Mohammad Reza Ansari

Tarbiat Modares University | TMU · Department of Mechanical Engineering

The present research aims to investigate the two-phase air/water flow in a vertical pipe using an electrical resistance sensor and a high-speed camera. An electrical resistance sensor is designed and embedded in the inner wall of the tube. A flow pattern map is drawn at the height of 270 cm from the testbed inlet for 320 different phase velocities...

In many atomizers, the breakup of the annular liquid sheet exiting from the atomizer is responsible for the formation of the spray and the determination of the spray characteristics. This paper studies the instability of the annular liquid sheet exiting from the effervescent atomizer at high gas to liquid mass flow ratios, in order to better unders...

The multiscale multiphase flow contains both small-scale (dispersed phase) and large-scale (continuous phase) structures. Standard interface-averaging multiphase models are appropriate for the simulation of flows including small-scale structures. Standard interface-resolving multiphase models are commonly used for the simulation of flow regimes con...

در بسیاری از اتمایزرها شکست ورقه حلقوی مایع خروجی از اتمایزر مسئول تشکیل اسپری و تعیین مشخصه های اسپری حاصل است. مقاله حاضر به مطالعه ناپایداری ورقه حلقوی مایع خروجی از اتمایزر مایع هوادهی شده، به منظور درک بهتر فرآیند شکست اولیه در این نوع اتمایزر، در نسبت های دبی جرمی گاز به مایع بالا پرداخته است. بدین منظور معادله پراکندگی بدست آمده از تحلیل پای...

The purpose of this study is to generate two-phase flow patterns and to obtain a flow pattern map for two phases as water and air in a vertical pipe which is made of transparent Plexiglas. The pipe specification is 50 mm diameter and 390 cm length. In this attempt the average velocity of the Taylor bubble will be calculate. In order to facilitate t...

در این مقاله از تحلیل پایداری خطی زمانی برای بررسی تاثییر لزجت مایع روی ناپایداری ورقه حلقوی مایع خارج شونده از اتمایزر مایع هوادهی شده استفاده شده است. معادله پراکندگی برای ورقه حلقویلزج مایع در حضور جریان های غیرلزج گازی درون و بیرون آن بدست آمده است. معادله بدست آمده برای شرایط جریانی ورقه حلقوی مایع خارج شونده از اتمایزر مایع هوادهی شده در نسبت...

در این مقاله از تحلیل پایداری خطی زمانی برای بررسی تاثییر لزجت مایع روی ناپایداری ورقه حلقوی مایع خارج شونده از اتمایزر مایع هوادهی شده استفاده شده است. معادله پراکندگی برای ورقه حلقویلزج مایع در حضور جریان های غیرلزج گازی درون و بیرون آن بدست آمده است. معادله بدست آمده برای شرایط جریانی ورقه حلقوی مایع خارج شونده از اتمایزر مایع هوادهی شده در نسبت...

Two-phase flow field upstream of the discharge orifice of effervescent atomizer has been numerically studied at 0.38 L/min liquid flow rate and different gas to liquid mass ratios of 0.32%, 0.62%, and 1.24%. The internal flow of the atomizer has been three-dimensionally simulated using the volume of fluid method. Aeration gas is considered as an id...

در بسیاری از اتمایزرها شکست ورقه حلقوی مایع خروجی از اتمایزر مسئول تشکیل اسپری و تعیین مشخصه های اسپری حاصل می باشد. در مقاله حاضر به منظور درک فرآیند شکست اولیه ورقه حلقوی مایع خروجی از اتمایزر مایع هوادهی شده، ناپایداری مدهای اغتشاشی شبه سینوسی و شبه اتساعی ورقه حلقوی مایع خارج شونده از این نوع اتمایزر بررسی شده است. بدین منظور ابتدا معادله پراکن...

In this research behaviour of a single droplet of the dielectric field under the effect of applied external uniform magnetic field is investigated. Previously, it was thought that no force is applied to the dielectric fluids when exposed to the uniform magnetic field. In order to determine the net effect of the applied uniform magnetic field, a sta...

اتمایزر مایع هوادهی شده جزو اتمایزرهای دو سیالی اختلاط داخلی است که جریان دوفازی گاز- مایع درون اتمایزر نقش مهمی در تعیین عملکرد آن دارد. از این رو در مقاله حاضر میدان جریان دوفازی درون اتمایزر نوع یک آزمایش شده توسط لین و همکاران به صورت سه بعدی و به کمک نرم افزار انسیس فلوئنت شبیه سازی شده است. اتمایزر نوع یک آزمایش شده توسط لین و همکاران، اتمایز...

