

An Analytical Solution for the Laminar Forced Convection in a Pipe with TemperatureDependent Heat Generation


Pages :
641650


Authors :
T. Pesso,
S. Piva,
An analytical solution is presented for the case of laminar forced convection in a pipe with heat generation linearly dependent on the local temperature of the fluid. The flow is fully developed and the boundary conditions of the third kind. Within the general analysis presented, some particular cases are identified and discussed. A detailed analysis of the thermal entrance is given. It is shown that in the fully developed region the temperature distribution does not depend on the axial coordinate. An analytical expression of the fully developed Nusselt number is given. Finally, the practical significance of the problem is discussed.





Upward Flow Boiling to DIWater and Cuo Nanofluids Inside the Concentric Annuli


Pages :
651659


Authors :
N. Vaeli,
M. M. Sarafraz,
S.M. Peyghambarzadeh,
F hormozi,
In this work, flow boiling heat transfer coefficients of deionized water and copper oxide waterbased nanofluids at different operating conditions have been experimentally measured and compared. The liquid flowed in an annular space. According to the experiments, two distinguished heat transfer regions with two different mechanisms can be seen namely forced convective and nucleate boiling regions. Results demonstrated that with increasing the applied heat flux, flow boiling heat transfer coefficient increases for both of test fluids at both heat transfer regions. In addition to, by increasing the flow rate of fluid, the heat transfer coefficient dramatically increases at both regions. Influence of inlet temperature of fluid to the
annulus as a complicated parameter has been investigated and briefly discussed. Results showed that inlet temperature of fluid displaces the boundary between forced convection and nucleate boiling areas such that with increasing the inlet temperature, nucleation mechanism become dominant mechanism at lower heat fluxes. Furthermore, higher heat transfer coefficient can be obtained due to interactions of bubbles and local agitations. Also, Chen type model was modified in terms of thermophysical properties and examined to experimental data. Results showed that experimental data are in a good agreement with those of obtained by the correlation with deviation up to 30%.





Demixing of a Binary Fluid Mixture in Case of MHD Flow with Heat and Mass Transfer due to a Point Sink


Pages :
661665


Authors :
Kabita Nath,
B.R. Sharma,
The present problem concerns with the effects of the magnetic field, mass flux diffusion and heat transfer on demixing of a binary mixture of incompressible viscous electrically conducting fluids in steady, laminar boundary layer flow in presence of a point sink at the vertex of a cone. The momentum, energy and concentration equations are reduced to nonlinear coupled ordinary differential equations by similarity transformations and are solved numerically by using MATLAB’s built in solver bvp4c. The local skin friction, the Nusselt number and the Sherwood number are tabulated for various values of the parameters. These numerical results have been demonstrated graphically from which it is observed that the effects of various parameters are to separate the components of the binary mixture by collecting the rarer and lighter component near the surface of the cone and throwing the heavier one away from it.





A Study of the Complex Flow Features Behind a Diffracted Shock Wave on a Convex Curved Wall


Pages :
667672


Authors :
adam muritala,
B. Skews,
craig law,
The complex flow features behind a diffracted shock wave on a convex curved wall is investigated using large scale experimentation complemented by numerical computation. The study aimed at explaining the global flow behavior within the perturbed region behind the diffracted shock wave. Experiments were conducted in a purpose built shock tube that is capable of generating a range of incident shock Mach numbers Mn ≤ 1.6. Analysis of higher Mach number shocks on different wall geometries were carried out using numerical code that has been validated by earlier authors. Many flow features that were only distinct at high Mach numbers are clearly identified at low Mach numbers in the present investigation. The separation point moves upstream at incident shock Mach number Mn = 1.5 but moves downstream at higher Mach numbers and is nearly stationary at Mn = 1.6. At incident shock Mach number 3.0 the movement of the separation point tends to be independent of the wall curvature as the wall radius approaches infinity. The present
investigatio is important in the design of high speed flow devices and in the estimation of flow resistance on
supersonic devices and space vehicles.





