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.

Effect of Nanofluid on Heat Transfer Enhancement for Mixed Convection Flow Over a Corrugated Surface

2020 ◽  
Vol 45 (4) ◽  
pp. 373-383
Author(s):  
Nepal Chandra Roy ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Richardson Number ◽  
Thermal Boundary Layer ◽  
Volume Fraction ◽  
Convection Flow ◽  
Mixed Convection Flow

AbstractA mathematical model for mixed convection flow of a nanofluid along a vertical wavy surface has been studied. Numerical results reveal the effects of the volume fraction of nanoparticles, the axial distribution, the Richardson number, and the amplitude/wavelength ratio on the heat transfer of Al2O3-water nanofluid. By increasing the volume fraction of nanoparticles, the local Nusselt number and the thermal boundary layer increases significantly. In case of \mathrm{Ri}=1.0, the inclusion of 2 % and 5 % nanoparticles in the pure fluid augments the local Nusselt number, measured at the axial position 6.0, by 6.6 % and 16.3 % for a flat plate and by 5.9 % and 14.5 %, and 5.4 % and 13.3 % for the wavy surfaces with an amplitude/wavelength ratio of 0.1 and 0.2, respectively. However, when the Richardson number is increased, the local Nusselt number is found to increase but the thermal boundary layer decreases. For small values of the amplitude/wavelength ratio, the two harmonics pattern of the energy field cannot be detected by the local Nusselt number curve, however the isotherms clearly demonstrate this characteristic. The pressure leads to the first harmonic, and the buoyancy, diffusion, and inertia forces produce the second harmonic.

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.

A Numerical Investigation of Laminar Mixed Convection Flow and Heat Transfer in a Lid Driven Cavity with Two Cylinders

2015 ◽  
Vol 789-790 ◽  
pp. 282-286 ◽  
Author(s):  
Khalil Khanafer ◽  
M. El Haj Assad
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Convection Flow ◽  
Mixed Convection Flow ◽  
Driven Cavity ◽  
Flow And Heat Transfer ◽  
The Impact

Mixed convection flow and heat transfer characteristics in a lid-driven cavity with two isothermally heated circular cylinders inside are studied numerically using a finite element formulation based on the Galerkin method of weighted residuals. The top lid of the cavity is moving rightwards with a constant speed. The two cylinders are maintained at an isothermal hot temperature, while the walls of the cavity are maintained at a cold temperature. Comparisons of streamlines, isotherms and average Nusselt number are presented to show the impact of the Richardson number, non-dimensional radius of the cylinder, and the location of the cylinders on the transport phenomena within the cavity. The results of this investigation show that the presence of the cylinders results in an increase in the average Nusselt number compared with a case with no cylinder. The average Nusselt number increases with an increase in the Richardson number for all non-dimensional radius of the cylinder studied in this work. It is seen that changing the boundary condition on one of the cylinders from isothermal to adiabatic has minimal effect on the average Nusselt number around the walls of the cavity.

Mixed Convection and Entropy Generation Characteristics Inside a Porous Cavity With Viscous Dissipation Effect

2009 ◽  
Author(s):  
A. K. M. Sadrul Islam ◽  
M. Ruhul Amin ◽  
Shama F. Barna ◽  
Arafat A. Bhuiyan ◽  
M. H. Banna
Keyword(s):  
Nusselt Number ◽  
Aspect Ratio ◽  
Boundary Conditions ◽  
Mixed Convection ◽  
Entropy Generation ◽  
Average Energy ◽  
Forced Flow ◽  
Convection Flow ◽  
Bejan Number ◽  
Left Wall

This paper examines and explains two-dimensional, steady mixed convection flow in a porous square vented cavity. The interaction between the buoyancy stemming from one or more heated elements inside a microstructure filled vented enclosure and an imposed forced flow forms the topic of this investigation. Analysis has been carried out for two different boundary conditions. Initial investigations are carried out for walls of the enclosure being isothermal. A second stage of analysis is performed keeping only the left wall isothermal and other three walls adiabatic. Natural convection takes place due to temperature difference between the isothermal wall and the fluid. Forced convection condition is imposed by providing an inlet and a square vent inside the enclosure filled with fluid saturated porous medium. The mathematical model is developed using modified Darcy flow model and energy equation. Through the adaptation of the well known finite element method, solution to this numerical problem is obtained. Governing parameters chosen are Peclet Number (Pe), Rayleigh Number (Ra), Aspect ratio (AR) and the width of the inlet as a fraction of the width (I/W) of the enclosure. For detailed analysis different value of these parameters such as five Rayleigh Numbers (1, 50, 100, 500 and 1000) and seven different Peclet Numbers (0.1, 1, 5, 10, 20, 50 and 100) are considered. Effect of inlet to cavity width ratio is examined within the range 0.1 ≤ I/W ≤ 0.5 for a particular aspect ratio. The performance of the enclosure in both cases; are determined by flow visualization and by analyzing different parameters such as Bejan Number, Nusselt Number and Entropy Generation Number. Isotherms, streamlines show substantial variation in their pattern or magnitude. Average Nusselt number and average Bejan Number increases whereas Average energy flux density decreases with increasing I/W. These fluctuations also vary for different Rayleigh or Peclet numbers. The results for both the boundary conditions are also compared to find the most effective value of I/W.

