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Hi John,
First, want you to know I have no experience with the NPG stuff. My
understanding that one of it principle "benefits" is its higher boiling
temperature. Second, there is no common liquid that has a specific heat as
high as water (water = 1.0), there are some (I think liquid sodium might
have a higher specific heat - but we won't go there). That means anything
you mix with water (including antifreeze) reduces the ability of water to
carry off heat. Now the advantage of not having a cracked block or corroded
radiator makes the trade off of antifreeze vs water a worthwhile thing. A
50/50 mixture will reduce the heat carrying capacity of water somewhere
around 1/3 (as best I recall from memory) as compared to pure water.
The other thing that I am not certain about, is exactly what having a
liquid that boils at 300+ deg does for you. It appears that its nuculated
boiling (which is responsible for the majority of heat transfer to a liquid)
characteristics may be its most significant benefit over water. However,
If your engine metal temps get too high (regardless of the coolant liquid)
then it would appear your engine will suffer. So what I am wrestling with is
if my coolant is running 300F am I actually transferring heat from my metal
to the liquid? We all know that Delta T (temperature difference) places a
big role in heat transfer and it would seem that the delta T here is
considerably reduced. But, then I know beans about nucleated boiling and
how that may change the equation - so to speak.
The primary requirement is for there to be sufficient capacity to remove
heat from the block at a rate that keeps block metal temps below some
critical value. Now, I am certain that NPG (like most any liquid) will
carry off heat from the block, but given its lower specific heat it would
appear that you would have to increase the flow rate to get the same amount
of heat carried away. I think they mention something like increasing the
flow rate by 27% due to this lesser capacity, so at least they are being up
front about it. I have no doubt that NPG can cool an engine, the question
really is what are you getting that makes it that much more worthwhile over
the water/antifreeze combination?
I also notice they claim that NPG+ permits engines to run "Hotter" without
boilover and also has more heat carrying capacity that the straight NPG.
That might have some benefit for reciprocating engines, but, given that the
rotary will suffer damage at lower temps than the normal reciprocating
engine would, it remains a question in my mind whether this buys anything
for the rotary user.
Its tough to beat pure water for removing heat. But, this NPG+ stuff might
be worthwhile considering - who's going first?? My 0.02 worth.
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
----- Original Message -----
From: "John Slade" <sladerj@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Tuesday, October 07, 2003 10:20 AM
Subject: [FlyRotary] Evans NPG+ cooling systems
I just read that some of the Subaru guys are using NPG+ coolant.
http://www.evanscooling.com/main31.htm
I just had a chat with Dave at Evans. It sounds like this stuff might be
helpful, plus these guys also make reasonably priced custom radiators.
Dave
was very knowledgable concerning the problems of cooling an "off-road"
vehicle, especially when it's a pusher :)
Anyone using or know anything more about this stuff?
John Slade
>> Homepage: http://www.flyrotary.com/
>> Archive: http://lancaironline.net/lists/flyrotary/List.html
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