genomik:
Thank you for a great thread. I too have some ideas very similar to yours. I was thinking of buying a computer fan and while deciding what kind, etc, I knew my terrarium needed air movement, specially since I have many orchids in it, so, I have a water fall and decided to make it work for water and air. I connected the plastic tube (that pushes air thru it to pump the water) half way, so half of the air pumps the water and the other half pump air into the reservoir and bubbles up. The waterfall works slower bringing less water up the tube, but for the time been is ok with me. I also have the top of my terrarium with a glass top split in two and glued in the middle, so I use two small wooden sticks, like the ones in ice cream bars and stick them in both sides of the front panel giving me about 1/2" of 'breathing' space, and it helps too.
Thanks again, for your thoughts!
Ana :)

I like your ideas, but do you really think that this would create enough air movement to help orchids? And isn't it MORE work to build a waterwheel or the other things, since you can buy a fan ready-made and just hook it up? it would look more natural if you could camoflage it, but otherwise it would still be some obvious man-made technology, however ancient, in an otherwise natural setting. Don't get me wrong, I'm not shooting your ideas down, I'm just not totally sold on how much better they are than computer fans and the like. In any terrarium larger than 2" square you are going to get air current by means of simple convection. Such a slow-moving thing like a water wheel wouldn't really add a lot, I don't think. Not enough to make a real difference, IMO. No more than having a frog hopping around in there, or even some crickets! I think that just leaving a slit of an opening in the front glass does a lot for air circulation, like Ana has. I know that the dutch use this a lot in their vivs, and it creates a nice air movement across the front glass so that it doesn't get all fogged and impede the view into the tank, and the air also flows up over the 'plant wall' and out the top of the tank. Either that or the air goes the other way, from top to bottom, but I can't remember. It works both ways though, and without any obvious 'technology'.

In the future I would like to do an oriental terrarium, and then I will likely utilize your 'waterleaf' idea in the form of a bamboo 'clacker' fountain, because I want it to look like a Japanese garden, and gardens are ordered, not so natural, so it will 'fit in' with the landscape. This and the other ideas you have would also look good in a terrarium designed to look like some overgrown ancient ruins, with fallen pillars and remnants of buildings all covered in creeping vines and whatnot. Now that would look really cool actually. . . sort of like Planet of the Apes. =)

Hi
Personally I think any terrarium beyond a brandy snifter should have a water feature. They add so much visual appeal.
I would disagree with you that simple is better.lol I love to fiddle with the systems If it's simple it can't possibly be working right lol Leftover from keeping SW aquaria I guess.I found I became obsessed with the systems
and parameters and there was no time left to look at the inhabitants lol I vowed this would not happen with terrariums but find I'm experimenting with water spitters.
air compressors,water cataracts and endless materials.
To me, this is about half the fun of any enclosed system.
Gary

I don't think a computer fan running on a cheap variable voltage wall-wart is very complex, and it's reliable, cheap and effective :) I also very much doubt that the heating due to friction is significant for ceiling fans. A more likely reason is that a low speed breeze is just as effective as a fast one for cooling, and obviously uses less energy. You can make a computer fan go slower by dropping the voltage, or putting two in series. Bigger fans move more air for a given voltage.

Ok, having got the negatives out of the way, I like your ideas - you are thinking outside the box (does that make sense for a terrarium?). Let me share a few things with you.

Firstly, there are two general kinds of fluid flow we can talk about: Laminar and turbulent. Laminar is 'more efficient', in that you can get more airmass moving (momentum) for a given input of energy. Turbulence chews up a considerable amount of energy, you can see this if you compare the water flowing out of a tap with a hose connector at the end, vs one without. The hose connector reduces the turbulence, increasing the rate at which the water can escape.

