I've heard of people packing intakes with regular ice, but why not dry ice? It is because it is not easy to find?

I'm thinking of making an Al carb bonnet with an ABS shroud around it. In this shrouded area I want to pack it with dry ice to cool the air as it enters the motor. The Al bonnet would take a chill and the plastic cover would insulate the chiller.

Has anyone played around with this sort of idea? Any cars out there with a frozen CO2 resevoir? I know the air would only be in contact with the Al (cooled by the CO2) for a second, but if it cooled it 10 degrees it should be worth 'some' power.

Then again, if an icewater/air intercooler give you maybe 10% the dryice cooler may not be worth the hassle.

It is a very simple concept. Please supply me with some feedback.

Ben T.

 

A second? At power peak air might be entering the carb at well over 200 ft/second. If your "cooler" was a foot long, it would take the air about 5 milliseconds to pass thru and only the air near the periphery would be exposed to the heatsink. IMO, you won't have much effect on the inlet air temp.

If you want to try a chiller: Draw the air in thru an air-air intercooler, but instead of air on the outside, spray nitrous into the fins of the IC. No nitrous into the intake, just across the IC. About 10-12 years ago this was done at Bonneville and reduced the inlet from over 100*F to maybe 60*F. Don't ask how much nitrous it took for a full run!

Why does it work? (No help from the peanut gallery, please )

 

I run alcohol. My intake is always cold

 

That was not meant literally. I meant a very short amount of time.

If I'm riding around with nitrous, I'd probably just direct under my carb too.

I think you're gauranteed good results that way.

Any other opinions? I'll try and find out on a more scientific level how much I could actually cool the air in my proposed heat exchanger.

Ben T.

 

First of all, "dry ice" is pretty expensive. It's the change of state of regular ice that causes the cooling effect by going from a solid to a liquid. When "dry ice" goes from a solid to gas, the "liquid" stage is skipped, and energy transfer (in the form of heat) isn't accomplished as sucessfully as a liquid ice slush melting over the metal intake. Now on LS1's with non-metal intakes, that's another story...

 

Old school wisdom on this:

It's a question of SURFACE AREA, not so much temperature. As was mentioned earlier in this thread, dry ice goes from solid to gas, no liquid stage. In it's solid form it can only touch the intake parts at the corners and edges that happen to lay against the intake. The rest of the "surface area" it has nice insulating pockets of air between it and the intake. Not ideal for cooling off large surface areas, which is required to have any reasonable shot at meaningful cooling of the intake air.

At the track you want some liquid in the bags so it can contact a large surface areas to suck heat out of the intake. That's why you normally see people using ice bags- it quickly melts some of the ice into 32* water which "mooshes" all around the cracks and crevices of the intake or whatever you have it laying on top of, sucking out a lot of heat quickly from a larger surface area.

Yes, "mooshes" is a technical term.

 

After carbon dioxide is cooled and compressed under high pressure to make liquid CO2 , dry ice is manufactured by allowing the liquid under pressure to expand to an ambient pressure. This produces Co2 “snow” that can be compressed into convenient dry ice blocks, nuggets or pellets. Dry ice at atmospheric pressure is -109 degrees Fahrenheit.

 

CO2's heat of sublimation (137 cal/g) is fairly high compared to the heat of fusion for H2O (80 cal/g).

It may take some fab work, but I imagine someone could rig up a dry-ice brick maker to deposit CO2 directly to the top of the intake manifold... and even cool the intake in the process. Wouldn't take much more effort than mouting a small porous frame on the intake fins.

Might make for some nervous track officals... fog coming from the engine bay an all but depositing the brick before a run (via a mobil CO2 tank in the lanes) would be fine for at least the launch I imagine.

If you'r going through this effort though, you better be professional:

TIG weld a small frame up from the corners of the intake manifold's top section. Last unit I used to make dry ice (a admittedly a few years back) used a type of cheese-cloth on the walls of the "box" that could freeze with the CO2's moisure, and give the CO2 a place to deposit. A 30 second shot of CO2 was more than enough for a small brick. Jus the bottom of the intake as one wall of the box.

Want really go full out? lathe the top of the manifold, then braze, TIG weld, or tap/bolt down a massive aluminum heatsink (Athlon?) to the top and use the fins as deposit areas.

Due to the SBC's design, phenolic spacers really arn't that convienent, but I've thought about this concept from time to time. The problem of course is that your cooling air for a split second... not the whole intake track.

A double-walled CAI was also another theory... (steel or maybe finned on the inside... ABS plastic on the outside)... but water condensation just doesn't sound like a great idea for MAF sensors.

possible? yes
substancially benefitical? maybe, depending on execuation
worth the cost, time, and weight penalty involved? probably not.

Just some thoughts, take em for what their worth.

 

True... unless you deposited the ice directly onto the intake.

Another option of course is to put a shallow layer of water in the "ice box" before using CO2 to freeze it. The sheet of ice formed on the manifold would work better for contact area and mooshing... at -74*C sublimation, I imagine the ice sheet would be substancially colder than water formation to prolong the fun. Water's higher higher heat capasity would probably cause longer CO2 "charge times" but I imagine that would result in a longer time before ambient temps return. Only draw backs might be the possiblity of dripping wate on the track, and the weight of the melted water you carry for the run... although both of those are present with a ice-bag version as well.

Interesting topic.

 

Well... that's not really the reason... it will sublimate just as easily AT the "boiling point" (which it doesn't really have at atmospheric pressure since there's no liquid phase, it's properly refered to as a sublimation point) as it will at 400*F. How far above the boiling point dry ice is at doesn't matter, the pressure and temperture of the environment does however.

The reason CO2 tanks are under pressure is that CO2 won't go to a liquid form under 4 bar or so (~60psi). Look for a CO2 phase diagram and you'll see why. This is why CO2 sublimates... the triple-point of CO2 is higher pressure and temperture than what most of us see when using CO2.

This is why CO2 is liquid in a pressurized tank, and why it forms dry ice if you release it into a suitable container that reduces the pressure to less tha 60 psi without heating it too much in the process.

 

check that... the triple-point is about 5 bar, and -56*C. (must be getting old)

Google goodie: http://onsager.bd.psu.edu/~jircitano/phase.html

 

ouch. You're not alone, many people choke on O-chem pretty bad. That's usually when prospective Chem-majors switch to easy stuff like nuclear physics and computer programing.

I aced O-chem... to be fair, there weren't many of us though. Has less to do with memorizing stats/names/etc... and more like learning math, just accept that it does happen that way.

<flame suit>
I really dug that class. (but don't tell anyone )
</fame suit>

 

I had that discussion sunday morning. The first organic chemistry scared away another ChemE major.

Glad we (lsu me) don't have to take that stuff. Thermo is bad enough.

Ben T.

 

Trust me... if you hate thermo AND o-chem... P-chem (physical chemistry) is a 4-month nightmare you'll never wake from.

I had no problems with o-chem, and the thermo stuff in Physics 244 was ok... but man, Physical Chemistry was a total mess. Glad that one's over.

Strange thing is, there were chem-majors in that one that just didn't give it a second though. Those Chem guys are a strange bunch. (...like Biochem guys are much better )

 

2 words: Flash Cards



After you make them, you'll probably have most of it memorized anyway... but lunch breaks, down time in labs, and commutes (if you take the bus/car pool) all turn into instant study sessions. I figure I probably got in at least an hour a day extra studying with those babies... much easier than whipping out a text book or a folded-up piece of paper. (and people won't stare at you for taking out a 6-pound, 800-page o-chem text book every 5-minutes )