Free Convection across Inclined Air Layers with One Surface V-Corrugated

1978 ◽  
Vol 100 (3) ◽  
pp. 410-415 ◽  
Author(s):  
S. M. ElSherbiny ◽  
K. G. T. Hollands ◽  
G. D. Raithby
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Flat Plate ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Flat Plates ◽  
Plate Spacing ◽  
Air Layers ◽  
Free Convective Heat Transfer

Experimental measurements are presented for free convective heat transfer across inclined air layers, heated from below, and bounded by one V-corrugated plate and one flat plate. The measurements covered three values for the ratio, A, (average plate spacing to V-height), namely, A = 1, 2.5 and 4. It also covered angles of inclination with respect to the horizontal, θ, of 0, 30, 45 and 60 deg, and a range in Rayleigh number of 10 < Ra < 4 × 106. The study proves, both theoretically and experimentally, that the free convective heat transfer is essentially the same, regardless of whether the V-corrugated plate is above or below. It was found that for the same average plate spacing, L, the convective heat losses across air layers bounded by one V-corrugated and one flat plate are greater than those for two parallel flat plates by up to 50 percent for the range studied. Experimental results are given as plots of Nusselt number versus Rayleigh number. A correlation equation is given for Nusselt number, Nu, as a function of A, θ and Ra.

Free Convective Heat Transfer Across Inclined Air Layers

1976 ◽  
Vol 98 (2) ◽  
pp. 189-193 ◽  
Author(s):  
K. G. T. Hollands ◽  
T. E. Unny ◽  
G. D. Raithby ◽  
L. Konicek
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Horizontal Layer ◽  
Experimental Measurements ◽  
Number Range ◽  
Transfer Rates ◽  
Air Layers ◽  
Free Convective Heat Transfer

This paper presents new experimental measurements on free convective heat transfer rates through inclined air layers of high aspect ratio, heated from below. The Rayleigh number range covered is from subcritical to 105; the range of the angle of inclination, φ measured from the horizontal is: 0 < φ < ∼70 deg. Although it was anticipated that the results might be identical to the results for the horizontal layer if one replaced Ra by Ra cos φ, significant departures from this behavior were observed, particularly in the range 1708 < Ra cos φ < 104, 30 deg ≤ φ < 60 deg. A recommended relationship giving the Nusselt number as a function of Ra cos φ and φ is reported. This relationship fits all data closely.

Natural convective heat transfer in a hemispherical cavity filled with ZnO–H2O nanofluid saturated porous medium

2018 ◽  
Vol 29 (10) ◽  
pp. 1850097 ◽  
Author(s):  
Abderrahmane Baïri ◽  
Najib Laraqi
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Volume Fraction ◽  
Saturated Porous Medium ◽  
Physical Parameters ◽  
Numerical Work

This three-dimensional (3D) numerical work based on the volume control method quantifies the convective heat transfer occurring in a hemispherical cavity filled with a ZnO–H2O nanofluid saturated porous medium. Its main objective is to improve the cooling of an electronic component contained in this enclosure. The volume fraction of the considered monophasic nanofluid varies between 0% (pure water) and 10%, while the cupola is maintained isothermal at cold temperature. During operation, the active device generates a heat flux leading to high Rayleigh number reaching [Formula: see text] and may be inclined with respect to the horizontal plane at an angle ranging from 0[Formula: see text] to 180[Formula: see text] (horizontal position with cupola facing upwards and downwards, respectively) by steps of 15[Formula: see text]. The natural convective heat transfer represented by the average Nusselt number has been quantified for many configurations obtained by combining the tilt angle, the Rayleigh number, the nanofluid volume fraction and the ratio between the thermal conductivity of the porous medium’s solid matrix and that of the base fluid. This ratio has a significant influence on the free convective heat transfer and ranges from 0 (without porous media) to 70 in this work. The influence of the four physical parameters is analyzed and commented. An empirical correlation between the Nusselt number and these parameters is proposed, allowing determination of the average natural convective heat transfer occurring in the hemispherical cavity.

scholarly journals An Interferometric Study of Free Convective Heat Transfer in a Double Glazed Window With a Between-Panes Venetian Blind

2021 ◽  
Author(s):  
Bertha Lai
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Flat Plates ◽  
Set Up ◽  
Free Convective Heat Transfer

The free convective heat transfer in a double-glazed window with between-panes Venetian blinds was measured using a Mach-Zehnder interferometer. A vertical cavity with differentially heated/cooled flat plates was set up with an internal blind at slat angles of ø=0⁰, ø=45⁰, and ø=90⁰ from the horizontal and tip-to-plate spacings of s=2mm, s=4mm, and s=8mm. Heat transfer measurements were taken with air as the test fluid and at Rayleigh numbers of Ra~4.5x10(4), RA~6.7X10(4), and Ra~13.1x10(4), based on cavity widths of W=28.7mm, W=32.7mm, and W=40.7mm, respectively. Finite fringe interferograms were used to obtain local and average heat transfer data. Infinite fringe interferograms were taken to visualize the temperature field within the cavity. A preliminary numerical study of the experimental geometry was also conducted. The results show that there was substantial variation in local heat transfer rates caused by the presence of the between-panes blind inside the window cavity. In general, experimental average Nusselt numbers were found to be lower than those of a cavity without blinds.

scholarly journals FREE CONVECTIVE HEAT TRANSFER FROM AN OBJECT AT LOW RAYLEIGH NUMBER

2013 ◽  
Vol 43 (1) ◽  
pp. 23-28
Author(s):  
Md. Golam Kader ◽  
Khandkar Aftab Hossain
Keyword(s):  
Heat Transfer ◽  
Rayleigh Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Difference Method ◽  
Vertical Direction ◽  
Large Enclosure ◽  
Uniform Grids ◽  
Heated Object ◽  
Free Convective Heat Transfer

