Sharif Digital Repository

In this study, the potential of using a polyacrylamide-silica nanocomposite (PAM-S) to control the filtration properties of bentonite water-based drilling muds under different salinity conditions was evaluated. Static filtration tests under low-pressure/low-temperature (LPLT) conditions accompanied by rheological measurements have been carried out to analyze the role of silica nanoparticles (NPs) and nanocomposites (NCs) in the base fluid properties. Moreover, high-pressure/high-temperature (HPHT) static filtration was also investigated to evaluate the thermal stability of PAM-S. Afterward, dynamic filtration has been conducted in a filtration cell equipped with an agitating system with a... 

The heat transfer simulations of turbine blades with internal cooling are faced with so many uncertainties, of which some originate from the secondary air system, including the inlet hot gas temperature and pressure and the cooling side boundary conditions, and the blade material. The main objective of this work is to carry out a suitable sensitivity analysis on a specific novel turbine vane to improve the thermal performance of its internal cooling system and to quantify how the uncertainties on the designed/calculated values can desirably/undesirably affect the maximum blade surface temperature, which can consequently affect the gas turbine engine efficiency. Furthermore, the sensitivity... 

In this article, the hydrodynamic analysis and noise of the propeller and the surface vessel hull were examined. The model selected in this study is a KRISO Container Ship (KCS) with a five-bladed propeller. Initially, the hydrodynamic analysis of the propeller in open water mode and then in self-propulsion mode was investigated using computational fluid dynamics. Simulations were carried out using a commercial solver, STAR-CCM+ (RANS equations with FVM and VOF model). Finally, the emitted noise from the propeller and the vessel hull was investigated using Fox William Hawkins equations. The pressure distribution and hydrodynamic performance (thrust, torque, efficiency) of the propeller in... 

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... 

Steam/water stratified flow would occur in transient condition (e.g. LOCA) in light water Nuclear Power Plants (NPPs). Due to high gradient of flow characteristics at the interface of steam/water flow, the prediction of flow characteristics (e.g. temperature, pressure, velocity, and Turbulent Kinetic Energy (TKE)) requires further attention and special interfacial models. Also, accurate simulation of these mentioned characteristics needs fine spatial mesh and very small time steps based on Computational Fluid Dynamics (CFD) standard criteria. In order to reduce the computational cost, the combination of thermal–hydraulic modelling and soft computing is considered as a new strategy in this... 

Human-generated droplets constitute the main route for the transmission of coronavirus. However, the details of such transmission in enclosed environments are yet to be understood. This is because geometrical and environmental parameters can immensely complicate the problem and turn the conventional analyses inefficient. As a remedy, this work develops a predictive tool based on computational fluid dynamics and machine learning to examine the distribution of sneezing droplets in realistic configurations. The time-dependent effects of environmental parameters, including temperature, humidity and ventilation rate, upon the droplets with diameters between 1 and 250μm are investigated inside a... 

The aim of this study was to determine whether specific three-dimensional aortic shape features, extracted via statistical shape analysis (SSA), correlate with the development of thoracic ascending aortic dissection (TAAD) risk and associated aortic hemodynamics. Thirty-one patients followed prospectively with ascending thoracic aortic aneurysm (ATAA), who either did (12 patients) or did not (19 patients) develop TAAD, were included in the study, with aortic arch geometries extracted from computed tomographic angiography (CTA) imaging. Arch geometries were analyzed with SSA, and unsupervised and supervised (linked to dissection outcome) shape features were extracted with principal component... 

The process of fluid flow displacement in porous media has recently gained great prominence owing to its widespread usage in a variety of industries, especially in the case of pore scale investigations. Although, many studies have been conducted to address pore-scale investigations in both modeling and experimental approaches, the role of interfacial tension and contact angle on pore-scale phenomena is less focused. In this work, direct pore-scale modeling was used to precisely examine the effect of interfacial tension and contact angle on the fluid flow at the microscale. Also, several pore-scale mechanisms, including Haines jump and dynamic breakup mechanisms, were observed. Therefore, the... 

The full-scale CFD simulations may not be recommended in preliminary steps of STHEs’ design and sensitivity analyses because of heavy computations. This work benefits from the sequential geometry repetitions in STHEs and presents a new semi-full-scale approach, which alleviates the need for full-scale simulation of STHEs. This approach first isolates the smallest zone, say block, which is sequentially repeated in the STHE domain. Second, this block is carefully simulated considering various thermal and flow working conditions. Third, the data collected from these CFD simulations are used to generate the required thermal and flow correlations for the chosen block at various working... 

UF6 gas flow in the total regions of a rotor with the radius of 0.1 m and the length of 1 m in axisymmetric and steady states was simulated using a new hybrid CFD-DSMC method in the OpenFOAM framework. Implicit coupled density-based scheme was performed for CFD method, and Variable Hard Sphere (VHS) and diffuse model were employed in DSMC method. Also, as an initial estimation, the local Knudsen number was applied to determine the interface location between the continuum-rarefied regions (r = 0.0855 m). Then it was modified (r = 0.084 m) to reduce the computational cost. The comparison results of pure CFD and CFD-DSMC methods illustrated that there were large differences between the flow... 

