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1.
We consider unsteady laminar natural convection flow of water subject to density inversion in a rectangular cavity formed by isothermal vertical walls with internal heat generation. The top and bottom horizontal walls are considered to be adiabatic, whereas the temperature of the left vertical wall is assumed to be greater than that of the right vertical wall. The equations are non-dimensionalized and are solved numerically by an upwind finite difference method together with a successive over-relaxation (SOR) technique. The effects of both heat generation and variations in the aspect ratio on the streamlines, isotherms and the rate of heat transfer from the walls of the enclosure are presented. Investigations are performed for water taking Prandtl number to be Pr=11.58 and the Rayleigh number to be Ra=105. 相似文献
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Combined forced and free convection flow in a fluid saturated inclined plane channel is investigated by taking into account
the effect of viscous dissipation. Steady parallel flow is considered assuming that the temperature gradient in the parallel
flow direction is constant, and the channel walls are subject to uniform symmetric heat fluxes. Two possible formulations
of the Darcy–Boussinesq scheme are considered, based on two different choices of the reference temperature for modelling buoyancy.
The first choice is a constant temperature, while the second is a streamwise changing temperature. It is shown that both approaches
substantially agree in the formulation of the balance equations for the range of values of the Darcy–Rayleigh number such
that viscous dissipation is important. The boundary value problem is solved analytically for any tilt angle, revealing that
it admits dual solutions for assigned values of the governing parameters. The rather important effect of viscous dissipation
in the special case of adiabatic channel walls is outlined.
E. Magyari is on leave from Institute of Building Technology, ETH—Zürich 相似文献
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S. Morsli A. Sabeur-Bendehina 《Journal of Applied Mechanics and Technical Physics》2013,54(6):913-920
The aim of the present work is to study the entropy generation in the natural convection process in square cavities with hot wavy walls through numerical simulations for different undulations and Rayleigh numbers, while keeping the Prandtl number constant. The results show that the hot wall geometry affects notably the heat transfer rate in the cavity. It has been found in the present numerical study that the mean Nusselt number in the case of heat transfer in a cavity with wavy walls is lower, as compared to heat transfer in a cavity without undulations. Based on the obtained dimensionless velocity and temperature values, the distributions of the local entropy generation due to heat transfer and fluid friction, the local Bejan number, and the local entropy generation are determined and plotted for different undulations and Rayleigh numbers. The study is performed for Rayleigh numbers 103 < Ra < 105, irreversibility coefficients 10?4 < φ < 10?2, and Prandtl numbers Pr = 0.71. The total entropy generation is found to increase with increasing undulation number. 相似文献
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This paper presents the fluid flow characteristics of natural convection flow in an anti-symmetrically heated parallel-plate
vertical channel using the Particle Image Velocimetry (PIV) system. The channel walls were subjected to uniform temperature
conditions, with one wall heated above ambient and the opposing wall maintained below ambient temperature. Velocity measurements
were conducted at three different sections on the horizontal plane to validate two-dimensionality of the flow and at three
different heights in the vertical plane to establish vertical mean velocity profiles. The results indicate that the flow recirculation
in the channel exhibits a similar character to that of a closed cavity and the induced flow rate is much lower than the one
for a channel with both walls heated. A correlation for the dimensionless flow rate is developed. 相似文献
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A numerical solution of the effect of a small fluctuating gravitational field characteristic of g-jitter is presented. Specifically the problem of free convection boundary layer flow near a three-dimensional stagnation point of attachment resulting from a step change in its constant surface temperature is considered. The transformed non-similar boundary layer equations are solved using the Keller-box method, which is essentially an implicit finite-difference scheme. Numerical results are given for a value of the Prandtl number, Pr = 0.72 with the forcing amplitude, ε, and the forcing frequency, Ω. It is shown that g-jitter affects considerably the flow characteristics, namely the skin friction and the rate of heat transfer. Comparison with earlier results for the case of constant gravity field show very good agreement. 相似文献
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This paper presents the results of velocity measurements of natural convection in symmetrically heated vertical channel using
the particle image velocimetry (PIV) system. Velocity measurements were conducted at three different sections on the horizontal
plane to validate the flow two-dimensionality and at three different heights in the vertical plane to establish vertical mean
velocity profiles. The results indicate a considerable influence of the Rayleigh number and aspect ratio on the mean velocity
profile. The results also indicate significant diffusion rates of the vertical mean velocity component and normal Reynolds
stresses towards the center of the channel. 相似文献
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Continuum equations governing transient, laminar, fully-developed natural convection flow of a particulate suspension through an infinitely long vertical channel are developed. The equations account for particulate viscous effects which are absent from the original dusty-gas model. The walls of the channel are maintained at constant but different temperatures. No-slip boundary conditions are employed for the particle phase at the channel walls. The general transient problem is solved analytically using trigonometric Fourier series and the Laplace transform method. A parametric study of some physical parameters involved in the problem is performed to illustrate the influence of these parameters on the flow and thermal aspects of the problem. 相似文献
11.
