You may need to model a vacuum condition, such as in a space (orbital) environment. In a vacuum, the viscosity and thermal conductivity properties should approach zero. Due to the solver stability concerns, we cannot assign zero to any of these material properties, but we can get close. For a fluid material, you have to do it indirectly through viscosity, density, specific heat capacity and Prandtl number. Fluid conductivity is defined as:
You should also set the gravity to zero to avoid any natural convection. Assign the ambient temperature as the initial temperature and other surface boundary conditions accordingly. In our testing, fixed temperature boundary conditions may have more stability than heat flux based conditions.
There are multiple solver types that can be used to simulate this scenario in SimScale. For more information on specific solver settings, please see the following public project: