Condensing exhaust in engine

[Shandor]

We have a device that needs to water emitted in an exhaust stream of a diesel engine. that is about all I can say about it.

So I am basically looking to route the exhaust through a condenser, collect the water and let the remaining exhaust pass through.

There are some issues with this. First if I do it early enough in the pipe (i.e. before any catalytic converters or anything) the water will be quite acidic.

Second, I want to limit the number of components required to do this. So I am thinking of using the condensed water as the media to remove heat also. Basically, collect water in the bottom of something that would look like a sink trap (but not full, otherwise I add significant pressure drop to the exhaust stream), pump that water at say 10 psi through a radiator, and into a spray nozzle that throws the cooled water into the exhaust stream to collect even more water. The pressure supplied by this pump would supply the water to other areas of the device also.

What do you think of this design? Is there something obivously better? Is it a dumb idea?

so my final questions are: how do I size the radiator and where to I get one? how do I size the flow rate for the cold water spray? I realize its about how much heat I want to remove in order to get the water to condense. but I am unsure of how to get at that.

Im a mechanical engineer who hates engines and thermo. mechatronics is my area.

 

[MikeHalloran]

Please re-write your first sentence. I don't understand what you are trying to do to the exhaust gas.





Mike Halloran
Pembroke Pines, FL, USA

 

[IRstuff]

Is this a one-of? or a production requirement?

What kind of precision/accuracy are you trying to measure at? How long do you have to collect the water?


TTFN

FAQ731-376

 

[Shandor]

Mike,

sorry I left out a word and the sentence IS confusing.

We have a device that needs to use the water that comes out of the exhaust of a diesel engine. Basically I need to take the exhaust from the engine and condense it because I need that water. I will collect the water and let the gases pass through.

The two designs I can think of are to have a coil inside the exhaust stream, which I will run cold water through (it will be pumped through another radiator on the outside to cool down the water inside that loop. then I would collect the water from the exhaust that drips off the coils.

The other design I can think of is to spray cold water into the exhaust stream. This should pull some water out of the exhaust stream. Then I would collect the water I sprayed + what condensed, run that through a radiator and spray it again. This way I would accumulate water for the device.

I need to collect about 20 ml of water/minute.

So I dont know how big the radiator must be, I dont know how fast I need to pump water (either for spray or cooling coil).


I hope this was more clear.

 

[Shandor]

IR stuff,

for now I need to make 2 of these devices. Ultimately that device would be mass produced.

I need to condense 20ml/min or so (on the whole diesel makes about as much water as fuel it burns, so a kilogram of fuel makes about a kilogram of water). at 20 mpg, each mile should make about 160g (or ml) of water. Its ok to condense more than this rate, its not ok to condense less.

I hope this is clearer.

 

[MikeHalloran]

On a boat, it's common to inject water into to the exhaust, to cool the gas enough so that fiberglass mufflers won't melt. I wouldn't add water to the gas stream on a road vehicle.

Cooling the exhaust gas to any extent will mess up the operation of any catalytic converters downstream, so your condenser should go after the cat.



Mike Halloran
Pembroke Pines, FL, USA

 

[Shandor]

OK lets say I do that (condense water after the catalytic converter).

What do you think is a better design? spraying water into the exhaust stream, or running the exhaust by a cooling coil?

more importantly, how do I size these components? I dont know how to calculate the correct flow rate (for the spray or the cooling coil). I also dont know how to size the radiator that will be needed to cool the water before it enters the exhaust stream. Any ideas on how I go about this?

 

[MikeHalloran]

Yeah, about that; condensing and collecting water, then pumping and cooling it and injecting it to condense and collect more, in a sort of tail recursion. Worrying about it has clouded your thinking. Simplify your problem.




Mike Halloran
Pembroke Pines, FL, USA

 

[dcasto]

There was a packaged unit call a REN Rainmaker made by Davco Ren. Ren also made automatic oil level controllers for industrial engines. It wouls use the air frfom the radiator to condense water. We then would pump the water into the radiator in remote loactios (desert).

