共查询到20条相似文献,搜索用时 15 毫秒
1.
The concentration convection in an isothermal fluid near an air bubble clamped between the vertical walls of a horizontal channel with a rectangular cross-section is studied experimentally and numerically. The channel is filled with an aqueous solution of a surfactant with a nonuniform concentration. As a result of the competition between the gravitational convection in the cavity volume and the Marangoni convection near the bubble surface, an oscillation flow regime is established. This regime is observed experimentally over several hours. In the numerical experiment, the oscillations are obtained in the presence of an initial horizontal surfactant concentration gradient. Against the background of gravitational convection, short bursts of Marangoni convection with ten times greater intensity are observed. The convective flow patterns and the oscillation periods obtained experimentally and numerically are in fairly good agreement. 相似文献
2.
We investigate natural convection in a fluid saturated rotating anisotropic porous layer subjected to centrifugal gravitational
and Coriolis body forces. The Darcy model (including the centrifugal, gravitational and Coriolis terms; and permeability anisotropy
effects) and a modified energy equation (including the effects of thermal anisotropy) is used in the current analysis. The
linear stability theory is used to evaluate the critical Rayleigh number for the onset of convection in the presence of thermal
and mechanical anisotropy. It is shown that the preferred solution comprises roll cells aligned parallel to the vertical z-axis. As a result, it is found that the Coriolis acceleration (or Taylor number) and the gravitational term play no role
in the stability of convection. 相似文献
3.
The effect of high-frequency translational vibrations on the occurrence of filtration convection in a plane horizontal layer
of a viscous incompressible liquid saturating a porous medium is studied. Constant temperature is maintained at the boundaries
of the layer. It is established that for any vibration direction different from the vertical (transverse) direction, convection
in gravity and thermal gravitational convection under both heating from above and heating from below can arise. In the case
of reduced gravity, values of the vibration parameter that lead to transition to zero gravity are established. The results
are obtained from an analysis of the averaged equations of filtration convection, derived for an arbitrary region.
This work was presented at the joint X European and VI Russian Symposium on Physical Sciences in Microgravity (St. Petersburg,
June 15–20, 1997).
Rostov State university, Rostov-on-Don 344090. Rostov State Academy of Building, Rostov-on-Don 344022. Translated from Prikladnaya
Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 3, pp. 22–29, May–June, 1999. 相似文献
4.
Mathematical modeling of gravitational heat convection in a closed rectangular domain with finite-thickness heat-conducting
walls in the presence of a heat-releasing element with a constant heat-release intensity located at the base of the domain
under conditions of convective-radiative heat transfer on one external boundary is performed. The influence of constitutive
parameters (Grashof number and relative thermal conductivity) and flow unsteadiness on local thermohydrodynamic characteristics
(streamlines and temperature field) and on the integral parameter (mean Nusselt number on the inner surface of the solid walls)
is analyzed. Results obtained for two models of the heat source (with a constant temperature and with a constant heat-release
intensity) are compared. 相似文献
5.
The paper outlines the theoretical studies of flows and heat transfer in near-critical media in the vicinity of the critical
thermodynamic point under microgravity and terrestrial conditions. The criteria determining the characteristics of thermal
gravitational convection and thermal acoustics complicated by the adiabatic compression effect, the distinctive features of
convection generation, and the hierarchy of non-Boussinesq mathematical models and the their calibration on the basis of the
Boussinesq model are discussed. 相似文献
6.
Based on the two-energy equation model, taking into account viscous dissipation due to the interaction between solid skeleton and pore fluid flow, temperature expressions of the solid skeleton and pore fluid flow are obtained analytically for the thermally developing forced convection in a saturated porous medium parallel plate channel, with walls being at constant temperature. It is proved that the temperatures of the two phases for the local thermal nonequilibrium approach to the temperature derived from the one-energy equation model for the local thermal equilibrium when the heat exchange coefficient goes to infinite. The temperature profiles are shown in figures for different dimensionless parameters and the effects of the parameters on the local thermal nonequilibrium are revealed by parameter study. 相似文献
7.
The steady-state laminar mixed convection of a binary gas mixture in a parallel-plate channel is investigated. The channel walls are subjected to different combinations of first-type thermal and solutal boundary conditions and different wall inclinations have been considered. A second-order accurate control-volume based numerical scheme is used for the resolution. In parallel with the numerical investigation, the governing conservation equations are also simplified for fully developed conditions and are shown to be controlled by a single parameter. An exact analytical solution is obtained for the main flow variables and transfer rates and serves as a validation tool for the numerical model. In addition, it establishes a criterion based on the two Grashof numbers, the Reynolds number and the channel inclination for the existence of a reversed flow. 相似文献
8.
