Reversed Flow Structure and Heat Transfer Measurements for Buoyancy-Assisted Convection in a Heated Vertical Duct

1992 ◽  
Vol 114 (4) ◽  
pp. 928-935 ◽  
Author(s):  
C. Gau ◽  
K. A. Yih ◽  
W. Aung
Keyword(s):  
Heat Transfer ◽  
Vertical Channel ◽  
Flow Region ◽  
Threshold Value ◽  
Convection Flow ◽  
Parallel Plates ◽  
Reversed Flow ◽  
Recirculating Flow ◽  
Buoyancy Parameter ◽  
Complex Phenomena

Buoyancy-assisted convection flow and heat transfer processes in a heated vertical channel are studied experimentally for situations where the buoyancy parameter Gr/Re2 is relatively large. The channel wall is made of two parallel plates, with one wall heated uniformly and the opposite wall insulated. A uniform air flow is made to enter the channel from the bottom. The reversed flow is visualized, which occurs initially near the channel exit for the case when Gr/Re2 is greater than a threshold value. The cold reversed flow enters the channel from the outside and forms a V-shaped recirculating flow region in the downstream part of the duct. This region gradually propagates upstream as the buoyancy parameter Gr/Re2 increases. The counterflow motion, leading to mixing between the heated buoyant fluid and the V-shaped recirculation, is shown to be highly unstable and characterized by generation of eddies and vortices when the value of Gr/Re2 is large. An increase in Re has the effect of pushing the reversed flow downstream and making the recirculating region wider. Temperature fluctuations are measured to provide insight into the complex phenomena being studied. The penetration depth of the reversed flow is measured and compared with prediction based on a simple model. Local and average Nusselt numbers are also measured and presented.

Flow and Mixed Convection Heat Transfer in a Divergent Heated Vertical Channel

1996 ◽  
Vol 118 (3) ◽  
pp. 606-615 ◽  
Author(s):  
C. Gau ◽  
T. M. Huang ◽  
W. Aung
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Flow Reversal ◽  
Forced Flow ◽  
Vertical Position ◽  
Convection Flow ◽  
Reversed Flow ◽  
Buoyancy Parameter ◽  
Divergent Channel

This paper concerns an experimental study of the mixed convection flow and heat transfer inside a divergent channel formed by two plane walls. One of the side walls is oriented vertically and is heated uniformly, and the opposite wall is tilted at an angle of 3 deg with respect to the vertical position and is insulated. The ratio of the height to wall spacing at the flow inlet, which is at the smaller opening of the channel is 15. The Reynolds number of the main forced flow ranges from 100 to 4000 and the buoyancy parameter, Gr/Re2, varies from 0.3 to 907. Flow reversal is found to occur for both assisted and opposed convection. The effect of channel divergence on the occurrence and structure of the reversed flow and the heat transfer is presented and discussed. It is found that the divergence of the channel decelerates the mainstream such that flow reversal is initiated at a much lower buoyancy parameter. The adverse pressure gradient tends to push the reversed flow upstream and leads to a deeper penetration of the reversed flow into the channel The destabilization effect of the divergent channel can lead to breakdown of vortices and to transition to turbulent flow. This can significantly enhance the heat transfer. Temperature fluctuation measurements at different locations are used to indicate oscillations and fluctuations of the reversed flow. The effect of the buoyancy parameter on the Nusselt number and the reversed flow structure is discussed. The average Nusselt number is determined and correlated in terms of relevant nondimensional parameters for pure forced and mixed convection, respectively.

scholarly journals Soret and dufour effects on free convection flow of a couple stress fluid in a vertical channel with chemical reaction

2013 ◽  
Vol 19 (1) ◽  
pp. 45-55 ◽  
Author(s):  
D. Srinivasacharya ◽  
K. Kaladhar
Keyword(s):  
Differential Equations ◽  
Chemical Reaction ◽  
Couple Stress ◽  
Vertical Channel ◽  
Couple Stress Fluid ◽  
Convection Flow ◽  
Parallel Plates ◽  
Soret And Dufour Effects ◽  
Similarity Transformations ◽  
Dufour Number

The Soret and Dufour effects in the presence of chemical reaction on natural convection heat and mass transfer of a couple stress fluid in a vertical channel formed by two vertical parallel plates is presented. The governing non-linear partial differential equations are transformed into a system of ordinary differential equations using similarity transformations. The resulting equations are then solved using Homotopy Analysis Method (HAM). Profiles of dimensionless velocity, temperature and concentration are shown graphically for various values of Dufour number, Soret number, Couple stress parameter and chemical reaction parameter.

