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1.
An analysis is presented to describe the boundary layer flow and heat transfer towards a porous exponential stretching sheet. Velocity and thermal slips are considered instead of no-slip conditions at the boundary. Thermal radiation term is incorporated in the temperature equation. Similarity transformations are used to convert the partial differential equations corresponding to the momentum and heat equations into highly non-linear ordinary differential equations. Numerical solutions of these equations are obtained by shooting method. It is found that the fluid velocity and temperature decrease with increasing slip parameter. Temperature is found to decrease with an increase of thermal slip parameter. Thermal radiation enhances the effective thermal diffusivity and the temperature rises. 相似文献
2.
Bikash Sahoo 《Meccanica》2010,45(3):319-330
The effects of partial slip on the steady flow and heat transfer of an electrically conducting, incompressible, third grade
fluid past a horizontal plate subject to uniform suction and blowing is investigated. Two distinct heat transfer problems
are studied. In the first case, the plate is assumed to be at a higher temperature than the fluid; and in the second case,
the plate is assumed to be insulated. The momentum equation is characterized by a highly nonlinear boundary value problem
in which the order of the differential equation exceeds the number of available boundary conditions. Numerical solutions for
the governing nonlinear equations are obtained over the entire range of physical parameters. The effects of slip, magnetic
parameter, non-Newtonian fluid characteristics on the velocity and temperature fields are discussed in detail and shown graphically.
It is interesting to find that the velocity and the thermal boundary layers decrease with an increase in the slip, and as
the slip increases to infinity, the flow behaves as though it were inviscid. 相似文献
3.
The aim of the present study is to investigate the flow of the Casson fluid by an inclined stretching cylinder. A heat transfer analysis is carried out in the presence of thermal radiation and viscous dissipation effects. The temperature dependent thermal conductivity of the Casson fluid is considered. The relevant equations are first simplified under usual boundary layer assumptions, and then transformed into ordinary differential equations by suitable transformations. The transformed ordinary differential equations are computed for the series solutions of velocity and temperature. A convergence analysis is shown explicitly. Velocity and temperature fields are discussed for different physical parameters by graphs and numerical values. It is found that the velocity decreases with the increase in the angle of inclination while increases with the increase in the mixed convection parameter. The enhancement in the thermal conductivity and radiation effects corresponds to a higher fluid temperature. It is also found that heat transfer is more pronounced in a cylinder when it is compared with a flat plate. The thermal boundary layer thickness increases with the increase in the Eckert number. The radiation and variable thermal conductivity decreases the heat transfer rate at the surface. 相似文献
4.
This paper considers the steady mixed convection boundary layer flow of a viscous and incompressible fluid near the stagnation-point
on a vertical surface with the slip effect at the boundary. The temperature of the sheet and the velocity of the external
flow are assumed to vary linearly with the distance from the stagnation-point. The governing partial differential equations
are first transformed into a system of ordinary differential equations, which are then solved numerically by a shooting method.
The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and
discussed. Both assisting and opposing flows are considered. The results indicate that for the opposing flow, the dual solutions
exist in a certain range of the buoyancy parameter, while for the assisting flow, the solution is unique. In general, the
velocity slip increases the heat transfer rate at the surface, while the thermal slip decreases it. 相似文献
5.
Ching-Yang Cheng 《Transport in Porous Media》2014,101(3):401-412
This work presents a boundary layer analysis for the free convection heat transfer from a vertical cylinder in bidisperse porous media with constant wall temperature. A boundary layer analysis and the two-velocity two-temperature formulation are used to derive the nonsimilar governing equations. The transformed governing equations are solved by the cubic spline collocation method to yield computationally efficient numerical solutions. The effects of inter-phase heat transfer parameter, modified thermal conductivity ratio, and permeability ratio on the heat transfer and flow characteristics are studied. Results show that an increase in the modified thermal conductivity ratio and the permeability ratio can effectively enhance the free convection heat transfer of the vertical cylinder in a bidisperse porous medium. Moreover, the thermal nonequilibrium effects are strong for low values of the inter-phase heat transfer parameter. 相似文献
6.