However, if you want to get the air close to a surface you need turbulence. Without the turbulence the air forms a boundary layer (on a windy day you'll notice that the air is more still closer to the ground, even in the middle of a paddock). In your example of stomata breathing you wanted to get the air closer to the leaf's surface, this would require turbulence. (Having said that, I think the gas diffusion rate for CO2 in air is faster than you'll be able to blow air, so I don't think this is really a problem.) To get turbulence you are better off with a narrow stream of fast moving air hitting some kind of obstacle.

This leads on to "matching". In electronics we have an idea called 'impedance matching', the same idea appears in fans and ducts, in water flows, in sound systems, pipe organs and car engines. The idea is that if you directly connect a thin tube with high 'whatsit' to a large tube with low 'whatsit' you'll get a reflection occuring at the boundary. This reflection causes signal loss, or energy loss (the same thing really :). In the little gramophone that we wound round and round we used an exponential horn to match the sharpish needle's high pressure, small volume sound to the room's low pressure, large volume. You have the same problem with your fan.

Water falling is a relatively high pressure, low volume fluid flow. We want to match that to the low pressure, high volume fluid flow of air. There are many simple ways to do this. All of your nifty ideas have been mechanical (converting the falling water to mechanical motion, and then back using a primitive fan (propellor type fans are vastly more efficient than ones that work by flapping, or by impulse means, btw). Can we do the impedance match any other ways?

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Goodness Nathan! I didn't understand much of that, but apparently you and genomik are two of a kind! =) I can't be of much help here, other than to say that I think the rain maker you speak of is used in Europe. I've linked a site that tells how to build such a thing (they call it 'pneumatic rain') below. I've heard it doesn't always work so well, but it does sound interesting. Go to the 'Gadgets' menu at the link.

Here is a link that might be useful: Pulsing rainmaker

Lots of good feedback on this. I imagine if one had a waterfall with alot of water volume going down it that might create some ventilation.

The pneumatic pulsing rainmaker is also a simple mechanism for moving water, which can be at least part of a part of a ventilation system. I think that this systems problem might be that it might make noise. I tried to build one of these 6 months ago, but the one way valve was not to be found and I went to 4 aquarium shops, 2 hardware stores and a irrigation store! What the heck is that one way valve?

Wouldn't it be cool if one pump could filter water, provide a water feature and create ventilation. That is lots of bang for the buck.

I wonder if anyone can think of anything that has already been made (ie, off the shelf) that could work here. Making a spinning wheel from scratch could be complicated, but rigging one from a already made plastic part could be easy. Anyone know of anything? Aquarium parts, guinea pig wheel, passive computer fan, other hobby, trains parts, etc. There has gotta be something somewhere that costs a few bucks that could be retrofitted for these ventilation systems. The vortex system mentioned is good. I think I have seen little plastic wheels somewehre but I cant think ioof where - maybe computer cooling or automobile cooling systems for example.

I would break ventilation into a few types:
1) Air Movement which is simply air moving around the system.
2) Fresh air: For instance a air tube going into the system.
3) Cooling or heating.

Some systems may address all of these, others just one or two.

Marineland sells little aquarium set-ups with their patented 'bio-wheel'. It is basically a water wheel, and I don't think it does anything special for an aquarium, so why bother? You're just paying more for something you don't need. Is that where you saw the little water wheels? I don't think you could buy them separately though, and since you would need to buy the whole tank and hood, even their smallest ones are not cheap at all. Much easier and cheaper to make your own from a few pieces of wood and some glue!

You just need a tromp to move air. It is just a vertical tube. The water falls down it, and sucks air with it and the air bubbles are released at the bottom. Short tube, lots of air moved. long tube less air moved. High waterfall, more air moved, low waterfall less air moved.
You can also look up pulser pump for more information
Brian

Here is a link that might be useful: internet glossary of pumps

Brian, have you noticed the date of the last post? Tue, Aug 31, 04 at 14:28, I dont think genomik has ever replied to or even posted to this site since then.LOL! When I started here I did the same thing, unknowingly answering post that were long forgotten, I look forward to your future post =)