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1.
The thermodynamic irreversible loss by condensation can have an important influence on the flow characteristics and thermal efficiency in air or nitrogen cryogenic turbo-expander involving spontaneous condensation flow. However, the design of wet type turbo-expander for cryogenic liquid plants has been constrained due to the complexity of nucleation theory and the difficulty of data measurement in cryogenic environments. This paper presents numerical simulations for prediction of nitrogen spontaneous condensation flow in cryogenic nozzles. The non-equilibrium simulations were performed using three nucleation theories with the help of ANSYS CFX solver. The standard Redlich-Kwong gas state equation and Eulerian–Eulerian governing equations were used in simulations. Comparison with the equilibrium condensation model the non-equilibrium condensation model achieves a better prediction of the flow characteristics for spontaneous condensation flow in cryogenic environments. The nucleation theory which is based on classical nucleation theory (CNT) and improved by Kantrowitz for non-isothermal effects shows a better prediction of pressure drop, location of condensation onset and supercooling compared with experimental data. The influence of varying nucleation theories on the calculation of nucleation rate, the supercooling distribution and the liquid mass fraction distribution were also analyzed.  相似文献   

2.
Liquid fraction measurement in cryogenic two-phase flow is a complex issue, especially for an industrial cryogenic system. In this paper, a simple thermal method is proposed for measuring the liquid fraction in cryogenic two-phase turbo-expander by an electric heating unit in experimental study. The liquid fraction of the cryogenic two-phase flow is determined through the heat balance built at the outlet of the turbo-expander (inlet of heating unit) and the outlet of the heating unit. Liquid fractions from 1.16% to 5.02% are obtained from five two-phase expansion cases. Under the same turbo-expander inlet pressure and rotating speed, five superheated expansion cases are tested to evaluate the wetness loss in two-phase expansion. The results show that the proposed method is successful in measuring the liquid fraction of cryogenic two-phase expansion for turbo-expander in an industrial air separation plant. The experimental isentropic efficiency ratio and the tested Baumann factor decrease with the increasing mean wetness. Based on prediction of Baumann rule, the cryogenic turbo-expander with low liquid fraction in two-phase expansion cases suffers from more severe wetness loss than that with the higher liquid fraction.  相似文献   

3.
低温氦透平膨胀机转子临界转速求解   总被引:4,自引:1,他引:3  
针对EAST低温氦透平膨胀机开启问题,对传统Riccati传递矩阵法进行了改进,利用Matlab强大的矩阵计算能力,结合PRO/E和CAD软件,综合考虑了影响转子临界转速的各种因素,编写出了高精度的计算程序,分析了EAST启动透平膨胀机B过程中转速随阀门开度和叶轮进口压力的变化曲线和实验数据,计算得出了透平膨胀机B转子的临界转速,为后来试验开启透平膨胀机和进行氦透平转子稳定性研究提供了理论依据。  相似文献   

4.
Using experimental research on two-phase choked flow of pressurized sub-cooled cryogenic liquids, design recommendations are presented for computing this flow for simple cryogenic liquids with single phase stagnation conditions. Accordingly a set of generalized charts have been drawn up based on an integration of the non-equilibrium model in the liquid region and the homogeneous equilibrium model elsewhere.  相似文献   

5.
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。  相似文献   

6.
The fundamental two-phase flow characteristics of slush nitrogen in a pipe are numerically investigated to develop effective cooling performance for long-distance superconducting cable. First, the governing equations of two-phase slush nitrogen flow based on the unsteady thermal non-equilibrium two-fluid model are constructed and several flow characteristics are numerically calculated taking into account the effects of the slush volume fraction, the thermodynamic behavior of slush, and the duct shape. Furthermore, the numerical results are compared with previous experimental results on pressure loss measurement and visualization measurement in two-phase slush nitrogen flow along the longitudinal direction of the pipe. Results of this research show that it is possible to reduce the pressure loss by using a two-phase slush flow under the high Reynolds number condition and by applying the appropriate volume fraction of slush particles. The optimized thermal flow conditions for cryogenic two-phase slush nitrogen with practical use of latent heat for slush melting are predicted for the development of a new type of superconducting cooling system.  相似文献   

