Journal of Fluids
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Open Access journal
ISSN (Print) 2356-7376
Published by Hindawi [334 journals]
- Plane Waves and Fundamental Solutions in Heat Conducting Micropolar Fluid
Abstract: In the present investigation, we study the propagation of plane waves in heat conducting micropolar fluid. The phase velocity, attenuation coefficient, specific loss, and penetration depth are computed numerically and depicted graphically. In addition, the fundamental solutions of the system of differential equations in case of steady oscillations are constructed. Some basic properties of the fundamental solution and special cases are also discussed.
PubDate: Wed, 13 Jul 2016 08:41:30 +000
- Effect of Yield Power Law Fluid Rheological Properties on Cuttings
Transport in Eccentric Horizontal Narrow Annulus
Abstract: Narrow annular drilling such as casing-while-drilling technique is gaining popularity due to its ability to mitigate nonproductive time during oil and gas drilling operations. However, very little is known about the flow dynamics in narrow annular drilling. In this study, the Eulerian-Eulerian two-fluid model was used to examine the influence of Yield Power Law fluid rheological properties on cuttings transport in eccentric horizontal narrow annulus. The flow was assumed as fully developed, laminar, and transient state. The present simulation model was validated against experimental data, where a mean percent error of −1.2% was recorded. Results revealed an increase in the radial distribution of cuttings transport velocity in the wide annular region as the consistency index, , and the flow behavior index, , increase. Nonetheless, increasing the yield stress, , had insignificant effect on the cuttings transport velocity. Three-dimensional profiles showed how cuttings preferred to travel in less resistant flow area, whereas cuttings concentration builds up in the narrow annular region. Furthermore, annular frictional pressure losses also increased as , , and increased. This study serves as a guide to properly optimize drilling fluid rheological properties for efficient cuttings transport and equivalent circulating density (ECD) management in narrow annular drilling.
PubDate: Sun, 03 Jul 2016 08:39:52 +000
- Mathematical Analysis on Heat Transfer during Peristaltic Pumping of
Fractional Second-Grade Fluid through a Nonuniform Permeable Tube
Abstract: This mathematical study is related to heat transfer under peristaltic flow of fractional second-grade fluid through nonuniform cylindrical tube with permeable walls. The analysis is performed under low Reynolds number and long wavelength approximation. The analytical solution for pressure gradient, friction force, and temperature field is obtained. The effects of appropriate parameters such as Grashof number, nonuniformity of tube, permeability of tube wall, heat source/sink parameter, material constant, fractional time derivative parameter and amplitude ratio on pressure rise, friction force, and temperature distribution are discussed. It is found that an increase in amplitude ratio and material constant causes increase in pressure but increase in nonuniformity of the tube causes decrease in pressure. It is also observed that variation of friction force against flow rate shows opposite behavior to that of pressure. Increase in temperature is also observed due to increase in heat source/sink parameter at inlet as well as downstream.
PubDate: Tue, 14 Jun 2016 11:48:56 +000
- Mathematical Modeling of Local Scour at Slender and Wide Bridge Piers
Abstract: Most existing equations for predicting local scour at bridge piers suffer from overprediction of the scour depths which results in higher foundation costs. To tackle this problem, a mathematical model for predicting bridge pier scour is developed herein based on an energy balance theory. The present study equation was compared to commonly used bridge scour equations using scour field data in USA. The developed equation has several advantages among which we have the following: it adds to the understanding of the physics of bridge pier scour, is valid for slender and wide piers, does not suffer from overprediction of scour depths, addresses clear water and live bed scour, and includes the effects of various characteristics of the bed material such as specific gravity (or density), porosity, size, and angle of repose. In addition, the developed equation accounts for the debris effect and aids in the design of scour mitigation methods such as collars, side bars, slots, and pier protective piles.