 

[btrueblood]

Spraying water into the gas stream, in an effort to condense more water from the stream, seems fruitless; you are just re-saturating the gas stream. Condense the water on coils and collect the drops.

 

[davefitz]

I think it would look great. Coonect a sink trap to the muffler, then attach the trap to the radiator and spray a garden hose over it. Call over the neighbor and ask him what he thinks of it. Tell him you read about it in popular mechanics.

 

[EdStainless]

Sounds sort of like gas sample coolers. A small can with a cooling coil in it.
Even if you do this after the cats, which you must, you will still need to use high alloy materials.

What is the relative humidity of exhaust gas? How cold will your coils need to be in order to get condensation?
I would expect that a small 12V inline pump and a radiator about the size of a small car's with a single fan on it should cool you loop enough.

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[IRstuff]

Have you considered the volume that this would take? I'm thinking that a couple of cubic feet are required for the exchanger with the exhaust and something comparable to an air conditioning compressor.

Seems somewhat Rube Goldberg-ish to collect barely 2.5 gallons of water per 8 hours of operation.

TTFN

FAQ731-376

 

[Shandor]

Thanks all.

To most of those comments. I'm not married to the water spray idea, it just removes one pump form the entire system. I dont understand why spraying COLD water into the exhaust stream would not condense out more water. but if it is coils, then coils it is.

IRstuff,
The reason I started posting here was to get some help on those exact issues. The water gets consumed as it is made, and if there is too much condensed I can reject it. But there must be a way to know how to size the condenser and the radiator, knowing the exhaust flow rate, and how much water I want to get out of the stream (21 ml/min).

 

[IRstuff]

I'm just saying that you're going to be carrying a lot more water to do the cooling than what you're asking for as a product.

And the water you do collect will be quite dirty, containing particulates as well as various acids.

TTFN

FAQ731-376

 

[Shandor]

no problem with the dirty water. Im not sure why I would be carrying so much extra water? Either by spray or by cooling loop, the only important water is that which goes through the loop. why would I need to carry extra (besides from dealing with expansion and leakage). Why would the volume of water other than what is in the radiator matter?

Are you saying the radiator would be so huge that I would be carrying a lot of water?

That is exactly the information I am looking for, how to size that radiator. I need to take 700 deg C vapor down to under 100C. how do I size the radiator and cooling loop?

 

[dcasto]

Its a prepetual motion machine. Spray in water to have it absorb 1000 btu/lb of heat plus oh 70 f to 1070 F of sensible heat of 500 BTU/lb all to cool some water and condense total amount of energy is 1400 BTU/lb becasue you don't nee the water back at 70 F.

OOP's what about all that CO2 and N2, rats there goes that cycle.....

 

[Shandor]

It cant be a perpetual motion machine. Are all these people promoting a perpetual motion machine?

http://www.iit.edu/~ipro304es02/Condenser1.html

http://www.valv.com/literature/documents/tbs-brochure.pdf

http://www.specialized-mechanical.com/products/bh_feedwater.html

Actually that IIT one is virtually identical to what I am proposing.

Here they run the process through pipes and spray water on the pipes

http://www.sandia.gov/energy-water/EastPresentations/WaterConserv.pdf

In terms of heat transfer, what is the difference if the exhaust is running in pipes or not? and as I said, I dont care about the dissolved CO2 and N2 and other crap in the water. So it doesnt look like I'm asking for the impossible.

regardless of spray method (which probably needs a very high flow rate) or running it through a coil, I still am asking forSo, I dont think it is perpetual motion. Particularly because work is being done collecting the condensate and pumping it through the radiator to cool it down. someone to help me understand how I size the coils and radiator.

 

[dcasto]

You write out the heat balance and follow the enthaphies, including the energy it takes to vaporize the subcooled water that will condense and then that energy will be transfered to the water in the exhaust to condense it. You can make the energy balance by putting enough energy into the pumps and fans to make it work, so you will trade off energy levels in favor of making water.

The rainmaker uses the hot air from the radiator fan, no extra energy added to the system and free water.

 

[IRstuff]

If you're going to spray water on the exhaust stream to collect water, how will you separate the collected water from the cooling water?

TTFN

FAQ731-376