Effect on Natural Convection of the Distance Between an Inclined Discretely Heated Plate and a Parallel Shroud Below

2002 ◽  
Vol 124 (3) ◽  
pp. 441-451 ◽  
Author(s):  
Oronzio Manca ◽  
Sergio Nardini ◽  
Vincenzo Naso
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Heated Plate ◽  
Heat Sources ◽  
Channel Spacing ◽  
Nusselt Numbers ◽  
Test Conditions ◽  
Inclination Angles ◽  
Rayleigh Numbers ◽  
Opposite Tendency

An experimental study on air natural convection on an inclined discretely heated plate with a parallel shroud below was carried out. Three heated strips were located in different positions on the upper wall. The distance between the walls, b, was changed in the range 7.0–40.0 mm and two values of the heat flux dissipated by the heaters were taken into account. Several inclination angles between the vertical and the horizontal were tested. The wall temperature distribution as a function of the channel spacing and the inclination angle, the source heat flux, the number and the arrangement of the heat sources are presented. The analysis shows that, for angles not greater than 85 deg, increasing the distance between walls does not reduce the wall temperatures, whereas at greater tilting angles (>85 deg) there is an opposite tendency. This is confirmed by flow visualization at angles equal to 85 deg and 90 deg and b=20.0 and 32.3 mm. Dimensionless maximum wall temperatures are correlated to the process parameters in the ranges 1.2s˙104⩽Ral cos θ⩽8.6s˙105; 0 deg⩽θ⩽88 deg; 0.48⩽l/b⩽1.6 and 10⩽L/b⩽32.6 with 1.0⩽d/l⩽3.0; the agreement with experimental data is good. The spacing which yields the best thermal performance of the channel is given. Local Nusselt numbers are evaluated and correlated to the local Rayleigh numbers and the tilting angles in the ranges 20⩽Rax′⩽8.0s˙105 and 0 deg⩽θ⩽88 deg. The exponent of monomial correlations between local Nusselt and Rayleigh numbers are in the 0.23–0.26 range. Comparisons with data from the literature, in terms of Nusselt number, exhibited minor discrepancies, mainly because of some difference in test conditions and of heat conduction in the channel walls.

An Experimental Study on Natural Convection Heat Transfer in an Inclined Square Enclosure Containing Internal Energy Sources

1988 ◽  
Vol 110 (2) ◽  
pp. 345-349 ◽  
Author(s):  
Jae-Heon Lee ◽  
R. J. Goldstein
Keyword(s):  
Natural Convection ◽  
Internal Energy ◽  
Extreme Values ◽  
Convection Heat Transfer ◽  
Energy Sources ◽  
Square Enclosure ◽  
Nusselt Numbers ◽  
Inclination Angles ◽  
The Right ◽  
Rayleigh Numbers

An experiment was carried out to study two-dimensional laminar natural convection within an inclined square enclosure containing fluid with internal energy sources bounded by four rigid planes of constant equal temperature. Inclination angles, from the horizontal, of 0, 15, 30, and 45 deg for Rayleigh numbers from 1.0 × 104 to 1.5 × 105 were studied. At inclined angles of 0 and 15 deg, there are two extreme values of temperature and temperature gradient within the fluid, while there is only one at 30 and 45 deg. Local and average Nusselt numbers are obtained on all four walls. As the inclination angle increases, the average Nusselt number increases on the right (upper) and bottom walls, decreases on the left (lower) wall and stays almost constant on the top wall.

scholarly journals Numerical study of natural convection in an enclosure with discrete heat sources on one of its vertical walls

2019 ◽  
pp. 448-448
Author(s):  
Mehmet Pamuk
Keyword(s):  
Natural Convection ◽  
Numerical Study ◽  
Heat Sources ◽  
Confined Spaces ◽  
Nusselt Numbers ◽  
Discrete Heat Sources ◽  
Computer Chips ◽  
Vertical Walls ◽  
Comparison Of The Results ◽  
Rayleigh Numbers

In this study, natural convection in a fluid-filled rectangular enclosure is analyzed using Comsol? commercial software. The fluid in which natural convection takes place is a dielectric liquid called FC-75. Attached to one of the vertical walls of the enclosure is an array of rectangular protrusions, each representing computer chips mounted on a PCB. The nominal power consumed by each chip is assumed to be 0.35W, 1.07W, 1.65W and 2.35W. This corresponds exactly to the values used in the experiments, which were performed once by the author of this study. The results of the experiment and the numerical study are shown as Nusselt numbers vs. Rayleigh numbers, both being the most important dimensionless parameters of natural convection. A comparison of the results has shown that Comsol? can achieve reliable results in similar problems, eliminating the need to build expensive experimental setups and spending time conducting experiments. The simulation results are aimed to be used in similar designs of electronic circuits in confined spaces.