PubDate: Tue, 14 Jun 2016 08:16:46 +000
- A Volumetric Approach to Wake Reduction: Design, Optimization, and
Abstract: Wake reduction is a crucial link in the chain leading to undetectable watercraft. Here, we explore a volumetric approach to controlling the wake in a stationary flow past cylindrical and spherical objects. In this approach, these objects are coupled with rigid, fluid-permeable structures prescribed by a macroscopic design approach where all solid boundaries are parameterized and modeled explicitly. Local, gradient-based optimization is employed which permits topological changes in the manifold describing the composite solid component(s) while still allowing the use of adjoint optimization methods. This formalism works below small Reynolds number (Re) turbulent flow (–10,000) when simulated using small Reynolds-averaged Navier-Stokes (RANS) models. The output of this topology optimization yields geometries that can be fabricated immediately using fused deposition modeling (FDM). Our prototypes have been verified in an experimental water tunnel facility, where the use of Particle Image Velocimetry (PIV) described the velocity profile. Comparisons with our computational models show excellent agreement for the spherical shapes and reasonable match for cylindrical shapes, with well-understood sources of error. Two important figures of merit are considered: domain-wide wake (DWW) and maximum local wake (MLW), metrics of the flow field disturbance whose definitions are described.
PubDate: Thu, 05 May 2016 08:40:06 +000
- Rheological Behavior of Physiological Pulsatile Flow through a Model
Arterial Stenosis with Moving Wall
Abstract: The paper presents a numerical investigation of non-Newtonian modeling effects on unsteady periodic flows in a two-dimensional (2D) constricted channel with moving wall using finite volume method. The governing Navier-Stokes equations have been modified using the Cartesian curvilinear coordinates to handle complex geometries, such as, arterial stenosis. The physiological pulsatile flow has been used at the inlet position as an inlet velocity. The flow is characterized by the Reynolds numbers 300, 500, and 750 that are appropriate for large arteries. The investigations have been carried out to characterize four different non-Newtonian constitutive equations of blood, namely, the (i) Carreau, (ii) Cross, (iii) Modified-Casson, and (iv) Quemada. In these four models, blood viscosity is a nonlinear function of shear rates. The Newtonian model has been investigated to study the physics of fluid and the results are compared with the non-Newtonian viscosity models. The numerical results are presented in terms of streamwise velocity, wall shear stress, pressure distribution as well as the vorticity, streamlines, and vector plots indicating recirculation zones at the poststenotic region. Comparison has also been illustrated in terms of wall pressure and wall shear stress for the Cross model considering different amplitudes of wall oscillation.
PubDate: Wed, 10 Jun 2015 12:17:41 +000
- Separation Criteria for Off-Axis Binary Drop Collisions
Abstract: Off-axis collisions of two equal size droplets are investigated numerically. Various governing processes in such collisions are discussed. Several commonly used theoretical models that predict the onset of separation after collision are evaluated based on the processes observed numerically. A separation criterion based on droplet deformation is found. The numerical results are used to assess the validity of some commonly used phenomenological models for drop separation after collision. Also, a critical Weber number for the droplet separation after grazing collision is reported. The effect of Reynolds number is investigated and regions of permanent coalescence and separation are plotted in a Weber-Reynolds number plane for high impact parameter collisions.
PubDate: Mon, 25 May 2015 06:08:33 +000
- Unsteady/Steady Hydromagnetic Convective Flow between Two Vertical Walls
in the Presence of Variable Thermal Conductivity
Abstract: Unsteady as well as steady natural convection flow in a vertical channel in the presence of uniform magnetic field applied normal to the flow region and temperature dependent variable thermal conductivity is studied. The nonlinear partial differential equations governing the flow have been solved numerically using unconditionally stable and convergent semi-implicit finite difference scheme. For steady case, approximate solutions have been derived for velocity, temperature, skin friction, and the rate of heat transfer using perturbation series method. Results of the computations for velocity, temperature, skin friction, and the rate of heat transfer are presented graphically and discussed quantitatively for various parameters embedded in the problem. An excellent agreement was found during the numerical computations between the steady-state approximate solutions and unsteady numerical solutions at steady-state time. In addition, comparison with previously published work is performed and the results agree well.
