Sharif Digital Repository

Coupling of lattice Boltzmann (LB) and phase-field (PF) methods is discussed for simulation of a range of multiphase flow problems. The local relaxation and shifting operators make the LB method an attractive candidate for the simulation of the single-phase as well as multiphase flows. For simulating interface dynamics, LB methods require to be coupled with an appropriate scheme representing interfacial dynamics. To this end, we have used a model based on the order parameter, which could be either an index function or a phase-field variable, and coupled it with a LB solver for the simulation of various classes of complex multi-physics and multiphase flows. The LB method is used to compute... 

Spontaneous imbibition of water into the matrix blocks because of capillary forces is an important recovery mechanism for oil recovery from naturally fractured reservoirs. In modeling this process, it has been assumed classically that local equilibrium is reached and, therefore, capillary pressure and relative permeability functions are only a function of water saturation, resulting in the appearance of the self-similarity condition. In some works published in the last 2 decades, it has, however, been claimed that local equilibrium is not reached in porous media, and therefore, opposite the classical local-equilibrium/self-similar approach, non-equilibrium effects should be taken into... 

Techniques of production data analysis for single-phase oil and gas reservoirs have advanced significantly over the past few years. These techniques range from traditional (Arps and Fetkovich) to modern (for the variation of operating conditions at the wellbore). The application of these techniques for analysis of the production data of a gas condensate reservoir may not yield reliable answers due to the fact that the flow of fluid in gas condensate reservoirs is not single-phase. This paper presents the treatment of a modern method of production data analysis (single-phase flow) to analyze the production data of a gas condensate reservoir (two-phase flow). For this purpose, a single-phase... 

A new computational algorithm is introduced in the present study to solve multimaterial topology optimization problems. It is based on the penalization of the objective functional by the multiphase volume constrained Ginzburg-Landau energy functional. The update procedure is based on the gradient flow of the objective functional by a fractional step projected steepest descent method. In the first step, the new design is found based on the projected steepest descent method to ensure the reduction in the objective functional, simultaneously satisfying the control constraints. In the second step, regularization step, an H1 regularity of the solution is ensured while keeping the feasibility of... 

Performance of polymer electrolyte membrane fuel cells (PEMFC) at high current densities is limited to transport reactants and products. Furthermore, large amounts of water are generated and may be condensed due to the low temperature of the PEMFC. Development of a two-phase flow model is necessary in order to predict water flooding and its effects on the PEMFC performance. In this paper, a multiphase mixture model (M2) is used, accurately, to model two-phase transport in porous media of a PEMFC. The cathode side, which includes channel, gas diffusion layer (GDL), microporous layer (MPL), and catalyst layer (CL), is considered as the computational domain. A multidomain approach has been used... 

A new algorithm for the solution of multimaterial topology optimization problems is introduced in the present study. The presented method is based on the splitting of a multiphase topology optimization problem into a series of binary phase topology optimization sub-problems which are solved partially, in a sequential manner, using a traditional binary phase topology optimization solver; internal solver. The coupling between these incomplete solutions is ensured using an outer iteration strategy based on the block coordinate descend method. The presented algorithm provides a general framework to extend the traditional binary phase topology optimization solvers for the solution of multiphase... 

We report the existence of interfacial instability in the two-dimensional channel flow of a sediment suspension whose particles diffuse in the carrier fluid due to shear-induced collisions. We derive partial differential equations that govern the deformations of the interface between the sediment suspension and the clear fluid, and devise a perturbation method that preserves the positivity of the particle volume fraction. We solve perturbed momentum, particle transport and deforming interface equations to show that a Kelvin-Helmholtz-type unstable wave develops at the interface for wavelengths longer than a critical value. Short-wavelength oscillations of the interface are damped due to... 

Purpose - In this paper, the flow of multiphase fluids in a one-dimensional homogeneous porous media involving the gravity effects is numerically studied using the dominant wave method. The paper aims to discuss these issues. Design/methodology/approach - The numerical scheme used for solving the pressure equations, obtained for the black-oil model, is a backward Euler scheme while the hyperbolic mass conservation equations, derived for both black-oil and Buckley-Leverett models, are solved using the dominant wave method. Higher-order schemes are achieved using either variable derivatives along with the minmod limiter or a MUSCL type interface construction scheme using the Fromm's limiter.... 

Switched reluctance machines (SRMs) suffer from ultra-low-frequency torque ripple in single pulse mode. This ripple is the result of an imbalance in phase currents, when multiphase excitation occurs. This paper investigates the origin of this imbalance and identifies the imbalanced phase. Excitation shifting strategy, which delays excitation of the imbalanced phase, is then proposed. The delay angle adjusts current amplitude in the imbalanced phase to attain a perfect balance between all phases. The excitation shifting strategy is a general solution, which is applicable to both three-phase and four-phase machines. In addition, the proposed method can be implemented by a much simpler drive... 

The relative permeability curves are key factors for assessment of reservoir performance by numerical simulators. The widely used one-parameter models are not sufficiently flexible for fitting laboratory measured relative permeability data. These models only show a concave upward trend and cannot represent the S-shape behavior of relative permeability. The other three-parameter models are too complex to use in practical reservoir engineering calculations. In this paper, a novel two-parameter model is proposed that maintains the simplicity of previous models while having great flexibility over a full range of saturation. The two parameters L and U control the shape of the lower and upper part... 

