Race Car Cooling S

I believe that you will find 30% of the rated horsepower as heat rejection would be an optimistic figure for a race car. Presuming you start with ice water, 180 BTU/lb heating, and 1000 BTU/lb for steam generation.

That's my issue in a nutshell. In my car I can burn roughly 2 gallons of fuel in a run or about 12.4 pounds. A gallon of fuel has about 130000 BTU energy content. Approximately 1/3 of that goes into the cooling system, 1/3 into power and 1/3 out the exhaust pipes according to an old Combustion Process engineering book I have. But, when I burn the 12.4 pounds that says I have enough waste heat to evaporate approximately 10 gallons of water if it starts out at 100F and evaporates at 202F at Bonneville altitude. This is where it gets confusing to me. There are several cars with this system and the water in the tank only gets warm to the touch. So a lot of heat must be going out of the system as radiant and convected heat off of the metal motor parts as well as having a tremendoes latent heat reserve themselves. A motor weighs approximately 450 pounds and it is basically iron so that has to soak up a lot of heat as it heats up the cooling water. What I am looking for is some confirmation of that and how much it might be? I can calculate the latent heat of the metal parts but what about radiant heating and convection from the air flow over the motor itself? Any ideas? If you had to guess how much of the 1/3 waste heat actually goes into the water given that there is radiant and convected heat?

And thanks for the reply! I appreciate it.

drmayf

Why are you carrying the extra weight? Surely a conventional air cooled radiator would be the lightest option, speaking as a petrol head, and as someone who is involved in the manufacture of heat exchangers, weight is everything in racing.

Well, you may be a petrol head and race in conventional venues, but land speed racing is quite different. Weight only affects the acceleration of a vehicle and not top speed. And at Bonneville the aerodynamics usually dictate that the car be really swoopy which usually cause it to have an airfoil shape in cross section. That makes for lift just like in a wing on an airplane. And wings fly. So most racers on the slat flats here and at Lake Gairdner add weight to keep the car on the ground. It also helps traction a bit. Coefficient of friction on salt on a good day is around 0.68. So weight is not a real issue in land speed racing. Heck the pontiac door slammer that ran a few years ago weighed more than 5000 pounds, lots of that in lead. And it only went over 300 mph! I don't go nearly that fast lol... different class and motor requirements. Thanks for the reply, I really do appreciate it!!

You are right. Most of the heat generated and dissipated by conventional radiators come from continuous engine run. The engines tend to take sometime to heat up and, if you mentioned that you are within a 3 min run, the fact is that, due to the short time, the heat losses in radiation and forced air convection are taking that heat while the water is absorbing only the remaining energy. Remember that most of motorcycles and some ancient cars had only convection cooling. I also remember one really old stationary piston engine used to drive a generator that had a metal cup integral to its head premanently filled with about 1 litter of water, that evaporated and absorbed the heat in permanent regimen. Used to work in that good days... and the piston had about 6 inches in diameter!

Interesting matter! I would never figure that someone would like to carry a water reservoir to serve as a heat sink...

I myself run a quarter mile car. I dont use a conventional radiator. most of the heat generated goes out the headders in short runs, all the water does is fill the water jackets and divest the cylinder walls of a small amount of heat. besides which, if you run it a little hot, you will squeeze a few more horsies out of it. not a bad thing. rad makes a difference if your run times are long.

I keep forgetting that I am not on the Land Speed List. In order to get the very fastest speeds the cars need to be as aerodynamic as they can be. Same as in drag racing with the fast cars. The front of the car is blanked off and the radiator had to leave that area anyway because I needed that particular space for turbos' plumbing. The area in front of where the radiator was is filled with fuel tank. I had a radiator there before with a fan and it got hot. Where a typical strip run is around 10 - 15 seconds for a typical bracket car, in a quarter of a mile, my runs can be 5 miles and take around 2 - 2 1/2 minutes at full power. There are other venues which are shorter at a mile but thats as short as they get. So I need to absorb the heat somewhere. For those interested, the car is a 1966 SUnbeam Alpine in which the outer skin is the only thing left of the original car. It fras a race frame, race suspension, and full 14 pt roll cage. The motor is a Ford 5.0 displacing 306 CID and uses all the big hp stuff inside. And it has twin turbo chargers as well. So I make plenty of power and that makes plenty of heat. Hey, thaks for replying, I appreciate it.

Question? Is the cooling system pressurized? (Dumb question, but I had to ask) Raising the pressure raises the boiling point, anti-freeze does to, but it may be banned.

