Novel Bubble-Induced Flow Designs

Novel bubble-induced flow designs apply a plethora of mechanisms that help differentiate each specific design from other novel and standard devices. Some changes are structural and include use of different materials and internals. Others include the use of novel methods to excite the bubble interface and induce gas-liquid mass transfer. Novel methods exclude devices that are created to study specific events relating to standard devices. For example, the study by Sotiriadis et al. (2005) using a specially designed bubble column where the phases move downward to specifically study bubble behavior, bubble size, and gas-liquid mass transfer in the downcomer of airhft reactors would fall in the excluded devices. 

An Introduction to Bioreactor Hydrodynamics and Gas-Liquid Mass Transfer, First Edition. Enes Kadic and Theodore J. Heindel. 

The ejector reactor uses a similar injection device as the submerged-jet reactor, but the created jet is injected into an airlift-like vessel. The gas-liquid mixture is allowed to go through a riser and into a separator. Since the gas phase separates, a density difference is created and liquid recirculates into the injection zone. These reactors are capable of operating with liquid velocities of at least 20 m/s. With this kind of turbulence, the ejector reactor outperforms stirred-tank reactors at equivalent operating conditions (Charpentier, 1981). 

Venturi-based reactors work similarly to submerged-jet and ejector reactors, but the big difference is that the liquid is injected into a high velocity gas-phase field, whereas the ejector reactors inject gas into a high velocity liquid-phase field. Hence, the venturi-based reactors create small liquid droplets similar to an atomizer. Venturi-based reactors are used as scrubbers or with quantities of gas phase present in the reactor volume. In contrast, ejector reactors create small bubbles that are used in liquid-phase dominated reactor volumes (Charpentier, 1981). 

Jet injectors may also be combined with monolith reactors. Monoliths are usually tube reactors with channeled flow. The reaction occurs at the gas-liquid interface as well as on the channel wall, which are usually catalytic or coated with catalytic material. Monoliths can be made into vertical (similar to bubble column) or horizontal tubes, airlift devices (whereby the riser would a monolith), or even into a mechanically stirred device. Usually, however, monoliths are designed like bubble columns or airhft reactors (Broekhuis et al., 2001). 

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Novel mechanical or bubble-induced flow designs are not trendsetters nor do they solve many of the and gas-liquid mass transfer problems. Miniaturized reactors, however, could decrease process design and implementation signiflcantly. The numbering-up method for these reactors reduces the time and amount of work necessary for scale-up the process is determined for one experimental unit and then the unit is copied multiple times. The rest of the work is spent on the industrial and economic problems rather than hydrodynamic and gas-liquid mass transfer issues commonly found in scale-up issues for other bioreactors. 

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