pipe diameter, flow rate and velocity

[Tom Raffield]

So the question is:

Should I stick with the 25mm diameter spray bar pipe and go for 20 or so 4ml holes to increase pressure (how many holes does your bar have @ian_m ?)
or
Should I use a smaller diameter spray bar pipe with more than 20 holes to increase pressure. I have a few pieces that I ordered in error before starting out.

I accept that my filter will not be able to yield as much as is stipulated on the box but I think I must sacrifice this in order to increase the velocity of the water leaving the spray bar. I am sure that my nutrients, CO2 and lighting is all fine and the issues must have come from the flow. Primarily through the Juwel internal filter, then through the poor nozzles on the FX4 and currently through an underpowered spray bar - none have delivered decent flow and distribution.

 

[ian_m]

(how many holes does your bar have @ian_m ?)

From the video I make it 2 x 9 (whole spray bar) + 6 (shortened spray bar) = 25 holes. This is a standard JBL 22mm spray bar.

 

[Zeus.]

Smaller holes can always be made larger 😉 start at 3.0mm and work up in 0.5mm increments

 

[Andrew Butler]

Comparing surface area of one outlet to the total number of smaller outputs doesn't work as Flow in pipes and the relative resistance is dependant on the diameter of the pipe and its length

Hi M8 😀

I use http://www.1728.org/flowrate.htm to get my flow rates when going from a 25mm pipe to many small holes in a spray bar. Using the cross sectional area of the 25mm and comparing to total cross sectional area of the holes in the spray bar doesnt work due to the 'Hagen–Poiseuille law'

I calculated the velocity from the pipe diameter and the pump/filter flow rate and say I got

a 28mm pipe and 3000l/h flow rate from pump/filter gives 135cm per sec Velocity

then I decide on the spraybar diameter holes say 4mm and use the 135cm per sec Velocity which yields 61 litres per hour

so to keep the same 3000l/h its 3000 /61 = 49 so 49 holes of 4mm diameter to yield 'about' the same flow rate

But if holes 5mm yeilds 95 l/h so 3000/95 = 31 holes.

well thats the method I used 😉

I'm a little confused Karl; you said earlier you calculated your holes the above way and now I think you're saying it doesn't work?

 

[Zeus.]

I'm a little confused Karl; you said earlier you calculated your holes the above way and now I think you're saying it doesn't work?

I used the calculation to work out the number of holes and size to get the same flow/output which is what you asked for

I'm looking to see what size pipe is needed for a filter to operate without being restricted so in other words how big the diameter of a pipe needs to be to allow a particular amount of litres per hour.

But I have posted and getting the energy/output to get the better tank turnover also 😉

 

[Zeus.]

I may have been focusing on the Poiseuille’s law too much- stating 'doubling the radius of a tube decreases resistance by a factor of

' so the size of the pipe makes a big difference to the resistance, but then when have to consider the viscosity of water!

Water doesnt have a high viscosity, well not as low as a gas

So the 'total area : pipe area rule being the way to go' -may be a close enough approximation for water in our tanks/pipes and filters. As when Andrew used it his results worked out in the same order as when I used my method which was more long winded also.

But all said the calculations only give the output in say litres per hour and the guide is x10 tank volume to filter output, but its implementation of the output thats makes the difference to tank turnover/Flow. I had one massive outlet great output and the tank flow was very poor. I fitted the spraybar many small holes which reduced the filters output but the many small 'jets' with high velocity water ' more energy' moved more water within the tank so better turnover/flow

 

[Tom Raffield]

Mid way through my tank maintenance for the week. Water is out, plants have been tidied up, snipped and replanted some of the hygrophilia polysperma.

Also taped up half the holes on the spray bar to give me 24 (4mm) holes. FX4 has the same amount of media inside that I reduced to last week. The video shows the results. Much more pressure - might drill a new bar with this number of holes or do you think I should go for more pressure? I did toy with going to a 20mm diameter spray bar from my current 25mm but thought that might be a bridge too far for the pump!

 

[Zeus.]

