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George B.;
Nucleate boiling (small steam bubbles
forming and dissipating) provides the highest heat transfer coefficient from
the surface to the coolant; better than no boiling. Film boiling, on the
other hand, is when there is a layer of steam between surface and coolant, and
the heat transfer coefficient drops precipitously. The occurrence of film
boiling is a very bad thing, causes serious hot spots in the walls, and can
damage the engine.
Al G.
P.S. Can we dis the background on
these messages?
-----Original
Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Echo Lake Fishing Resort (Georges Boucher)
Sent: Monday, June 27, 2005
11:51 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: NPG + use
in aircraft??
"boiling removes heat" I have a hard time
understanding that quote. When racers started using PG they were able to run
15:1 compression on "pump" fuel
due to the fact that boiling coolant created
hot spots in the combustion chambers & in turn causes pre-ignition (they
also reversed the coolant flow direction to bring the cooled coolant to the
hottest part of the system, & all this with no pressure cap. The one
disadvantage I see in the 13b is that it can't handle the potential higher boiling
point of PG. I have a 3.0 L V6 that I reversed the cooling system on to use
in the Christavia (that was before I got hooked on the 13B)
-------Original Message-------
Subject: [FlyRotary] Re: NPG + use in
aircraft??
Has anyone used the NPG+ coolant in an
aircraft? What are the pros and cons?
NPG+ is standard issue in the 912S,
and perhaps the 912 also. If I'm not mistaken, Dave Leonard
is running NPG+ now, and I'm running NPG-R.
The Evan's marketing folks can give
you way more pros than I can think of, but I do think it's working
very well. The primary benefit is the fact that it's
native boiling point is in the 375F range, so you don't have to
worry about a cascade effect of boil over if you unexpectedly run hot, lose
pressure, etc. It's also not supposed to be subject to localized
boiling around hot spots in the engine. Evan's claims this as a big
benefit, but others, such as Tracy, think this boiling helps remove
heat. It's a bit more environmentally friendly too, so it won't
hurt the rats in John's hanger.
The high boiling temp means that you
don't need to run a pressurized system, which is my favorite part.
There's less stress on the system, and any leak that occurs, will be much
slower (initially) than if there was pressure. I added an air
separator tank, with a level sensor inside, so if I get a leak, I'll know
about it before it gets to the level of the top of the engine. That was
the best detection method I could think of.
The down side is the cost, and the
fact that it doesn't transfer heat as effectively as traditional EG/water
mix. Your temps will almost certainly go up some, but at least you
won't boil over.
If the oil temp is below 180 F but the coolant
is above 220F, is this detrimental to the 13B??
Define "above" :-) I
don't think there's anything harmful about 220F, or a bit over that for
coolant, since cars do it all the time. I believe the power will
be reduced a bit at those temps though, and perhaps there will be more wear
on the engine. I've heard that, but can't say if
it's significant, or even true.
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