In this paper large-eddy simulation is used to study buoyancy-induced flow in a rotating cavity with an axial throughflow of cooling air. This configuration is relevant in the context of secondary air systems of modern gas turbines, where cooling air is used to extract heat from compressor disks. Although global flow features of these flows are well understood, other aspects such as flow statistics, especially in terms of the disk and shroud boundary layers, have not been studied. Here, previous work for a sealed rotating cavity is extended to investigate the effect of an axial throughflow on flow statistics and heat transfer. Time- and circumferentially-averaged results reveal that the thickness of the boundary layers forming near the upstream and downstream disks is consistent with that of a laminar Ekman layer, although it is shown that the boundary layer thickness distribution along the radial direction presents greater variations than in the sealed cavity case. Instantaneous profiles of the radial and azimuthal velocities near the disks show good qualitative agreement with an Ekman-type analytical solution, especially in terms of the boundary layer thickness. The shroud heat transfer is shown to be governed by the local centrifugal acceleration and by a core temperature, which has a weak dependence on the value of the axial Reynolds number. Spectral analyses of time signals obtained at selected locations indicate that, even though the disk boundary layers behave as unsteady laminar Ekman layers, the flow inside the cavity is turbulent and highly intermittent. In comparison with a sealed cavity, cases with an axial throughflow are characterised by a broader range of frequencies, which arise from the interaction between the laminar jet and the buoyant flow inside the cavity. 相似文献
7.
M. M. Rahman 《Meccanica》2011,46(5):1127-1143
This paper presents heat transfer process in a two-dimensional steady hydromagnetic convective flow of an electrically conducting
fluid over a flat plate with partial slip at the surface of the boundary subjected to the convective surface heat flux at
the boundary. The analysis accounts for both temperature-dependent viscosity and temperature dependent thermal conductivity.
The local similarity equations are derived and solved numerically using the Nachtsheim-Swigert iteration procedure. Results
for the dimensionless velocity, temperature and ambient Prandtl number within the boundary layer are displayed graphically
delineating the effect of various parameters characterizing the flow. The results show that momentum boundary layer thickness
significantly depends on the surface convection parameter, Hartmann number and on the sign of the variable viscosity parameter.
The results also show that plate surface temperature is higher when there is no slip at the plate compared to its presence.
For both slip and no-slip cases surface temperature of the plate can be controlled by controlling the strength of the applied
magnetic field. In modelling the thermal boundary layer flow with variable viscosity and variable thermal conductivity, the
Prandtl number must be treated as a variable irrespective of flow conditions whether there is slip or no-slip at the boundary
to obtain realistic results. 相似文献
8.
《应用数学和力学(英文版)》2017,(1)
The heat transfer of a magnetohydrodynamics nanofluid inside an annulus considering the second-order slip condition and nanoparticle migration is theoretically investigated.A second-order slip condition,which appropriately represents the non-equilibrium region near the interface,is prescribed rather than the no-slip condition and the linear Navier slip condition.To impose different temperature gradients,the outer wall is subjected to q2,the inner wall is subjected to q1,and q1 q2.A modified two-component four-equation non-homogeneous equilibrium model is employed for the nanofluid,which have been reduced to two-point ordinary boundary value differential equations in the consideration of the thermally and hydrodynamically fully developed flow.The homotopy analysis method(HAM) is employed to solve the equations,and the h-curves are plotted to verify the accuracy and efficiency of the solutions.Moreover,the effects of the physical factors on the flow and heat transfer are discussed in detail,and the semi-analytical relation between N uB and NBT is obtained. 相似文献
9.
S. Mukhopadhyay M. Golam Arif M. Wazed Ali 《Journal of Applied Mechanics and Technical Physics》2013,54(6):928-936
The boundary layer flow and mass transfer toward an exponentially stretching porous sheet are analyzed in this paper. Velocity slip is considered instead of the no-slip condition on the boundary. Self-similar equations are obtained by using similarity transformations. Numerical solutions of these equations are obtained by the shooting method. It is found that the fluid velocity and concentration decrease with increasing slip parameter. The fluid velocity decreases with increasing suction parameter. 相似文献
10.
