Inlet and outlet design for a cylindrical tank

[vetenar]

I am designing an inlet tube and a screened outlet for a cylindrical tank with a top opening hole (which determines the water level). I hope I could receive some suggestions and advice on the approach or some texts/equations I should check out. I am still in the process of learning fluid dynamics and have read about the basics (such as Bernoulli's principle).

The cylindrical tank (40 L) is for fish larval rearing:
- water flow rate $\leq$ 1 L/min, provided $\leq$ 10 hr/day
- outlet mesh $\approx$ 150 $\mu m$, so that the food can flow out, but the larvae will not be damaged as they pass by. It should have enough surface area to avoid clotting and should be easy to take down for cleaning.
- one (or more) aeration line to generate circular motion of water. Aeration rate should be only big enough so that the larvae would spend more time in the middle of the tank (they are mostly carried by water current).

The difficulty is that it has to be able to wash all the food out within several hours.
I have tried several things already, but there are too many things to test at once. The shape and position of the screen outlet, the flow rate, the shape and position of the inlet tube, the position and rate of aeration. And so far the screen outlet remains the biggest problem; it either clots or could not wash the food out. I imagine this is also related to aeration and flow direction.

Any help is fully appreciated. Thanks very much in advance.

 

[jrmichler]

Can you post a sketch and/or photo of your entire setup? What species of fish? How many eggs - hundreds or millions? Are you hatching eggs, then releasing? Or growing to a larger size?

Here's a link to an egg hatching jar in a mobile fish hatchery for walleyes:
The white eggs are dead. This hatchery has an average hatching success rate over 90%.

 

[vetenar]

Can you post a sketch and/or photo of your entire setup? What species of fish? How many eggs - hundreds or millions? Are you hatching eggs, then releasing? Or growing to a larger size?

Thank you for the video and I am sorry about the vagueness of my question.

The species is Atlantic herring. The tank is only for growing larvae. Eggs will be incubated in another system, and then hatched larvae will be transferred to the tank. Each tank will have a few hundreds of larvae.

This is my test tank so far:

I have
- one aeration tube opposite the water outlet. During feeding time, there will be no water inflow, and aeration will be the only source to create water motion in the tank.
- one water inlet tube. When feeding time is over, water flows into the tanks and flushes the food out. Now the water is coming out from the bottom of the tube at about 1 L/min. I haven't tested where best to put it or the pressure of the water inlet yet, possibly I will need to drill some holes on the side of the tube.
- the screened outlet connected to the outlet hole. Since the water is coming out through the holes under the water level, it is insufficient to flush the food out. I think one screened outlet which also has holes up to the water surface level might work, but I still have not figured out how to make the screen mesh which covers this entirely.

The tanks are not connected to the system yet, so everything except for the outlet hole can be redesigned. My plan is to fix the design of the screened outlet and then test the other parameters together.

 

[jrmichler]

Dang. I wish I had paid better attention when I was in the hatchery last spring. Walleyes For Tomorrow (http://walleyesfortomorrow.org/) has several mobile fish hatcheries operating in Wisconsin. The egg circulation seen in the Post #2 video is from a once through water flow system. The water is pumped from the lake, through the egg jars, with the overflow going to a fry tank. The outlet of the fry tank has a filter. The water flows through the filter and back to the lake. I do not recall any details of the filter.

Check out the American Fisheries Society. They publish an excellent book on walleyes, and may have something relevant to Atlantic herring.

If you want more information, PM me and I will put you in contact with some people that have built and are operating these walleye wagons AKA mobile fish hatcheries.

Side note for your amusement: I was chairperson of one of the local chapters of Walleyes For Tomorrow for three years, even though I am not a fisherman.

 

[vetenar]

Walleyes For Tomorrow seems like a very cool project. Thank you for the information.
I was indeed troubled by the filter for the water outlet. After more digging and testing, I realized that most tanks have their water outlet located at the bottom center, and it would have two standpipes - the outer one is covered by filter mesh; the inner one determines the water level. But in my case, the water outlet is at the top. Instead, a "Banjo sieve" is used.
It turns out I should have only observed the water (and forget about the organisms) at the beginning. After putting things one at a time in the tank, it gave me a better idea of how each will affect water movement. Banjo sieve does work much better. And the filter sieve should not be submerged (?).