propylene glycol correction
propylene glycol correction
(OP)
Our testing found the the freezing point of the prop/water mixture was -15F. From the chart found on the net below the mixture is approximately 46% prop/ 54% water
Freezing Point
Propylene Glycol Solution
(% by mass) 30 40 50 60
Temperature 7 -8 -29 -55
The operating temperature of the mixture is 45 deg F. The application is an air cooled chiller. The system as installed did not have a flow measuring device installed in the piping. During a recent shutdown a nexus twin-tube pitot
was installed in a nice straight run of 3" pipe.
http://www.nexusvalve.com/productDocuments/TwinTube_Pitot.pdf
Our testing indicated that the pressure drop across the twin tube was 8" wc. In the flow chart provided in the link below the flow for a 3" twin tube w/ an 8" delta P is 100 GPM based on water at 60 deg F.
http://www.nexusvalve.com/productDocuments/Nextrol-Flow-Chart.pdf
Question:
1)What is the correction factor for the flow rate of mixture based on the data given above?
2) If there is a "layman's version" of the criteria that are used to develop the correction factor, I'd be interesting in hearing it.
Thanks
Mark
Freezing Point
Propylene Glycol Solution
(% by mass) 30 40 50 60
Temperature 7 -8 -29 -55
The operating temperature of the mixture is 45 deg F. The application is an air cooled chiller. The system as installed did not have a flow measuring device installed in the piping. During a recent shutdown a nexus twin-tube pitot
was installed in a nice straight run of 3" pipe.
http://www.nexusvalve.com/productDocuments/TwinTube_Pitot.pdf
Our testing indicated that the pressure drop across the twin tube was 8" wc. In the flow chart provided in the link below the flow for a 3" twin tube w/ an 8" delta P is 100 GPM based on water at 60 deg F.
http://www.nexusvalve.com/productDocuments/Nextrol-Flow-Chart.pdf
Question:
1)What is the correction factor for the flow rate of mixture based on the data given above?
2) If there is a "layman's version" of the criteria that are used to develop the correction factor, I'd be interesting in hearing it.
Thanks
Mark





RE: propylene glycol correction
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: propylene glycol correction
It's from Lyondell, labelled "Viscosity of Aqueous Propylene Glycol Solutions."
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: propylene glycol correction
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RE: propylene glycol correction
V = (2 * DP / rho)^.5
V is velocity pressure, rho is density.
It looks like your mix is around ~43-44% range. Density of water at 60°F is 1000 kg/m3; density of your mix is about 1045 kg/m3.
So your density is about 4½ percent higher making the velocity pressure you read 2.1% lower. So correct UP your 100 gpm flow rate by 2.1%, or 2.1 gpm (this difference would probably be too fine to do on the chart).
For mass flow, I believe it would then be compounded because it is rho * area * velocity. Taking density into account again here would make the mass flow an additional 4.5% higher.
I believe this is correct without over thinking it... hopefully it helps.
-CB
RE: propylene glycol correction