In this article nonsimilarity solution for mixed convection from a horizontal surface in a saturated porous medium was obtained
for the case of variable surface heat flux. The entire mixed convection regime, ranging from pure forced convection to pure
free convection, is considered by introducing a single nonsimilarity parameter. Heat transfer results are predicted by employing
four different flow models, namely, Darcy's law, the Ergun model, and the Brinkman-Forchheimer-extended Darcy model with constant
and variable porosity. The variable porosity effect is approximated by an exponential function. Effects of transverse thermal
dispersion are taken into consideration in the energy equation, along with variable stagnant thermal conductivities. The formulation
of the present problem shows that the flow and heat transfer characteristics depend on five parameters, that is, the power
in the variation of surface heat flux, the nonsimilarity mixed-convection parameter, the inertia effect parameter, the boundary
effect parameter, and the ratio of thermal conductivity of the fluid phase to that of the solid phase. Numerical results for
the local Nusselt number variations, based on the various flow models, are presented for the entire mixed convection regime.
The impacts␣of different governing parameters on the heat transfer results are thoroughly investigated.
Received on 7 August 1997 相似文献
9.
The stability and onset of convection in a rotating fluid saturated porous layer subject to a centrifugal body force and placed at an offset distance from the center of rotation is investigated analytically. The marginal stability criterion is established in terms of a critical centrifugal Rayleigh number and a critical wave number for different values of the parameter representing the dimensionless offset distance from the center of rotation. At the limit of an infinite distance from the center of rotation the results are identical to the convection resulting from heating a porous layer from below subject to the gravitational body force. At the other limit, when the parameter controlling the offset distance approaches zero, the results converge to previously found solutions for the convection in a porous layer adjacent to the axis of rotation. The results provide the stability map for all positive values of the parameter controlling the offset distance from the center of rotation, hence bridging the gap between the two extreme limit cases. 相似文献
10.
The double diffusion effect on the mixed convection flow over a horizontal porous sensor surface placed inside a horizontal channel is analyzed.With the appropriate transformations,the unsteady equations governing the flow are reduced to non-similar boundary layer equations which are solved numerically for the time-dependent mixed convection parameter.The asymptotic solutions are obtained for small and large values of the time-dependent mixed convection parameter.The results are discussed in terms of the skin friction,the heat transfer coefficient,the mass transfer coefficient,and the velocity,temperature,and concentration profiles for different values of the Prandtl number,the Schmidt number,the squeezing index,and the mixed convection parameter. 相似文献
11.
Stability analysis of free convection in a liquid-saturated sparsely-packed porous medium with local-thermal-non-equilibrium (LTNE) effect is presented. For the vertical boundaries free–free, adiabatic and rigid–rigid, adiabatic are considered while for horizontal boundaries it is the stress-free, isothermal and rigid–rigid, isothermal boundary combinations we consider. From the linear theory, it is apparent that there is advanced onset of convection in a shallow enclosure followed by that in square and tall enclosures. Asymptotic analysis of the thermal Rayleigh number for small and large values of the inter-phase heat transfer coefficient is reported. Results of Darcy–Bénard convection (DBC) and Rayleigh–Bénard convection can be obtained as limiting cases of the study. LTNE effect is prominent in the case of Brinkman–Bénard convection compared to that in DBC. Using a multi-scale method and by performing a non-linear stability analysis the Ginzburg–Landau equation is derived from the five-mode Lorenz modal. Heat transport is estimated at the lower plate of the channel. The effect of the Brinkman number, the porous parameter and the inter-phase heat transfer coefficient is to favour delayed onset of convection and thereby enhanced heat transport while the porosity-modified ratio of thermal conductivities shows the opposite effect. 相似文献
12.
This paper describes the thermal convection and heat transfer in a cylindrical fluid layer rotating around a horizontal axis, with various constant temperatures set at the layer boundaries. The influence of the rotational speed of the cylindrical fluid layer on the convective heat transfer in this layer is studied. The study results are presented as functions of dimensionless parameters that characterize the action of two convective mechanisms: centrifugal and thermal-oscillatory. It is shown that, with low rotational speed, the heat transfer is determined by quasistationary gravitational convection. 相似文献
13.
The results of investigating specific features of the behavior of a liquid subject to thermal gravitational convection in the inner, outer and coupled problems under conditions of near-weightlessness are generalized. The results of calculating the flows in a liquid-gas system in a variable acceleration vector field are presented. 相似文献
14.
We investigate Rayleigh–Benard convection in a porous layer subjected to gravitational and Coriolis body forces, when the
fluid and solid phases are not in local thermodynamic equilibrium. The Darcy model (extended to include Coriolis effects and
anisotropic permeability) is used to describe the flow, whilst the two-equation model is used for the energy equation (for
the solid and fluid phases separately). The linear stability theory is used to evaluate the critical Rayleigh number for the
onset of convection and the effect of both thermal and mechanical anisotropy on the critical Rayleigh number is discussed. 相似文献
15.
