How to use TEGs to create power with your exhaust heat

[Galane]

What I'm interested in TEGs for is to power a TEC air conditioner. Wouldn't need enough TEGs to replace the alternator, just enough to be chillin' some antifreeze+water.

Concept is to mount an AC condensor in the usual place but pump engine coolant through it and through heat exchanger blocks on both sides of some TECs. Valves would separate the coolant into two loops, one between the TECs hot side and the condensor, the other between the TECs cold side and the heater core inside the cab of my 1982 GMC truck.

For winter use the valves would cut out the TECs unit and re-route through the heater core normally. The condensor could be cut in as an additional radiator if needed for extra cooling when the truck has a heavy load.

I suspect one of the newer style condensors with the flat tubes that have many small channels would work better than the old style with the about 0.25" round tube.

If it could keep summer heat in the cab down any at all, it'd be useful. The cooled air would all be going out onto the floor since the truck has none of the ductwork and vents that came with factory AC.

There's a huge amount of room under the hood and the bed of the truck, unlike the 1991 Chevy pickup where the drivetrain came from. Best part of such a setup is the cooling would be 'free', no efficiency impact on the engine aside from the tiny amount of power draw for a couple of electric pumps to circulate the fluid.

Would connecting the TEGs in parallel with the alternator help lower its load or would that do nothing?

[Phantom]

I know that they work better with a larger temperature differential but how large do you need?

At some point it will not generate more energy even if you add more heat.

Looking at the spec sheet you linked to the best conversion rate is cold 30C (86f) and hot between 150-225C (302-437F). So you only need about 216f to 351f difference.
When the hot side is increased to 300C or a temp difference of 486F the conversion rate drops from 6% to 5%.

I would assume that the above numbers happen due to how fast the material can shed the heat on the cold side before it gets heat soaked and the temp differential goes down.

[IamIan]

Originally Posted by Galane

What I'm interested in TEGs for is to power a TEC air conditioner.

Might want to consider one of the small electric (50w to 150w range) compressor/heat-pumps for air conditioning instead .. you can get significantly more BTU of heat transfer for the same Wh electrical input.

[teknomage2012]

Originally Posted by t vago

I would suggest placing these TEGs in the immediate vicinity of your upstream O2 sensor, and just behind and downstream of your downstream O2 sensor. If the O2 sensors can take the heat, the TEGs should also be fairly happy there.

Edit: And are you sure you want to rely on ambient air to generate your temperature differential? Seems like you're going to want to put some cooling fins on to take away this heat, and use some sort of forced airflow, at a minimum. Maybe a coolant loop would be better.

You could include tube in tube design; where a larger square tube is placed over the cooling finns. The downstream side could end in a tapered nozzel to a Venturi that uses the exhaust stream to pull through cooling air over the cooling fins.

[Galane]

Originally Posted by IamIan

Might want to consider one of the small electric (50w to 150w range) compressor/heat-pumps for air conditioning instead .. you can get significantly more BTU of heat transfer for the same Wh electrical input.

Where do I find one of those and are they small enough to mount to the AC bracket on a 1991 Chevy 350 from a pickup? I installed the AC delete bracket and pulley there. Would've been nice if the truck already had AC but the city government went as cheap as possible back in 1982.

[Isaac Zackary]

I thought I'd throw in my 2 cents.

I don't think that overheating these things will be a problem if you have enough cooling. Yes, an exhaust manifold can reach 800*F, but nobody every tries to cool the exhaust manifold. With these thermo-electric-generators you need to cool one side of them in order to generate electricity. By cooling them you also cool the exhaust pipe they are attached to. We're talking hundreds of degrees differences, maybe even cooling them with 100*F or cooler water. If you're cooling them with 100*F water it will be nearly imposible to even reach close to the 600*F overheat mark.

It sounds like you could cool them with engine coolant and then have the benefit that it warms up your engine more quickly too.

[teoman]

What is the expected life of these? I have not seen any data on that.

[IamIan]

Originally Posted by teoman

What is the expected life of these? I have not seen any data on that.

I'm sure it varies from product to product and details of the usage conditions .. but at the highest $ end .. these claim up to 12% conversion efficiency at up to 600deg C and up to 20 year operational life expectancy.

And at the very top (in the 70s) .. The TE modules used in the RTG used on the Voyager 1 are still running launched in 1977.

[freebeard]

I won't link directly because language, but AvE put up a vijeo on Youtube 2 days ago called Rocket Stove Peltier Charger | Seebeck Generator that demonstrates Ecomodder-level 'fabricobbling'.

What we learn is they work great until the solder connections melt.

[IamIan]

Originally Posted by CFECO

Back when I was designing a car to compete in the Auto X-Prize Competition, I was working on a exhaust heat recovery generator. I planned to create steam which would drive a small engine, either piston or turbine, which would turn a generator. My first test boiler was a length of stainless brake line coiled inside of a housing, that the exhaust from a small engine emptied into the middle of the boiler at the bottom. It went up the inside of the coil, flowing over the top of the coil and and exited at the bottom outside of the coil. On the few tests I was able to perform, steam was produced in less than a minute, so the ability to remove heat from the exhaust was easily accomplished. Work was halted when I was forced to move, lost my workspace, and most of my computer files including drawings and calculations. Such is life. The "engine" I was going to test first, was a turbine out of a pneumatic wrench, and the second was a multi cylinder 2 stroke engine for RC aircraft. There would have to be other systems constructed, pressure pump, condenser, and the generator head itself. The F-1 guys have simplified this greatly by have a direct drive generator driven from the turbo shaft, Nice! I wonder what kind of generator works at those RPM levels? Oh well, my two cents worth.

Looks like others are still moving forward with the steam approach to gather energy from the exhaust line.

Some nice things about that approach.

• The sleeve around the exhaust can be smaller than air based heat exchangers and directly applied TE modules.
• As steam it lowers the required high temperature requirements of the TE used.
• The contact surface area involved in heat transfer will be better than a flat / square trying to extract heat energy from a round exhaust tube inside of the square / flat.