scholarly journals GEOMETRICAL OPTIMIZATION OF MIXED CONVECTIVE FLOWS OVER TRIANGULAR ARRANGEMENT OF CYLINDERS

2016 ◽  
Vol 15 (2) ◽  
pp. 84
Author(s):  
G. M. Barros ◽  
M. Dos S. Pereira ◽  
D. M. do Carmo ◽  
R. Cemin ◽  
L. A. Isoldi ◽  
...  
Keyword(s):  
Nusselt Number ◽  
Drag Coefficient ◽  
Richardson Number ◽  
Fluid Dynamic ◽  
Dynamic Performance ◽  
Boussinesq Approximation ◽  
Circular Cylinders ◽  
Optimal Ratio ◽  
Convective Flows ◽  
Design For All

The present study consists on the numerical evaluation of a triangular arrangement of circular cylinders submitted to transient, two-dimensional, incompressible, laminar and mixed convective flows. The geometrical evaluation is performed by means of Constructal Design. For all simulations it is considered Reynolds and Prandtl numbers of ReD = 100 and Pr = 0.71. Moreover, three different values of Richardson number are investigated: Ri = 0.1 (which represents flows dominated by forced convective), 1.0 (which represents an equilibrium between forced and natural driven forces) and 10.0 (which represents flows with dominance of natural convective). The conservation equations of mass, momentum and energy are solved with the use of Finite Volume Method (FVM). The buoyancy forces are tackled with the Boussinesq approximation. The area occupied by the triangular arrangement of cylinders is a geometric constraint of the problem and the cylinders have the same diameter. The main purpose is to evaluate the effect of Richardson number over the drag coefficient (CD) and Nusselt number (NuD) between the cylinders and the surrounding flow, as well as, over the optimal ratio ST/D (ratio between transversal pitch and the cylinder) for two different values of the ratio SL/D = 1.5 and 2.5 (ratio between longitudinal pitch and the cylinders diameter). Results showed that the effect of ST/D over drag coefficient and Nusselt number is strongly affected by the magnitude of Richardson number. Concerning the Nusselt number, for Ri = 0.1 the optimal geometry which maximizes the NuD is reached for the highest magnitude of ST/D, while for Ri = 10.0 an intermediate optimal ratio of ST/D maximizes the NuD. The Richardson magnitudes also have large influence over the fluid dynamic and thermal behavior of fluid flow for all evaluated geometries. An increase in the ratio SL/D improved the heat exchange of the flow, but decreased the fluid dynamic performance.

scholarly journals Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

2016 ◽  
Vol 139 (2) ◽  
Author(s):  
Francesco Fornarelli ◽  
Antonio Lippolis ◽  
Paolo Oresta
Keyword(s):  
Nusselt Number ◽  
Flow Pattern ◽  
Richardson Number ◽  
Near Field ◽  
Circular Cylinders ◽  
Momentum Exchange ◽  
Force Coefficients ◽  
The Earth ◽  
Spacing Ratio ◽  
Oscillatory Character

In this paper, we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are isothermal and they are aligned with the earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center-to-center spacing (s = 3.6d–4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found, and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri=−1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact, the transition occurs due to rearrangement of the near-field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.

scholarly journals Mixed convection heat transfer from a heated circular cylinder

2019 ◽  
Vol 54 (1) ◽  
pp. 83-88
Author(s):  
H Laidoudi ◽  
M Bouzit
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Drag Coefficient ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Circular Cylinders ◽  
Governing Equations ◽  
Thermal Buoyancy ◽  
Flow And Heat Transfer ◽  
Mixed Convection Heat Transfer

