Micro and nano bubbles
أ.د. أيمن بكرى
د. شريف حسان
Venturi-type bubble generator is one of the promising methods for producing fine bubbles, which motivates researchers to carry out extensive experimental and theoretical studies. This article reviewed published papers concerning the performance of Venturi-type bubble generators as well as the bubble transportation and breakup mechanisms in Venturi channels. Several consensuses are summarized as follows:
1) The probability size distribution of the generated bubbles and their average diameter are the main parameters reflecting the performance of the Venturi-type bubble generator, which depends primarily upon the flow conditions (liquid flow rates) and the geometry configuration. In particular, the liquid flow rate and divergent angle are the most important factors, an appropriate combination of flow conditions and geometry configuration will generate well-controlled bubble size for practical applications.
2) Bubbles passing through a Venturi channel experience a more complex transportation process than that in a conventional channel.
In the divergent section, the rapid bubble deceleration and the dramatic bubble expansion and shrinkage have significant effects on the final bubble breakup.
3) In the divergent section, the pressure recovery and the recirculation flow lead to the bubble breakup to a great extent. However, the mechanisms dominating bubble breakup in Venturi channels are not clarified yet due to the complex flow structure in the divergent section of the Venturi channel. Further work is required on the bubble transportation process and elucidates the bubble breakup mechanisms in Venturi-type bubble generators