Taking into account the slip flow effects, Newtonian heating, and thermal radiation, two-dimensional magnetohydrodynamic (MHD) flows and heat transfer past a permeable stretching sheet are investigated numerically. We use one parameter group transformation to develop similarity transformation. By using the similarity transformation, we transform the governing boundary layer equations along with the boundary conditions into ordinary differential equations with relevant boundary conditions. The obtained ordinary differential equations are solved with the fourth-fifth order Runge-Kutta- Fehlberg method using MAPLE 13. The present paper is compared with a published one. Good agreement is obtained. Numerical results for dimensionless velocity, temperature distributions, skin friction factor, and heat transfer rates are discussed for various values of controlling parameters. 相似文献
11.
The boundary layer flow of a Casson fluid due to a stretching cylinder is discussed in the presence of nanoparticles and thermal radiation. All physical properties of the Casson fluid except the thermal conductivity are taken constant. Appropriate transformations yield the nonlinear ordinary differential systems. Convergent series solutions are developed and analyzed. The numerical results for the local Nusselt and Sherwood numbers are demonstrated. It is found that an increase in the strength of the Brownian motion decays the temperature noticeably. However, the rate of heat transfer and the concentration of the nanoparticles at the surface increase for larger Brownian motion parameters. 相似文献
12.
The boundary layer flow of a nanofluid past a stretching/shrinking sheet with hydrodynamic and thermal slip boundary conditions is studied. Numerical solutions to the governing equations are obtained using a shooting method. The results are found for the skin friction coefficient, the local Nusselt number, and the local Sherwood number as well as the velocity, temperature, and concentration profiles for some values of the velocity slip parameter, thermal slip parameter, stretching/shrinking parameter, thermophoresis parameter, and Brownian motion parameter. The results show that the local Nusselt number, which represents the heat transfer rate, is lower for higher values of thermal slip parameter, thermophoresis parameter, and Brownian motion parameter. 相似文献
13.
This study aims to investigate numerically the laminar flow and heat transfer in a pseudoplastic non-Newtonian falling liquid
film on a horizontal cylinder for the constant heat flux and isothermal boundary conditions. The inertia terms are taken into
account. An implicit finite difference method is carried out to solve the governing boundary layer equations. The effects
of operational parameters on the hydrodynamic and heat transfer characteristics are examined and discussed in detail. The
results presented show that the local and average Nusselt numbers varies significantly as a function of the concentration
of aqueous carboxymethylcellulose (CMC) solutions and the cylinder diameter. Higher concentration of aqueous CMC solutions
generate larger heat transfer coefficients. Finally, a comparison with the experimental and numerical results available in
the literature for Newtonian fluids shows clearly that the present analysis is reasonably accurate.
Received on 29 March 2001 / Published online: 29 November 2001 相似文献
14.
Two one-parameter series of real solutions describing the process of deceleration and acceleration of a viscoplastic medium under the action of a time-varying pressure gradient are obtained. The problem of axisymmetric unsteady viscoplastic flow is reduced to the solution of the Stefan boundary-value problem for the heat conduction equation with a nonlinear condition on the boundary of the quasi-rigid core. By a self-similar change of variables the problem can be reduced to a second-order ordinary differential equation. The solutions of this equation are represented in terms of Bessel and elementary functions. As a result, two one-parameter series of solutions, the first of which describes the acceleration and the second the deceleration of a viscoplastic medium in a pipe under the action of a time-varying pressure gradient are obtained. 相似文献
15.
A transient free convective boundary layer flow of micropolar fluids past a semi-infinite cylinder is analysed in the present study. The transformed dimensionless governing equations for the flow, microrotation and heat transfer are solved by using the implicit scheme. For the validation of the current numerical method heat transfer results for a Newtonian fluid case where the vortex viscosity is zero are compared with those available in the existing literature, and an excellent agreement is obtained. The obtained results concerning velocity, microrotation and temperature across the boundary layer are illustrated graphically for different values of various parameters and the dependence of the flow and temperature fields on these parameters is discussed. An increase in the vortex viscosity tends to increase the magnitude of microrotation and thus decreases the peak velocity of fluid flow. An increase in the vortex viscosity in micropolar fluids is shown to decrease the heat transfer rate. 相似文献
16.