7.
为了研究泵内压降和水力损失耦合诱导泵内液氮空化,采用Zwart空化模型和RNG k-ε湍流模型,并使用CEL语言将饱和蒸气压随温度变化函数关系式导入CFX软件中进行求解,对不同流量下低温泵的空化特性曲线进行分析。研究结果表明,低温泵内压力、温度和空泡体积分数分布与空化的发展程度有关,由于水力损失的作用,小流量工况下,泵内会出现涡状流,从而对叶轮内空化产生影响。  相似文献   

8.
High speed turbo-expander is an essential refrigerating component in cryogenic systems. In addition to thermodynamic performance, its stability in transient high speed operation is also of great concern for its comprehensive performance. Oil free foil bearing has a great application potential in high speed turbomachinery by virtue of its high stability with no extra external supplying gas. In this paper, finite element model of a 150 Nm3/h cryogenic turbo-expander using foil bearing for air separation is configured for a case study. Influence of bearing structural stiffness and damping characteristics on the rotor-foil bearing system are evaluated for stable operation. Static structural stiffness and damping coefficients of the protuberant foil journal bearing and thrust bearings are obtained from the static loading and deflection tests. With the tested coefficients, rotordynamic performances of the rotor-bearing system is analyzed numerically and compared with the transient experimental results.  相似文献   

9.
Time- and temperature-dependent effects are critical for the operation of non-volatile memories based on ferroelectrics. In this paper, we assume a domain nucleation process of the polarization reversal and we discuss the polarization dynamics in the framework of a non-equilibrium statistical model. This approach yields analytical expressions which can be used to explain a wide range of time- and temperature-dependent effects in ferroelectrics. Domain wall velocity derived in this work is consistent with a domain wall creep behavior in ferroelectrics. In the limiting case of para-electric equilibrium, the model yields the well-known Curie law. We also present experimental P-E loops data obtained for soft ferroelectrics at various temperatures. The experimental coercive fields at various temperatures are well predicted by the coercive field formula derived in our theory.  相似文献   

10.
A thermo/kinetics computer model has been developed to predict the precipitation behavior of complex precipitates in Nb-Ti bearing steels under hot deformation condition. The equilibrium concentration of substitutional elements in austenite and the driving force for precipitation are calculated by the thermodynamic model. The time dependence of volume fraction and mean radius of precipitates is predicted by the kinetics model on the basis of classical nucleation and growth theory. In the kinetics model, the effect of hot deformation on precipitation is taken into account in terms of increase in nucleation sites and the enhanced diffusivity of substitutional solutes along dislocation, the decrease of solute concentration in austenite, and the driving force for precipitation are determined by a mean field approximation method. More importantly, the present model treats nucleation and growth as a concomitant process by using the finite differential method, which is different from the traditional one that treats nucleation and growth as a sequential stage. The model has been further validated by the experimental data in the literature.  相似文献   

11.
In order to reduce the non-equilibrium condensation occurring in ejector primary nozzle, wet steam model was adopted to investigate the relationship between steam superheated level and non-equilibrium condensation within ejector primary nozzle. Simulation data of axial static pressure along primary nozzles were validated with experimental data reported in literature. The non-equilibrium condensation process from homogeneous nucleation to droplet growth stage and the resulting products were carefully studied. Moreover, six inlet superheated levels from 5 K to 30 K with the increment of 5 K were compared, and simulation results showed that the increase of superheated level from 5 K to 30 K causes 40.22% delay in the location and 43.92% reduction in the intensity of the condensation shock. Furthermore, there is about 24.30% liquid mass fraction decrease when the superheated level raises to 30 K and total entropy generation increases slowly with the increase of superheated level.  相似文献   

