# Coolant Channel

The effect of the coolant on the heat transfer at the exterior cladding surface can be modeled using the `CoolantChannel`

feature.

The presence of some input parameters causes others to be ignored.

The following parameters are given precedence over settings in the input file:

**Heat Transfer Coefficients**: If _heat_transfer_coefficient_ is given, its value will be assigned to the given boundary. All other parameters related to the heat transfer coefficient calculation are ignored.**Enthalpy**: If`coupledEnthalpy`

is present, the value of that parameter will be used for enthalpy. Otherwise, the heat flux is calculated based on`linear_heat_rate`

, specification of`number_axial_zone`

, and specification of`heat_flux`

, in highest precedence order. The integrated heat flux is computed based on the same precedence.As an example, if

`number_axial_zone`

and`heat_flux`

are specified,`heat_flux`

will be ignored.These are used as inputs to the heat transfer coefficient correlations.

### Coolant Material

The `coolant_material`

is water by default. It can be instead set to sodium. The default heat transfer correlation is the modified Schad correlation for liquid sodium in a triangular subchannel. The Lyon's Law correlation and Seban-Shimazaki correlation for flow within a tube are available as well. With sodium coolant chosen, calculations for phase change are disabled. By default, the subchannel geometry is set to triangular if the user selects sodium coolant, but this can be changed to a square channel if desired. Other subchannel geometries are forced if `flow_area`

, `hydraulic_diameter`

, `heated_perimeter`

, and `heated_diameter`

are all provided. The modified Schad correlation always requires the rod diameter and pitch to be provided.