A New Method to Calculate Centrifugal Pump Performance Parameters for Industrial Oils


Pages :
673681


Authors :
mohammad hassan shojaeefard,
behzad salimian rizi,
Mojtaba Tahani,
Abolfazl Khalkhali,
Pumping of oil instead of water using centrifugal pumps causes rapid increase in the hydraulic losses which results significant reduction in head and efficiency. Therefore, deriving analytical methods to calculate variation of pump performance parameters versus working fluid viscosity is very important. In the present study, a novel method is proposed to calculate the head (H), efficiency ( ) and input power ( in P ) based on the loss analysis for pumps using industrial oils. A computer code is developed based on represented method and the results of this method are compared with experimental results for a centrifugal pump of type KWP KBloc65 200. The results show good agreement between analytical and experimental methods. Finally, using such computer code, diagrams of head, efficiency and input power versus working fluid viscosity are plotted.The results show an interesting point known as “sudden rising head” which is observed experimentally and
numerically in literatures.





ThreeDimensional Design of Axial Flow Compressor Blades Using the BallSpine Algorithm


Pages :
683691


Authors :
Ali Madadi,
M.J Kermani,
M. NiliAhmadabadi,
Recently a new inverse design algorithm has been developed for the design of ducts, called ballspine (BS). In the BS algorithm, the duct walls are considered as a set of virtual balls that can freely move along some specified directions, called ‘spines’. Initial geometry is guessed and the flow field is analyzed by a flow solver. Comparing the computed pressure distribution (CPD) with the target pressure distribution (TPD), new balls positions for the modified geometry are determined. This procedure is repeated until the target pressure is achieved. In the present work, the ballspine algorithm is applied to threedimensional design of axial compressor blades. The design procedure is tested on blades based on NACA65410 and NACA65610 profiles and the accuracy of the method is shown to be very good. As an application, the pressure distribution of the blade with NACA65610 profiles is modified and the pressure gradient in the aft part of the blade is decreased and selected as target pressure distribution. The corresponding geometry which satisfies the target
pressure is determined using the BS design algorithm.





MHD Mixed Convection Heat Transfer in a Vertical Channel with TemperatureDependent Transport Properties


Pages :
693701


Authors :
k. V. Prasad,
Kuppalapalle Vajravelu,
An analysis is carried out to study the effects of temperaturedependent transport properties on the fully developed free and forced MHD convection flow in a vertical channel. In this model, viscous and Ohmic dissipation terms are also included. The governing nonlinear equations (in nondimensional form) are solved numerically by a second order finite difference scheme. A parametric study is performed in order to illustrate the interactive influences of the model parameters; namely, the magnetic parameter, the variable viscosity parameter, the mixed convection parameter, the variable thermal conductivity parameter, the Brinkmann number and the Eckert number. The velocity field, the temperature field, the skin friction and the Nusselt number are evaluated for several sets of values of these parameters. For some special cases, the obtained
numerical results are compared with the available results in the literature: Good agreement is found. Of all the parameters, the variable thermophysical transport property has the strongest effect on the drag, heat transfer characteristics, the streamwise velocity, and the temperature field.





Ammonia Decomposition for Hydrogen Production in Catalytic Microchannels with Slip/Jump Effects


Pages :
703712


Authors :
Azad Qazi Zade,
Metin Renksizbulut,
Jacob Friedman,
The rarefaction effects on the catalytic decomposition of NH3 in ruthenium–coated planar microchannels is numerically simulated in the Knudsen number range 0.0150.03. A colocated finite–volume method is used to solve the governing equations. A concentration jump model derived from the kinetic theory of gases is employed to account for the concentration discontinuity at the reactive walls. A detailed surface reaction mechanism for ammonia decomposition on ruthenium along with a multicomponent species diffusion model are used to study the effects of concentration jump coupled with velocity slip and temperature jump on the walls. The velocityslip, temperaturejump and concentrationjump boundary conditions have miscellaneous effects on flow, temperature and species concentration fields. The results suggest that the velocityslip boundary condition only slightly influences the species distribution at the edge of the Knudsen layer as well as inside the channel, while the temperaturejump boundary condition affects the heat and mass transfer characteristics the most. The concentrationjump effect, on the other hand, can counter balance the temperaturejump effects in some cases.





