Temperature effects on oxygen transfer: How does increasing temperature typically influence oxygen transfer in bioreactors, considering both KLa and the saturation concentration C* of oxygen?

Introduction / Context:Oxygen transfer involves both transport kinetics (KLa) and thermodynamics (saturation concentration C*). Temperature influences liquid properties, gas solubility, and microbial physiology. Engineers must balance faster mass transfer kinetics with reduced gas solubility at elevated temperatures.

Given Data / Assumptions:

• Viscosity decreases with temperature, boosting turbulence and diffusion.
• Gas solubility in liquids generally decreases as temperature rises.
• Other variables (salt, pressure, antifoams) are held constant for this comparison.

Concept / Approach:KLa tends to increase with temperature because reduced viscosity enhances mixing and increases the liquid-side mass transfer coefficient KL; diffusivity also rises, shrinking effective film thickness. Conversely, oxygen solubility follows Henry-type behavior where the Henry constant increases with temperature, lowering C*. Thus higher temperature often yields higher KLa but lower C*, creating competing effects on OTR = KLa * (C* - C).

Step-by-Step Solution:

Verification / Alternative check:Empirical kLa correlations include temperature via viscosity and diffusivity terms; gas solubility tables show monotonic decreases in oxygen solubility with rising temperature at constant pressure and salinity.

Why Other Options Are Wrong:

• Lowering KLa but increasing C*: opposite to typical trends.
• Increasing both or lowering both: not supported by standard physical behavior.
• No effect: temperature clearly affects both properties.

Common Pitfalls:Assuming an OTR increase is guaranteed with higher temperature; if C* drop dominates, net OTR can decrease despite higher KLa. Balance is system-specific.

Final Answer:Increasing KLa but lowering C*o