Half a croissant, on a plate, with a sign in front of it saying '50c'
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reclaim car coolant heat

reclaim energy from car coolant
 
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A closed circuit steam engine which uses the waste heat in car coolant water (that's what the radiator is for) to make electricity.

Aha! I hear you say, but the water is only about 80 degrees c so minor technical problem with the old boiling point of water..

Touche I say, steam engine is in a closed circuit, running at about 3ps absolute (i.e. 12 psi below atmospheric), so it would work.

Yeah, I know about thermocouples, but they ain't cheap and BMW has, no doubt, patented the heat recapture off the exhaust pipe, unless Google is fibbing to me...


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       If it's in a closed circuit, you could use something with a much lower boiling temp than water, which (I think, help me out here, halfbakers!) would facilitate better energy transfer since it would operate in a higher-pressure environment.
Alterother, Jun 26 2009
  

       at what temp/pressure does a steam engine become useful ?
FlyingToaster, Jun 26 2009
  

       The average light off temperature at which the catalytic converter begins to function ranges from 400 to 600 degrees F. The normal operating temperature can range up to 1,200 to 1,600 degrees F.(Copyright AA1Car.com)   

       May be a better heat source?
Bdsman64, Jun 27 2009
  

       It's been thought of many times, but hasn't made it to the real world because it's too hard to maintain/unreliable/(in this case) needs a supply of clean water. Stirling engines are better suited to this, and they're not reliable enough for cars either.
mitxela, Jun 27 2009
  

       "The average light off temperature at which the catalytic converter"   

       That's true but I bet those pesky BMW people have patented it..   

       Anyway, the exhaust should be water-cooled after the catalytic converter cos it'd be a bit quieter and easier to run the rest of the pipe, boats use rubber tube. Anyone who's ever tried to get a replacement exhaust section to line up with the rest of it will know what a swine it is....   

       "a much lower boiling temp than water, which (I think, help me out here, halfbakers!) would facilitate better"   

       I took a quick peek at boiling temperatures and the best one I found (and I could be wrong) was paraffin. Fluids which would be good are either expensive or toxic or flammable or all three, lucky eh?   

       "needs a supply of clean water. " It's a closed circuit, there's a condenser after the generator to condense the steam back into water, which then goes back into the boiler.   

       Aha, you're going to say, so it's still leaking heat..yes, some heat. If you really wanted to go to great lengths, you could daisy chain the systems so each one fed of the waste heat of the preceding one, but I think you'd get a problem as the vacuum would have to be higher in each successive one to make it work. I was looking for a vacuum gauge to try this out and found one on the net that seemed to advertised as measuring to less than no pressure, very good trick :)   

       As a minor point, coolant seems to run at about 85 degrees and the CPU of a pc is now about 70 degrees..   
      
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