PRODUCTION AND HYDRODYNAMIC PROPERTIES OF MICROBUBBLE MEDIUM

Some aspects of production of gas-liquid bubble systems with very small bubbles (microbubble medium) are discussed. Using photographic measurements parameters of a microbubble medium are determined (bubble mean diameter ~ 40 µm). Results of simple hydrodynamic experiments with this medium are described. Measurements of the drag coefficient of a solid ball in the microbubble medium are performed at Reynolds number from 0.1 up to 2.2 × 10⁴ and with gas void fraction less than 2.5 percent. It is shown that with an increase in gas void fraction drag coefficient slightly increases. For Reynolds number less than 10 this apparent increase in friction is due only to the change of effective parameters of the medium. Flow of the microbubble medium in horizontal tubes was investigated under the conditions where the air fraction and the Reynolds number were between 0.0 and 0.7 percent, and between 10³ and 2.5 × 10⁴ respectively. The results indicated that in laminar and transitional range for microbubble flows a pseudo-turbulent regime is realized due to the air bubbles. A large increase in the wall friction coefficient take place, which depends monotonically on void frac¬tion. However in the high turbulent range, Re > 3.5 × 10³, no noticeable change in the wall friction was found.