Quote:
Originally Posted by Daox
<snip>
The numbers aren't super amazing, but they are substantial I think. I think its reasonable to assume we can get 400°F temp air with 200 CFM giving us a possible 5600W, but at 50% heat exchanger efficiency we're looking at 2800W. If we compare this to MetroMPG's block heater vs time chart (test on his Metro), that would give us a 70F coolant temp rise in 12 minutes. Obviously, this also isn't realistic because everything has a warm up time. The manifold isn't going to instantly be making 400F air, and certainly not at 200 CFM.
|
Other side of the coin is what can you get from your exhaust?
From my back-of-the-envelope calculations the energy that leaves your Metro exhaust in the form of heat is about 6 kW, so I would not expect that you will get more than that.
(Why: 1 liter displacement, assuming 2000 rpm, that means internal airflow 1000 liters per minute, around 17 liters per second worth of heat in exhaust gases hot around 300 Kelvins.
lets assume it is air with thermal capacity about 1,2 Joule per liter per Kelvin, lets assume you can cool it down to ambient temp - whole 300 Kelvins to be optimistic. That gives me Q=F*cp*dT=6120 W. Correct me if i am wrong)
Just out of curiosity,
what is the exhaust tip temperature? The temperature difference between manifold and ?opening? (how do you call the very end of exhaust?) can tell the maximum amount of energy you can reasonably get from your heat exchanger, because that is the heat your exhaust system radiates to the
atmosphere now.
- i would propose something like hose-in-hose heat exchanger: enclose whole exhaust system with aluminum flashing leaving 1-2 cm gap around, optionally put insulation on the flashing, seal well. Cold air is sucked at the end of the car and goes to the engine compartment all the way, pre-heated by exhaust. Maybe try to use the flexible aluminum duct you used to make WAI?