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1.
The method of similarity solution is used to study the influence of lateral mass flux and thermal dispersion on non-Darcy
natural convection over a vertical flat plate in a fluid saturated porous medium. Forchheimer extension is considered in the
flow equations and the coefficient of thermal diffusivity has been assumed to be the sum of molecular diffusivity and the
dispersion thermal diffusivity due to mechanical dispersion. The suction/injection velocity distribution has been assumed
to have power function form Ax
l
, where x is the distance from the leading edge and the wall temperature distribution is assumed to be uniform. When l=−1/2, similarity solution is possible, and the results indicate that the boundary layer thickness decreases where as the
heat transfer rate increases as the mass flux parameter passes from injection domain to the suction domain. The increase in
the thermal dispersion parameter is observed to enhance the heat transfer. The combined effect of thermal dispersion and fluid
suction/injection on the heat transfer rate is discussed.
Received on 9 September 1996 相似文献
2.
The problem of natural convective heat transfer for a non-Newtonian fluid from an impermeable vertical plate embedded in a fluid-saturated porous medium has been analyzed. Non-Darcian, radiative and thermal dispersion effects have been considered in the present analysis. The governing boundary layer equations and boundary conditions are cast into a dimensionless form and simplified by using a similarity transformation. The resulting system of equations is solved by using a double shooting Runge–Kutta method. The effect of viscosity index n, the conduction–radiation parameter R, the non-Darcy parameter Gr*, the thermal dispersion parameter Ds and the suction/injection parameter fw on the fluid velocities, temperatures and the local Nusselt number are discussed. 相似文献
3.
This paper presents both a numerical and analytical study in connection with the steady boundary layer flow and heat transfer
induced by a moving permeable semi-infinite flat plate in a parallel free stream. Both the velocities of the flat plate and
the free stream are proportional to x
1/3. The surface temperature is assumed to be constant. The governing partial differential equations are converted into ordinary
differential equations by a new similarity transformation. Numerical results for the flow and heat transfer characteristics
are obtained for various values of the moving parameter, transpiration parameter and the Prandtl number. Approximate analytical
solutions are also obtained when the suction or injection parameter is very large. It is found that dual solutions exist for
the case when the fluid and the plate move in the opposite directions. 相似文献
4.
The boundary layer flow and heat transfer on a stretched surface moving with prescribed skin friction is studied for permeable surface. Three major cases are studied for isothermal surface (n=0) stretched corresponding to different dimensional skin friction boundary conditions namely; skin friction at the surface scales as (x ?1/2) at m=0, constant skin friction at m=1/3 and skin friction scales as (x) at m=1. The constants m and n are the indices of the power law velocity and temperature exponent respectively. Similarity solutions are obtained for the boundary layer equations subject to power law temperature and velocity variation. The effect of various governing parameters, such as Prandtl number Pr, suction/injection parameter f w , m and n are studied. The results show that for isothermal surface increasing m enhances the dimensionless heat transfer coefficient for fixed f w at the suction case and the reverse is true at the injection case. Furthermore, for fixed m, as f w increases the dimensionless heat transfer coefficient increases. Large enhancements are observed in the heat transfer coefficient as the temperature boundary condition along the surface changes from uniform to linear where the dimensional skin friction is of order (x) at m=1. This enhancement decreases as the suction increases. 相似文献
5.
Heat transfer characteristics of a non-Newtonian fluid on a power-law stretched surface of variable temperature with suction
or injection were investigated. Similarity solutions of the laminar boundary layer equations describing heat transfer and
fluid flow in a quiescent fluid were obtained and solved numerically. Velocity and temperature profiles as well as the Nusselt
number, Nu, were studied for two thermal boundary conditions; uniform surface temperature and variable surface temperature,
for different parameters; Prandtl number Pr, temperature exponent b, velocity exponent m, injection parameter d and power-law index n. It was found that decreasing injection parameter d, and power-law index n and increasing Prandtl number Pr and surface temperature exponent b enhance the heat transfer coefficient.
Received on 27 April 2000 相似文献
6.
Laminar mixed convection from a continuously moving vertical surface with suction or injection 总被引:1,自引:0,他引:1
The boundary layer flow over a uniformly moving vertical surface with suction or injection is studied when the buoyancy forces
assist or oppose the flow. Similarity solutions are obtained for the boundary layer equations subject to power law temperature
and velocity boundary conditions. The effect is of various governing parameters, such as Prandtl number Pr, temperature exponent
n, injection parameter d, and the mixed convection parameter λ=Gr/Re2, which determine the velocity and temperature distributions and the heat transfer coefficient, are studied. The heat transfer
coefficient increases as λ assisting the flow for all d at Pr=0.72 however, for n=−1 it decreases sharply with λ. On the other hand, increasing λ has no effect on heat transfer coefficient for Pr=10 at n=0, and 1 for almost all values of d studied. However, for n=−1 it has similar effect as for Pr=0.72. It is also found that Nusselt number increases as n increases for fixed λ and d.
