A Ultrasound Velocities in 25% Propylene Glycol + Water between 20-40C

[MMRite]

TL;DR Summary

I'm using a transit-time ultrasonic flow meter with water presets, but my fluid is 25% propylene glycol and 75% water. I need data on how the speed of sound in this mixture varies from ~20°C to 40°C to improve measurement accuracy. Any help or references would be appreciated!

Hi everyone, I'm working with an ultrasonic transit-time flow meter that has preset settings calibrated for water. However, my application involves a 25% propylene glycol and 75% water mixture, and I suspect the speed of sound in this mixture deviates enough from water to affect accuracy. I'm looking for experimental data or reliable estimates of how the speed of sound in this mixture changes with temperature (ideally from ~20°C to 40°C). If anyone has access to such data or knows of relevant studies, I’d really appreciate your help!

 

[.Scott]

The first thing I would check is whether you device has a calibration procedure.
What is the model number? Have you checked the user's manual?

Failing that, I would try to create a pre-measurements calibration procedure - one that you would use to set over the water presets.
Failing that, I would try to create a post-measurement calibration procedure.

 

[MMRite]

I’m using an Omega FTD-25 flowmeter. I’ve reviewed the user manual, and it doesn’t include a specific calibration procedure. However, it does mention that when working with a fluid not already preset in the device, it requires two user inputs: sound velocity and viscosity.

Since I couldn’t find reliable sound velocity data for my fluid (25% propylene glycol + water) at varying temperatures, I’m planning to use an in-line electromagnetic flowmeter as a reference. My idea is to compare the EM flowmeter’s readings with the ultrasonic meter’s transit time data to back-calculate the actual sound velocity in the fluid.

From what I understand, the flowmeter uses the sound speed and viscosity values primarily as a sanity check to ensure the readings it’s getting are physically plausible.

 

[.Scott]

That User's manual is pretty light on calibration information.
On page 17:

§3.12 How to get a scale factor for calibration: A scale factor is the ratio between the ‘actual flow rate’ and the indicated value by the flow meter. The scale factor can be determined by calibration with flow calibration equipment.

So, once you know how far off it is, there is a "scale" value that should allow you to get a roughly correct value reported.

Another issue is going to be how precise that "25%" is. You may need to calibrate for a total of three factors: actual glycol concentration (or other known variable that changes that concentration), temperature, and indicated flow rate.

That "scale" may only be useful in getting approximate flow rates out under the most typical conditions.

Which lead to a couple of other questions - how will that calibrated flow rate value be used? - and how accurate/precise does it need to be to fulfill that purpose?

 

[Baluncore]

Google scholar.
https://scholar.google.com.au/scholar?hl=en&as_sdt=0,5&q=speed+of+sound+in+propylene+glycol&oq=

Density, Speed of Sound, and Refractive Index of Aqueous Binary Mixtures of Some Glycol Ethers at T = 298.15 K
Paywall.
https://pubs.acs.org/doi/10.1021/je901072c