Numerical Investigation Of Two-phase Flow Research Articles

Numerical investigation of two-phase flow through tube bundles based on the lattice Boltzmann method

In pursuit of stable operation in thermal hydraulic engineering, this paper researches two-phase flow through tube bundles by the lattice Boltzmann method. The single-relaxation-time lattice Boltzmann model and the multicomponent, multiphase pseudo-potential lattice Boltzmann model are adopted. Specifically, the two-phase flow past double-tandem circular cylinders, double-parallel circular cylinders, in-line tube bundles and staggered tube bundles with various spacing ratios is investigated. The vortex variable distribution and vortex shedding law under different working conditions are further compared to obtain the time-averaged drag, oscillating drag and Strouhal number. The variation law of lift coefficient and lift power spectrum with different spacing ratios is revealed. With increasing spacing ratio, the mutual interference between the double-tandem circular cylinders is weakened, the amplitude of the time-averaged drag on the double-parallel circular cylinders is reduced and the lift power spectrum changes from a double-peak distribution to a single-peak structure. The drag and lift of the center column of in-line tube bundles are lower than those on both sides, while the oscillating drag of the odd-row columns of staggered tube bundles is higher than that of even-row columns. These results contribute toward laying a solid foundation for future research on multiphase tube bundle flow issues in nuclear engineering.

Experimental and numerical investigation of two-phase flow and mass transfer in a self-excited oscillation pulse jet pump

The pulse water jet pump is widely used for many industrial purposes owing to the presence of pressure fluctuations that can considerably improve the erosive action of a jet. However, literature regarding the cavitating water jet flow patterns and underlaying mass transfer mechanisms remains relatively scarce due to existing measurement obstacles. To reveal underlying relationships between pump geometrical configuration and its performance, this study presents an experimental and numerical investigation of a self-excited oscillation water jet pump. Firstly, an experimental rig was built, and the performance of the pump was assessed against various operating conditions. Then, a numerical model based on the same pump geometry and operation conditions was developed to provide detailed predictions of the internal cavitating flow patterns. Reasonably good agreements were found between the numerical predictions and experimental measurements, which indicate that the developed numerical model can accurately predict the flow entrainment process in the self-excited oscillation pulse jet pump. Internal cavitating flow patterns in terms of streamlines, pressure contours, and velocity profiles were explored for different pump geometric configurations by adjusting the nozzle-throat distance. Relationships between these influential factors and pump mixing capacity were provided. This paper presents an in-depth understanding of the self-excited oscillation pulse water jet and systematically explores the impacts of pump geometries and operating conditions on its performance.

Flow morphology and heat transfer analysis for high-pressure steam condensation in an inclined tube part II: Numerical investigations

In this part of the paper, we introduce and discuss the numerical investigation of two-phase flow and heat transfer during steam condensation inside an inclined tube. For that we developed and employed a three-dimensional two-phase computational fluid dynamics model in ANSYS CFX which comprises wall condensation and direct contact condensation. Wall condensation is covered by a new subgrid model for the thin liquid film. For modelling of the heat transfer on the steam-liquid interface, three different heat transfer correlations have been implemented to check their performance. Simulation results were compared with experimental data of the COSMEA facility, which has been documented in part I of this paper. Particular focus was given to the development of the liquid film inside the tube and its effects on the wall heat transfer. Moreover, we compared the CFD simulations with system code simulations performed with the ATHLET submodule of AC2.

Numerical investigation of two-phase flow in a horizontal porous evaporator with localised heating using non-Darcian flow and two equations model

In this article, a new mathematical model, based on the modified enthalpy formulation of Two-Phase Mixture Model (TPMM), is developed by considering non-Darcy flow and Local Thermal Non-Equilibrium (LTNE) conditions to describe numerically the two-dimensional problems of the complete evaporation process inside an asymmetrically heated porous evaporator. The governing equations have been discretised using Finite Volume Method (FVM) on a fixed non-staggered grid layout. The in-house code has been validated against experimental data and the results show good agreement between them. Three different models have been employed for the partitioning of the wall heat flux. Only the effect of the heat flux has been analysed, while all other parameters and properties have been kept fixed during the present investigation. The numerical simulations indicated that the locally high heat flux significantly influences the working fluid flow performances, and lead to extend the superheated vapour region towards the exit of the evaporator. The results also show that the two-phase zone significantly expanded in the axial direction and does not occupy a large portion inside the channel due to the energy transport through the two-phase region is significantly higher in the flow direction as compared to the transverse direction, caused by the decrease in the effective diffusion coefficient in this region and higher axial velocity. Numerical analysis reveal that the different models for the partitioning of the wall heat flux have almost no influence on the overall predictions, except in the vicinity of the wall. The results clearly demonstrate that the numerical simulations with the modified h-formulation by considering non-Darcy law and LTNE model are indispensable for the problem of complete evaporation process, particularly under the high both heat flux and inlet velocity conditions.