Enhanced Oil Recovery techniques are gaining more attention worldwide as the proved oil reserves are declining and the oil price is hiking. Although many giant oil reservoirs in the world were already screened for EOR processes, the main challenges such as low sweep efficiency, costly techniques, possible formation damages, transportation of huge amounts of EOR agents to the fields especially for offshore cases, analyzing micro-scale multi-phase flow in the rock to the large scale tests and the lack of analyzing tools in traditional experimental works, hinder the proposed EOR processes. Our past experiences on using nanotechnology to the upstream cases, especially EOR processes, revealed... 

Mass transfer in the liquid phase of gas-liquid multiphase flows usually takes place at a considerably slower rate than the transfer of momentum, so mass flux boundary layers are much thinner than momentum boundary layers. In Direct Numerical Simulations (DNS) the resolution requirement for flows with mass transfer are therefore significantly higher than for flow without mass transfer. Here we develop a multiscale approach to compute the mass transfer from buoyant bubbles, using a boundary-layer approximation next to the bubble and a relatively coarse grid for the rest of the flow. This approach greatly reduces the overall grid resolution required  

The water-gas shift reaction occurs competitively to the main reaction of the Ir-catalysed methanol carbonylation process. To study the effect of seven factors including temperature, pressure, iridium, ruthenium, methyl iodide, methyl acetate and water concentrations on the formation of hydrogen and carbon dioxide as a result of the water-gas shift reaction and other side reactions in the carbonylation of methanol to acetic acid, the experimental design method combined with response surface methodology (RSM) was utilised. Central composite design at five levels (with α=1.63) was used to design experiments. A quadratic model that included the main and interaction effects of variables for H 2... 

Phase identification is an important aspect of flash calculations which can affect the phase and chemical equilibria. A new simultaneous approach for reactive mixtures, based on τ-method which relies on modification equation for mole fraction summation, is introduced in this paper. In the proposed methodology, phase identification and solution of governing equations can be performed simultaneously and effectively. In addition, prior knowledge of the number of phases in advance is not required. Present methodology has been verified with the help of case studies and results are discussed in the present paper. The results indicate that the present method gives us information about presence of... 

The aim of this work is to investigate the non-equilibrium effects of phase change in cavitating flows. For this purpose, the concept of phase change thermodynamic probability is used along with homogeneous model to simulate two-phase cavitating flows. For simulation of unsteady behaviors of cavitation, which have practical applications, unsteady PISO algorithm based on the non-conservative approach is utilized. For multi-phase simulation, single-fluid Navier-Stokes equations, along with the volume fraction transport equation, are employed. In this paper, phase change thermodynamics probabilities and cavitation model is briefly summarized. Thus, derivation of the cavitation model, starting... 

Spontaneous imbibition of water into the matrix blocks because of capillary forces is an important recovery mechanism for oil recovery from naturally fractured reservoirs. In modeling this process, it has been assumed classically that local equilibrium is reached and, therefore, capillary pressure and relative permeability functions are only a function of water saturation, resulting in the appearance of the self-similarity condition. In some works published in the last 2 decades, it has, however, been claimed that local equilibrium is not reached in porous media, and therefore, opposite the classical local-equilibrium/self-similar approach, non-equilibrium effects should be taken into... 

A numerical treatment for the prediction of cavitating flows is presented and assessed. The algorithm uses the preconditioned multiphase Euler equations with appropriate mass transfer terms. A central difference finite volume scheme with suitable dissipation terms to account for density jumps across the cavity interface is shown to yield an effective method for solving the multiphase Euler equations. The Euler equations are utilized herein for the cavitation modeling, because some certain characteristics of cavitating flows can be obtained using the solution of this system of equations with relative low computational effort. In addition, the Euler equations are appropriate for the assessment... 

Airlift Systems (ALS) are widely used in various industrial applications. As the main part of the flow through ALS's upriser pipe, is formed by gas-liquid flow, the analysis of such systems will be accompanied by problems of two-phase flow modelling. Several effective variables are involved in ALS; thereupon comprehensive method is needed to consider these parameters. Exergy analysis can be considered as a simple solution for the realisation of the preferred domain of ALS's operation. Here, this method has been proposed to examine the performance of ALS. Based on thermodynamic principles, an analytical model has been implemented in each phase and the respective experimental data have been... 

Techniques of production data analysis for single-phase oil and gas reservoirs have advanced significantly over the past few years. These techniques range from traditional (Arps and Fetkovich) to modern (for the variation of operating conditions at the wellbore). The application of these techniques for analysis of the production data of a gas condensate reservoir may not yield reliable answers due to the fact that the flow of fluid in gas condensate reservoirs is not single-phase. This paper presents the treatment of a modern method of production data analysis (single-phase flow) to analyze the production data of a gas condensate reservoir (two-phase flow). For this purpose, a single-phase... 

In this paper, the effect of different parameters on the thermal operation of a Closed Loop Pulsating Heat Pipe (CLPHP) has been investigated. These parameters include the working fluid, the inclination angle, the filling ratio, and the input heat flux. The effect of nanoparticle mass concentrations has been analyzed as well. It was observed that the CLPHP can decrease thermal resistance up to 11.5 times compared to the same empty copper tube with thermal resistance of 9.4 K/W. Optimum thermal operation for a system with the water-silver nanofluid was achieved at conditions of the 50% filling ratio with thermal resistance of 0.9 K/W, and for the water-titanium oxide system, the optimal...