Question

In a bioreactor, what is the term used to describe the resistance to mass transfer across the gas-liquid interface?

• A. Interfacial tension
• B. Gas holdup
• C. Mass transfer coefficient
• D. Film thickness

Hint:

• Two-Film Theory Assumes stagnant films on gas and liquid sides of the interface, where mass transfer occurs by molecular diffusion.
• Resistance to mass transfer is primarily within these films.
• Factors affecting film thickness (and thus \(k_L\)): Agitation, turbulence, fluid properties.
• Overall Volumetric Mass Transfer Coefficient (\(k_L a\)): Combines liquid-side coefficient (\(k_L\)) and interfacial area per unit volume (\(a\)). Higher \(k_L a\) means better mass transfer (lower resistance).

Answer 1

The Correct Option is D

In the context of a bioreactor, the term used to describe the resistance to mass transfer across the gas-liquid interface is film thickness. This refers to the thin layer of liquid that exists at the interface between the gas phase and the liquid phase. The mass transfer process involves the movement of a substance from one phase to another, and resistance during this process is significantly influenced by the characteristics of this film. Typically, several factors contribute to this resistance, such as:

• Physical Properties: The viscosity and diffusivity of the liquid can affect how easily molecules can move through the film layer.
• Film Stability: A stable and consistent film maintains a uniform resistance, whereas an unstable film can cause fluctuating resistance levels.
• Hydrodynamics: The flow conditions within the bioreactor, including agitation and flow patterns, can impact the film thickness and consequently the resistance.

Understanding film thickness is crucial for optimizing the mass transfer efficiency in a bioreactor, as it directly impacts the rate at which gases are transferred into the liquid medium.