氦低温透平膨胀机的设计和内部流动特性研究

为验证氦低温膨胀机叶片设计的有效性,利用了NUMECA和CFX软件对设计透平流道进行设计工况下的数值模拟计算及分析,其中分别对工作轮流道、喷嘴流道和整体流道进行计算分析,获得了较好的温度场、压力场、相对速度场分布和较高的等熵效率,结果表明了数值计算结果是可信的,叶型设计是合理的。     

Flow field analysis of high-speed helium turboexpander for cryogenic refrigeration and liquefaction cycles

Turboexpander constitutes one of the vital components of Claude cycle based helium refrigerators and liquefiers that are gaining increasing technological importance. These turboexpanders which are of radial inflow in configuration are generally high-speed micro turbines, due to the low molecular weight and density of helium. Any improvement in efficiency of these machines requires a detailed understanding of the flow field. Computational Fluid Dynamics analysis (CFD) has emerged as a necessary tool for the determination of the flow fields in cryogenic turboexpanders, which is often not possible through experiments.In the present work three-dimensional transient flow analysis of a cryogenic turboexpander for helium refrigeration and liquefaction cycles were performed using Ansys CFX®, to understand the flow field of a high-speed helium turboexpander, which in turn will help in taking appropriate decisions regarding modifications of established design methodology for improved efficiency of these machines. The turboexpander is designed based on Balje's n_sd_s diagram and the inverse design blade profile generation formalism prescribed by Hasselgruber and Balje. The analyses include the study of several losses, their origins, the increase in entropy due to these losses, quantification of losses and the effects of various geometrical parameters on these losses. Through the flow field analysis it was observed that in the nozzle, flow separation at the nozzle blade suction side and trailing edge vortices resulted in loss generation, which calls for better nozzle blade profile. The turbine wheel flow field analysis revealed that the significant geometrical parameters of the turbine wheel blade like blade inlet angle, blade profile, tip clearance height and trailing edge thickness need to be optimised for improved performance of the turboexpander. The detailed flow field analysis in this paper can be used to improve the mean line design methodology for turboexpanders used in helium refrigeration and liquefaction cycles.     

Modeling of the very low pressure helium flow in the LHC cryogenic distribution line after a quench

This paper presents a dynamic model of the helium flow in the cryogenic distribution line (QRL) used in the Large Hadron Collider (LHC) at CERN. The study is focused on the return pumping line, which transports gaseous helium at low pressure and temperature over . Our aim is to propose a new real-time model of the QRL while taking into account the non-homogeneous transport phenomena. The flow model is based on 1D Euler equations and considers convection heat transfers, hydrostatic pressure and friction pressure drops. These equations are discretized using a finite difference method based on an upwind scheme. A specific model for the interconnection cells is also proposed. The corresponding simulation results are compared with experimental measurements of a heat wave along the line that results from a quench of a superconducting magnet. Different hypotheses are presented and the influence of specific parameters is discussed.     

A reciprocating liquid helium pump used for forced flow of supercritical helium

The performance of a small double acting piston pump for circulating helium in a closed heat transfer loop is described. The pump was manufactured by LINDE AG, Munich, West Germany. The measured flow rate of supercritical helium was about 17 gs^?1 (500 lhr^?1) with a differential pressure of Δρ = 0.5 × 10⁵Nm^?2 at a working pressure of p = 6 × 10⁵Nm^?2. At differential pressures beyond 0.5 × 10⁵Nm^?2 the volumetric efficiency decreases.     

Improved correlations for computations of liquid helium two phase flow in cryogenic transfer lines

The available experimental data, Vishnev et al. [6], implies that the widely used homogenous equilibrium model and the Martinelli–Nelson equation do not map correctly the pressure drop data for horizontal liquid helium two phase flow particularly in cases for high vapour fraction. Hence, considering the empirical nature of Martinelli–Nelson equation, suitable parameters and terms have been suggested so that, the pressure drop can be better predicted. The proposed equation being a third order in ‘x’ (vapour fraction) is more accurate to predict the characteristic behavior of liquid helium two phase flow as observed in experiments [6], Mamedov et al. [7], and Deev et al. [8], which the available equations are unable to predict.     

Thermally induced oscillations of helium in cryogenic apparatus

The results of an experimental study of thermally induced oscillations are presented. Relations are given for the determination of the stability limit and amplitudes of the oscillations.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 32, No. 4, pp. 691–696, April, 1977.     

Effect of crystal rotation on thermocapillary flow in a shallow molten silicon pool

In order to understand the effect of crystal rotation on thermocapillary flow, we conducted a series of unsteady three-dimensional numerical simulations of thermocapillary flow in a shallow molten silicon pool with Czochralski configuration. The crucible sidewall is maintained at constant temperature. Bottom and free surfaces are adiabatic. The temperature difference between the crucible and the crystal is 16 K and crystal rotation rate varies from ?10 and 10 rpm. The simulation results indicate that the spoken pattern rotates slowly with the crystal rotation at low rotation rate. When rotation rate exceeds a critical value, the spoken pattern becomes the hydrothermal waves. This transition exists hysteresis.     

