Viscosities

[TravisMack]

When calculating large anti-freeze solution systems (>40 gallons), does one need to consider the extreme daily minimum temperature, or the average daily minimum temperature?

On one particular project, AF sol'n at average daily minimum (20°F) is 30 psi under curve. At extreme daily minimum (-21°F), system is 100 psi over curve. A dry system is ~35 psi over the curve with pipe sizing to keep volumes under 750 gal capacity.

Which condition does one go with? The contract drawings state "layout and calculate per NFPA 13." RFI did not produce an answer. The AHJ is unsure. He thinks the extreme daily minimum may be excessive, but is doing his own research on the topic.

What does the collective here think?


Travis Mack
MFP Design, LLC

 

[stookeyfpe]

Travis

I'm having a hard time grasping this problem. Can you post a link for the anti-freeze solution?

Thanks,

 

[cdafd]

"daily minimum temperature, or the average daily minimum temperature?"

code says "expected daily minimum temperature for the locality"

so looks like you would go with expected and not average


if that is your question

http://www.bom.gov.au/climate/cdo/about/definitionstemp.shtml

OR:

Minimum Temperature
The daily minimum temperature is defined as the lowest temperature (in degrees F) measured at a station during the 24-hour period beginning at 0600 UTC. Official verification for the day is given at 0600 UTC the following day in the synoptic code information. The temperature error, E(Tmin), is scored in the same manner as is listed above.

http://www.met.fsu.edu/orgs/contest/score_howto.html

 

[TravisMack]

Stookey:

Here is the link for the solutions:

http://www.lyondell.com/lyondell/techlit/techlit/2514.pdf

The viscosity at 21F for a 50% solution is about 30 cps. The viscosity at -20F for the same solution is about 190 cps. The HydraCalc program I use for these calcs requires you to input the density of the solution and the viscosity at your temperature.

There is greater than a 100 psi swing in req'd pressures between the 2 values.

A reviewer got back to me. The average low temps are in the 20F range. The -20F is a record low set ~60 years ago. There has only been 20 days in the last 20 years where the temps are below 0F. I have been asked to provide calculations using viscosities for 0F. That appears to be a viscosity of around 65 cps. The system will work at that point.


Travis Mack
MFP Design, LLC

 

[firepe]

Travis,

Clearly you should use the worst case conditions.

Anything less is an ENGINEERING judgement/decision.

 

[TravisMack]

I am not making a judgment call at all. I am doing what those in charge have said to do. The local AHJ has said that he wanted me to use 0F for the viscosities.

Additionally, I had a response from NFSA that says to follow the diagrams in NFPA 13 A10.5.1 for the temperatures.

The information provided from NFSA coincides with the direction of the local AHJ. Therefore, the decision / judgment is not mine. It the AHJ would have said to use 0°K, I would have done that , not that anything would move at that temp I am not trying to pass the buck, just trying to get direction and opinions of how others would handle the situation, or may have done in the past.

Maybe all of the global warming guys are right and this would not be an issue at all

I am happy that some here have their FPE and are willing to provide helpful opinions. I thank those of you for that.

Travis Mack
MFP Design, LLC