CONJUGATE MIXED CONVECTION IN AIR-COOLED HEAT SINKS USING A NON-BOUSSINESQ APPROACH

This work reports a numerical study of the mixed convection in finned duct flow that occurs in heat sinks devices. The laminar flow is considered fully developed and the convection-conduction coupling is treated by a conjugated approach. The mathematical formulation of this problem is constituted by the mass, momentum and energy equations. The partial differential equations system is solved by the Galerkin finite element method, adopting a pressure Poisson equation to establish the pressure-velocity coupling and to obtain a mass conserving flow. The results using the classical Boussinesq approximation (density varies linearly with the temperature in the buoyancy-term) are compared with the non-Boussinesq approach (density variation in all terms of the governing equations) showing that both the heat transfer and friction factor are affected by the new considerations. The duct aspect ratio and the solid to fluid thermal conductivity ratio influences on the heat transfer rate are also analyzed. This analysis tool was also shown appropriate for the optimization of electronic components air-cooled heat sinks.

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Prandtl Number Effects on Mixed Convection Between Rotating Coaxial Disks

International Journal of Rotating Machinery ◽

10.1155/s1023621x96000036 ◽

1996 ◽

Vol 2 (3) ◽

pp. 161-166 ◽

Cited By ~ 6

Author(s):

Chyi-Yeou Soong

Keyword(s):

Heat Transfer ◽

Prandtl Number ◽

Mixed Convection ◽

Boussinesq Approximation ◽

Density Variation ◽

Influential Factor ◽

Rotating Disks ◽

Temperature Relation ◽

Flow And Heat Transfer ◽

Prandtl Numbers

Prandtl number characterizes the competition of viscous and thermal diffusion effects and, therefore, is an influential factor in thermal-fluid flows. In the present study, the Prandtl number effects on non-isothermal flow and heat transfer between two infinite coaxial disks are studied by using a similarity model for rotation-induced mixed convection. To account for the buoyancy effects, density variation in Coriolis and centrifugal force terms are considered by invoking Boussinesq approximation and a linear density-temperature relation. Co-rotating disks(Ω2=Ω1)and rotor-stator system(Ω1≠Ω2=0)are considered to investigate the free and mixed convection flows, respectively. For Reynolds number, Re, up to 1000 and the buoyancy parameter, B=βΔT, of the range of|B|≤0.05, the flow and heat transfer characteristics with Prandtl numbers of 100, 7, 0.7, 0.1, and 0.01 are examined. The results reveal that the Prandtl number shows significant impact on the fluid flow and heat transfer performance. In the typical cases of mixed convection in a rotor-stator system with|B|=0.05, the effects in buoyancy-opposed flowsB=0.05are more pronounced than that in buoyancy-assisted ones.

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NUMERICAL STUDY OF A TRIANGULAR FIN INSERTED IN A SQUARE CAVITY WITH UPPER SLIDING SURFACE SUBJECTED TO A MIXED CONVECTION EFFECT

Revista de Engenharia Térmica ◽

10.5380/reterm.v16i1.62196 ◽

2017 ◽

Vol 16 (1) ◽

pp. 81

Author(s):

A. L. Razera ◽

T. M. Fagundes ◽

R. J. C. Fonseca ◽

L. Z. Lessa ◽

A. Schmidt ◽

...

Keyword(s):

