Mixed Laminar Convection in Trombe Wall Channels

1988 ◽  
Vol 110 (1) ◽  
pp. 31-37 ◽  
Author(s):  
S. K. Chaturvedi ◽  
T. O. Mohieldin ◽  
G. C. Huang
Keyword(s):  
Reynolds Number ◽  
Natural Convection ◽  
Stream Function ◽  
Vertical Channel ◽  
Flow Patterns ◽  
Forced Flow ◽  
Transfer Coefficients ◽  
Type Pattern ◽  
Trombe Wall ◽  
Laminar Convection

The two-dimensional, steady, combined forced and natural convection in a vertical channel is investigated for the laminar regime. To simulate the Trombe wall channel geometry properly, horizontal inlet and exit segments have been added to the vertical channel. The vertical walls of the channel are maintained at constant but different temperatures while the horizontal walls are insulated. A finite difference method using up-wind differencing for the nonlinear convective terms, and central differencing for the second order derivatives, is employed to solve the governing differential equations for the mass, momentum, and energy balances. The solution is obtained for stream function, vorticity, and temperature as the dependent variables by an iterative technique known as successive substitution with overrelaxation. The flow and temperature patterns in the channel are obtained for Reynolds numbers and Grashof numbers ranging from 25 to 100 and 10,000 to 1,000,000, respectively. Both local and overall heat transfer coefficients are computed for the channel aspect ratio varying from 5 to 15. For a given value of Grashof number, as the Reynolds number is increased, the flow patterns in the vertical channel exhibit a change from natural convection like flow patterns in which a large recirculating region is formed in the vertical part of the channel, to a forced flow type pattern. This is also the case with isotherms. The size of the recirculating region in the channel increases with increasing value of Gr/Re2. At low Reynolds number, the stream function, and isotherms are qualitatively similar to those reported for the natural convection in rectangular slots.

scholarly journals Unsteady Flow of Reactive Viscous, Heat Generating/Absorbing Fluid with Soret and Variable Thermal Conductivity

2014 ◽  
Vol 2014 ◽  
pp. 1-15 ◽  
Author(s):  
I. J. Uwanta ◽  
M. M. Hamza
Keyword(s):  
Thermal Conductivity ◽  
Natural Convection ◽  
Skin Friction ◽  
Sherwood Number ◽  
Vertical Channel ◽  
Variable Thermal Conductivity ◽  
Finite Difference Schemes ◽  
Transfer Coefficients ◽  
Flow Parameters ◽  
Viscous Heat

This study investigates the unsteady natural convection and mass transfer flow of viscous reactive, heat generating/absorbing fluid in a vertical channel formed by two infinite parallel porous plates having temperature dependent thermal conductivity. The motion of the fluid is induced due to natural convection caused by the reactive property as well as the heat generating/absorbing nature of the fluid. The solutions for unsteady state temperature, concentration, and velocity fields are obtained using semi-implicit finite difference schemes. Perturbation techniques are used to get steady state expressions of velocity, concentration, temperature, skin friction, Nusselt number, and Sherwood number. The effects of various flow parameters such as suction/injection (γ), heat source/sinks (S), Soret number (Sr), variable thermal conductivityδ, Frank-Kamenetskii parameterλ, Prandtl number (Pr), and nondimensional timeton the dynamics are analyzed. The skin friction, heat transfer coefficients, and Sherwood number are graphically presented for a range of values of the said parameters.

Laminar convection of a radiating gas in a vertical channel

1971 ◽  
Vol 46 (3) ◽  
pp. 513-520 ◽  
Author(s):  
R. Greif ◽  
I. S. Habib ◽  
J. C. Lin
Keyword(s):  
Exact Solution ◽  
Natural Convection ◽  
Temperature Difference ◽  
Convective Flow ◽  
Vertical Channel ◽  
Heat Fluxes ◽  
Temperature Profiles ◽  
Dimensionless Velocity ◽  
Heated Channel ◽  
Laminar Convection

An exact solution is obtained for the problem of fully-developed, radiating, laminar convective flow in a vertical heated channel. The effect of radiation is to decrease the temperature difference between the gas and the wall, thereby reducing the influence of natural convection. Thus, the reduction in velocity occurring in a heated upflow is less for a radiating gas. Graphs are presented for the dimensionless velocity and temperature profiles and for the volume and heat fluxes.

