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Temperature-Dependent Material Properties

This article highlights developments to be released in FLOW-3D version 9.4.

The Users Have Spoken

Thermophysical properties of some fluids and solids vary significantly with temperature. Taking into account this behavior is important for obtaining accurate numerical solutions. Version 9.4 of FLOW-3D allows users to define these properties as a function of temperature in a tabular form.

This new development follows years of mild resistance from the developers at Flow Science. The main reason for this reluctance was the belief that uncertainties in measuring material properties at different temperatures, especially at elevated values, and also uncertainty associated with numerical approximations, did not justify the effort and would only add an unnecessary complication to the user's modeling headaches. The ability to define separate (constant) properties for liquid and solid phases of alloys was the only variable property model available.

However, significant improvements in FLOW-3D's modeling capabilities, as well as in the accuracy of experimental data acquisition in the past few years, made this limitation a weak link in the code. As a result, and in response to persistent pressure from users, this capability is now available. Almost all properties of fluid and geometry components, including the fluid/solid heat transfer coefficients, can now be defined as a function of temperature. The data can be entered either directly into the material database or into the simulation setup file (shown below) and later saved to the database. Viscosity can also be defined as a function of strain rate using tabular data.

Temperature-Thermal Conductivity
Enter data into the simulation setup file (shown above), or directly into the material database.

Using Tabular Data

The material database has been redesigned accordingly. Specifically, each material is now represented by its own file. The tabular data can be loaded from or saved to and edited in the database. When loaded into a simulation, the data is transferred to the prepin file for better portability of the simulation files. The Fluids and Meshing & Geometry tabs of the GUI have also been modified to allow for easier modification and display of the tabular property data. In the initial release of version 9.4, specific heats of fluid #1 and #2 cannot vary with temperature. We plan to remove this limitation in a patch release. The ability to use constant properties has been retained and users can continue using input files created by previous versions of FLOW-3D.