In this article, two-phase slug regime in a duct with rectangular cross-section is investigated numerically, using the volume of fluid (VOF) method. Equations of mass, momentum and advection of volume fraction are solved accompanying k-∈ realizable turbulence equations. To ensure the creditability, numerical results have been compared with experime...

The effect of the mixing chamber length on the effervescent atomizer internal two-phase flow and the liquid film thickness at the exit of the atomizer at different gas-to-liquid mass ratios of 0.08%, 0.32%, and 1.24% has been investigated. The results of the internal two-phase flow simulation of the atomizer by the volume of fluid model showed that...

Two-phase flow was simulated within the effervescent atomizer by the volume of fluid interface tracing model. Different gas-to-liquid mass ratios (GLRs) of 0.08, 0.32, 1.24 and 4.9% at 0.38 L min−1 liquid flow rate have been studied. The purpose of this simulation is to study two-phase flow regimes within the effervescent atomizer and their effects...

In this research, interaction and oblique coalescence of bubbles under buoyancy force was simulated, numerically. The governing equations are continuity and momentum equations which have been discretized using the finite volume method and the SIMPLE algorithm. For simulating the interface of two phases, the level set method has been incorporated. L...

در تحقیق حاضر جریان داخلی اتمایزر گازدار، در نسبت های دبی جرمی گاز به مایع 0.08%، 0.32%، 1.24% و دبی مایع 0.38 L/min، به کمک مدل تعقیب سطح مشترک حجم سیال و برای سه طول مختلف از محفظه اختلاط شبیه سازی شده است. هدف از این شبیه سازی بررسی اثر طول محفظه اختلاط در ضخامت فیلم مایع خارج شونده از اتمایزر گازدار در نسبت های دبی جرمی گاز به مایع مختلف می باش...

In the present study two-phase flow within the effervescent atomizer has been simulated by the volume of fluid interface tracing model using 0.08%, 0.32%, 1.24%, and 4.9% gas-to-liquid mass ratios and 0.38 L/min liquid flow rate. The purpose of this simulation is to study two-phase flow regimes within the effervescent atomizer and their effect on t...

In present study, the rising of superheated vapor bubble in saturated liquid is simulated using volume of fluid method in OpenFOAM cfd package. The surface tension between vapor–liquid phases is considered using continuous surface force method. In order to reduce spurious current near interface, Lafaurie smoothing filter is applied to improve curva...

اتمیزاسیون سوخت عمدتا از اتمایزرهای فشاری، فشاری - چرخشی یادوسیالی استفاده میشود. اتمایزر گازدار جزو اتمایزرهای دوسیالی اختلاط داخلی است که برخلاف سایر انواع اتمایزرهای دوسیالی، گاز اتمایزر برای تشکیل مخلوط دوفازی در بالادست روزنه تخلیه با سرعت بسیار پایین به درون مایع تزریق می شود. جریان دوفازی گاز-مایع درون اتمایزر گازدار نقش مهمی در تعیین عملکرد...

In the present study, a new solver named phaseChangeHeatFoam is implemented on the OpenFOAM cfd package to simulate boiling and condensation. The solver is capturing the interface between two immiscible phases with a color function volume of fluid (CF-VOF) method. The two fluids (vapor and liquid) are assumed Newtonian and incompressible. The surfa...

The sloshing of liquid is occurred in a large variety of applications like reservoir containing liquid fuel, Liquefied Natural Gas (LNG), water and etc. In this paper, the critical frequency was found by comparing exciting frequency. The effects of density enhancement on decreasing the amplitude of produced waves and also the pressure imposed on th...

Objectives: In this study, sloshing interface in the 2D and 3D tanks were investigated by Open FOAM software Methods/ Statistical Analysis: The obtained results were in good agreement with experimental results. 2D and 3D results that were based on the first natural frequency excitement and ratio of A⁄L<0.1 (stimulation amplitude relative to the len...

Introduction Team-based learning is one of the methods concerned in medical education. Teaching and learning have some principles known as Merrill’s first principles that are a basis for effective education. This study examined the effect of using team-based learning combined with Merrill’s Principles on achieving learning objectives in nursing stu...

