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I was thinking about using the exhaust pipe heat to get some warm water for a shower. My thinking was to first to wrap the pipe with galvinized sheet metal about 2 ft long, wrap a coil of 1/4 copper around the exhaust pipe to collect the heat and have a pump to circulate it to a holding tank.There would be to flexable hoses on the lines for exhaust pipe movement. When I want to take a shower just turn the pump on during the drive before my destination and hopefully have at least warm water for a shower. I would use the same pump for the shower head with a deverter valve to the head.
I just barely made it through Thermodynamics, but I would be worried about steam. If the system is too hot when you let the water in you could get a lot of steam pressure and blow things up. Even if you plan to start circulating the water when the exhaust it cool, I'd be worried about steam pockets from the water that was left in the coil the last time it was used.
A safer bet might be to put a valve in the hot side of your coolant system that can divert some of your coolant to flow through a coil heat exchanger in your water tank.
Or a double heat exchanger. Do the coil around the exhaust that you described above, but run coolant through it (coolant has a much higher boiling point than just water), and route the coolant to a heat exchanger coil in the water tank.
Just a thought.
06-08-2008, 10:30 PM
My few thoughts:
Placement would be key to effectiveness. As a point of reference it takes 600*f to "light off" the O2 sensors that are not heated. A study using TempiLaq temperature indicating paints may help.
Conduction across multiple metal boundaries will reduce efficiency. If those boundaries are not bonded, but rather only in mechanical contact, then efficiency is further reduced.
System will need to be designed such that steam is vented rather than retained. Simply drawing from the bottom and returning to the top of the storage tank should do this, but experimentation is required to confirm.
Seems possible and reasonable, but Advise caution.
Good point on the steam I guess I never thought that it would get that hot, I do have a deisel and exhaust temps can get rather high. I guess I need to see just how hot it gets at the point of the copper coil on the exhaust.
06-09-2008, 03:17 AM
Why reinvent the wheel? What you want is available off the shelf.
Or you can build it from plans here:
The idea and ready-made products have been available for years, and it's just a basic heat exchanger plumbed between the engine and heater core. It's much simpler than your exhaust idea.
Here's a test report on one product.
My above concerns aside, there might be advantages to using the exhaust, as you had planned, rather than the engine coolant.
One is that I would imagine that an exhaust-driven heat exchanger could produce hot water faster than a coolant-driven system. I imagine that the coolant-driven system would have to bring the entire coolant system up to temp along with the fresh water. Using an exhaust-driven system would probably produce hot water a lot quicker, thus saving fuel (Assuming, of course, that you want to take a shower at a time when the engine hasn't already been running).
I would still recommend a double heat exchanger system with coolant as a medium.
Here (http://www.me.columbia.edu/me3410/spring06/group01/Assembly/Mechanical/Preheater.html)is a link to an exhaust-driven heat exchanger designed by folks at Columbia U, as part of a veggie-oil generator set. I thought their write-up might give you some ideas.
06-10-2008, 04:14 AM
When my buddy gets back from Romania this weekend I'll ask him some Q's for you about your idea. His specialty is flameless heating units (this is his company, wellquip.ca) he was the first to perfect the technology. Even beat out his old co. Stewart & Stevenson. They use exhaust heat to heat all kinds of things. One use is to heat frac oil as its bing transported to a well site, same idea as you have for the water. They are able to draw several million BTU/hr. off a big Cat/Cummins when its loaded up and working. They use a flapper/y and divert the exhaust to a heat exhanger, etc etc.
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