Received on 26 March 1997 相似文献
7.
The paper presents a study of the laminar mixed convection adjacent to vertical continuously stretching sheets, taking into account the effects of variable viscosity and variable thermal diffusivity. The similarity solutions are reported for isothermal sheet moving with a velocity of the form uw=Bx0.5 and a continuous linearly stretching sheet with a linear surface temperature distribution. The equations of conservation of mass, momentum and energy, which govern the flow and heat transfer, are solved numerically by using the shooting method. The numerical results obtained for the flow and heat transfer characteristics reveal many interesting behaviors. The numerical results show that, variable viscosity, variable thermal diffusivity, the velocity exponent parameter, the temperature exponent parameter and the buoyancy force parameter have significant influences on the velocity and temperature profiles, shear stress and Nusselt number in two cases air and water. 相似文献
8.
V. V. Terekhov V. I. Terekhov 《Journal of Applied Mechanics and Technical Physics》2017,58(2):254-263
The structure and heat transfer in a turbulent separated flow in a suddenly expanding channel with injection (suction) through a porous wall are numerically simulated with the use of two-dimensional averaged Navier–Stokes equations, energy equations, and v 2–f turbulence model. It is shown that enhancement of the intensity of the transverse mass flux on the wall reduces the separation region length in the case of suction and increases the separation region length in the case of injection up to complete boundary layer displacement. The maximum heat transfer coefficient as a function of permeability is accurately described by the asymptotic theory of a turbulent boundary layer. 相似文献
9.
The effects of thermal dispersion and thermal radiation on the non-Darcy natural convection over a vertical flat plate in a fluid saturated porous medium are studied. Forchheimer extension is considered in the flow equations. The coefficient of thermal diffusivity has been assumed to be the sum of molecular diffusivity and the dispersion thermal diffusivity due to mechanical dispersion. Rosseland approximation is used to describe the radiative heat flux in the energy equation. Similarity solution for the transformed governing equations is obtained. Numerical results for the details of the velocity and temperature profiles which are shown on graphs have been presented. The combined effect of thermal dispersion and thermal radiation, for the two cases Darcy and non-Darcy porous medium, on the heat transfer rate which are entered in tables is discussed. 相似文献
10.
The effect of lateral mass flux on mixed convection heat and mass transfer in a saturated porous medium adjacent to an inclined
permeable surface is analyzed. A similarity solution is obtained when surface temperature and concentration, free stream velocity
and injection/suction velocity of fluid are prescribed as power functions of distance from the leading edge. The cases when
the flow and buoyancy forces are in the same and opposite directions are discussed both for aiding and opposing buoyancy effects.
The governing parameters are the mixed convection parameter Gr, the Lewis number Le, the buoyancy ratio N, the lateral mass flux parameter f
w, representing the effects of injection or withdrawal of fluid at the wall, and λ which specifies three cases of the inclined
plate. The interactive effect of these parameters on heat and mass transfer rates are presented. It is observed that the diffusion
ratio (Le) has a more pronounced effect on concentration field than on flow and temperature fields. It is found that the rates
of heat and mass transfer increase with suction and decrease with injection of the fluid.
Received on 31 August 2000 / Published online: 29 November 2001 相似文献
11.
A one layer model of laminar non-Newtonian fluids (Ostwald-de Waele model) past a semi-infinite flat plate is revisited. The stretching and the suction/injection velocities are assumed to be proportional to x1/(1−2n) and x−1, respectively, where n is the power-law index which is taken in the interval . It is shown that the boundary-layer equations display both similarity and pseudosimilarity reductions according to a parameter γ, which can be identified as suction/injection velocity. Interestingly, it is found that there is a unique similarity solution, which is given in a closed form, if and only if γ=0 (impermeable surface). For γ≠0 (permeable surface) we obtain a unique pseudosimilarity solution for any 0≠γ≥−((n+1)/3n(1−2n))n/(n+1). Moreover, we explicitly show that any pseudosimilarity solution exhibits similarity behavior and it is, in fact, similarity solution to a modified boundary-layer problem for an impermeable surface. In addition, the exact similarity solution of the original boundary-layer problem is used, via suitable transverse translations, to construct new explicit solutions describing boundary-layer flows induced by permeable surfaces. 相似文献
12.
