The PROPS file

• Its nature
• Why it was created
• Its contents
• How PHOENICS users can modify it; the use of MATFLG
• Its limitations
• Better ways of introducing property-related information

The nature of the PROPS file

Some properties of some frequently-used materials are listed in a file called PROPS, residing in d_earth.

The properties are:-

1. the density, in kg/m**3
2. the kinematic viscosity, in m**2/s, or Poisson's Ratio (dimensionless) in the case of solids
3. the specific heat at constant pressure, in joules/(kg*degC)
4. the thermal conductivity, in watts/(m*degC)
5. the thermal expansion coefficient, in (degC)**(-1)
6. the compressibility, or the reciprocal of Young's Modulus in the case of solids, in m**2/Newton

Why the PROPS file was introduced

1. In the beginning

   When PHOENICS was first created, fluid flow was in the centre of attention. It was true that the fluids had to flow around and between solids; but these were at first regarded as mere obstacles.

   Their presence was acknowledged by assigning values to "porosity factors", indicating what proportions of the volume or surface areas of each computational cell were accessible to the fluid, namely by values of the variables: VPOR, NPOR, EPOR and HPOR.

   What went on within the solids was not considered; so the only material properties of interest were those of the fluid (or fluids if two-phase flows were in question).

2. When conjugate heat transfer became important

   Soon however attention had to be given to the temperature distributions within the solids, which thus became fully-participating parts of the domain of study; and their temperatures could be computed only by way of quantitative knowledge of their:

   • densities,
   • thermal conductivities and
   • specific heats

   Since these properties differ from material to material, and different cells were occupied by different materials, the idea arose of using a material marker variable, which was given the name PRPS, having a unique value for each material.

   The locations of the materials could thus be indicated by ascribing a PRPS value to each cell; and the there-prevailing material properties could then be deduced by consultation of a material-properties file.

   The PROPS file was created for precisely that purpose.

3. When stresses within solids had also to be computed

   What went on inside the solids became even more important when PHOENICS was taught how to compute the stresses within the solids simultaneously with their temperatures and with the velocities of the fluids around them.

   The compressibility location in the PROPS file then needed, for solids, to be occupied by the reciprocal of Young's Modulus; and the position by used by fluids for the viscosity could be occupied, for a solid, by the Poisson's Ratio.

Contents of the PROPS file

1. The properties table

   The main part of the table can be seen by clicking here.

   Evidently the table is arranged in row-and-column manner, with

   • seven columns, the first being for the material index, IMAT, and the remainder for the 6 allowable properties;
   • for each material at least two rows, of which one contains its name, and another, with the IMAT value on the left, contains either real numbers or GRNDx;
   • further rows containing real numbers, below any rows containing GRNDx; and
   • possibly other lines which are treated as comments because they contain blanks in the first two columns,

   The arrangement is:

   • gases at the top (IMAT from 0 to 39 );
   • then "anonymous" fluids (IMAT from 40 to 50)
   • liquids in the middle (IMAT from 51 to 99)
   • solids at the bottom (IMAT from 100 to 197)
   • two fictitious materials (IMAT = PORPRP and VACPRP).

2. SOLPRP, PORPRP and VACPRP

   In order to guide EARTH in its use of PROPS-file information, the above arrangement is reflected by the setting of the above three variables, in the first three active lines of the file.

   • SOLPRP, usually 100, which indicates the lowest IMAT which represents a solid. Fluids are always ascribed lower-than-SOLPRP values.
   • PORPRP, usually 198, which is the IMAT assigned to a fictitious solid which influences the flow process only by imposition of the no-fluid-slip condition at its boundaries.
   • VACPRP, usually 199, which is the IMAT assigned to a fictitious solid which prevents fluid from entering its space, but exerts no frictional effect.