Natural Convection Heat Transfer From Vertical Triangular Ducts

2009 ◽  
Author(s):  
Mohamed E. Ali ◽  
Hany Al-Ansary
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Rayleigh Numbers

Experimental investigations have been reported on steady state natural convection from the outer surface of vertical triangular cross section ducts in air. Three ducts have been used with equilateral side length of 0.044, 0.06 and 0.08 m. The ducts are heated using internal constant heat flux heating elements. The temperatures along the vertical surface and the peripheral directions of the duct wall are measured. Axial (perimeter averaged) heat transfer coefficients along the side of each duct are obtained for laminar and transition to turbulent regimes of natural convection heat transfer. Axial (perimeter averaged) Nusselt numbers are evaluated and correlated using the modified Rayleigh numbers for laminar and transition regime using the vertical axial distance as a characteristic length. Critical values of the modified Rayleigh numbers are obtained for transition to turbulent. Furthermore, total overall averaged Nusselt numbers are correlated with the modified Rayleigh numbers for all ducts. The local axial (perimeter averaged) heat transfer coefficients are observed to decrease in the laminar region and increase in the transition region. Laminar regimes are obtained at the lower half of the ducts and its chance to appear decreases as the heat flux increases.

scholarly journals Natural convection air flow in vertical upright-angled triangular cavities under realistic thermal boundary conditions

2016 ◽  
Vol 20 (5) ◽  
pp. 1407-1420 ◽  
Author(s):  
Jaime Sieres ◽  
Antonio Campo ◽  
José Martínez-Súarez
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Aperture Angle ◽  
Temperature Fields ◽  
Uniform Heat Flux ◽  
Thermal Boundary Conditions ◽  
Nusselt Numbers ◽  
Horizontal Wall ◽  
Rayleigh Numbers

This paper presents an analytical and numerical computation of laminar natural convection in a collection of vertical upright-angled triangular cavities filled with air. The vertical wall is heated with a uniform heat flux; the inclined wall is cooled with a uniform temperature; while the upper horizontal wall is assumed thermally insulated. The defining aperture angle ? is located at the lower vertex between the vertical and inclined walls. The finite element method is implemented to perform the computational analysis of the conservation equations for three aperture angles ? (= 15?, 30? and 45?) and height-based modified Rayleigh numbers ranging from a low Ra = 0 (pure conduction) to a high 109. Numerical results are reported for the velocity and temperature fields as well as the Nusselt numbers at the heated vertical wall. The numerical computations are also focused on the determination of the value of the maximum or critical temperature along the hot vertical wall and its dependence with the modified Rayleigh number and the aperture angle.

Effect of 3D Diffusion Over Vertical Thin Rectangular Geometries in Natural Convection Heat Transfer

2006 ◽  
Author(s):  
Mustafa Gursoy ◽  
Mehmet Arik ◽  
Tunc Icoz ◽  
Michael Yovanovich ◽  
Theodorian Borca-Tasciuc
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Fluid Motion ◽  
Heat Removal ◽  
Air Entrainment ◽  
Published Data ◽  
Diffusion Term ◽  
Nusselt Numbers ◽  
Wide Range ◽  
Rayleigh Numbers

Natural convection over vertical plates is a very well known problem in heat transfer. There are many available correlations to predict Nusselt numbers for a wide range of Rayleigh numbers. These benchmark studies on natural convection for vertical plates were conducted on rather large surfaces leading to Rayleigh numbers in the range of 0.1 to 109. In natural convection the sole driving force of fluid motion is the change in fluid density, when the diffusive limit is small compared to convective heat transfer. However, conduction to air, as well as air entrainment from sides also contributes to the heat removal from heater surfaces. An experimental study has been carried out with small and large heaters compared to published data for 2×103<Ra<4×107. Square surfaces of 12.5 and 25.4 mm, and rectangular heaters of sizes 25.4×101.6 and 25.4×203.2 mm were tested for a range of heat inputs such that the surface temperatures are controlled between 30 °C and 80 °C. It is found that published correlations underpredict the Nusselt numbers as much as 20%. It is observed that widely known correlations underpredict the experimental values since the 3D conduction and side air drifts on heat transfer are not accounted for in these correlations. However, the cuboid model which includes the 3D diffusion term showed much better agreement with the experimental results.

Mixed Convection in Air in an Open Ended Cavity With a Moving Plate Parallel to the Cavity Open Surface

2005 ◽  
Author(s):  
Assunta Andreozzi ◽  
Nicola Bianco ◽  
Vincenzo Naso ◽  
Oronzio Manca
Keyword(s):  
Heat Flux ◽  
Natural Convection ◽  
Mixed Convection ◽  
Plate Motion ◽  
Uniform Heat Flux ◽  
Geometrical Parameters ◽  
Heated Plate ◽  
Open Surface ◽  
Moving Plate ◽  
Plate Temperature

In this study, a numerical investigation of mixed convection in air in an open ended cavity, with a moving plate parallel to the cavity open surface, is carried out. The moving plate has a constant velocity, whereas a vertical plate of the open cavity is heated at uniform heat flux. All the other walls are adiabatic. The numerical analysis is obtained by means of the commercial code FLUENT. Two configurations, assisting and opposing, are analyzed. In the assisting configuration, natural convection is supported by the plate motion, whereas, in the opposing configuration, natural convection and plate motion have opposing effects. The effect of different geometrical parameters, heat flux and moving plate velocity are analyzed. Results in terms of heated plate and moving plate temperature profiles are presented and simple monomial correlation equations for both the configurations are proposed between the terms Nu/Re0.6 and Ri.

