Multipass radiator

[jakobnev]

I had this idea on how to decrease the aero-penalty of cooling your engine:


(coolant flows right to left in the picture)

By making the radiator behave more like an opposing flow heat-exchanger it should be possible to reduce the amount of air that needs to flow across it. Since most radiators are over-sized for ecomodder needs, the decrease of max cooling power should be no problem.

[ThermionicScott]

Call it the "Leeloo Dallas Multipass Radiator" and I'm in.

[JRMichler]

Twice the air flow per square foot of radiator frontal area, plus all the turns, will restrict air flow and cause cooling problems on hot days.

Better to put in an oversize radiator. The larger radiator will give better air temperature rise, which will give the same total cooling using less air. Less air through the radiator is less air drag. Such a system may need diverging vanes to spread the air from the small grille opening evenly over the entire radiator.

[jakobnev]

Interesting, I think I disagree with every point you made.

Twice the air flow per square foot of radiator frontal area, plus all the turns, will restrict air flow and cause cooling problems on hot days.

Three times, but no, the flow will be low, but it's unlikely it will be a problem for ecomodders.
Restriction has to be added anyway, it might as well be at the radiator as at the grille opening. (Clean vs dirty air filters and all that.)

Better to put in an oversize radiator.

Like I stated, the radiator is already oversized, and most cars won't fit a bigger one anyway.

The larger radiator will give better air temperature rise, which will give the same total cooling using less air.

Opposing flow heat exchangers give the highest physically possible temp rise, multiple passes from cold to hot side of the radiator will approximate that. All that air passing through the colder side of the radiator only, would not get very much heat rise.

Less air through the radiator is less air drag.

Ok, this I agree with, that's why I think it's best to heat all the air as much as possible.

[samwichse]

I feel like your "snake" passages are too small. Assuming everthing is at a constant height, your fan is drawing through a duct 1/4 its cross-sectional area (and due to boundary effects, probably only able to pass 1/5-1/6 the volume of air it can). Obviously you have to work within the restrictions of your existing engine compartment, but something like this would be much better (keeps ducting as constant area as possible)... sorry for the potato-drawn image.

[jakobnev]

Well, the drawing was just to show the principle.

[JRMichler]

Counterflow heat exchangers are most effective when both fluids have large temperature changes as they pass through the heat exchanger. Automotive cooling systems have relatively small temperature change on the water side, therefore counterflow has small benefit.

If you have the space to make air flow as shown, then you have the room to make the radiator thicker. The air will then go through as in existing radiators, but come out closer to the water temperature. If, that is, the air flow is reduced to the minimum with a properly designed grille block.

There is an excellent book that covers this subject: Compact Head Exchangers, by Kays and London.

[jakobnev]

Counterflow heat exchangers are most effective when both fluids have large temperature changes as they pass through the heat exchanger. Automotive cooling systems have relatively small temperature change on the water side, therefore counterflow has small benefit.

Good point, depending on how small, it might not be worth the effort.

If you have the space to make air flow as shown, then you have the room to make the radiator thicker.

It's not that practical to thicken a radiator DIY-style, you have to replace it. (or add one in front) Ducts are much easier to build. (and more often free)

There is an excellent book that covers this subject: Compact Head Exchangers, by Kays and London.

[rmay635703]

If you want zero aero penalty have long lengths of tubing along the nose hood and belly pan distributing heat along body panels, when heat is critical then open the traditional radiator opening.

[seifrob]

Originally Posted by rmay635703

If you want zero aero penalty have long lengths of tubing along the nose hood and belly pan distributing heat along body panels, when heat is critical then open the traditional radiator opening.

What is the temperature of black hood during sunny day?