Originally Posted by markdem
i want to...have a 25mm input, but then...a ~100mm pipe going from that, and then back into a 25mm output... Do you think there will be a problem with water flow or anything like that??
No, I don't think using 100mm pipe would be a problem at all; it should work fine. The only problem I can imagine with that would be finding 100mm T-fittings with a 25mm side outlet. You could always use those size-adapter plugs, but I'm a perfectionist, and I would hate to not have parts that are exactly the right size.
But, whatever, if the you can adapt it down, and it doesn't leak, who cares, right? It will be in the cabinet under the tank where no one sees it.
If you cannot find T-fittings at the regular plumbing shop, just like with the compression fittings, you might have to go to a plumbing specialty supplier to find them.
Ok guys, I will apologize in advance, but I feel myself slipping into "essay mode"... Read on...
When dealing with water flow as it applies to heat exchangers, you kind of have the same concerns as with a biological filter: surface area, flow rate, and turbulence. What this all boils down to is a term you hear frequently in reference to UV sterilizers: "contact time". More contact is good - to a point. In all of these cases, you reach a point of diminishing return. In a filter, it's a balance between getting as much fish waste removed as possible, and starving the bacteria - or worse - producing H2S. In a UV sterilizer, it's a balance between zapping the weak germs, and zapping the strong ones. In a heater, it's a balance between water and steam.
And in all of these cases, you want a reasonably expedient flow rate.
In our case, we are looking to be cheap, so we will not fiddle with surface area or turbulence. The heater tube will be smooth, and will not be changed. However.......if you did
want to fiddle with these, you might be able to increase both the surface area of the tube, and the water turbulence around it, in a number of ways, but the main one I have in mind would involve introducing more metal into the unit.
(that funny noise you just heard is the gears in my head starting to rattle and roll... but mostly rattle)
What I have in mind is to add cooling fins to the heater tube. This would increase both surface area and
turbulence. A great example can be seen on this web page where a guy built a DIY CPU cooler for his computer: http://www.overclockers.com/tips1215/index.asp
. If you look at the third picture down the page, you can see a copper tube with fins that he soldered on by himself. He used a simple piece of copper plumbing, a propane plumbing torch, plumbing solder, and some spare bits and pieces of copper. The only thing I would do differently is twist the fins so they are a little more in line with the tube. This is so the water flows more hydro-dynamically (I almost said "aero-dynamically"
) around them, instead of across them and thus impeding water flow.
If fins were added as I describe, it would necessitate some small changes to the design of the heater. 1) In order to fit the "finned" tube into the large pipe after you add the cooling fins, you would have to use a large threaded fitting at the end, in addition to the compression fitting where the wires go in. This is because if you glued it all together as my diagram shows, the compression fitting would be too small to slide the tube in. 2) Since metal tubing is being used (rather than a glass tube with one end closed), you'd have to put a cap on the bottom end of the metal tube. Alternatively, use compression fittings at both ends of the tube so that it sticks out at both ends of the heater. 3) Because copper is involved, I would worry about copper toxicity poisoning the fish in the tank, so I would try to get the thing electroplated. This could be done at any auto-finishing shop. I would think a double or triple coating of chrome would be fine, but I am not sure about how reactive and/or toxic that would be in an aquarium, but I would think it would be better than copper. Other possibilities would be gold or platinum, but those would blow a hole in your budget you could fly the Space Shuttle through.
Markdem, as for problems with water flow, that question has two answers. If you are just a teensie bit crazy like me, and you try to make this crazy contraption with cooling fins, I would select a size of pipe just a little larger that the outside diameter of the cooling fins, perhaps giving 1cm of clearance. If you don't
add the fins, and just do it "smoothie", I would think 1-2cm of space between the heater tube and the outside pipe would be fine. So 100mm pipe might be a bit large, but will still work just fine... After all we're not building a heat exchanger for a Space Shuttle. (what is this fixation I have with Space Shuttles today?)
Ok well, my essay fuel has fizzled out... I will step off the soap box now.