New scrubber design/idea, please critique

[randomaeiou]

So this is another updated design, drawn to scale. Have incorporated inner tube and done some rough calculations.

Unfortunately, commonly available lights comes at maximum 18w - if there are any better alternatives within size constraints I'd love to know. Trying to fit 16mm elbow in with the fluorescent bulb made me realize just how teeny this design is - it's gone from the size of a beer/soft drink can to the size of a can of tinned fruit! Had to increase diameter to 10cm to accomodate everything. Current screen width is ~12inches. Fully usable area is about 40-50 square inches, give or take. Based on rule-of-thumb numbers posted here on the FAQ and elsewhere, this should be enough for moderate filtration of a ~18-20g setup?

Calculation using 250gph gives 17+ m/s flow velocity within the 5mm gap, not accounting for the cross section taken up by the screen and algae, which will only make it faster. Using density of 1.025 and 15m/s flow and 5mm gap and the viscosity of plain water gives a Reynold's number in the region of 86000, which should be well into transition zone of turbulent flow, and could be into totally turbulent flow altogether. To boost this further, using a higher gph (I plan to buy an AquaClear 70 rated at 300gph/1185lph to run this setup, along with an inline heater and a Hydor Flo rotating outflow device, both of which *will* cause some flow velocity loss) pump and/or increasing the gap between the inner and outer tubes will work. An increase of the gap from 5 to 6mm leads to a 20% increase in the Reynold's number!!! (Well, not exactly, since flow velocity will drop, but hey... )

Am very excited by all this. Will need to find a plastics handyman to build this for me - I have little plastics DIY experience, but I know plenty of people that do! Have read, however, that acrylic soaks and warps in water and is strongly not recommended for applications involving extended water exposure, perhaps I might look at PVC or some other plastic instead! It seems polycarbonate is readily available in clear tubing form... I need 3 short sections of clear tubing of varying diameters, along with 3 circular sheets of 12cm diameter, 2 black/opaque and 1 transparent, shouldn't be too difficult, I hope... Oh, and a 16mm 90 degree elbow and a straight 16mm outflow, and plenty of sealant/glue.

(apologies about mixing imperial and metric - I work in metric, but it seems a lot of aquarium stuff is done in imperial, so I interconvert as necessary!)

[Rumpy Pumpy]

Not sure that a 5mm wide gap between the cylinders is going to allow quite enough space for the screen and any significant amount of algae growth. I think I'd try at least 15 mm there.

[randomaeiou]

Hmm, yes, I was worried someone might say that.

Simple solution would be to change the inner setup around the bulb - rather than use a thicker tube to leave 5mm of water space, it could be changed to just the tube around the bulb, and a simple plate at the top for spreading the water evenly. That one should leave a 5mm gap only so that the water is faster and less likely to allow algae buildup and clogging near the outlet. Haven't done my calculations for this, but I imagine the Reynold's number might suffer a hit somewhat...

[Tien23]

I was working up a design like this. I am glad I found someone else who is doing the same. Has anyone built this design yet? My only worry is that the light might get to hot and possibly melt the plastic. Any thoughts? One of the designs looks like the bulb is entirely sealed off. Also, I want to confirm that I am visualizing this correctly. There is an outer tube and then an inner tube that is barely smaller. A screen is inserted between them. The light is contained and kept from moisture within the inner tube. Does this sound right?

[SantaMonica]

There are one or two designs like this, which are effectivly single-sided (not as efficient), and I'll be posting them soon in the "OK" examples.