PubDate: Wed, 20 May 2015 06:24:46 +000
- Effects of Heat and Mass Transfer on the Peristaltic Transport of MHD
Couple Stress Fluid through Porous Medium in a Vertical Asymmetric Channel
Abstract: The intrauterine fluid flow due to myometrial contractions is peristaltic type motion and the myometrial contractions may occur in both symmetric and asymmetric directions. The channel asymmetry is produced by choosing the peristaltic wave train on the walls to have different amplitude, and phase due to the variation of channel width, wave amplitudes and phase differences. In this paper, we study the effects of heat and mass transfer on the peristaltic transport of magnetohydrodynamic couple stress fluid through homogeneous porous medium in a vertical asymmetric channel. The flow is investigated in the wave frame of reference moving with constant velocity with the wave. The governing equations of couple stress fluid have been simplified under the long wave length approximation. The exact solutions of the resultant governing equations have been derived for the stream function, temperature, concentration, pressure gradient, and heat transfer coefficients. The pressure difference and frictional forces at both the walls are calculated using numerical integration. The influence of diverse flow parameters on the fluid velocity, pressure gradient, temperature, concentration, pressure difference, frictional forces, heat transfer coefficients, and trapping has been discussed. The graphical results are also discussed for four different wave shapes. It is noticed that increasing of couple stresses and heat generation parameter increases the size of the trapped bolus. The heat generation parameter increases the peristaltic pumping and temperature.
PubDate: Mon, 09 Mar 2015 06:43:51 +000
- Phase Separation Behavior and System Properties of Aqueous Two-Phase
Systems with Polyethylene Glycol and Different Salts: Experiment and
Abstract: The phase separation behaviors of PEG1000/sodium citrate, PEG4000/sodium citrate, PEG1000/ammonium sulfate, and PEG4000/ammonium sulfate aqueous two-phase systems were investigated, respectively. There are two distinct situations for the phase separation rate in the investigated aqueous two-phase systems: one state is top-continuous phase with slow phase separation rate and strong bottom-continuous phase with fast phase separation rate and weak volume ratio dependence. The system properties such as density, viscosity, and interfacial tension between top and bottom phases which have effects on the phase separation rate of aqueous two-phase systems were measured. The property parameter differences between the two phases increased with increasing tie line length and then improved the phase separation rate. Moreover, a modified correlation equation including the phase separation rate, tie line length, and physical properties of the four aqueous two-phase systems has been proposed and successfully tested in the bottom-continuous phase, whose coefficients were estimated through regression analysis. The predicted results of PEG1000/sodium citrate aqueous two-phase systems were verified through the stationary phase retention in the cross-axis countercurrent chromatography.
PubDate: Tue, 24 Feb 2015 16:31:35 +000
- Magnetohydrodynamic Mixed Convection Stagnation-Point Flow of a Power-Law
Non-Newtonian Nanofluid towards a Stretching Surface with Radiation and
Abstract: Two-dimensional MHD mixed convection boundary layer flow of heat and mass transfer stagnation-point flow of a non-Newtonian power-law nanofluid towards a stretching surface in the presence of thermal radiation and heat source/sink is investigated numerically. The non-Newtonian nanofluid model incorporates the effects of Brownian motion and thermophoresis. The basic transport equations are made dimensionless first and the complete nonlinear differential equations with associated boundary conditions are solved numerically by finite element method (FEM). The numerical calculations for velocity, temperature, and nanoparticles volume fraction profiles for different values of the physical parameters to display the interesting aspects of the solutions are presented graphically and discussed. The skin friction coefficient, the local Nusslet number and the Sherwood number are exhibited and examined. Our results are compatible with the existing results for a special case.
PubDate: Thu, 19 Feb 2015 12:08:56 +000
- Analysis of Heat and Mass Transfer on MHD Peristaltic Flow through a
Tapered Asymmetric Channel
Abstract: This paper describes the peristaltic flow of an incompressible viscous fluid in a tapered asymmetric channel with heat and mass transfer. The fluid is electrically conducting fluid in the presence of a uniform magnetic field. The propagation of waves on the nonuniform channel walls to have different amplitudes and phase but with the same speed is generated the tapered asymmetric channel. The assumptions of low Reynolds number and long wavelength approximations have been used to simplify the complicated problem into a relatively simple problem. Analytical expressions for velocity, temperature, and concentration have been obtained. Graphically results of the flow characteristics are also sketched for various embedded parameters of interest entering the problem and interpreted.
