Finite volume method for one dimensional steady state diffusion
Finite volume method in computational fluid dynamics is a discretization technique for partial differential equations that arise from physical conservation laws. These equations can be different in nature, e.g. elliptic, parabolic, or hyperbolic. First well-documented use was by Evans and Harlow (1957) at Los Alamos. The general equation for steady diffusion can be easily be derived from the general transport equation for property Φ by deleting transient and convective terms.
General Transport equation can be define as
is density and is conservative form of all fluid flow,
is the Diffusion coefficient and is the Source term.
is Net rate of flow of out of fluid element(convection),
is Rate of increase of due to diffusion,
is Rate of increase of due to sources.
Conditions under which the transient and convective terms goes to zero:
For one-dimensional steady state diffusion, General Transport equation reduces to:
The following steps comprehend one dimensional steady state diffusion -
- Divide the domain in equal parts of small domain.
- Place nodal points midway in between each small domain.
- Create control volume using these nodal points.
- Create control volume near the edge in such a way that the physical boundaries coincide with control volume boundaries.(Figure 1)
- Assume a general nodal point 'P' for a general control volume.Adjacent nodal points in east and west are identified by E and W respectively.The west side face of the control volume is referred to by 'w' and east side control volume face by 'e'.(Figure 2)
- The crux of Finite volume method is to integrate governing equation all over control volume, known discretization.
- Nodal points used to discretize equations.
- At nodal point P control volume is defined as (Figure 3)
is Cross-sectional Area Cross section (geometry) of control volume face, is Volume,is average value of source S over control volume
- It states that diffusive flux Fick's laws of diffusion from east face minus west face leads to generation of flux in control volume.
- diffusive coefficient and is required in order to interpreter useful conclusion.
- Central differencing technique  is used to derive diffusive coefficient.
- In practical situation source term can be linearize
- Merging above equations leads to
- Compare and identify above equation with
Solution of equations
- Discretized equation must be set up at each of the nodal points in order to solve the problem.
- The resulting system of linear algebraic equation Linear equation is then solved to obtain distribution of the property at the nodal points by any form of matrix solution technique.
- The matrix of higher order  can be solved in MATLAB.
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