glycol leak in closed-loop cooling system

[eyanardag]

Hi All

I'm investigating a slow but continuous leak (~5ml in 3 days) in a closed loop cooling system. The working fluid is polypropylene glycol.

There are no visible leaks, so I'm wondering if the coolant could be diffusing/evaporating through tubing elements which are all plastic. Some literature also seemed to suggest that glycol could react with some plastics and be absorbed by them.

Has anyone encountered a similar problem? I'd appreciate any direction to concentrate my efforts.

Thank you

 

[IRstuff]

Is this just a single measurement? How did you determine there was a loss? Is it the same from week to week?

TTFN

FAQ731-376

 

[eyanardag]

Thanks for the reply IRstuff. I've just started looking into this, but other people have been monitoring the system periodically. We monitor the coolant levels in the circulation tank and this has been a continuous problem.

 

[danw2]

what's the system capacity that you can detect a 5mL loss?

 

[eyanardag]

the circulation tank capacity is 200mL and I use a syringe to fill up to a mark.

 

[IRstuff]

But is it continuously losing 5 ml every 3 days, which means that it empties completely in 120 days?

Since this is an ongoing problem, you can rule out the plumbing, since it should either be saturated in absorption, and/or you'd be seeing glycol residue on the exterior of the hoses.

Of course, things are rarely truly "closed loop", since you need something to allow for thermal expansion.

What temperature range is the coolant exposed to?
How do you handle the boiloff, if any?

TTFN

FAQ731-376

 

[eyanardag]

IRstuff

Yes it would empty out if no one refills the system, but it hasn't been allowed to do so.

The tank isn't filled to the brim, which is supposed to account for the thermal expansion I think.

The system operates fairly tightly around 50C. I'm told the glycol content is there for antibacterial measures.

Would it be possible for small quantities of coolant to diffuse through the hoses and evaporate before detection? What would glycol resudue look like? I have seen some small white dots on the tubes, but was associating those with spills since they are close to hose ends. Maybe I will clean them up and see if they reappear.

thanks for your help

 

[IRstuff]

How well sealed is the tank?

TTFN

FAQ731-376

 

[IRstuff]

Can you check the specific gravity of the coolant and verify that it does, or does not, change as the coolant level drops?

50°C is quite warm, and if the solution is mostly water, you could lose quite a bit through evaporation.

TTFN

FAQ731-376

 

[eyanardag]

just a follow up for those who might encounter a smilar problem...

tests I'm running indicate that there is significant coolant loss through polyurathane tubing we have. In comparison, FEP tubing seems have no loss in the same arrangement.

 

[Whoops]

"... could be diffusing/evaporating through tubing elements which are all plastic."

Is it oxygen barrier tube?

Oxygen will permeate through the walls of non-barrier tube. The dissolved oxygen will react with hot glycol, producing acidic compounds. I don't know how hot it has to be, whether this would account for the loss of the liquid or what the products of the reaction are. The glycol manufacturers may be able to advise you. Glycol car coolant/antifreeze (usually ethylene glycol) should be changed every few years for this reason. The hoses allow the passage of some O2 and once the soluton becomes acidic, galvanic corrosion of the engine parts becomes very rapid.

A pH test might indicate whether there is problem.

FEP?