In the calculation of flow-limiting orifice plates according to HG/T20570, does avoiding choked flow also result in the loss of the flow-limiting function?
Thread Content
To avoid choked flow in pipelines using flow control orifice plates, the pressure behind the orifice plate (P2) must not be less than 55% of the pressure before the plate (P1)； However, when calculating the flow restriction orifice plate, the pressure ratio P2/P1 before and after each orifice plate must be ≤ Y. At that time, the fluid flow rate can be restricted to a certain value, indicating the calculated d. It is effective; otherwise, the pressure drop must be changed or the pipe diameter adjusted, and recalculation must be performed until the requirements are met. And the value of γ is often less than 0.55. Isn’t this contradictory? To avoid choking the flow, does it also fail to serve the purpose of flow control?
HG is not a calculation for choked flow, because it requires a stepped pressure drop, and the pressure drop at each stage must not exceed that of choked flow. He is: a stepped pressure-reducing orifice plate close to the choked flow.
I’m not quite sure; please clarify. Is it necessary to ensure that the pressure ratio P2/P1 before and after each orifice plate is ≤ Y?
This post was last edited by HEJIYUER on 2021-9-5 at 17:35. Although the design conditions meet those for a choked flow, HG’s approach is to avoid flow restriction and instead use multi-stage voltage reduction. For example, P1=10 BARA, P2=2 BARA, Q=100. Level 1: P1=10, P2=5.5 (design for near-blocking flow). Level 2: P1=5.5, P2=3 (design for near-blocking flow). Level 3: P1=3, P2=2 (design for differential pressure flow). Only when P1/P2 is at a ratio of 10/2 will the actual flow rate be the designed value of 100. However, as the third stage P2 increases, the preceding two stages are far from the choked flow state, and the flow rate is determined by the resistance coefficients of the three orifice plates; therefore, flow restriction is not possible ； When the third stage P2 decreases, the second stage enters choked flow, which determines the flow rate of the entire pipeline. (However, the definition of gas throttling is that when P2/P1 is less than 0.55, the flow rate remains constant as P2 changes.) ）
Thank you for your advice. I’ll take some more time to think about it. Thanks~