An Experimental Study of Natural Convection Heat Transfer in Concentric and Eccentric Horizontal Cylindrical Annuli

1978 ◽  
Vol 100 (4) ◽  
pp. 635-640 ◽  
Author(s):  
T. H. Kuehn ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Laminar Convection

An experimental study has been conducted to determine the influence of eccentricity and Rayleigh number on natural convection heat transfer through a fluid bounded by two horizontal isothermal cylinders. Eccentricity of the inner cylinder substantially alters the local heat transfer on both cylinders, but the overall heat transfer coefficients change by less than 10 percent over the range of eccentricities investigated. Heat transfer results using the concentric geometry are given for Rayleigh numbers from 2.2 × 102 to 7.7 × 107 which includes regions of conduction, laminar convection, and partially turbulent convection.

Laminar Mixed Convection of Large-Prandtl-Number Nanofluids in Horizontal Tube: Experiment, Correlation, and Criterion

2012 ◽  
Author(s):  
Wei Li ◽  
Si-Pu Guo ◽  
Zhao-Zan Feng ◽  
Zhao-Yan Zhang ◽  
Ze-Cong Fang
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Natural Convection ◽  
Prandtl Number ◽  
Single Phase ◽  
Low Reynolds Number ◽  
Convection Heat Transfer ◽  
Horizontal Tube ◽  
Forced Flow ◽  
Convection Heat

This paper describes an experimental investigation into combined forced and natural convection heat transfer for large-Prandtl-number nanofluids flow in a horizontal tube at low Reynolds number (9 < Re < 450). By the inclusion of nanoparticles, the contribution of natural convection to the overall convective heat transfer can be either deteriorated under the same heat flux or enhanced under a given Grashof number. The huge increasing of the viscosity and Prandtl number were turned out to be the major reason for the observed deterioration and enhancement, respectively. Moreover, the measured heat transfer behavior of nanofluids was illustrated to be in good agreement with the single-phase-based evaluation. However, the experimental data obtained could not be totally reconciled with existing correlations, which relate mainly to specific pure liquids or relatively higher Reynolds number. Therefore, new correlations have been derived by using single-phase fluid approach. These correlations fit our data to within ± 10 percent and also agree with the data in literature quite well. Such results verify that nanofluids can be treated as a homogeneous mixture with effective thermophysical properties. In addition, the new correlations grasp the essence of natural convection and can reduce to both normal forced convection and pure natural convection equations at limiting cases. Whether a flow can be treated as pure forced flow or not (i.e., natural convection effects cannot be neglected) is a crucial problem remains to be determined for the assessment of performance of nanofluids in low-Reynolds-number convection heat transfer application. Generally, the boundary curve function involves the variable parameter of forced main flow (Graetz number) and natural secondary flow (Rayleigh number), constituting a criterion suitable for defining transition of forced flow to mixed flow.

Numerical Evaluation of 2D and 3D Steady and Unsteady Flows of a Pair of Opposing Confined Impinging Air Jets

2009 ◽  
Author(s):  
Victor Chiriac ◽  
Jorge L. Rosales
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Unsteady Flow ◽  
Flow Patterns ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Complex Flow ◽  
Air Jets ◽  
2D And 3D ◽  
The Impact

The steady and unsteady laminar flow and heat transfer characteristics for a pair of opposing confined impinging slot jets in 2D and 3D were evaluated numerically at two Reynolds numbers. The present study continues the authors’ earlier work [1] and identifies the main similarities and differences arising from the expansion to the third dimension. At lower Reynolds number jet (Re = 300), the flow interaction produces a symmetric, steady flow hydrodynamic pattern with the jets being deflected laterally for the 2D flow. At Re = 300, the 3D slot jet produces almost the same values as the 2D case, yet the flow is slightly asymmetrical and unsteady. However, by further increasing the Reynolds number to 750, a complex and highly unsteady flow develops for both 2D and 3D simulations. The symmetry of both the 2D and 3D flows is disrupted and the resulting complex flow patterns reveal the vortex pairing effects, leading to the jet “buckling and sweeping” motion, enabling the enhanced local heat transfer. The convective heat transfer coefficients and the unsteady flow development between the jets are thoroughly investigated, with the flow unsteadiness also characterized by analyzing the stagnation point displacement on the channel walls. The comparison between the 2D and 3D flow patterns indicate that the 3D opposite jets enhance the unsteady effects compared to the 2D unsteady opposite jets. The complex vortex patterns resulting from the unsteady jets interaction, as well as the velocity, vorticity and temperature fields for both 2D and 3D cases are thoroughly evaluated. The comparison between the 2D and 3D impinging air jets is documented and the impact on chip/microelectronics cooling is highlighted.

