Body integrated radiator method, requires no grill or openings...

[donee]

Hi James...,

Well, my comment was somewhat simplified. What happens when one slows down from highway speed to standing at a light is that the thermal gradient across the thickness of the metal from the inside of the combusting chamber, to the water jacket side. Running down the highway, the inside surface of the metal is quite warm. The water flowing in the water jacket caries the heat away as the pump is going quite fast, and the water flows is large. Now come to a stop, and the water flow is very much lower. But there is still heat stored in the inner layers of the engine metal. That heat transfers to the coolant, but because of the slow pump, not to the air. This causes the coolant temperature and pressure to increase a whole bunch. To improve the heat flow out of the coolant, the fans come on to incease the mass of air per unit time that flows over the radiator. Which caries away proportionally more heat.

Some sorta fan mechanism is needed. Now the Prius and other engine stopping vehicles still have the radiator fans. The Prius has two actualy. Although, I think I have only heard them come on once or twice in the 2 1/2 years I have had the car. The Prius has an electric coolant pump for the inverter coolant circuit. I imagine its variable speed.

[Bicycle Bob]

Napier used surface cooling on one of their early Brooklands racers, and the idea was revived for at least one racing aircraft in the 30s. Weight and vulnerability to damage are the main drawbacks. Heat pipes require a pump if the source is not below the sink. Aluminum has the best heat conduction per pound by a healthy margin. An easy way to experiment might involve flattening out the evaporators around old refrigerator freezers.

[donee]

Hi All,

As far as Aluminum not being tough enough, there are Aluminum/Copper alloys that would probably be appropriate. Alloy 2024 sticks in my mind, but that may not be correct. The copper would enhance thermal conductivity, too. Compared to some of the silicon alloys (6063) is harder and tougher.

[Otto]

My boat idea was a water to water heat exchanger, rather than saltwater through the engine. My Bayliner 5.7 liter engine has water to water heat exchange via conduits in the outdrive, and sits in a deep V fiberglass hull.

Methinks better to have something like a Subaru flat 6 engine, with its coolant circulating against the inner surface of an aluminum hull. Being an superb heat conductor, the aluminum would dissipate the heat well beyond the bounds of the heat exchanger jacket, making the entire hull one big heat exchanger. (The water around here is ~50 degrees year 'round.) That way, salt stays on the outside of the boat, coolant stays inside, and we hopefully have no corrosion problems. Electrolysis being what it is, this may be more complicated.

As for aircraft use, again using an aluminum skin as heat exchanger, the best route would be oil coolant, as used in BMW oilhead boxer motorcycle engines. (I have two. Oil is lubricant and coolant, and uses a small ram-air radiator in the nose of the fairing, accounting for ~60% of heat dissipation, the balance being from air cooling of the cylinders by the slipstream.) Cooling drag being a large portion of aerodynamic drag, use of the aircraft skin itself as heat exchanger could be a source of major aero improvement.

In that vein, and back to the original topic of this thread, a car skin would make a great radiator, except for the problems already noted with safety, etc.. An aluminum belly pan could serve this purpose and help aerodynamics as well. Subject to puncture, though.

[blackjackel]

Originally Posted by donee

Hi All,

As far as Aluminum not being tough enough, there are Aluminum/Copper alloys that would probably be appropriate. Alloy 2024 sticks in my mind, but that may not be correct. The copper would enhance thermal conductivity, too. Compared to some of the silicon alloys (6063) is harder and tougher.

That brings another question into my mind... do they sell copper radiators? Aluminum is not nearly as efficient as copper for heat transfer....

[donee]

Hi Blackjackel,,

In a radiator application, I do not think the difference between copper and aluminum is significant. Because the walls of the radiator are very thin, on purpose. So the conduction losses are going to be small. In a heat-sink, its another matter. Where the heat has to be conducted into the fins. In a radiator, the liquid conducts the heat to the fins.

[slopemeno]

Bicycle Bob is correct- quite a few air racers that were usually liquid cooled were able to completely dispose of the radiator by going to "skin-cooling".

What some of you might not know is that the radiators as seen on World War II fighters actually gave a net reduction in overall drag, and a tiny amount of thrust due to the heating of the air passing through the radiator. The North American P-51 is probably best known for this effect, but other planes like the Hawker Hurricane had the same effect.

Most radiators are plastic these days...not exactly a great in my experience.

[Tango Charlie]

Originally Posted by aerohead

Bakers could slide sheets of bread dough under cars at traffic lights! Hybrid baking! Sorry!

Too funny!
Have you ever had hot dogs warmed on the exhaust manifold? It's a cheap way to eat on the road!

[twentysixtwo]

All of these are cool ideas but the underlying problem is that you won't be able to reject enough heat - the surface area for heat transfer in your average radiator is more surface area than the entire outside of your vehicle! ((assume 16"x24" radiator which is dual row 1/2" fins and .125 spacing = 43 square feet. This is just the fin area and not the tube area - note that they are all aluminum and very thin.

If you are stopped at a light, your fan still pushes air through the radiator, but if you use a body panel you are SOL.

An air cooled vehicle will be far worse as you will need to duct significantly more air through the engine compartment as the key loop is far less efficient (The real heat transfer is from the combustion chamber)

Heat pipes are far less efficient than forced liquid cooling.

[twentysixtwo]

Originally Posted by slopemeno

Most radiators are plastic these days...not exactly a great in my experience.

End tanks are typically glass filled nylon.......fins and tubes still aluminum...