I did toy with going to a 20mm diameter spray bar from my current 25mm but thought that might be a bridge too far for the pump

If the 20mm pipe was being feed at both ends maybe, but a 25mm will tend to give similar 'powered' jets of water for the whole length of the pipe but the 20mm will/maybe have more 'powerful' jets at the end where the pipe attaches to the outlet of the filter IMO.

Leave the tape on for a while, mine has had tape over holes for months without it coming off 😉 will take at months to see the results at least, then you may need to tune it further like tape all the holes up and have a different configuration of say 36 (3mm) holes or 24 (3.5mm) holes

 

[Tom Raffield]

As I have spare sections of 1m pipe I drilled a new one 😀 There is a little dripping at the left hand side where the filter outlet joins but I have literally bent the FX4 tube, added a Fluval rubber joiner and shoved it into the spray bar. Very technical If I wasn't worried about cocking it up I would get a proper 90 elbow joint to fit the Fluval+Spray bar and that would allow me to get the spray bar nearer the left tank wall. This is the main area in the tank where I imagine that water movement is lowest.

For now, I think I'm going to leave everything and just watch and wait. Normal water changes and maintenance and that will be it. I will post results to keep people up to date but possibly not in this spray bar thread.

Note: The next thing for playing with (eventually) will be the CO2 diffusion. The nilocg reactor from the states is a no go as it costs almost $80 postage alone! I'd rather pay someone over here to make me one!

 

[foxfish]

Best to use bends rather than elbows, the route from your filter outlet to the spray bar needs to be as direct and smooth as possibly if you want max flow and pressure.

 

[Zeus.]

Had a measure and count of my holes today from my spray spraybar which my Fluval FX6 filter feeds post reactors and heaters 4.0mm x23 and 3.5mm x4 the last four just spray on the sides of glass as was getting some surface backflow


no chance of it hitting the glass 1.5m away



Spray bar is 25mm feeds both ends but had to reduce the fitting to 20mm and back to 25mm to fit though the bracing

 

[Tom Raffield]

Heading towards tank maintenance tomorrow.

Spray bar seems to be doing ok. Although when my Fluval stopped, as it is supposed to every 12 hours, there was some serious burping and a surge of bubbles when it turned back on. Could that be my CO2 getting stuck what with the bazooka being aimed straight into it?

And thought i’d take these photos. Any thoughts on what is still causing it? The black spotting appears to be worse and the orange spotting on the leaves too. I’ve also noticed some GSA on the glass so am putting back the phosphates into my EI mix. My water changes should ensure I never get too much of anything in there.

Say I haven maxmised my spray bar to its full potential, what other options are there for increasing flow? And just a thought - but will the position of my drift wood totally screw up flow and distribution to the sword on the back left?

 

[Matt @ ScapeEasy]

Why do you switch your filter off every 12 hours? Or have I misunderstood?

 

[Tom Raffield]

Why do you switch your filter off every 12 hours? Or have I misunderstood?

It does this automatcially to allow for release of air bubble build up. It’s a feature of the FX series. I probably wasn’t very clear!

 

[Zeus.]

Although when my Fluval stopped, as it is supposed to every 12 hours, there was some serious burping and a surge of bubbles when it turned back on.

Mine use to do that when I was using it as a CO2 reactor, I compensated for it by having its power switch off say 15 mins before CO2 on time for a minute, then the FX6 could do its auto restart routine then it would be on for 12hrs. But the FX6 couldn't cope with the CO2 I was injecting without throwing bubbles out on its own.

I have the FX6 on a schedule ATM as its output feeds my CO2 reactors so at midnight every day power stops for a minute and the FX6 does its thing and then it doesnt stop mid CO2/Photoperiod, Just another Joy of having a PLC 😉

 

[Tom Raffield]

So, a little update.

The tank isn't looking bad. Especially in the middle. The monte carlo however is getting 'dug up' by the shrimp so I may need to rethink the plant i use as foreground there.

Towards the back corners the Amazon swords are growing well but starting to show the orange deficiency on the leaves that I have posted about before. I want to attempt to further increase flow to ensure that CO2 is fully getting around the tank. The corners are partly 'dead spots' due to the spray bar not extending that far and possibly due to the curved front glass of the Vision.

