Sharif Digital Repository

In the present research a numerical investigation has been made to evaluate the results of analytical approach in the analysis of micro channel heat sink (MCHS) which is increasingly used in the cooling of high heat dissipating electronic devices. In this regard the effects of geometrical and flow parameters affecting the absolute thermal resistance of MCHS have been analyzed. The effect of using different fluids in the value of the thermal resistance is considered as well. The accuracy of analytical method in predicting heat transfer and fluid flow regimes in micro channel is checked in comparison with numerical method. The effects of hydraulic and thermal entrance lengths of these systems... 

The purpose of this work is to develop a physical simulation model for the purpose of studying the effect of various design parameters on the performance of a packaged liquid chiller. A computer model which simulates the steady-state cyclic performance of a vapor compression chiller is developed for the purpose of performing detailed physical design analysis of actual industrial chillers. The model can be used for optimizing design and for detailed energy efficiency analysis of packaged liquid chillers. The simulation model takes into account presence of all chiller components such as compressor, shell-and-tube condenser and evaporator heat exchangers, thermostatic expansion valve and... 

Improvements in sealing mechanism between the rotating and the stationary parts of a rurbomachine can extensively reduce the endwall leakage flow. In this regard, abradable seals are incorporated into compressor and turbine blade-tip region. In a gas turbine, equipped with abradable seals, tip of the rotor blade is designed to cut into the material coating of the casing and to form a close fitted circumferential groove for the movement of the blade tip. As a result, the resistance to the leakage flow in the tip gap region increases due to smaller tip clearances (available without any rub-induced damages). Minimizing the tip clearance size can lead to an increase in performance and stability.... 

A numerical model has been developed for studying the flow and heat transfer characteristics of single phase liquid flow through a microchannel. In this work the heat transfer characteristics of pressure driven and electroosmotic flow through microchannels have been studied. The governing equations are the Poisson-Boltzmann and Navier-Stokes equations which have been solved numerically using the standard Galerkin and the Mixed 4-1 finite element methods, respectively. Finally the energy equation is solved numerically using the Stream-wise Upwind Petrov Galerkin (SUPG) method. Two dimensional Poisson-Boltzmann equation was first solved to find the electric potential field and net charge... 

In reply to the comment of Lu and An on our publication paper [Phys. Rev. E 70, 016304 (2004)], we show that the consideration of water vapor exchange at the bubble interface is essential for obtaining our results and the adiabatic model is too simple to produce the differences. Moreover, in spite of smallness of the compressional viscosity term at the collapse, the illustrated differences are reasonable due to the strong nonlinearity of the bubble dynamics at the collapse and its sensitivity to even small perturbations. We emphasize on the correctness of our calculation results and our simulation programs are now available on the web. © 2005 The American Physical Society  

An experimental investigation is performed to explore the characteristics of sprays produced by a liquid-liquid coaxial swirl injector in a non-combusting environment. Phase Doppler anemometry is used for the measurement of velocity and Sauter Mean Diameter of droplets across and along the injection axis for various inner- and outer mass flow rates. Results of the combined spray are compared with those of inner- and/or outer spray alone. The results indicate that the inner injector has a larger influence on the flow field of the combined spray compared to the outer one. Further, the maximum velocity of the combined spray is close to the center of the spray thickness and the velocity... 

The casing treatment and flow injection upstream of the rotor tip are two effective approaches in suppressing instabilities or recovering from a fully developed stall. This paper presents numerical simulations for a high-speed transonic compressor rotor, NASA Rotor 37, applying a state-of-the-art design for the blade tip injection. This is characterized by introducing a jet flow directly into the casing treatment machined into the shroud. The casing treatment is positioned over the blade tip region and exceeds the impeller axially by ∼30 per cent of the tip chord both in the upstream and in the downstream directions. To numerically solve the governing equations, the three-dimensional finite... 

A new equation of state based on the Statistical Associating Fluid Theory (SAFT) is presented to study the phase behavior of associating and non-associating fluids. In the new equation of state, the hard sphere contribution to compressibility factor of the simplified version of the SAFT (SSAFT) is replaced with that proposed by Ghotbi and Vera. The Ghotbi-Vera SSAFT (GV-SSAFT) was also extended to study the phase behavior of associating and non-associating mixtures. The GV-SSAFT like the SSAFT equation of state has three adjustable segment parameters for non-associating fluids and five parameters for associating fluids. The experimental data of liquid densities and vapor pressures for pure... 

Most available numerical methods face problems, in the presence of variable topographies, due to the imbalance between the source and flux terms. Treatments for this problem generally work well for structured grids, but most of them are not directly applicable for unstructured grids. On the other hand, despite of their good performance for discontinuous flows, most available numerical schemes (such as HLL flux and ENO schemes) induce a high level of numerical diffusion in simulating recirculating flows. A numerical method for simulating shallow recirculating flows over a variable topography on unstructured grids is presented. This mass conservative approach can simulate different flow... 

Patterns formed by the flow of an inhomogeneous fluid (suspension) over a smooth inclined surface were studied. It was observed that fractal patterns are formed. There exists a threshold angle for the inclination above which global fractal patterns are formed. This angle depends on the particle size of the suspension. We observed that there are two fractal dimensions for these patterns, depending on the area from which the pattern is extracted. If the pattern is taken from the top which only consists of the beginning steps of the pattern forming, one finds two fractal dimensions, i.e. 1.35-1.45 and 1.6-1.7, in which the first one is dominant. And if the entire pattern is taken, then fractal... 