M. Chandrasekar 《Heat and Mass Transfer》2003,40(1-2):157-165
The Governing Principle of Dissipative Processes (GPDP) formulated by Gyarmati into non-equilibrium thermodynamics is employed
to study the effects of heat transfer, two dimensional, laminar and constant property fluid flow in the boundary layer with
suction and injection. The flow and temperature fields inside the boundary layer are approximated by simple third degree polynomial
functions and the variational principle is formulated over the region of the boundary layer. The Euler–Lagrange equations
of the principle are obtained as polynomial equations in terms of momentum and thermal layer thicknesses. These equations
are solvable for any given values of Prandtl number Pr, wedge angle parameter m and suction/injection parameter H. The obtained
analytical solutions are compared with known numerical solutions and the comparison shows the fact that the accuracy is remarkable. 相似文献
17.
Mahantesh M. Nandeppanavar K. Vajravelu M. Subhas Abel M. N. Siddalingappa 《Meccanica》2013,48(6):1451-1464
In this paper we analyze the flow and heat transfer of an MHD fluid over an impermeable stretching surface with variable thermal conductivity and non-uniform heat source/sink in the presence of partial slip. The governing partial differential equations of the problem are reduced to nonlinear ordinary differential equations by using a similarity transformation. The temperature boundary conditions are assumed to be linear functions of the distance from the origin. Analytical solutions of the energy equations for Prescribed Surface Temperature (PST) and Prescribed Heat Flux (PHF) cases are obtained in terms of a hypergeometric function, without applying the boundary-layer approximation. The effects of the governing parameters on the flow and heat transfer fields are presented through tables and graphs, and they are discussed. Furthermore, the obtained numerical results for the skin friction, wall-temperature gradient and wall temperature are analyzed and compared with the available results in the literature for special cases. 相似文献
18.
Faiza A.Salama 《Acta Mechanica Sinica》2011,27(4):531-540
A boundary layer analysis is presented to investigate numerically the effects of radiation,thermophoresis and the dimensionless heat generation or absorption on hydromagnetic flow with heat and mass transfer over a flat surface in a porous medium.The boundary layer equations are transformed to non-linear ordinary differential equations using scaling group of transformations and they are solved numerically by using the fourth order Runge-Kutta method with shooting technique for some values of physical parameters.Comparisons with previously published work are performed and the results are found to be in very good agreement.Many results are obtained and a representative set is displayed graphically to illustrate the influence of the various parameters on the dimensionless velocity,temperature and concentration profiles as well as the local skin-friction coefficient,wall heat transfer,particle deposition rate and wall thermophoretic deposition velocity.The results show that the magnetic field induces acceleration of the flow,rather than deceleration(as in classical magnetohydrodynamics(MHD) boundary layer flow) but to reduce temperature and increase concentration of particles in boundary layer.Also,there is a strong dependency of the concentration in the boundary layer on both the Schmidt number and mass transfer parameter. 相似文献
19.
The effect of flow slip on the nanofluid boundary layer over a stretching surface is studied. The present results provide a basic understanding on the effects of the slip boundary condition on heat and mass transfer of nanofluids past stretching sheets subject to a convective boundary condition from below. The results show that an increase of thermophoresis parameter or slip factor would decrease the reduced Nusselt number in some cases. 相似文献
20.
Manuel García-Villalba Guillermo Palau-Salvador Wolfgang Rodi 《Flow, Turbulence and Combustion》2014,93(1):171-187
This paper presents a large eddy simulation of forced convection heat transfer in the flow around a surface-mounted finite-height circular cylinder. The study was carried out for a cylinder with height-to-diameter ratio of 2.5, a Reynolds number based on the cylinder diameter of 44 000 and a Prandtl number of 1. Only the surface of the cylinder is heated while the bottom wall and the inflow are kept at a lower fixed temperature. The approach flow boundary layer had a thickness of about 10% of the cylinder height. Local and averaged heat transfer coefficients are presented. The heat transfer coefficient is strongly affected by the free-end of the cylinder. As a result of the flow over the top being downwashed behind the cylinder, a vortex-shedding process does not occur in the upper part, leading to a lower value of the local heat transfer coefficient in that region. In the lower region, vortex-shedding takes place leading to higher values of the local heat transfer coefficient. The circumferentially averaged heat transfer coefficient is 20 % higher near the ground than near the top of the cylinder. The spreading and dilution of the mean temperature field in the wake of the cylinder are also discussed. 相似文献