Anti-Freeze Question 2

[reidh]

Does anybody know where I can obtain the curve for pressure vs. boiling temperature of ethylene glycol at various concentrations? I am trying to determine the effect that putting a higher-pressure cap will have on the system's cooling capacity.

Thanks You.

-Reidh

 

[patprimmer]

Try searching ethylene glycol to find a manufacturer.

The manufacturer will most likely be a very large multinational petrochemical company.

They will probably have the info on their web site.

Regards

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[reidh]

Perhaps I am not looking in the right places, but I have checked Dow's website (per a previous suggestion on this forum) as well as Prestone, Peak, and Rotella's website without finding this information.

I always attempt to do my due dilligence before posting so as not to waste other's time.

Thank you.

-Reidh

 

[patprimmer]

If they do not have it, I don't know where else to look.

You could always set up a pressure cooker and a thermometer, a pressure gauge, and an adjustable pressure relief valve, then read the pressure and temperature as the valve cracked for various loads on the valve. A few points should soon make a curve obvious.

A bit of a hassle, but maybe quicker than further searches.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[reidh]

I may just have to try that.

If I can make time to set up that experiment, I will post the results here once I have completed.

Thanks again.

-Reidh

 

[TheBlacksmith]

Quick and nasty - get a raditor testor, most of them are marked with both the freezing point and the boiling point (usually referenced to a 15# radiator cap). While it may not tell you the concentration, most manufacturers do, so for example, the infamous 50/50 should, if I remember should yield a freezing point of -34F and a boiling point of +253 with a 15# cap. But you get the idea. I think for most usuable concentrations, maybe from 70/30 to about 30/70, the boiling point is rather linear with pressure.

 

[NCShane]

The pressure has much more effect on boiling point than the glycol.

From Bosch handbook:
glycol %by vol. Boiling Pt. deg. C
0 100
10 101
20 102
30 104
40 106
50 108

Pressure effect (H2O only)
PSI Boiling Pt. deg. C
14.7 100
17.8 107
22.1 116
26 124
30 132
35 142
39.4 152

 

[swall]

Ah yes, the good old Bosch Handbook. When all else fails.

 

[reidh]

Thanks NCShane.

I am curious if I can extrapolate between these two tables? That is, if a 50% mix of water/coolant yields an 8% gain in boiling temperature, can I assume for example that at 22.1 inches of H2O the boiling point is approximately 125 C (116*1.08) for a 50/50 mix?

-Reidh

 

[IceStationZebra]

I have always wanted a nice chart with different glycol ratios and pressures vs freeze/boil performance but have never found one after MANY hours of searching the net. But I have pieced together some bits of info.

Here are two good charts that show boil and freeze performance with a 14-15psi cap. (Note that manufacturers do not recommend >70% glycol)

As for the pressure relationship, I have seen values from 0.5-3.25°F increase in the boiling point for every psi increase. Most are in the 2.5-3.25 range, but unfortunately none of them specified the exact conditions (H2O only, ethylene glycol/water mix, etc) A good rule of thumb seems to be ~3°F/psi.

Hope this helps. IceStationZebra

 

[IceStationZebra]

I also found this bit on the Stewart Components web site.
--------------------------------------------------
Radiator Caps: In a cooling system, a higher pressure equates to a higher boiling point for the coolant. Higher coolant pressures also transfer heat from the cylinder heads more efficiently. We recommend using a radiator cap with the highest pressure rating that the radiator is designed to accept. In general, performance radiators will accept 22-24 PSI, and professional racing radiators will accept a 29-31 PSI.

The coolant will typically only build to 16-18 PSI, due to expansion up to 200°F. However, if the engine does overheat due to external factors, the pressure inside the cooling system could reach as high as 28 PSI. Once the radiator cap has opened and vented coolant, the engine will not cool down until it has been turned off. The radiator cap is basically a "safety valve", so always use the highest pressure radiator cap that the radiator will tolerate. If you are unsure of the pressure rating for your radiator, check with the manufacturer for the maximum recommended operating pressure.
-----------------------------------------------------
Summary
1. Higher pressure will help increase your boiling point as long as the cap doesn't open.
2. A higher pressure can not decrease your operating temp - provided your not currently experiencing boiling over
3. Most sites seem to indicate that the radiator is the weak link, though I would also be worried about the hose connections.

 

[dcasto]

for 50% EG by weight, here are the boiling points at different pressures

PSIG DEG F
0 224
1 228
2 231
3 234
4 237
5 240
6 243
8 248
10 253
12 258
14 262
16 266
18 270
20 274
22 277
24 280
25 282

 

[IceStationZebra]

dcasto - thanks for the info. Where did you find it?

