Relationship betwen pressure and flow in experiment shown

parislad

If I set up an experiment as shwon in the schematic attached,

where the effective length of the tubing is 25m (this then goes to a short length of smaller area tubing), and the pressure applied is contant,

what kind of relationship should I expect between pressure drop and flow rate? I don't know velocity out or the area of the outlet.

I initially thought of Bernoulli's principle - could you say that dP = 0.5*rho*v^2 ?

Thanks

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boneh3ad

Assuming no other losses in your system (such as friction or the pipe contraction) then your answer is correct. Those assumptions may or may not be reasonable depending on your situation though. It will get you a decent estimate though.

rcgldr

It depends on how much the smaller pipe restricts the flow. If there was no smaller section of tubing, then although velocity and flow rate remain constant pressure decreases with flow distance through the pipe due to friction with the 25 meters of tubing and viscosity within the water (the pressure energy is converted into heat). If the smaller pipe is much smaller than the main section of pipe and significantly reduces the overall flow rate, then the pressure drop within the 25 meter section of pipe is much less.