Radiator suggestions

1) Locate an automotive type in the turbulent air behind the car

2) Expose the tank to the sir stream, a large flat bottom exposed on the underside of the car.

When Howard Huges was developing a steam powered car, one of his engineers was working on the problem of distance between water stops. They were adding radiators everywhere, even in the doors. It was added surface area for heat rejection. Howard rejected the idea. If you got T-boned, you got cooked by live steam.

Good luck

Yup, I have 28 - 32 psig pressure caps on the radiator and the filler on the engine. The overflow on the radiator is plugged with the one on the filler going to my large catch can. But the water tank itself is not pressurized and the reason for that is that the water in the tank then can get no hotter than the barometric pressure will let it, which in August is about 202 deg F for boiling. As to the other suggestions, we are getting far afield. This system works, I am just trying to determine the amount of water needed in the tank. Next week, I will be cutting and welding that tank together. What I am needing now is a more honest estimate of the heat that goes into the radiator water that is transferrred to the tank water, how much heat radiates from the motor and how much convects from the motor in the engine compartment. As I mentioned before, When I use the old rule of thumb of about 33 pervent of the heat going into the radiator I find that they amount of heat is enough to evaporate about 10 gallons of water and on the cars that have this kind of cooling, that does not happen. They only get warm. Hey, thanks for the out of thebox thinking though! I do appreciate it!

Just a vagrant thought:

How about a one pass system?

If weight is really not a problem, why just not dump the coolant?

Say 20 g.p.m for 3 min. = 60 g. or 480 lb.s water.

Volume looks doable, and if the dump passed through a jacket

on the exhaust, you might devise a usable steam jet to boost speed,

(assuming the rules permit such a device).

Vagrant thoughts welcome! In fact I had not considered such a system. I will have to look into that a bit more. There are a couple of issue right up front though. I have no room for that much water; dumping it overboard could affect other drivers when they run down a wet salt course; and losing that much weight could have weight and balance effects. As to the steam rocket part, cool! But again water on the track and the temp for that has to be pretty high to make it work with any efficiency. A local friend and I are currently planning on converting a IC motor over to run on steam and we think we have the answers on that. Just have to find bits and pieces not to see if the concept we have will work.. Hey, thanks for the reply! I really do appreciate it!!

Most of your waste heat doesn't get to the coolant. t goes out the exhaust with the gasses. Thats why your figures don't add up.

the only way you are going to get a usable result without guessing is to mesure the heat rise. thats simple enough. connect the water passage exits to the inlet, warm the engine to a little over operating temperature, let it soak back to your preferred op temp then run the engine for 1 min or some other specific period at teh RPM and power setting you wish to run at and measure the heat rise in the water at the connection between inlet and outlet. The temperature rise for the water quantity used in the engine on the run will give you the degrees per gallon per minute being sent to the water. Allowing you to design your tank.

dumping water into the exhaust will cool it very quickly, reducing its volume; effectively increasing the exhaust size and decreasing pressure losses. you have to be careful not to dump so much into the very hot gasses that it either dissociates, which heats the end of the exhaust up or causes more backpressutre by increasing the exhaust mass. Of course you will lose your cooling ability with the water loss....

That's where my troubles lie, I think. I have been using numbers from an old text book, "Combustion Engine Processes" dated around 1967. There is a figure in it which depicts where the heat goes: 30% into shaft work, 7% into radiation, 33% into the exhaust, and 30% into the cooling water. As I mentioned before, when I use that 30% or so I find enough heat to boil away about 10 gallons of water. My motor burns approximately 12.4 pounds of fuel in a run and at 30% (I just used 1/3) and with gasoline having about 130000 BTU/gallon per pound I have about 78,000 BTU available to heat the water. At Bonneville the ambient air temp is about 95F and that is what I used for my starting calculatons. The barometric pressure is usually around 12.6 psia and that gives a boiling temperature of about 202F give or take a degree or two. I try to use an energy balance to find the gallonage of coolant required. What I did:

Q (Ttot BTU avail) = [q1 (heat required to bring 95 F water to 202F/lbm) + q2 (heat to keep the water at 202F and boiling/lbm)] time the mass of the water

I "know" everything here except the mass of the water so solving for that is pretty easy. And I know that the latent heat of boiling water is about 970 BTU/lbm and I used 107 B/lbm to heat the water from 95F to 202F. This 107 BTU/lbm to heat the water initially may be my problem but I am not smart enough to know. Thermodynamics was not my forte in colege.