PubDate: Mon, 26 Jan 2015 12:58:47 +000
- Suction/Injection Effects on the Swirling Flow of a Reiner-Rivlin Fluid
near a Rough Surface
Abstract: The similarity equations for the Bödewadt flow of a non-Newtonian Reiner-Rivlin fluid, subject to uniform suction/injection, are solved numerically. The conventional no-slip boundary conditions are replaced by corresponding partial slip boundary conditions, owing to the roughness of the infinite stationary disk. The combined effects of surface slip (), suction/injection velocity (), and cross-viscous parameter () on the momentum boundary layer are studied in detail. It is interesting to find that suction dominates the oscillations in the velocity profiles and decreases the boundary layer thickness significantly. On the other hand, injection has opposite effects on the velocity profiles and the boundary layer thickness.
PubDate: Mon, 05 Jan 2015 10:11:28 +000
- Numerical Characterization of the Performance of Fluid Pumps Based on a
Abstract: The performance of fluid pumps based on Wankel-type geometry, taking the shape of a double-lobed limaçon, is characterized. To the authors’ knowledge, this is the first time such an attempt has been made. To this end, numerous simulations for three different pump sizes were carried out and the results were understood in terms of the usual scaling coefficients. The results show that such pumps operate as low efficiency (
PubDate: Tue, 30 Sep 2014 00:00:00 +000
- Modeling the Uniformity of Manifold with Various Configurations
Abstract: The flow distribution in manifolds is highly dependent on inlet pressure, configuration, and total inlet flow to the manifold. The flow from a manifold has many applications and in various fields of engineering such as civil, mechanical, and chemical engineering. In this study, physical and numerical models were employed to study the uniformity of the flow distribution from manifold with various configurations. The physical model consists of main manifold with uniform longitudinal section having diameter of 10.16 cm (4 in), five laterals with diameter of 5.08 cm (2 in), and spacing of 22 cm. Different inlet flows were tested and the values of these flows are 500, 750, and 1000 L/min. A manifold with tapered longitudinal section having inlet diameters of 10.16 cm (4 in) and dead end diameter of 5.08 cm (2 in) with the same above later specifications and flow rates was tested for its uniformity too. The percentage of absolute mean deviation for manifold with uniform diameter was found to be 34% while its value for the manifold with nonuniform diameter was found to be 14%. This result confirms the efficiency of the nonuniform distribution of fluids.
PubDate: Sun, 24 Aug 2014 07:21:52 +000
- Double Diffusive Convection in a Layer of Maxwell Viscoelastic Fluid in
Porous Medium in the Presence of Soret and Dufour Effects
Abstract: Double diffusive convection in a horizontal layer of Maxwell viscoelastic fluid in a porous medium in the presence of temperature gradient (Soret effects) and concentration gradient (Dufour effects) is investigated. For the porous medium Darcy model is considered. A linear stability analysis based upon normal mode technique is used to study the onset of instabilities of the Maxwell viscolastic fluid layer confined between two free-free boundaries. Rayleigh number on the onset of stationary and oscillatory convection has been derived and graphs have been plotted to study the effects of the Dufour parameter, Soret parameter, Lewis number, and solutal Rayleigh number on stationary convection.
PubDate: Thu, 17 Jul 2014 11:05:52 +000
- Numerical Simulation of Water Jet Flow Using Diffusion Flux Mixture Model
Abstract: A multidimensional diffusion flux mixture model was developed to simulate water jet two-phase flows. Through the modification of the gravity using the gradients of the mixture velocity, the centrifugal force on the water droplets was able to be considered. The slip velocities between the continuous phase (gas) and the dispersed phase (water droplets) were able to be calculated through multidimensional diffusion flux velocities based on the modified multidimensional drift flux model. Through the numerical simulations, comparing with the experiments and the simulations of traditional algebraic slip mixture model on the water mist spray, the model was validated.
