I have calculated the speed of sound for different fractions of water and steam at 10 Bar.a
with IAPWS 1995 model which is supposed to be very accurate,
software Prode Properties + Excel
the calc's are done in Excel,
in a cell I put the macro

=StrMSS(1)

which returns the speed of sound for vapor, liquid and vapor + liquid mixtures

for water at 453 K 10 Bar.a Prode Properties calculates 1392 m/s

for water (0.999 fraction) + steam (0.001 fraction) at 453.028 K 10 Bar.a Prode Properties calculates 9.73 m/s

for water (0.001 fraction) + steam (0.999 fraction) at 453.028 K 10 Bar.a Prode Properties calculates 470.55 m/s

for steam at 453.5 K 10 Bar.a Prode Properties calculates 501.58 m/s

I am surprised to see those very low values (9.73 m/s) for low values of vapor mass fraction,
I have some tabulated data which confirm the trend but still I am unable to understand the origin of phenomena, could you give some explanations?[/QUOTE]