One of the program's most powerful features for thermal analysis is its ability to analyze phase change problems, such as a melting or solidifying process. Some of the applications for phase change analysis include:
The casting of metals, to determine such characteristics as the temperature distribution at different points during the phase change, length of time for the phase change to occur, thermal efficiency of the mold, etc.
Production of alloys, where chemical differences instead of physical differences cause the phase change.
Heat treatment problems.
To analyze a phase change problem, you perform a nonlinear transient thermal analysis. The only differences between linear and nonlinear transient analyses are that, in nonlinear analyses:
You need to account for the latent heat, which is heat energy that the system stores or releases during a phase change. To account for latent heat, define the enthalpy of the material as a function of temperature (see below):
Enthalpy, which has units of heat/volume, is the integral of density times specific heat with respect to temperature:
H = 
pc(T)dT
In nonlinear analysis, you must specify a small enough integration time step for the solution. Also, turn on automatic time stepping so that the program can adjust the time step before, during, and after the phase change.
Use lower-order thermal elements, such as PLANE55 or SOLID70. If you have to use higher-order elements, choose the diagonalized specific heat matrix option using the appropriate element KEYOPT. (This is the default for most lower-order elements.)
You may find the line search option helpful in phase change analyses. To exercise the line search option, use the LNSRCH command.