Large Eddy Simulation of Flow and Heat Transfer in the Developing Flow Region of a Rotating Gas Turbine Blade Internal Cooling Duct With Coriolis and Buoyancy Forces

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
Evan A. Sewall ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Flow Region ◽  
Internal Cooling ◽  
Heat Transfer Augmentation ◽  
Flow And Heat Transfer ◽  
Buoyancy Parameter ◽  
Developing Flow ◽  
Large Eddy

The problem of accurately predicting the flow and heat transfer in the ribbed internal cooling duct of a rotating gas turbine blade is addressed with the use of large eddy simulations (LES). Four calculations of the developing flow region of a rotating duct with ribs on opposite walls are used to study changes in the buoyancy parameter at a constant rotation rate. The Reynolds number is 20,000, the rotation number is 0.3, and the buoyancy parameter is varied between 0.00, 0.25, 0.45, and 0.65. Previous experimental studies have noted that leading wall heat transfer augmentation decreases as the buoyancy parameter increases with low buoyancy, but heat transfer then increases with high buoyancy. However, no consistent physical explanation has been given in the literature. The LES results from this study show that the initial decrease in augmentation with buoyancy is a result of larger separated regions at the leading wall. However, as the separated region spans the full pitch between ribs with an increase in buoyancy parameter, it leads to increased turbulence and increased entrainment of mainstream fluid, which is redirected toward the leading wall by the presence of a rib. The impinging mainstream fluid results in heat transfer augmentation in the region immediately upstream of a rib. The results obtained from this study are in very good agreement with previous experimental results.

scholarly journals Unsteady/Steady Hydromagnetic Convective Flow between Two Vertical Walls in the Presence of Variable Thermal Conductivity

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
M. M. Hamza ◽  
I. G. Usman ◽  
A. Sule
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Steady State ◽  
Skin Friction ◽  
Numerical Solutions ◽  
Nonlinear Partial Differential Equations ◽  
Vertical Channel ◽  
Approximate Solutions ◽  
Variable Thermal Conductivity ◽  
Convection Flow

Unsteady as well as steady natural convection flow in a vertical channel in the presence of uniform magnetic field applied normal to the flow region and temperature dependent variable thermal conductivity is studied. The nonlinear partial differential equations governing the flow have been solved numerically using unconditionally stable and convergent semi-implicit finite difference scheme. For steady case, approximate solutions have been derived for velocity, temperature, skin friction, and the rate of heat transfer using perturbation series method. Results of the computations for velocity, temperature, skin friction, and the rate of heat transfer are presented graphically and discussed quantitatively for various parameters embedded in the problem. An excellent agreement was found during the numerical computations between the steady-state approximate solutions and unsteady numerical solutions at steady-state time. In addition, comparison with previously published work is performed and the results agree well.

A Pseudospectral Analysis of Laminar Natural Convection Flow and Heat Transfer Between Two Inclined Parallel Plates

2006 ◽  
Author(s):  
Serkan Kasapoglu ◽  
Ilker Tari
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Boundary Conditions ◽  
Boussinesq Approximation ◽  
Temperature Fields ◽  
Convection Flow ◽  
Parallel Plates ◽  
Natural Convection Flow ◽  
Constant Wall Temperature ◽  
Laminar Natural Convection

Three dimensional laminar natural convection flow of and heat transfer in incompressible air between two inclined parallel plates are analyzed with the Boussinesq approximation by using spectral methods. The plates are assumed to be infinitely long in streamwise (x) and spanwise (z) directions. For these directions, periodic boundary conditions are used and for the normal direction (y), constant wall temperature and no slip boundary conditions are used. Unsteady Navier-Stokes and energy equations are solved using a pseudospectral approach in order to obtain velocity and temperature fields inside the channel. Fourier series are used to expand the variables in × and z directions, while Chebyshev polynomials are used to expand the variables in y direction. By using the temperature distribution between the plates, local and average Nusselt numbers (Nu) are calculated. Nu values are correlated with φ, which is the inclination angle, and with Ra·cosφ to compare the results with the literature.

scholarly journals G-jitter fully developed heat transfer by mixed convection flow in a vertical channel with constant heat flux

2020 ◽  
Vol 16 (1) ◽  
pp. 105-108
Author(s):  
Wan Nor Zaleha Amin ◽  
Ahmad Qushairi Mohammad ◽  
Mohammed Abdulhameed ◽  
Sharidan Shafie
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mixed Convection ◽  
Fourier Method ◽  
Vertical Channel ◽  
Constant Heat Flux ◽  
Convection Flow ◽  
Infinite Length ◽  
Fluid Temperature ◽  
Constant Heat

A theoretical study of mixed convection heat transfer was carried out in an infinite length of vertical channel with both open ends. One of the vertical plates was prescribed with constant heat flux. The effect of g-jitter was also taken into consideration. The Fourier method was utilized to solve the resulting governing equations. The behavior of the fluid temperature and velocity of the flow were studied and presented graphically in this paper. The graphical results were later on analyzed and discussed. The behavior of steady state flow was also investigated. Results confirmed that as wall temperature increased, the fluid temperature increased. The velocity increased due to increments in mixed convection and oscillation parameter, on the other hand, it decreased as a frequency of g-jitter increased. 