Turbulent swirling decay pipe flow has been investigated numerically in a vertical straight fixed pipe. The swirling flow is created by means of a rotating honeycomb which produces the solid body rotation at the inlet of the fixed pipe. Since there are no experimental data at the inlet of the fixed pipe; different axi-symmetric approaches may be considered to model the honeycomb effects at the downstream flow. Considering the appropriate approach and using the resulting flow field properties from the exit of the modeled swirl generator which are applied as the inlet boundary condition for the fixed pipe, several high Reynolds turbulence models are used to predict this type of the swirling... 

One main challenge in numerical treatment of incompressible fluid flow problems is to suppress the decoupling of pressure and velocity fields. The challenge has prompted research toward suggesting and implementing various coupling strategies. In this work, a novel strategy which suitably couples pressure and velocity in a collocated grid arrangement is presented. The current strategy develops a unique cell-face velocity expression which provides infinite cell-face velocity magnitudes in the algorithm. A smoothing factor is incorporated in the cell-face velocity expression in order to produce a wide range of velocity magnitudes. The smoothing factor provides a smooth transition from an unreal... 

Using the newly introduced asymptotic expansion method to obtain equations of state for hard sphere fluid, new simple equations of state for hard disks based on known virial coefficients are derived. Comparison of the obtained equations of state with computer simulation data shows that they are accurate in the whole fluid region. © 2007 Elsevier B.V. All rights reserved  

The use of collocated grid schemes in control-volume-based methods has resulted in developing different strategies for coupling mass and momentum governing equations. Defining two different velocity components at cell faces is one remedy to suppress the possible checkerboard problem in the solution domain. These velocity components are widely known as convected and convecting velocities which are normally used in the momentum and mass governing equations, respectively. However, the linearization of the nonlinear governing equations generates a number of lagged velocity components which must be carefully treated in a manner to preserve the conceptual definition of the convected and convecting... 

Steady-state laminar and incompressible fluid flow and forced-convection heat transfer from a circular cylinder and an array of circular cylinders in the presence and no-presence of porous media are investigated. Various mathematical and numerical models are compared and the effects of porous media on heat transfer enhancement are studied. Navier-Stokes equations are used for the analysis of laminar fluid flow and heat transfer. However, the Darcy and extended Darcy-Brinkman models are used for the analysis of fluid flow and heat transfer in porous media. The cylinders are at constant temperature and the analysis is restricted to the low- and intermediate-Peclet-number regimes (Pr = 1, Re ≤... 

The mixed-convection flow from a hot vertical impinging jet on a colder horizontal disc has been studied. The geometry is analogous to a conventional burning gas cooktop. A numerical simulation of the system has been carried out using the finite-element method to study the dependence of fluid flow and heat transfer on the geometric, thermal, and fluid flow parameters. Results show that heat transfer efficiency versus several parameters such as inlet velocity magnitude and flue gas temperature has an optimum value, in which heat transfer efficiency is maximum. With thermal conductivity of the solid wall, velocity angle, and solid wall diameter heat transfer efficiency has increasing behavior.... 

In this investigation a new model was developed to calculate gas pressure at the melt/foam interface (Gap) resulting from foam degradation during mould filling in the lost foam casting (LFC) process. Different aspects of the process, such as foam degradation, gas elimination, transient mass, heat transfer, and permeability of the refractory coating were incorporated into this model. A computational fluid dynamic (CFD) code was developed based on the numerical technique of the Solution Algorithm-Volume of Fluid (SOLA-VOF) utilizing model, for the simulation and prediction of the fluid flow in the LFC process. In order to verify the computational results of the simulation, a thin plate of grey... 

A general three-dimensional aeroelastic solver is developed based on coupled finite element and boundary element methods and applied to investigate the flutter boundaries in supersonic flows. The boundary element method is applied to three-dimensional unsteady supersonic potential flow as the aerodynamic model and coupled with the finite element method for structural modelling, in order to construct the system of aeroelastic equations. The aeroelastic equations are solved for the flutter prediction using the frequency domain approach. Flutter boundaries for two types of wing planforms at supersonic speeds are determined and compared with the existing experimental results and previous... 

Patterns formed by the flow of an inhomogeneous fluid (suspension) over a smooth inclined surface were studied. It was observed that fractal patterns form. There exists a threshold angle for the inclination above which global fractal patterns are formed. This angle depends on the particle size of the suspension. We observed that there are two fractal dimensions for these patterns, depending on the area from which the pattern is extracted. If the pattern is taken from the top which only consists of the beginning steps of the pattern forming, one finds two fractal dimensions, i.e. 1.35-1.45 and 1.6-1.7, in which the first one is dominant while, if the entire pattern is taken, then a fractal... 

To study of vibration effect on fluidization behaviour of high moisture materials, a laboratory vibro-fluidized bed dryer was designed and fabricated. The blower was selected based on transferring velocity of particles and pressure drop caused by airflow through the bedplate and the channels. It was centrifugal type with backward blades, static pressure of 3.5 kPa, flow rate of 0.4 m 3/s and impeller diameter of 0.4 m. The dryer was constructed with 4.9 kW electrical heater capacity, bed plate with holes diameter of I mm and 140626 holes/m 2. The dryer chamber was made of Plexiglass with 0.16×0.16 m square section and 0.5 m height The bedplate was vibrated mechanically, which was adjustable...