Why Steady-state Pressure drop across a simple pipe in Simscape not in line with the manual calculation?

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Jay 2022-3-5

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https://ww2.mathworks.cn/matlabcentral/answers/1664419-why-steady-state-pressure-drop-across-a-simple-pipe-in-simscape-not-in-line-with-the-manual-calcula

编辑： Jay 2022-3-5

TFmodel.slx

I have a constant gas flow source connected with a pipe model. The mass flow is 2 kg/s. The pipe is with diameter 160mm, length 100m. I have attached the simulink model.

According to help page, I calculated the pressure drop as 128 * mu_I * m_dot * Length / (rho_I * pi * D^4) ~= 180 Pa if mu_I = 18 * 10 ^(-6) and rho_I is 1.2 kg/m^3 for air at 20 degree.

The simscape simulation shows the pressure drop is 9000 Pa (see figure below), which is way off than the calcuated value. I know the density is underestimated as the steady-state pressure is 3.5 bar instead of 1 ATM. If taking that into account, the calculated value is even smaller.

Since 3.5 bar is not a very high pressure, I pressume the dynamic viscosity is not too much affected by the pressure. mu_I = 18 * 10 ^(-6) is perhaps acceptable in the calculation? Could anyone help to explain where the calculation went wrong or why this discrepancy happens? THANKS.