3. How Earth interprets the entries in the table
   • As already mentioned, lines with blanks in columns 1 and 2 are treated as comment lines; blank lines are ignored.
   • Active lines are in free format, and contain 6 (or 7) entries (fields ).
   • Spaces or commas may be used as field separators.
   • Fields 2 - 7 may contain a constant, or one of the GRND1 - GRND9 flags.
   • Any property law available from GREX may be specified through PROPS.
     Thus:
     
     • when placed in the DENSity column:
       • GRND1 sets DENS=RHO1A + RHO1B*h1 , where h1 is the enthalpy
       • GRND2 sets DENS=1./( RHO1A + RHO1B*h1 )
       • GRND3 sets DENS=RHO1A * ( p1 + PRESS0 )**RHO1B + RHO1C
       • GRND4 sets DENS=RHO1A + RHO1B*t1, where t1 is temperature
       • GRND5 sets DENS=RHO1B * (p1+PRESS0) / t1 where p1 is pressure
       The values in the corresponding lines are therefore those of RHO1A, RHO1B and RHO1C, as appropriate.

     • When placed in the VISCosity column:
       • GRND1 sets VISC = ENULA + ENULB*t1 where t1 is phase-1 temp.
       • GRND2 sets VISC = ENULA + ENULB*t1 + ENULC*t1**2
       • GRND3 sets VISC = ENULA + ENULB*t1**ENULC.
       • GRND4 sets VISC = ENULA * (LGEN1)**(ENULB-1.0) / (2.0 * RHO)
       • GRND5 sets VISC = [ENULA + ENULB/SQRT(LGEN1)] / RHO
       • GRND6 sets VISC = ENULA*t1**1.5/((ENULB + t1)*RHO)

   • Any constants required must be specified on the following active lines, these constants having the same definitions as in the GREX formulae.
     Thus for density=GRND3 (Isentropic Gas Law), the constants have the same definitions as RHO1A, RHO1B and RHO1C for RHO1=GRND3.

   • If more than one property is variable, as indicated by GRNDx, the constants will be read in the order of field specification above.
     One additional active line will then be read for each variable property.

How users can modify the PROPS file, or make their own

Users can, if they wish, edit the props file held in d_earth. However, they are advised instead either to:

• create in their working directory a separate, props-like file of their own, having a unique 4-character name; or
• insert in their Q1 file the required property-defining lines.

In the former case, the Q1 file should set the PIL variable CSG10 to the name of the file to be read.

In the latter case, CSG10 must be set to 'Q1 '. Then EARTH will scan Q1 for a set of material properties at the beginning of a run.

The start of the property section is marked by the line which contains, starting in column 3 or beyond: MATFLG=T; NMAT=n .
Here n is the number of materials for which properties are to be read.

Both in separate files and in Q1's, comment lines and blank lines are allowed.

In Q1 files, lines of embedded PIL are allowed. Note however that:

• standard PIL arithmetic operations are NOT allowed in the property-definition lines.
• Users are not allowed to redefine existing materials; so the IMAT values which they use must differ from those of those already used in PROPS.

Examples of the use of the Q1 file to set properties are to be found in Library cases 502, 510, 511, 576 and 614 .

See the entry PRPS for details of how to use the property data stored in PROPS.

The limitations of the PROPS-file system

1. Only six properties are provided for.

2. They can be given only either:
   1. constant values, or
   2. the variations allowed by the rather few built-in coding sequences activated by the GRNDx values.

3. The PROPS-file lines of the second kind are impossible for a user to interpret without recourse to the documentation (and they are difficult to interpret even then).

Better ways of introducing property-related data

These are:

• PLANT and
• In-Form.

Both methods allow property formulae of arbitrary complexity to be supplied and interpreted.

PLANT, although powerful and economical, requires the use of a re-compilable version of PHOENICS. Therefore In-Form, which works with non-recompilable PHOENICS, is to be preferred.

In-Form can do much more than set properties; but its property-setting capabilities can be reviewed by clicking here and here.

wbs