Misting vs. Icing Radiator

[gas pumper]

We considered 50% alcohol/water for a dry ice remote cooling on our lakester two or three years ago.  We emailed SCTA and the response was alcohol was flammable under any condition. And since it was non sealed because we needed to vent off the CO2 gas, that mix of liquid wasn't suitable.  We already knew we couldn't use green traditional anti freeze. 
What we came up with was a salt water solution, 20oz of salt per gal of water. This was the saturation point. We only ran it once and went back to just ice and water. Keeping it simple. Dry Ice is available at Smith's in NV.

Frank

[SPARKY]

Boomton Boys --- here's to you guys being able to do 2-- over 20--back to back   


JUST love this thread  once again points out the incredible range of experience, creativity, and helpfulness of the LSR family

[NathanStewart]

I have never understood the need for a radiator in a tank at all. It seems redundant. If you have cool water in the tank to start with, you just circulate that into the engine (using a thermostat). The radiator is just dispersing the engine heat into the water the same way the engine cooling jacket does only the radiator is a more inefficient way to do it. Additionally, you do have to circulate the water around the radiator just as if it were air, which again is redundant.

If you have cool water in the tank it means you have a cool or cold engine.  Most high output/performance engine tuning is done with the engine already at operating temp.  If you leave the line cold, you're likely still in your cold start/warm up enrichment phase which is adding in a bunch of fuel because cold fuel doesn't like to vaporize.  Then, at some point in your run, you reach operating temp but then you immediately transition past that point because you cranking out more BTUs than your cooling system can absorb or expel.  Now, the engine is hot, your detonation threshold is lower and engine damage is more likely to happen.  With just a water tank you only get one transfer of heat - from the engine to the tank water.  There is little or no heat transfer from the tank to the air.  The time to saturate this heat system isn't very long.

With the radiator in a tank, you get a second transfer of heat - from the engine to the radiator to the tank water.  What you're getting here is more time.  The system will also eventually saturate but it's much longer that just a single transfer will get you.  You can leave the line already warm and the temp transient is minimal.  You don't have to circulate the tank water but it might help some if you do.       

I ran my turbo Hayabusa for 5 miles runs with nothing but a 9 gallon water tank. The water was hot at the end, but the engine never overheated. That engine produces up to 500hp at 28 pounds and believe me, that is a lot of BTUs.

500hp at high boost from a 1.3L engine is a lot but 500hp isn't a lot of hp relative to other vehicles on the salt.  The radiator in a tank setup has shown to work very well for motors making 50-200% more power than a turbo busa.

[bdwilson24]

We considered 50% alcohol/water for a dry ice remote cooling on our lakester two or three years ago.  We emailed SCTA and the response was alcohol was flammable under any condition. And since it was non sealed because we needed to vent off the CO2 gas, that mix of liquid wasn't suitable.  We already knew we couldn't use green traditional anti freeze. 
What we came up with was a salt water solution, 20oz of salt per gal of water. This was the saturation point. We only ran it once and went back to just ice and water. Keeping it simple. Dry Ice is available at Smith's in NV.

Frank

So you weren't allowed to use the dry ice because of the need for venting? If we were to do a total-loss type of system with evaporating water or liquid nitrogen, we would have the same issue; hopefully, there are some exceptions. I will be talking to the SCTA today to discuss some of the limitations. Our motor controllers call for the use of antifreeze, but I think it's because the motor controller is able to operate in temperatures below freezing, so I will likely just run water through the controllers.

Are total-loss systems common at Bonneville? Now that I'm hearing that the car won't be weighed until after a run, a total-loss system is something I would definitely favor to drop some weight by the end of the run.

Boomton Boys --- here's to you guys being able to do 2-- over 20--back to back   


JUST love this thread  once again points out the incredible range of experience, creativity, and helpfulness of the LSR family

I definitely agree!

