Contact Time Model Reference

The Contact Time phase interaction model estimates how long two VOF phases have been in contact with each other. A typical application is estimating the probability of surface reactions such as oxidation. The transported quantity is the contact area multiplied by the contact time.

Table 1. Contact Time Model Reference
Provided By [phase interaction] > Models > Optional Models
Example Node Path [phase interaction] > Models > Contact Time
Requires

A VOF Multiphase simulation.

A phase interaction with the VOF-VOF Phase Interaction model activated.

In the Phase Interaction Model Selection dialog:

  • Optional Models: Contact Time
Properties Key properties are: Convection, Min Volume Fraction, Min Interface Fraction.

See Contact Time Model Properties.

Activates Model Controls (child nodes) See Contact Time Condition.
Field Functions See Field Functions.

Contact Time Model Properties

Convection
Specifies a convection.
  • 1st-order

    Selects the first-order convection.

  • 2nd-order

    Selects the second-order convection.

Min. Volume Fraction
Time is accumulated only if the volume fraction of the host phase exceeds the specified threshold.
Min. Interface Fraction
Contact time is computed only when interfacial area exceeds the specified fraction of the cube root of the cell volume.

Contact Time Condition

You specify the contact time condition as a scalar profile. Contact time is accumulated where both phases are in contact and the selected profile method returns a nonzero value.

For example, if you want to determine the contact time between an air and a melt phase when the melt phase is in the liquid state, you can use a field function defined as:

($SolidVolumeFractionMelt < 1) 1 : 0.

Once the solid volume fraction of the melt reaches unity in the simulation, the field function returns zero and the contact time area stops accumulating.

A transport equation is solved to accumulate Contact Time Area, which is the Contact Area multiplied with the Contact Time of the phase.

Field Functions

Contact Area of Phase
The contact area of the phase.
Contact Time Area of Phase
The contact area multiplied by the contact time of the phase.
Contact Time of Phase
The contact time of the phase, which equals Contact Time Area divided by Contact Area.

This is only an approximation of the actual contact time; its accuracy depends on the simulation. For example, consider a fluid rising in a vertical tube that has a decreasing cross-sectional area. When the area is initially large, the contact area multiplied by contact time is also large. At the end, the free surface of the fluid reaches the height with a small cross-sectional area. If the accumulated value of contact area multiplied by contact time is divided by the recent smaller cross-sectional area, the calculated contact time can exceed the simulation time.