氦低温系统中油过滤技术研究

说明了低温系统螺杆压缩机使用润滑油的作用，分析指出对于氦气进行油过滤的重大意义，并详细介绍了氦低温系统中油的过滤系统。通过研究油分离的原理及方法，对各过滤环节进行深入研究，为低温系统长期稳定、安全、可靠地运行奠定基础。     

冷氦增压系统换热器换热性能研究

为研究各种流量工况下冷氦增压系统中换热器的换热性能和压力损失,开展了冷氦增压系统搭载发动机试验和数值仿真研究,研究结果表明通过换热器的冷氦气体流量增大,换热器的出口温度降低且对换热器压力损失增加,数值仿真结果与试验结果吻合较好,换热器性能试验研究为提升冷氦增压系统工作性能打下基础。     

液氢温区冷氦增压系统试验研究

针对某型号火箭冷氦增压系统,建设了液氢温区冷氦增压系统试验平台,通过试验得到了冷氦气源压力和温度、冷氦加热器性能、模拟贮箱压力和温度的变化规律.结果表明:低温制冷机组配合高压低温换热贮罐可以真实模拟箭上的冷氦气源;根据对增压过程中贮箱压力的分析表明排气方式可以真实模拟箭上推进剂消耗过程中贮箱压力的变化情况;另外,试验中压力信号器、电磁阀和贮箱工作正常,验证了火箭冷氦增压系统的可靠性.     

Effect of number of turns and configurations on the heat transfer performance of helium cryogenic pulsating heat pipe

The pulsating heat pipe (PHP) is a potential alternative to highly conductive metals such as copper for long distance heat transfer. Effective thermal conductivity and heat transfer capacity of a PHP are two of the most critical factors for practical applications. In this paper, a helium based PHP, which consists of 48 parallel tubing sections, was developed. The lengths of the evaporator, adiabatic and condenser sections are 50 mm, 100 mm and 50 mm respectively. The condenser section was thermally anchored to a Gifford-McMahon cryocooler (GM cryocooler) with a cooling capacity of 1.5 W at 4.2 K. A maximum effective thermal conductivity of 12330 W/m∙K was obtained when 1.1 W heat was applied to the evaporator section at a fill ratio of 70.5%. With the same geometric parameters and operational parameters, the effect of the number of turns on the heat transfer performance was figured out by comparing the 48-turn PHP with an 8-turn PHP. The results show that the temperature difference between the evaporator and condenser sections of the 48-turn PHP is much smaller than that of the 8-turn PHP. The dry-out temperature response, effective thermal conductivity and heat transfer capacity of them are obtained and analyzed. Furthermore, two configurations of the 48-turn PHP, a parallel configuration and a series configuration, are defined. An optimum configuration is proposed and makes a reference to the design of a cryogenic PHP for applications.     

Feasibility of a cryogenic multiplexer for spaceborne applications

Several electronic device technologies (MOS, CMOS, GaAs) have been investigated for their suitability in an analogue signal multiplexer operating throughout the temperature range 4 K < T < 77 K. Constraints on leakage currents, channel resistance and radiation hardness led to the selection of GaAs as the candidate technology. Selected test results are presented and some problem areas identified.     

1.8K常压超流氦低温系统的设计与分析

中国科学院等离子体物理研究所ITER CC导体测试装置背景超导磁体,由4.2 K液氦浸泡冷却,能够提供7 T背景场,为了满足超导导体测试需要更大背景场(10 T)的要求,将采用1.8 K超流氦浸泡冷却。针对该测试装置的低温系统设计了一种1.8 K常压超流氦低温系统,给出了该系统的关键组成部分并对获取1.8 K常压超流氦的流程进行了分析。针对预冷与节流相结合获取1.75 K超流氦方案进行了分析和计算,同时针对此方案给出了其物理过程的T-s图,计算了1.75 K超流氦液体得率。     

Velocity of ultrasound propagation in solutions of helium in cryogenic liquids

The speed of ultrasound propagation is measured in neon-helium solutions. The effect of a helium impurity on ultrasound propagation speed in cryogenic liquids is analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 51, No. 4, pp. 603–608, October, 1986.     

An experimental study on the mechanical behaviour of two polyurethane resins used for geotechnical applications

The objective of this paper is to experimentally investigate the mechanical behaviour of different polyurethane expanding resins, which are widely used for ground improvement and foundation remediation. This study is the first step towards the primary objective, which is to define a design procedure for this type of intervention. This study encompasses two goals: (1) develop a relationship between the density of the resin and the confinement pressure in expansion conditions, and (2) measure the mechanical parameters from simple compression tests on resin specimens. Experimental tests were performed on two different types of resin, and the results reveal that the higher the confinement stress is during the expansion phase, the greater the hardened resin density. Moreover, the resin density and confinement stress are linked by a well-defined law. The laboratory tests show how the stress–strain behaviour is strongly non-linear and that both the elastic and strength parameters greatly depend on the boundary conditions during the expansion phase.     

Heterogeneous nucleation mechanism in the flow of a superheated cryogenic liquid

A hypothesis on heterogeneous nucleation in a liquid volume is used as a basis for obtaining a relation to close a system of equations which describes non equilibrium discharge.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 3, pp. 371–375, March, 1984.