[SPARKY]

no LIQUID discharges on the track

[bdwilson24]

I just made a phone call to SCTA and they said that using dry ice or liquid nitrogen and venting it may be a good idea, but I will need to submit a special-construction request. I'm going to see what I come up with and do that.

By the way, thanks to the responses I've gotten on here, I did a much more realistic analysis and it did allow me to drop my motor power requirements and heat load by a substantial amount!

[gas pumper]

We considered 50% alcohol/water for a dry ice remote cooling on our lakester two or three years ago.  We emailed SCTA and the response was alcohol was flammable under any condition. And since it was non sealed because we needed to vent off the CO2 gas, that mix of liquid wasn't suitable.  We already knew we couldn't use green traditional anti freeze. 
What we came up with was a salt water solution, 20oz of salt per gal of water. This was the saturation point. We only ran it once and went back to just ice and water. Keeping it simple. Dry Ice is available at Smith's in NV.

Frank

So you weren't allowed to use the dry ice because of the need for venting? If we were to do a total-loss type of system with evaporating water or liquid nitrogen, we would have the same issue; hopefully, there are some exceptions. I will be talking to the SCTA today to discuss some of the limitations. Our motor controllers call for the use of antifreeze, but I think it's because the motor controller is able to operate in temperatures below freezing, so I will likely just run water through the controllers.

Are total-loss systems common at Bonneville? Now that I'm hearing that the car won't be weighed until after a run, a total-loss system is something I would definitely favor to drop some weight by the end of the run.



I definitely agree!

WE could run the dry ice. We could not run the alcohol mix, we used salt water.  We were followed by the fire truck from the cloud of vapor from the dry ice coming out the back vent.  Them guys really watch close!

[ETM]

I have never understood the need for a radiator in a tank at all. It seems redundant. If you have cool water in the tank to start with, you just circulate that into the engine (using a thermostat). The radiator is just dispersing the engine heat into the water the same way the engine cooling jacket does only the radiator is a more inefficient way to do it. Additionally, you do have to circulate the water around the radiator just as if it were air, which again is redundant.

Also, I have to disagree that the vaporization of water by misting the radiator is better cooling. When you mist a radiator by spraying water mist on it, there may not be any vaporization at all. The water droplets may pick up some heat, but never vaporize. So you blow in cool mist, and warm mist comes out. Then you still have to have a way to get the mist out, which means venting it.

...

In order to reduce hot spots you want to have good coolant flow in the block and heads.  In order to control localized steaming at hot spots in your cylinder head(s) you need to maintain a decent amount of water pressure inside the block.

At first glance circulating the tank water thru the engine makes sense but there are drawbacks to that. In that scenario the tank has to be overbuilt in order to withstand the max potential pressure of the cooling system.  This also would limit the shape of the tank as it would have to be structurally sound under pressure.  If the engine coolant is kept separated from  the water tank the required coolant pressure inside the block is maintained and separated from the water pressure in the tank.

A liquid to liquid exchanger solves this problem.  It is as simple as a water tank with a coil of tubing submerged in it.  The tubing is part of the pressurized closed engine cooling system.  Either by rule, budget or accident - the submerged radiator is a poor-man's version of this system.


As far as misting goes you have to have some air flow for that to work.  I have a BMW road racer that normally runs cool but can have issues at 8.5k RPM in the summer heat in Buttonwillow.  It has a factory washer fluid bottle and pump filled with distilled water connected to a mister in front of the radiator.  It turns on at 205 and off at 190.  Takes about 60 seconds to drop that far at race speeds.  Its nice insurance.

[jacksoni]

I have seen reports of using C02 sprayed on an intercooler for cooling and Gary Eaker on his 296mph Firebird in 1991 (? exact year) used N2O for the same purpose. No nitrous into the engine, just for intercooling. C02 available at welding supply might be easier than liquid N2 to handle and of course N2O is available as well, though more expensive I would assume. Either would need proper venting of course.

