Interface Conditions

The Interface attributes for the Heat module are listed below. You can assign a specific independent Interface attribute to each Interface. You can specify the Interface type for a selected Interface under the Heat module in the Properties panel.

Conjugate Wall also has the option to include Heat Source, Radiation and the effect of small gaps (Contact Resistance).

The Conjugate Wall option uses a harmonic averaging of the effective Conductivity at the Interface. Conjugate Wall is the default at any Interface separating a liquid and solid. Harmonic averaging is required for accurate calculation of the heat flux between materials with different conductivities. The alternative to the Conjugate Wall option is the Default Interface option, in which the conductivity at the Interfaces between the cells uses a simpler linear average, as in the rest of the domain. This is not as accurate if there is a sharp change in conductivity across the Interface.

• Heat Source—The Heat Source option allows the introduction of a Heat Source at an Interface. You can add the Heat Source as an average Heat Source Per Area(Flux per Area) or Total Heat Source (total flux). The Heat Source that you add is distributed to either side of the Interface based on the respective thermal properties of the neighboring cells. You cannot use the Heat Source option at an Interface in conjunction with the Radiation option.

• Radiation—The radiative heat source is distributed to either side of the Interface based on the respective thermal properties of the neighboring cells. You cannot use the Heat Source or Contact Resistance at an Interface in conjunction with the Radiation option.

• Contact Resistance—The Contact Resistance option models the effect of a thin gap or layer of material at an Interface between two materials. You can specify the gap Thickness and the Conductivity of the material.

Contact Resistance is useful for including the effects of very small gaps between objects, without the expense or complication of a very fine mesh in between. The Contact Resistance only includes the effect of the conductivity across the thickness of the gap, and does not include the effect of any lateral conduction. The Conductivity in the gap is input in units of W/m-K and the Thickness in terms of meters (m). You cannot use the Contact Resistance at an Interface with the Radiation option.

The Default Interface is the default option for an Interface connecting similar materials. You can also elect this for the Interface between dissimilar materials.

For the Default Interface option, the conductivity at the Interfaces between the cells uses a simple linear average. It has the advantage of simplicity and speed, but is not accurate if there is a sharp change in Conductivity across the Interface. For such Interfaces, you should specify Conjugate Wall instead. Despite its name, the Default Interface is not always the default choice for the Interface between the cells. For example, the Interface between a solid and fluid is automatically set, by default, as a Conjugate Wall.