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Old 03-22-2007, 11:26 AM   #1
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Pex as heat exchanger?

I was at Home Depot yesterday trying to get the last things I need for my veggie set up. I was gonna create a coiled copper heat exchanger and was flinching at the cost of copper. I saw this stuff called Pex which is a flexiable plastic compound made to substitute for copper. It's rated to 200 degrees and seems to bend well.

Unless there are any drawbacks I'm not aware of, it seems to be a good canidate for an in tank heat exchanger to move coolant. It costs $12 for 50ft of 1/2in oppossed to $55 for copper.

Any history or opinions?
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Old 03-22-2007, 01:02 PM   #2
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Pex is cool stuff. Find out how much they charge to rent the crimping tool for the day. My only concern with it would be whether or not it was resistant to oil, acid, and other nasties in the veggie oil. Of course parts of my system are made of rubber fuel line that isn't resistant to that junk so......
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Old 03-23-2007, 12:04 PM   #3
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I was on biodiesel.infopop forum, (lots of info) and some guys who are liscenced pex installers were saying that heating the pex a bit, not to the point where it's clear, but enough will cause it to expand and become pliable, after you put it over the barb it will contract and hold tight as hell. One guy said he had about 150 of those types of connections running it as floor heating in his house. No leak, but then again he's not getting it up to 160+.

I haven't worked with this stuff before but if it works it would be a great alternative to copper.
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Old 03-23-2007, 01:13 PM   #4
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When it comes to water circulating in a closed loop through my fuel, I'd prefer to use the code approved attachment method, but that's just me. Did I mention that I have a hard time with heating things up? I usually burn them, myself, or both.
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Old 03-28-2007, 07:01 PM   #5
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you say it's good to 200? you'll be running coolant through this? seems like you might be pushing the temp rating a bit.

copper is cheap compared to what could happen if you start injecting antifreeze into your motor.
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Old 03-28-2007, 08:15 PM   #6
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Well I figuered I'll set up the pex line, at least to test it for future reference. With the busses temp gauge reading 180-190 the pex got hot enough so that I can only hold it for about 4-5 seconds until it was to hot to hold. It seemed very strong and I tried to bend at the conections and It felt like it would kink if I really tried but not just from any average force. The connections are outside of the tank anyway, so the only way to leak coolant into the tank is if it burst in the pex line itself.

I need to get one on those Infrared Thermometers but the closest autozone is like 1 hour 15 mins away. They got one for $40, the only one I found in my area is $130 from napa.
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Old 03-28-2007, 08:51 PM   #7
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If you can wait for shipping, you might take a look at this:
http://www.harborfreight.com/cpi/cta...emnumber=93983
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Old 03-28-2007, 09:13 PM   #8
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They sell those IR thermos here for $15 on sale sometimes. I'd look on eBay if I were you. Sure, shipping can be a killer, but if you can get one for $40 shipped without going to get it....it's that time-value of money thing.
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Old 03-29-2007, 08:35 PM   #9
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I would be concerned about what might happen if you start to over heat for some reason, you may push that temperature envelope. In general, electrical conductivity is a good indication of a materials thermal conductivity.
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Old 03-29-2007, 11:55 PM   #10
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Quote:
Originally Posted by asnowsquall
I In general, electrical conductivity is a good indication of a materials thermal conductivity.
That is a VERY good point.
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