Another silly idea, ducted fans for a radiator! Options

[TonyAKAVW]

So I've been thinking about different ways to get air up to the radiator in the subaru conversion where the radiator is in the engine bay. The standard way to do it is to have a couple of normal radiator fans sucking air from beneath the car.

Here's another idea... What if I constructed an array of ducted fans as in the diagram below. Basically they would force air up the shroud and through the radiator. One advantage to this is that it would take advantage of the entire surface of the radiator, rather than a round section that a fan would push through.

Something I'm trying to figure out is the conversion between thrust and CFM of air moved. Most of these fans are for hobby RC airplanes and are rated in ounces of thrust, rather than moved volume of air.

-Tony

[jsteele22]

Hi Tony,

I think with air-handling equipment, the relationship between flow (CFM) and thrust is in general pretty complicated, and usually given (if at all) in terms of a graph. If only one parameter is specified, you can be sure it is only true under the most ideal (i.e., worthless) case. So CFM is usually specified for no restriction on airflow; try to blow the air thru a duct or restriction and the CFM drops rapidly. And thrust (or pressure difference) is specified with the outlet blocked off; let any air escape and the pressure differential drops. Morale : don't trust the specs unless you get a graph ! In the case of a ducted fan like you describe, I would imagine the manufacturer has a tad of honesty and specifies the thrust as the force per unit area at a specific distance from the exhaust end of the duct, assuming no restrictions on airflow. Clearly, if you're pushing the air through a duct or restriction the thrust is gonna suffer.


In reality, I think the way to approch a problem like this one is either : a) tons of careful engineering, (IMG:http://www.914world.com/bbs2/html/emoticons/cool.gif) trial and error, or c) both. Oh yeah, or d) copy what's already been done. I think the existing fans made for radiators are probably the surest route. You know they can handle years of the heat, vibration, dust, and grime of an engine bay, and they manage to get sufficient air flow in conditions not much different from yours (i.e., the car at rest or low speed). If you're worried about using the full area of the radiator, I'd think there's room to separate the fan from the radiator a little more and have the duct flare smoothly to the full radiator size.