[Seldom Seen Slim]

This is my guess only -- but I'd be very careful about using nitrous or anything remotely fuel-like for anything other than the engine per se.  I would fully expect any inspector that sees a bottle labelled "nitrous oxide" or "nitromethane" or "super-duper secret bug juice" - would immediately assume that you've got a Smokey Yunick system going to run the stuff to the intake ports of the engine and declare the whole shebang either as Fuel Class Only - or just plain illegal.  That's even if you're using it for cooling purposes only, of course.

As my personal example -- a couple of years ago I ran afoul of the fuel rules when trying to run in gas class.  There was not bottle anyplace on the bike, but since the wiring and tubing, etc, were still there -- I was assumed to maybe have hidden a bottle someplace and either had toi withdraw - or run in fuel class.

[jacksoni]

This is my guess only -- but I'd be very careful about using nitrous or anything remotely fuel-like for anything other than the engine per se.  I would fully expect any inspector that sees a bottle labelled "nitrous oxide" or "nitromethane" or "super-duper secret bug juice" - would immediately assume that you've got a Smokey Yunick system going to run the stuff to the intake ports of the engine and declare the whole shebang either as Fuel Class Only - or just plain illegal.  That's even if you're using it for cooling purposes only, of course.

As my personal example -- a couple of years ago I ran afoul of the fuel rules when trying to run in gas class.  There was not bottle anyplace on the bike, but since the wiring and tubing, etc, were still there -- I was assumed to maybe have hidden a bottle someplace and either had toi withdraw - or run in fuel class.

SSS- your are exactly correct. In fact, Gary Eaker had to run in a fuel class for that reason even though was a gas car. However, as the OP is looking to cool the motors in his electric streamliner, might not be an issue.

[hotrod]

The other issue with N2O is the potential for thermal decomposition into an oxidizer if anything ever gets too hot while bathed in N2O vapor.

At approximately 968 deg F. Nitrous oxide breaks down and becomes an oxidizer accelerating combustion. If the electric motor were to ever go sparky sparky while the N2O was present in quantity you would have an oxidizer accelerated fire on your hands. That breakdown reaction is also exothermic (generates heat) and can lead to explosive energy release.

There is a reason they use the stuff as an oxidizer in rockets, and an oxidizer in race engines and sometimes as a monopropellant in some applications.

[fordboy628]

The other issue with N2O is the potential for thermal decomposition into an oxidizer if anything ever gets too hot while bathed in N2O vapor.

At approximately 968 deg F. Nitrous oxide breaks down and becomes an oxidizer accelerating combustion. If the electric motor were to ever go sparky sparky while the N2O was present in quantity you would have an oxidizer accelerated fire on your hands. That breakdown reaction is also exothermic (generates heat) and can lead to explosive energy release.

There is a reason they use the stuff as an oxidizer in rockets, and an oxidizer in race engines and sometimes as a monopropellant in some applications.

Exactamundo!!!

I would not consider using nitrous as a "coolant" after witnessing an engine compartment explosion on a door-slammer drag car, where the driver was seriously injured.   The cause of the explosion was determined to be a leaking nitrous setup coupled with a failed/cracked header.

The ferocity of the explosion was very impressive, that's why it is used as a rocket fuel . . . . . . .    Needless to say, the car was seriously messed up as well . . . . . . .

Fordboy

[bdwilson24]

The other issue with N2O is the potential for thermal decomposition into an oxidizer if anything ever gets too hot while bathed in N2O vapor.

At approximately 968 deg F. Nitrous oxide breaks down and becomes an oxidizer accelerating combustion. If the electric motor were to ever go sparky sparky while the N2O was present in quantity you would have an oxidizer accelerated fire on your hands. That breakdown reaction is also exothermic (generates heat) and can lead to explosive energy release.

There is a reason they use the stuff as an oxidizer in rockets, and an oxidizer in race engines and sometimes as a monopropellant in some applications.

Exactamundo!!!