Hand in hand with the flourish of the biodiesel industry, glycerol (GLY) as an inconvenient by-product has generated environmental and sustainability concerns. Devising measures for efficient transformation of GLY into value-added products is a promising solution. In this contribution, the transformation of GLY to lactic acid (LA) as a valuable chemical was investigated in a continuous process for industrial applications. In this regard, a catalytic method using heterogeneous Cu nanoparticles in NaOH solution was studied in a microreactor by a CFD simulation. A seven-inlet micromixer comprising an optimized mixing unit was incorporated for uniform distribution of the species. The effects of... 

Solid oxide fuel cells (SOFCs) introduce a promising electrochemical conversion technology to generate electricity directly from fuel oxidization. A three-dimensional (3D) numerical model is proposed to evaluate the SOFC performance by employing computational fluid dynamics (CFD) approach based on the finite element method. This research includes simultaneously solving momentum, energy, and mass transport equations linked with the electrochemical reactions. First, the modeling results of a SOFC system with a rectangular channel in the absence of obstacles are compared with the experimental data, showing very good agreement. The effects of different shapes and numbers of obstacles on fuel... 

This paper introduces a new methodology for designing and optimizing the performance of hydraulic Cross-Flow turbines for a wide range of operating conditions. The methodology is based on a one-step approach for the system-level design phase and a three-step, successive numerical analysis approach for the detail design phase. Compared to current design methodologies, not only does this approach break down the process into well-defined steps and simplify it, but it also has the advantage that once numerical simulations are conducted for a single turbine, most of the results can be used for an entire class of Cross-Flow turbines. In this paper, after a discussion of the research background, we... 

Functional endoscopic sinus surgery (FESS) is performed to treat sinusitis when treatment with medication fails. In the present study, three different virtual maxillary sinus endoscopic surgeries were performed on a realistic 3-D computational model of the nasal cavity of an adult male under the supervision of a specialist. They included only uncinectomy, uncinectomy + 8mm Middle Meatal Antrostomy (MMA) and uncinectomy + 18 mm MMA. Simulations were performed for two human activity respiratory rates, including rest and moderate activities, and effects of different surgeries and respiratory rates on maxillary sinus were investigated. It was found that after endoscopic sinus surgery, the volume... 

The current study is allocated to experimental evaluation of the multiphase flow of fine solid particles (FSPs) as well as comprehensive numerical study in an annular space under static, laminar, and turbulent flow conditions with consideration of the inner pipe eccentricity and rotation. The experimental investigation was carried out using an annular pipe flow loop. The numerical modeling and simulation of the multiphase flow in the annular space have been performed using the Euler-Euler approach. The unsteady-state multiphase model based on the kinetic theory of granular flow (KTGF) is developed to investigate the particulate flow characteristics in the annular space. Moreover, Standard... 

Circulating tumor cells (CTCs) isolation from a blood sample plays an important role in cancer diagnosis and treatment. Microfluidics offers a great potential for cancer cell separation from the blood. Among the microfluidic-based methods for CTC separation, the inertial method as a passive method and magnetic method as an active method are two efficient well-established methods. Here, we investigated the combination of these two methods to separate CTCs from a blood sample in a single chip. Firstly, numerical simulations were performed to analyze the fluid flow within the proposed channel, and the particle trajectories within the inertial cell separation unit were investigated to... 

Wettability alteration is the principal low-salinity-effect (LSE) in many oil-brine-rock (OBR) systems. Our recent experimental results have demonstrated that wettability alteration by low salinity is slow. It is expected that the electrical behavior of oil/brine and rock/brine interfaces and the water film geometry control both the transient hydrodynamic pressure, and the time-scale of ionic transport in the film, thus the kinetics and degree of wettability alteration. In this paper, the electro-diffusion process induced by the imposed ionic strength gradient is simulated by solving Poisson-Nernst-Planck equations in a water film bound between two charged surfaces, using a finite... 

In this article, the hydrodynamic analysis and noise of the propeller and the surface vessel hull were examined. The model selected in this study is a KRISO Container Ship (KCS) with a five-bladed propeller. Initially, the hydrodynamic analysis of the propeller in open water mode and then in self-propulsion mode was investigated using computational fluid dynamics. Simulations were carried out using a commercial solver, STAR-CCM+ (RANS equations with FVM and VOF model). Finally, the emitted noise from the propeller and the vessel hull was investigated using Fox William Hawkins equations. The pressure distribution and hydrodynamic performance (thrust, torque, efficiency) of the propeller in... 

Manta ray swimming or bio-inspiration propulsion system, as a special type of marine propulsion system, is used for submersible vehicles that require high-speed maneuverability and stability, such as glider and AUV. In a manta ray swimming, the thrust force is generated by a couple of undulation and oscillation of wing, so that the direction of undulation wave and oscillation is upright and perpendicular to the direction of thrust force, respectively. It is possible to combine these two movement modes (flapping motion) on the three-dimensional model without considering the effects of wing twisting and flexibility to simplify and better understand the physical behaviors or special study of... 

Nowadays, as the oil reservoirs reaching their half-life, using enhanced oil recovery methods is more necessary and more common. Simulations are the synthetic process of real systems. In this study, simulation of water and surfactant injection into a porous media containing oil (two-phase) was performed using the computational fluid dynamics method on the image of a real micro-model. Also, the selected anionic surfactant is sodium dodecyl sulfate, which is more effective in sand reservoirs. The effect of using surfactant depends on its concentration. This dependence on concentration in using injection compounds is referred to as critical micelle concentration (CMC). In this study, an...