Sharif Digital Repository

An analytical solution is presented to study the heat transfer characteristics of the combined pressure - electroosmotically driven flow in planar microchannels. The physical model includes the Joule heating effect to predict the convective heat transfer coefficient in two dimensional microchannels. The velocity field, which is a function of external electrical field, electroosmotic mobility, fluid viscosity and the pressure gradient, is obtained by solving the hydrodynamically fully-developed laminar Navier-Stokes equations considering the electrokinetic body force for low wall zeta potentials. Then, assuming a thermally fully-developed flow, the temperature distribution and the Nusselt... 

In reservoirs that have been water flooded or gas injected, it is still a significant amount of the remaining oil. Water alternative gas injection is a tertiary oil recovery method which was used for the first time in Canada for recovering remained oil in place of reservoir. The pore-scale mechanisms of this process are not fully understood yet. Such knowledge is essential for accurate modelling of reservoir. In this study various experiments on the WAG process is carried out by means of high pressure glass type micromodel instrument. The micromodel apparatus in this experiment was capable to operate at pressures up to 3500 Psi and temperatures up to 85°C which is similar to conventional... 

This research is dedicated to show the possibility of using solar radiation pressure by solar sails for interplanetary flights. In this paper, in addition to the Introduction of solar sailing and physics of solar radiation pressure, the solar sail orbital dynamics for optimal trajectory of an ideal solar sail spacecraft has been studied. It considers the problem of optimal controlling the sail angle so as to execute a minimum-time coplanar orbit transfer from the circular initial orbit to the circular target orbit. The direct collocation optimal control technique is used to transform the state equations to a set of nonlinear algebraic constraint equations. The results of state and control... 

In this work, after construction of a copper chloride laser, the effect of using different buffer gases on the output power has been examined. The voltage, current, laser pulses and the far field pattern of laser intensity were measured at the optimum buffer gas pressure. At these favorable conditions, the effect of using diaphragms in different diameters on the specific output power has been studied. By finding the desirable diaphragm size which creates the best temperature gradient in the laser tube the specific output record power of 123 (Watt/Lit) was obtained  

The temperature distribution in a finned tube bundle of an A-type air cooler is investigated. The heat transfer is governed by natural convection. By using a special steam condenser the effect of steam pressure on temperature fields formed outside the bank of finned tubes is studied. It is found that the distribution is approximately the same at various pressures with minor differences. The effects of two-phase flow on temperature distribution are also considered. All 3D temperature contours show maximum values, which highly depend on steam pressures. Moreover, asymmetric steam feeding and probable fouling inside the tubes are possible causes of contour shapes. The experimental Nusselt... 

The effect of pressure has been studied on structural and electronic properties of LaOFeAs high-T c superconductor by ab initio density functional theory by using pseudopotential Quantum Espresso code. The lattice parameters and ionic positions in the ambient pressure and some high pressure up to 20 GPa have been calculated. The obtained data versus the simple scaling relation for the ionic positions and distances for mechanical pressures have been discussed. The results of band structure and magnetic moment calculations of this compound versus the applied pressure are presented in this paper. The results are compared with the other experimental and computational data in the literature  

The effects of fluorine doping on the electronic structure of LaO1−xFxFeAs superconductor have been investigated by ab initio density functional theory using pseudopotential quantum espresso code. Firstly, we have studied the role of fluorine doping on the electronic structure of LaO1−xFxFeAs by calculation of band structure, density of states, and Fermi surfaces at various doping levels x = 0.00, 0.25, and 0.50. The lattice parameters and ionic position have been determined by optimizing crystal structure. Our results show that doping decreases cell volume similar to mechanical pressure and shifts the bands and states near the Fermi level toward the lower energies. According to the Fermi... 

In this study, the effect of moving pressure source and channel parameters on the generated waves in a channel was numerically investigated; draught, angle of attack, and profile shape as parameters of pressure source, and water depth and blockage factor as channel parameters for wave height. Firstly, the chosen Computational Fluid Dynamics (CFD) approach was validated with the experimental data over a range of speeds. Then, the CFD study was conducted for further investigations. It was shown that that by enlarging draught, angle of attack, and beam of the pressure source, the wave height generated would be increased. Channel study showed that it was possible to increase the wave height... 

In this article, energetic implosion of a single vapor bubble induced by a standing acoustic wave is theoretically studied and the Sonoluminescing bubble parameters involved in Sonofusion in Deuterated acetone (C3D 6O) are investigated. Parameters such as radius, wall velocity, interior temperature and pressure of the bubble influenced by various driving pressure amplitudes in Deuterated acetone at ∼0 °C are investigated. Based on the obtained results, the possibility of thermonuclear fusion inside imploding cavitation bubbles is discussed. The interior pressure of C 3D6O vapor bubbles at the collapse time is extremely high and the increase of the pressure amplitude increases the pressure... 

In this paper, the fully developed electroosmotic flow of power-law fluids in rectangular microchannels in the presence of pressure gradient is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A complete parametric study reveals that the pressure effects are more pronounced at higher values of the channel aspect ratio and smaller values of the flow behavior index. The Poiseuille number is found to be an increasing function of the channel aspect ratio for pressure assisted flow and a decreasing function of this parameter for pressure opposed flow. It is also observed that the Poiseuille number is... 

