propylene glycol correction

[mgmasc]

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

 

[IRstuff]

The viscosity of PG/W is highly dependent on temperature.

TTFN

FAQ731-376

 

[IRstuff]

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

FAQ731-376

 

[willard3]

Although this is a simple search for properties of propylene glycol, you didn't do it?

http://www.arttec.net/Solar/1-13-04/DowFrost_HD.pdf

 

[ChasBean1]

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

 

[IXITRUM]

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.