Author Topic: heat exchanger  (Read 264 times)

vegoil

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heat exchanger
« on: October 17, 2018, 06:21:25 PM »
dose anyone know if this heat exchenger has been used on the exhaust on a Lister CS to heat water?
or if it can work?
OR is there sump-thing better?
please have a look on Ebay.

 160mm Exhaust Gas Heat Exchanger Flue Gas Heat Exchanger AWT-7/160-VA

John

glort

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Re: heat exchanger
« Reply #1 on: October 17, 2018, 08:20:37 PM »

The amount of heat one will gain from exhaust is limited.  I would certainly not think that the expense on such a HE would be worth while.

It's hard to tell exactly what this setup is like from the diagram but I would think it not very efficent. The majority of the gasses can go straight up the middle with only the boundary layer gasses on the edge touching the heat transfer surface and giving up their energy to it.  I can't tell if the outside as well as the inside of the tube is in the gas passageway or just  the internals of the coil which would greatly reduce the surfae area of the gasses.

For decent efficiency, the coils should be slightly spaced and the end of the coil capped so the gasses are forced out and around the coils touching the inside, sides and the outer surfaces of the coil.  Blowing the gasses straight through the middle would probably have something pathetic like a 10% efficiency if that. The design is poor IMHO and probably only works on a fire place because of the massive volume of gasses and wasted energy therein.
In an engine, I reckon you'd be lucky to slightly warm a bucket of water an hour with this.


If you wanted to do a co gen system I would simply be using a Tube in Tube design which that essentially is.  Get some 1.5" round tube and put it in something bigger, say 2.5".  See if someone like an exhaust shop can coli or at least bend it back on itself to make it shorter if needed then insulate it.
Still won't be great but it will be better than this flue heater and a lot cheaper.

You could also get a gas how water system, remove the gas burner and direct the exhaust gas up through the center flue and capture the exhaust heat that way. This would also give you an insulated storage.  This warmed water could be then fed into your regular hot water system as a pre heater which would reduce the temp rise the heater had to put in the water and thus reduce your energy usage. Gas heaters have a Diffuser that sits in the Middle of the flue to break up the gas stream and cause a Turbulence so the contact area of the gasses is a lot more than just the boundary layer which quickly cools and then is ineffective in any more heat transfer. 

Smaller " Finned" and plate HE's are more efficient but blowing exhaust through them would probably foul them up in very quick time. You could have an amount of water going through them  injection style to keep them clean but then that is likely to take away a lot of heat energy in itself.
A tube in tube system would probably need an occasional flush to keep buildup from being excessive but not to the degree that the deposits from smaller passageway HE's would need.

Another way of doing this would probably be to completely enclose a smallish car Muffler.  All one would need to do is build a box around it with just the outlets protruding for connection.  Mufflers swirl and slow the gas speed and generally have good external surface area. The bigger you used the better but there will be a cross over point where all the useful heat is given up.  As there isn't a lot to start with from a CS, I would not think a very large muffler would be needed.  Boxing in a muffler should be easy to Fabricobble  either DIY or for a sheet metal shop.
Tap in a water inlet and out let at opposing ends and it would be done.

Should be cheap and effective.

saba

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Re: heat exchanger
« Reply #2 on: October 17, 2018, 08:55:54 PM »
Good answer from glort, the one you propose on ebay is for a woodstove not really suitable. Some people use swimming pool heaters if you can get one cheap give it a try.

AT the moment i am using a old oil cooler with brass pipes inside, it works super and condensates the exhaust gasses. Only thing it clogs up with soot. And it's a ..... to clean.

Next plan, if I ever have time, is to install the inside of a condensing natural gas central heating boiler, it has a drain for the condens and it's sort of made for it.

Greetings Bernhard

vegoil

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Re: heat exchanger
« Reply #3 on: October 17, 2018, 10:20:39 PM »
thanks for the answers.

 I have already looked at pool HE plus a lot more on the internet
I have also thought about a pipe in a pipe. the exhaust I have is 73mm OD and I have a pipe that could go over it at 103mm ID that would give a gap of 15mm water jacket I have room to make one up to 1 meter long and another 600mm long. maybe weld spiral  inside the water jacket. ( just thinking out loud)

the cost of the build would be minimal  as I have all the parts needed and its all stainless pipe

I also have the just the core of a bronze oil cooler 850mm long 200 round (very very heavy) plus I had been thinking ahead about how to clean the d***d thing

what do you think?