There are different approaches and methods to predict the interface changes in two-phase flows. Among these methods, volume-of-fluid (VOF) and level-set (LS) are some of the most famous ones. Common VOF schemes are mass conservative but cannot predict the surface tension with a good accuracy. In contrast, LS uses a continuous sign function which in...

In the present work, models that predict contact angle of droplet with solid surface are considered and compared. Two phases were assumed to be Newtonian, incompressible and immiscible fluids. OpenFOAM software is applied to simulate the two phases interface by using Color function VOF (CF-VOF) method. Different models for contact angle of droplet...

Underwater explosion phenomena is a complicated problem, however, it has different and important applications. This type of explosion includes strong shock waves with generation of low pressure cavitations zone and deformable interfaces. The main objective of this article is simulation of interaction of shock wave with interface of two-phase gas-li...

In this research two-phase slug flow regime in T-junction branching divider is examined in two regular and irregular groups. Simulation is accomplished by OpenFOAM open source software. Simulation uses single fluid with volume of fluid (VOF) method to follow gas-liquid two-phase flow interface. Constant velocity boundary condition for inlet, consta...

Present research has been done with the aim of investigating hydrodynamic behavior of slug flows in a transparent acrylic tube with inner diameter of 40 mm and height of 3.33 m. The vertical experimental system constructed in Two-Phase Flow lab in Tarbiat Modares University was used to perform the necessary experiments. By using image processing te...

In the present research, two-phase flow is studied adiabatically in vertical plexigalss tubes with inner diameters of 40 mm and 70 mm in heights of 1.73 m and 3.22 m. For this reason a large scale experimental set-up has been designed, constructed and operated according to construction standards. Flow pattern maps are presented for both tubes and e...

We present a combined trust region–line search structured algorithm for solving constrained nonlinear least-squares problems. The approach is based on adaptive structured scheme due to Mahdavi-Amiri and Bartels of the exact penalty method of Coleman and Conn for nonlinearly constrained optimization problems. The structured adaptation also makes use...

In this paper, two-phase air–water flow was investigated experimentally and simulated numerically using VOF method. The tests are conducted in Multiphase Flow Lab. of Tarbiat Modares University. In order to evaluate the rib effect on flow regimes, experimental investigation was conducted with ribs of different width and pitch where assembled on fro...

The VOSET method is discussed as a new coupled algorithm which is fully geometrical, mass-conserved and computes surface tension force as accurate as other CLSVOF methods. The algorithm of the method is used in a code which is developed for two-phase flow simulations. Validation of the code showed that the method produces spurious currents of a ver...

In the present study, volume of fluid method in Open FOAM open source CFD package will be extended to consider phase change phenomena due to condensation process. Both phases (liquid– vapor) are incompressible and immiscible. Vapor phase is assumed in saturated temperature. Interface between two phases is tracked with color function volume of fluid...

One of the obstacles in simulation of two phase flow is parasite currents. These currents cause unphysical distortion at interface which impairs interface capturing and numerical results. In the present study, two methods (using Filter and s-CLSVOF) are implemented in OpenFOAM two phase flow solver called interFoam to reduce parasite current. Three...

In this research, bubble free rise in a viscous Newtonian fluid is simulated and studied using the coupled method of two volume-of-fluid and level-set methods, called VOSET, in a Cartesian two-dimensional domain. In addition to satisfying the mass continuity, this approach uses a continuous function to model the surface tension force which reduces...

This paper presents a comprehensive formulation for the security constrained optimal power flow (SCOPF) problem considering valve loading effect, multiple fuel option, and prohibited operating zones of units as well as alternating current network modeling and contingency constraints. Also, the SCOPF formulation includes the integer variables, such...

In this article, a high-resolution diffuse interface method is investigated for simulation of compressible two-phase gas–gas and gas–liquid flows, both in the presence of shock wave and in flows with strong rarefaction waves similar to cavitations. A Godunov method and HLLC Riemann solver is used for discretization of the Kapila five-equation model...

We have recently proposed a structured algorithm for solving constrained nonlinear least-squares problems and established its local two-step Q-superlinear convergence rate. The approach is based on an earlier adaptive structured scheme due to Mahdavi-Amiri and Bartels of the exact penalty method. The structured adaptation makes use of the ideas of...

In this paper, direct numerical simulation of two-phase incompressible gas-liquid flow for simulation of bubble motion in a microtube is presented. Microtube radius is 10 µm. The interface is tracked using volume of fluid (VOF) method with continuous surface force (CSF) model. The flow is solved using a finite volume scheme, based on PISO algorithm...