So where am I going wrong? In any case, thanks you for posting a reply, I really do appreciate it

REading your reply I suddenly realised your calculations are probably all correct... sorry about that old chap but 'normal' cars don't run at 100% power, they trickle around on 1-40Kw at the engine. High power Speed bursts are so small that much heat never really gets into the water immediately so the cooling radiator takes teh heat out faster than it goes in.

In your case you are running flat out with no downward heat exchange so you are putting all the waste heat (from full power) into one bottle so to speak. The water will boil unless you have huge amounts... and of course teh engine temperature will rise as the coolant temperature rises.

I think I have an acceptable solution

Place a sealed pressure container with a very effective dessicant in it. heat the container pre-race to drive off the water in the dessicant, seal the outlet, then connect a tube to the water container with a variable orifice valve in the line. Then pump the air out of the system without opening the dessicant container valve.

As you open the valve, VERY slowly just a tiny bit (to let vapour into the dessecant tank), the evaporating water vapour in the water tank will cool the water, which absorbs the waste engine heat.

The concept is to convert the energy into a more portable form. Aluminium car engines run about 80 degrees C, cast iron a little hotter (water temp that is)

There are numerous other ways too achieve cooling, but I think this one is cheap, easy to make, easy to reset and small. I've seen this method freeze ice almost immediately. you could also use a bottle of liquid nitrogen vaporizing through a heat exchanger coil in the water tank (in this case the lower the boiling point and higher the latent heat of evaporation the better!

Hope this helps or at least gets you started on something!

Well, that is certainly novel! And I will keep that in my hip pocket. But my basic question still has not been addressed and that is I can calculate the amount of water to keep the engine cool or at least from getting hotter than boiling but other cars with more hp and same size tank only has the water get warm to the touch. So more heat is going elsewhere than into the cooling water. My original questions were geared to tying to find rational answers for why my answers were not agreeing with practice.

ANd it seems nobody else has any ideas either. I think I will do some more homework and figure out the surface areas of the motor, guess at the airflow around it, and make a stab at figuring out the radiation effect and convectioneffects and the amount necessary to heat the motor perse. And see if that reduces the heat load into the water tank. What I have will in practice work and has worked. I just do not know why,lol..

In any case, thanks for replying and helping. I really do appreciate it and the really trick way to cool water... I will do some more looking into that fo rsure.

P.S. Water's mass is 1Kg per litre or 4 Kg per US Gallon. 4.5 Kg per Imp. Gallon

If you do play with steam at 25-30 PSI pressure be very careful. It can be done but it can also cause injury and/or explosion.

On the otherside, if you run once through, why discharge liquid water. I can imagine 25 PSI, 210 or 220 degree F water evaporating very quickly on a salt flat. Use a temperature and pressure relief valve set at the right conditions and set to carefully discharge in a safe direction. For a five or ten minute run it would probably keep the engine from damaging itself, and eliminate the drag of air through a radiator.

Check http://www.watts.com/pdf/PG-TP-ASME.pdf for some info to think about.

Sorry, but I am lost on this. I do not have 25 - 30 psi steam pressure. The actual cooling system for the car is a normal radiator system with nascar pressure caps of 28-32 psig. The radiator system is very similar to the one in your car sitting in your driveway with one exception. Instead of drawing air through the radiator to cool it, I am going to use water. The radiator will be placed into a tank of water which is vented to the atmosphere at 12.6 psia (race venue barometric pressure). The radiator will transfer water to the tank vater which will evaporate at approximately 202 degrees (boiling point for water at that approximate pressure). I do not want nor plan to dump the evaporation steam onto the course because the salt surface gets wet and when it is wet it has even less coefficient of friction than when dry. Ya'll remember the questions I asked at the start of this thread? I was looking for help regarding how much heat is actually going into the cooling water, how much of the heat is covected away from the motor, and how much is radiated from the block. I did mention to one reply that I was, with an associate, trying to convert an IC engine to steam: however, that will be at 300 psig and about 400 deg F. Not the same project at all. And yes, I worry about steam explosions.

Now this sounds like I am throwing mud at your comments, but please do not take it that way, I was just refreshing everyone's thinking process that this wasn't the original reason for the thread. I really do appreciate comments and I genuinely appreciate replies and comments because I meet a lot of interesting people that way.

