Encyclopaedia Index

The PROPS file


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
The PROPS file may be inspected by clicking here.

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:

    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

    The arrangement is:


    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.

  3. How Earth interprets the entries in the table

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:

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:

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

Although the PROPS-file approach to the setting of material properties has been successfully employed for many years, it has the following limitations and drawbacks:
  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

In order to escape from these limitations, PHOENICS has been provided with two further methods of setting properties which are both more flexible and easier to use.

These are:

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.