Flow and heat transfer over a permeable sensor surface placed in a squeezing channel is analyzed. A constant transpiration
through the sensor surface is assumed. Locally non-similar momentum and energy equations are solved by three different methods,
against the transpiration parameter τ, for different values of the squeezing parameter b, and Prandtl number Pr. From the investigation, it is found that when the channel being squeezed, the skin-friction reduces but the heat transfer
coefficient increases. Increase in the value of the squeezing parameter onsets reverse flow at the sensor surface when fluid
is being injected and the affect is enhanced with the increase of injection through the surface. It is further observed that
increase of suction of fluid through the sensor thins the thermal and the momentum boundary layer regions, whereas injection
of fluid leads to thickening of both the thermal and the momentum boundary layer regions. Heat transfer from the surface of
the sensor increases with the increase of the value of Pr for the entire range of surface mass-flux parameter τ.
M. A. Hossain is on leave of absence from University of Dhaka. 相似文献
13.
The steady laminar incompressible free convective flow of a nanofluid over a permeable upward facing horizontal plate located
in porous medium taking into account the thermal convective boundary condition is studied numerically. The nanofluid model
used involves the effect of Brownian motion and the thermophoresis. Using similarity transformations the continuity, the momentum,
the energy, and the nanoparticle volume fraction equations are transformed into a set of coupled similarity equations, before
being solved numerically, by an implicit finite difference numerical method. Our analysis reveals that for a true similarity
solution, the convective heat transfer coefficient related with the hot fluid and the mass transfer velocity must be proportional
to x
−2/3, where x is the horizontal distance along the plate from the origin. Effects of the various parameters on the dimensionless longitudinal
velocity, the temperature, the nanoparticle volume fraction, as well as on the rate of heat transfer and the rate of nanoparticle
volume fraction have been presented graphically and discussed. It is found that Lewis number, the Brownian motion, and the
convective heat transfer parameters increase the heat transfer rate whilst the thermophoresis decreases the heat transfer
rate. It is also found that Lewis number and the convective heat transfer parameter enhance the nanoparticle volume fraction
rate whilst the thermophoresis parameter decreases nanoparticle volume fraction rate. A very good agreement is found between
numerical results of the present article for special case and published results. This close agreement supports the validity
of our analysis and the accuracy of the numerical computations. 相似文献
14.
The analysis of heat transfer to the non-Newtonian power-law fluid flow past a continuously moving flat porous plate in presence of suction/injection with heat flux has been presented. We have obtained the solution using the method of successive approximations, starting with zero approximation. It has been observed that the results obtained forn=1 are in good agreement with the corresponding results for Newtonian fluid. For various values of flow indexn and the suction/injection parameter, temperature profiles and rate of heat transfer have been presented graphically. The effect of suction is to decrease in temperature and the rate of heat transfer, while reverse nature occurs for injection.
Wärmeübertragung bei Nicht-Newton'schen Fluiden, die dem Potenz-Ansatz gehorchen, entlang einer stetig bewegten, flachen, porösen Platte mit Wärmestrom
Zusammenfassung Hier ist die Berechnung der Wärmeübertragung bei Nicht-Newton'schen Fluiden entlang einer sich stetig bewegenden, flachen Platte mit Wärmestrom dargestellt worden, bei der die Grenzschicht abgesaugt bzw. eingeblasen wird. Die Lösung erhielten die Verfasser mit dem Verfahren der sukzessiven Approximation, beginnend mit der Nullapproximation. Es ist festgestellt worde, daß die erhaltenen Ergebnisse fürn=1 mit den Ergebnissen für Newton'sche Fluide übereinstimmen. Für verschiedene Werte des Strömungsindexesn und des Absaug-/Einblasparameters sind die Temperaturprofile und die Wärmeübertragungsraten graphisch dargestellt worden. Beim Absaugen ergibt sich eine Erniedrigung der Temperatur und der Wärmeübertragungsrate, während genau das Gegenteil beim Einblasen eintritt.相似文献
15.
In this study, laminar boundary layer flow over a flat plate embedded in a fluid-saturated porous medium in the presence of
viscous dissipation, inertia effect and suction/injection is analyzed using the Keller box finite difference method. The flat
plate is assumed to be held at constant temperature. The non-Darcian effects of convection, boundary and inertia are considered.
