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Mathematical Characterization of Bénard-Type Geothermal Scenarios Using Discriminated Non-dimensionalization of the Governing Equations

  • M. Cánovas EMAIL logo , I. Alhama and F. Alhama ORCID logo
Published/Copyright: January 23, 2015

Abstract

The classical non-dimensionalization process of governing equations is a low-cost method commonly applied for a first approximation to the dimensionless numbers that determine the solution patterns in many problems; however, this procedure fails in complex problems, where it is not even possible to define reference quantities – because they are not established in the statement of the problem – to make the dependent or independent variables dimensionless. The application of discrimination corrects this obstacle and allows suitable dimensionless groups to be defined. These, in turn, have two interesting properties: (i) they are of order of magnitude unity, and (ii) they have a clear meaning in terms of balance of physical quantities that counteract each other in a domain or sub-domain of the problem. In this paper, discriminated non-dimensionalization is applied to geothermal scenarios of Bénard-type convective flow, large horizontal boundary sides under a temperature gradient in porous media, to determine the dimensionless groups that control the steady temperature and stream patterns and, from these, the order of magnitude of the main unknowns of the problem. The results were checked numerically for many cases.

MSC: 76S05
PACS: 35B36

Nomenclature

cp

specific heat (J/Kg°C)

Cte

a constant fraction of the unity (dimensionless)

g

gravitational acceleration (m/s2)

H

height of the domain (m)

k

thermal conductivity (W/m°C)

K

hydraulic conductivity (m/s)

L

length of the domain (m)

P

pressure (N/m2),

q

fluid flow (m/s)

t

time (s)

T

temperature (°C)

u

horizontal velocity (m/s)

v

vertical velocity (m/s)

x, y

rectangular coordinates (m)

α

thermal diffusivity (m2/s)

β

thermal expansion coefficient (°C-1)

ψ

Streamfunction (m2/s)

φ

porosity (dimensionless)

μ

fluid viscosity (kg m−1s−1)

ρ

density (kg/m3)

Subscripts
1, 2, …

refer to different arbitrary functions

b

refers to bottom boundary

bl

refers to boundary layer

c

refers to core region of the cell

DD

refers to discriminate dimensionless number or group

f

refers to fluid

hidden

refers to a characteristic or reference quantity not defined in the statement of the problem

l

refers to left side boundary

m

average value

o

Relative to a the reference temperature

r

refers to right side boundary

s

refers to solid matrix

sim

referred to values from numerical simulation

t

refers to the top boundary

x, y

refer to spatial direction

Superscripts

denotes dimensionless quantity or variable

*

reference magnitude

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Received: 2014-6-11
Accepted: 2014-11-14
Published Online: 2015-1-23
Published in Print: 2015-2-1

©2015 by De Gruyter

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