Condensing exhaust in engine
Condensing exhaust in engine
(OP)
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. :)
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. :)





RE: Condensing exhaust in engine
Mike Halloran
Pembroke Pines, FL, USA
RE: Condensing exhaust in engine
What kind of precision/accuracy are you trying to measure at? How long do you have to collect the water?
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Condensing exhaust in engine
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.
RE: Condensing exhaust in engine
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.
RE: Condensing exhaust in engine
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
RE: Condensing exhaust in engine
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?
RE: Condensing exhaust in engine
Mike Halloran
Pembroke Pines, FL, USA
RE: Condensing exhaust in engine
RE: Condensing exhaust in engine
RE: Condensing exhaust in engine
RE: Condensing exhaust in engine
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.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm
RE: Condensing exhaust in engine
Seems somewhat Rube Goldberg-ish to collect barely 2.5 gallons of water per 8 hours of operation.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Condensing exhaust in engine
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).
RE: Condensing exhaust in engine
And the water you do collect will be quite dirty, containing particulates as well as various acids.
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Condensing exhaust in engine
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?
RE: Condensing exhaust in engine
OOP's what about all that CO2 and N2, rats there goes that cycle.....
RE: Condensing exhaust in engine
http://www.iit.edu/~ipro304es02/Condenser1.html
http://
http
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://ww
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.
RE: Condensing exhaust in engine
The rainmaker uses the hot air from the radiator fan, no extra energy added to the system and free water.
RE: Condensing exhaust in engine
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Condensing exhaust in engine
After a lot of poking around I found out that this method of condensing water is called a "direct contact condenser" and is one of the most efficient methods of condensing water out of a vapor stream. Most applications dont have the cooling fluid being the same as the condensing fluid so this method would be inappropriate. but for my case it will be very effective.
now if someone could help me figure out how big the radiator needs to be, and what the pump rate should be, that would be great.
Or forgetting that method, and lets just say i have a heat pipe with a heat sink on the inside of the vapor stream and a heatsink outside. How big do they have to be?
RE: Condensing exhaust in engine
RE: Condensing exhaust in engine
Will also require frequent cleaning and replacing of the coil.
RE: Condensing exhaust in engine
yes that is something like what I was thinking (for a non-direct contact version), but I am asking about sizing that sort of a system. how much surface area would I need. how big does the AC radiator need to be?
dcasto,
how did you come up with those numbers? I guess I am trying to understand the set of equations that get you there. Obviously if I need 300 gallons to do this, that wont work for me. But I dont need to extract ALL the water, just about 25ml/min (you are saying that all that will only extract 1ml/min, this can not be right, I've seen that rate come out the tailpipe of my car without any heat exchange).
The exhaust stream is about 11% by mole of H2O, it is also between 250 and 700 deg C. I do not know if this exhaust stream is saturated with water as I can not find a calculator or pyschrometric chart that goes that high in temp. It seems that getting the water down to 96F will take out most of the the water out of the stream (I think maximum water content of a 100 degree vapor stream is about 4 or 5% by mole). the water content of the stream is approximately 160 ml/minute (at cruising speed), I dont need that much.
I may be barking up the wrong tree, but it seems this has been done before, I just dont know how.
htt
ht
Yes they talk about a refrigerated 'blanket' around the tail pipe, but how big is the refrigeration unit?
They also talk about a shell and tube design. This leads me to beleive that this can be done pretty compactly with the spray method which is more efficient.
RE: Condensing exhaust in engine
Mike Halloran
Pembroke Pines, FL, USA
RE: Condensing exhaust in engine
RE: Condensing exhaust in engine
ht
That condenser makes way more water than I need and it doesnt look too big.
RE: Condensing exhaust in engine
A DDC 16V4000 (~3650BHP, 48l, 2 turbos) typically uses a wye exhaust collector/riser. The branches are 12" diameter, one elbow and 1.5 ft of tube, and the run is 18" diameter about 2 feet long. The total length of interest would be about 4 feet.
When such a riser is jacketed, and the jacket is cooled with winter North Sea water that has gone through the engine's heat exchanger once (maybe 40F at most), I have one report of condensate flow of 5gpm, I'm guessing with the engine running at ~1000HP or so on just one turbo. I estimate that engine's riser had a surface area of 18 square feet condensing at the time.
The gas flow will not cause condensed water to flow uphill away from the engine, so jacketed risers require full time drains at the turbo flanges. You will of course want to slope your pipe so the water runs away from the turbo and cat.
Mike Halloran
Pembroke Pines, FL, USA
RE: Condensing exhaust in engine