Flow Characteristic Study in a Configuration of Sudden Expansion with Central Restriction and Fence – Viewed as an Annular Flow Dump Combustor


Pages :
713725


Authors :
Tridibesh Das,
S. Chakrabarti,
In this paper, a numerical study on flow characteristics in configurations of sudden expansion with central restriction and fence viewed as annular flow dump combustor has been carried out for Reynolds number (Re) ranging from 50 to 200, percentage of central restriction (CR) from 10% to 40% and aspect ratio (AR) from 2 to 6 with a fixed fence subtended angle (FSA) of 10 degree and with a fixed distance of fence from throat respectively. The effect of each variable on streamline contour and velocity profile has been studied in detail. Results have been compared with the configuration of sudden expansion with central restriction only. From the study it is concluded that the configuration of sudden expansion with central restriction and fence with higher flow Reynolds number, higher central restriction and higher aspect ratio offers more benefit in terms of the mixing possibility compared to the case of sudden expansion with central restriction only.





Numerical Study of Forced Air Cooling of a Heated Porous Foam Pyramid Array


Pages :
727734


Authors :
Anderson Kevin,
Maryam Shafahi,
Alfredo Guiterrez,
The current study employs CFD to study the forced air cooling of a pyramid shaped porous foam absorber. Herein, a three by three (33) array of porous foam absorbers heated with an external heat flux is modeled using the differential equations governing heat and fluid flow through porous media based on the Brinkman Darcy flow equations and an effective thermal conductivity to account for the porous medium. The numerical simulations are carried out using the COMSOL commercial Computational Fluid Dynamics (CFD) Finite Element based software package. The results of this verification exercise were within 18% of the prior numerical results and within 14% of the archived measured results. Typical results for the velocity and temperature profiles within the porous foam absorbers are shown. A comparison of Nusselt number between our CFD simulations and the heat transfer theory is plotted, showing agreement on the order of 11%. A parametric study involving heat flux, cooling air inlet velocity, porous foam porosity, and porous foam permeability showed that there is a relationship between porosity and the temperature distribution within the porous media. The primary finding of our study is that the more porous the foam absorber media is, the more dependent the effective thermal conductivity is on the thermal conductivity of the fluid used for cooling. If the fluid is air, which has a very low thermal conductivity, the effective thermal conductivity is decreased as the porosity increases, thus diminishing removal of heat from the foam array via the cooling air stream. Based on the parametric study, the best case operating conditions which may allow the pyramidal foam absorber to stay within the max allowable temperature are as follows: porosity = 0.472, inlet air cooling velocity = 50 m/s.





Weak Nonlinear Double Diffusive MagnetoConvection in a Newtonian Liquid under Gravity Modulation


Pages :
735746


Authors :
B. S. Bhadauria,
Palle Kiran,
A theoretical analysis of thermoconvective instability in an electrically conducting two component fluid layer is carried out when the gravity field vary with time in a sinusoidal manner. Newtonian liquid is considered between two horizontal surfaces, under a constant vertical magnetic field. The disturbance is expanded in terms of power series of amplitude of convection, which is assumed to be small. We use the linear matrix differential operator method to find the Ginzburg–Landau amplitude equation for the modulated problem. Use the solution of the Ginzburg–Landau equation in quantifying the amount of heat and mass transports in terms of Nusselt and Sherwood numbers. It is found that, the effect of magnetic field is to stabilize the system. Effect of various parameters on the heat and mass transport is also discussed. Further, it is found that the heat and mass transports can be controlled by suitably adjusting frequency and amplitude of
gravity modulation.





Melting with Viscous Dissipation on MHD Radiative Flow from a Vertical Plate Embedded in NonDarcy Porous Medium


Pages :
747752


Authors :
Hemalatha K,
J. Prasad,
We analyzed in this paper the effect of radiation on melting from a vertical plate embedded in porous medium in MHD mixed convection with viscous dissipation under nonDarcy (Forchheimer) conditions. Both aiding and opposing flows are considered in the study. The numerical results were obtained for velocity and temperature variation in melting region and presented in a graphical form. Heat transfer in the melting region has also been studied and the effect of melting parameter and radiation on Nusselt number are presented in graphical form.





Entropy Generation Analysis for Stagnation Point Flow in a Porous Medium over a Permeable Stretching Surface


Pages :
753765


Authors :
M. M. Rashidi,
F. Mohammadi,
S. Abbasbandy,
Mohammed S. Alhuthali,
This paper presents entropy generation analysis for stagnation point flow in a porous medium over a permeable stretching surface with heat generation/absorption and convective boundary condition. We have used Von Karman transformations to transform the governing equations into ordinary differential equations.Thevelocity, temperature and concentration profiles obtained using the Homotopy Analysis Method. The HAM is a valid mathematical tool for most of nonlinear problems in science and engineering. Finally we have computed the entropy generation number. The effect of the Prandtl number, Brinkman number, Reynolds number, suction/injection parameter, Biot number, Lewis number, Brownian motion parameter, thermophoresisparameterand constant parameters on velocity, concentration and temperature profiles are analyzed. Moreover the influences of the Reynolds number and Brinkman number on the entropy generation are presented.The entropy generation number increases with increasing the Brinkman and Reynolds number.





