Ultrasound velocities in h20/propylene glycol mixtures

[gosatomnadzor]

I started with a 100% water sample, and measured the speed of ultrasound using 1MHz transducer, and in 10% increments added propylene glycol to the sample fixture until I reached 100% propylene glycol.

Curiously, the velocity of ultrasound waves when plotted against % propylene glycol resembled a bell curve with the peak velocity at a mixture of 50% propylene glycol / 50% water mixture. See picture attached for graph. Does anyone have an explanation why the velocity increases until 50-50 mixture, then tails off as % propylene glycol increases?

 

[nasu]

I started with a 100% water sample, and measured the speed of ultrasound using 1MHz transducer, and in 10% increments added propylene glycol to the sample fixture until I reached 100% propylene glycol.

Curiously, the velocity of ultrasound waves when plotted against % propylene glycol resembled a bell curve with the peak velocity at a mixture of 50% propylene glycol / 50% water mixture. See picture attached for graph. Does anyone have an explanation why the velocity increases until 50-50 mixture, then tails off as % propylene glycol increases?

I don't have an explanation for the specific values but it is not a surprising behavior.
It is known that the density of aqueous solutions is not a linear function of density.
Other properties (including bulk modulus) may have similar non-linear behavior.
So the speed of sound may may have various non-linear dependence on concentration.
By the way, what are the units on your y axis?
The speed in pure water is around 1500 m/s or 1.5 mm/μs.

 

[gosatomnadzor]

Nasu,

thank you for info, y-axis units are mm/μs,
I'll stick the real curve in for your info later, last night I was trying to go from my own recollection of the curve I generated in my lab.

GosAtomNadzor

 

[gosatomnadzor]

Here are the actual results and graph - attached

I appreciate the replies

 

[nasu]

Thank you for sharing your data.
The values look OK. If you could measure the density of the solution at these concentrations then you could separate the effect of density variation from changes in elastic properties.
What is the goal of your measurements?

 

[gosatomnadzor]

Nasu,
the goal of our measurements is to design an ultrasound camera acoustic lens set for use in cold weather pipe corrosion non-destructive ultrasound measurements. going from pure water to a mix of h20/propylene glycol changes indexes of refraction for ultrasound lenses as the velocity of ultrasound changes.

thanks
G.A.N