Radiator question, for thermodynamics/heat transfer experts |
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Radiator question, for thermodynamics/heat transfer experts |
bondo |
Feb 2 2005, 12:26 AM
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#1
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Practicing my perpendicular parking Group: Members Posts: 4,277 Joined: 19-April 03 From: Los Osos, CA Member No.: 587 Region Association: Central California |
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. |
davep |
Feb 2 2005, 11:15 AM
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#2
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914 Historian Group: Benefactors Posts: 5,154 Joined: 13-October 03 From: Burford, ON, N0E 1A0 Member No.: 1,244 Region Association: Canada |
Ah, a topic dear to my heart, and a little within my realm of expertese.
Using counterflow you can get better heat transfer, and that is a good thing. However, by reducing your airflow down to 1/3 of the original design, your cooling will be reduced down to about 1/3 as well. You may be lucky and only lose 50% but I doubt you could get that lucky. Adding counterflow layers is an incremental effect, but having lots of airflow is crucial. The main thing here is that the heat is being dumped into the air. To reduce the airflow by two thirds would require a temperature rise three times greater, and that will not happen in your design. Sorry. It is difficult if not impossible to cheap out on the rad AND the hoses connecting it to the engine. You have to have the correct combination of airflow and waterflow. Remember that the greater the waterflow, the greater the HP required for the pump, and that reduces the rear wheel HP. The HP used by the pump is transferred as heat to the water coolant, and that adds to the load on the rad. However, if the waterflow is too small, the engine will overheat because the circulation cannot take it away as fast as it is produced. If you want the engine to live, then you have to determine the heat dumped into the coolant by the engine under full load. Then the pump has to move that heat ( so much GPM times deltaT). Finally the rad and airflow must transfer that same amount of heat to the air. It is not trivial. |
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