This paper performs the effects of thermal buoyancy and the triangular arrangement of circular cylinders on fluid flow and heat transfer within a horizontal channel, the governing equations involving continuity; momentum and energy are solved in two-dimensional, laminar and steady flow regime. The average Nusselt number and drag coefficient are computed for the range of these conditions: Ri = 0 to 2 at fixed value of Pr = 1, Reynolds number Re = 30 and geometrical configurations (blockage ratio of β = 0.1). In order to observe the flow structure and temperature field under the gradual effect of thermal buoyancy, the streamlines and isotherm contours are illustrated. It is found that, a gradual increase in the value of buoyancy strength creates an asymmetrical flow around the cylinders. Interesting variations of drag coefficient and average Nusselt number are plotted with respect to Richardson number for each cylinder. Bangladesh J. Sci. Ind. Res.54(1), 83-88, 2019

Analysis of mixed convection past a heated sphere

2018 ◽  
Vol 233 (3) ◽  
pp. 601-616 ◽  
Author(s):  
Dipjyoti Nath ◽  
Sukumar Pati ◽  
B Hema Sundar Raju
Keyword(s):  
Reynolds Number ◽  
Nusselt Number ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Drag Coefficient ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Thermal Characteristics ◽  
Sphere Surface ◽  
Critical Richardson Number

The hydrodynamic and thermal characteristics for laminar axisymmetric mixed convection from a heated sphere are analyzed numerically in this work. The governing transport equations of conservation of mass, momentum, and energy have been solved using a higher order compact scheme. The results are presented in terms of the distribution of the streamlines, isotherms, and vorticity contours, and local Nusselt number along the sphere surface together with drag coefficient and average Nusselt number. We identify critical Richardson number above which separation of flow is suppressed. It is revealed that the drag coefficient decreases with an increase in the Reynolds number (Re) and the decrease is more profound for lower range of Re. It is further revealed that the drag coefficient increases monotonically with an increase in the Richardson number, while the same decreases with the increase in the Prandtl number. The average Nusselt number increases monotonically with the increase in Reynolds number, Prandtl number, and Richardson number.

scholarly journals NUMERICAL INVESTIGATION OF TURBULENT FORCED CONVECTIVE FLOWS OVER A PAIR OF CIRCULAR CYLINDERS

2012 ◽  
Vol 11 (1-2) ◽  
pp. 77 ◽  
Author(s):  
E. D. Dos Santos ◽  
F. M. V. Da Silva ◽  
I. C. Acunha Jr. ◽  
M. M. Galarça ◽  
L. A. Isoldi ◽  
...  
Keyword(s):  
Turbulent Flows ◽  
Fluid Dynamic ◽  
Circular Cylinders ◽  
Streamwise Direction ◽  
Convective Flows ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Thermal Patterns ◽  
Prandtl Numbers ◽  
Volume Method

The present study presents large eddy simulation (LES) of forced convective heat transfer in transient, two-dimensional, incompressible turbulent flows over a pair of cylinders with two different arrangements: 1) with two circular cylinders in tandem (both cylinders are in line with the streamwise direction of the flow, β = 0º) and 2) two side-by-side circular cylinders (where both cylinders are placed transversally to the streamwise direction of the flow, β = 90º). The dynamic Smagorinsky model is employed for the sub-grid treatment. The simulations are based on the finite volume method solution for the conservation equations of mass, momentum and energy. Both simulations are performed with Reynolds and Prandtl numbers of ReD = 22000 and Pr = 0.71, respectively. The results showed that the transient fluid dynamic and thermal patterns are strongly affected by the configuration of circular cylinders. The kind of arrangement led to a difference of nearly 20 % for time-averaged Nusselt number (NuD).

