The Egg guys no longer operate at the normal 200F when they install NPG. I
don't recall the exact number, but they operate around 215F (cruise). Which
explains most of your theoretical differences.
They gain a significant safety bonus in the boil over temp. That safety
margin is what it's all about. At least from the risk perspective.
So by operating at a higher Delta T, they compensate for the reduced
efficiency of the fluid.
I've heard you guys describe the importance of operating coolant around
185F or so? Are you sure of that limit? Is that just a recommended thing,
or hard and fast limit. I'm always skeptical of stuff like that.
Hi Al,
Appreciate your (anybody else welcome also) views
on one other thing that is still bothering me about the use of NPG.
Given that NPG+ has a specific heat of 0.66 at
212F or 20% less than the 0.82 for the 50/50 mixture and
given that NPG+ is approx 7% more dense than the 50/50
- then that for the same flowrate for both it would seem that NPG
still has a 13% lesser overall capacity for heat transfer (at the same
temps 212F and flow rates).
Also assume that the engine is produce the same
heat load (Q),lets take alook at what temperature we might see with NPG+
compared to the 50/50 solution. We have from the oldie but goody Q =
c*M*DeltaT the ability to solve for the temperature increase,
DeltaT.
Delta T = Q/cM, now if the combined effects of c
and m provide 13% less heat transfer capability than the 50/50 mixture
that would indicated that to carry away the same Q at the same flow rate, the
delta T of NPG+ would need to increase by 13%. So if I were getting 180F
with the 50/50 for the same Q load (and flow rate) then with NPG+, I
would expect 180 *1.13 = 203F. Yet, if I understood correct we
have reports that lesser temperatures results noted by users of NPG
- this leaves me a bit puzzled.
If my assumption is correct thus far, then I am
at a loss to understand the reports of lesser cooling temps when using NPG+,
it would seem just the opposite would happen, that is - the coolant
temperature would increase.
Now, If the coolant temp with NPG+ actually
does remain the same (or decreased) for the same Q and flow rate,
then it could indicate the engine heat load is not being carried away as
well as with the 50/50. IF the reports of lesser cooling
temps occurs when switching to NPG+ are correct, then it would
appear to me that the engine must then be operating under a higher heat load
(i.e heat not being transfer to the radiators as effectively) . This
doesn't even take into consideration the possibly lesser flow rate of NPG+ for
the same pump speed as the 50/50 due to its higher 3 times higher viscosity
(at 212F).
Yes, I have no problem understanding that
boil-over has been eliminated - but, is NPG actually cooling as well as
coolant temps may lead one to believe? I mean with NPG, I could have a
excessive block temperature and still not have boil-over - but my rotary
engine would likely have suffered damage.
What am I missing? Inquiring minds (even
old ones) want to know {:>)
Ed A