Response of hot wire anemometer probes to a stream of air bubbles in a water flow

The response of a hot wire anemometer in bubbly two-phase air-water flow was studied. For the conventional hot wire design and operation at low overheat, it was found that the sensor does not enter the bubble completely, thus making measurements inside the bubble virtually impossible. This is due to a liquid film which attaches to the wire. For small bubbles it results in splitting of the bubble into two. Three types of interactions are identified-direct, glancing and partial hits. Direct and glancing hits result in identical signal level changes and hence discrimination between bubble and no-bubble signals, whereas partial hits give considerably reduced signal level changes. Application of such measurements to determination of local void fraction by use of signal probability density plots is also considered