PubDate: Wed, 16 Jul 2014 07:34:04 +000
- Pulsatile Non-Newtonian Laminar Blood Flows through Arterial Double
Abstract: The paper presents a numerical investigation of non-Newtonian modeling effects on unsteady periodic flows in a two-dimensional (2D) pipe with two idealized stenoses of 75% and 50% degrees, respectively. The governing Navier-Stokes equations have been modified using the Cartesian curvilinear coordinates to handle complex geometries. The investigation has been carried out to characterize four different non-Newtonian constitutive equations of blood, namely, the (i) Carreau, (ii) Cross, (iii) Modified Casson, and (iv) Quemada models. The Newtonian model has also been analyzed to study the physics of fluid and the results are compared with the non-Newtonian viscosity models. The numerical results are represented in terms of streamwise velocity, pressure distribution, and wall shear stress (WSS) as well as the vorticity, streamlines, and vector plots indicating recirculation zones at the poststenotic region. The results of this study demonstrate a lower risk of thrombogenesis at the downstream of stenoses and inadequate blood supply to different organs of human body in the Newtonian model compared to the non-Newtonian ones.
PubDate: Thu, 29 May 2014 13:26:10 +000
- Viscous Flows Driven by Uniform Shear over a Porous Stretching Sheet in
the Presence of Suction/Blowing
Abstract: An analysis is carried out to study the steady two-dimensional flow of an incompressible viscous fluid past a porous deformable sheet, which is stretched in its own plane with a velocity proportional to the distance from the fixed point subject to uniform suction or blowing. A uniform shear flow of strain rate β is considered over the stretching sheet. The analysis of the result obtained shows that the magnitude of the wall shear stress increases with the increase of suction velocity and decreases with the increase of blowing velocity and this effect is more pronounced for suction than blowing. It is seen that the horizontal velocity component (at a fixed streamwise position along the plate) increases with the increase in the ratio of shear rate β and stretching rate (c) (i.e., β/c) and there is an indication of flow reversal. It is also observed that this flow reversal region increases with the increase in β/c.
PubDate: Sun, 25 May 2014 12:33:49 +000
- Linear Stability Analysis of Thermal Convection in an Infinitely Long
Vertical Rectangular Enclosure in the Presence of a Uniform Horizontal
Abstract: Stability of thermal convection in an infinitely long vertical channel in the presence of a uniform horizontal magnetic field applied in the direction parallel to the hot and cold walls was numerically studied. First, in order to confirm accuracy of the present numerical code, the one-dimensional computations without the effect of magnetic field were computed and they agreed with a previous study quantitatively for various values of the Prandtl number. Then, linear stability analysis for the thermal convection flow in a square horizontal cross section under the magnetic field was carried out for the case of Pr = 0.025. The thermal convection flow was once destabilized at certain low Hartmann numbers, and it was stabilized at high Hartmann numbers.
PubDate: Tue, 29 Apr 2014 08:12:16 +000
- Peristaltic Motion of Non-Newtonian Fluid with Heat and Mass Transfer
through a Porous Medium in Channel under Uniform Magnetic Field
Abstract: This paper is devoted to the study of the peristaltic motion of non-Newtonian fluid with heat and mass transfer through a porous medium in the channel under the effect of magnetic field. A modified Casson non-Newtonian constitutive model is employed for the transport fluid. A perturbation series’ method of solution of the stream function is discussed. The effects of various parameters of interest such as the magnetic parameter, Casson parameter, and permeability parameter on the velocity, pressure rise, temperature, and concentration are discussed and illustrated graphically through a set of figures.
PubDate: Thu, 10 Apr 2014 09:10:57 +000
- Enhancement of Impinging Jet Heat Transfer Using Two Parallel Confining
Plates Mounted near Rectangular Nozzle Exit
Abstract: Impinging jet heat transfer on a target plate was enhanced by using two parallel confining plates mounted between a rectangular nozzle end plate and a jet target plate. The target plate was set equal to 2, 3, 4, and 5 times the jet exit width, , and the gap ratio of two parallel confining plates, , were changed from 2.7 to 8.0 only by impinging length and from 2.7 to 6.7 by . Two confining parallel plates mounted near the jet exit produced swing-type flow under some conditions. As a result, the maximum Nusselt number attained around the stagnation point was augmented by about 50% compared to the one for normal impinging jet without the two parallel plates and then spatial mean Nusselt number was increased by about 40%.
