How to calculate the pressure loss of a local resistance by hand?

I tried modelling a simple Fluid network with a local resistance:

The local resistance uses "By loss coefficient vs. Re table" as model parameterization and the loss coefficient is set to 1.5 for every Re-Number

The resistance area is set to be the cross sectional area of a pipe with a diameter of 0.02m.

To better understand what happens I tried to calculate the same by hand and see if I can come up with the same result:

In this case there is p1=0, u1=0, h2=0 and p2=0. So the equation simplifies to:

, with

That gives:

->

With the cross sectional area of the pipe results the Volumetric Flow of the System.

My Problem here is that the measured Volumetric flow is not equal to my calculated value.

The matlab code I used is attached.

What am I doing wrong?

Thanks in advance!

Answer 1

[Zenin Easa Panthakkalakath]

Hi,

I see that you've used Bernoulli's equation to do the hand calculation with an additional term for the loss due to friction. However, the equation has a few assumptions that must be met by the model to get close to accurate results.

For instance, the compressibility of the fluid may not be addressed in the calculation. Also, the equation is only valid in a steady state system.

Consider using Navier-Stokes equation in order to do the hand calculations.

Regards,

Zenin