Use this node to define the temperature and the position of the interface of a phase change material, using the Stefan condition. It is applicable on exterior boundaries adjacent to Fluid, Solid, and Porous Medium domains, in 2D, 2D axisymmetric, and 3D components.

For an equivalent condition on interior boundaries, use the Phase Change Interface node instead. The settings for these two nodes are similar, except that some properties entering in the expression of the Stefan velocity should be specified on exterior boundaries, depending on which side of the phase change interface the solid phase is located, outside or inside the computational domain. See the Phase Change Interface and Heat Flux sections for details. On interior boundaries the heat flux and solid phase properties are computed from the adjacent domains.

Select an option in the Material type list to specify if the inputs of the Heat Flux section are defined in the material or spatial frame:

First, set the Phase change temperature, Tpc (SI unit: K), and the Latent heat, Ls → f (SI unit: J/kg), associated to the transition from solid to fluid phase. A positive value should be set for the latent heat.

Then, choose which side of the phase change interface is the Solid side, either Inside or Outside the computational domain.

When the solid phase is outside the computational domain, the Solid density, ρs (SI unit: kg/m3), and the Solid translation velocity, us (SI unit: m/s), should be specified.

When the solid phase is inside the computational domain, the Fluid density, ρf (SI unit: kg/m3) should be specified.

Both solid and fluid densities are used to evaluate the fluid velocity at the interface, vf, defined as:

Finally, choose the method of Heat flux jump evaluation. By default the Lagrange multiplier option is selected and introduces a variable on the boundary, the Lagrange multiplier, to prescribe the temperature and calculate the heat flux jump accurately.

Alternatively, select Temperature gradient to prescribe the temperature condition using a strong constraint and evaluate the heat flux jump from the temperature field gradient at the interface.

The Temperature gradient option leads to a formulation that is easier to handle from a numerical point of view, especially for the iterative solvers, however the accuracy of the heat flux jump is strongly dependent on the size of the mesh next to the boundary. In this case a very fine mesh may be needed to reach the same degree of accuracy as the default option with a default mesh. See Weak Constraints in the COMSOL Multiphysics Reference Manual for more details on the use of Lagrange multipliers.

See Moving Boundary Smoothing in the Phase Change Interface node for details about this section.

Click to select the General inward heat flux (default), Convective heat flux, or Heat rate button. Note that the Convective heat flux option is only available when the solid phase is inside the computational domain. The settings are the same as in the Heat Flux node, see Heat Flux for details.

Physics tab with interface as Heat Transfer in Solids and Fluids, Heat Transfer in Solids, Heat Transfer in Fluids, or Heat Transfer in Porous Media selected: