Porous media to intensify natural convection in rectangular enclosures used in building techniques

2020 ◽  
Vol 31 (04) ◽  
pp. 2050061
Author(s):  
A. Baïri ◽  
A. Martín-Garín ◽  
J. A. Millán-García
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Simple Algorithm ◽  
Constant Heat Flux ◽  
Physical Parameters ◽  
Volume Method

This numerical study quantifies the natural convective heat transfer occurring in an elongated rectangular cavity whose hot vertical wall generates a constant heat flux while the opposite one is kept isothermal at cold temperature. The study shows that when a layer of porous material is affixed to the hot wall, the aerodynamic phenomena are modified and increase the natural convective transfer. Several configurations were processed, obtained by varying the matrix’s thermal conductivity of the layer, the aspect ratio of the cavity and the Rayleigh number in wide ranges. The numerical solution is obtained by means of the control volume method based on the SIMPLE algorithm. A correlation of the Nusselt–Rayleigh type is proposed, allowing determination of the convective heat transfer for any combination of these physical parameters. It can be applied in various engineering fields including passive heating in building which can be improved by the simple and easy-to-implement assembly version discussed here.

Effect of Periodic Imposed Heat Flux on Three-Dimensional Natural Convection in a Partially Heated Cubical Enclosure

2016 ◽  
Vol 831 ◽  
pp. 83-91
Author(s):  
Lahoucine Belarche ◽  
Btissam Abourida
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Numerical Study ◽  
Control Volume ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Maximum Temperature ◽  
Cubical Enclosure ◽  
Simplec Algorithm ◽  
Volume Method

The three-dimensional numerical study of natural convection in a cubical enclosure, discretely heated, was carried out in this study. Two heating square sections, similar to the integrated electronic components, are placed on the vertical wall of the enclosure. The imposed heating fluxes vary sinusoidally with time, in phase and in opposition of phase. The temperature of the opposite vertical wall is maintained at a cold uniform temperature and the other walls are adiabatic. The governing equations are solved using Control volume method by SIMPLEC algorithm. The sections dimension ε = D / H and the Rayleigh number Ra were fixed respectively at 0,35 and 106. The average heat transfer and the maximum temperature on the active portions will be examined for a given set of the governing parameters, namely the amplitude of the variable temperatures a and their period τp. The obtained results show significant changes in terms of heat transfer, by proper choice of the heating mode and the governing parameters.

scholarly journals A numerical study of free convective heat transfer within domed skylight cavities

2021 ◽  
Author(s):  
AmirAbbas Sartipi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Control Volume ◽  
Energy Performance ◽  
Vortex Cell ◽  
Design Elements ◽  
Gap Ratio

Domed skylights are important architectural design elements to deliver daylight and solar heat into buildings and connect buildings' occupants to outdoors. To increase the energy efficiency of skylighted buildings, domed skylights employ a number of glazing layers forming enclosed spaces. The latter are subject to complex buoyancy-induced convection heat transfer. Currently, existing fenestration design computer tools and building energy simulation programs do not, however, cover such skylights to quantify their energy performance when installed in buildings. his work presents a numerical study on natural laminar convection within concentric and vertically eccentric domed cavities. The edges of domed cavities are assumed adiabatic and the temperature of the interior and exterior surfaces are uniform and constant. The concentric and vertically eccentric domed cavities were studied when heated from inside and heated from outside, respectively. A commercial CFD package employing the control volume approach is used to solve the laminar convective heat transfer within the cavity. The obtained results showed steady flow for small Grashof numbers. For moderate and large Grashof numbers, depending on the gap ratio and the cases of heating from inside or outside, the flow may be steady or transient periodic with a single vortex-cell or multi vortex-cells. The Nusselt number for the case of heated from inside is greater than the case of heated from outside. The numerical results show that the changes in the gap ratio have smaller effect on Nusselt number in high profile domed skylights than lower profile domed skylights.

A Numerical Study of the Natural Convective Heat Transfer From a Partially Covered Recessed Isothermal Vertical Surface

2005 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Plane Surface ◽  
Vertical Wall ◽  
Vertical Plane ◽  
Adiabatic Wall ◽  
Isothermal Surface ◽  
Resistance To Heat

A numerical study of natural convective heat transfer from a heated isothermal vertical plane surface has been considered. There are relatively short horizontal adiabatic surfaces normal to the isothermal surface at the top and bottom of this isothermal surface these horizontal adiabatic wall surfaces then being joined to vertical adiabatic surfaces. There is a thin surface that offers no resistance to heat transfer that is parallel to the vertical isothermal surface and which partly covers this surface. The situation considered is a simplified model of a window, which is represented by the vertical isothermal wall section, that is recessed in a frame, which is represented by the horizontal adiabatic surfaces, which is mounted in a vertical wall, which is represented by the vertical adiabatic surfaces, and which is exposed to a large surrounding room. The window is covered by a partially open plane blind which is represented by the vertical thin surface that offers no resistance to heat transfer. The flow has been assumed to be laminar and two-dimensional. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces. The governing equations, written in dimensionless form, have been solved using a commercial finite-element based code. Results have only been obtained for a Prandtl number of 0.7.

scholarly journals A numerical study of free convective heat transfer within domed skylight cavities

