When the flow solver needs to interpolate a value of 
at a given
temperature, 
, and pressure, 
, (for example, the
common calculation of 
) there are three possible regions for
the interpolation to happen: supercritical (point 1), vapor (point 2) and liquid
(point 3).
For any of these regions there are three possible interpolation options available in the flow solver available by setting the following expert parameter:
EXPERT PARAMETER: prop interp option = 1, 2, or 3 (default) END
Option 1 tells the flow solver to use no saturation clipping, option 2 always uses saturation clipping assuming that saturation data has been extended along the critical isotherm, and option 3 (Default) uses no saturation clipping above the critical pressure.
: Interpolation in the supercritical region
For this region there is a slight difference between option 2 and option 3 interpolation.
Option 2: Interpolation for vapors or liquids is performed the same as if the point were below the critical point.
Option 3: First, the solver checks if 
and 
. If this condition
is met, then the procedures given below are used. If not, then a standard bilinear
interpolation is used from the four table values that enclose the desired point.
This would correspond to point 1 on the figure.
: Vapor side interpolation below the critical point
Option 2 and option 3 are equivalent in this case.
If 
and 
then the flow solver detects if the interpolated value must be
clipped to the saturation value. This is done by first looking up the table location
where the value of 
is located and
then calculating 
and 
. If 
then the solver does not need to clip to saturation and standard
bilinear interpolation is used. If 
then the solver simply sets the interpolated value of
to 
.
: Liquid side interpolation below the critical point
Important:
For liquids the recipe is almost the same as for a vapor. First the solver looks
up the table location where the value of 
is located and
calculates 
and 
. If 
then the solver does not need to clip to saturation and standard
bilinear interpolation is used. If 
then the solver simply sets the interpolated value of
to 
.