The effects of certain low frequency phenomena on the calibration of hot wires

A. E. Perry, A. J. Smits, M. S. Chong

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Temperature-sensitive constant-current wires operating at very low resistance ratios have been tested for temperature fluctuation response. A significant step in the response was found to occur with a centre-frequency of typically 1/6 Hz. The step size was observed to be as large as 30% and grew from zero to its maximum value in about a decade. Analysis shows that this phenomenon is associated with axial conduction of heat to and from the prongs. If it is recognized that prongs have finite thermal inertia then a modification of the boundary conditions to the equations of Betchov (1948) predicts this step, in agreement with the simple asymptotic analysis of Maye (1970). Experiments indicate that a similar phenomenon occurs with velocity-sensitive wires. Axial conduction appears to be the most likely cause. Aeroelastic deflexions and non-uniform cooling caused by bowing of the wire make precise predictions impossible. Here the differences in step size between wires were observed to be as large as 10% (or 20% in mean-square energy), the centre-frequency was usually beyond 10 Hz for the wires tested and the step extended over a much broader frequency range than in the temperature-sensitive case. The effect occurred at all velocities, resistance ratios and wire geometries. An analysis based on non-uniform cooling of the wire filament predicts the correct frequency range and shows that steps of 10% in frequency response are quite plausible.

Original languageEnglish (US)
Pages (from-to)415-431
Number of pages17
JournalJournal of Fluid Mechanics
Issue number3
StatePublished - Feb 1979

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering


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