Split Pipe Pressure Drop

No

No, of course depending on your flow....... your turbulent flow will increase due to the increase in ratio of the wall area to volume of fluid being carried through the pipe.

For a constant total flow the velocity in given example will decrease since 5^2=25 and 4*3^2= 36.

Re= w*d/visc for same viscosity we obtain for the first case Re1≈ Q/25*5= Q/5 and in the second case

Re2≈ Q/4/9*3 = Q*3/36 =Q/12

In fact turbulence will DECREASE since Re values are less!!!!!!!!!!!!!!!!!!!!!

I should have worked the numbers of the cross section and flow........ ga

No. For a given length and dia of pipe headloss varies with flow as Q². As Q per pipe is down by factor 4 (assuming the smaller pipes are same length and arranged symmetrically) headloss per m in smaller pipe is down by 16.

For a given flow in turbulent conditions headloss varies with dia approx as 1/D⁵. So with dias 50 and 30, headloss up by (50/30)⁵ = 12.9. So headloss per m pipe in smaller = 12.9/16 = 0.8 times. Smaller pipe gives higher Reynolds No. which tends to reduce the Moody friction factor, but increases the relative roughness which has the opposite effect. You need to put some figures in if you want better accuracy.

No. This is cause by several things. The most predominate is the increase in wall surface for the smaller pipes. This is also why firefighters use Large Diameter Hose (HDL) for transferring large quantities of water to supply from the hydrant to the engine. Also when pumping from an engine to a manifold for smaller hoses. If the engine is pumping 500 ft with a pressure of 50psi you only have to increase the pressure on the pump by about 15 psi. To pump the same volume with 2 inch hoses in parallel would require an extra 100 psi or more to transfer the water. The larger hoses are usually 5" while the hoses held by a firefighter(s) are no bigger than 2-1/2". Even that takes several people to manage it.

Good Luck, Old Salt

I had posted similar on post #2. But I never did the calculation on the actual numbers supplied

phoenix911-

I crunched some actual numbers based on current pumping/frictional loss tables. These are for a hypothetical situation using 2" dia hose and 5" dia hose. For 5" hose being pumped at 1,000gpm for 200' the frictional loss (fl)will be 8.0 psi. Therefore to pump with 5", the pump pressure will have to be boosted by 8.0psi to obtain 1,000gpm.

For 2" hose the frictional loss is 50psi for 250 gpm and a length of 100ft. (from tables). Take each hose for 250gpm at 200ft and the FL is 2x50psi = 100psi. Using 4ea in parallel flowing 250 gpm each for a total of 1,000gpm the FL for each remains the same for each hose. Four hoses in parallel flowing 250 gpm each with a friction loss of 100psi for 200ft will require the pump to be set at 100psi higher to get the 1,000gpm out at 100psi.

These calculations are hypothetical only. Each situation requires its own calculations. These do not include frictional losses for any appliances or other contributing unit that creates frictional losses.

Good Luck, Old Salt

help me solve this.. need to find pressure drop at each floor of this building. any tips?