Conjugate Heat Transfer (CHT) Capability

This summarizes the design and details of the conjugate heat transfer capabilities with the linear finite volume system through the SIMPLE executioner.

This capability is activated by specifying a boundary on the "cht_interfaces" parameter. Other cht-related parameters can control the iteration between the solid and fluid energy equations. Once the capability is activated it will check if the used boundary conditions are compatible or not. In general, we introduced CHT versions of common boundary conditions such as LinearFVRobinCHTBC and LinearFVDirichletCHTBC that are dedicated for CHT applications.

For coupling purposes several new functors are created under the hood:

  • heat_flux_to_solid_* (where * is the interface boundary name),

  • heat_flux_to_fluid_* (where * is the interface boundary name),

  • interface_temperature_solid_* (where * is the interface boundary name),

  • interface_temperature_fluid_* (where * is the interface boundary name),

where the first two describe the heat flux from one domain to the other, while the other express the interface temperatures from both sides.

Energy Conservation Equations

The energy conservation equations for fluid and solid domains are:

Where and are the fluid and solid specific enthalpies, and are the thermal conductivities, and and are the external heat sources.

Boundary Conditions

The coupling of the solid and fluid domains is done through boundary conditions that ensure:

  1. Continuity of Interface Temperature**

  2. Continuity of Conductive Flux at the Interface**

Coupling Methods

The methods currently recommended for CHT utilize LinearFVDirichletCHTBC and LinearFVRobinCHTBC in the two different ways listed below. The Robin BC can also emulate a Neumann BC by setting the "h" parameter to 0.

  • Neumann-Dirichlet Coupling

1:  function NeumannDirichletCoupling
2:       Initialize ,
3:       while Convergence criteria not met do
4:            1. Solve fluid equation
5:            2. Update heat flux from fluid to solid
6:            3. Solve solid equation
7:            4. Update boundary temperature
8:       end while
9:  end function

  • Robin-Robin Coupling

1:  function RobinRobinCoupling
2:       Initialize ,
3:       while Convergence criteria not met do
4:            1. Solve fluid equation with Robin boundary condition using and
5:            2. Update wall temperature
6:            3. Update heat flux
7:            4. Solve solid equation with Robin boundary condition using and
8:            5. Update wall temperature
9:            6. Update heat flux
10:       end while
11:  end function

The Robin-Robin method introduces virtual heat transfer coefficients and to enhance stability and convergence.