Sharif Digital Repository

The core behaviour of a nuclear reactor might be fluctuated (deviations from the normal operating conditions) in operating conditions due to various reasons. Control rod vibrations and the alterations of coolant temperature and velocity could be the main reasons for the fluctuations. These fluctuations lead to neutronic flux noise and subsequently power noise. The main objective of the current thesis was to study the thermal-hydraulic noise of the PWRs in two-phase with the emphasis on VVER-1000, which is similar to the Bushehr-1 nuclear reactor. By considering the possibility of existing two-phase flow (maximum allowable quality is about 14%) in hot channel of the PWRs, thermal-hydraulic... 

In recent years, there have been a tremendous research performed in the field of sestems containing small scales. However, besides all advantages of such systems, microfluidic systems have extraordinary difficulties and pumping liquid drops as part of some of these systems has been very important issue. An approach related to flow control is use of surface acoustic waves (SAW), which is known as acoustofluidic device. So far, most researches have only qualitatively investigated acoustic flux phenomenon. On the other hand, computational research is ongoing more emphasizing on accuracy, optimization, and obtaining more detailed physical understanding of SAW applications. Investigation of the... 

It is aimed in this study to numerically investigate the effect of contact angle on the heat transfer coefficient in oil-water two-phase flow. For this purpose, the finite element method (FEM) is used to solve the unsteady Navier-Stokes and energy equations. The level set method is also used to capture the interface between the phases. In the first part of the study, two-phase flow of the water and calibration oil is considered in a T-junction geometry at contact angles of 5°, 40°, and 75°. It is observed that the flow patterns formed in the microchannel depend on the initial flow condition which results in the hysteresis phenomenon. Investigating the effect of wall contact angle on the... 

The present thesis aimed to develop a thermal-hydraulic model for simulation of multi-stream plate-fin heat exchangers. In this study, a multi-scale point of view was employed for three-dimensional simulation of multi-stream plate-fin heat exchangers. This is a cost-effective method that reflects the effects of complex phenomena at the micro-scale in the macro-scale model. In this model, fluid and solid matrix temperature distributions were obtained in the three-dimensional space, considering conduction heat transfer through separating plates, side plates, cap plates, and transverse conduction through fins. The modular form of the model has facilitated layer-by-layer simulation of parallel... 

The present article studies the isothermal and non-isothermal water injection into naturally fractured oil reservoirs by numerical simulation. The fractures in naturally fractured reservoirs can possess different characteristics. In addition. a remarkable number of naturally fractured reservoirs contain relatively heavy oils that could not be extracted economically; hence. the thermal recovery methods are extensively used for these reservoirs. Hot water injection is one of the thermal recovery methods that has not been explored enough compared to its alternatives. In this study. the effectiveness of the hot water injection over the cold (isothermal) water injection in oil production is... 

Due to the wide application of plate-fin heat exchangers in various industries such as the petrochemical industry, aerospace industry, air conditioning systems, separation and liquefaction of gases, especially natural gas, boiling, condensation, and transportation industries, proper design of these heat exchangers is necessary. Most of the previous researches in the field of heat exchanger modeling has been done in single-phase mode. The two-phase modeling has been performed, often thermodynamically, and the effects of turbulence and surface tension have been ignored. Thus, in the present study, numerical modeling of the two-phase plate-fin heat exchanger is presented. In this project,... 

One of the most important factors in global warming is greenhouse gases such as carbon dioxide. Separating carbon dioxide from industrial activities such as fossil fuel power plants and storing it in the underground water can help combat the global warming challenge. In this research, numerical modeling of carbon dioxide sequestration in the aquifers under isothermal conditions is investigated. The process of storing carbon dioxide in aquifers consists of four main stages. In the first stage, the injected carbon dioxide accumulates into the aquifers under the impermeable bed. In the second stage, some carbon dioxide is trapped by the capillary forces inside the porous media's pores. In the... 

This reaserch is study on the performance of evaporation tubes used in mini jet engines which has been done experimentally using laboratory equipment. In this study, researchers have tried to simulate the laboratory conditions as much as possible to the real conditions inside the mini-jet engine, increase the accuracy of the results and increase the results and bring them closer to the results inside the mini-jet engine. The experiments are divided into two categories, cold and hot In cold tests, an attempt is made to study and investigate the types of two-phase flow regimes created by applying different fluid and air flow rates, and to select annular flow regimes from among them.... 

Droplet microfluidic platform generates monodisperse droplets in a desired size through immiscible multiphase flows inside microchannels. Droplets are individual reactor and can be used for bio(chemical) analyses. Also, for materials fabrication, droplet microfluidics offers a versatile platform for generation of nano- or micro-sized particles and microcapsules that are widely used in drug delivery. In addition to the monodispersity, high-throughput generation is also necessary in many applications. Therefore, droplets must be formed in stable regimes (dripping and squeezing) in the highest possible frequency. In this study, the flow-focusing geometry, which is the most common geometry in... 

The purpose of this thesis is to study the analogy of space-time fluid flow around Earth and to investigate the hydrodynamic forces caused by this fluid on NASA's Probe B satellite. According to recent research, Einstein's and Navier-Stokes equations are the same. The properties of space-time fluid, including equation of state, compressibility, viscosity, flow field around Earth, and the hydrodynamic forces entering Probe B satellite, are unknown. There are two views about the viscosity of space-time fluid. Spherical mass of the three-dimensional spherical sink and the nature of the sphere located in the probe satellite without a spherical solid particle It are considered within this flow.... 

