Sharif Digital Repository

The proper understanding of rheological characteristics of CGA based fluids is of crucial importance in determining the performance of the fluid, in order to maintain the most effective fluid properties for safe, efficient, and economical drilling operation. This paper presents a concise investigation on the effect of concentration of the three main components of a novel environmentally friendly lightweight CGA based drilling fluid, i.e., xanthan gum biopolymer, starch, and biosurfactant, to the Herschel-Bulkley rheological model parameters. The three parameters of Herschel-Bulkley model, i.e., yield stress, fluid consistency, and fluid flow index were calculated by fitting the experimental... 

Pushing a fluid with a less viscous one gives rise to the well known Saffman-Taylor instability. This instability is important in a wide variety of applications involving strongly non-Newtonian fluids that often exhibit a yield stress. Here we investigate the Saffmann-Taylor instability in this type of fluid, in longitudinal flows in Hele-Shaw cells. In particular, we study Darcy's law for yield stress fluids. The dispersion equation for the flow is similar to the equations obtained for ordinary viscous fluids but the viscous terms in the dimensionless numbers conditioning the instability now contain the yield stress. This also has repercussions on the wavelength of the instability as it... 

Ammonia detoxification is one of the main functions of the liver results in production of urea. In this study ammonia elimination and urea production was simulated in a microchannel mimicking the hepatic porto central axis. Navier- Stockes equations along with convection equations were solved for the related species in the entire domain. Since the Reynolds number was small (~1) the fluid flow regime was laminar. Urea cycle was modeled regarding its four main enzymes. Twelve rate equations were also solved in order to obtain the concentration of each metabolites participating in urea cycle. Concentration of the urea reached its maximum ca. 1.2e-5 M at the end of the channel which is in good... 

The aim of this research is to design an implantable integrated microfluidic system in order to regularly measure the glucose level in the human body, nonenzymatically, using the microdialysis method. The main compartments of this system are a micropump, array of hollow microneedles and an electrochemical sensor. At the base of the microneedles, there are located semipermeable membranes, that when the pumped dialysis fluid passes over them, the glucose of the interstitial fluid diffuses into the dialysis fluid and then, in the sensor section, it is measured nonenzymatically using the amperometry method. Both the arrangement of the miconeedles and the amount of the dialysis fluid flow are... 

Hybrid nanofluids are new and most fascinating types of fluids that involve superior thermal characteristics. These fluids exhibit better heat-transfer performance as equated to conventional fluids. Our concern, in this paper, is to numerically interpret the kerosene oil-based hybrid nanofluids comprising dissimilar nanoparticles like silver (Ag) and manganese zinc ferrite (MnZnFe2O4). A numerical algorithm, which is mainly based on finite difference discretization, is developed to find the numerical solution of the problem. A numerical comparison appraises the efficiency of this algorithm. The effects of physical parameters are examined via the graphical representations in either case of... 

Purpose: The purpose of this paper is to investigate the effects of geometrical parameters, eccentricity and perforated fins on natural convection heat transfer in a finned horizontal annulus using three-dimensional lattice Boltzmann flux solver. Design/methodology/approach: Three-dimensional lattice Boltzmann flux solver is used in the present study for simulating conjugate heat transfer within an annulus. D3Q15 and D3Q7 models are used to solve the fluid flow and temperature field, respectively. The finite volume method is used to discretize mass, momentum and energy equations. The Chapman–Enskog expansion analysis is used to establish the connection between the lattice Boltzmann equation... 

Purpose: This paper aims to to simulate the flow and heat transfer during free convection in a square cavity using double-multi-relaxation time (MRT) lattice Boltzmann method. Design/methodology/approach: The double-MRT lattice Boltzmann method is used, and the natural convection fluid flow and heat transfer under influence of different parameters are analyzed. The D2Q5 model and D2Q9 model are used for simulation of temperature field and flow field, respectively. The cavity is filled with CuO-water nanofluid; in addition, the thermo-physical properties of nanofluid and the effect of nanoparticles’ shapes are considered using Koo–Kleinstreuer–Li (KKL) model. On the other hand, the cavity is... 

Effects of inclination angle on natural convective heat transfer and fluid flow in an enclosure filled with Al2O3-water nanofluid are studied numerically. The left and right walls of enclosure are kept in hot and cold constant temperature while the other two walls are assumed to be adiabatic. Considering Brownian motion and thermophoresis effect (two important slip velocity mechanisms) the two-phase mixture model has been employed to investigate the flow and thermal behaviors of the nanofluid. The study was performed for various inclination angles of enclosure ranging from γ = 0° to γ = 60°, volume fraction from 0% to 3%, and Rayleigh numbers varying from 105 to 107. The governing equations... 

In this paper, a pressure splitting formulation is proposed for Weakly Compressible SPH (WC-SPH) method and its capability in the suppression of the spurious oscillations is studied by conducting a stability analysis. The proposed formulation is implemented within the framework of a consistent SPH method. The predictions from the theoretical analysis are verified by the results of numerical test-cases. This method is applied to the incompressible fluid flow around periodic array of circular cylinders. The accuracy and the convergence of the results are investigated for benchmark problems. The results are also compared with those of the conventional WC-SPH method. In a similar test-case, the... 