PubDate: Tue, 25 Mar 2014 12:47:11 +000
- Double-Diffusive Convection in Presence of Compressible Rivlin-Ericksen
Fluid with Fine Dust
Abstract: An investigation is made on the effect of suspended particles (fine dust) on double-diffusive convection of a compressible Rivlin-Ericksen elastico-viscous fluid. The perturbation equations are analyzed in terms of normal modes after linearizing the relevant set of equations. A dispersion relation governing the effects of viscoelasticity, compressibility, stable solute gradient, and suspended particles is derived. For stationary convection, Rivlin-Ericksen fluid behaves like an ordinary Newtonian fluid due to the vanishing of the viscoelastic parameter. The stable solute gradient compressibility has a stabilizing effect on the system whereas suspended particles hasten the onset of thermosolutal instability. The Rayleigh numbers and the wave numbers of the associated disturbances for the onset of instability as stationary convection are obtained and the behaviour of various parameters on Rayleigh numbers has been depicted graphically. It has been observed that oscillatory modes are introduced due to the presence of viscoelasticity, suspended particles, and stable solute gradient which were not existing in the absence of these parameters.
PubDate: Tue, 04 Feb 2014 13:30:07 +000
- Hydraulic Analysis of Water Distribution Network Using Shuffled Complex
Abstract: Hydraulic analysis of water distribution networks is an important problem in civil engineering. A widely used approach in steady-state analysis of water distribution networks is the global gradient algorithm (GGA). However, when the GGA is applied to solve these networks, zero flows cause a computation failure. On the other hand, there are different mathematical formulations for hydraulic analysis under pressure-driven demand and leakage simulation. This paper introduces an optimization model for the hydraulic analysis of water distribution networks using a metaheuristic method called shuffled complex evolution (SCE) algorithm. In this method, applying if-then rules in the optimization model is a simple way in handling pressure-driven demand and leakage simulation, and there is no need for an initial solution vector which must be chosen carefully in many other procedures if numerical convergence is to be achieved. The overall results indicate that the proposed method has the capability of handling various pipe networks problems without changing in model or mathematical formulation. Application of SCE in optimization model can lead to accurate solutions in pipes with zero flows. Finally, it can be concluded that the proposed method is a suitable alternative optimizer challenging other methods especially in terms of accuracy.
PubDate: Thu, 16 Jan 2014 11:16:28 +000
- Free Convection Heat and Mass Transfer MHD Flow in a Vertical Porous
Channel in the Presence of Chemical Reaction
Abstract: The objective of the present study is to examine the fully developed free convective MHD flow of an electrically conducting viscous incompressible fluid in a vertical porous channel under influence of asymmetric wall temperature and concentration in the presence of chemical reaction. The heat and mass transfer coupled with diffusion-thermo effect renders the present analysis interesting and curious. The analytical solution by Laplace transform technique of partial differential equations is used to obtain the expressions for the velocity, temperature, and concentration. It is observed that under the influence of dominating mass diffusivity over thermal diffusivity with stronger Lorentz force the velocity is reduced at all points Further, low rate of thermal diffusion delays the attainment of free stream state. Flow of aqueous solution in the presence of heavier species is prone to back flow.
PubDate: Thu, 12 Dec 2013 08:34:07 +000
- On the Stability of a Compressible Axial Flow with an Axial Magnetic Field
Abstract: We consider the stability problem of inviscid compressible axial flows with axial magnetic fields following the work of Dandapat and Gupta (Quarterly of Applied Mathematics, 1975). A numerical study of the stability of some basic flows has been carried out and it is found that an increase in the magnetic field strength has a stabilizing effect on subsonic flows and a destabilizing effect on supersonic flows. An analytical study of the stability problem has also been done in the present paper, but this analytical study is restricted by the approximation and , where is the Mach number and is the imaginary part of the complex phase velocity . A semicircular region depending on the magnetic field parameter and the Mach number is found for subsonic disturbances and as a consequence it is found that sufficiently strong magnetic field stabilizes all subsonic disturbances. Under a weak magnetic field, it is shown that short subsonic disturbances are stable.
