷量。     

U型脉管制冷机冷头连接管的实验研究

设计了一台U型脉冲管制冷机,并对直线连接管和U型连接管两种不同的冷头连接管进行了实验研究。对冷头连接管与脉管之间的各种导流结构进行比较,找到了最佳的导流方式,并在此基础之上,研究了连接管管径对制冷机制冷性能的影响。结果表明,存在一个连接管最佳直径使得U型脉管制冷机获得最高的制冷效率;U型连接管相比较直线连接管会引起弯管损失,当输入声功越大时,损失越大;本实验中,最佳的U型脉管制冷机性能相对直线型脉管制冷机情况下降了18%。     

关于"太阳在银河系中所受引力与到银心距离r的关系"的讨论

讨论了银道面内的引力场强分布和太阳在银河系中所受引力与到银心距离r的关系，指出引力场强g并不是与r的平方成反比，这是由于银河系的大小和形状不能忽略造成的．强调了万有引力定律的适用条件．     

On the calculation of the bremsstrahlung in the region of the plasma frequency

On the basis of the classical theory of radiation produced in incomplete Coulomb interaction, a formula is derived for the coefficient of the bremsstrahlung of fully ionized plasma. In the region of rectilinear approximation a comparison is made with the results of the quantum formula derived from the Born approximation. Furthermore, the influence of dispersion upon the emission coefficient is taken into account; some relations for the region of dispersion are given.     

On the predictability of the positions of the convergence zones in the ocean

The disagreement between the experimental and calculated positions of the first convergence zone are known from many publications. The most probable cause for such a disagreement, namely, the incorrect specification of the input data for the calculations, is considered. The lack of simultaneity between the hydrological surveys of the region and the acoustic experiments is emphasized. The experimental data obtained by the author in five ocean regions are presented. These data characterize the diurnal variability of the distance from the source to the nearest boundary of the convergence zone. The relations proposed by different researchers for calculating the sound speed from the temperature, salinity, and hydrostatic pressure are analyzed. It is shown that these relations lead to a substantial difference in the estimated depth dependence of the hydrostatic gradient of the sound speed. The position of the first convergence zone is calculated for the propagation conditions determined by vertical temperature and salinity profiles with the subsequent recalculation of these profiles into sound speed profiles by using eight different formulas known from the literature. It is shown that different formulas lead to different values of the distance to the first zone; this difference is substantially greater than that between the calculations and experiment. The necessity of improving the recalculation relations in view of the experimental data on sound propagation in natural oceanic waveguides, including the data on the actual positions of the convergence zones, is emphasized.     

Dependence of the Intensity of the Spectral Lines and the Composition of the Sample and the Plasma Parameters of the Unipolar Arc

The investigation was made of the dependence of the intensity of Tl, Ga, Mo, Mg, Mn, Sn, Bi, Ni, Zn, Pt and Au spectral lines and the plasma parameters (temperature T, electron concentration n_e, degree of 6 ionnization α) from concentration of lithium additive.     

Extracting the wavefunction of the LSP at the LHC

We consider associated production of squarks and gluinos with the lightest supersymmetric particle (LSP), or states nearly degenerate in mass with it. Though sub-dominant to pair production of color SU(3)-charged superpartners, these processes are directly sensitive to the wavefunction composition of the lightest neutralinos. Exploiting event-shape variables - including some introduced here for the first time - we are able to identify the composition of the LSP by selecting events involving a single high-pT jet recoiling against missing transverse energy. We illustrate the proposed technique on a set of benchmark cases and propose methods for applying these results in more realistic experimental environments.     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.     

On the Question of the Source of the Apokamp

Technical Physics - The object of this work is the apokamp—a new type of plasma jet, which is formed from a bright offshoot emerging at the bending point of a channel of a high-voltage...