This paper presents a new approach based on Benders decomposition (BD) to solve hydrothermal unit commitment problem with AC power flow and security constraints. The proposed method decomposes the problem into a master problem and two sets of sub-problems. The master problem applies integer programming method to solve unit commitment (UC) while the...

In this study, the behavior of a single bubble in a dielectric viscous fluid under a uniform magnetic field has been simulated numerically using the Level Set method in two-phase bubbly flow. The two-phase bubbly flow was considered to be laminar and homogeneous. Deformation of the bubble was considered to be due to buoyancy and magnetic forces ind...

In this study, Hardt evaporation model is implemented in OpenFOAM CFD package. Hardt evaporation model is suitable for phase change in micro size which the temperature of interface deviated from saturation temperature. Both phases are immiscible and incompressible and interface is resolving with VOF method. Newtonian flows are solved using a finite...

This paper presents a new and accurate method for modeling dynamic and transient behaviors of slug initiation and growth in horizontal ducts. In this analysis, a hyperbolic, two-pressure, five-equation, two-fluid model predicted the dynamic behavior of a complicated slug flow regime. The model was modified by including friction with the wall and at...

In this paper the field equations of compressible oscillating flow in the regenerator of Pulse Tube Refrigerators (PTRs) are solved. To obtain an analytical solution, successive approximation technique is applied to continuity, momentum, gas and matrix energy equations and ideal gas equation of state. In this respect, the flow field variables are e...

We present a structured algorithm for solving constrained nonlinear least squares problems, and establish its local two-step Q-superlinear convergence. The approach is based on an adaptive structured scheme due to Mahdavi-Amiri and Bartels of the exact penalty method of Coleman and Conn for nonlinearly constrained optimization problems. The structu...

This article presents a new hybrid solution approach based on Benders decomposition and outer approximation to solve the security-constrained unit commitment problem. The security-constrained unit commitment model includes both thermal and hydro unit commitment as well as AC network modeling. The proposed solution method decomposes the security-con...

Recently, we have presented a projected structured algorithm for solving constrained nonlinear least squares problems, and established its local two-step Q-superlinear convergence. The approach is based on an adaptive structured scheme due to Mahdavi-Amiri and Bartels of the exact penalty method. The structured adaptation also makes use of the idea...

In this research, adiabatic two-phase air–water flow was investigated, and results for smooth and ribbed rectangular ducts are presented here. The test fluids were air and water at approximately atmospheric conditions. Three ribs of different heights were used; the rib width and pitch were held constant. The ribs were positioned in the duct at thre...

In this article, the hydro dynamical instability initiation criterion in two-phase air-water stratified flow in a horizontal duct is investigated. Many models previously used to examine the hydro dynamical instability initiation suffer from an inability to achieve convergence and fail to obtain consistent results because they have complex character...

We have recently proposed a structured algorithm for solving constrained nonlinear least-squares problems and established its local two-step Q-superlinear convergence rate. The approach is based on an earlier adaptive structured scheme due to Mahdavi-Amiri and Bartels of the exact penalty method. The structured adaptation makes use of the ideas of...

In this article, the effect of bubble viscosity on internal circulation within a bubble has been analyzed numerically. The Finite Volume Method and SIMPLE algorithm have been used for field solution. This algorithm calculates the pressure field in addition to the velocity components that do not appear in related literature. A level-set method has b...

Sloshing, or liquid free surface oscillation, in containers has many important applications in a variety of engineering fields. The modal method can be used to solve linear sloshing problems and is the most efficient reduced order method that has been used during the previous decade. In the present article, the modal method is used to solve a nonli...

This paper presents a methodology for modeling slug initiation and growth in horizontal ducts. Transient two-fluid equations are solved numerically using a class of high-resolution shock capturing methods. The advantage of this method is that slug formation and growth in a stratified regime can be calculated directly from the solutions to the flow...

In this article, the hydrodynamical instability initiation criterion in two-phase stratified flow in a horizontal duct is examined. The nonlinear two mass and two momentum conservation equations are used for numerical simulation using the two-phase two-fluid model. The model is solved using the Finite Volume and Spectral Methods, respectively. This...

In this article, two-dimensional partial differential equations with time representation of nuclear power reac-tor kinetics are considered for spatial reactor dynamics and thermo hydraulic behavior analysis of a large thermal advanced gas cooled reactor (AGR) type used for nuclear power generation. The equations include the neutron flux equation an...