John

BruceM

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Re: heat exchanger
« Reply #4 on: October 17, 2018, 11:32:43 PM »
As I recall, Mobile Bob came up with a design for a diesel exhaust HE that he claimed was easy cleaning/maintenance. I'd suggest going over to the microcogen forum an asking for his help.

Exhaust HE is a lot like elaborate gray water systems-  everyone abandons them in time because of all the labor in cleaning them.  So a design that was oriented around ease of cleaning from the get go makes a lot of sense. 

I never followed this area closely as my Listeroid is WAY too far away to be useful for heating, nor do I run it for long enough periods in the winter.  You are at likely only collecting about 1500 watts of heat from a 6/1 running full load with 2400 watts on the generator. Unless the engine is very close to your point of use, the breakeven for the cost of insulating the long plumbing run well could make your breakeven point beyond the life of the engine, or perhaps yours.









EdDee

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Re: heat exchanger
« Reply #5 on: October 17, 2018, 11:57:10 PM »
Hi Guys,

I have been using a tube in tube exchanger for a few years now. On about 8hp, with around 2kw load, the 3m long exchanger heats up 300L approx from around 15C to 75C in about 2 to 3 hours.... Currently we have the lister down for rebuild and have been using a babbington burner on a 700mm long exchanger doing the same job, but burning about 30 to 40% more fuel for the same time period... the bab puts out way more heat, much more goes to the stack because of the short exchanger, but in most more ways, better to run from a heating pov if electricity is not needed...

Cheers
Ed
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glort

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Re: heat exchanger
« Reply #6 on: October 18, 2018, 01:42:08 AM »
thanks for the answers.

 I have already looked at pool HE plus a lot more on the internet

I am familiar with pool heaters and I would suggest the Fins are too widely spaced to pick up enough heat from the exhaust gas. That said, if you enteres the exhaust along the length of the HE so it was diagonal to the fins and skimmed across them spreading the gfas out rather than straight through, it may slow the gas speed and be more effective.

One thing, you would only have to enclose one side of the HE and it would be real easy to clean, just give it a hose.


Quote
I have also thought about a pipe in a pipe. the exhaust I have is 73mm OD and I have a pipe that could go over it at 103mm ID that would give a gap of 15mm water jacket I have room to make one up to 1 meter long and another 600mm long. maybe weld spiral  inside the water jacket. ( just thinking out loud)

The " Turbulator" would be essential to break up the boundary layer gasses and get all the heat out of the exhaust stream. The more swirl and the lower the gas speed the more heat will be given up.
I did this with a WVO burner for heating veg oil.  Blowing about 150KW of heat straight down a 3" pipe was not real effective.  Throwing random bits of perforated steel inside  which made the flame go every which way even though the steel sat on the bottom edge of the pipe and only went  way across the diameter, improved the thing out of sight.
Water heaters use a thin , flat strip of metal that is pressed like a tree design and some have a twisted spiral.

 You wouldn't need much gap between the pipes either, 15MM of moving water will dissipate a LOT of heat energy.  I would think if you bent the pipes in one another and they touched it would also not matter because the contact area will be small and the water either side of the touching surfaces will carry the minuscule amount of heat away.

Quote
I also have the just the core of a bronze oil cooler 850mm long 200 round (very very heavy) plus I had been thinking ahead about how to clean the d***d thing

If you look at liquid to liquid intercoolers on boats and the like, they are in a stainless outer shell with  endcaps that are bolted on and have seals on the ends. the cooling water is generally T'd off at a 90 degree angle so the water passages can be rodded out to get rid of sand, shell grit and other debris.

