Abstract
The equation which governs the similarity solution for free convection boundary-layer flow along a vertical permeable surface with prescribed surface heating and mass transfer rate is discussed. The solution is seen to depend on two non-dimensional parameters;m, the power-law exponent, and γ, the mass transfer parameter. It is shown that solutions exist for allm>−1 for γ>0 (fluid injection) whereas for γ<0 (fluid withdrawal), solution exist form>m 0(γ), wherem 0 is determined as a function of γ. Solutions for large mass transfer rates are obtained, for both γ>0 and γ<0. For γ>0 the form of the asymptotic solution for γ large is seen to depend on the value ofm. Solutions form large are derived, these are seen to be different depending on whether γ is positive or negative.
Zusammenfassung
Es wird die Gleichung diskutiert, welche die Ähnlichkeitslösung für eine durch freie Konvektion induzierte Grenzschichtströmung entlang einer senkrechten durch-lässigen Oberfläche unter einem aufgeprägtem Wandwärmefluß und Massenstrom beschreibt. Die Lösung hängt von zwei dimensionslosen Parametern ab: dem Exponentenm im Potenzgesetz-Ansatz und Stoffaustauschparameter γ. Es zeigt sich, daß Lösungen für allem>−1 bei γ>0 (Fluidzufuhr) existieren, während für γ<0 (Fluidabzug) die Begrenzungm>m 0(γ) besteht, wobei sichm 0 als Funktion von γ bestimmt. Bei großen Stoffaustauschraten existieren Lösungen für γ>0 und γ<0. Für γ≫0 hängt die Form der asymptotischen Lösung vom Wert des Parametersm ab. Für großesm ergeben sich unterschiedliche Lösungen, je nachdem, ob γ positiv oder negativ ist.
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Abbreviations
- A 0 :
-
constant, Eq. (13)
- f :
-
reduced stream function
- g :
-
acceleration due to gravity
- k :
-
thermal conductivity
- K :
-
constant, Eq. (15c)
- \(\bar K\) :
-
permeability of the porous medium
- l :
-
streamwise length scale
- L :
-
constant, Eq. (15c)
- m :
-
power-law exponent, Eq. (2a)
- q w :
-
measure of the heat flux
- Ra :
-
Rayleigh number
- T :
-
temperature
- ū:
-
velocity components in the\(\bar x\) directions
- \(\bar v\) :
-
velocity components in the\(\bar y\) directions
- \(\bar v_w \) :
-
mass transfer rate
- \(\bar x,\bar y\) :
-
Cartesian coordinates along the plate and normal to it, respectively
- α:
-
constant, Eq. (24)
- α* :
-
thermal diffusivity of the porous medium
- β:
-
constant, Eq. (24)
- β* :
-
coefficient of thermal expansion
- γ:
-
fluid injection or fluid withdrawal parameter, Eq. (4)
- δ:
-
parameter, Eq. (15a)
- η:
-
similarity variable
- ε:
-
parameter, Eq. (8a)
- ψ:
-
stream function
- −:
-
dimensionless variables
- ′:
-
differentiation with respect to the independent variables
- w :
-
condition at the wall
- ∞:
-
ambient condition
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Chaudhary, M.A., Merkin, J.H. & Pop, I. Similarity solutions in free convection boundary-layer flows adjacent to vertical permeable surfaces in porous media: II prescribed surface heat flux. Heat and Mass Transfer 30, 341–347 (1995). https://doi.org/10.1007/BF01463925
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DOI: https://doi.org/10.1007/BF01463925