In this paper, effect of magnetic field on a bubble within two-phase bubbly flow studied by using a Level Set method. Two-phase flows under effect of external fields especially magnetic field have a wide range of medicine and engineering applications, such as magneto hydrodynamic problems (MHD), gas and oil facilities, fusion nuclear reactors, nucl...

The introduction of liberalized electricity markets in many countries has resulted in more highly stressed power systems. On the other hand, operating points of a power system are acceptable in the feasible region, which is surrounded by the borders of different stabilities. Power system instability is critical for all participants of the electrici...

Loading of today power systems continuously increases especially in the developed countries and liberalized electricity markets. On the other hand, operating points of a power system are acceptable in the feasible region usually surrounded by the borders of different stabilities. Power system instability is critical for all participants of the elec...

In this article, the transient condition of two-phase stratified gas–liquid flow was investigated using numerical simulation. The basis of the method involves the one-space dimensional transient solution of the governing equations using the two-fluid model. In this paper, an analogy between the SIMPLE algorithm in two-space dimensional single-phase...

In this article, we examine the transient response of a co-current double-pipe heat exchanger with respect to the inlet temperature change. For this investigation, a method whose main feature is analytical solution of the energy equation for one element of the heat exchanger is developed. The governing equations are linearized with respect to space...

In this paper, the effect of wavelength on the disturbed interface of a two-phase stratified regime will be discussed. It is assumed that the two phases are completely separated and are flowing parallel to each other along the duct. In order to analyze the stability of the two-phase stratified flow, a small disturbance is considered at the interfac...

This paper simulates the dynamical response of a countercurrent heat exchanger. The model, which is employed for this purpose for the first time, employs the numerical method based on the analytical solution of the energy equation. The details of this method are introduced in the paper. Furthermore, the transient behavior of the system is considere...

This paper reviews the use of the single-pressure model in two-phase flow modeling in previous literature, and develops and demonstrates the equations for the two-pressure model. Many of the models investigated previously suffer from an inability to achieve convergence and consistent results because they have complex characteristic values. Two diff...

This paper reviews the use of the single-pressure model in two-phase flow modeling in previous literature, and develops and demonstrates the equations for the two-pressure model. Many of the models investigated previously suffer from an inability to achieve convergence and consistent results because they have complex characteristic values. Two diff...

In this attempt effect of pipeline equipment behavior was considered on water hammer numerically. The effect includes opening / closing of the shut off valves, loss of coefficient of the outlet bypass pipe for the air chamber, elasticity of the pipeline and loss coefficient due to friction. In order to study the behavior, mass and momentum conserva...

Transient conditions of two-phase air-water flow were numerically analyzed. The wave growth from a stratified flow regime in a horizontal duct was considered. Conservation equations were solved by finite difference method. The analyses on the onset of wave initiation was compared with the empirical correlations of other researchers. This analysis c...

Thermalhydraulic transient phenomena of a steam-water two-phase flow was calculated numerically in order to investigate the onset of slugging from a stratified flow in a horizontal duct. Conservation equations were solved by the finite difference method using a two-phase flow analyzer ‘MINCS’. The analysis was performed to investigate the initiatio...

Two-phase air-water flow was studied experimentally under atmospheric conditions Wave growth and slugging from stratified flow regime in a horizontal duct were analyzed by using a video camera. The result for slug initiation was compared with the instability criteria based on linear analysis and the empirical correlations of other researchers. The...

Two-phase air-water flow was studied experimentally under atmospheric conditions. Wave growth and slugging from stratified flow regime in a horizontal duct were analyzed by using a video camera. The result for slug initiation was compared with the instability criteria based on linear analysis and the empirical correlations of other researchers. The...

We describe a structurally projected exact penalty algorithm for solving constrained nonlinear least squares problems. The projected structure makes use of the general exact penalty method of Coleman and Conn [3, 4] and the projected Hes-sian updating scheme of Nocedal and Overton [9] for general nonlinear programs, both appropriately adapted to th...

In this study, a single bubble behavior in dielectric viscous fluid under the uniform magnetic field has been simulated numerically by using a level set method in two-phase bubbly flow. The two-phase bubbly flow considered to be laminar and homogenous. Deformation of the bubble was considered due to buoyancy and magnetic forces induced from the ext...

Thesis--University of Tsukuba, D.Eng.(A), no. 756, 1990. 3. 23