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

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Discussion Overview

The discussion centers on the speed of sound in a 25% propylene glycol and 75% water mixture, particularly how it varies with temperature between 20°C and 40°C. Participants are exploring the implications of this variation for the accuracy of an ultrasonic transit-time flow meter calibrated for water.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant is seeking experimental data or estimates for the speed of sound in the propylene glycol-water mixture at specified temperatures, noting concerns about accuracy with the ultrasonic flow meter.
  • Another participant suggests checking the flow meter's calibration procedure and user manual, indicating the importance of establishing a calibration method for the new fluid.
  • A participant mentions using an Omega FTD-25 flowmeter and highlights the need for user inputs of sound velocity and viscosity when working with non-preset fluids.
  • There is a proposal to use an in-line electromagnetic flowmeter as a reference to back-calculate the sound velocity based on comparative readings.
  • Concerns are raised about the precision of the 25% glycol concentration and the need to calibrate for multiple factors, including temperature and indicated flow rate.
  • A participant provides links to scholarly articles on the speed of sound in propylene glycol, noting access limitations due to paywalls.

Areas of Agreement / Disagreement

Participants have not reached a consensus on the speed of sound in the mixture or the calibration methods. Multiple competing views and approaches to the problem remain evident.

Contextual Notes

Participants express uncertainty regarding the accuracy of the flow meter under varying conditions and the implications of the glycol concentration on measurements. The discussion includes references to external studies, but access to data is limited.

Who May Find This Useful

This discussion may be of interest to those working with ultrasonic flow meters, researchers studying fluid dynamics, and individuals involved in applications using propylene glycol-water mixtures.

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TL;DR
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!
 
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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.
 
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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.
 
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?
 

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