Several binary mixtures of gases have proven useful in thermoacoustic devices because of their improved Prandtl numbers and the option to adjust the resonance by changing the sound speed. DELTAE's fluid library contains two such mixtures: He-Ar and He-Xe. These fluids are specified by a string on a line after a segment's numerical parameters, as are other fluids, but the string contains a 5 character field that represents the fraction of helium in the mixture (for example, 0.981hexe or 0.889hear, containing 98.1% and 88.9% helium, respectively).
If all but the first of the fluids (in the BEGIN segment) are specified using sameas 0 statements, it is possible to use the helium fraction of the mixture as an iteration variable for resonance tuning. Simply select 0h from the (u)se menu option (it may instead be a plot variable, if you choose). In the .out file, the fluid written out will reflect the final concentration used.
Our equations for He-Xe properties are not valid for Xe fractions in excess of 0.5.