12.
Current standards for sizing nozzles, venturis, orifices, control and safety valves are based on different flow models, flow coefficients and nomenclature. They are generally valid only for single-phase gas and liquid flow. Common to all is the concept of one-dimensional nozzle flow in combination with a correction factor (e.g. the discharge coefficient) to correct for non-idealities of the three-dimensional flow. With the proposed partial non-equilibrium HNE-DS method an attempt is made to standardize all sizing procedures by an appropriate nozzle flow model and to enlarge the application range of the standards to two-phase flow. The HNE-DS method, which was first developed for saturated and non-flashing two-phase flow, is extended for initially sub-cooled liquids entering the throttling device. To account for non-equilibrium effects, i.e. superheated liquid due to rapid depressurisation, the non-equilibrium coefficient used in the HNE-DS method is adapted to those inlet flow conditions. A comparison with experimental data demonstrates the good accuracy of the model.  相似文献   

13.
Flow behavior of particles is simulated by means of two-fluid model combining with kinetic theory of granular flow in a liquid-solid stirred vessel with baffles. The Huilin-Gidaspow drag model is used to obtain interphase interaction of liquid and solids phases. The virtual mass force is considered in simulations. The moving reference frame is applied to the rotation of numerical domain. Predictions are compared with experimental data measured by Pianko-Oprych et al. (2009) in a liquid-solid stirred vessel. This comparison shows that the present model can capture the liquid-solid flow in a liquid-solid stirred vessel. The distributions of velocity and solids volume fraction are predicted at the different heights. The effects of particle density on flow behavior of particles are generally scarce using CFD. Simulations indicate the stirred vessel consists of three regions based on distributions of velocity and turbulent kinetic energy, they are blade circulation region, conical induced region and near-wall region. As an increasing of the impeller speed, the turbulence kinetic and solids phase velocity rise, and the particles fluctuation is intensified.  相似文献   

14.
X.B. Zhang  L.M. Qiu  Y. Gao  X.J. Zhang 《低温学》2008,48(9-10):432-438
Cavitation is the formation of vapor bubbles within a liquid where flow dynamics cause the local static pressure to drop below the vapor pressure. This paper presents the steady computational fluid dynamic (CFD) results of cavitation in liquid nitrogen flow through hydrofoils and ogives with so-called “full cavitation model”. The model is reexamined to assess the performance prediction from the standpoint of cryogenic fluids with the assumption of thermal equilibrium between vapor phase and liquid phase. The fluid thermodynamic properties are specified along the saturation line using the “Gaspak 3.2” databank. The thermal effects and accompanying property variations due to phase change are modeled rigorously. The thermodynamic cavitation framework is validated against experimental data of NASA hydrofoil and ogive. The global sensibility of the cavitation solution with respect to the cavitation model coefficients and the free-stream velocity is investigated in detail and the choking phenomenon is reported with high Mach number. The full cavitation model with the default coefficients is applicable for cavitation prediction in liquid nitrogen, taking into account of the thermodynamic effects.  相似文献   

15.
设计了一套氦透平膨胀机实验系统,该系统可以用来对工作在液氢—常温区范围内的不同规格的氦透平膨胀机进行性能测试,还可以用于开展以氦为工质的低温环境下透平膨胀机实验研究,以期掌握氦透平膨胀机的关键技术并进一步提高氦透平膨胀机的性能。  相似文献   

16.
针对超低温冷却加工液氮可控传输难题,分析了热流量、管路压降等复杂因素对液氮可控传输的影响机制,提出了基于AMESim的液氮可控传输性能分析方法,建立了受热管道液氮两相流动传热数值模型,并在此基础上,研制出一套液氮可控传输原理性系统。通过对比实验表明,提高系统的输入压力能够增大低温流体的流量,缩短系统进入热平衡状态的时间,提高输出流体的干度和流型的稳定性;研制出的液氮可控传输原理性系统在输入压力为1.3 MPa时,在一定的开口范围内,能够稳定输出流量可控的低干度流体,且符合超低温冷却加工的要求。  相似文献   

