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Natural convection heat transfer from round horizontal plate

Wärmeübertragung an einer kreisförmigen, horizontalen Platte bei freier Konvektion

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Abstract

A new approach to the model of natural convection from a horizontal, isothermal round plate and a simplified analytical solution of this model have been presented. In this model two separate regions with different fluid motions have been distinguished. In the first region, inside the boundary layer, the fluid flows concentrically towards the centre of the plate, while in the second one (stagnation region) the fluid is motionless. The presented theory has been verified experimentally.

Zusammenfassung

Ein neuer Lösungsweg für das Modell der freien Konvektion an einer isothermen, kreisförmigen, horizontalen Platte und eine vereinfachte analytische Lösung für dieses Modell werden hier vorgestellt. An diesem Modell wird zwischen zwei Bereichen mit verschiedenen Fluidbewegungen unterschieden. Im ersten Bereich, innerhalb der Grenzschicht, strömt das Fluid konzentrisch in Richtung Plattenmitte, während im zweiten Bereich (Stau-Bereich) die Flüssigkeit in Ruhe ist. Diese Theorie wurde experimentell überprüft.

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Abbreviations

a=λ/c p ·ϱ :

thermal diffusivity

A :

cross-section area (Fig. 2)

A1:

control surface of the plate

c p :

specific heat at constant pressure of the fluid

D :

diameter of the plate

F :

coefficient of boundary layer shape, def. (12)

g :

gravitational acceleration

h :

thickness of the tested fluid in experimental devices

H :

height of a fluid column (see Fig. 3)

i :

specific enthalpy

K,K1:

constants (Eqs. 16 and 26)

m :

mass flux

Nu D =αD/λ :

Nu R =αR/λ — Nusselt numbers

p :

pressure

\(\dot q\) :

heat flux density

Q :

heat flux

R :

radius of the plate

Ra D =g β ΔTD 3/(ν a):

Ra R =g β ΔTR 3/(ν α)Rayleigh numbers

s :

radius of the free buoyant stream (see Fig. 2)

s 1 :

radius of stagnation region

T :

temperature

W :

velocity

x :

length of the boundary layer

x :

horizontal coordinate to the surface

y :

vertical coordinate to the surface

α :

heat transfer coefficient

β :

coefficient of volumetric expansion

δ :

thickness of boundary layer

δ s :

thickness of boundary layer at region of its transformation

θ :

dimensionless temperature

Δ :

difference

λ :

thermal conductivity

ν :

kinematic viscosity

ϱ :

fluid density

Φ :

coefficient defined by Eq. (35)

cr:

critical

w :

related to the wall

x :

related to thex direction or to fluid properties inside boundary layer

y :

related to they direction

∞:

fluid ambient condition

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Lewandowski, W.M., Kubski, P. & Khubeiz, J.M. Natural convection heat transfer from round horizontal plate. Wärme- und Stoffübertragung 27, 281–287 (1992). https://doi.org/10.1007/BF01589965

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