فهرست مطالب nasrin aminizadeh

In this study, we investigated the phase behavior of rods with square ( ) and circular (diameter D) cross sections between two hard walls using the Parsons-Lee theory and applying the Zwanzig approximation. Our focus is to find wall-to-wall separations (H) and the size of particles in which the phase of the system changes without occurring a phase transition. It was determined that if the distance between the plates is smaller than the length of the particles, for any particle whose length (L) to diameter ratio is greater than 1, the second order phase transition occurs, and most of the particles are placed in a certain direction parallel to the plates, which this type of phase transition takes place at lower densities with increasing particle’s aspect ratio. We also came to the conclusion that if the distance between the plates is greater than  and , despite the phase change of the system with increasing particle density, no phase transition will occur. In addition, it was found that the cylindrical shaped particles show some unexpected behaviors, which could be due to the inappropriate performance of the applied theory or their real physical behavior, which requires more detailed studies to resolve the ambiguity.

In this research, interaction influences of magnetic field and solid nanoparticles on three-dimensional forced convection flow in a horizontal duct with an inclined backward-facing step are studied. The nanofluid is considered as the working fluid in duct. The Blocked region method is applied to simulate the inclined backwardfacing step in Cartesian coordinates. To obtain the velocity and temperature fields, the Navier-Stokes and energy equations are solved using the Finite volume method and SIMPLE algorithm. Influences of Hartmann number ( ) and concentrations of nanoparticles ( 𝜙 ) on the velocity and temperature fields in duct and distributions of fiction coefficient and Nusselt number along the bottom wall of duct are analyzed with full details. Results of this research clearly show that the hydrodynamics and thermal behaviors of flow are considerably dependent on the magnetic field strength and volume fractions of nanoparticles. In fact, the highest values of fiction coefficients and heat transfer rates on the bottom wall are related to the case of and 𝜙 .

In the present paper, numerical simulations of laminar forced convection flow and entropy generation analysis in a 2-D duct with two sudden expansions are investigated. These two expansions are created by four inclined backward facing steps and beget the separation flows and vortex regions. The vortex regions have the significant effects on the heat transfer rates and flow irreversibility. The inclination angle of steps is one of effective parameters on the control of the separation flows, heat transfer rates and flow irreversibility. In this paper, after calculation of velocity fields and temperature distributions, the effect of the step inclination angle on the separated flows, Nusselt number, friction coefficient, entropy generation number and Bejan number is studied. To obtain the temperature distributions and velocity fields, the set of governing equations including mass, momentum and energy equations are solved by the finite volume methods and computational fluid dynamic (CFD) techniques. For simulating the inclined surfaces of steps in Cartesian coordinates, the blocked-off method is used. Also, thermodynamic second law analysis is employed to calculate the entropy generation and flow irreversibility. Finally, the effect of the Brickman number on the entropy generation number and Bijan number is investigated graphically.

In this research paper, irreversibility analysis of laminar forced convection flow in a duct with variable cross-section are numerically studied. Two-dimensional Cartesian coordinate system is used to solve the set of governing equations and also the blocked-off method is considered for simulation of the inclined surfaces. To obtain the velocity and temperature fields, the basic equations are numerically solved using the finite volume method and SIMPLE algorithm. To determine the flow irreversibility, the entropy generation number is calculated according to the thermodynamic second law. The geometrical effects of duct on the distributions of streamlines, friction coefficient, Nusselt number, entropy generation, and Bejan number are presented with details. The results show that the duct heights and inclination angle of surfaces have great effects on the flow irreversibility and the hydrodynamics and thermal behaviours. Also, comparison of the present numerical results with the available data published in the open literature shows an excellent consistency.