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Old 24-06-2013, 03:46   #1
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Which Heat Conductive Material to Boost My Exhaust Heat Exchanger? Exhaust

Hi - I have a curly copper pipe heatex for domestic hot water wrapped around the iron exhaust pipe, but the curly copper coil is a bit too big and I want to improve the contact between the two metals.

Which product to use ?

Aluminium would be good but would corrode, stainless would be good but would I use stainless steel wool or some other product?.

Remember, the aim is not to insulate but to conduct! That said, an extra outer lagging layer would also be a good idea - what should I use that for?!

thanks in advance

J
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Old 24-06-2013, 04:34   #2
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Re: Which Heat Conductive Material to Boost My Exhaust Heat Exchanger? Exhaust

Depending on the gap in question, you could try heatsink paste; i.e. this stuff:

http://australia.rs-online.com/web/c...r&x=-767&y=-21

Finished with lagging like the stuff Harley riders wrap around their exhaust pipes to stop their legs from baking.

Another option perhaps would be to shim the circumference of the pipe with copper foil to provide a more positive contact with the tube.
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Old 24-06-2013, 04:42   #3
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Re: Which Heat Conductive Material to Boost My Exhaust Heat Exchanger? Exhaust

J,

first a bunch on questions since I am not at all sure that what you plan is such a good idea.

How will you circulate the water through this pipe? I assume you have a hot water storage tank, since a "one shot2 heating requires a completely different setup. Do you have a pump?

Second, and my greater worry: How will you stop it from heating? Stopping the pump won`t suffice unless you drain the whole coil - which again is virtually impossible unless you have an exhaust going straight up. If you don't stop heating, at some point your system will partially go to steam, which means your safety valve (you do have one, correct?) will open and you will dump your hot fresh water.

Remember - there is a reason why everybody else goes the other way around and uses the engine cooling loop for heating: First, you've got the pump already, second, the temperature under normal conditions will never get to a critical level, and third, it is already freeze protected - so no worries in Winter. If you haven't progressed too far, that's where I would recommend you go...

Oliver
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Old 24-06-2013, 17:01   #4
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Re: Which Heat Conductive Material to Boost My Exhaust Heat Exchanger? Exhaust

Wrap your copper tubing with a stretched out stainless steel spring like you might have on a screem door. Longer the better. Stretch it out so the 18" spring is 3' long. If you can not get springs that long, shorter springs would work but it's pain to hook them all together. I suppose you could make your own spring out of stainless wire, Just wrap the wire around a wood dowle about 3/8" in dia. The object is to get as many wraps as possible of the spring around the tubing. This will increase the diameter of your copper tubing about 3/4". Hopefully this is enough to give you good contact with the exh pipe.
As for Lagging, the asbestos wrap for Harley exh pipes coated with silicone works well as it does not get all grimy after time., Just smear it on artfully
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Old 05-07-2013, 04:58   #5
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Re: Which Heat Conductive Material to Boost My Exhaust Heat Exchanger? Exhaust

Thanks to all. Oliver , good points ! ~ i have an Edson water tank / heater, there is a fluid coil inside it, and a PRV (pressure release valve) for the domestic hot water. the fluid coil connects to any 'hot source'. this could be the engines coolant. or any fluid in a coil wrapped round the exhaust pipe. this circulates (I hope) without a pump, because the bottom of the tank's coil is cooler, and the top hotter, causing a circulation, or at least heat transference. In theory the whole 40L tank and coil could turn to steam, but I think this would take days. But a PRV for this circuit still sounds a good idea.
Does anyone have a view on that?
many thanks
John
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