Freeze damage proof tube length

[fsdenis]

This more a thermal problem than electronic, at the moment.<p>I am trying to use less wood to heat 85 gallons of hot shower water.<p>I have a flexible boiler that can tolerate being used outside and freeze without being damaged. It expands when frozen and contracts back when it thaws.<p>I use rubber hose (3/4" ID) connecting to the flex boiler inlet tube (copper pipe, 1.5" long and 3/4" ID) and outlet tube.<p>This assembly can freeze every night, thaw by 11:00 am the next morning and not be damaged by freezing repeatedly.<p>I have an idea for improving the efficiency (85 gallons of hot water for less wood gathered and burned) of this system that requires longer copper pipes than 1.5".<p>The question is how long may these pipes be, coupled to hose on one end and flexible boiler on the other, freeze daily 60 or more times per season, and not be damaged (expanded until they break) in a season?<p>A simpler question: Has any other renewable energy (or other type of lunatic) done the experiments that say how long a piece of hard tubing may I get away with freezing many times without the ice breaking the tube?<p>P.S. What is a flexible boiler? I haven't been clear about this.<p>A flexible boiler can be a teapot with a flat bottom that can push outward when the water inside freezes and expands about 11%. When the water thaws, the flat bottom contracts back to its original position. So, the teapot can freeze without being damaged.<p>The flexible boiler I'm working on now is a sandwich of two sheets of galvanized steel about 1 foot square. There is a bolt in the middle to keep the sandwich from expanding (flexing) too much when I fill it with water from an unpressurized tank about 12 feet above it.<p>The boiler, on the top side, has two 1.5" long and 3/4" diameter copper tubes welded (brazed) to it to permit hot water to rise to the tank and cold water to come down from the tank. (Thermosyphon pumping). The edges are folded over and brazed all around the sandwich.<p>I'm trying to work down the exact size and shape of this thing now. Once I've got it working well, then comes the electronics: dealing with electrolytic corrosion if I can't avoid it with materials choices.<p>[ November 07, 2004: Message edited by: windmiller ]</p>

[Externet]

Hi.
I do not understand your post well, but for the last paragraph, my lunatic side would insert an empty aquarium hose with very sealed ends inside full lenghts of any rigid pipes.
The expansion at freezing compresses the air within the aquarium hose, making enough room for the ice and no bursting of the pipes should happen.
I am waiting for the right opportunity to test my theory, does anyone know of or done such thing?
Miguel

[dyarker]

The easiest way not to burst pipes by freezing is drain them before the fire goes out. Not the 85 gallons, just the pipe.<p>Alternate, corregated tube.
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It expands and contracts. How many times? Don't know, more than straight tube though.<p>hint: If I can guess what you're up to, pre-heat should work better than post-heat.<p>[ November 07, 2004: Message edited by: Dale Y ]</p>

[fsdenis]

Externet:<p>My impression over years of reading is that your solution (inserting compressible plastic or rubber cylindrical shapes into rigid pipes to prevent freeze damage by absorbing the 11% expansion of ice) has been tried many times and has worked many times in solar hot water systems.<p>The usual objection is that one might be forced to use the next size larger rigid pipe to keep resistance to flow down.<p>The problem I have with it is I don't know how to keep it from contact with the pipe inside. If it is in contact with the pipe and the pipe is in contact with a flame, then I'm concerned that it might melt and become useless. <p>But I don't know that this would happen and I may try it to see.<p>Thanks for your idea.<p>P.S. Kell, below, has posted a confirmation of your idea. Looks very much worth a try.
Fred<p>[ November 08, 2004: Message edited by: windmiller ]</p>

[fsdenis]

Dale Y:<p>I am attempting to replace a propane "teapot" backup heater for my solar water heating system with a wood fired backup heater.<p>Propane has nearly doubled in price in the past year here and has "gone over the top" for tolerable cost of operation.<p>The "teapot" heater is made from a stainless steel teapot with a flexible steel bottom. It lasts about 5 or 6 years, freezing many nights each winter, before it springs a leak due to electrolytic corrosion. Then I buy another teapot, weld (braze) a lid over the spout, add two copper tubes 1 1/2" long and 3/4" ID near the teapot dome top and put it into service.<p>If it turns out that I can have these 3/4" ID copper tubes about 6 to 7 inches long without worry about their expanding and breaking when they freeze, then I have a chance of building a number of these flex boilers into a stove and having fire flow on both sides of each. This should improve my efficiency or wood savings.<p>Ultimately, I would like to charge the stove with a known adequate amount of wood to heat a tankful of hot water, light it and forget it.<p>The problem with draining the plumbing nightly is that it would be a daily maintenance operation. A nuisance usually. And a real mess to fix when I forget to do it and take freeze damage. <p>What I want is something that takes no more time or discipline to do well than the propane heater.
Nor is any more complicated to live with.<p>I hadn't thought of the metal corrugated tubing. It might tolerate fire on the outside as well as freezing on the inside. And it is readily available at hardware stores. Seems worth an experiment.<p>Thanks for the idea Dale.<p>Fred

[kell]

As you heat copper tubing full of water over an open flame, the tubing will stay at the temperature of the water inside it. In other words, at or below water's boiling point. Plastic tubing inserted in it will also stay at the temperature of the water. If you have plastic that can withstand immersion in boiling water, you don't have to worry about melting the plastic.<p>Have you ever heated water in a paper bag over a campfire?

[fsdenis]

Kell:<p>Thanks for the confirmation of the plastic tube inserted in copper idea. <p>The plastic tubing used for installing screens in screen doors will tolerate boiling water temperatures. I have some.<p>I never have tried boiling water in a paper bag over a campfire. But everybody that knows me believes I would try such a thing. If I thought of it.