Are you trying to calculate how much of a heat sink you need? I'm a little lost as to what you need to know. If you want to finish a run and have your heat sink up to the temperature of the engine that's fine, but how much margine of error do you want? And dont forget, the hotter your heat sink gets, the slower the temperature transfer occurs. You must have some weight and size restrictions, I think I'd work out a rule of thumb with the data you have and experiment, I think I'd want the sink at 10 degrees cooler then optimum engine temp as a safety margine.

Sorry about not being as clear as I should be for statement of the problem. But you pretty much nailed it. Except for the experimentaion part. This is a race car that gets to run at Bonneville Salt Flats twice a year. So having something that works is pretty much a necessity before you go. It may be that I build something and try it out and modify that for 2008. And what I was hoping to do was make some rule of thumb type formulation/modle that might help others who want to do this. My car is small and does not have room for really large water tank. Just about every useable space is filled with stuff. Where I got into trouble in determining what size water tank I needed to submerge the radiator into was when I used 33% of the gasoline heat content as the amount of heat for heating the water. An old engineering text book on combuston engine processes said this was what it was. I know how much fuel I used in a run so I can calculate the amount of waste heat heat available in the fuel used based on using the 33%. I set up a simple energy balance using heat from the fuel = amount of water to keep it just at boiling at a pressure altitude of 12.6 psia. I considered the water tank to be a starting 100F and finishing at 202F. I tried to include just the part of bringing the water from 100 to 202 and then keeping the water at 202... This gave me a water tank of about 10 gallons. But that seems to have evaporated all of that 10 gallons (at least in my head). However, there is another car similar in function to mine having the same size system and even makes more hp so it is burning more fuel yet his water tanks only gets warm to the touch. My questions were how much waste heat really goes into the radiator and cooling system in fact? IS 33% the right amount? Does a lot of it go into heat convection from the surfaces of the motor? Does a lot of it go into radiation from the surfaces? As you may have surmised, Thero is not my thing, although some familiarity wih it. I would be happy as a pig in poop if someone could help me set up a simple model by which a noob could size a system base on parameters of his motor, car, etc. Full attribution in the article I am writing for my web site would be given (http://www.mayfco.com just clkick on the only active link to get inside and troll around).

many thanks

Nice! I have a real appreciation of what you're up to now, although I think you've got your work cut out doing the calcs. I was making a list of points of heat loss, just for fun, and quit at about 50! I think your figures may be applied to a thermally sealed system, but an engine is designed to loose heat. How about this for an idea that may be of use. We run Glycol chillers at -20 degrees centigrade, -4 Fahrenheit; so, for your heat sink, have a portable freezer on hand with a supply of glycol / water solution at a nice cool temperature, and use that to top up you heat sink after every run. This will minimize the amount of mass you have to carry for a quite low outlay! All you need is the freezer and a few bottles of antifreeze. You also get the added benefit of a supply of cool drinks.

P.S. I've put your site in my favorites so I can keep abreast of what's happening.

Hey, thanks for the reply! I do appreciate it! Now, I have completed the beta version of the spreadsheet I built to determine cooling water tank size. When you consider this isn't a moon shot and that it is ok to be somewhat conservative then it gets easier (Ihave trouble with the aerospace part, that was my career and I am always looking for the nth decimal place of accuracy, lol). What I did: I determined the amount of heat produced in one second by gasoline with a known BTU content. I then estimated the amount of iron and aluminum mass in the motor, followed by estimating the conduction surface areas of the iron and aluminum parts. I made an energy balance equation where the heat went into both the motor mass for heating it up to 180 degrees (thermostat full open) while conducting heat from the surfaces. When the engine reached the thermostat set point, then I pump water in pounds per second to the tank and from the tank. I use the hot water from the motor to heat the tank water, and the cold water from the tank to be heated by the motor and gasoline. I also included a surface area calculation on the water tank to conduct heat away from the tank. Yes it was not a friendly wrestling match to get it all working. Right now, the engine temp will rise to the thermostat set point, begin pumping and transferring the heat that would have caused the engine temp to elevate to the water tank instead. Seems to work ok. This is a first order approximation only and adding the bells and whistles like the plumbing losses, maybe adding radiation cooling would all help to reduce the amount of water needed in the tank. But this works for me right now! I have a couple of guys beating on the spreadsheet right now and when done, I will post it on my web site in the analysis section and make it downloadable. So keep checking for new stuff. I will attempt to write up the what I did as well although it is messy. I am sure that had I wanted to go the finite element method I could have included lots of the other parameters to make it more accurate. I also have a software package that can do PID controller stuff so I may try to implement it in that as well. Just for fun, lol...

drmayf, way out in pajrump, nv