Unsteady Hydromagnetic Natural Convection Flow of a Heat Absorbing Fluid within a Rotating Vertical Channel in Porous Medium with Hall Effects


Pages :
767779


Authors :
Gauri Seth,
Bidyasagar Kumbhakar,
Rohit Sharma,
Unsteady hydromagnetic natural convection flow of a viscous, incompressible, electrically conducting and temperature dependent heat absorbing fluid confined within a parallel plate rotating vertical channel in porous medium is investigated. Fluid flow within the channel is induced due to impulsive movement of one of the plates of the channel. Exact solution for the governing equations for fluid velocity and fluid temperature are obtained by Laplace transform technique. The expressions for the shear stress at the moving plate due to primary and secondary flows and those of rate of heat transfer at the moving and stationary plates are also derived. In order to gain some physical insight into the flow pattern, asymptotic behavior of the solution for fluid velocity and fluid temperature are analyzed for small and large values of time. The numerical values of primary and secondary fluid velocities and fluid temperature are displayed graphically whereas those of shear stress at the moving plate and rate of heat transfer at both the moving and stationary plates are presented in
tabular form for various values of pertinent flow parameters.





The Influence of Ekman Number on Flows Over an Oscillating Isothermal Vertical Plate in a Rotating Frame


Pages :
781791


Authors :
Muhammad asjad Imran,
Dumitru Vieru,
Itrat Abbas Mirza,
Unsteady flows of a Newtonian fluid past an oscillating infinite isothermal vertical plate in a rotating frame are studied. Two closed forms of the velocity field are determined by means of Laplace transform method and by the technique of coupling of the homotopy perturbation method with the Laplace transform method. The equivalence of the obtained expressions for the velocity is provided. The friction coefficients are determined and, the influence of Ekman number on the velocity field is analyzed by graphical illustrations. It is obtained that, the faster frame rotations reduce the thickness of moving fluid layer.





Modelling the Effect of Variable Viscosity on Unsteady Couette Flow of Nanofluids with Convective Cooling


Pages :
793802


Authors :
Ahmada Ali,
O. D. Makinde,
This paper investigates numerically the effects of variable viscosity on unsteady generalized Couette flow of a water base nanofluid with convective cooling at the moving surface. The Buongiorno model utilized for the nanofluid incorporates the effects of Brownian motion and thermophoresis. The nonlinear governing equations of continuity, momentum, energy and nanoparticles concentration are tackled numerically using a semi discretization finite difference method together with RungeKutta Fehlberg integration scheme. Numerical results for velocity, temperature, and nanoparticles concentration profiles together with skin friction and Nusselt number are obtained graphically and discussed quantitatively.





Mixed Convection Flow of Casson Nanofluid over a Stretching Sheet with Convectively Heated Chemical Reaction and Heat Source/Sink


Pages :
803813


Authors :
T. Hayat,
Muhammad Bilal Ashraf,
Sabir Shehzad,
Ahmed Alsaedi,
The present study addresses the mixed convection flow of nonNewtonian nanofluid over a stretching surface in presence of thermal radiation, heat source/sink and first order chemical reaction. Casson fluid model is adopted in the present study. Magnetic field contribution is incorporated in the momentum equation whereas the aspects of nanoparticles are considered in the energy and concentration equations. Convective boundary conditions for both heat and mass transfer are utilized. Similarity transformations are employed to reduce the partial differential equations into ordinary differential equations. Series solutions of the resulting problem are obtained. Impacts of all the physical parameters on the velocity, temperature and concentration fields are analyzed graphically. Numerical values of different involved parameters for local skin friction coefficient, local Nusselt and Sherwood numbers are obtained and discussed.





