Flow up or down with inline heater?

[PBM3000]

I'm about to construct an inline heater enclosure to run it externally (from a canister filter). Assuming restriction is no greater anywhere than that of my 12/16 tubing, will this addition decrease pressure/flow to the spray bar? I don't see how it can but would like your wisdom and experience...

 

[Zeus.]

Any increase in length or different flow patterns will add up with a reduction in flow OFC. But as long as you don't create constrictions or tight bends the reduction in flow should be mimimal/acceptable.
Better if flow though heater is up.

 

[zozo]

Anything you put additionaly in line will have some effect on the flow in form of restriction, that's a natural law you can not get around. But it might not be enough to have significant negative and noticable impact. Ofcourse depending on the capacity of your pump..

Just take some fluid dynamics into account whit the construction.. For example, take diameter into account and do not make it too narrow, but that isn't to be difficult with 12/16 tube.. But just for a heads up try at least to create an opening that is the same if not a bit larger than the inner surface (Circle) area of the tube to prevent a bottle neck.
That would be ¼ x π x D² .. Is 0.785 x 12 x12 = 113mm surface area for a 12/16 tube.

Than if you put a heater into a tube you will need at least 113mm square space left around the heater. Less will be a boottle neck.. Doesn't need to be spot on but a proximate is enough. But if you like to nerd than calculate the square surface of the heater same way and add 113mm and reverse the calculation back to diameter, that should be the minimum inner tube diamter you like to use to inclose the heater.

Than if you need to go with a bend, than never make it a straight 90° bend with a 90°T.. Take a 45° T and a 45° knee is together 90° and make it follow the flow, this gives the least restriction.

For example this is my inline heater DIY creation..

 

[PBM3000]

Well, you lost me at 'maffs'!

My heater diameter is 25mm and the tube I've bought is 40mm. Is that okay?

Mine will have a 90deg elbow IN, T connector OUT. I see your logic but it's a bit late to change now. I guess it'll work though?

 

[zozo]

It looks more difficult than it is, actualy it's quite simple, but it's also quite a lot to take in that i can't help. Loosing flow just aint an easy yes or no answer if your not a math savant. And i'm not and unfortunately i can't paint on grit paper that would make it easier to explain why/how surface area is calculated in square.
I understand thats rather distracting because tube is round and this needs to be virtualy squared to get surface area.. It's actualy the same as calculating aqaurium volume, square surface area bottom panel x height. In case of a circle (or a cylindrical vase/ aqaurium volume) we do not have a square, but if we want to make a grit with square milimeters inside a circle to find out it's surface area we have to calculate that with an excisting formula. For now we neglect the height/lenght, but volume is not irrelevant in distributing fluids. Come back to this later.

"0.785 x diamater x diameter" to cut of the round corners from the square. As said for a 16/12mm tube the inner diameter of the tube is 12.. 0.785 x 12 x 12 = 113 mm square surface area in the inner tube.

Now you stick a heater in a PVC tube. As bellow the grey is the PVC tube, red is the heater, blue the free space around it. Now your feeding this space with 16/12 tube that has 113mm surface of water bumping in to the heater. That you need to force around the heater with the least of restriction. Than the simple sum is if all the free space around the heater is less than 113mm square it will be a bottle neck, you are reducing the space causing more strain on the pump to push it through. Thus greater flow loss..

Now you ask is 40mm PVC tube enough for a 25mm heater.. I could say yes, but i actualy can't know because we are concerned with the inner diameter of the tube. The outside diameter of 40 actualy doesn't tell me much. There are several types of PVC tube with different wall thicknes.. If this tubes wall thicknes is 3mm than you have 6mm less inner tube diiameter. leaves you with 34mm inner tube for real. With a 25mm heater in it's centre gives you 4,5mm free space around it at each side.

Does this equal the 113mm square of the tube that feeds it? Approximately doing a quick headbut, i would say, probably more than enough, give it a go.

Less dificult and beeing a bit more on the sure side of the story you need to calculate it.. With diameter heater = 25mm so the surface area the water bumps into is

0.785 x 25 x 25 = 490mm

we need al least 113mm free space around it not to create to much of a bottle neck. 490 + 113 = 603 square surface area.. So the find out the least tube diamter to use is reverting 603mm square back to a circle to get a diameter That's the fun part even more distracting and a just leave it all rounded up without decimals not to go completely bonkers

603 / 0.785 = 768
√ 768 = 28

So the least inner tube diameter you should have to inclose the heater is 28mm..

But yet we don't know your inner tube diamter we assume you have 36mm as said more than enough.. Tricky thing, in fluid dynamics and loosing flow we have to come back to the relevancy of volume.. Because volume equals weight and now you create a lenght of pipe with a heater in it that collects a X volume of water that the pump has to push out again to a 16/12 mm hose to tha aqaurium. The greater this volume the more force the pump will need to push it out. Obviously to loos less flow we need to make this volume as small as possible and eqaul to the volume in the same lenght from the initial tube used.

Anyway i don't want to go completely

on you..

Anyway 40mm is it OK? Dunno it's more than enough.. Will you lose flow, yes, how much? depends.. With a slightly narrower tube that equals an inner diameter of at least 28mm would be more optimal and lose less. With using a more rounded x 45° bend around the corner even beter. So a standard 32mm PVC presure pipe could already be sufficient.. Because PVC pressure pipe has a lesser wall thicknes than standard PVC sewage pipe.

Sorry.. But regarding the OP Flow up or Down, there is no easy answer.. DIY with fluid dynamics is and stays an approximate trail and error of keep trying without going complletely nerdy on it....

 

[PBM3000]

Wow. I can tell that you’ll never be unemployed! Good stuff, thanks.

I have already needed to stem the flow a little in the current setup so that’ll give me some leeway. I’ll report back with my findings - although they’ll be subjective rather than objective!