Engineers - Drilled hole question. Physics ?

MadMan-JaMeS

MadMan-JaMeS

MadMan-JaMeS

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Hello,

I need some help by some clever people.

I am looking to adapt a sump for my Freshwater Fish Tank.

I need to know how much water would flow through a 5mm hole, so i can work out how many i need to drill in some perspex to let enough water flow through. Potentially upto 12,000ltrs per hour.

APNXC7A.jpg


The red lines represent the perspex. Sheet 1 will be drilled below the blue line. Sheet 2 above it.

The green is the flow of water, and i'll have a pump in the last chamber to send it back up to the tank.

I can't leave a gap under, or above the perspex as the middle will be filled with plastic things moving around and the idea is the keep them in that compartment.

Essentially how much water would a 5mm hole let through. There will be no lid on this so no real forces at play apart from mavity.

I did try googling but i can't find an answer
 
MadMan-JaMeS said:
Hello,

I need some help by some clever people.

I am looking to adapt a sump for my Freshwater Fish Tank.

I need to know how much water would flow through a 5mm hole, so i can work out how many i need to drill in some perspex to let enough water flow through. Potentially upto 12,000ltrs per hour.

APNXC7A.jpg


The red lines represent the perspex. Sheet 1 will be drilled below the blue line. Sheet 2 above it.

The green is the flow of water, and i'll have a pump in the last chamber to send it back up to the tank.

I can't leave a gap under, or above the perspex as the middle will be filled with plastic things moving around and the idea is the keep them in that compartment.

Essentially how much water would a 5mm hole let through. There will be no lid on this so no real forces at play apart from mavity.

I did try googling but i can't find an answer
Click to expand...

No need for google, you can run a test with a 1ltr bottle. Simply see how long it takes to fill the bottle through the hole. Little bit of maths after and you are away. It's how I built the sump for my old 6ft marine tank... man I miss that tank, might have to get another on day.
 
Have two baffles for the water to flow through each side and contain your moving media in a crate made with plastic mesh. Drilling loads of 5mm holes isn’t a great idea, over time they will block up.
 
The rate at which it will flow through the holes depends on the water pressure at the point of the holes, which will depend on how much volume of water there is above the holes.

MadMan-JaMeS said:
There will be no lid on this so no real forces at play apart from mavity.
Click to expand...
Water pressure (not from a pump [ from a bit of googling this is called hydro static pressure]) is just the effect of mavity through water.
 
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Look here:

https://www.efunda.com/formulae/fluids/draining_tank.cfm#calc

Set fluid density to 997 kg/m^3
set spout exit diameter to 0.5cm

Adjust the height.

At 10cm it's 27ml/s
At 20cm it's 38ml/s

if you can get the feed into tank 1 to match the flow through the hole then the height will stay constant. It's a differential equation though. Honestly I think rather than working it out mathematically you should just do trial and error.

Also please take note that the height at which the holes are will affect the flow rate at the holes. So if you have multiple holes, put them at the same depth otherwise you're going to have a lot more problems working this out.
 
MadMan-JaMeS said:
Potentially upto 12,000ltrs per hour.
Click to expand...
That's 3.33 litres per second.

At 20cm depth of water you will get 0.038 l/s per hole, I don't know the maths exactly (I don't know if the pressure will stay the same if you increase the number of holes) but I think if you do 88 holes of 5mm diameter, all at 20cm depth you'll be fine. Or do one row of 44 at 20 and another row of 44 at 21. The issue you're going to have is, can you keep the depth of the water constant?

Thinking about it more you're going to have the issue of the pressure in the middle tank pushing back against it. This is far from a trivial problem. The pump in the third tank will create negative pressure too, drawing from the middle tank, which will affect from the first tank. This is above my paygrade :p good luck.
 
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Thanks, its the only way i could do it on my work pc.

I think trial and error will have to suffice then.

Thinking if i drill around 240 5 mm holes in each baffle it should let more than enough water through. If i need more so be it.
 
MadMan-JaMeS said:
Hello,

I need some help by some clever people.