The current study aims at introducing a 2D and fast-running code for the issues pertinent to design, analysis and safety in modular high temperature reactors. While the porous media approach is only applied to pebble bed type, the analysis in this paper covers both pebble bed and prismatic reactor. A time-dependent mass equation along with energy conservation equation for the cooling gas and a time-dependent energy conservation equation for the solid was solved. Appropriate series of constitutive equations (e.g. heat transfer coefficient, effective heat conductivity of solid, heat transfer coefficient, pressure drop etc.) has been recruited as well. In addition a finite-volume method is... 

A precise thermal-hydraulics model is of great importance for developing more effective designs of High Temperature Gas Cooled Reactors (HTGR). Recently, several advancements have been made in the methods of analysis of porous media which could be of significant value in the development of more precise and robust codes. The objective of this research is to incorporate some of the most recent improvements in the development of a new 2D program for thermal-hydraulics analysis of modular high temperature reactors. The program is mainly based on the solution of a coupled set of mass, energy and momentum conservation equations for the gas flow, along with the energy conservation equation in the... 

In this paper, a passive microfluidic device for continuous real time blood plasma separation has been studied and optimized. A numerical model is used to solve both the fluid flow and the particles confined within it. Red blood cells are considered as particles with diameter of 7μm. A parametric study is performed in order to characterize the effect of different parameters on separation and purity efficiency. In this study, four different variables were introduced to design the microfluidic device for blood plasma separation including: the angle between the daughter channels and the main channel, the widths, the diffuse angle and the number of daughter channels. Results show that the... 

Nonlinear dynamics of an extensible cantilevered pipe conveying pulsating flow is considered in this paper. The fluid flow fluctuates harmonically and exhausts via a nozzle attached to the end of the pipe. Taking into account the extensibility assumption, the coupled nonlinear lateral–longitudinal equations of motion are derived using Hamilton's principle and discretized via Galerkin's method. The adaptive time step Adams algorithm is applied to extract the time response, and then the bifurcation, power spectral density and phase plane maps are plotted for some case studies. Effects of some geometrical parameters such as flow mass, pulsating flow frequency, gravity, nozzle mass and nozzle... 

In this work, forced-convection heat transfer of magnetic-sensitive nanofluids has been investigated in the presence of rotating magnetic field. In this regard, the laminar, Newtonian, incompressible, and two-dimensional (2D) fluid flow in a horizontal duct subject to constant wall temperature boundary condition was modeled. Moreover, the fluid was supposed to be non-electrical conductive and the magnetic field source comprised of two time varying components perpendicular to each other. Influences of magnetic field intensity and frequency, inlet fluid velocity, and spin viscosity on the forced-convection heat transfer of the magnetic nanofluids were investigated. It was found that the... 

A fast and efficient reduced order formulation is presented for the first time to study dynamics and stability of conical/cylindrical shells with internal fluid flows. The structural and fluid formulations are developed based on general assumptions to avoid any deficiency due to modeling. Their respective solutions and the final solution to the coupled field problem are also developed in a way to be capable of capturing any desirable set of boundary conditions. In addition to the flexibility provided by the solution methodology and generalization provided by the formulation, current solution proposes an additional advantage over others which is the minimal computational cost due to the... 

In this study, an extrinsically enriched element free Galerkin (EFG) method is proposed for the thermo-hydro-mechanical simulation of saturated porous media. By taking advantage of partition of unity property of moving least square shape functions, weak discontinuities such as material interfaces are modeled using the Ridge enrichment function and impermeable strong discontinuities are simulated using the Heaviside function. Some guidelines are proposed for the selection of EFG numerical parameters to ensure the stability and accuracy of the results. Numerical examples are provided to illustrate the capability of the proposed approach for fully coupled THM analysis of discontinuous porous... 

In this paper, a three-dimensional simulation of fully coupled multiphase fluid flow and heat transfer through deforming porous media is presented in the context of EFG mesh-less method. Spatial discretization of the system of governing equations is performed using EFG and a fully implicit finite difference scheme is employed for temporal discretization. Penalty method is used for imposition of essential boundary conditions. The developed numerical tool is employed to simulate two problems of nuclear waste disposal and CO2 sequestration in deep underground strata. The obtained results demonstrate the capability and robustness of the developed EFG code. © 2018 Elsevier Ltd  

The three-dimensional power law fluid flow through rough microchannels has been studied numerically to determine the effects of the topographic structures on the thermal and hydrodynamic characteristics of the system. Rectangular, triangular and sinusoidal element shapes have been considered in order to investigate the effects of roughness height, width, pitch and channel separation on the pressure drop and heat transfer. Uniform wall heat flux boundary condition has been applied for all the peripheral walls. The results indicate that the global heat transfer performance can be improved or reduced by the roughness elements at the expense of pressure head when compared with the smooth... 

Optical and thermal analysis of the most well-known solar concentrator system; parabolic trough collector (PTC) are investigated and analyzed. To evaluate performance of the PTC, four cities of Iran with different weather conditions are chosen as case studies. Effective parameters such as concentration ratio, incident angle correction factor, collector mass flow rate are considered. The main objective of this work is evaluation of the solar energy potential using PTC in under consideration cities with different climates. Numerical modeling of the analysis is done using MATLAB software. Simulation results shows that Shiraz, with an average annual thermal efficiency of 13.91% and annual useful... 

Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented...