This work aims to investigate the capability of perfluorocarbon (PFC) emulsions in enhancing oxygen transfer in bioreactors. Based on the penetration theory, a model has been derived for evaluating the potential oxygen transfer enhancement effects of PFC emulsions with very fine PFC particles. Defined as the ratio between the maximum oxygen transfer rates in systems with and without the emulsions, the enhancement factor achievable with dilute PFC emulsions can be estimated as the square root of the product of ratios of oxygen permeability and solubility in media with and without the emulsions. The effect of PFC emulsions on oxygen transfer in low‐shear cultivation systems was further studied experimentally with direct measurements of volumetric oxygen transfer coefficients, 𝔨Lα, in bioreactors and with microbial fermentations conducted under low‐shear conditions. It was found that significantly higher cell populations could be maintained at an aerobic state by using systems supplemented with the investigated emulsions. The experimentally determined values of oxygen transfer enhancement factor compare well with the theoretical values for emulsions with up to 15% (v/v) PFC. The feasibility of enhancing oxygen transfer in bioreactors by introduction of adequate amounts of PFC emulsions was clearly demonstrated.

: With plunging breaking waves, air bubble entrainment is caused by the top of the wave forming a plunging jet and entraining air when it impacts the water in front of the wave. The potential for air bubble entrainment is related directly to the plunging jet impact characteristics. New experiments were performed in a two-dimensional wave flume.The breaking process was investigated with a high-speed video camera. The results provide new information on the breaking point characteristics, the jet impact conditions and the energy dissipation process. The entrainment of air bubbles is detailed. And the rate of energy dissipation by plunging breakers is estimated.

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