Also, a couple more points
1. I noticed that the first chart has a slight error. The red line should start at 32deg-F with a 0% propylene glycol concentration (i.e. 100% water).

2. If you are working with a diesel engine with wet liners, higher pressure should help suppress the localized boiling and resulting cavitation erosion.

3. FYI - Water has a higher specific heat than an ethylene glycol or propylene glycol coolant mix. Therefore, it provides the best heat transfer performance in a cooling system. Glycol solutions are used to raise the boiling point (especially important for water pockets around the exhaust valves), provide anti-freeze protection, corrosion inhibitors to protect the metals in the cooling system, and a lubricant for the water pump. In terms of the relative heat transfer performance of ethylene glycol versus propylene glycol coolant bases, they are pretty much equal when mixes according to the manufacturers’ recommendations, usually a 50/50 water to glycol mix. Ethylene glycol coolant solutions provide slightly higher heat transfer performance over propylene glycol solutions at low coolant flow rates.
So....
- For maximum heat transfer performance in non-freezing climates (or racing) use water as a coolant with an additive to provide a corrosion inhibitor and water pump lubricant.
- For street vehicles use 30-50% ethylene glycol depending on lowest expected temperature. >30% will provided the needed corrosion protection and water pump lubrication. If a cooling system is marginal, only overheating on the hottest of days or while towing, increasing the proportion of water in the coolant or running straight water with an additive during the summer may solve the problem. Remember to run a standard 50/50 solution during the rest of the year.
- For extreme winter service use a 50-70% ethylene glycol coolant solution. Remember that the lower percentage of water will reduce the cooling capacity during warm weather.

IceStationZebra

 

[patprimmer]

Although glycols have a lower specific heat which lowers the heat transfer performance at a given temperature and flow rate, the increased boiling temperature allows the engine to run at a higher coolant temperature. this increases the heat transfer of the radiator due to the greater temperature difference between the air and the coolant, but decreases the heat transfer at the cylinder and cylinder head due to the lower temperature difference between the metal and the at the coolant.

This means a higher coolant temperature, but more boil over protection. A very slight power and fuel economy improvement might be a side benefit as the engine will have slightly better thermal efficiency.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dcasto]

I cheated, I used my chemical plant similation program that has a databases for thousands of chemicals.

 

[IceStationZebra]

Good points Pat.

I was trying to reason in my head if there is an optimum coolant ratio for the best cooling - but my educated guess is that it depends on several variables. Its a balance between boiling point and heat transfer. I suspect the NASCAR boys run a 29-31psi cap to get a higher boiling point while running mostly water. On one coolant supplier's web site (I forget which) they were touting their super racing "coolant" which was really just an anti-corrosion/lubricant package - it didn't even affect the freeze point!

ICZ

 

[dcasto]

IceStationZebra, Interesting, race cars wouldn't need the freeze depresion of regular cars. As a Toyota affection-auto, I see where most tuned Supra owners use "water-wet". I've loked at some sight trying to fiquire out what the magic stuff is, I'd gues a silcon based surfactant that won't allow any micro-boiling and loss of heat transfer right on the skin layer of the metal. If you know any more about that it might help with heat transfer problems and maybe we could find the generic version for 25% of the cost of the branded stuff.

 

[NickE]

water-wetter from redline is a lube, corrosion inhibitor, and surfactant.

I think it works. By lowering the surface tension, this should allow an infentesmal amount of better contact btw the coolant and the surfaces inside the cooling system. Hence incresing the heat transfer by conduction.

It made my daily driver coolant, (50/50 premix), get kinda gunky after 30,000mi. I quit using it.

Note the second paragraph is just a SWAG, it might mean nothing.

nick

 

[patprimmer]

Nick

I think you are correct.

Better heat transfer allows more cooling of the coolant in the radiator, but causes more heat to be transfered from the head and block. Result, similar final coolant temperature, but lower thermodynamic efficiency of the engine.

Just as well it makes negligible difference as water already has very good heat transfer.

Corrosion inhibitor and lubrication are certainly worthwhile attributes.

Regards

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Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[mcroadracer]

How about 100% propylene glycol or a propylene glycol/ethylene glycol mix as a coolant. The heat transfer isn't as good, but the boiling point is way up. Racers are using it as an alternative to water and water wetter. I heard of a Corvette team using water and (I think) a 90 psi radiator cap!