I am looking to adapt a sump for my Freshwater Fish Tank.

I need to know how much water would flow through a 5mm hole, so i can work out how many i need to drill in some perspex to let enough water flow through. Potentially upto 12,000ltrs per hour.

APNXC7A.jpg


The red lines represent the perspex. Sheet 1 will be drilled below the blue line. Sheet 2 above it.

The green is the flow of water, and i'll have a pump in the last chamber to send it back up to the tank.

I can't leave a gap under, or above the perspex as the middle will be filled with plastic things moving around and the idea is the keep them in that compartment.

Essentially how much water would a 5mm hole let through. There will be no lid on this so no real forces at play apart from mavity.

I did try googling but i can't find an answer
Click to expand...


To answer your main question, a 5mm hole will let as much water through as you want, provided the material it is drilled through can withstand the pressure differential (edit: and you can create that pressure differential).

The questions you need to be asking are:

1) What is an acceptable flow velocity?

2) What vacuum pressure do I require from my pump to produce this flow velocity

With answers to these questions you can calculate the total area required. Without dimensions it's hard to take it any further.
 
Why do you want a fluidised sump anyway am Assuming you wanna use something like k1?

pretty sure you would need a powerhead or similar inside the media chamber with an outlet at each side of the chamber to give the media the most movement.

to be completely honest unless your either really wanting to try something different and have relatively cheap fish, i would be sticking
To proven methods like a canister Filter OR an off the shelf fluidised sump.

i think the diyking guy made a fluidised sump before using a couple of air pumps, yes her you go!

 
I think it will be a case of adjusting your pump speed such that you reach a nice steady state where the pump isn't experiencing periods of running dry and hence causing overflow in the other compartment. More holes will of course allow higher speeds. Also 12000 litres/h is quite a large turnover for a fish tank. I think 1200 litres/h sounds more sensible but even that may still be a bit high.
 
NoobCannon said:
Why do you want a fluidised sump anyway am Assuming you wanna use something like k1?

pretty sure you would need a powerhead or similar inside the media chamber with an outlet at each side of the chamber to give the media the most movement.

to be completely honest unless your either really wanting to try something different and have relatively cheap fish, i would be sticking
To proven methods like a canister Filter OR an off the shelf fluidised sump.

i think the diyking guy made a fluidised sump before using a couple of air pumps, yes her you go!

Click to expand...

watched that video many times. He doesn’t really go into specifics about hole size or how many.

the actual tank is 7x3x2ft and the sump is 5.5x2x2.

Its fludised now but i want to add some chambers so it looks better and can put more mechanical filtration in
 
MadMan-JaMeS said:
watched that video many times. He doesn’t really go into specifics about hole size or how many.

the actual tank is 7x3x2ft and the sump is 5.5x2x2.

Its fludised now but i want to add some chambers so it looks better and can put more mechanical filtration in
Click to expand...

do you have a picture? I take your sump has baffles? I think with an fluidised sump you have two up and over rather than under baffles to contain the media. Do you have a picture of your current setup?

ive used stuff like knitting mesh before it has tiny holes but takes loads of flow.
 
@NoobCannon no picture unfortunately.

currently it is just a bare tank, water comes in and go through filter socks. The whole thing is full of k1 and then a return pump at the other end. A couple of heaters are loose in the bottom along with air stones.

I’m sure if i drill a lot of 5mm holes it will allow enough water through.
 
MadMan-JaMeS said:
@NoobCannon no picture unfortunately.

currently it is just a bare tank, water comes in and go through filter socks. The whole thing is full of k1 and then a return pump at the other end. A couple of heaters are loose in the bottom along with air stones.

I’m sure if i drill a lot of 5mm holes it will allow enough water through.
Click to expand...

only trouble your gonna have is how quickly those holes fill with algae/detritus. Like i said i used to use knitting mesh as filter screens, it has tiny holes but handled loads of flow (gradually reducing as it blocked up). Assuming This is a marine tank are you Not factoring A Skimmer in somewhere?
 
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