Impact of gap-ratios on buoyancy-assisted mixed convection flow and heat transfer in unconfined framework with two side-by-side cylinders

2021 ◽  
pp. 095440622110179
Author(s):  
Aniruddha Sanyal ◽  
Amit Dhiman
Keyword(s):  
Heat Transfer ◽  
Richardson Number ◽  
Dominant Role ◽  
Boussinesq Approximation ◽  
Circular Cylinders ◽  
Convection Flow ◽  
Thermal Buoyancy ◽  
Gap Ratio ◽  
Side Gap ◽  
The Impact

An analysis has been carried out to understand the consequences of side-by-side gap-ratio on thermal buoyancy-assisted two-dimensional flow past a pair of heated circular cylinders for a dominant viscous flow field. This is implemented through studies at Reynolds number ( Re) ranging from 5 to 40, Prandtl number ( Pr) 0.7, gap-ratio ( T/D) 1.5 to 4 and Richardson number ( Ri) 0 to 1. An ANSYS-based incompressible flow solver is used with Boussinesq approximation to account for density variations in the momentum equation. One can realize features like the steady-separated and steady-unseparated flow on varying flow and thermal parameters. Unlike streamlines, non-interacting isotherms are non-existent in the current numerical framework. The influence of gap-ratio on enhancement in Nusselt number ( Nu) is the best realized at T/D = 1.5 and buoyancy-aided effects play a dominant role for enhancement in Nu at diffusion and/or viscous-dominant conditions occurring at Re = 5. Correlations are developed to quantify the impact of T/D, Re, and Richardson number Ri on Nu. For the first time, Nu’s correlation based on varying side-by-side gap-ratio has been stated in a single expression. Finally, a comparison for the heat transfer enhancement/reduction in Nu under a similar numerical framework is provided with cases of high-Pr flow and/or different relatable flow arrangements for circular and square cylinders.

A Numerical Study of a Heat Sink Fin Under a Laminar Impinging Jet

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Z. Q. Lou ◽  
C. Yap ◽  
A. S. Mujumdar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Sink ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Dynamic Performance ◽  
Impinging Jet ◽  
Dielectric Fluid ◽  
Fluid Medium ◽  
Spacing Ratio

Impinging jet heat transfer is a promising method to cool electronic components. In this paper, a numerical study has been carried out to examine the conjugate heat transfer under a confined impinging jet using a plate-fin heat sink as the target plate. Effects of geometric parameters such as fin number, fin height, and fin-to-spacing ratio are examined over a range of jet Reynolds numbers using dielectric fluid FC-72 as the fluid medium. Thermal resistance, pressure drop, and Nusselt number are the main criteria used to evaluate the thermal and fluid dynamic performance of this flow system. Furthermore, the effects of fin height, fin-to-spacing ratio, and jet Reynolds number on impinging jet heat transfer are obtained. The concept of an effective Nusselt number is introduced for computing the heat transfer effectiveness of heat sinks with different fin numbers.

The Flow and Mixed Convection around Tandem Circular Cylinders at Low Reynolds Number

2017 ◽  
Vol 378 ◽  
pp. 59-67
Author(s):  
Houssem Laidoudi ◽  
Blissag Bilal ◽  
Mohamed Bouzit
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Mixed Convection ◽  
Drag Coefficient ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Richardson Number ◽  
Circular Cylinders ◽  
Thermal Buoyancy ◽  
Flow And Heat Transfer

A numerical investigation is carried out to understand the effects of thermal buoyancy and Reynolds number on flow characteristics and mixed convection heat transfer over three isothermal circular cylinders situated in a tandem arrangement within a horizontal channel. The distance between cylinders is fixed at the value of 2.5 widths of the cylinder. The obtained results are presented and discussed for the range of conditions as: Re = 5 to 40, Ri = 0 to 2 at fixed Pr number of 1 and blockage ratio β = 0.25. The main results are depicted in terms of streamlines and isotherm contours to analyze the effect of thermal buoyancy on fluid flow and heat transfer rate. Moreover, the overall drag coefficient and Nusselt number are computed to elucidate the role of Reynolds number and Richardson number on the flow and heat transfer. It is found that increase in the Richardson number increases the drag coefficient of the upstream cylinder whereas it decreases the heat transfer rate of this cylinder. The superimposed of thermal buoyancy created a new sort of recirculation zones between the tandem cylinders.