Three-Dimensional Laminar Natural Convection in an Inclined Air Slot With Hexagonal Honeycomb Core

1991 ◽  
Vol 113 (4) ◽  
pp. 906-911 ◽  
Author(s):  
Y. Asako ◽  
H. Nakamura ◽  
Z. Chen ◽  
M. Faghri
Keyword(s):  
Natural Convection ◽  
Numerical Solutions ◽  
Transfer Problem ◽  
Three Dimensional ◽  
Convection Heat Transfer ◽  
Temperature Fields ◽  
Honeycomb Core ◽  
Inclination Angles ◽  
Side Walls ◽  
Rayleigh Numbers

Numerical solutions are obtained for a three-dimensional natural convection heat transfer problem in an inclined air slot with a hexagonal honeycomb core. The air slot is assumed to be long and wide such that the velocity and temperature fields repeat themselves in successive enclosures. The numerical methodology is based on an algebraic coordinate transformation technique, which maps the complex cross section onto a rectangle, coupled with a calculation procedure for fully elliptic three-dimensional flows. The calculations are performed for Rayleigh numbers in the range of 103 to 105, inclination angles in the range of −90 to 80 deg, Prandtl number of 0.7, and for five values of the aspect ratio. Three types of thermal boundary condition for the honeycomb side walls are considered. The average Nusselt number results are compared with those for a rectangular two-dimensional enclosure.

scholarly journals Effect of Various Tilted Positions of a Thin Fin on Natural Convection of Laminar Viscous Flow in a Square Cavity

2021 ◽  
Vol 39 (5) ◽  
pp. 1634-1642
Author(s):  
Syed Fazuruddin ◽  
Seelam Sreekanth ◽  
G Sankara Sekhar Raju
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Finite Difference ◽  
Average Nusselt Number ◽  
Vertical Position ◽  
Inclination Angles ◽  
Rayleigh Numbers

An exhaustive numerical investigation is carried out to analyze the role of an isothermal heated thin fin on fluid flow and temperature distribution visualization in an enclosure. Natural convection within square enclosures finds remarkable pragmatic applications. In the present study, a finite difference approach is performed on two-dimensional laminar flow inside an enclosure with cold side walls and adiabatic horizontal walls. The fluid flow equations are reconstructed into vorticity - stream function formulation and these equations are employed utilizing the finite-difference strategy with incremental time steps. The parametric study includes a wide scope of Rayleigh number, Ra, and inclination angle ϴ of the thin fin. The effect of different Rayleigh numbers ranging Ra = 104-106 with Pr=0.71 for all the inclination angles from 0°-360° with uniform rotational length of angle 450 of an inclined heated fin on fluid flow and heat transfer have been investigated. The heat transfer rate within the enclosure is measured by means of local and average Nusselt numbers. Regardless of inclination angles of the thin fin, a slight enhancement in the average Nusselt number is observed when Rayleigh number increased for both the cases of the horizontal and vertical position of the thin fin. When the fin has inclined no change in average Nusselt number is noticed for distinct Rayleigh numbers.

An Unsteady Double-Diffusive Natural Convection in an Inclined Rectangular Enclosure with Different Angles of Magnetic Field

2016 ◽  
Vol 13 (04) ◽  
pp. 1641015 ◽  
Author(s):  
Sabyasachi Mondal ◽  
Precious Sibanda
Keyword(s):  
Magnetic Field ◽  
Natural Convection ◽  
Staggered Grid ◽  
Convection Flow ◽  
Rectangular Enclosure ◽  
Nusselt Numbers ◽  
Inclination Angles ◽  
The Magnetic Field ◽  
Buoyancy Ratio ◽  
Double Diffusive

An unsteady double-diffusive natural convection flow in an inclined rectangular enclosure subject to an applied magnetic field and heat generation parameter is studied. The enclosure is heated and concentrated from one side and cooled from the adjacent side. The other two sides are adiabatic. The governing equations are solved numerically using a staggered grid finite-difference method to determine the streamline, isotherm and iso-concentration contours. We have further obtained the average Nusselt numbers and average Sherwood numbers for various values of buoyancy ratio and different angles of the magnetic field by considering three different inclination angles of the enclosure while keeping the aspect ratio fixed. The results indicate that the flow pattern, temperature and concentration fields are significantly dependent on the buoyancy ratio and the magnetic field angles. It is found that different angles of the magnetic field suppress the convection flow and its direction influences the flow patterns. This leads to the appearance of inner loop and multiple eddies.

Sign in / Sign up

Export Citation Format

Share Document