My thought is: I want to add one of my koralia circulation pumps back into the tank. Do I go in the corner and hope to add circulation there? Although the curved glass might deflect the flow another direction. Or, do I go for the larger koralia and place it slap bang in the middle of the tank under the spray bar. I could drill another spray bar and leave the middle of it blocked. The koralia would act as a central force and I would then get more pressure at the ends of the spray bar.

I am still on the lookout for a plumbing piece to make the join from my Fluval hose to the bar a little more sound. I am also still investigating options for an inline CO2 diffuser (or similar) with the hope of getting an even better diffusion rate although using the FX4 as a reactor/filter appears to be doing an acceptable job at the moment.

What do you guys think?

 

[Edvet]

Curved tanks are notoriously hard to get good flow in. Experimenting is the key word. Try the cheapest solution first😀

 

[Aquahorti]

If you want good flow, getting a powerhead is probably a better solution than spraybars. The problem with spraybars is the flow entering the turbulent flow regime at the small holes in the spraybar. The problem with turbulent flows is the loss of hydraulic power, and should you want to find out if you are moving towards turbulent flow all you need to do is calculate the Reynolds Number for the fluid flow at the particular point of interest. The hydraulic power is the thing that will make the water do work in the tank, so the more hydraulic power you are losing in the hoses and pipes will result in less flow around the tank.

There are tradeoffs and as Edvet said experimenting is key (unless you have some good fluid dynamics simulation software), but reading a bit about fluid dynamics will give good pointers as to where to go, or just look at what reefers have been doing for years for real shortcuts.

 

[Tom Raffield]

If you want good flow, getting a powerhead is probably a better solution than spraybars. The problem with spraybars is the flow entering the turbulent flow regime at the small holes in the spraybar. The problem with turbulent flows is the loss of hydraulic power, and should you want to find out if you are moving towards turbulent flow all you need to do is calculate the Reynolds Number for the fluid flow at the particular point of interest. The hydraulic power is the thing that will make the water do work in the tank, so the more hydraulic power you are losing in the hoses and pipes will result in less flow around the tank.

There are tradeoffs and as Edvet said experimenting is key (unless you have some good fluid dynamics simulation software), but reading a bit about fluid dynamics will give good pointers as to where to go, or just look at what reefers have been doing for years for real shortcuts.

I won't pretend to follow all of that! Haha!

I have used multiple circulation pumps in the past which have not worked out. The tank is looking the best it has done for a long, long time and I think this is due to the spray bar and the larger filter (Fluval FX4). The far left hand side is the area where there may be an issue - the plants are telling me this! The largest Koralia I have might be the next thing back into the tank to see if I can help the problem spot but I don't want to have a negative influence somewhere else in the tank.

 

[Andrew Butler]

The tank is looking the best it has done for a long, long time and I think this is due to the spray bar and the larger filter (Fluval FX4). The far left hand side is the area where there may be an issue - the plants are telling me this!

Hey Tom,
So what you are saying is the spraybar is working right along the tank apart from the section where it doesn't cover?
If this is the case then maybe it's time to revisit ways of getting the feed for the spraybar up and over.............

I am still on the lookout for a plumbing piece to make the join from my Fluval hose to the bar a little more sound. I am also still investigating options for an inline CO2 diffuser (or similar) with the hope of getting an even better diffusion rate although using the FX4 as a reactor/filter appears to be doing an acceptable job at the moment.

I know we've talked about it before but you could use a few 90's, maybe even a tee (or 2 if you split it) if your bracing allowed to get the feed up and over - it works fine on my aquarium without causing a drop in flow rate.
This way you could get the spraybar closer to the ends and maybe do away with your dead spot.
As for adding inline CO2 you could tee into your flow; maybe not the best method but it might work.
To do this you could get 2no 25 x 16 x 25mm reducing tees (maybe a couple of 16mm 90s) and put an inline atomiser in a piece of hose along the 16mm - there would be neater ways of doing this.

I think adding any additional powerheads in would significantly disturb the flow pattern you have already.