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Transient Analysis of Heat Transfer by Natural Convection Along a Vertical Wavy Surface

  • Sadia Siddiqa EMAIL logo , M. Mahfooz and M. A. Hossain
Published/Copyright: May 16, 2017

Abstract

The problem considered in this paper deal with the transient behavior of heat transfer by natural convection flow of fluid along an infinite vertical heated wavy surface. The governing equations are transformed into dimensionless form and solutions are obtained for the two dimensional flow for both pure (α=0) and uneven surface (α ≠ 0). For pure vertical surface boundary layer equations are solved in the (i) upstream (small τ) (ii) downstream (large τ) and (iii) entire (0<τ<∞) regimes using analytical and numerical techniques. A very good agreement is found when results of above mentioned regimes are compared. Further, for wavy surface solutions are obtained for the entire time regime and results are discussed in terms of average Nusselt number coefficient and isotherms. Numerical results are served to reveal the influence of the physical parameters such as the Prandtl number, Pr, and wavy geometry, α, for the surface conditions.

MSC 2010: 35Q79; 76-XX

Nomenclature

x, y

Coordinate system (m)

X, Y

Dimensionless coordinate system

u, v

Dimensional x and y component of velocity (ms–1)

U, V

Dimensionless X and Y component of velocity

U˜

Characteristic velocity

F

Dimensionless stream function

T

Dimensional time (s)

T

Dimensional temperature (K)

Pr

Prandtl number

P

Pressure (Nm–2)

qx

Nusselt number

L

Wavelength of the wavy surface (m)

K

Conductivity (Wm–1K–1)

G

Gravitational acceleration (ms–2)

Cp

Specific heat of fluid at constant pressure (kJkg–1K–1)

τw

Skin-friction

Gr

Grashof number

Greek symbols
ε

Amplitude of the wavy surface (m)

α

Amplitude-wavelength ratio, ε/L

βT

Volumetric coefficient of thermal expansion

σ

Dimensionless coordinate of the wavy surface

σ¯

Coordinate of the wavy surface, eq. (1)

μ

Dynamic viscosity (kgm–1s–1)

υ

Kinematic viscosity (m2s–1)

ρ

Fluid density (kgm–3)

θ

Dimensionless temperature

tˆ

Dimensionless time

ψ

Stream function

η

Non-dimensional similarity variable

Subscripts

Free stream condition

W

Surface condition

T

Temperature

X

Local value

i, j

Evaluated at the ith and jth nodal point in the y- and x-directions, respectively

Superscripts

Differentiation with respect to η

N

Evaluated at the nth point in the τ-direction

References

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Received: 2016-2-3
Accepted: 2017-3-1
Published Online: 2017-5-16
Published in Print: 2017-5-24

© 2017 Walter de Gruyter GmbH, Berlin/Boston

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