Hotwire/film anemometry for room air motion studies.

Application of hot wirelfilm ariemometry in room air flows presents difficulties because: (1) the effect of natural convection due to the heated wire beconies significant for low air velocity measurements; (2) the angle sensitivity of a hot wire becomes small at low air velocities, which makes it difficult to resolve the direction of each velocity component. This study aimed at quantifying the uncertainty of tlie hot wire anernornetry and examining the angle sensitivity of a hot wire in low air velocity measurements. Based on the experiments, it was concluded that: (1) the uncertainties due to natural convection in the velocity measurements with a single component hot wire probe operating at 200 °C wire temperature are within +- 15 % ,+- 5 % , +- 3 % , +- 1 % and 0.5 % for velocities of 0.05 - 0.1 m/s, 0.1 - 0.15 m/s, 0.15 - 0.25 m/s and 0.25 - 0.5 m/s, respectively, and correction can be made based on the visualization of the room air flow pattern to achieve higher accuracy; (2) air velocity components can not be measured simultaneously with multi-component hot wire probes if the air velocity is below 0.2 m/s since the angle sensitivity of the probe will be heavily contaminated by the noise signal due to the natural convection.