Midas NFX Heat Transfer Joule Heating and Thermal Stress

Definition

The NFX thermal/electrical thread covers steady and transient heat transfer, temperature-dependent conductivity and capacitance, latent heat, convection, radiation, internal heat generation, Joule heating, and structural thermal-stress coupling.

Heat Transfer Formulation

The manual presents transient heat transfer as an energy balance with heat flux, internal heat generation, specific heat, density, and temperature rate. Fourier's law relates heat flux to thermal gradient, and finite element discretization leads to

C(T) T_dot + K(T) T = R(q_ext, r)

with backward difference time integration and Newton-Raphson iteration for nonlinear temperature-dependent properties.

Element Matrices and Results

Thermal element conductivity and capacitance matrices are documented for 1D, 2D, and 3D elements. Thermal results include flux components, flux resultant, thermal-gradient components, and gradient resultant at element centers.

Joule Heating

Joule heating introduces electric potential and current density. The source couples electric conduction and heat transfer through generated electric energy, producing a coupled block matrix in temperature and electric potential. Temperature-dependent electric conductivity creates nonsymmetric coupled stiffness terms.

Thermal Stress Handoff

Thermal structural coupling is treated through temperature loads and thermal expansion. In laminated composite context, the source also distinguishes average temperature change and through-thickness temperature gradient, which create membrane and bending resultants.

Solver Development Use

For a custom solver, this page suggests a staged implementation: scalar heat equation first, nonlinear temperature-dependent material second, structural thermal strain third, and coupled electric-thermal Joule heating only after scalar field assembly and result recovery are stable.

Connections

Finite Element Heat Transfer and Field Problems gives the general field-problem frame.
Finite Element Thermal Stress Analysis gives the structural thermal strain and equivalent-force frame.
Abaqus Transport Acoustic and Electromagnetic Materials provides a sibling field-property reference.
Midas FEA Heat Transfer and Hydration Analysis and Midas Civil Heat of Hydration and Thermal Stress Analysis are MIDAS thermal-stress siblings.

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