SET_CONDITION

This command is available with the POLY and ED-EXP modules.

Specify the equilibrium conditions for the calculation. All kinds of state variables, as well as most of the M/W/V/F-suffixed state variables (for normalization) and R-suffixed state variables (with respect to chosen reference states), can be used as conditions. In addition to temperature and pressure conditions, a multicomponent system can have mixed types of conditions. You should repeat this command for a multicomponent system until the degree of freedom in the defined system becomes zero. When a FIXED phase status is used on a specific phase (use CHANGE_STATUS), it is equivalent to one condition (implying that particular phase is stable in the defined system).

Syntax

set_condition

 

Each condition must be given explicitly, but can be given on the same line (separated by a comma (,) or an empty space) or on separate lines with each one started with the command.

SET_COND T=1273, P=1E5, W(C)=.0015, X(LIQ,CR)=.22, ACR(N)=.2

or

SET_COND T=1273, P=1E5

SET_COND W(C)=.0015, X(LIQ,CR)=.22 ACR(N)=.2

In this example, the temperature is set to 1273 K, the pressure to 1 bar (1E5 Pascal), the mass (weight) fraction of C to 0.0015 and the mole fraction of Cr to 0.22 and the activity of N to 0.2.

Prompt

State variable expression: <State variable name or linear expression> or a linear expression of state variables.

Some of the state variables that can be used in conditions are:

  • T: temperature in the system (in K)
  • P: pressure in the system (in Pascal)
  • N: system size (mole number in moles)
  • B: system size (mass in grams)
  • N(<component>): mole number of a component in the system
  • X(<component>): mole fraction of a component in the system
  • W(<component>): weight fraction of a component in the system
  • For the SET_CONDITION command this is ACR(<component>): activity of a component in the system. For the SET-ALTERNATIVE_CONDITION command, this is ACR(<phase>,<component>) (activity of a component in a phase)
  • For the SET_CONDITION command this is MUR(<component>): chemical potential of a component in the system. For the SET-ALTERNATIVE_CONDITION command, this is MUR(<phase>,<component>) (chemical potential of a component in a phase)
  • X(<phase>,<component>): mole fraction of a component in a phase
  • W(<phase>,<component>): weight fraction of a component in a phase
  • ACR(<species>,<phase>): activity of a species referred to a phase
  • MUR(<species>,<phase>): chemical potential of a species referred to a phase
  • H: enthalpy in the system (in J)
  • HM(<phase>): enthalpy of a phase (in J/mol)

There are many state variables that can be used in conditions. For more information, enter an INFO STATE_VARIABLES command. A condition is normally a value of a single state variable with its value.

T=1273.15  P=1E5

X(C)=.002

W(CR)=0.5

ACR(CR)=0.85

X(FCC,C)=.001

H=-250000

HM(BCC)=-225000

A condition can also be a value of a linear expression involving more than one state variable. For example,

X(LIQ,S)-X(PYRR,S)=0

This means that it is a condition that the mole fraction of S component should be the same in the LIQUID and PYRRHOTITE phases. In practice, that should be the congruent melting point.

After the equal sign only a numeric value is allowed in the expression.
 

Factor: <A factor for the state variable, or a continuation>

This question means you did not answer the previous question. The program is then expecting a single state variable or a complete state variable expression, or the numeric factor in an expression with only one state variable. In a state variable expression a state variable may be preceded by a constant factor. An example of this is:

2*MUR(FE)+3*MUR(O)=-35000

This means that it should be a condition that two times the chemical potential of FE plus three times the chemical potential of O should be -35000 J/mol.
 

State variable: <A specified state variable, or a continuation>

This question is prompted if a single state variable name has not given in either the prompt State variable expression or Factor, or a state variable expression is given but the expression is incomplete, for example, T- or 2*MUR(FE)+, for which the program is then expecting a continuation of the unfinished expression. You need to specify a state variable or a complete state variable expression, or complete the unfinished state variable expression. If a numeric factor is given before this prompt, only one state variable can be specified; otherwise, the program only takes the first state variable to complete the expression (i.e. the factor times the state variable).
 

Value /X/: <A numeric value, a constant or a variable>

The value of the condition. This can be a numeric value, a constant or a variable. A suggestion is given as the default value. The special value NONE means that the condition is removed; for example T=NONE takes away the temperature condition.