Natural Convection Between Two Horizontal Cylinders in an Adiabatic Circular Enclosure

1993 ◽  
Vol 115 (1) ◽  
pp. 158-165 ◽  
Author(s):  
C. J. Ho ◽  
W. S. Chang ◽  
C. C. Wang
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Inclination Angle ◽  
Numerical Study ◽  
Convection Flow ◽  
Vertical Orientation ◽  
Recirculating Flow ◽  
Visualization Experiments ◽  
Horizontal Cylinders ◽  
Gap Width

A numerical study of natural convection flow structure and heat transfer has been undertaken for air around two horizontal, differentially heated cylinders confined to an adiabatic circular enclosure. Parametric simulations were performed to assess the effects of gap width between cylinders as well as the inclination angle of the enclosure with respect to gravity. Results clearly indicate that the fluid flow complexity and heat transfer characteristics of air amid the cylinders and enclosure wall are strongly affected by the Rayleigh number, the inclination angle, and the gap width between the cylinders. With the exception of the vertical orientation, heat exchange between the differentially heated cylinders is predominantly controlled by a counterclockwise recirculating flow enclosing them. In addition, flow visualization experiments were conducted for the physical configuration under consideration, and a generally good agreement for the flow pattern was observed between the predictions and the experiments, further validating the present numerical simulation.

Unsteady Magnetohydrodynamic Mixed Convective Flow of a Reactive Casson Fluid in a Vertical Channel Filled with a Porous Medium

2021 ◽  
Vol 408 ◽  
pp. 33-49
Author(s):  
Lazarus Rundora
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Porous Medium ◽  
Fluid Flow ◽  
Vertical Channel ◽  
Casson Fluid ◽  
Convection Flow ◽  
Temperature Dependent ◽  
Temperature Dependent Viscosity ◽  
Dependent Viscosity

This article analyses the thermal decomposition in an unsteady MHD mixed convection flow of a reactive, electrically conducting Casson fluid within a vertical channel filled with a saturated porous medium and the influence of the temperature dependent properties on the flow. The fluid is assumed to be incompressible with the viscosity coefficient varying exponentially with temperature. The flow is subjected to an externally applied uniform magnetic field. The exothermic chemical kinetics inherent in the flow system give rise to heat dissipation. A technique based on a semi-discretization finite difference scheme and the shooting method is applied to solve the dimensionless governing equations. The effects of the temperature dependent viscosity, the magnetic field and other important parameters on the velocity and temperature profiles, the wall shear stress and the wall heat transfer rate are presented graphically and discussed quantitatively and qualitatively. The fluid flow model revealed flow characteristics that have profound ramifications including the increased heat transfer enhancement attributes of the reactive temperature dependent viscosity Casson fluid flow.

Enhancement of Heat Transfer of Mixing Convection in a Vertical Channel by a Moving Block

2013 ◽  
Vol 29 (1) ◽  
pp. 95-107 ◽  
Author(s):  
W.-S. Fu ◽  
J.-C. Huang ◽  
Y.-Y. Wang ◽  
Y. Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Rate ◽  
Channel Flow ◽  
Transfer Rate ◽  
Three Dimensional ◽  
Vertical Channel ◽  
Convection Flow ◽  
Enhancement Of Heat Transfer ◽  
Lower Velocity ◽  
Lower Magnitude

AbstractEnhancement of a heat transfer rate of mixed convection flow in a three-dimensional vertical channel with insertion of a moving slender block is investigated numerically. A slender block is installed along the direction of the channel flow, and the movement of the slender block is in periodic motion and transverse to the channel flow. The interaction between the moving block and the channel flow destroys and suppresses the velocity and thermal boundary layers on the heat surface periodically. Various ratios of the Richardson numbers (Gr/Re2) are simulated. The results show that under a higher velocity of the channel flow and a lower magnitude of Gr/Re2, the enhancement of heat transfer rate is better. Oppositely, under a lower velocity of the channel flow and a higher magnitude of Gr/Re2, the effect of natural convection driven by the buoyancy force is stronger and it is unfavorable to the heat transfer. A counter effect of the heat transfer rate is observed. These phenomena which are seldom analyzed before by numerical simulation are carried out in this study.

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