2021 ◽  
Author(s):  
AmirAbbas Sartipi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Control Volume ◽  
Energy Performance ◽  
Vortex Cell ◽  
Design Elements ◽  
Gap Ratio

Domed skylights are important architectural design elements to deliver daylight and solar heat into buildings and connect buildings' occupants to outdoors. To increase the energy efficiency of skylighted buildings, domed skylights employ a number of glazing layers forming enclosed spaces. The latter are subject to complex buoyancy-induced convection heat transfer. Currently, existing fenestration design computer tools and building energy simulation programs do not, however, cover such skylights to quantify their energy performance when installed in buildings. his work presents a numerical study on natural laminar convection within concentric and vertically eccentric domed cavities. The edges of domed cavities are assumed adiabatic and the temperature of the interior and exterior surfaces are uniform and constant. The concentric and vertically eccentric domed cavities were studied when heated from inside and heated from outside, respectively. A commercial CFD package employing the control volume approach is used to solve the laminar convective heat transfer within the cavity. The obtained results showed steady flow for small Grashof numbers. For moderate and large Grashof numbers, depending on the gap ratio and the cases of heating from inside or outside, the flow may be steady or transient periodic with a single vortex-cell or multi vortex-cells. The Nusselt number for the case of heated from inside is greater than the case of heated from outside. The numerical results show that the changes in the gap ratio have smaller effect on Nusselt number in high profile domed skylights than lower profile domed skylights.

scholarly journals Convective Heat Transfer of Al2O3 and CuO Nanofluids Using Various Mixtures of Water-Ethylene Glycol as Base Fluids

2017 ◽  
Vol 7 (2) ◽  
pp. 1496-1503
Author(s):  
K. Boukerma ◽  
M. Kadja
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Ethylene Glycol ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Thermal Performance ◽  
Volume Fraction ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Volume Fractions

In this work, a numerical study has been performed on the convective heat transfer of Al2O3/Water-Ethylene Glycol (EG) and CuO/(W-EG) nanofluids flowing through a circular tube with circumferentially non-uniform heating (constant heat flux) under the laminar flow condition. We focus on the study of the effect of EG-water mixtures as base fluids with mass concentration ranging from 0% up to 100% ethylene glycol on forced convection. The effect on the flow and the convective heat transfer behavior of nanoparticle types, their volume fractions (φ=1-5%) and Reynolds number are also investigated. The results obtained show that the highest values of the average heat transfer coefficient is observed between 40% and 50% of EG concentration. The average Nusselt number increases with the increase in EG concentration in the base fluid, and the increase in the Reynolds number and volume fraction. For concentrations of EG above 60%, and for all volume fractions, the increase of thermal performance of nanofluids became inversely proportional to the increase of Reynolds number. In addition, CuO/(W-EG) nanofluids show the best thermal performance compared with Al2O3/ (W-EG) nanofluids.

scholarly journals Numerical Study of Turbulent Flows and Convective Heat Transfer of Al2O3-Water Nanofluids In A Circular Tube

2020 ◽  
Vol 77 (2) ◽  
pp. 1-12
Author(s):  
Abdelkader Mahammedi ◽  
Houari Ameur ◽  
Younes Menni ◽  
Driss Meddah Medjahed
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Turbulent Flows ◽  
Convective Heat ◽  
Circular Tube ◽  
Numerical Study ◽  
Constant Heat Flux ◽  
Flux Boundary Condition ◽  
Pressure Losses

The convective heat transfer of Al2O3-water nanofluids through a circular tube with a constant heat flux boundary condition is studied numerically. Turbulent flow conditions are considered with a Reynolds number ranging from 3500 to 20000. The numerical method used is based on the single-phase model. Four volume concentrations of Al2O3-water nanoparticles (0.1, 0.5, 1, and 2%) are used with a diameter of nanoparticle of 40 nm. A considerable increase in Nusselt number, axial velocity, and turbulent kinetic energy was found with increasing Reynolds number and volume fractions. However, the pressure losses were also increased with the raise of Re and nanoparticles concentration.

Natural convective heat transfer in the air-filled interstice between inclined concentric hemispheres

2017 ◽  
Vol 27 (10) ◽  
pp. 2375-2384 ◽  
Author(s):  
Nacim Alilat
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Design Methodology ◽  
Numerical Approach ◽  
Constant Heat Flux ◽  
Horizontal Position ◽  
Content Type ◽  
Thermal Boundary Conditions ◽  
Volume Method

Purpose The main purpose of this work is to quantify the convective heat transfer occurring between two inclined and concentric hemispheres. Design/methodology/approach The inner one is an electronic assembly generating a constant heat flux during operation. The outer hemisphere is maintained isothermal at cold temperature. The interstitial space is air-filled. The base of the equipment can be inclined with respect to the horizontal plane by an angle ranging from 0° (horizontal position with dome faced upwards) to 180° (horizontal position with dome faced downwards). Findings Nusselt–Rayleigh correlations are proposed for several configurations obtained by varying the generated power and the base inclination. The large resulting Rayleigh number ranging between 2.4 × 105 and 1.7 × 107 allows using these new and original correlations in various engineering fields, such as electronics in the present work. The calculations are realized by means of a 3D numerical approach based on the finite volume method. Originality/value The geometry and the thermal boundary conditions considered in the present survey are suitable for applications in many engineering areas.

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