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where f is a user defined free energy (SI unit: J/m3).

 

The expression for the external free energy must be manually

 

differentiated with respect to and then entered into the field labeled

Note

f . In most cases, the external free energy is zero.

 

 

Variables and Expressions

Unlike the level set method, the phase field method does not require expressions for the unit normal to the interface or smoothed delta functions, so they are not available for analysis. Variables that are defined are the chemical potential, which can be rewritten in terms of the dependent variable .

G = -------

2

and the surface tension force F G .

The mean curvature (1/m) of the interface can be computed by entering this expression:

G

= 2 1 + 1 – ---

Reference For the Phase Field Interface

1. P. Yue, C. Zhou, J.J. Feng, C.F. Ollivier-Gooch, and H.H. Hu, “Phase-field Simulations of Interfacial Dynamics in Viscoelastic Fluids Using Finite Elements with Adaptive Meshing,” J. Comp. Phys., vol. 219, pp. 47–67, 2006.

T H E O R Y F O R T H E P H A S E F I E L D I N T E R F A C E | 235

236 | C H A P T E R 7 : M A T H E M A T I C S , M O V I N G I N T E R F A C E B R A N C H

8

B u b b l y F l o w a n d M i x t u r e M o d e l B r a n c h e s

The fluid flow interfaces are grouped by type under the Fluid Flow main branch in the Model Wizard. This chapter discusses applications involving the Bubbly Flow and Mixture Model interfaces found under the Multiphase Flow branch (). The Mechanisms for Modeling Multiphase Flow helps to choose the best one to start with. Also see Multiphase FlowBranch for other multiphase flow interfaces.

In this chapter:

•The Bubbly Flow Interfaces

•The Mixture Model Interfaces

•Theory for the Bubbly Flow Interface

•Theory for the Mixture Model Interface

237

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