Heat Transfer ◽

Mixed Convection ◽

Numerical Study ◽

Design Method ◽

Boussinesq Approximation ◽

Computational Domain ◽

Steady Flows ◽

Square Cavity ◽

Constructal Design ◽

Triangular Fin

This article investigates numerically, using the Constructal Design method, a system that combines a square cavity with upper sliding wall and a triangular fin subjected to the mixed convection effect. The objectives are to evaluate the influence of the fin aspect ratio (H1/L1) on the average Nusselt number on the fin surface and to analyze the effect of the fraction of the area of the triangular fin relative to the square cavity (φ). The proposed problem is assumed two-dimensional, laminar, incompressible and steady flows. For the buoyancy forces it is considered the Boussinesq approximation. In order to generalize the results, the problem is solved in dimensionless form. The fluid flowing through the cavity presents the thermophysical properties defined by the Prandtl number (Pr = 0.71). The buoyancy force in the flow is defined by the Rayleigh number (RaH = 104), while the flow regime is governed by the Reynolds number (ReH = 102). The optimum fin geometry that maximizes the heat transfer between the finned cavity and the surrounding fluid is obtained through the Constructal Design method. The numerical solution of the conservation equations of mass, momentum and energy is calculated with the finite volume method, using the commercial fluid dynamics software FLUENT®. The geometry and mesh computational domain were developed in GAMBIT® package. As results, it was found that the optimal configurations of H1/L1 presented a gain in the thermal performance of up to 15% in relation to the other geometries. In addition, the heat transfer has great dependence on the variation of the fraction of area (φ).

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EFFECT OF QUADRATIC DENSITY VARIATION ON MIXED CONVECTION STAGNATION POINT HEAT TRANSFER AND MHD FLUID FLOW IN POROUS MEDIUM TOWARDS A PERMEABLE SHRINKING SHEET

Journal of Porous Media ◽

10.1615/jpormedia.v19.i12.50 ◽

2016 ◽

Vol 19 (12) ◽

pp. 1083-1097 ◽

Cited By ~ 9

Author(s):

Rakesh Kumar ◽

Shilpa Sood

Keyword(s):

Heat Transfer ◽

Porous Medium ◽

Fluid Flow ◽

Mixed Convection ◽

Stagnation Point ◽

Density Variation ◽

Shrinking Sheet

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Pin-Fin Heat Sink With Horizontal Base and Blocked Edges

Heat Transfer: Volume 2 ◽

10.1115/ht2008-56205 ◽

2008 ◽

Cited By ~ 1

Author(s):

D. Sahray ◽

H. Shmueli ◽

N. Segal ◽

G. Ziskind ◽

R. Letan

Keyword(s):

Heat Transfer ◽

Free Convection ◽

Contact Resistance ◽

Cross Section ◽

Heat Input ◽

Heat Sink ◽

Numerical Study ◽

Heat Sinks ◽

Transfer Enhancement ◽

Pin Fin

In the present work, horizontal-base pin fin heat sinks exposed to free convection in air are studied. They are made of aluminum, and there is no contact resistance between the base and the fins. For the same base dimensions the fin height and pitch vary. The fins have a constant square cross-section. The edges of the sink are blocked: the surrounding insulation is flush with the fin tips. The effect of fin height and pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the Fluent 6 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed for various fin heights. Also assessed are effects of the blocked edges as compared to the previously studied cases where the sink edges were exposed to the surroundings.

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A finite element analysis on combined convection and conduction in a channel with a thick walled cavity

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-07-2013-0239 ◽

2014 ◽

Vol 24 (8) ◽

pp. 1888-1905 ◽

Cited By ~ 3

Author(s):

M.M. Rahman ◽

Hakan Oztop ◽

S. Mekhilef ◽

R. Saidur ◽

A. Chamkha ◽

...

Keyword(s):

Heat Transfer ◽

Finite Element ◽

Mixed Convection ◽

Conjugate Heat Transfer ◽

Transfer Problem ◽

Thick Wall ◽

Thermal Conductivity Ratio ◽

Element Analysis ◽

Content Type ◽

Combined Convection

Purpose – The purpose of this paper is to examine the effects of thick wall parameters of a cavity on combined convection in a channel. In other words, conjugate heat transfer is solved. Design/methodology/approach – Galerkin weighted residual finite element method is used to solve the governing equations of mixed convection. Findings – The streamlines, isotherms, local and average Nusselt numbers are obtained and presented for different parameters. It is found heat transfer is an increasing function of dimensionless thermal conductivity ratio. Originality/value – The literature does not have mixed convection and conjugate heat transfer problem in a channel with thick walled cavity.

