Discussion Forum

"How is the intended method to calculate thermal expansion of fluids or gases?"
...... is my whole question in short words

Someone asked this years ago, but no answer was registered.
see www.comsol.com/community/forums/general/thread/10927/


I attach some small COMSOL-Files and screenshots of my trials with a very simple model

Generally the "thermal expansion" is calculated by the "solid mechanics" node.
But I assume water is not really a solid mechanics material and some parameters for water lack the available parameters like thermal expansion coefficient (2.07e-2), Youngs modulus (2.09e9) and poisson number (0.5). That is in the moment I add the "solid mechanics" node, materials claim the lack.
So probably a different module is intended to calculate thermal expansion of fluids or gases.
But which one was intended to be used ??
("Fluid-solid -Interaction" sounds good from its name, but is placed in the "Fluid flow" module and it does not seem to be suiable.)

Nevertheless I tried to calculate the fluid expansion by adding the lacking parameters manually and model its expansion.

Geometry: A cylinder
Material: Water
Physics: "Heat transfer in solids" with included "heat transfer in fluids" and "boundary heat source"
Physics: "Solid mechanics"
Multiphysics: "Temperature Coupling" and "Thermal Expansion"
Study: "Time dependend"

I get an error message:
Undefined value found.
- Detail: Undefined value found in the stiffness matrix.
There are 1678 equations giving NaN/Inf in the matrix rows for the variable comp1.u.
at coordinates: (-0.0955014,-0.029656,0), (-0.0895277,-0.044551,0), (-0.0812485,-0.0582982,0), (-0.1,0,0), (-0.098869,-0.0149976,0), ...
There are 1678 equations giving NaN/Inf in the matrix rows for the variable comp1.v.
at coordinates: (-0.0955014,-0.029656,0), (-0.0895277,-0.044551,0), (-0.0812485,-0.0582982,0), (-0.1,0,0), (-0.098869,-0.0149976,0), ...
There are 1678 equations giving NaN/Inf in the matrix rows for the variable comp1.w.
at coordinates: (-0.0955014,-0.029656,0), (-0.0895277,-0.044551,0), (-0.0812485,-0.0582982,0), (-0.1,0,0), (-0.098869,-0.0149976,0), ...
and similarly for the degrees of freedom, NaN/Inf in the matrix columns.