Exhaust Heat Recovery - Steam Power

[Christ]

I don't want to suggest that the coolant system is closed loop, but it's supposed to be, to a given temperature/pressure.

All the heat energy that goes into the coolant only allows it to get up to something like 14PSI, right?

[AC_Hacker]

I understand that this topic is titled "Exhaust Heat Recovery - Steam Power".

In one post, Daox set a modestly low performance bar for this thread:

Originally Posted by Daox

If we can recapture even 5% of that heat energy, we would harvest 450W which is enough to charge the battery without any drag on the engine. Anything more than that is simply icing on the cake to do whatever we want with it. I can't imagine it will be incredibly hard to capture 5%.

But in a previous post, Daox had this to say about peltiers/TECs:

Originally Posted by Daox

That would be the peltiers/TECs I mentioned earlier. Their efficiency is horribly low, 8% or less I think.

Curiously, the efficiency of the peltiers/TEC approach could actually exceed the low performance bar for the steam method by a considerable margin, and would appear to have none of the complexity and weight issues of steam.

So my question is why walk right past a possible solution?

Originally Posted by Daox

Alright fellas, back on topic here. If you want to talk about turbos and peltiers or other ideas please start your own thread (or post in one of the many already started).

-AC_Hacker

[Daox]

You'd have to capture 100% of the heat energy in the exhaust to get 8% of the electricity. It is impossible to capture all of it, so you'll get somewhere less than 8%. I also believe the cost of TECs is prohibitive due to the number that you'd need.

[Patrick]

Originally Posted by Christ

More than likely near impossible. There are surely more than 22CFM of air flowing in the exhaust for direct capture, but again, at what pressure? You'd choke the engine out trying to power the tool directly, I fear.

However, if the system were closed loop, never allowed to actually become steam, water is ~800 times more dense than air of a similar temperature, right?

22/800= .0275CFM of heated water flow.

That might not be correct, and I'm sure someone else knows how it should really be, but maybe it's at least encouraging?

What I'm suggesting is that pressurized water will take FAR less volume to produce the same power for a given pressure.

If you figure that your tool takes 22CFM at 90PSI, it *should* only take less than .25CFM of water at the same pressure. That means you can lower the pressure significantly while upping the flow rate, and you'll achieve the same end.

So, if you can't get the pressure up to the 90PSI that most air tools require for max load/power, you could just flow more volume at a lower pressure, like 1CFM of water at 60PSI or 2CFM of water at 30 PSI (not accurate figures, etc.)

Also, since you mention that your grinder felt lacking in power -

1. It wasn't meant to be strong, by any means, so no news there.
2. The power curve of air-powered tools is not even close to linear. It spikes somewhere in the chart, and that's about where it's most efficiently run for the power/air pressure/volume charade.

A couple things. If your water idea is a closed-loop system, I don't think it's going to work unless there's some phase change ala an air conditioning system. If you have water on both sides of the engine with the same pressure it's not going to move. Also, I think that .25 cfm is not going to cut it. The rotor is barely going to turn unless the fluid expands (think steam).

I think we need either a high-pressure stream of fluid flowing through the engine, a fluid that expands in the engine, or both. Water won't expand much until it reaches 212 degrees and turns to steam, then it will expand a lot (1700:1).

Someone mentioned earlier that someone had tried the exhaust pipe steam idea and it didn't work. I think this might be due to the fact that steel is not that great a conductor of heat. Copper is much better, by about 10X. So I would suggest replacing a section of exhaust pipe with copper tubing wrapped with a smaller diameter copper tube, similar to this: Graywater Heat Recovery (DHR) System: GFX Make the water inlet at the exhaust (tailpipe) end, and the outlet closest to the engine. This makes the output water the hottest. I think 10X the heat just might make some usable power.

[jdgFirefly]

Some other considerations:

- Smaller alternator and reduced electrical loads
- Connect two die grinders to the alternator. the steam must be connected in parallel to double capacity. (obviously this will be harder to rig up though)

As stated above it's the steam expansion that produces the usable power not the density of the fluid. Fluid density will come into play when designing a turbine but it's always the the expansion of the fluid that's the driving force.

