# Calculating the change in flow rate with a change in pipe diameter

At datum height I have a pipe A (ID = 25mm) that discharges water at a volumetric flow rate of 10l/min, and unknown pressure. When this pipe is connected to a polyethylene pipe B (ID = 12mm), 50m long running to a height of 6m, then the end of this pipe B discharges water at 3l/min

Do I have enough information to calculate what the change in discharge rate at the end of pipe B would be if pipe B was of diameter 25mm instead of 12mm, and if so how could I? The equations I'm seeing seem to require a pressure measurement.

I've seen this answer, but it appears to ignore friction losses.

I'm guessing minor losses from the transition at the join of unlike pipe sizes can probably be ignored for an approximate answer.

• Yes, I think there is a pressure that partially offsets the 6m head differential to result in a reduced flow rate at the discharge point. I don't think the change in pipe diameter would change the flow rate, but discharge velocity.
– r13
Apr 8 at 3:09
• What Re are you operating at? You Colebrook equation may signify significantly. Check Cimbala and Çengel's textbook. Apr 8 at 12:31
• You can have a look at this question also. It describes the methodology for the pressure drop, which you can modify. Apr 8 at 15:14