4 ms·
I don't see how you can have it both ways. Either there isn't much waste heat, or there is lots of it and you can potentially harness that still.
by eloff 5y ago
I don't see how you can have it both ways. Either there isn't much waste heat, or there is lots of it and you can potentially harness that still.
- stickfigure 5y agoLet me make an analogy: Your petrol car has a heat engine. It converts about 20% of the heat energy released by combustion into mechanical energy. The rest goes out the tailpipe. Yet harnessing that remaining energy is not so simple because the temperature gradient is (relatively) small. The thermoelectric effect also requires large temperature gradients, and efficiency is proportional to the gradient.
- eloff 5y agoI think the car is a bad example because the temperature gradient is high and it should be possible to harness some of that waste heat. We just don't try. With hybrids we could definitely put that electricity to use, so I'm surprised no attempt is made to harness it. Especially for long haul trucking it could be worth it, but they're aren't diesel electric hybrid trucks that I'm aware of. Or at least they're not common. I do understand your point though.
- stickfigure 5y agoWe do try! Some power plants and ships pipe turbine exhaust through a boiler and steam engine to increase fuel efficiency: https://en.wikipedia.org/wiki/Combined_cycle_power_plant https://en.wikipedia.org/wiki/Combined_cycle_power_plant Might be tough to fit all that under the hood though.
- eloff 5y agoI was talking about in cars specifically. It would seem to me that adding some kind of TEG around the engine and part of the exhaust system might be worth it on a hybrid vehicle. https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator I guess it would depend on if you can make it cheaply enough.
- stickfigure 5y agoSounds like folks are working on it: https://en.wikipedia.org/wiki/Automotive_thermoelectric_generator https://en.wikipedia.org/wiki/Automotive_thermoelectric_gene... The numbers being floated about seem to be 4-5% fuel efficiency gain. Significant, but as you say it depends on the price.
- duskwuff 5y agoA thermoelectric generator is to heat what a hydroelectric plant is to water. Neither one of them consumes its respective resource; they just capture some energy as it naturally flows from one space to another. Seeing water at the bottom of a dam, or heat on the exterior of the RTG, doesn't mean that any energy has been wasted; it just means it's reached its resting point.
- eloff 5y agoYeah, that makes sense. If the heat at the bottom of the dam, to mix your metaphors, has no further to fall, that is the temperature gradient compared with the external environment is low, then you're right, you can't really do anything useful with it in a practical way.