PubDate: Tue, 10 Dec 2013 08:09:18 +000
- Thermal Jump Effects on Boundary Layer Flow of a Jeffrey Fluid Near the
Stagnation Point on a Stretching/Shrinking Sheet with Variable Thermal
Abstract: A mathematical model will be analyzed in order to study the effects of thermal jump and variable thermal conductivity on flow and heat transfer near the stagnation point on a stretching/shrinking sheet in a Jeffrey fluid. The highly nonlinear partial differential equation of Jeffrey fluid flow along with the energy equation are transformed to an ordinary system using nondimensional transformations. The arising equations are solved for temperature, velocity, shear stress, and heat flux using finite difference method. The effect of the influences parameters is discussed. For nonradiation regular viscous fluid our results are as that by Nazar et al. (2002).
PubDate: Thu, 05 Dec 2013 18:49:48 +000
- Free Convective MHD Flow Past a Vertical Cone with Variable Heat and Mass
Abstract: A numerical study of buoyancy-driven unsteady natural convection boundary layer flow past a vertical cone embedded in a non-Darcian isotropic porous regime with transverse magnetic field applied normal to the surface is considered. The heat and mass flux at the surface of the cone is modeled as a power law according to and , respectively, where denotes the coordinate along the slant face of the cone. Both Darcian drag and Forchheimer quadratic porous impedance are incorporated into the two-dimensional viscous flow model. The transient boundary layer equations are then nondimensionalized and solved by the Crank-Nicolson implicit difference method. The velocity, temperature, and concentration fields have been studied for the effect of Grashof number, Darcy number, Forchheimer number, Prandtl number, surface heat flux power-law exponent (), surface mass flux power-law exponent (), Schmidt number, buoyancy ratio parameter, and semivertical angle of the cone. Present results for selected variables for the purely fluid regime are compared with the published results and are found to be in excellent agreement. The local skin friction, Nusselt number, and Sherwood number are also analyzed graphically. The study finds important applications in geophysical heat transfer, industrial manufacturing processes, and hybrid solar energy systems.
PubDate: Mon, 18 Nov 2013 13:56:45 +000
- CFD Analysis of Energy Separation in Ranque-Hilsch Vortex Tube at
Abstract: Study of the energy separation phenomenon in vortex tube (VT) at cryogenic temperature (temperature range below 123 K) has become important because of the potential application of VT as in-flight air separator in air breathing propulsion. In the present study, a CFD model is used to simulate the energy separation phenomenon in VT with gaseous air at cryogenic temperature as working fluid. Energy separation at cryogenic temperature is found to be considerably less than that obtained at normal atmospheric temperature due to lower values of inlet enthalpy and velocity. Transfer of tangential shear work from inner to outer fluid layers is found to be the cause of energy separation. A parametric sensitivity analysis is carried out in order to optimize the energy separation at cryogenic temperature. Also, rates of energy transfer in the form of sensible heat and shear work in radial and axial directions are calculated to investigate the possible explanation of the variation of the hot and cold outlet temperatures with respect to various geometric and physical input parameters.
PubDate: Thu, 14 Nov 2013 09:19:56 +000
- Slip-Flow and Heat Transfer in a Porous Microchannel Saturated with
Abstract: This study aims to numerically examine the fluid flow and heat transfer in a porous microchannel saturated with power-law fluid. The governing momentum and energy equations are solved by using the finite difference technique. The present study focuses on the slip flow regime, and the flow in porous media is modeled using the modified Darcy-Brinkman-Forchheimer model for power-law fluids. Parametric studies are conducted to examine the effects of Knudsen number, Darcy number, power law index, and inertia parameter. Results are given in terms of skin friction and Nusselt number. It is found that when the Knudsen number and the power law index decrease, the skin friction on the walls decreases. This effect is reduced slowly while the Darcy number decreases until it reaches the Darcy regime. Consequently, with a very low permeability the effect of power law index vanishes. The numerical results indicated also that when the power law index decreases the fully-developed Nusselt number increases considerably especially, in the limit of high permeability, that is, nonDarcy regime. As far as Darcy regime is concerned the effects of the Knudsen number and the power law index of the fully-developed Nusselt number is very little.
PubDate: Thu, 14 Nov 2013 08:16:00 +000