Propylene Glycol 5% or 20%

Hi All,

I am busy with a secondary circuit that utlises propylene glycol (PG) - at present the piping material is Copper (but I'm thinking also of Steel).

For effciency, the PG is only require at 5% (of volume) as the supply temperature is only -1oC (-1 deg C).

However, I have been advised that 5% is too little and I should use 20% mixture.

The main reason given to me was corrosion.

Can anyone elaborate this further.

Thanks

Ahhh,

Whoever advised you about the 20% min is mixing apples and pears.

Quite a few of the suppliers of Glycol is mixing it with inhibitors, thus for the inhibitor mix to be strong enough you will need >20% in your system.

You can buy the inhibitor separately and use whatever Glycol mixture is optimal for your application.

Quote:

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Originally Posted by samiam

Hi All,

I am busy with a secondary circuit that utlises propylene glycol (PG) - at present the piping material is Copper (but I'm thinking also of Steel).

For effciency, the PG is only require at 5% (of volume) as the supply temperature is only -1oC (-1 deg C).

However, I have been advised that 5% is too little and I should use 20% mixture.

The main reason given to me was corrosion.

Can anyone elaborate this further.

Thanks

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Viking's advice is good.
I am also led to believe that the higher the glycol content the higher the viscosity. Therefore more duty is required for the same Temperature outputs.
Manufacturers usually have a glycol % table in relation to Chilled water temps.
So getting and maintaining concentrations is quite important and not allways checked!
Grizzlyhttp://www.refrigeration-engineer.co...ons/icon14.gif

Samiam,

1] 10% PG mixture has freezing point of -2.7degC & density 1013kg/m3.
2] 20% PG mixture has freezing point of -7degC & density 1025kg/m3.

thus, corrosion to our design at such mixing percentage is vital.

you should consider deeply the PG% because the last thing you want is freezing inside your heat exchnager.

I am not an expert, but have some knowledge on PG%.
One thing to consider is the weather at your location. If the outside temp is below the the freezing point of your solution, and you stop circulating, any outside components can freeze. The same can happen if you have a power failure.
Higher concentrations will carry less heat away and are less efficent.
One reason to keep the % high is to protect the system from biological growth. As I recall this is about 25% for PG. I may be off on this.
I recall one system. which I mentioned before on this forum, which stopped working one day. It used Ethylene Glycol (Automotive Antifreeze, not recommended) to chill molds for plastic bottles. My tipoff was when I noticed the deep green color. I asked if they had recently added antifreeze. They showed me a pile of empty jugs.
I added several gallons of water and function returned immediately. The same prinicipal applys to PG. Charts are available on the net.

Hi Gents,

Thanks for the feedback - I will invetsigaet further the inhibitors required that could cause corrosion.

Thanks

Quote:

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Originally Posted by samiam

Hi Gents,

Thanks for the feedback - I will invetsigaet further the inhibitors required that could cause corrosion.

Thanks

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Hmmm,

Me thinks you are better off looking for inhibitors that prevents corrosion.

:)
:D

Hi Samiam,

Its worth considering the evaporating temperature of the refrigerant in deciding the % vol required.

Assuming the leaving water temperature to be -1 deg c, the refrigerant within the heat exchanger will be less, in the region of -6 deg / -8deg.

To avoid spot freezing in the exchanger, calculate the % vol of glycol to be at least this point. A saftey margin is advisable.

Billy Ray