A Weakly Non Linear Stability Analysis of Heat Transport in Anisotropic Porous Cavity Under Time PeriodicTemperature Modulation


Pages :
815824


Authors :
Amit kumar Mishra,
Mukesh Kumar,
In this paper, we have analyzed the effect of time periodic temperature modulation on convective stability in anisotropic porous cavity. The cavity is heated from below and cooled from above. A weakly nonlinear stability analysis is done to find Nusselt number governing the heat transport. The infinitely small disturbances are expanded in terms of power series of amplitude of modulation. Analytically the nonautonomous Ginzburg landau amplitude equation is obtained for the stationary mode of convection. The effects of various parameters like Vadasz number, mechanical and thermal anisotropic parameters, amplitude of oscillations, frequency of modulation and aspect ratio of the cavity on heat transport is studied and plotted
graphically. It is observed that the heat transport can also be controlled by suitably adjusting the external and internal parameters of the system.





On the Dynamic Behavior of a Liquid Droplet Impacting upon a Wall Having Obstacles


Pages :
825833


Authors :
Boseon Kang,
In this paper, the effects of a step edge and a stationary droplet on the dynamic behavior of a droplet impacting upon a wall are experimentally studied. The main parameters were the distance from the step edge to the center of the impacting droplet and the centertocenter distance between the stationary and impacting droplets. Photographic images showed the coalescence dynamics, shape evolution and contact line movement of the impacting droplet. The spread length is presented for the step edge and two coalescing droplets. The droplets exhibited much different dynamic behavior depending on the location of the step edge. The momentum of the impacting droplet was better transferred to the stationary droplet as the centertocenter distance between the two droplets was reduced, resulting in more spreading of the coalescing droplet.





Onset of the Mutual Thermal Effects of Solid Body and Nanofluid Flow over a Flat Plate Theoretical Study


Pages :
835843


Authors :
Amir Malvandi,
Faraz Hedayati,
D. D. Ganji,
The falling and settling of solid particles in gases and liquids is a natural phenomenon happens in many industrial processes. This phenomenon has altered pure forced convection to a combination of heat conduction and heat convection in a flow over a plate. In this paper, the coupling of conduction (inside the plate) and forced convection of a nonhomogeneous nanofluid flow (over a flat plate) is investigated, which is classified in conjugate heat transfer problems. Twocomponent fourequation nonhomogeneous equilibrium model for convective transport in nanofluids (mixture of water with particles<100nm) has been applied that incorporates the effects of the nanoparticles migration due to the thermophoresis and Brownian motion forces. Employing similarity variables, we have transformed the basic nondimensional partial differential equations to ordinary differential ones and then solved numerically. Moreover, variation of the heat transfer and concentration rates with thermal resistance of the plate is studied in detail. Setting the lowest dependency of heat transfer rate to the thermal resistance of the plate as a goal, we have shown that for two nanofluids with similar heat transfer characteristics, the one with higher Brownian motion (lower nanoparticle diameter) is desired.





Unsteady Free Convection Flow past a Vertical Plate with Heat and Mass Fluxes in the Presence of Thermal Radiation


Pages :
845854


Authors :
S. Das,
R. N. Jana,
A. J. Chamkha,
The problem of unsteady free convection flow past an infinite vertical plate with heat and mass fluxes in the presence of thermal radiation is studied. The dimensionless coupled linear partial differential equations governing the flow are solved by employing the Laplace transform technique. Exact solutions have been obtained for the fluid velocity, temperature and mass concentration for the cases of both uniform heat flux (UHF) and uniform wall temperature (UWT). The numerical results for the fluid velocity, temperature and mass concentration are presented graphically for various pertinent flow parameters and discussed in detail.





Investigating Flat Plate Drag Reduction Using Taguchi Robust Design


Pages :
855862


Authors :
Ghodrat Ghassabi,
Mohsen Kahrom,
Research has shown when a rectangular cylinder is located near a flat plate, the flat plate skin friction coefficient changes as a function of the rectangular aspect ratio, gap height between the rectangular and flat plate, distance of rectangular from the flat plate leading edge, and speed of free stream. However, there is no comprehensive experimental study on the comparison of the results of the flat plate skin friction coefficient for all the interactions between effective variables in the presence and absence of the obstacle. On the other hand, testing all possible combinations of effective variables will not be reasonable. In this paper, maximum and minimum ratios of the flat plate skin friction coefficients with and without the rectangular cylinder were determined using robust Taguchi design. Design of experiments method was applied for decreasing the number of experiments without losing the required information in the first step. Then, experimentation was
done in a wind tunnel, the maximum speed of which was 13 m/s. Finally, the flat plate skin friction coefficient was optimized using Taguchi method and Minitab software. Results showed that presence of the rectangular cylinder near the flat plate decreased the average skin friction coefficient of the flat plate for all the possible combinations of the effective variables. Additionally, maximum value of the flat plate skin friction reduction was about 40%.





