Effect of a protective coating on the frequency characteristics of film transducers in thermoanemometers
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An expression is derived for the thermal characteristic impedance. Equations are obtained for calculating the amplitude-frequency and the phase-frequency characteristics of planarfilm transducers with protective coating.
KeywordsStatistical Physic Frequency Characteristic Protective Coating Characteristic Impedance Film Transducer
heat transfer coefficient
thermal diffusivity in solid state
length of film on sensing element, normal to the direction of the stream
width of film on sensing element, parallel to the direction of the stream
thickness of substrate
kinematic viscosity of fluid
thermal characteristic impedance
thermal characteristic resistance
temperature of hot film (°C)
temperature of protective coating, at distanceLc from the film
temperature of substrate, at distance lb from the film
- lc=λT, lc=λT/2, etc.
thickness of protective coating, equal to thermal wavelength, equal to half the thermal wavelength, etc.
thermal flux from hot film to protective coating
thermal flux from hot film to substrate
heat transferred from protective coating to fluid stream
characteristic impedance of transient heat transfer from film to coating (°C·sec/J)
characteristic impedance of transient heat transfer from film to substrate (°C·sec/J)
relative sensitivity, dB
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