Backyard Aquaponics
A place to discuss aquaponics

How would you plan to bend the tube into the loops Steve?

In the interst of free info (and the reality that i'm no where organised enuf to make and sell things ) :

on a lathe, make up a little jig, slide the tube into it, turn the lathe on (geared to slowest speed) and guide tube in.

copper toxicity to yabbies and fish is natures cruel joke on us............copper is so much easier to work with and is so much better a thermal conductor.

I thought stainless collapsed unless there was one of those ball in tube type benders used. Though elsewhere I have read that annodised will bend??

What would this jug look like and are you talking any old wood lathe? Does the jig also serve the purpose of making the coil circ bigger.

would be easier to draw, but i can't be buggered turning on my scanner ATM.

basically a piece of 20cm pipe with a 6mm hole in one (linear) end.

slide 6mm stainless into hole, brace tube with hands and turn on lathe, it will wrap around the 20mm pipe.

Its been a while since i worked with 6mm ss tube, so you might need a
A little "doova-whatsis" on the tool holder of the lathe as the guide for the tube (ss is pretty tuff).

i'll do up a picture 2morrow after work.

SS won't kink if you keep a minimum bend radius, 20mm will be HEAPS

You may need an oxy or propane torch to make it easier steve. I have had trouble doing it this way on a lathe for copper and it is not easy. Although if the ID was large enough and the jig feed the tube in straight enough it might work... I am concerned with bending the tube like VB said... Although ball bearings are cheap and you could try putting some in the tube to stop kinking, as long as you can get them out.

Cool - thanks Steve.

Tim, u must have been using "hard drawn" copper i did one in 3/8" annealed copper by HAND on a 10cm pipe. Shite, just realised i've been saying 20mm when i meant 20CM! will go back and change it were i can

I was talking 12 mm copper coil with a 10 cm ID. I was assuming you would be using similar dimensions. But smaller (6 mm) would be alot easier.

Filled the tube with sand before attempting to bend

Hi you mean stainless like this one you know where i got it steve

A heat exchanger relies on having a sufficient difference in temperature to transfer heat at the required power. roughly speaking, the heat transfered through a pipe wall is boundary layer + wall + boundary layer. In this case the inner boundary layer is probably R0.1, the wall R0.001 for copper or R0.1 for plastic and R0.1 for the outer layer. Add them up and you're looking at a total heat transfer coeff of 0.2 or 0.3m^2 C/W. Thus, 5-6W/m^2 C. If you have 40 foot of half inch pipe, that's 40foot * pi * inch/4:
You have: 40foot*pi*inch/4
You want: m^2
Definition: 0.24321959 m^2

So we're looking at a thermal efficiency of about 1.5W/C. So if the water in the pipe is 10C warmer you'll transfer about 15W of heat. That's not very much.

You need to reduce the boundary layer to have any useful effect. This means moving the water past the tube quickly. Probably the simplest approach would be to have two concentric tubes, one with tank water, one with heated water. Move the flows in opposite directions. Biofilms are going to be a problem (except perhaps in a copper pipe).

solar heating of water in tubes works because you a) have a large surface area and b) the sun will heat the surface until the energy balances out. I would just put the warmed water straight into the tank.

Why bother with heat exchangers when you can heat water much more effectively (and inexpensively) by pumping tank water directly through black poly pipe exposed to the sun.......as is the case with most of the the swimming pool heating systems.

You could also use a solar pond as a heat source. Either way, you're going to have to use a pump to move the water.



VB......the average "any old wood lathe" would be far too fast (even on the slowest speed) to do what steve is suggesting. He's talking about an engineer's lathe where you can get the speeds down to walking pace.

Gary

I will not use black poly in this way as I am concerned about leaching of chemicals.

F&F is that from a water heater? PS - you are a skyte, not everyone has your scrounging skills or contacts