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Chapter 8
Dynamic Behavior of Pumping Systems

Excerpt

Many of the dynamic analyses conducted during the design phase of a pump station or for trouble shooting problems are invariably involved in the startup and shutdown of centrifugal pumps, flow controls, and in the opening and closing of valves during operation scenarios. Interaction between system hydraulic dynamics and associated control protocols could also trigger severe dynamics and catastrophic failure or system overall reliability issues. Expansion of pump stations to cope with either capacity increases or changes in conditions or products can be a challenge. The addition of various units in series or parallel with different pump head-flow characteristics, and drivers' type and inertias, require attention and thorough analysis.

In order to understand the dynamic behavior of a pumping system, the governing equation describing the unsteady incompressible flow through various piping elements needs to be solved in both temporal and spatial domains. A constant area pipe is described by the continuity and momentum equations. Therefore, the fundamental governing one-dimensional equation is described first and are solved using the method of characteristics. Since the pump driver exerts a torque on the rotating shaft, which in turn, conveys energy to the impeller to develop a total dynamic head across the pump, the dynamic behavior of this system is also described and combined with the unsteady flow of the connecting piping system. The transient-state pressures at some locations in the system may be reduced to or below the vapor pressure of the liquid. This may produce vapor cavities in the flow or may cause the liquid column to separate. Rejoining of the separated columns or collapse of the cavities results in a large pressure rise, which may damage the piping system. This chapter deals with these dynamic phenomena frequently observed in pumping systems.

  • 8.1 Introduction
  • 8.2 Unsteady Governing Equations and Solution Techniques
  • 8.2.1 Governing of Equation for Constant Area Pipes
  • 8.2.2 Solution Techniques
  • 8.3 Boundary Conditions
  • 8.3.1 Flow Transients Across Other Elements
  • 8.3.2 Flow Transients of an Accumulator
  • 8.4 Dynamics Behaviour of Centrifugal Pumps
  • 8.4.1 Homologous Relations
  • 8.4.2 Full Pump Characteristics
  • 8.4.3 Dynamic Equation
  • 8.4.4 Pump and Motor Inertias
  • 8.5 Water Hammer, Cavitation, and Column Separation
  • 8.5.1 Water Hammer
  • 8.6 Cavitation and Column Separation
  • 8.6.1 Steam Condensation-Induced Water Hammer
  • 8.7 Examples and Case Studies
  • 8.7.1 Styrene Transfer System
  • 8.7.2 Lube Oil System for a Large Process Gas Compressor
  • 8.7.3 Pump Characteristics
  • 8.7.4 Controls Valves
  • 8.7.5 First Problem
  • 8.7.6 Second Problem
  • References

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