Assessment of Dynamic Pressure Losses in Reciprocating Compression Plants

The term dynamic pressure loss is used somewhat freely in the reciprocating compression industry to describe pressure losses thatare associated with the dynamic component (rather than steady-state) of the flow through the piping system in a compressor station. Conventionally, dynamic pressure losses are determined by assuming a periodically pulsating 1-D flow profile and calculating the transient pipe friction losses by multiplying a friction factor from the Moody diagram with the flow dynamic pressure component (1/2pv2) for each time step for a single time-discretized pulsation period. In reality, the dynamic pressure loss is more complex and is not a single component but rather consists of three different physical effects. These three effects are not necessarily interrelated and have to be individually assessed to determine a true pressure drop of unsteady and periodically pulsating flow. These three pressure loss components are: (1) unsteady flow profile viscous losses, (2) transient inertial losses, (3) fluid to piping driven dynamic structurallosses. The first and second are well understood (although usually ignored or incorrectly calculated) while the third requires an improved physical understanding of the piping system as it involves fluid and structural energy interaction. Specifically, the dynamic structural component of dynamic pressure losses which area due to flow pulsation driven piping vibrations are not well understoodand have not been previously quantified, particularly for resonant piping flow. A number of experiments were performed by SwRI in a reciprocating compressor closed loop facility to determine these loss components using dynamic pressure and vibration measurements for a number of resonant, non-resonant, and resonant-clamped pipe operating conditions. Results show that the dynamic structural loss component can be significant and cannot be ignored when predicting dynamic pressure losses. This paper describes findings from these experiments

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