--- Recover heat from exhaust --- I got just the right heat exchanger!

[basslover911]

Oh and bgd73 ... I know tractors in the past used convection for their radiators I dont know what happened to that... so I know it is possible...

[chuckm]

Just a slightly different track to suggest. Instead of using water as your working fluid, could you use refrigerant (R-134a)? The lower specific heat and boiling point will help your efficiency (even though the heat energy extracted may be the same as with water, turbines and the like run via temperature/pressure differences). Then, with an aftercooler condenser, you may be able to use the phase change to extract energy more efficiently by generating a higher pressure diffential. The circuit would be muffler/exchanger --> turbine or other expander --> aftercooler condenser (probably just an automotive condenser unit) --> check valve --> muffler/exchanger.

[dwtaylorpdx]

Originally Posted by extragoode

I'd love to do this and started a thread discussing it about this time last year. I just couldn't come up with any practical way to accomplish it. I also didn't know that's what was done on race cars, but it makes sense, plus those guys will do anything to get more total power out of the engine. Do you know of any aftermarket parts for this that would work on my pickup? Or on any production vehicle, or are all the setups you're talking about completely custom?

Starting thread now....

Dave

[basslover911]

Originally Posted by chuckm

Just a slightly different track to suggest. Instead of using water as your working fluid, could you use refrigerant (R-134a)? The lower specific heat and boiling point will help your efficiency (even though the heat energy extracted may be the same as with water, turbines and the like run via temperature/pressure differences). Then, with an aftercooler condenser, you may be able to use the phase change to extract energy more efficiently by generating a higher pressure diffential. The circuit would be muffler/exchanger --> turbine or other expander --> aftercooler condenser (probably just an automotive condenser unit) --> check valve --> muffler/exchanger.

Thats EXACTLY what I have had in mind. The only thing is weather the fluid will work by natural convection or not (it WILL if the fluid can become steam, but I dont know if it stays in a fluid state).

Another thing, doesn't R-134a have to be pressurized? That (1) raises the boiling point and (2) makes the system a tiny bit more complicated than a non pressured system.

[moorecomp]

Originally Posted by basslover911

Well thats my only problem, wondering how much flow there would actually be by natural convection.

And really natural convection is the only real way to do it, because if you use a pump it kind of defeats the purpose of the other pump that is producing electricity... Unless the pump simply gives it a "head start" and the heat further accelerates the flow... would that work?

Ive been trying to look around for videos on maybe sience labs or something that can show heating on one side of a pipe and the water actually moving to the other side of the pipe (so I can see how hot it really needs to get (or the temperature difference between each side for that matter)... but I cant find any...

It sounds like you are describing a Stirling Engine.

No need to use a liquid, it will operate using a heated gas. Since approx. 1/3 of the energy released by combustion goes out the exhaust ( Thermal Efficiency of Engines by EPI, Inc. ), it seems you should be able to recover a fairly significant portion of that. I do know it is expensive for the few Stirling engine powered devices out there.

Here is a link to a guy who has built a few on his own.

DS Stirling Page

And this has a lot of info and links.

Stirling Engine DIY « Blog for newenergydirection.com

If you could develop a viable stirling cycle powered 12v alternator that runs using the waste heat radiated from a cars exhaust pipes, then get rich and share the money and glory with the ecomodding community.

[chuckm]

Originally Posted by basslover911

Thats EXACTLY what I have had in mind. The only thing is weather the fluid will work by natural convection or not (it WILL if the fluid can become steam, but I dont know if it stays in a fluid state).

Another thing, doesn't R-134a have to be pressurized? That (1) raises the boiling point and (2) makes the system a tiny bit more complicated than a non pressured system.

Re convection: Hmm... you might need a solenoid valve and a high pressure bypass in order to charge your system. As the fluid is heated by your exchanger, the pressure goes up. Orient the exchanger so that the hot side tap is on top, ensuring that only vapor leaves the unit for your engine (sterling, turbine, or whatever). Put the solenoid valve in the hot line, along with a pressure relief bypass (for when you turn the car off!). From your engine, you run through the condenser to extract the remaining heat and increase the pressure differential across your turbine. From the condenser, run through the check valve and back to the exhaust exchanger. If you can use the check valve to force the fluid to flow in a particular direction, then convection will do fine.

Yes, it does have to be pressurized, so I can fully acknowledge issue 2. That's why I'd just rob the parts off of a junkyard AC. Yes, the boiling point is raised, by the high pressure, but that's not actually a problem. R-134a buys you two phase operation in a lower temperature regime than water. Google "R-134a table" for info. At atmospheric pressure, R-134a boils at -15degF. Hike the pressure up to 160psia and the boiling point only becomes 110degF. If I were designing a system, I'd want my cold side to condense around the 110-120degF mark, allowing me to dump the heat off in almost any weather condition (depending on where you mount the condenser).