Free convective heat transfer from a heated object in very large enclosure is investigated in thepresent work. Numerical investigation is conducted to explore the fluid flow and heat transfer behavior in thevery large enclosure with heated object at the bottom. Heat is released from the heated object by naturalconvection. Entrainment is coming from the surrounding. The two dimensional Continuity, Navier-Stokesequation and Energy equation have been solved by the finite difference method. Uniform grids are used in theaxial direction and non-uniform grids are specified in the vertical direction. The differential equations arediscretized using Central difference method and Forward difference method. The discritized equations withproper boundary conditions are sought by SUR method. It has been done on the basis of stream function andvorticity formulation. The flow field is investigated for fluid flowing with Rayleigh numbers in the range of 1.0 ?Ra ? 1.0×103 and Pr=0.71. It is observed that the distortion of flow started at Rayleigh number Ra=10. It isobserved that the average heat transfer remains constant for higher values of Reyleigh number and heatingefficiency varies with Ra upto the value of Ra=35 and beyond this value heating efficiency remains constant.DOI: http://dx.doi.org/10.3329/jme.v43i1.15775

A Numerical Study of the Effect of Triangular Waves on Natural Convective Heat Transfer From an Upward Facing Heated Horizontal Isothermal Surface

2016 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Surface Waves ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Heated Surface ◽  
Isothermal Surface

A numerical study of natural convective heat transfer from an upward facing, heated horizontal isothermal surface imbedded in a large flat adiabatic surface has been undertaken. On the heated surface is a series of triangular shaped waves. Laminar, transitional, and turbulent flow conditions have been considered. The flow has been assumed to be two-dimensional and steady. The fluid properties have been assumed constant except for the density change with temperature giving rise to the buoyancy forces. This was with treated using the Boussinesq approach. The numerical solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The k-epsilon turbulence model with full account being taken of buoyancy force effects has been employed. The heat transfer rate from the heated surface expressed in terms of a Nusselt number is dependent on the Rayleigh number, the number of waves, the height of the waves relative to the width of the heated surface, and the Prandtl number. This study obtained results for a Prandtl number of 0.74 which is effectively the value for air. An investigation of the effect of the Rayleigh number, the dimensionless height of the surface waves, and the number of surface waves on the Nusselt number has been undertaken.

A Numerical Study of the Simultaneous Natural Convective Heat Transfer From the Upper and Lower Surfaces of a Thin Isothermal Horizontal Circular Plate

2016 ◽  
Author(s):  
Patrick H. Oosthuizen ◽  
Abdulrahim Kalendar
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Rate ◽  
Convective Heat ◽  
Transfer Rate ◽  
The Mean ◽  
Adiabatic Section

Natural convective heat transfer from the top and bottom surfaces of a thin circular isothermal horizontal plate which, in general, has a centrally placed adiabatic section has been numerically investigated. The temperature of the plate surfaces is higher than the temperature of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occurs over the plate. The heat transfer from the upper and lower surfaces of the plate as well as the mean heat transfer rate from the entire surface of the plate have been considered. The flow has been assumed to be axisymmetric and steady. The k-epsilon turbulence model with account being taken of buoyancy force effects has been used and the solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The heat transfer rate from the heated plate has been expressed in terms of a Nusselt number based on the outside plate diameter and the difference between the plate temperature and the fluid temperature far from the plate. The mean Nusselt number is dependent on the Rayleigh number, the ratio of the diameter of the inner adiabatic section to the outer plate diameter, and the Prandtl number. Results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. The variations of the mean Nusselt number averaged over both the upper and lower surfaces and of the mean Nusselt numbers for the upper surface and for the lower surface with Rayleigh number for various adiabatic section diameter ratios have been studied. The use of a reference length scale to allow the correlation of these mean Nusselt number-Rayleigh number variations has been investigated.

A Computational Fluid Dynamics Investigation on the Effect of the Angular Velocities of Hot and Cold Turbulator Cylinders on the Heat Transfer Characteristics of Nanofluid Flows Within a Porous Cavity

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Yan Cao ◽  
Yu Bai ◽  
Jiang Du ◽  
Saman Rashidi
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Turbulent Flow ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Porous Cavity ◽  
Cu Nanoparticle ◽  
The Impact

Abstract In the present study, turbulent flow of a Cu-water nanofluid through a porous cavity is investigated using a numerical method. Two rotating cylinders with different temperatures are placed inside the porous enclosure to generate turbulent structures. Forced and natural convective heat transfer mechanisms are compared for different Cu nanoparticle concentrations. The natural convection within the enclosure is resulted from buoyancy forces as an effect of temperature differences among hot and cold cylindrical turbulators. To investigate the effect of the cavity geometry on the natural convection heat, the simulations are done for various Rayleigh number values. Accordingly, Rayleigh number increment provides higher Nusselt number values. However, in turbulent flow regimes, forced convection may weaken the natural convection. It is proven that for lower Reynolds numbers, the Nusselt number reaches higher values because of buoyant-driven convective heat transfer deterioration. Moreover, the angular velocity directions of both cylinders slightly affect the Nusselt number. Besides, the impact of porosity on the heat transfer rate is studied for different Darcy numbers. It is concluded that, for lower Ra numbers, as Darcy number rises, the average Nusselt number through the cavity is slightly boosted. In addition, it is shown that for cases with high Ra and Re values, Cu nanoparticle addition adversely affects the heat transfer process. At Ra = 1011, as Cu nanoparticle increases from 0 to 0.02 and 0.04, the average Nu decreases up to 17.65% and 27.48%, respectively.

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