Sharif Digital Repository

Regarding the geometric structural characteristics of innovative dual cooled annular fuel and the possibility of heat split and flow distribution among the internal and external channels, the development of new computational tools is essential for estimating safety margins and accurate assessment of its thermal-hydraulic performance. The SADAF code (Subchannel Analysis Dual cooled Annular Fuel) by COBRA-EN code is developed for this purpose. In the SADAF code, using COBRA-EN code for subchannel analysis in internal and external subchannels, a program has been developed to compute new variables that need to be considered in the thermal-hydraulic assessment. Also, fuel heat transfer... 

Freeze desalination (FD) works upon the separation of impurities from pure water during ice crystals formation. The required cold source could be supplied by the cold energy of liquefied natural gas (LNG). In the current study, freeze desalination of seawater is explored by directly exploiting the cold energy of LNG within an appropriate range of temperature after producing work in a power generation cycle. A detailed discussion has been given on the inlet temperature of LNG to the FD unit for the first time. The direct utilization has the privilege of eliminating the addition of a secondary refrigerant and its refrigeration cycle to the FD process. A multi-objective optimization is... 

Proppants transport is an advanced technique to improve the hydraulic fracture phenomenon, in order to promote the versatility of gas/oil reservoirs. A numerical simulation of proppants transport at both hydraulic fracture (HF) and natural fracture (NF) intersection is performed to provide a better understanding of key factors which cause, or contribute to proppants transport in HF–NF intersection. Computational fluid dynamics (CFD) in association with discrete element method (DEM) is used to model the complex interactions between proppant particles, host fluid medium and fractured walls. The effect of non-spherical geometry of particles is considered in this model, using the multi-sphere... 

The deformation and breakup dynamics of a compound ferrofluid droplet under shear flow and uniform magnetic field are numerically studied in this paper. Utilizing magnetic field provides the possibility to obtain better control over the compound droplet morphology and breakup in a simple shear flow. To solve the governing equations for interfaces motion and hydrodynamics, the conservative phase field lattice Boltzmann model is employed, and a finite difference approach is applied for calculating the magnetic field. To verify the accuracy of present simulations, the results are validated with those of four relevant benchmarks including liquid lens between two stratified fluids, three-phase... 

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective... 

The sloshing phenomena in a partially filled tank can affect its stability. Modifications of tank instability due to the movement of the tank carrier, are key design points for the stability of a carrier. Even though the sloshing phenomenon has already been investigated using the BEM-FDM technique, the research in this paper covers this phenomenon in a porous media, which is new in 2-D coordinates. For this purpose, a Laplace equation has been used for potential flow, and kinematic and dynamic boundary conditions have been applied to the free surface. Also, a formulation has been developed for a free surface in porous media. BEM has been used for solving the governing equation and FDM... 

We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics (CFD) with the discrete element method (DEM). This numerical method allows us to incorporate the fluid-particle interactions (drag force, contact force, Saffman lift force, Magnus lift force, buoyancy force) using momentum exchange and the non-Newtonian behavior of the fluid. The interactions of particle-particle, particle-wall, and particle-drill pipe are taken into account with the Hertz-Mindlin model. We compare the transport of spheres with non-spherical particles (non-smooth sphere, disc, and cubic) constructed via the... 

This paper presents an analysis of the combined electro-osmotic and pressure-driven axial flows of viscoelastic fluids in a rectangular microchannel with arbitrary aspect ratios. The rheological behavior of the fluid is described by the complete form of Phan-Thien–Tanner (PTT) model with the Gordon–Schowalter convected derivative which covers the upper convected Maxwell, Johnson–Segalman and FENE-P models. Our numerical simulation is based on the computation of 2D Poisson–Boltzmann, Cauchy momentum and PTT constitutive equations. The solution of these governing nonlinear coupled set of equations is obtained by using the second-order central finite difference method in a non-uniform grid... 

The optimal design of a casting feeding system is considered. The problem is formulated as the volume constrained topology optimization and is solved with the finite element analysis, explicit design sensitivity, and numerical optimization. In contrast to the traditional topology optimization where the objective function is defined on the design space, in the presented method, the design space is a subset of the complement of the objective function space. To accelerate optimization procedure, the nonlinear unsteady heat transfer equation is approximated with a Poisson-like equation. The feasibility of the presented method is supported with illustrative examples. © 2007 Springer-Verlag