Results for the local heat transfer parameter and the local skin friction parameter as well as the velocity and temperature
profiles are presented for various values of the governing parameters. The non-Darcian effects are shown to decrease the velocity
and to increase the temperature. It is also shown that the local heat transfer parameter and the local skin friction parameter
increase due to suction of fluid while injection reverses this trend. It is disclosed that the effect of the viscous dissipation
for negative values of Ec (T
w
< T
∞) is to enhance the heat transfer coefficient while the opposite is true for positive values of Ec (T
w
> T
∞). The results are compared with those available in the existing literature and an excellent agreement is obtained. 相似文献
16.
MHD mixed free-forced heat and mass convective steady incompressible laminar boundary layer flow of a gray optically thick electrically conducting viscous fluid past a semi-infinite inclined plate for high temperature and concentration differences is studied. A uniform magnetic field is applied perpendicular to the plate. The density of the fluid is assumed to reduce exponentially with temperature and concentration. The usual Boussinesq approximation is neglected due to the high temperature and concentration differences between the plate and the ambient fluid. The Rosseland approximation is used to describe the radiative heat flux in the energy equation. The boundary layer equations governing the flow are reduced to ordinary differential equations, which are numerically solved by applying an efficient technique. The effects of the density/temperature parameter n, the density/concentration parameter m, the local magnetic parameter Mx and the radiation parameter R are examined on the velocity, temperature and concentration distributions as well as the coefficients of skin-friction, heat flux and mass flux. 相似文献
17.
K. A. Yih 《Heat and Mass Transfer》1998,34(1):55-61
A boundary layer analysis is used to investigate the heat and mass transfer characteristics of mixed convection about a vertical
flat plate embedded in a saturated porous medium under the coupled effects of thermal and mass diffusion. The plate is maintained
at prescribed surface temperature/concentration (PST/PSC) or prescribed heat/mass flux (PHF/PMF). The nonsimilar governing
equations are obtained by using a suitable transformation and solved by Keller box method. Numerical results for the local
heat transfer rate and the local mass transfer rate are presented for various parameters. The local heat and mass transfer
rates increase with increasing n and m and buoyancy parameter ξ. When buoyancy parameter ξ is very small (large) the value of local Nusselt and the local Sherwood
number correspond with the pure forced (free) convection, respectively. Increasing buoyancy ratio N (or N
*) increases the local heat and mass transfer rates. It is apparent that Lewis number has a pronounced effect on the local
mass transfer rate than it does on the local heat transfer rate. Furthermore, increasing Lewis number decreases (increases)
the local heat (mass) transfer rate.
Received on 8 December 1997 相似文献
18.
The problem of the self-similar boundary flow of a “Darcy-Boussinesq fluid” on a vertical plate with temperature distribution
T
w(x) = T
∞+A·x
λ and lateral mass flux v
w(x) = a·x
(λ−1)/2, embedded in a saturated porous medium is revisited. For the parameter values λ = 1,−1/3 and −1/2 exact analytic solutions
are written down and the characteristics of the corresponding boundary layers are discussed as functions of the suction/ injection
parameter in detail. The results are compared with the numerical findings of previous authors.
Received on 8 March 1999 相似文献
19.
C.-H. Chen 《Heat and Mass Transfer》1998,33(5-6):471-476
The analysis of laminar mixed convection in boundary layers adjacent to a vertical, continuously stretching sheet has been
presented. The velocity and temperature of the sheet were assumed to vary in a power-law form, that is, u
w
(x)=Bx
m
and T
w
(x)−T
∞=Ax
n
. In the presence of buoyancy force effects, similarity solutions were reported for the following two cases: (a) n=0 and m=0.5, which corresponds to an isothermal sheet moving with a velocity of the form u
w
=Bx
0.5 and (b) n=1 and m=1, which corresponds to a continuous, linearly stretching sheet with a linear surface temperature distribution, i.e. T
w
−T
∞=Ax. Formulation of the present problem shows that the heat transfer characteristics depends on four governing parameters, namely,
the velocity exponent parameter m, the temperature exponent parameter n, the buoyancy force parameter G
*, and Prandtl number of the fluid. Numerical solutions were generated from a finite difference method. Results for the local
Nusselt number, the local friction coefficient, and temperature profiles are presented for different governing parameters.
Effects of buoyancy force and Prandtl number on the flow and heat transfer characteristics are thoroughly examined.
Received on 17 July 1997 相似文献
20.
The method of non-similarity solution is used to study the influence of thermal dispersion on combined convection from vertical surfaces in a porous medium saturated with a power-law type non-Newtonian fluid. The coefficient of thermal diffusivity has been assumed to be the sum of molecular diffusivity and the dispersion thermal diffusivity due to mechanical dispersion. The transformed conservation laws are solved numerically for the case of variable surface heat flux conditions. Results for the details of the velocity and temperature fields as well as the Nusselt number have been presented. 相似文献