# One-Dimensional Steady-State Convection and Diffusion

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 Revision as of 16:14, 2 June 2010 (view source)← Older edit Revision as of 06:11, 14 July 2010 (view source)Newer edit → Line 19: Line 19: |{{EquationRef|(2)}} |{{EquationRef|(2)}} |} |} - Equation {{EquationNote|(1)}} is subject to the following boundary conditions: + Equation (1) is subject to the following boundary conditions: {| class="wikitable" border="0" {| class="wikitable" border="0" Line 79: Line 79: |{{EquationRef|(9)}} |{{EquationRef|(9)}} |} |} - is the Peclet number that reflects the relative level of convection and diffusion. Pe becomes zero for the case of pure diffusion and becomes infinite for the case of pure advection. The exact solution of eqs. {{EquationNote|(6)}} - {{EquationNote|(8)}} can be obtained as + is the Peclet number that reflects the relative level of convection and diffusion. Pe becomes zero for the case of pure diffusion and becomes infinite for the case of pure advection. The exact solution of eqs. (6) - (8) can be obtained as {| class="wikitable" border="0" {| class="wikitable" border="0"

## Revision as of 06:11, 14 July 2010

Exact Solution The objective of this subsection is to introduce various discretization schemes of the convection-diffusion terms through discussion of the one-dimensional steady state convection and diffusion problem. For a one-dimensional steady-state convection and diffusion problem, the governing equation is $\frac{d(\rho u\varphi )}{dx}=\frac{d}{dx}\left( \Gamma \frac{d\varphi }{dx} \right)$ (1)

where the velocity, u, is assumed to be known. Both density, ρ, and diffusivity, Г, are assumed to be constants. The continuity equation for this one-dimensional problem is $\frac{d(\rho u)}{dx}=0$ (2)

Equation (1) is subject to the following boundary conditions: $\varphi =\varphi _{0},\text{ }x=0$ (3) $\varphi =\varphi _{L},\text{ }x=L$ (4)

By introducing the following dimensionless variables $\Phi =\frac{\varphi -\varphi _{0}}{\varphi _{L}-\varphi _{0}},\text{ }X=\frac{x}{L}$ (5)

the one-dimensional steady-state convection and diffusion problem can be nondimensionalized as $\text{Pe}\frac{d\Phi }{dX}=\frac{d^{2}\Phi }{dX^{2}}$ (6) $\begin{matrix}{}\\\end{matrix}\Phi =0,\text{ X}=0$ (7) $\begin{matrix}{}\\\end{matrix}\Phi =1,\text{ }X=1$ (8)

where $\text{Pe}=\frac{\rho uL}{\Gamma }$ (9)

is the Peclet number that reflects the relative level of convection and diffusion. Pe becomes zero for the case of pure diffusion and becomes infinite for the case of pure advection. The exact solution of eqs. (6) - (8) can be obtained as $\Phi =\frac{\varphi -\varphi _{0}}{\varphi _{L}-\varphi _{0}}=\frac{\exp (\text{Pe}X)-1}{\exp (\text{Pe})-1}$ (10)

which will be used as a criterion to check the accuracy of various discretization schemes.