Traffic issue
Thread Content
I have a basic question for fellow enthusiasts: In a gas pipeline system with steady flow, can it be said that the volumetric flow rate remains constant throughout the entire pipeline system? Even when encountering sections where the diameter of the pipeline changes, the volumetric flow rate stays the same; it is only the flow velocity and cross-sectional area that change. That is, qv1 = qv2, or flow velocity 1 times area 1 equals flow velocity 2 times area 2. Is this understanding correct?
Why? Isn’t Bernoulli’s equation the same?
That’s right; it’s the law of conservation of mass – you can’t have 100 going in and 200 coming out
This is true for incompressible fluids. But this is not accurate for a compressible fluid like gas. It’s not entirely clear whether the volumetric flow rate mentioned in your question refers to the nominal volumetric flow rate or the actual volumetric flow rate under operating conditions. For the volumetric flow rate under operating conditions, Bernoulli’s equation P1V1/T1=P2V2/T2 applies; temperature changes are neglected, so P1V1=P2V2, where both V1 and V2 represent the volumetric flow rate under those operating conditions. V=u*S. Therefore, P1u1S1 = P2u2S2. (u1, u2 are the fluid flow velocities, and S1, S2 are the cross-sectional areas). For volumetric flow rates under standard conditions, V1=V2 (both V1 and V2 are volumetric flow rates under standard conditions)
The diameter of the pipe changes, which is equivalent to throttling; as a result, the pressure also changes. At this point, using the ideal gas law P1V1=P2V2, since P1≠P2, it follows that V1≠V2. Can it be said that the flow rate has changed? Also, why is V1=V2 under standard conditions? Still dizzy :)
The mass flow rate remains the same, while the volume flow rate is dependent on temperature and pressure.
The volumetric flow rates can vary, but after standardization they become the same, which means mass conservation
Mass is conserved, but volume is not necessarily conserved; there is some compression……