# Right distribution with spray bars on front??



## killi69 (19 Jun 2012)

I understand that one of the most efficient ways to distribute CO2 is to mount the spray bars horizontally on the back panel just below the surface, creating a flow across the surface towards the front, downwards across the front panel and then back over the substrate towards the back.

As illustrated by ceg4048 in this thread http://www.ukaps.org/forum/viewtopic.php?f=37&t=20097&hilit=ceg4048+flow+front&start=20;


> by ceg4048 » Wed Feb 15, 2012 11:02 pm
> 
> ...Ideally, if you had strong enough filters you would use a configuration like this that stretches all the way across the length of the tank:



I wanted to know what people think about mounting the spray bars directly on the front panel instead - horizontally and facing downwards.  

I currently use spray bars mounted vertically at both back corners (connected to in-line UP atomiser).



 

The tank is 60cm tall and I fear that the CO2 is not reaching the bottom with the current set up as I am experiencing some melt of my crypts.  I am considering moving the spray bars to sit horizontally at the top of the front panel instead, facing downwards.  With filter intakes situated in the back corners, would this set up still create the desired flow (down across front and over substrate towards the back)?

Any advice greatly appreciated.  Many thanks  ,

Andre


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## ceg4048 (20 Jun 2012)

Hi,
    The arrangement shown in your image is very inefficient, but this inefficiency can be overcome by increasing the flow strength, especially if this is a small tank. In larger tanks (i.e. greater than 50 USG) it becomes more and more difficult to overcome. This problem becomes exacerbated by increased plant mass which create more obstacles to uniform and unidirectional flow.

It's really difficult to predict the effectiveness of your proposed re-configuration because the flow patterns are not intuitive. It could easily be that the carpet and plants in the front do well but that the plants in the rear start to suffer.

What it looks like you were attempting to do in that image above was to force the water in the tank to play ping-pong.  Fluids don't move this way unless they are confined to a pipe or to a duct. The result of trying to impose a complicated pattern is usually interference and stagnation as different areas of the water squirt out causing incoherence. This is like herding cats, very difficult.

Instead, try to imagine a single body of water moving uniformly such we see on a beach. The wave of water lapping onto the sand is a tube of water approaching the beach uniformly as a single wave. The water forms it's own pipe, or tube, without being confined, and falls onto the sand in unison when it finally runs out of energy. You can then see a uniform line of white foam along the beach. The water line then retreats uniformly as the rip tide pulls on the flattened tube. With uniform flow along a single axis of the 3-dimensional space, nutrients and CO2 are distributed uniformly. That is how the coral reef get fed, for example, and that's why the reef grows uniformly.

In order to simulate this in a rectangular box, imagine looking at the tank from the right side panel. You want to form a tube along the long axis of the tank that looks from the side like this image below. The front of the tank would be on your left (where the airplane is in this image) and the back of the tank is on the right. Flow moves up from the bottom, goes across the top to the left, and then down, to be pulled across the bottom to start the cycle again. This can only happen uniformly if the difference in pressures are consistent. On the right side, just below the top of the wave, the pressure is low which pulls flow up from the bottom. At the top left, the pressure is high forcing movement in that direction. The barrier of the front glass diverts the flow downwards. The low pressure at the upper right corner pulls the flow across the bottom and up. This can only be achieved uniformly as I show in my image in the referenced thread. The velocity of the jets in the spraybar lowers the pressure just below the spraybar which pulls water up from the bottom. This maintains the cycle and holds the shape of the circle. That is why I have the spraybars along the entire length of the tank, to keep the circle and therefore hold the "tube" of flow.




Hope this helps!

Cheers,


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## killi69 (20 Jun 2012)

Thanks ceg for your detailed response .  

I agree that the 'front to back' circular flow is the most effective.  However, with my layout of two large mounds of wood filled in with fern plants on either side of the tank, there will be 'dead ends' behind these islands where the flow will be blocked off. I suppose it will still be better to have the plants at the front looking at their full potential and put up with the blocked flow behind these mounds.

I do not think that increasing the flow rate is really an option as the current flow is already on the high side for the target group of fish for this tank (killifish).


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