Ultrasound velocities in h20/propylene glycol mixtures

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Discussion Overview

The discussion revolves around the measurement of ultrasound velocities in mixtures of water and propylene glycol, exploring the observed bell curve relationship between the percentage of propylene glycol and the speed of ultrasound waves. The context includes experimental results and implications for designing ultrasound equipment.

Discussion Character

  • Experimental/applied
  • Technical explanation

Main Points Raised

  • One participant observed that the velocity of ultrasound waves increased with the addition of propylene glycol until reaching a 50% mixture, after which the velocity decreased, resembling a bell curve.
  • Another participant noted that the non-linear relationship between density and concentration in aqueous solutions could explain the observed behavior of ultrasound speed, suggesting that other properties like bulk modulus may also exhibit non-linear dependence on concentration.
  • A participant inquired about the units of measurement on the y-axis of the graph, confirming they were in mm/μs.
  • One participant suggested measuring the density of the solutions at various concentrations to distinguish the effects of density from changes in elastic properties.
  • The goal of the measurements was clarified as being related to designing an ultrasound camera acoustic lens set for non-destructive testing in cold weather, highlighting the importance of understanding how the mixture affects the index of refraction for ultrasound lenses.

Areas of Agreement / Disagreement

Participants generally agree on the observed trend of ultrasound velocity with varying concentrations of propylene glycol, but there are differing views on the underlying reasons for this behavior, and the discussion remains unresolved regarding the specific mechanisms at play.

Contextual Notes

Participants noted the non-linear behavior of density and other properties but did not resolve the implications of these observations on the ultrasound velocity measurements.

gosatomnadzor
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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?
 

Attachments

  • U-S VELOCITY V. PROPGLYC PERCENT.png
    U-S VELOCITY V. PROPGLYC PERCENT.png
    3.6 KB · Views: 1,414
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gosatomnadzor said:
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.
 
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
 
Here are the actual results and graph - attached

I appreciate the replies
 

Attachments

  • prop glycol and water u-s velocities.jpg
    prop glycol and water u-s velocities.jpg
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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?
 
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
 

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