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propylene glycol correction

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

RE: propylene glycol correction

FYI, the chart that I have for PG/W show roughly a 50% increase in viscosity between 60ºF and 45ºF.  

It's from Lyondell, labelled "Viscosity of Aqueous Propylene Glycol Solutions."

TTFN

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RE: propylene glycol correction

I'd look at density, not viscosity. The pitot tube equation only has density as a factor:

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

Did anyone have any tip for the percentage increase in friction loss if I use 50% Poprylene glycol instead of water.  This is for engine jacket water, so I figure that at the cold start the temperature would be around 32 def F and it would rise up to 210 deg F.  I search through lots of article, and i can only find that they refer back to darcy equation which is way too much.  Help is greatly appreciated.  Thanks.

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