## 13.55. PLANE55 - 2-D Thermal Solid Matrix or VectorGeometryShape Functions Integration Points
Conductivity Matrix and Heat Generation Load VectorQuad Equation 11–128 2 x 2
Triangle Equation 11–108

1 if planar
3 if axisymmetric

Specific Heat MatrixSame as conductivity matrix. Matrix is diagonalized as described in Lumped Matrices.Same as conductivity matrix
Convection Surface Matrix and Load VectorSame as conductivity matrix evaluated at the face2

### 13.55.1. Other Applicable Sections

Heat Flow describes the derivation of the element matrices and load vectors as well as heat flux evaluations. SOLID70 - 3-D Thermal Solid describes fluid flow in a porous medium, accessed in PLANE55 with KEYOPT(9) = 1.

### 13.55.2. Mass Transport Option

If KEYOPT(8) > 0, the mass transport option is included as described in Heat Flow Fundamentals with Equation 6–1 and by of Equation 6–22. The solution accuracy is dependent on the element size. The accuracy is measured in terms of the non-dimensional criteria called the element Peclet number (Gresho()): (13–98)

where:

 V = magnitude of the velocity vector L = element length dimension along the velocity vector direction ρ = density of the fluid (input as DENS on MP command) Cp = specific heat of the fluid (input as C on MP command) K = equivalent thermal conductivity along the velocity vector direction

The terms V, L, and K are explained more thoroughly below: (13–99)

where:

 Vx = fluid velocity (mass transport) in x direction (input as VX on R command) Vy = fluid velocity (mass transport) in y direction (input as VY on R command)

Length L is calculated by finding the intersection points of the velocity vector which passes through the element origin and intersects at the element boundaries.

For orthotropic materials, the equivalent thermal conductivity K is given by: (13–100)

where:

 Kx, Ky = thermal conductivities in the x and y directions (input as KXX and KYY on MP command) For the solution to be physically valid, the following condition must be satisfied (Gresho()): (13–101)

This check is carried out during the element formulation and an error message is printed out if Equation 13–101 is not satisfied. When this error occurs, the problem should be rerun after reducing the element size in the direction of the velocity vector.