In this study, crosslinked and non-crosslinked carboxymethylcellulose (CMC) membranes were prepared with different concentrations of polymer. Then, the permeability of pure CO2, N2, and CH4 was measured through these membranes in dry state to investigate the influence of polymer concentration and applied feed pressure on permeability and permselectivity. The permeability of CO2 through membranes was higher than the other gases. A comparison of permeabilities revealed that the permeability of N2, CO2, and CH4 increased on an average of 33, 40 and 20 percent, respectivly, by increasing the feed pressure from 6 to 10... 

The Fontan surgery is performed on patients with a single ventricle heart defect to prevent the combination of highlyoxygenated and poorly-oxygenated blood. Blood flow in total cavopulmonary connection (TCPC) which culminates an ordinary Fontan operation is practically steady-state but this flow is not appropriate for respiratory systems. This article investigates an approach in Fontan surgery that has been recently proposed in order to make the pulmonary blood flow pulsating. Moreover, for investigating the compliance of vessels and its effects on blood flow in TCPC, we have used the FSI (Fluid Structure Interaction) method as well as rigid wall assumption for comparison purposes. Our TCPC... 

Analytical solution of shock wave propagation in pure gas in a shock tube is usually addressed in gas dynamics. However, such a solution for granular media is complex due to the inclusion of parameters relating to particles configuration within the medium, which affect the balance equations. In this article, an analytical solution for isothermal shock wave propagation in an isotropic homogenous rigid granular material is presented, and a closed-form solution is obtained for the case of weak shock waves. Fluid mass and momentum equations are first written in wave and (mathematical) non-conservation forms. Afterwards by redefining the sound speed of the gas flowing inside the pores, an... 

Based on a quasi-adiabatic model, the parameters of the bubble interior for a moving single bubble sonoluminescence (m-SBSL) in water are calculated. By using a complete form of the hydrodynamic force, a unique circular path for the m-SBSL in water is obtained. The effect of the ambient pressure variation on the bubble trajectory is also investigated. It is concluded that as the ambient pressure increases, the bubble moves along a circular path with a larger radius and all bubble parameters, such as gas pressure, interior temperature and light intensity, increase. A comparison is made between the parameters of the moving bubble in water and those in N-methylformamide. With fluid viscosity... 

Asphaltene precipitation and deposition is a serious issue in all facets of petroleum production and processing. Despite the numerous experimental efforts concerning asphaltenes, the effect of temperature on asphaltene precipitation and aggregation in live oils remains an elusive and controversial subject in the available literature. In this work, a series of high pressure-high temperature depressurization experiments were designed to assess the effect of temperature on asphaltene precipitation and aggregation in light live oils. Asphaltene related experiments were performed using a high pressure microscope and high pressure-high temperature filtration setup on a light live oil with a low... 

The study of water hammer in air-water, two-phase flows in hydraulic structures such as pressurized pipelines and tunnels, siphons, culverts, and junctions is of great importance for design purposes. Water hammer if combined with a periodic slug flow would lead to severe periodic transient pressure fluctuations inside the conduit. Laboratory experiments have been conducted to investigate waterhammer pressure inside a horizontal rectangular conduit carrying a two-phase, air-water slug flow. Tests were performed in an experimental apparatus comprising a 6.8-m-long transparent pipeline 0.06 m wide and 0.1 m high. By rapidly closing a control gate at the end of the conduit, propagating pressure... 

Using the Shan-Chen lattice Boltzmann multi-phase model, we investigate the effect of adding microstructured grooves to the walls of a 2D parallel-plate channel on the pressure drop in the channel. The effects of the size of the grooves on the pressure drop in the channel were considered. It was observed that the pitch of the grooves has a considerable effect on the pressure drop in the channel, and even for some values of the pitch we observe an increase in the pressure drop. As the pitch decreases, a lower pressure drop is achieved. The results also show that as the ratio of the solid-liquid contact surface to the whole surface is decreased, the pressure drop decreases. It is also observed... 

The interfacial properties of crude oil are highly complex and are not yet well understood. This study aimed to evaluate the effect of temperature (30-80°C) and pressure (3.44-27.58MPa) on the dynamic interfacial tension (IFT) of crude oil/aqueous solutions consisting of 15000ppm of salt containing different chloride anions, e.g. NaCl, KCl, MgCl2, and CaCl2. To reach this goal, several parameters, such as dynamic and equilibrium IFT, adsorption time, diffusivity of resin, and asphaltene as surface-active agents from bulk of crude oil towards fluid/fluid interface and surface excess concentration of them at the interface, were compared as a function of temperature, pressure, and ion type. The... 

The interfacial properties of crude oil are highly complex and are not yet well understood. This study aimed to evaluate the effect of temperature (30–80 °C) and pressure (3.44–27.58 MPa) on the dynamic interfacial tension (IFT) of crude oil/aqueous solutions consisting of 15 000 ppm of salt containing different chloride anions, e.g. NaCl, KCl, MgCl2, and CaCl2. To reach this goal, several parameters, such as dynamic and equilibrium IFT, adsorption time, diffusivity of resin, and asphaltene as surface-active agents from bulk of crude oil towards fluid/fluid interface and surface excess concentration of them at the interface, were compared as a function of temperature, pressure, and ion type.... 

Pressure dependence of the onsite Coulomb interactions of the BaFe2As2 has been studied by employing the constrained random phase approximation within first-principle calculations. Analyzing total and projected density of states, a pseudogap is found for dxy band at the energy roughly 0.25 eV higher than the Fermi level. Also, by applying pressure the spectral weight of the dxy orbital vanishes while other orbitals remain metallic. The different screening channels, as discussed in four different models, affect significantly on the Hubbard U while the Hund J remains almost unchanged. The average onsite bare and partially and fully screened Coulomb interactions increase with different rates...