Local Flow Regime Transition Criteria of Gas-Liquid Two-phase Flow in Vertical Upward Tube with a Horizontal Rod

The upward multiphase cross flow and heat transfer in the vertical tube may occur in oil production and chemical facilities. In this study, the local flow patterns of an upward gas-water two phase cross flow in a vertical tube with a horizontal rod have been investigated with an optical probe and the digital high speed video system. The local flow patterns are defined as the bubble, slug, churn and annular flow patterns. Optical probe signals are ana- lyzed in terms of probability density function, and it is proved that the local flow patterns can be recognized by this method. The transition mechanisms between the different flow patterns have been analyzed and the corresponding transitional models are proposed. Finally, local flow pattern maps of the upward gas-water two-phase flow in the vertical tube with a horizontal rod are constructed.

Local Flow Regime Transition Criteria of Gas-Liquid Two-phase Flow in Vertical Upward Tube with a Horizontal Rod

The upward multiphase cross flow and heat transfer in the vertical tube may occur in oil production and chemical facilities. In this study, the local flow patterns of an upward gas-water two phase cross flow in a vertical tube with a horizontal rod have been investigated with an optical probe and the digital high speed video system. The local flow patterns are defined as the bubble, slug, churn and annular flow patterns. Optical probe signals are ana- lyzed in terms of probability density function, and it is proved that the local flow patterns can be recognized by this method. The transition mechanisms between the different flow patterns have been analyzed and the corresponding transitional models are proposed. Finally, local flow pattern maps of the upward gas-water two-phase flow in the vertical tube with a horizontal rod are constructed.

Experimental analysis on adjusting performance of vapor-liquid two-phase flow controller

The vapor-liquid self-adjusting controller is an innovative automatic regulating valve.In order to ensure adjusted objects run safely and economically,the controller automatically adjusts the liquid flux to keep liquid level at a required level according to physical properties of vapor-liquid two-phase fluid.The adjusting mechanics,the controller’s performance and influencing factors of its stability have been analyzed in this paper.The theoretical analysis and successful applications have demonstrated this controller can keep the liquid level steady with good performance.The actual application in industry has shown that the controller can satisfactorily meet the requirement of industrial production and has wide application areas.

An Experimental Study on the Flow Characteristics of OilWater Two-Phase Flow in Horizontal Straight Pipes

The flow patterns and their transitions of oil-water two-phase flow in horizontal pipes were studied. The experiments were conducted in two kinds of horizontal tubes, made of plexiglas pipe and stainless steel pipe with 40 mm ID respectively. No. 46 mechanical oil and tap water were used as working fluids. The superflcial velocity ranges of oil and water were: 0.04-1.2m·s-1 and 0.04-2.2m·s-1, respectively. The flow patterns were identified by visualization and by transient fluctuation signals of differential pressure drop. The flow patterns were defined according to the relative distribution of oil and water phases in the pipes. Flow pattern maps were obtained for both pipelines. In addition, semi-theoretical transition criteria for the flow patterns were proposed, and the proposed transitional criteria are in reasonable agreement with available data in liquid-liquid systems.

Visualization Investigation on Temperature Oscillation and Two-Phase Behaviors of A Flat Loop Heat Pipe

To better analyzing the temperature oscillation and the two-phase behavior inside a flat loop heat pipe,visual studies were conducted.Under the 20℃ water cooling and horizontal orientation,the effects of the filling ratio and heat loads on the temperature oscillation were analyzed.Based on the experimental data,the results indicate that owing to the increased system pressure,the temperature oscillation decays as the filling ratio increases from 34%to 58%.Meanwhile,during the startup process,temperature oscillation tends to occur during the boiling and steady stages due to the more violent two-phase behavior,while the temperature curves are smooth during the slow evaporation stage.Moreover,as the heat load increases,the evaporation becomes more intense at the active zone of evaporator,leading to a faster startup process and a higher oscillation frequency.Besides,owing to the synergistic effect of two-phase flow in the compensation chamber caused by heat leak and subcooled liquid backflowing,a“breathing”oscillation behavior of the vapor-liquid interface is observed at the compensation chamber,which further leads to the unstable operation behavior of the loop heat pipe system.