scholarly journals Turbulent mixed convection in asymmetrically heated vertical channel

2012 ◽  
Vol 16 (2) ◽  
pp. 503-512 ◽  
Author(s):  
Ameni Mokni ◽  
Hatem Mhiri ◽  
Palec Le ◽  
Philippe Bournot
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Vertical Channel ◽  
Channel Length ◽  
Forced Flow ◽  
Mean Velocity ◽  
Flow Development ◽  
Heated Channel ◽  
The Mean

In this paper an investigation of mixed convection from vertical heated channel is undertaken. The aim is to explore the heat transfer obtained by adding a forced flow, issued from a flat nozzle located in the entry section of a channel, to the up-going fluid along its walls. Forced and free convection are combined studied in order to increase the cooling requirements. The study deals with both symmetrically and asymmetrically heated channel. The Reynolds number based on the nozzle width and the jet velocity is assumed to be 3 103 and 2.104; whereas, the Rayleigh number based on the channel length and the wall temperature difference varies from 2.57 1010 to 5.15 1012. The heating asymmetry effect on the flow development including the mean velocity and temperature the local Nusselt number, the mass flow rate and heat transfer are examined.

Mixed Convection in Ducts With Asymmetric Wall Heat Fluxes

1987 ◽  
Vol 109 (4) ◽  
pp. 947-951 ◽  
Author(s):  
Win Aung ◽  
G. Worku
Keyword(s):  
Mixed Convection ◽  
Parallel Plate ◽  
Numerical Study ◽  
Vertical Channel ◽  
Quantitative Information ◽  
Heat Fluxes ◽  
Forced Flow ◽  
Uniform Wall ◽  
Laminar Convection ◽  
Asymmetric Heating

Results are presented of a numerical study dealing with combined free and forced laminar convection in a parallel plate vertical channel with asymmetric wall heating at uniform heat fluxes (UHF). The forced flow at the inlet is assumed to be spatially uniform and directed vertically upward. Quantitative information is provided pertaining to the effects of buoyancy and asymmetric heating on the hydrodynamic and thermal parameters. For values of Gr/Re up to 500 no flow reversal is predicted, in contrast to the case of uniform wall temperatures (UWT) recently reported. Other fundamental differences between UHF and UWT also are indicated.

Modeling mass transfer and substrate utilization in the boundary layer of biofilm systems

1998 ◽  
Vol 37 (4-5) ◽  
pp. 139-147 ◽  
Author(s):  
Harald Horn ◽  
Dietmar C. Hempel
Keyword(s):  
Boundary Layer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Film Theory ◽  
Substrate Utilization ◽  
The Other ◽  
Concentration Profiles ◽  
Hydrodynamic Conditions ◽  
Time Axis ◽  
Transfer Coefficients

The use of microelectrodes in biofilm research allows a better understanding of intrinsic biofilm processes. Little is known about mass transfer and substrate utilization in the boundary layer of biofilm systems. One possible description of mass transfer can be obtained by mass transfer coefficients, both on the basis of the stagnant film theory or with the Sherwood number. This approach is rather formal and not quite correct when the heterogeneity of the biofilm surface structure is taken into account. It could be shown that substrate loading is a major factor in the description of the development of the density. On the other hand, the time axis is an important factor which has to be considered when concentration profiles in biofilm systems are discussed. Finally, hydrodynamic conditions become important for the development of the biofilm surface when the Reynolds number increases above the range of 3000-4000.

Sign in / Sign up

Export Citation Format

Share Document