A computational study has been carried out to analyse complex interaction of radiation with turbulent natural convective flow of dry and humid air in open-ended channels. Transient flow simulations are undertaken in the channel with one uniformly heated wall and adiabatic side walls for different values of emissivity of active walls with and without participating medium. To adequately present turbulence and radiation, a computational model included large eddy simulations for the turbulent flow coupled with discrete ordinates method for radiation transfer. Spectral line-based weighted-sum-of-grey-gases for the absorption properties of water vapour has been adopted. Complex three-dimensional vortical structures are identified which directly affect the temperature distribution on the heated wall. Including wall to wall radiation resulted in significant changes in the heat transfer, reaching 14 °C temperature drop at the hot wall with wall emissivity of 0.9. Mixing and cooling rates in this case were increased by up to 25%. Including gas radiation for the humid air with the water vapour molar fraction of 0.02 corresponding to saturated conditions at inlet temperature of 25 °C did not have a significant effect on the mean flow and temperature values comparing with wall to wall radiation. However, turbulent statistics have changed significantly resulting in a delayed transition to turbulence near the active wall of the channel and increased turbulent activity near the cold wall. The model developed in the present study is also applicable in fire management, where the aim is to reduce the damage that occurs when a PV module is exposed to high temperatures. 相似文献
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Ali Nouri-Borujerdi Amin R. Noghrehabadi D. Andrew S. Rees 《Transport in Porous Media》2007,69(3):343-357
This paper considers the onset of free convection in a horizontal fluid-saturated porous layer with uniform heat generation.
Attention is focused on cases where the fluid and solid phases are not in local thermal equilibrium, and where two energy
equations describe the evolution of the temperature of each phase. Standard linearized stability theory is used to determine
how the criterion for the onset of convection varies with the inter-phase heat transfer coefficient, H, and the porosity-modified thermal conductivity ratio, γ. We also present asymptotic solutions for small values of H. Excellent agreement is obtained between the asymptotic and the numerical results. 相似文献
13.
The natural convection boundary layer flow with conduction-radiation interaction of a viscous incompressible fluid along
an isothermal horizontal surface has been studied. The equations valid in the upstream, downstream as well as in the entire
regime are obtained. Solutions of the non-similar equations governing the flow for the entire regime and the downstream regime
are obtained by employing an efficient implicit finite difference approximation together with the Keller box method, for a
Prandtl number of 0.73. Also, the effects of the pertinent parameters, R
d, the radiation-conduction parameter and θw, the surface heating parameter are shown graphically in terms of the local skin-friction and the local rate of heat transfer.
Comparison of the results obtained for the upstream and the downstream regimes shows good agreement over the entire regime.
Effects of R
d and θw are also shown on the streamlines and the isotherms.
Received on 15 December 1998 相似文献
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This note presents transient motion of a viscous and incompressible fluid in a vertical channel due to free convective currents occuring as a result of application of constant heat flux at one wall and constant temperature on other wall. The method of Laplace transform is used to solve the problem. The transient behaviour of flow on velocity and temperature fields are shown on the graphs. 相似文献
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M. ASHRAF N. JAMEEL K. ALI 《应用数学和力学(英文版)》2013,34(10):1263-1276
A study is presented for magnetohydrodynamics (MHD) flow and heat transfer characteristics of a viscous incompressible electrically conducting micropolar fluid in a channel with stretching walls. The micropolar model introduced by Eringen is used to describe the working fluid. The transformed self similar ordinary differential equations together with the associated boundary conditions are solved numerically by an algorithm based on quasi-linearization and multilevel discretization. The effects of some physical parameters on the flow and heat transfer are discussed and presented through tables and graphs. The present investigations may be beneficial in the flow and thermal control of polymeric processing. 相似文献
18.
N. Samyuktha R. Ravindran M. Ganapathirao 《Journal of Applied Mechanics and Technical Physics》2017,58(1):116-128
An analysis is performed to study the effects of the chemical reaction and heat generation or absorption on a steady mixed convection boundary layer flow over a vertical stretching sheet with nonuniform slot mass transfer. The governing boundary layer equations with boundary conditions are transformed into the dimensionless form by a group of nonsimilar transformations. Nonsimilar solutions are obtained numerically by solving the coupled nonlinear partial differential equations using the quasi-linearization technique combined with an implicit finite difference scheme. The numerical computations are carried out for different values of dimensionless parameters to display the distributions of the velocity, temperature, concentration, local skin friction coefficient, local Nusselt number, and local Sherwood number. The results obtained indicate that the local Nusselt and Sherwood numbers increase with nonuniform slot suction, but nonuniform slot injection produces the opposite effect. The local Nusselt number decreases with heat generation and increases with heat absorption. 相似文献
19.
The jet flows induced around a submerged channel due to the hot inner channel walls and the flow inside the channel are calculated. The formation of high-and low-density regions at the inlet and outlet of the channel is detected. The dependence of the flow rate on the channel orientation relative to the gravity force is analyzed. The onset of coherent flow structures results in the development of unsteady oscillating flows. Natural convection in the fluid is studied using the JoinCAD/FEM program package. The regularized Oberbeck-Boussinesq equations are solved using a finite-element method with the same order of the approximating functions. 相似文献
20.
Present paper deals with temperature driven mass deposition rate of particles known as thermophoretic wall flux when a hot
flue gas in natural convection flow through a cooled isothermal vertical parallel plate channel. Present study finds application
in particle filters used to trap soot particles from post combustion gases issuing out of small furnaces with low technical
implications. Governing equations are solved using finite difference marching technique with channel inlet values as initial
values. Channel heights required to regain hydrostatic pressure at the exit are estimated for various entry velocities. Effect
of temperature ratio between wall and gas on thermophoretic wall flux is analysed and wall flux found to increase with decrease
in temperature ratio. Results are compared with published works wherever possible and can be used to predict particle deposition
rate as well as the conditions favourable for maximum particle deposition rate. 相似文献