Mechanisms and applications of layer/spinel phase transition in Li-and Mn-rich cathodes for lithium-ion batteries

Li-and Mn-rich(LMR)cathode materials have received tremendous attention due to the highly reversible specific capacity(>250 m Ah·g^(-1)).In the analysis of its crystal structure,the two-phase composite model gains increasing acceptance,and the phase transition behaviors in LMR cathode materials have been extensively studied.Herein,the structure controversy of LMR cathode materials,and the mechanisms of phase transition are summarized.Particularly,the causes of initiating or accelerating the phase transition of LMR cathode materials have been summarized into three main driving forces,i.e.,the electrochemical driving force,the component driving force and the thermodynamic driving force.Additionally,the applications of phase transition behavior in improving the electrochemical performance of LMR cathode materials,including the construction of spinel surface coating and spinel/layered hetero-structure are discussed.

MATHEMATICAL MODELING OF PARTICLEFLUID TWO-PHASE FLOW

Two-phase flow is modeled by considering interactions between partocles and their surrounding fluid at three scales: micro-scale of particle size, meso-scale of cluster size, and macro-scale for the overall particulate system consisting of clusters carried by the surrounding dilute phase.A further constraint has been found necessary to describe the stability of the twophase flow: the total energy always seeks a minimum for the dynamics of such particulate systems.The modeling can be used to explain numerous phenomena in particle-fluid flow, such as flow regime transitions and the heterogeneity of the two-phase system. It not only reflects the physical nature of the particle-fluid flow, but also makes possible quantitative description for both gas-solid (G/S) and liquid-solid (L/S) systems.

Numerical method for simulating rarefaction shocks in the approximation of phase-flip hydrodynamics

A finite-difference algorithm is proposed for numerical modeling of hydrodynamic flows with rarefaction shocks, in which the fluid undergoes a jump-like liquid-gas phase transition. This new type of flow discontinuity, unexplored so far in computational fluid dynamics, arises in the approximation of phase-flip(PF) hydrodynamics, where a highly dynamic fluid is allowed to reach the innermost limit of metastability at the spinodal, upon which an instantaneous relaxation to the full phase equilibrium(EQ) is assumed. A new element in the proposed method is artificial kinetics of the phase transition, represented by an artificial relaxation term in the energy equation for a "hidden"component of the internal energy, temporarily withdrawn from the fluid at the moment of the PF transition. When combined with an appropriate variant of artificial viscosity in the Lagrangian framework, the latter ensures convergence to exact discontinuous solutions, which is demonstrated with several test cases.

Numerical Study of Void Fraction Distribution Propagation in Gas-Liquid Two-Phase Flow

A dynamic propagation model was developed for waves in two-phase flows by assuming that continuity waves and dynamic waves interact nonlinearly for certain flow conditions. The drift-flux model is solved with the one-dimensional continuity equation for gas-liquid two-phase flows as an initial-boundary value problem solved using the characteristic-curve method. The numerical results give the void fraction dis- tribution propagation in a gas-liquid two-phase flow which shows how the flow pattern transition occurs. The numerical simulations of different flow patterns show that the void fraction distribution propagation is deter- mined by the characteristics of the drift-flux between the liquid and gas flows and the void fraction range. Flow pattern transitions begin around a void fraction of 0.27 and end around 0.58. Flow pattern transitions do not occur for very high void concentrations.

Refrigerant Distribution Characteristics in Vertical Header of Flat-Tube Heat Exchanger without Internal Protrusion

A heat exchanger that arranges flat tubes horizontally has a vertical header that distributes the refrigerant to each tube. When the heat exchanger works as an evaporator, differences in flow conditions at each branch, such as the ratio and distribution of vapor and liquid, due to the differences in densities and momentums of vapor and liquid in the two-phase flow make equal distribution difficult. This paper describes the distribution characteristics of a four-branch header that has a rectangular cross-section without the internal protrusion of flat tubes in the case of the inflow of the refrigerant R32 from the bottom of the header by using an equipment that can estimate the distribution ratio of the liquid and vapor phase to each branch. This paper also discusses the distribution characteristics on the basis of the flow visualization in the header. The flow visualization shows that a liquid level that contains vapor phase exists in the header and affects the distribution greatly.

THE LINEAR SEPARATED FLOW MODEL FOR TWO－PHASI FLOW INSTABILITY IN BOILING CHANNELS

This paper presents linear separated model describing two-phase now instability. By employing the method of separated model and system control theory, dynamic system characteristic equations of describing two-phase flow instability are derived.It can be decided system stability depending on the characteristic value of characteristic equations. The calculated results agree well with the experimental data.