Question 1

What fill ratio should I use for a stirred tank reactor?

Accepted Answer

For typical stirred tank reactors, a fill ratio of 0.75-0.85 is standard. This provides adequate freeboard for liquid surge, vortex formation from agitation, and vapor disengagement. For highly foaming or gas-sparged systems, reduce to 0.50-0.65. Unstirred storage tanks can use up to 0.90-0.95.

Question 2

Why does the volume-to-surface ratio matter in reactor design?

Accepted Answer

The volume-to-surface ratio increases with vessel size, meaning larger reactors have proportionally less surface area for heat transfer. This is critical for exothermic reactions where heat must be removed to prevent thermal runaway. It explains why reactions easily controlled in a lab flask may require internal cooling coils or external heat exchangers at production scale.