Applications of Shallow Water SPH Model in Mountainous Rivers


Pages :
863870


Authors :
Ridong Chen,
Songdong Shao,
Xingnian Liu,
Xiaoquan Zhou,
In this paper, the Shallow Water Equations (SWEs) are solved by the Smoothed Particle Hydrodynamics (SPH) approach. The proposed SWESPH model employs a novel prediction/correction twostep solution algorithm to satisfy the equation of continuity. The concept of buffer layer is used to generate the fluid particles at the inflow boundary. The model is first applied to several benchmark water flow applications involving relatively large bed slope that is typical of the mountainous regions. The numerical SWESPH computations realistically disclosed the fundamental flow patterns. Coupled with a sediment morphdynamic
model, the SWESPH is then further applied to the movement of sediment bed load in an Lshape channel and a river confluence, which demonstrated its robust capacity to simulate the natural rivers.





Mathematical Analysis of Single and TwoPhase Flow of Blood in Narrow Arteries with Multiple Contrictions


Pages :
871883


Authors :
DS Sankar,
Atulya K Nagar,
A Vanav kumar,
The pulsatile flow of blood in narrow arteries with multiplestenoses under body acceleration is analyzed mathematically, treating blood as (i) singlephase HerschelBulkley fluid model and (ii) twophase Herschel Bulkley fluid model. The expressions for various flow quantities obtained by Sankar and Ismail (2010) for singlephase HerschelBulkley fluid model and Sankar (2010c) for twophase HerschelBulkley fluid model are used to compute the data for comparing these fluid models in a new flow geometry. It is noted that the plug core radius, wall shear stress and longitudinal impedance to flow are marginally lower for twophase HB fluid model than those of the singlephase HB fluid model. It is found that the velocity decreases significantly with the increase yield stress of the fluid and the reverse behavior is noticed for longitudinal
impedance to flow. It is also noticed that the velocity distribution and flow rate are higher for twophase HerschelBulkley fluid model than those of the singlephase HerschelBulkley fluid model. It is also recorded that the estimates of the mean velocity increase with the increase of the body acceleration and this behavior is reversed when the stenosis depth increases.





Experimental Study of Heat Transfer Enhancement in a Heated Tube Caused by WireCoil and Rings


Pages :
885892


Authors :
Saeed Vahidifar,
M. Kahrom,
This study investigates heat transfer characteristics and the pressure drop of a horizontal double pipe heat exchanger with wire coil inserts. The amplification of convection heat transfer coefficient in the heat exchanger reduces the weight, size and cost of heat exchanger. One way of augmenting the heat transfer is to disturb the boundary layer. When an object is placed in a boundary layer, it affects the flow structure and alters the velocity and thermal profiles. The change is affected by the formation of jets and wakes in the boundary layer as it alters modifies transfer and friction coefficients on the wall. This paper studies the characteristics of the heat transfer and the pressure drop of a double pipe horizontal tube heat exchanger with an inserted wire coil and rings. Wire coil acts as a swirl flow, which increases turbulence and roughness
whereas rings increase heat transfer as a promoter of turbulence and roughness. The experimental data sets were extracted from wire coils and rings tested within a geometrical range with a pitch of (P/D=1, 2, 4) and wire diameter of (d/D=0.05, 0.07, 0.11). For wire coil with d/D=0.11, P/D =1 and Reynolds number of 10000, the overall enhancement efficiency amounted to 128%.





Bubble Dynamics for Nucleate Pool Boiling of Water, Ethanol and Methanol Pure Liquids under the Atmospheric Pressure


Pages :
893898


Authors :
samane hamzekhani,
Majedeh Maniavi Falahieh,
Mohammad Rasoul Kamalizadeh,
Mohammad Salmaninejad,
Bubble dynamics is the most important subphenomenon, which basically affects the nucleate pool boiling heat transfer coefficient. In this research, bubble departure diameter values were experimentally measured for heat fluxes up to 110 kW.m2. Experiments were carried out for pool boiling of pure liquids, including water, ethanol and methanol on a horizontal smoothed cylinder, at atmospheric pressure. For ethanol and methanol, rigid spherical bubbles with small contact area were observed. The spherical shapes seem to be because of small diameters.For all test fluids, experimental results show that bubble diameter increases with increasing heat flux. Most predictions have a similar trend for increasing bubble diameter versus increasing heat flux. Also, the existing wellknown and most common used correlations are comparatively discussedwith the present experimental data. Finally, a new model for the prediction of vapor bubble departure diameter, based on Buckingham theory, in nucleate boiling is proposed, which predicts the experimental data with a
satisfactory accuracy.





