two phase flow

In the present study, for the first time, a finite volume coupled solver is developed for the simultaneous numerical solving of two-phase incompressible fluid flow equations at low Reynolds numbers, and for solving the the interface position equation by applying interface boundary conditions using the foam-extend platform. The studied flows with interface and mesh motion are considered to be laminar and in the range of Reynolds numbers less than 100. The Foam-extend is a fork of OpenFOAM, an opensource object-oriented C++ library for computational continuum mechanics. This solver is based on the interface tracking algorithm, which is developed using an innovative technique called zero-thickness cell. This technique removes the distance effect for the cell adjacent to the interface, and the interface is modeled with zero thickness cells. The main advantage of the present coupled solver compared to the previously developed solvers is that in this solver, all the equations in both phases are coupled with each other by cells adjacent to the interface and with an the interface position equation. All the governing equations and the interface position equation are assembled in a single linear system of equations and simultaneously solved. In fact, unlike the usual segregated procedure of solving two phase flows, where the phases are solved with lagged value boundary conditions, in the present solver, the phases are solved simultaneously with the interface conditions in an implicit manner and in the same block matrix system. The movement of the interface was done separately, and in another step. For this purpose, the kinematic condition was implemented. The computational performance of the coupled solver was evaluated by solving the equations of two-phase fluid flow inside a channel and on a backward-facing step. In the beginning, a preliminary investigation was done for the case, where both phases were completely independent and decoupled. Matching the interface with the streamlines, as well as the reasonable and justifiable movement of the surface, has been observed from the physical point of view. Also, the damping of the numerical oscillations generated on the interface and changing the flow variables will be investigated. The present results are in excellent agreement with other results reported in the literature.

In the present study, the effect of blade angle on two-phase flow (liquidsolid) distribution in a stirred tank with a pitched-blade turbine (PBT) was simulated using computational fluid dynamics (CFD). To simulate the solid-liquid two-phase flow, the standard k-ԑ turbulence model coupled with the Eulerian-Eulerian (E-E) Multi-Fluid Model was employed. The two-phase flow properties along the tank axis were computed and validated by the available data in the literature. Then, the effect of the blade angle on the fluid flow inside the tank as well as the solid phase volume fraction distribution were investigated. Results indicated that increasing the blade angle from 45 to 75 degrees at a constant speed, increased the maximum radial velocity and power consumption by 45.6% and 217%, respectively.

In this paper, the phenomenon of liquid drop penetration inside the porous medium is studied by the two-phase fluid volume method. Considering the importance of two-phase and multi-phase flows and achieving the least error in the simulation of this phenomenon, in this research, a model for simulating the two-phase flow of droplet penetration in porous media is proposed, the proposed model has more agreement with experimental results compared with other similar models available in literature, the improvement is the novelty of this paper. The behavior of drop penetration has been predicted by the fluid volume method. The effect of changes in surface tension, viscosity, contact angle, viscosity and permeability and drop spreading level in porous media have been investigated. When the contact angle of the drop is 60 and 20 degrees, the changes of the expansion level are almost the same. The speed of spreading and penetration of water drop without the presence of gravity with surface tension of 0.02 is less than the other two surface tensions of 0.001 and 0.0072, while with the presence of gravity, water droplet with surface tension of 0.001 spreads and penetrates more than the other two cases. The results showed that the fluid volume method used in this research was 9% more accurate than the network Boltzmann method based on the Chan and Shen method with the physics of the same problem compared to the experimental results.

In Zn-Ag2O flow batteries, the electrolyte as one of active substances in electrochemical reactions flows circulatory in the narrow distance between electrodes, and in order to avoid of short circuit inside the battery cells, the spacers are used between their electrodes. In these batteries, the hydrogen gas bubble due to electrochemical reactions is produced on the cathode and then released within the electrolyte flow and a two-phase current is formed. Especially at high-rate discharge processes, this event can reduce the electrochemical active surface of the electrodes, increase the ohmic resistance, and thereby, reduce in the battery capacity. In this paper in order to solve this problem, the behavior of gas bubbles on the electrodes and within the electrolyte flow and their effect on the electrochemical active surface by considering two types of cross-sectional surfaces for spacers, is studied numerically. The results shown that the gas bubbles within the two-phase electrolyte flow spent more time behind the spacers with square cross-section compared to the case of spacers with a circular cross-section at the narrow distance between the electrodes. Therefore, this delay has led to other gas bubbles reaching each other in the electrolyte flow and as a result, they are combined. This event is investigated with two positive and negative approaches in this article.

In This research numerical investigation of two phase flow structure and heat transfer in microchannels with0.55 and 0.7 millimeter hydraulic diameter has been done. For this purpose, Ansys Fluent software has beenused and has wrote a UDF code for modeling of phase change process in this software. Inlet flow has beenassumed as super heat vapor of R134a and microchannel wall boundary condition is considered as constantheat flux. Effect of geometric cross section of microchannel in 3 cross section circular, square and trapezoidwith inlet mass flux range 100-600 𝑘𝑔/(𝑚2𝑠) on heat transfer coefficient and pressure drop has beenevaluated. Also two phase flow structure in two mentioned hydraulic diameter with same boundary conditionhas been studied. Under the same conditions of input mass flux and cross-section of the microchannel, it wasobserved that heat transfer coefficient in microchannel with 0.55 millimeter hydraulic diameter, is higherabout 15%. Also in a specific range of input mass flux, pressure drop in 0.55 millimeter hydraulic diameteris 3 times higher than 0.7 millimeter hydraulic diameter. Also in both two hydraulic diameter 0.55 and 0.7millimeter, square, circular and trapezoid microchannel have higher heat transfer coefficient in respect.