alcohol boil off systems

[SteveB]

Noticing several of the more competitive racers use an alcohol boil off oil cooler system rather than the air/oil cooler system, I wondered if anyone could fill in the details of their construction, specs ect....

[mayday51]

alcohol boil off?
.......that is called a still......

.....a boil-off system is a water/ water-mix
.......uses heat loss by phase change to cool oil,coolant or whatever is flowing through the cooler......

[AAFO_WSagar]

Mayday,

I'm not *totally* sure on this but I think the mix in the cooling solution is actually a mix of the funny stuff and water because of the faster evap rate of alcohol.. could be wrong but I think that's correct...

Wayne

[Scotty G]

Yep...

H2O and booze!

[mayday51]

Yep ! you guys have it right......

>.....system is a water/ water-mix <

.......water or water mix........usually less than 75% alcohol
(to lower flamability).......

......pure water does it change at 210F..(standard psse)
boils at lower temps as pressure drops...
.....depending on alcohol blend the boil-off temp can be changed

.....we have used a boil-off on our land speed (Bonneville style)
cars to cool engine and gearboxes...

...it does great over it's limits (total heat vs. time)

....most times we run "standard " radiators and coolers
.........less service headache,and greater capacity for size


Thanks Guys!

Mayday51

[SteveB]

Boil off systems

One of the specific things I was wondering was about getting the a/c to and from RNO. Obviously there is sufficient coolant available for 7 or 9 laps around the course, but how is the ferry flight to and from managed. Is there some sort of level sensor that alerts the pilot to the fact that the boil off system is running low on h20 and needs to be serviced? Obviously at cruz power settings it would take longer to boil off the coolant than running hot laps, but this has to be a concideration. thx

[Scotty G]

Steve,

This is a question I posed to Pete Law during our numerous interviews over the years.

At race power, one thing makes horsepower - and that is heat - or BTU's. A BTU is an economical way of assigning a number value to the heat generated. Therefor, you now have a mathematical way to figure out how much cooling capacity you need.

Big race power = big BTU heat within the motor. This transfer's big BTU heat to the oil and/or coolant. That means you need a large cooling capacity of the boil-off system, or a radiator/spraybar setup.

But cruise power is far below a race setting, so there isn't near the heat generated there. Pete told me Stiletto (with the boil off system he designed) would run out of gas, oil, pilot comfort and pilot bladder capacity way before it ran out of coolant.

I'm sure, if you ask Mike Brown, he can give you a ballpark figure on September Fury's cruise performance in relation to the boil off system. It's probably pretty good. (It's another Pete Law design.)

Scotty G

[SteveB]

Boil off

Scotty, thanks for the reply, if Pete says so, it's the truth. Now for the bottom line, ballancing the weight penalty vs drag reduction. Obviously some teams are using the system, some aren't, that being said did Pete indicate it was worth it? thx

[Scotty G]

I'll answer that one via Bill Kerchenfaut... When talking about Dago Red, he said it's heavier than Strega and Voodoo. He's built in a lot of redundant systems and such. But Dago goes out and damn near does 500...

He thinks weight doesn't play as big a role as some think. Remember... Racing Mustangs are down around 7000 - 7200 lbs. Versus the wing loading, we're splitting hairs over another X lbs of fluid that will ultimately not be there as the race goes on.

Everybody is in the "weight" ballpark, so it doesn't appear that the difference of a couple of hundred pounds (expecially in a Sea Fury) makes a big difference.

Just my .02 via some inside guys.

[SteveB]

Boil off

Scotty, good point. When you start looking at the weight numbers it really does come down to a small difference overall. You probably add some weight with the new cooler (I assume it is slightly larger), add some weight for the cooler housing, the weight of the cooling water/booze boiled off is probably pretty close to a wash as you wouldn't need to fly spray bar water anymore. There would be another weight gain with the water/booze you wouldn't want to burn off, thus being concidered unusable. mmmmm-food for thought. Thanks for the conversation. SteveB

[Scotty G]

I'm not sure if the cooler unit would be any larger, since the cooling properties of the liquid are so much greater. It's probably the same size or smaller that an airflow unit.

But you're totally right. No spray-bar setup for the oil cooler...

[Unregistered]

Scotty's on the money here.

Any water cooled heat exchanger is going to be much more efficient and smaller than an air cooled unit, all things being equal. Air cooled units need fins (more surface area) to compensate for the extremely low airside heat transfer coefficient. Water cooled units will do better with bare tubes, i.e. much smaller uint.

All of this does not take into account the air temp versus the boil-off coolant temp. Air temps would be in the order of what, 80-90 degrees where as the boil-off coolant temp would be closer to 200 or so. That's a large factor on the Mean temperature difference (MTD) that drives the rate of heat transfer. I am sure the efficiency/size/weight of the boil off system still overcomes that lower MTD or they would not do it. Then of course there is that little gremlin known as drag. No large intake scoop required for a boil off system which I am sure has a lot to do with the selection of such a system.

Just rambling...
GP