Based on the history of computational fluid dynamics, choosing a proper method for three-dimensional investigation of two-phase flows is always challenging. In this research, the flow of atomization of a liquid jet was investigated. Also, Using GPU technique made our computations about 40 times faster. The numerical results are in good agreement with available numerical and experimental data. Based on our results, jet flow can achieve different regimes at different Weber and Reynold. Jet flow was found in dripping and Rayleigh instability regimes when Weber number was set to 1.79 and 3.10, respectively. Also, the transition between dripping and jetting was estimated at We between 2 to 3. In... 

Conventional methods of solving partial differential equations such as finite difference method, finite volume method, and finite element method require mesh generation in the problem domain. When these methods are applied to solve problems involving shock propagation, crack propagation or deformable domain, or in the case of mesh refinement, multiple mesh regenerations are needed which is laborious and time consuming. In recent years, meshless methods have been developed to avoid difficulties of mesh-based methods. Meshless Local Petrov-Galerkin (MLPG) method is a truly meshless method that does not rely on mesh neither in function approximation nor in the integration of the weak form. In... 

Rapid variation in permeability with strong anisotropy are common features in subsurface reservoirs. When formulating a finite-volume pressure equation scheme, continuous normal flux and pressure are key physical constraints that must be imposed at control-volume interfaces, across which strong discontinuities in permeability can occur.
The derivation of algebraic flux continuity conditions for full-tensor discretization operators has lead to families of efficient locally conservative flux-continuous control-volume distributed (CVD) finite- volume schemes for determining the discrete pressure and elocity fields in subsurface reservoirs [5, 9, 11, 13].
When applying these... 

Naturally Fractured Reservoirs (NFRs) play an important role in petroleum industry and the global economy.. The reservoirs of the most complex geological structures in petroleum engineering science, on the other hand the largest sources of hydrocarbons are considered throughout the world and especially in our country. Therefore, characterization and modeling them frst step to develop best practices for hydraulic fracturing gap, optimal design of production Method and evaluate potential reservoirs. Physics of the present work is 2D two-phase immiscible flow under gravittational effect through fractured porous media and the most practical formulas for transfer function in dual porosity-dual... 

This dissertation is devoted to the mathematical theory of two-dimensional injection of incompressible, irrota-tional, and inviscid fluids issuing from two infinitely long nozzles into a free stream.. In general, there is a free interface with constant jump of the Bernoulli constant on it, which is different and more difficult than the previous related works. Physically, it is called the collision fluid. The main result in this paper is that for given two co-axis symmetric infinitely long nozzles, imposing the incoming mass fluxes in the two nozzles, there is a unique piecewise smooth fluid collision function such that its free interface arises from the collision of fluids. It is a... 

In this thesis, the separation process for used and relatively new catalysts of residue fluid catalytic cracking unit by applying an electric field was evaluated. The main purpose of this dissertation is to simulate and design a separation system for separating used and relatively new catalysts of the FCC process in the electrostatic fields. In this regard, various separators were studied, and most of them were simulated under different circumstances. Finally, after examining and analyzing the particle behavior in each of the scenarios, the proposed system was introduced as more effective and efficient than the other separators in order to achieve the ideal separation of the used and... 

The use of stepped weirs dates back at least 3500 years. In this research, the hydrodynamics of gabion stepped weirs have been investigated as a three-dimensional simulation of two-phase flow air-water using Flow3D software and the method of computational fluid dynamics (CFD) analysis. In order to solve the Reynolds-Averaged Navier-Stokes (RANS) equations, the RNG turbulence model (k-ε) was used and the free surface elevation of fluid was determined by the volume of fluid (VOF) method. The experimental results of Wutrish and Chanson (2014) over gabion stepped weirs are used to validate the numerical model simulations. Gabion stepped weirs with steps of 3, 7.5, and 10 cm in height, as well as... 

The Ranque-Hilsch vortex tube (RHVT) has no moving parts through which a high-pressure fluid gains on rotational velocity by passing radially through the inlet nozzles and then enters the vortex chamber. Subsequently, the high-pressure fluid becomes divided into two relatively distinctive hot and cold axial flows. Today, while RHVT is of great industrial interest due to its simplicity in manufacturing and operation; however, the mechanism of energy dissociation, which is dominated by the complex coupled interaction of the viscous thermo-fluid characteristics and geometrical properties, is not fully understood and no clear theory has been proposed to explain the energy dissociation so far.... 

In nuclear power plants, the fission reaction takes place inside the fuel rods, and the heat generated inside the fuel rods is transferred through the clad wall to the cooling fluid, which is single-phase, subcooled and in the turbulence zone. In the hot channel of the reactor core, where the axial and radial heat flux reaches its maximum state, the fluid leaves the single-phase state and some steam is formed in the area close to the clad wall.Therefore, in some cases, in the hot channel, the steam near the clad wall may reach a point that reduces the heat transfer coefficient, rapidly increases the wall temperature and thus destroys or melts the sheath surface. If this happens, it means... 

Selection of appropriate thermohydraulic tool for analyzing nuclear reactors is a trade of between accuracy and calculation run-time. Nuclear reactors analyses perform on two levels including system and sub-channel. In this regard or the system codes' one-dimensional approach is selected or the CFD codes for considering the three-dimensional and non-equilibrium phenomenon are employed. In this research a T-H tool for prediction of light-water cooled reactors core is developed. Although this code requires lower CPU and run-time in comparison with CFD codes, in contrast with system codes can report non-equilibrium and three-dimensional phenomenon. This code has a modular implementation based...