I think for cleaning a HE in this application, all you are really going to need is an infusion of soapy water now and then.  Maybe at worst a bit of KOH or NAOH to shift the carbon and then give it a rinse.
I think Bruce is wise as usual with his suggestion to build the thing with cleaning in mind.  You could do the thing Vertical or at least at a downwards slope so you could clean from the bottom up which would allow a bit of a soak and then drain.  I would also tend to reverse flow the exhaust.  Push it down rather than let it go up.  Outlet of course will be closest to the engine where the gas temp is hottest and you are taking max heat from the coldest  part of the gas being at the far end from the engine giving the most thermal difference and therefore opportunity for heat transfer.



veggie

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Re: heat exchanger
« Reply #7 on: October 18, 2018, 05:23:34 PM »

One thing that I was thinking about over the years is a pipe-to-air exchanger on the exhaust.
If you are planning to heat the same room that the engine located, maybe a very long run of exhaust pipe within the room (before exiting the building) would give off a fair bit of heat like a radiator.
The long pipe would work best if fitted with cooling fins. (Called a Fin-Tube)
The idea being that most of the exhaust gas would be cooled drastically before exiting the building by losing it's heat to the finned pipe.

just a thought...

veggie
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BruceM

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Re: heat exchanger
« Reply #8 on: October 18, 2018, 05:35:08 PM »
No free lunch-  cooling exhaust gas yields precipitation of goop inside pipe, reducing heat transfer and ultimately a horrible cleanup job.  For exhaust heat capture, that issue must somehow be accommodated. 

I'd love to see what Mobile Bob came up with...his work on efficiency of automotive alternators at higher voltages was very impressive. 


glort

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Re: heat exchanger
« Reply #9 on: October 18, 2018, 06:14:28 PM »
If you are planning to heat the same room that the engine located, maybe a very long run of exhaust pipe within the room (before exiting the building) would give off a fair bit of heat like a radiator.

Having had a bit to do with alternative heaters in various forms, I am always amused to see how people Duct Flues out of the home/ area to be heated ASAP.  Some have the exhaust going straight through a wall and to the outside of the building.  Very few realise the heat in the exhaust and take advantage.
Ideally you want heater ( wood/oil/ etc) burner at one end of the space to be heated and the  flue exit at the oother giving the longest resident time of the gasses to transfer their heat to the flue and surrounding air.

The Russian Type stoves which have very long zig zagging passageways set in a large thermal mass work well and are efficent because they extract the maximum energy through the long exhaust passage and  sink it into a thermal mass which gently radiates the heat over time.

Perhaps with the long exhaust pipe, it could be placed along a wall say at a slight upward angle.  The engine exhaust input could be near the end of the pipe but enter in a T from the top. The pipe would exit both ends of the room.  At the lower end the pipe could be capped with a removable plug. For cleaning a hose or a long handled brush like those used for cleaning Chimineys could be inserted from the higher end and the Drain plug on the lower end removed therefor allowing the soot to  Flow right on out. Because the exhaust entered from the top of the pipe, the engine would not ingest any water.  It would simply flow out and past the tube.

I wonder what a small amount of water injected into the exhaust tube when it was hot would do?  Experience would suggest the carbon is pretty easily shifted and if the water was entered in a hot section where it could change to steam, it would probably dislodge a loot of buildup.  Perhaps an amount of detergent could be added to increase the effectiveness.

Injecting water into the engine itself may also help.
I have noticed going back to my early days with WI that the increased performance of a vehicle lasted a good time past when the water ran out.
The engine carbonizing up I do not believe is a possibility because if the fall off was that quick, the engine would  keep deteriorating  quickly and soon fail.
My un tested and unexamined theroy is the WI helps clean the exhaust, mainly the muffler of deposits allowing better gas flow.  Until the Deposits build to a level where exhaust gas pressure forces them out, the vehicle runs better through lesser exhaust restriction.

It is very easy to see the amount of black residue that is expelled when an engine is Given the water straight down the throat treatment. It is also easy to scrape thick Layers of carbon of an exhaust outlet. 

I think given a length of pipe which both ends can be opened for wet flushing or Physical removal with a brush, cleaning should be easy and the heat transfer effective.

BruceM

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Re: heat exchanger
« Reply #10 on: October 18, 2018, 06:50:04 PM »
"I think given a length of pipe which both ends can be opened for wet flushing or Physical removal with a brush, cleaning should be easy and the heat transfer effective."

Sounds like a good plan, Glort.  Veggie's clamp on tube fins is also a good way to increase surface area.

I have a crazy idea-  what if the exhaust was directed into a barrel of water, with a diffuser to get lots of small bubbles throughout the tank for good gas to water heat exhange.  With lots of pex or copper tube for heat exchange in the tank.  You'd have to dispose of the water periodically, perhaps after adding detergent and agitating via drill mixer.  Of course this would only work if you could use heated water below 100F/boiling.