Fluidelastic Instability (Connors Equation) Calculator

Determine Connors critical crossflow velocity (Vcrit) and Instability Ratio (IR) to prevent catastrophic self-excited tube whirling and rapid failure.

Vibration & Crossflow Parameters

Tube Natural Frequency f_n (Hz):

Tube Outer Dia d_o (mm):

Effective Tube Mass m_e (kg/m): Metal + Inside Fluid + Virtual Shell Added Mass

Shell Fluid Density ρ_s (kg/m³):

Logarithmic Decrement δ₀ (Damping): Liquid: 0.05 - 0.15 | Gas: 0.02 - 0.05

Connors Instability Factor β: TEMA recommendation: β = 2.4 - 3.3

Actual Crossflow Velocity v_actual (m/s):

Instability Margin & Critical Threshold

Connors Critical Velocity:

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Instability Ratio (IR):

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Mass-Damping Parameter:

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Max Safe Operating Velocity:

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Fluidelastic Stability Verdict:

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Frequently Asked Questions

Why is fluidelastic instability (FEI) the most destructive vibration mechanism in heat exchangers?

Unlike vortex shedding which produces bounded resonance, fluidelastic instability is a self-excited feedback loop where vibrating tubes dynamically distort flow paths, extracting unlimited energy from the crossflow. Tube amplitudes explode until tubes clatter into each other and shear off within hours.

What is the Connors equation?

Formulated by Harold Connors in 1970, Vcrit = β·fn·do·√[(me·δ₀)/(ρ·do²)] defines the threshold crossflow velocity beyond which fluid damping turns negative and unstable whirling begins.

What is the required TEMA design margin against fluidelastic instability?

TEMA standards require the Instability Ratio IR = Vactual / Vcrit to be strictly below 0.75 (providing a 25% minimum margin of safety) across all operating flow rates and upset conditions.