I would not consider using nitrous as a "coolant" after witnessing an engine compartment explosion on a door-slammer drag car, where the driver was seriously injured.   The cause of the explosion was determined to be a leaking nitrous setup coupled with a failed/cracked header.

The ferocity of the explosion was very impressive, that's why it is used as a rocket fuel . . . . . . .    Needless to say, the car was seriously messed up as well . . . . . . .

Fordboy

It wouldn't be N2O; just liquid N2, which is chemically inert, so it couldn't really burn. If we used it, we would pump it through the system from a commercially pure liquid N2 tank to the heat exchanger, then it would evaporate into the atmosphere. My main concerns would be the size and weight of the container needed to hold enough of the stuff. I may be leaning toward one of the dry ice slurry ideas instead for those reasons. Venting the evaporating liquid nitrogen would be a little easier than venting the sublimating dry ice (solid CO2) though, and N2 gas is totally breathable where CO2 gas is less ideal to have in the driver's compartment if it's not vented properly. Having a slurry of some substance with dry ice also means that I wouldn't be able to dump as much weight by the end of the run unless the carrier substance would also evaporate, so that's another trade-off. Ideally, I want a system that is low-volume, high initial weight for ballast, and loses enough weight by the end of the run to put us under 1,100 lbs.

We are also not using an internal combustion engine, so I don't think there would be any places in our system where the pressure and temperature would be anywhere near the requirements of burning N2O if the evaporating N2 were to have enough energy to react with the air to become N2O. For rockets and IC engines, the pressures and temperatures are definitely enough to burn N20, and I don't understand what the benefits would be of using nitrous oxide as a coolant; that seems extremely dangerous like you both said.

[JimL]

I dont know what traction motors you are planning, but is there a need to preheat them before you push off the line?  

If not, why not externally cool them before you launch and then delay liquid N cooling until you are close to their upper spec range?  This could mean less coolant tank weight for your build.  We ran ice water through the motor and inverter of the Prius BEFORE each run in 2004.  The engineers said we were 10% more efficient (in the early part of the run) to leave the line with the motor-generators very cold.

There is very little you can do for the traction issue in a sub-1100 pound car.  Your early acceleration is least inhibited by aero drag, and will not be your window of maximum calorie production during the run.  With a fixed drive ratio (just guessing you will be around 4:1?), your three phase energy events have more actual time between peak current flow.  That final heat build will also be less if you can delay your transition from sine wave to square wave.  That was part of the reason I chose the particular speed to transition that Prius, where we had a 250 C limit on certain components (which would commit automatic shutdown of the inverter).

This could mean regulating the cooling in order to keep the operating temp at the highest practical delta for best heat transfer efficiency.  Your period of max coolant flow rate  may only be about a 40 second (or less) window to bump that record.  

As an aside, we found our best speed with that Prius was to attain our peak speed in the middle of the measured mile because the battery and electronics heat was at the point of "diminishing returns".  After that point the car began losing speed at a gradually accelerating rate (despite the opposite effect of aero drag).  As you can see, the push out method and timing was very important to the result.

We had the IC engine to blame for part of that problem (hybrids steal a lot of power from the engine to try and maintain the battery...net gain at high speed is basically nothing for Bonneville use).  You might find a similar approach to your time/speed plan that would allow you to manage cooling capacity while reaching your goal.  Picture a speed curve, centered on your timed mile, with the least practical loss during the last half of the mile as you prevent complete thermal forced shutdown.

I am not very well versed with this electric power stuff, but I keep thinking about that best available speed out of 1100 pounds of "stuff" that has ALL its available energy stored before it leaves the line.  Your AVERAGE speed for that final measured mile is all that matters.  There have been many of us put in some decent records with a car or bike that was "slowing down at the end" where heat build is the final issue.

It doesnt matter, as long as you can work out your plan and manage it.  Thanks for joining this forum with your interesting project....the doctors say it is healthy for us old people to put our brains back to work, now and then!