17.
A finite element based method has been developed for computing time-averaged fluid-induced radial excitation forces and rotor dynamic forces on a two-dimensional centrifugal impeller rotating and whirling in a volute casing. In this method potential flow theory is used, which implies the assumption of irrotational inviscid flow. In comparison with other analyses of fluid-induced impeller forces, two main features have been included. Firstly, the hydrodynamic interaction between impeller and volute isproperly modelled. Secondly, the variation of the width of the volute has been adequately included in the two-dimensional analysis by a modification of the equation of continuity. A regular perturbation method is used to deal with the effects of the whirling motion of the impeller. The excitation forces are calculated from the zeroth-order problem in which the impeller axis is placed at the volute origin. The rotor dynamic forces associated with the whirling motion of the impeller are derived from the first-order solution. The force components, tangential and normal to the whirl orbit, are predicted as functions of the impeller--volute geometry, the flow conditions and the whirl speed ratio. The method is applied to a centrifugal pump experimentally tested at the California Institute of Technology. Comparisons between predictions and experimental data show the capabilities of the proposed method to reproduce the main features of fluid-induced impeller forces in centrifugal pumps. © 1997 by John Wiley & Sons, Ltd.  相似文献   

18.
In this paper, effects of liquid volume fraction, temperature and work pressure in cryogenic vessels on the pressure rise rates in cryogenic vessels are analyzed. Graphs of the relation between storage-pressure and heat flow received by the container per unit of volume for various volume fractions are proposed, and also graphs of the relation between time and pressure of non-loss storage for various volume fractions are presented. The best volume fraction is defined. Also, the graphs of the relation between environmental temperature and the performance of non-loss storage are proposed. In addition, the phenomenon of liquid-temperature layering is analyzed and methods to reduce this layering are suggested. These results have significance in the design, usage and selection of cryogenic vessels.  相似文献   

19.
Cryogenic slush fluids, such as slush hydrogen and slush nitrogen, are two-phase, single-component fluids containing solid particles in a liquid. Since their density and refrigerant capacity are greater than those of liquid-state fluids alone, there are high expectations for use of slush fluids as functionally thermal fluids in various applications, such as fuels for spacecraft engines, clean energy fuels to improve the efficiency of transportation and storage, and as refrigerants for high-temperature superconducting equipment. In this research, a three-dimensional numerical simulation code (SLUSH-3D), including the gravity effect based on the thermal non-equilibrium, two-fluid model, was constructed to clarify the flow and heat-transfer characteristics of cryogenic slush fluids in a horizontal circular pipe. The calculated results of slush nitrogen flow performed using the numerical code were compared with the authors’ experimental results obtained using the PIV method. As a result of these comparisons, the numerical code was verified, making it possible to analyze the flow and heat-transfer characteristics of slush nitrogen with sufficient accuracy. The numerical results obtained for the flow and heat-transfer characteristics of slush nitrogen and slush hydrogen clarified the effects of the pipe inlet velocity, solid fraction, solid particle size, and heat flux on the flow pattern, solid-fraction distribution, turbulence energy, pressure drop, and heat-transfer coefficient. Furthermore, it became clear that the difference of the flow and heat-transfer characteristics between slush nitrogen and slush hydrogen were caused to a large extent by their thermo-physical properties, such as the solid–liquid density ratio, liquid viscosity, and latent heat of fusion.  相似文献   

20.
Pronounced hydrodynamic and thermodynamic non-equilibrium exist in the flow of refrigerant through a short tube orifice under typical operating conditions. A non-equilibrium two-fluid model (TFM) for refrigerant two-phase critical flow inside the short tube orifice is developed. Both inter-phase velocity slip and inter-phase temperature difference are taken into account in the model. The mass flow rate, the two-phase velocity and temperature distributions in a short tube orifice are simulated. Comparisons among the experimental data of refrigerants R134a, R12, R22, R410A and R407C flowing through short tubes, the predictions by the TFM and by the homogeneous equilibrium model (HEM) show that the TFM gives acceptable predictions with the deviations of ±20%, while the HEM underestimates the flow rate by 20% or so.  相似文献   

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