Abstract

For single gas and vapour bubbles, the equivalent diameter, the rise velocity, and the frequency were measured on single artificial sites in distilled water. The air bubbles were emitted from glass nozzlęs with internal diameters of 0.3 mm, 0.6 mm, 0.9 mm and metallic orifice plates 2 mn and 4 nm in
diameter. Electrically heated needles have been employed to produce vapour bubbles. The needles made of brass and stainless steel were placed in glass tubes so a kind of pin fin were produced. The diameter of the pin fin at the base ranged from 0.27 mm to 0.78 mm and height from 0.48 mm to 4.8 mm. The experiments were conducted at atmospheric pressure. A technique based on Particle Image Velocimetry for measurement of bubble size and rise velocity has been developed and frequency of bubble departure was measured using a variable frequency stroboscope.