I'm still wondering about a a/c compressor being used as an expander (motor). the physical size of a typical car a/c compressor is considerable larger than a typical air tool which suggests to me that it flows more CFM. If anyone has an old compressor sitting on a shelf please put some compressed air to the inlet (or outlet?) to see if it will run as a motor. It should run as a motor unless it has valves that don't allow it.

If it works, an AC system can be turned into a closed loop heat engine. simply run a small belt from the compressor to the alternator, disconnect the evaporator and run the lines to you new boiler. The condenser will now be low pressure so a small pump will be needed to push the condensate back into the higher pressure boiler to complete the cycle. Done and Done.

[Piwoslaw]

An 'inverted A/C system' is more or less a steam system, only with refrigerant instead of water. In this case we may use something other than water for our "steam", which would be appreciated in colder climates. But water (in a vacuum) would be OK for testing.

I'm not sure that an A/C compressor would spin when you blow air through it. The compressor probably has a one-way valve at the piston intake. Even without it, pumping air into the compressor would force the piston down to its lowest position and that's that. The compressor would need to have at least 3 pistons and some semi-complicated valve system to force air into the right piston at the right moment in the cycle. Something like a steam locomotive? Hint, hint, wink, wink

I'm not sure about reversing the newer scroll type compressors.

Soooo.... Replace an A/C system's compressor with an air motor we're getting somewhere.

[jdgFirefly]

Originally Posted by Piwoslaw

An 'inverted A/C system' is more or less a steam system, only with refrigerant instead of water. In this case we may use something other than water for our "steam", which would be appreciated in colder climates. But water (in a vacuum) would be OK for testing.

I'm not sure that an A/C compressor would spin when you blow air through it. The compressor probably has a one-way valve at the piston intake. Even without it, pumping air into the compressor would force the piston down to its lowest position and that's that. The compressor would need to have at least 3 pistons and some semi-complicated valve system to force air into the right piston at the right moment in the cycle. Something like a steam locomotive? Hint, hint, wink, wink

I'm not sure about reversing the newer scroll type compressors.

Soooo.... Replace an A/C system's compressor with an air motor we're getting somewhere.

You could be right, but If I understand correctly most automotive compressors are a swash plate style piston pump, which have a rotating orifice plate or the orifice and swash plate are fixed and the pistons and cylinders rotate together. So it shouldn't make a difference if pressure is added or made. the swash plate setup always has multiple cylinders, so the stalling you mentioned shouldn't be a problem. The scroll compressors also only has inlet and outlet ports, no valves, so I can't see any reason for it not working in revers as a motor.

The only setup i can think of that wouldn't work as a motor is if the compressor uses reed type valves like in most piston air compressors. Other wise a compressor should work as a motor if it has mechanical valves, orifice plate or just inlet and outlet like a scroll, twin screw and vane compressor.

It may be that there is many different styles in production, so its just a matter of knowing what your looking at when searching in the junk yard.

In any case I think its worth further investigation. I will try to remember to take apart different compressors next time I'm in the junk yard. (I think the innards of a scroll compressor will look good on my book shelf anyways)

[jdgFirefly]

I forgot to show this pic of a compressor. notice the pistons are arranged around the shaft and both ends of the piston are used. Should get nice smooth power out of it. On both ends you can see the orifice plates I was talking about (I'm not sure my terminology is correct) and the swash plate in the middle.

[AC_Hacker]

Electricity from Waste Heat

From this site:

Ener-G-Rotors' technology is based on the Rankine cycle, in which heated fluid flowing through a tube heats a pressurized fluid in a second tube via a heat exchanger. The second tube is a closed loop; the so-called working fluid flowing through it (a refrigerant with a low boiling point, in the case of Ener-G-Rotors) vaporizes and travels into a larger space called an expander. There, as the name would imply, it expands, exerting a mechanical force that can be converted into electricity.

Instead of turning a turbine, the expanding vapor in Ener-G-Rotors' system turns the gerotor ...[which turns an alternator.]

Animated Gerotor GIF here (file exceeds ecomodder size limit).

Gerotor = Gerotor - Wikipedia, the free encyclopedia

Looks tough to make?

How about this:

US $12.50 OBO + $17.18 Shipping.

It's possible.

-AC_Hacker

* * *

[Patrick]

A lot of automotive oil pumps are gerotors.