Measurements of Laminar Mixed Convection Flow Adjacent to an Inclined Surface

1987 ◽  
Vol 109 (1) ◽  
pp. 146-150 ◽  
Author(s):  
N. Ramachandran ◽  
B. F. Armaly ◽  
T. S. Chen
Keyword(s):  
Nusselt Number ◽  
Mixed Convection ◽  
Local Nusselt Number ◽  
Convection Flow ◽  
Nusselt Numbers ◽  
Buoyancy Parameter ◽  
Laminar Mixed Convection ◽  
Inclined Surfaces ◽  
Inclined Surface ◽  
Good Agreement

Measurements of laminar mixed forced and free convection air flow adjacent to an upward and a downward facing, isothermal, heated inclined surface (at 45 deg) are reported. Local Nusselt number and the velocity and temperature distributions are presented for both the buoyancy assisting and the buoyancy opposing flow cases for a range of buoyancy parameter 0 ≤ ξ ≤ 5 (ξ = Grx/Rex2). The measurements are in good agreement with predictions which define a laminar mixed convection regime for buoyancy assisting flow as 0.1 ≤ ξ ≤ 7, and for buoyancy opposing flows as 0.06 ≤ ξ ≤ 0.25 for this inclination angle of 45 deg. Simple mixed convection correlations for the local and average Nusselt numbers for inclined surfaces are also presented and they agree very well with predicted results. As expected, the local Nusselt number increases with increasing buoyancy parameter for assisting flows and decreases for opposing flows. For a given buoyancy parameter and Reynolds number, a downward facing surface provides essentially the same Nusselt number as the upward facing surface for the conditions examined in the experiment.

Mixed Convection From a Cylinder With Low Conductivity Baffles in Cross-Flow

2002 ◽  
Vol 124 (6) ◽  
pp. 1064-1071
Author(s):  
Bassam A/K Abu-Hijleh
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Average Nusselt Number ◽  
Cross Flow ◽  
Maximum Heat ◽  
Buoyancy Parameter ◽  
Maximum Heat Transfer ◽  
Laminar Mixed Convection

The problem of laminar mixed convection from an isothermal cylinder with low conductivity baffles in cross flow was solved numerically. The average Nusselt number was calculated at different combinations of number of baffles, baffle height, Reynolds number, and buoyancy parameter. The reduction in the Nusselt number is as much as 75 percent. When using a small number of baffles at low values of buoyancy parameter, an odd number of baffles reduced the Nusselt number more than an even number of baffles, especially at high values of Reynolds number. This is not the case at high values of buoyancy parameter. There is an optimal baffle height, Reynolds number dependent, for maximum heat transfer reduction beyond which an increase in baffle height does not result in further decrease in heat transfer.

MHD-mixed convection flow in a lid-driven trapezoidal cavity under uniformly/non-uniformly heated bottom wall

2017 ◽  
Vol 27 (6) ◽  
pp. 1231-1248 ◽  
Author(s):  
T. Javed ◽  
Z. Mehmood ◽  
Ioan Pop
Keyword(s):  
Magnetic Field ◽  
Heat Transfer ◽  
Nusselt Number ◽  
Mixed Convection ◽  
Bottom Wall ◽  
Local Thermal Equilibrium ◽  
Convection Flow ◽  
Mixed Convection Flow ◽  
Content Type ◽  
Left And Right

Purpose The purpose of this paper is to analyze numerical results for heat transfer through mixed convection in an incompressible steady lid-driven fluid flow inside a trapezoidal cavity in the presence of a uniform magnetic field. Design/methodology/approach In this study, the authors have considered three different cases, in which left and right walls of the cavity are tilted at different angles of 0, 30 and 45 degrees, respectively. Both left and right side walls of the cavity are taken cold and the upper wall is insulated and assumed moving with constant speed, whereas the bottom wall is considered to be heated uniformly/non-uniformly. To eliminate pressure term, penalty method is applied to governing Navier–Stokes’ equations. The reduced equations are solved by Galerkin weighted residual technique of finite element method. Grid-independent results are obtained and shown in terms of plots for streamlines, isotherms, Nusselt number and average Nusselt number for a wide range of flow parameters, including Rayleigh numbers Ra, Prandtl number Pr and Hartman number Ha. Findings It has been observed that the effects of moving lid become negligible for Ra = 100,000, whereas increasing Rayleigh number results in stronger streamline circulation and convection dominant effects inside the enclosure. Local Nusselt number Nu along the bottom wall is observed to be maximum at edges and it reduces while moving toward the center from edges, and attains minimum value at the center of the bottom wall. Research limitations/implications The problem is modeled for laminar and incompressible flow, induced magnetic field has been considered negligibly small and local thermal equilibrium has been assumed. Originality/value In this investigation, the authors have presented new and original results for mixed convection flow inside a lid-driven trapezoidal cavity under the influence of a magnetic field. Hence, this study would be important for the researchers working in the area of heat transfer in cavity flows involving magnetic effects to become familiar with the flow behavior and properties.

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