Producing small scale temperature fluctuations in an airstream

Area of Science:

• Fluid dynamics
• Heat transfer
• Aerodynamics

Background:

• Accurate thermal measurements are crucial for understanding fluid dynamics.
• Existing methods may have limitations in frequency response and spatial resolution.

Purpose of the Study:

• To introduce and validate a novel hot wire technique for thermal analysis.
• To assess the heat transfer characteristics in a low-speed airstream.
• To explore applications in sensor calibration and turbulent heat transfer investigation.

Main Methods:

• Utilized a 4.5-micrometer hot wire for heating a low-speed airstream.
• Applied direct current (dc) and alternating current (ac) excitation.
• Measured thermal noise spectrum and thermal signal propagation.
• Performed heat transfer calculations.

Main Results:

• Observed a white thermal noise spectrum up to 2 kHz for dc excitation.
• Achieved a clear thermal signal up to 2 cm from the hot wire with ac heating (400 Hz).
• Calculations confirmed efficient heat transfer between the hot wire and the airstream.

Conclusions:

• The hot wire technique provides reliable thermal data across a range of frequencies.
• This method is effective for calibrating temperature sensors' frequency response.
• It offers a valuable tool for studying turbulent heat transfer in diverse flow scenarios.