Vibration, dynamics and noise

formerly BETA Machinery Analysis and SVT Engineering Consultants

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Surge Sensitivity Calculator

Inertia number evaluation – a simplified method to calculate surge sensitivity

This free calculation tool can determine your compressor application's risk of surge. It provides a quantitative score using the non-dimensional inertia number to determine the optimal level of surge analysis given the compressor’s proclivity to surge.

Please input your values below:

Name Value Unit Explanation and Assumptions
Rotor Max Speed rpm Max speed possible for compressor
Max Head at Surge kJ/kg Max head at surge line
Max Mass Flow at Surge kg /sec Max mass flow on surge line
# of Wheels on Drive Train  
Type of Drive
Effective Speed rpm
Inertia: Calculated Value kg-m2
or Inertia: User Input kg-m2 * User may input inertia directly or program will calculate it based on regression fit and N, type of drive, and wheel count.
Inertia Value for Model kg-m2
Piping Length in Recycle Loop ft
Speed of Sound ft/sec SOS for gas mixtures in ft /sec
  • Light nat gas, SG = 0.6, SOS = 1350
  • Heavy gas mix, SG = 0.85, SOS = 1000
  • Pure CO2, SOS = 800
  • Pure nitrogen, SOS = 1150
  • Pure ethylene, SOS = 950
Tau - Time Delay sec *Assume 0.15 sec valve time delay

Ni, Inertia Number

Surge sensitivity inertia number risk evaluation

Summary: Wood Group VDN Service Offering

Level 1 – Surge Sensitivity Calculator – FREE, helps to answer these  questions?

  • Overall risk of your installation to surge?
  • Elaborate on the experience with designs?
  • Complications of multiple units, multiple modes of operation?

Level 2 – Helps to determine:

  • Optimal valve size (cold recycle, and hot recycle if needed)
  • Specifies necessary valve response time
  • Better assessment of risk (impedance line slope)
  • Qualitative assessment of installation risks, (ie. need for hot recycle, dynamic study)
  • Fast, can often turn around in less than a week (provided information is available

Contact us for inquiries, technical support, and pricing for a Level 2 analysis.

Level 3 – Accurate assessment of real surge behavior

  • Uses the most accurate surge modeling available to test the surge control system performance
  • Models the actual piping layout, valves, and components
  • Identifies dangerous operating scenarios
  • Recommends detailed design improvements
  • The most comprehensive assessment of surge risk, with solutions to mitigate risks

Please contact us for Level 3 inquiries.

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