Radiator question, for thermodynamics/heat transfer experts Options

[bondo]

Hopefully I can get some input on this without too much of the inevitable "that won't work" (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

I'm cutting down a large tall radiator into a shorter one.. 1/3 the height to be exact. The 3 layers of radiator will be set up in a cross flow, sequentially. The hottest water will enter the rearmost later, travel across, then across again in the middle layer, and across yet again in the front layer. The idea is the hottest water gets the hottest air, and the coldest water gets the coldest air. This way delta T stays pretty constant.. I'm thinking of it as trying to heat the air as much as possible, which would cool the water as much as possible.

So I realize that cooling capacity will be reduced, as I will be dealing with 1/3 as much air. But then the cooling capacity must be more than 1/3, because it's 3 layers thick instead of 1. My question is what percentage of the original cooling capacity should I be expecting? Would it do me any good to do 5 layers instead of 3? (by adding 2/3 of a second radiator)

The original radiator cooled the same engine just fine, in a heavier car, with an AC condenser preheating the air. I will be running an electric pump, so I will have an advantage at idle.

[ArtechnikA]

i think you're going to have a hard time getting any air through any layers...

you -can- heat up the air really hot by the simple expedient of reducing the airflow, but the object of the game is not to heat the air, it is to cool the water. hotter air does not equate to cooler water. (IOW - you are not as much interested in reducing temperature as rejecting heat. ( where heat == temp * mass ).

i understand your logic on the sequence, but i still think it is backward -- coolers are most efficient at higher delta-T. (still, i see in my mind a conventional coiled-tube lab distillery and we always plumbed those with the coldest inlet water at the exit - but that was not about efficiency, it was about achieving the lowest possible temperature - not the same thing...)

QUOTE

I will be running an electric pump, so I will have an advantage at idle.

will you also be running BIG electric fans to move some air?

QUOTE

So I realize that cooling capacity will be reduced, as I will be dealing with 1/3 as much air.

not just 1/3 as much air, 1/3 as much surface area exposed to the ambient temp freeestream air. i doubt that's a simple multiple (1/3 * 1/3 == 1/9) but i'm thinking it's on that order.

probably this technique has been documented in the HVAC and thermodynamics texts, none of which i have, but it is described in several references i do have on race car and aircraft plumbing, usually on the "don't" page of "do's and don'ts" ...

if you're determined to build such a thing, and if i were you i wouldn't count on my armchair analysis as a gospel, i'd put temperature sensors in front of each layer and behind the last, and in the water stream before and after each layer. and then test it.

i think that if reducing the frontal surface area is really your design goal, you would be better served finding one deep cooler than stacking multiple layers. but i'd take this as a hint: i have never seen any really deep coolers ...

just MHO, since you ask ...