Thermowell wake frequency calculations are essential for preventing fatigue failure caused by flow-induced vibration, typically following the ASME PTC 19.3 TW standard. An Excel calculator must incorporate process conditions, material properties, and geometry to determine the Wake Frequency Ratio (
Different companies have different safety factors or material libraries. An Excel sheet can be easily modified to include specific company-approved material properties (like Young’s Modulus for exotic alloys) that generic software might lack.
Where ( \nu ) is the kinematic viscosity of the fluid (e.g., ( 1.0 \times 10^-6 , m^2/s ) for water at 20°C, or ( 1.5 \times 10^-5 , m^2/s ) for air at 20°C). wake frequency calculation excel sheet
fs=Nr⋅Vdf sub s equals the fraction with numerator cap N sub r center dot cap V and denominator d end-fraction = (Strouhal_No * Velocity) / D_tip
| Re range | Strouhal number | |----------|----------------| | < 1e5 | 0.18 | | 1e5 – 3.5e6 | 0.20 | | > 3.5e6 | 0.22 | Where ( \nu ) is the kinematic viscosity of the fluid (e
Comprehensive Guide to Thermowell Wake Frequency Calculations in Excel
| Velocity (m/s) | Angle (deg) | Proj. Diameter (m) | f_shed (Hz) | Resonance? | |----------------|-------------|--------------------|-------------|-------------| | 5 | 0 | 0.5 | 2.0 | OK | | 10 | 0 | 0.5 | 4.0 | RESONANCE | | 15 | 30 | 0.5 | 6.0 | OK | ( 1.0 \times 10^-6
Where:
= (Af * B_root) / (L_length^2) * SQRT(E_modulus / Density_mat) Afcap A sub f is a correlation factor based on the taper ratio ( Step 2: Calculate the Vortex Shedding Frequency ( Shedding frequency relies on the Strouhal number ( Nrcap N sub r ), fluid velocity, and tip diameter:
In cell B8:
For a cylinder in a cross-flow, the Strouhal number is not constant. It depends on the Reynolds number (( Re )). Therefore, a robust Excel sheet must compute ( Re ) first, then select the appropriate ( S_t ).
