# Interfaces¶

In CHT, interfaces define the relationship between the common boundaries of the Solid and Fluid regions. For these overlapping boundaries the user can define the Momentum and Thermal conditions as described below.

## Momentum Types¶

the Momentum types defines the velocity conditions at the interface. The two Momentum types available for the interfaces are the No-slip and Slip.

### No-Slip¶

The ‘no-slip’ option imposes a friction wall (or real wall) condition by setting the velocity components (tangential and normal) to Zero value at the interface i.e $$V_t=V_n=0$$

### Slip¶

The ‘slip’ option imposes a frictionless wall condition. In this case the tangential velocities at the interface are adjusted according to the flow conditions, while the normal component is Zero.

## Thermal Types¶

The Thermal types define the temperature conditions at the interface. The two Thermal types available for the interfaces are the Adiabatic and Coupled.

This option applies a fixed temperature value at the interface that is specified by the user. In this case thermal energy cannot be exchanged between the domains and this value is kept constant over the interface throughout the simulation. An example application is isolation case.

### Coupled¶

This option applies a mixed condition for temperature that is used for heat-transfer through the interfaces from one region to the other. It adjusts the temperature on the two coupled interfaces and specifies gradients to satisfy conservation equations on both sides.

Important

The Thermal typeCoupled‘ is the recommended choice for conjugate heat transfer between regions.

Note

If the user does not define any interface, then by default all the interface surfaces are assigned the No-Slip momentum type and Coupled thermal type condition. Similarly, if the user defines an interface for only some of the interface surfaces, the rest are by default assigned the No-Slip momentum type and Coupled thermal type.