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Improved Energy Efficiency of Mixed Convection Heating Process in Eccentric Annulus

Advances in Mechanical Engineering ◽

10.1177/16878140211039150 ◽

2021 ◽

Vol 13 (8) ◽

pp. 168781402110391

Author(s):

Ben Abdelmlek Khaoula ◽

Ben Nejma Fayçal

Keyword(s):

Heat Transfer ◽

Energy Efficiency ◽

Rayleigh Number ◽

Mixed Convection ◽

Heat Transfer Rate ◽

Transfer Rate ◽

Rotation Speed ◽

Numerical Study ◽

Heating Process ◽

Eccentric Annulus

This paper deals with a numerical study of mixed convection heat transfer in horizontal eccentric annulus. The inner cylinder is supposed hot and rotating, however the outer one is kept cold and motionless. The numerical problem was solved using COMSOL Multiphysics® which is based on finite element method. The resolution of the partial differential equations was conducted through an implicit scheme with the use of the damped Newton’s method. The present numerical analysis concerns the effect of eccentricity, rotation speed and Rayleigh number on the flow patterns, heat transfer rate, and energy efficiency of the process. It was found that the heat transfer rate increases with the increase of Rayleigh number. In addition, the heat transfer rate drops with the increase of rotation speed. Finally, we have demonstrated that maximum energy efficiency is achieved not only with higher Rayleigh number but also it is maximum with small eccentricity.

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A numerical study of free convective heat transfer in a double-glazed window with a between-pane Venetian blind

10.32920/ryerson.14657121.v1 ◽

2021 ◽

Author(s):

Tony Avedissian

Keyword(s):

Heat Transfer ◽

Convective Heat Transfer ◽

Heat Transfer Rate ◽

Convective Heat ◽

Transfer Rate ◽

Numerical Study ◽

Thermal Conductivity Ratio ◽

Number Range ◽

Free Convective Heat Transfer ◽

Venetian Blind

The free convective heat transfer in a double-glazed window with a between-pane Venetian blind has been studied numerically. The model geometry consists of a two-dimensional vertical cavity with a set of internal slats, centred between the glazings. Approximately 700 computational fluid dynamic solutions were conducted, including a grid sensitivity study. A wide set of geometrical and thermo-physical conditions was considered. Blind width to cavity width ratios of 0.5, 0.65, 0.8, and 0.9 were studied, along with three slat angles, 0º (fully open, +/- 45º (partially open), and 75º (closed). The blind to fluid thermal conductivity ratio was set to 15 and 4600. Cavity aspects of 20, 40, and 60, were examined over a Rayleigh number range of 10 to 10⁵, with the Prandtl number equal to 0.71. The resulting convective heat transfer data are presented in terms of average Nusselt numbers. Depending on the specific window/blind geometry, the solutions indicate that the blind can either reduce or enhance the convective heat transfer rate across the glazings. The present study does not consider radiation effects in the numerical solution. Therefore, a post-processing algorithm is presented that incorporates the convective and radiative influences, in order to determine the overall heat transfer rate across the window/blind system.

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Natural Convection in a Horizontal Cavity Partially Occupied by a Porous Media Saturated by a Coolant Liquid

Volume 1: Symposia, Parts A and B ◽

10.1115/fedsm2006-98236 ◽

2006 ◽

Author(s):

Fakhreddine S. Oueslati ◽

Rachid Bennacer ◽

Habib Sammouda ◽

Ali Belghith

Keyword(s):

Heat Transfer ◽

Porous Media ◽

Natural Convection ◽

Flow Structure ◽

Boussinesq Approximation ◽

Density Variation ◽

Heat Fluxes ◽

Complex Flow ◽

Coupled Equations ◽

Complex Flow Structure

The natural convection is studied in a cavity witch the lower half is filled with a porous media that is saturated with a first fluid (liquid), and the upper is filled with a second fluid (gas). The horizontal borders are heated and cooled by uniform heat fluxes and vertical ones are adiabatic. The formulation of the problem is based on the Darcy-Brinkman model. The density variation is taken into account by the Boussinesq approximation. The system of the coupled equations is resolved by the classic finite volume method. The numerical results show that the variation of the conductivity of the porous media influences strongly the flow structure and the heat transfer as well as in upper that in the lower zones. The effect of conductivity is conditioned by the porosity which plays a very significant roll on the heat transfer. The structures of this flow show that this kind of problem with specific boundary conditions generates a complex flow structure of several contra-rotating two to two cells, in the upper half of the cavity.

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