Knowledge Center

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	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

Levels of support

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

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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