The double diffusive convection in a horizontal couple stress fluid saturated anisotropic porous layer, which is heated and
salted from below, is studied analytically. The modified Darcy equation that includes the time derivative term is used to
model the momentum equation. The critical Rayleigh number, wavenumber for stationary and oscillatory modes, and frequency
of oscillations are obtained analytically using linear theory. The effect of anisotropy parameter, solute Rayleigh number,
Lewis number, couple stress parameter, and Vadasz number on the stationary, oscillatory, and finite amplitude convection is
shown graphically. It is found that the thermal anisotropy parameter, couple stress parameter, and solute Rayleigh number
have stabilizing effect on the stationary, oscillatory, and finite amplitude convection. The mechanical anisotropy parameter
has destabilizing effect on stationary, oscillatory, and finite amplitude convection. The Lewis number has stabilizing effect
in the case of stationary and finite amplitude modes, with dual effect in the case of oscillatory convection. Vadasz number
advances the onset of oscillatory convection. The heat and mass transfer decrease with an increase in the values of couple
stress parameter, while both increase with an increase in the value of solute Rayleigh number and mechanical anisotropy parameter.
The thermal anisotropy parameter and Lewis number have contrasting effect on the heat mass transfer. 相似文献
16.
The criteria for the onset of thermocapillary convection in a horizontal radiating fluid layer heated by an incident thermal radiative energy source are determined. The fluid layer is an absorbing and isotropically scattering medium confined between a free upper surface and an insulated rigid lower surface. Linear analysis is performed on the continuity, momentum, energy, and approximate radiative equations. The resulting disturbance equations are solved using a numerical optimization technique to obtain the eigenvalues governing the onset of convective motion. The influence of thermal radiation on the critical Marangoni number is examined. Attention is drawn to the physical significance of the heat transfer mode, gravitational force, the scattering effect, and the surface radiative properties. The conditions leading to the onset of convection are presented as functions of the optical thickness, scattering albedo, Planck number, surface emissivities, and transmissivities. 相似文献
17.
Thermal gravitational convection in a supercritical medium is studied at parameter values higher than those corresponding the liquid-gas phase transition point. Steady convective flow and heat transfer are modeled in an extended region with a square cross-section, the temperatures on the lateral boundaries being constant and different. Both Boussinesq flows, in which spatial variations of the density and the thermodynamic parameters are small, and non-Boussinesq flows with considerably spatially-variable physical properties are considered. The effect of the temperature inhomogeneity parameter on the distinctive features of the flow and the heat transfer is determined. 相似文献
18.
Onset of convection in a layer of couple-stress fluid-saturated porous medium is investigated for different types of basic
temperature gradients. The boundaries are considered to be adiabatically insulated to temperature perturbations. The eigenvalue
equations of the perturbed state obtained from the normal mode analysis are solved analytically using a regular perturbation
technique with wave number as a perturbation parameter and also numerically using the Galerkin technique. The critical stability
parameters obtained from these two techniques are in excellent agreement and an increase in the value of couple-stress parameter
is found to delay the onset of convection. The results also indicate that the piecewise linear temperature profile hastens
the onset of convection when compared to linear, parabolic, and inverted parabolic temperature profiles. In addition, the
influence of thermal depth on the critical conditions is assessed in the case of piecewise linear temperature profiles, and
it is observed that the critical thermal depth decreases marginally with an increase in the couple-stress parameter. 相似文献
19.
This work is focused on the numerical modeling of steady, laminar, heat and mass transfer by MHD mixed convection from a semi-infinite,
isothermal, vertical and permeable surface immersed in a uniform porous medium in the presence of thermal radiation and Dufour
and Soret effects. A mixed convection parameter for the entire range of free-forced-mixed convection is employed and the governing
equations are transformed into non-similar equations. These equations are solved numerically by an efficient, implicit, iterative,
finite-difference scheme. The obtained results are checked against previously published work on special cases of the problem
and are found to be in excellent agreement. A parametric study illustrating the influence of the thermal radiation coefficient,
magnetic field, porous medium inertia parameter, concentration to thermal buoyancy ratio, and the Dufour and Soret numbers
on the fluid velocity, temperature and concentration as well as the local Nusselt and the Sherwood numbers is conducted. The
obtained results are shown graphically and the physical aspects of the problem are discussed. 相似文献
20.
Instability of mechanical equilibrium and initiation of plane steady-state convective flows in an infinite horizontal fluid layer heated from below (Rayleigh-Benard problem) are investigated. The convection model for an isothermal incompressible fluid is not assumed to have small thermal expansion (contrary to the Oberbeck-Boussinesq approximation). The influence of a supplementary thermal expansion parameter on the convection process is numerically investigated. The results are compared with the known results for the Oberbeck-Boussinesq approximation. It is shown that subcritical instability is possible if the thermal expansion parameter increases. The linearization and Lyapunov-Schmidt methods are applied.Rostov-on-Don. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 5, pp. 3–10, September–October, 1995. 相似文献
|