Numerical investigation of entrapped air pockets on pressure surges and flow structure in a pipe

This research presents a numerical investigation of two-phase flow during the expulsion of entrapped air in a non-confined pipe. A modified version of the volume of fluid (VOF) approach is employed considering the effect of compressibility in the liquid. A modification is introduced to the original approach relating the density changes in the liquid to the pressure changes using the fluid bulk modulus. The bulk modulus is also modified to consider the pipe elasticity, the air bubble entrainment and the two-phase flow regime in a pipe. Fluid–structure interaction (FSI) code is developed and used to calculate the motion of the downstream orifice wall during the impact of the water column on the pipe end wall. The numerical results of the pressure variation agree well with experimental data. The two-phase flow structure and physics behind the pressure waves are investigated. The numerical results show that to capture the amplitude and time interval of the pressure surges, the effect of FSI should be considered during the expulsion of the entrapped air. Additionally, the effects of initial air pocket size, supply pressure and orifice size on the pressure increase are investigated. The developed VOF-FSI approach can be employed as a numerical tool to investigate the transient flow during pipe filling.

Numerical Investigation of Two-Phase Flow Over Unglazed Plate Collector Covered With Porous Material of Wire Screen for Solar Water Heater Application

This paper presents three-dimensional numerical simulation results of the effect of surface tension on two-phase flow over unglazed collector covered with a wire screen. The homogenous model is used to simulate the flow with and without the effect of porous material of wire screen and surface tension. The Eulerian-Eulerian multiphase flow approach was used in this study. The phases are completely stratified, the interphase is well defined (free surface flow), and interphase transfer rate is very large. The liquid–solid interface, gas–liquid interface, and the volume fraction for both phases were considered as boundaries for this model. The results show that the use of porous material of wire screen will reduce the velocity of water flow and help the water flow to distribute evenly over unglazed plate collector. The possibility of forming any hot spot region on the surface was reduced. The water velocity with the effect of surface tension was found higher than the one without this effect, due to the extra momentum source added by surface tension in longitudinal direction. The use of porous material of wires assures an evenly distribution flow velocity over the inclined plate, therefore helps a net enhancement of heat transfer mechanism for unglazed solar water collector application.

Numerical investigation of two-phase flow in anisotropic porous evaporator

This work deals with modelling and numerical simulation of complete evaporation process inside anisotropic porous media. Based on the modified enthalpy formulation of Two-Phase Mixture Model (TPMM) along with the assumption of Local Thermal Non-Equilibrium (LTNE), a modified formulation has been proposed that can easily accommodate the anisotropy in the porous media properties. The governing equations have been solved using the Finite Volume Method (FVM) on staggered grid layout. The simulations have been carried out by applying the proposed smoothing algorithm for the effective diffusion coefficient in order to avoid the non-physical jump in the predicted temperature distribution during the numerical simulations. The effects of the permeability ratio, solid thermal conductivity ratio, thermal conductivity of the solid phase and the Darcy number have been investigated. The computed results show that the anisotropy of permeability and thermal conductivity of the solid phase have significant effect on the initiation and termination of phase change process. It is also observed that the anisotropic properties of the porous medium have significant influence on the flow behaviour and heat transfer rate from that expected under isotropic conditions. The results indicated that the effect of thermal conductivity of the solid phase plays an important role and hence adequate care must be taken while designing such evaporators. The results also show that the smoothing algorithm is successful in dealing with the rapid change in the effective diffusion coefficient during the simulations of complete evaporation process.

