Documentation update

[fpepe-polito]

Because of the modifications to the source code and the new options that are being introduced, the documentation should be updated. This issue has been opened to store suggestions for documentation improvement and to track useful information that may be needed to use recently-introduced additional options and methods.

[fpepe-polito]

In issue #4, the possibility to add user-defined correlations in general form has been introduced. The user can now define a new material in the [Materials] section of the input file, and write down correlations for each property, in the form: <material_name> = <expression>. The parsing of the expression used for the correlation is performed by means of the library for symbolic mathematics sympy, thus the format of the expression must follow some rules in order not to have errors. In details:

• the mathematical expression must use the Python syntax for operations and functions. For example, using ** for powers, / for division, * for multiplication, and classical built-in functions like exp for exponentials, sqrt for square roots, and log for logarithms;
• correlations can only be functions of the temperature, expressed as T. Any other variable name (such as t, x, etc.) will raise an error.

[fpepe-polito]

In issue #11 checks on properties validity range have been introduced or better handled where already existent (lbh15 materials). Now, an error is raised in case the material is defined or updated at a temperature that is outside of the largest property validity range, while a warning is raised in case the temperature is above or below the validity range for a specific property, but still inside the largest one.
Moreover, in the documentation it must be specified that only 'default' properties (i.e. 'density', 'heat_capacity', 'viscosity', and 'thermal_conductivity') can be defined by the user. If another property is added, an error is raised. In case of user-defined tables for material properties interpolation, the first culumn must contain temperatures, otherwise an error is raised.

[fpepe-polito]

In issue #14, the possibility to choose whether to keep the properties radially uniform or not has been introduced. The documentation should be updated accordingly. In particular:

• the radially_isotropic_properties keyword should be added to the possible keys of the setup section in the user manual;
• new version of the energy equation with the conductive term evaluated at the interfaces of subchannels should be added to the theory manual.

[fpepe-polito]

In issue #17, the average heat capacity to be used in the energy balance calculation has been modified. It is now computed as the averaged heat capacity weighted on mass flow rates and temperature increases through all the cells of the computational domain:
$\bar{c_p} = \frac{1}{\dot{m}\Delta{T}} \sum_{n=1}^{N_{SLICE}}\sum_{i=1}^{N_{SC}}{\dot{m_i}c_{p,i,n}\Delta{T_{i,n}}}$
where: $\dot{m}$ is the total bundle mass flow rate, $\Delta{T}$ is the bulk temperature rive over the whole bundle, $\dot{m_i}$ is the i-th subchanell mass flow rate, $c_{p,i,n}$ is the i-th subchannel heat capacity at the n-th axial slice, $\Delta{T_{i,n}}$ is the temperature rise in the i-th subchannel at the n-th axial slice.
This term is then multiplied by the bulk terperature rise and the total bundle mass flow rate to get the energy balance.

[fpepe-polito]

Issue #21 introduced the possibility of solving the energy equation for enthalpy. The documentation should be updated accordingly. In particular:

• A new section should be added to the Theory Manual to describe the modified energy equation and its discretization.
• The new input file keyword, solve_enthalpy, in the [Setup] section should be noted in the User Manual.

[lelaus]

Issue #27 introduced a new solver targeting mixed convection regime. The documentation should be updated accordingly. In particular:

• A new section should be added to the Theory Manual to describe the newly introduced solver and its implementation;
• The new input file keywords and the cases in which to use the newly introduced solver should be noted in the User Manual.