How to calculate flow loss between 90 and 45 degree fittings

[Oscar Gonzalez]

Hi everyone. Let me give a little bit of background on the problem I need help understanding.

I want to plumb an aquarium that has a sump and move the water from the sump to the main aquarium using a pump and 1" PVC pipe. The total system pipe length is going to be roughly 10 feet total with some elbows in between. I've read that using two 45 degree fittings is better than one 90 but this is the thing I want to understand that is not clear to determine if it is worth the gain from using the two 45 vs one 90 (on multiple places in the setup).

How do I calculate the flow loss (not pressure) of using one 90 degree fittings vs two 45 degree ones? What is the math behind this principle? I've been reading some fluid mechanic literature but so far I think it is just too technical for a simple human like me to try to apply it in a simple aquarium setup.

I saw a video here of some company that did a test with the two types of fittings and basically discovered that there is no really impact on chosing the 90 or 45 degree fittings for this application which confused me a lot since from what I've been reading there should be pressure head loss from using the 90 vs the 45s, but I haven't been able to find anywhere online that explains what does pressure loss have to do with flow rate. I feel like they should have found some difference in using one fitting or the other, or maybe their setup is just too small that the flow loss is insignificant, or maybe they just did it completely wrong. If you could help me understand the logic behind all this it would be great, or point me in the right direction to understand this topic a little better.

Thanks a lot for your time.

 

[anorlunda]

https://www.engineeringtoolbox.com/resistance-equivalent-length-d_192.html

That link gives pipe length equivalents for elbows. Then you can use whatever calculation method you want for flow.

 

[Ranger Mike]

see other post on this excellent physics forum

https://www.physicsforums.com/threads/pressure-drop-in-elbows-bends-in-a-pipe.179830/

From my dynometer testing days, on race engines, any elbows, bends and restrictions affect the oil pump pressure.

copied from another post on internet..
Loss of pressure can be calculated using the formula hL =K v2/2g, where hL is the velocity head, v is velocity of flow, and g is the acceleration of gravity.

f is the friction factor (which may be found in tables or determined experimentally):

Turns result in f as follows:
90 degree turn ("L") = 60f
90 degree Sweep = 30f
45 degree sweep = 10f
T straight through = 20f
T through branch = 60f

The absolute most restrictive type of turn is the 90 degree turn ("L") & the T through branch (60f).

Using two 45 degree fittings is a better choice over 90 degree elbows.

 

[gmax137]

Where I work the standard references are Crane Tech Paper No. 410 Flow of fluids through valves, fittings, and pipes, and Idel'chik Handbook of Hydraulic resistance. Crane used to be cheap (I got mine new from Crane for $8 but that was "a long time ago") and Idel'chik used to be hard to find (mine says NTIS AEC-TR-6630). Look in used bookstores or online if you can't afford new editions.

The Crane book is worth reading cover to cover a few times if you need to do practical fluid flow problems.