Numerical investigation of two-phase flow encountered in electrically enhanced oil recovery

The study of two-phase immiscible flow in porous media using electrokinetics is important in different fields including the remediation of hydrocarbon contaminated soils and enhanced oil recovery. While electrokinetic technology has been traditionally used for treatment and decontamination of hydrocarbon polluted sites, electrically enhanced oil recovery (EEOR) is relatively new. Although a few laboratory and field experiments have investigated the potential promise of the EEOR method, further investigation is necessary to better understand the fundamentals and the importance of different parameters/processes that affect the oil production in this method. This study presents a numerical investigation of two-phase flow in EEOR method in an attempt to provide insight into the feasibility of, and the important parameters involved in this method. A sensitivity analysis is performed on important parameters involved in EEOR combined with water flooding. Most of the investigated reservoir and operational parameters were found to be significant and critical to the transport phenomena controlling the oil production. In addition, the results showed that the applied electrical gradient involved in EEOR combined with water flooding contributes to a small increase in oil production.

Numerical Investigation of Two-Phase Flow of Non-Newtonian Fluid Discharged from a Sauce Dispenser

Fluid dispensers are widely used in various food processing applications. The present work investigates a two-phase flow of sauce discharged from a dispenser. Preliminary simulations were conducted to study the effects of non-Newtonian properties on the resulting flow. It was found that the non-Newtonian properties of the sauce tends to distribute the flow more toward the mid-plane of the fluid field. Transient, liquid-air flow simulations were conducted to study the effects of surface tension and geometry of the dispenser on the liquid film in ambient air. The volume of fluid (VOF) method was used to track the interface between phases. Gravity was taken into account since it is comparable with the inertia force. It was found that the breakup time of the liquid film increases as the Weber number decreases and the breakup length of the liquid film increases as the Froude number increases. Practical Applications In food processing applications, various sauces are to be dispensed onto the meal tray. To ensure uniform reheating of the packaged food as well as retaining the moisture content, ideal coverage is required. When sauce leaves the dispenser, it starts to interact with the ambient air and results in a two-phase flow. Understandings of the shape of the liquid film as well as its breakup during the dispensing process are crucial to sauce dispenser design. Through numerical investigations of the dispensing process, the present work proposes optimized dispenser geometry and provides physical insights of the breakup time and the breakup length of the liquid film. Based on these findings, better design of the sauce dispenser can be achieved.

Numerical Investigation of Two-Phase Flow in Natural Gas Ejector

Increasing production and recovery from the mature oil and gas fields often requires a boosting system when the gas pressure is lower than that demanded by the transportation or process system. The supersonic ejector, considered to be a cost-effective way to boost the production of a low-pressure gas well, was introduced into the industrial field. However, the exploitation of natural gas often accompanies with water. The computational fluid dynamics (CFD) technique was employed to investigate the two-phase effect (water droplets) on the performance of natural gas ejector for the motive pressure ranging from 11.0 MPa to 13.0 MPa, induced pressure from 3.0 MPa to 5.0 MPa, and backpressure from 5.1 MPa to 5.6 MPa, while the injected water flow rate was less than 0.03 kg s−1. The numerical results show that the entrainment ratio of the two-phase operation was higher than that of the single-phase operation with the variation of backpressure. Meanwhile, the entrainment ratio increased with the increase of injected water flow rate into the primary flow. When the water was injected into the secondary flow, the entrainment ratio decreased as the injected water flow rate increased, but the critical backpressure remained unchanged.

Small Froude number asymptotics in two-dimensional two-phase flows

A nonlinear wave equation is derived describing the behavior of gas- and liquid-fluidized beds in the small Froude number regime. It represents a two-dimensional perturbation of the Korteweg--de Vries equation and is shown to constitute a valid approximation of the original system. While greatly simplifying the analytical and numerical investigation of two-phase flow in fluidized beds, it also leads to the conclusion that the underlying model does not significantly discriminate between gas- and liquid-fluidized beds near the stability limit. An amplitude equation is derived governing the growth and stability of solitary plane waves. The results are linked to those obtained by previous nonapproximative analyses. It is expected that this analysis is applicable to other multiphase and traffic flow models due to the similarity in the governing equations and the completeness of the reduced wave equation.

Numerical investigation of two-phase flow with coagulation and fragmentation of particles in axisymmetric laval nozzles

The method and results of a calculation of the parameters of a polydis-perse two-phase flow with coagulation and fragmentation of particles in collisions are described. The problem is considered in a two-dimensional formulation. The secondary particles (fragments) formed by fragmentation are assumed to have arbitrary mass and velocity distributions.