As discussed at the start of the tutorial, the calculated pressure drop across the porous region can be compared to the theoretical pressure drop derived from the mass flow rate.
The value produced by this report will be displayed in the Output window as 1.289424e+02 Pa.
A pressure of -8.986156e+00 Pa will be displayed, therefore the observed pressure drop is 137.9 Pa.
To determine the theoretical pressure drop:
The mass flow rate through the porous region will be displayed as -2.956532e-02 kg/s. Since the fluid density is 1.205 kg/m3 and the cross-sectional area of the porous region 0.00786 m2, this corresponds to a superficial velocity through the region of 3.122 m/s. Putting this superficial velocity into Eqn. 1, with L = 0.03 m, gives a pressure drop of 147.8 Pa across the porous region, which means that the calculated pressure drop is within 7% of the theoretical drop. This is acceptable because the theoretical pressure drop formula assumes a constant superficial velocity in the porous medium. In the above comparison, we have used instead an average velocity value based upon the mass flow rate, implying that the theoretical value is only an approximation to the actual pressure drop.