scholarly journals Effect of thermal buoyancy on flow pattern from a pair of side-by-side confined triangular cylinders

2020 ◽  
Vol 55 (1) ◽  
pp. 9-14
Author(s):  
H Laidoudi ◽  
M Bouzit
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Drag Coefficient ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Richardson Number ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Thermal Buoyancy ◽  
Energy Equations

The effects of ax ial and radial thermal buoyancy on fluid flow and mixed convection heat transfer from a pair of identical triangular cylinders in side-by-side arrangement confined within a straight channel. The numerical simulations are carried out by solving continuity, momentum and energy equations using the commercial code ANSYS-CFX. The obtained results are presented and discussed within the range of following conditions: Richardson number Ri = 0 to 2, Reynolds Re = 20, and Prandtl number Pr = 1 at fixed value of blockage ratio β = 0.2. The main results are depicted in terms of streamline and isotherm contours to analyze the fluidic and energetic behaviors. The total drag coefficient and average Nusselt number are also computed. Moreover, a simple correlation indicating the variations of drag coefficient and average Nusselt number versus Richardson number are also provided. It was found that for axial effect of thermal buoyancy, increase in buoyancy strength enhances the heat transfer rate for both cylinders. In other hand, for radial effect, increase in buoyancy strength increases the heat transfer rate of down cylinder and it is reduced for the upper cylinder. Bangladesh J. Sci. Ind. Res.55(1), 9-14, 2020

Numerical Investigation of Laminar Impinging Jet Heat Transfer to Finned Heat Sinks

2005 ◽  
Author(s):  
Z. Q. Lou ◽  
C. Yap ◽  
A. S. Mujumdar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
Dynamic Performance ◽  
Impinging Jet ◽  
Heat Sinks ◽  
Dielectric Fluid ◽  
Fluid Medium ◽  
Spacing Ratio

A numerical study has been carried out to examine the conjugate heat transfer under a confined impinging jet using a plate-fin heat sink as the target plate. Effects of geometric parameters such as fin number, fin height and fin-to-spacing ratio are examined over a range of jet Reynolds numbers using dielectric fluid FC-72 as the fluid medium. Thermal resistance, pressure drop and Nusselt number are the main criteria used to evaluate the thermal and fluid dynamic performance of this flow system. Furthermore, the effects of fin height, fin-to-spacing ratio and jet Reynolds number on impinging jet heat transfer are obtained. The concept of an effective Nusselt number is introduced for computing the heat transfer effectiveness of heat sinks with different fin numbers.

Stationary fluid convection modes with a Gaussian viscosity dependence of temterature

2016 ◽  
Vol 11 (2) ◽  
pp. 218-225
Author(s):  
V.S. Kuleshov
Keyword(s):  
Computer Code ◽  
Boussinesq Approximation ◽  
Simple Type ◽  
Transfer Coefficients ◽  
Convective Flows ◽  
Heat Transfer Coefficients ◽  
Fluid Convection ◽  
Flat Cell ◽  
Volume Method ◽  
Viscosity Dependence

The results of a numerical modeling of thermo-gravitational convection of abnormally thermo-viscous fluid in a closed square cavity with two vertical adiabatic walls and two horizontal isothermal walls are presented. A model Newtonian liquid for which the dependence of viscosity on temperature is described by a bell function (Gaussian curve) is considered. The natural convection of inhomogeneous liquid is described by the closed mathematical model based on the continuous mechanics equations written in Oberbeck-Boussinesq approximation, where the fluid density is a linear function of temperature. To simulate the fluid flow dynamics, the modified computer code based on the implicit finite volume method and SIMPLE-type algorithm with the second-order temporal accuracy is realized using multiprocessor technology. The effect of the viscosity abnormality on stationary modes of convective flows are studied, the integral heat transfer coefficients in a flat cell are calculated.

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