The new DEVICE (v.5) introduces a new thermal solver (HEAT) along with the existing electrical solver (CHARGE). To accommodate the thermal fluids (gas or liquid) in thermal simulations, the material database now has a new type of material, “Fluid.”
In electrical simulation with the CHARGE solver, the Fluid-type material is considered to be an insulator and it is defined by its dielectric constant like the “Insulator” material type.
I thermal simulation with the HEAT solver, the Fluid-type material is defined by the thermal and physical properties of fluids (gas or liquid). The screenshot below shows the properties that need to be defined for a fluid in the material database. The thermal properties of the default “Air” material in the material database is shown here.
The way a fluid type material is used in a thermal simulation is through the material interface. The HEAT solver solves the heat transport in solid materials only and includes the effect of any surrounding fluids through convective boundary conditions defined at the material interfaces. For example, if you have air on top of your silicon waveguide and you want to want to simulate the heat loss due to convection in air, you will need to set up a convection boundary condition at the material interface between silicon and air. There are different models available for different types of convective boundary conditions.
Once the (fluid) material property and the interface boundary condition is defined, the solver solves the heat transport in the solid (neglecting the fluid) and applied the convective boundary condition at the solid-fluid interface.