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.

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.

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

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.

Effect of Periodic Flow Structure on Heat Transfer in Milliscale Confined Impinging Newtonian and Non-Newtonian Flow

2018 ◽  
Author(s):  
Ajay Chatterjee ◽  
Drazen Fabris
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Steady Flow ◽  
Convective Heat ◽  
Relative Length ◽  
Periodic Flow ◽  
Transfer Rates ◽  
Flow And Heat Transfer ◽  
Parallel Surfaces

Impinging flows are widely used to enhance convective heat transfer by promoting separation, recirculation and higher rates of local convection. We consider unsteady flow and heat transfer effects in a prototypical T-shaped geometry as an impinging jet. Depending on the relative length scales, the steady laminar flow in this geometry may lose stability and transition to time periodic flow even at a low Reynolds number. A key feature of the periodic structure is the presence of ‘twin’ circulation regions adjacent to the jet column, and separation vortices anchored at the impinging surface in place of the wall jet in steady flow. The separation vortices are located above shear layers lying along the confining plane of the geometry which is flush with the jet exit. Consequently, convective heat transfer is enhanced across this plane. We present calculations to show the effect of the structure of the periodic flow on heat transfer rates across the two parallel surfaces. For a shear thinning fluid the local Nusselt number at the confining surface averaged over a long length scale (∼ 50 times the nozzle width) is more than twice as large compared to that in steady flow, while for the Newtonian fluid the mean Nusselt number increases about 60%. A mild increase in the transport rate across the impinging surface is also observed. Thus flow periodicity due to instability of the steady flow field provides a mechanism to increase the total heat transfer rate across the two surfaces.

Free Convective Heat Transfer in a Liquid-Filled Vertical Annulus

1985 ◽  
Vol 107 (3) ◽  
pp. 596-602 ◽  
Author(s):  
V. Prasad ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Laminar Flow ◽  
Prandtl Number ◽  
Convective Heat Transfer ◽  
Flow Regime ◽  
Convective Heat ◽  
Radius Ratio ◽  
Number Range ◽  
Vertical Annulus

An experimental study of convective heat transfer in liquid-filled vertical annulus of radius ratio κ = 5.338 has been conducted for the height-to-gap width ratio A = 0.5, 1, and 1.5. By using water, heptane, and ethylene glycol as the test fluids, a Rayleigh number range of 8 × 106 < Ra < 3 × 1010, and a Prandtl number range of 4 < Pr < 196 have been covered. Curvature effects on the temperature field are significant and result in a lower effective sink temperature for the boundary layer on the isothermally heated inner wall. The Nusselt number Nu thus increases with radius ratio κ. However, the slope of ln (Nu) versus ln (κ) curve is not a constant, and decreases with an increase in κ. The effect of Prandtl number is weak. In the laminar flow regime, the Nusselt number is weakly dependent on the aspect ratio when Nu and Ra are considered in terms of the annulus height L. The start of laminar flow regime is delayed with an increase in radius ratio. For A = 0.5, κ = 5.338, the critical Grashof number is GrL = 7 × 104, which decreases with an increase in A. Turbulence is initiated when the local Grashof number Grx ≃ 4 × 109.

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

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.

Numerical Study of Natural Convective Heat Transfer From a Very Short Isothermal Cylinder Mounted on a Flat Adiabatic Base

2013 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Cylinder Surface ◽  
Ansys Fluent ◽  
Transfer Rates ◽  
Number Variation ◽  
The Mean

Natural convective heat transfer from a vertical isothermal cylinder mounted on a flat adiabatic base has been numerically studied. The cylinder has an exposed top surface. The cylinder is relatively very short, i.e., has a height that is equal to or less than the cylinder diameter. Both the cases where the cylinder is pointing upward and where it is pointing downward have been considered. The governing equations have been numerically solved using the commercial CFD solver ANSYS FLUENT©. Results have only been obtained for Prandtl number = 0.74. The mean heat transfer rates have been expressed in terms of a Nusselt number, consideration being given both to the heat transfer rate from the entire cylinder surface and to the heat transfer rates from the side and top surfaces of the cylinder. The effect of the dimensionless cylinder height–to–diameter ratio on the Nusselt number variation has been studied in detail.

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