Effect of Sparse Distribution Pores in Thermohaline Convection in a Micropolar Ferromagnetic Fluid


Pages :
899910


Authors :
R. Sekar,
Raju Dr. K.,
Thermoconvective instability in multicomponent fluids has wide range of applications in heat and mass transfer. This paper deals with the theoretical investigation on a horizontal fluid layer of micropolar ferromagnetic fluid heated from below and salted from above saturating a porous medium subjected to a transverse uniform magnetic field using Brinkman model. The salt is a ferromagnetic salt which modifies the magnetic field established. The effect of salinity has been included in the magnetization and density of the ferromagnetic fluid. A theory of linear stability analysis and normal mode technique have been carried out to analyze the onset of convection for a fluid layer contained between two free boundaries for which exact
solution is obtained and the stationary and oscillatory instabilities have been carried out for various physical quantities. The results are depicted graphically and the stabilizing and destabilizing behaviors are studied.





Dual Solutions for MHD Jeffery–Hamel NanoFluid Flow in Nonparallel Walls Using Predictor Homotopy Analysis Method


Pages :
911919


Authors :
Navid Freidoonimehr,
M. M. Rashidi,
The main purpose of this study is to present dual solutions for the problem of magnetohydrodynamic Jeffery–Hamel nanofluid flow in nonparallel walls. To do so, we employ a new analytical technique, Predictor Homotopy Analysis Method (PHAM). This effective method is capable to calculate all branches of the multiple solutions simultaneously. Moreover, comparison of the PHAM results with numerical results obtained by the shooting method coupled with a RungeKutta integration method illustrates the high accuracy for this technique. For the current problem, it is found that the multiple (dual) solutions exist for some values of governing parameters especially for the convergent channel cases (α = 1). The fluid in the nonparallel walls, divergent and convergent channels, is the drinking water containing different nanoparticles; Copper oxide (CuO), Copper (Cu) and Silver (Ag). The effects of nanoparticle volume fraction parameter (φ), Reynolds number (Re), magnetic parameter (Mn), and angle of the channel (α) as well as different types of nanoparticles on the flow characteristics are discussed.





Investigation of Transient MHD Couette flow and Heat Transfer of Dusty Fluid with TemperatureDependent Oroperties


Pages :
921929


Authors :
sobhan mosayebidorcheh,
Taha Mosayebidorcheh,
M. Hatami,
D. D. Ganji,
In the present study, transient MHD Couette flow and heat transfer of dusty fluid between two parallel plates and the effect of the temperature dependent properties has been investigated. The thermal conductivity and viscosity of the fluid are assumed as linear and exponential functions of temperature, respectively. A constant pressure gradient and an external uniform magnetic field are considered in the main flow direction and perpendicular to the plates, respectively. A hybrid treatment based on finite difference method (FDM) and differential transform method (DTM) is used to solve the coupled flow and heat transfer equations. The effects of the variable properties, Hartman number, Hall current, Reynolds number and suction velocity on the Nusselt number and skin friction factor have been discussed. It is found that when Hartman number increases, skin friction of the upper and lower plates increases.





Buoyancy Effects on Unsteady MHD Flow of a Reactive ThirdGrade Fluid with Asymmetric Convective Cooling


Pages :
931941


Authors :
Tirivanhu Chinyoka,
O. D. Makinde,
This article examines the combined effects of buoyancy force and asymmetrical convective cooling on unsteady MHD channel flow and heat transfer characteristics of an incompressible, reactive, variable viscosity and electrically conducting third grade fluid. The chemical kinetics in the flow system is exothermic and the asymmetric convective heat transfers at the channel walls follow the Newton’s law of cooling. The coupled nonlinear partial differential equations governing the problem are derived and solved numerically using a semiimplicit finite difference scheme. Graphical results are presented and physical aspects of the problem are discussed with respect to various parameters embedded in the system.





