Abstract Summary (Max 250 words)
Efficient removal of volatile components from viscous fluids under vacuum is a critical operation in large‑scale agitated vessels. In batch reactors, this operation proceeds through boiling, transition, and surface‑evaporation stages, with the last being governed by gas–liquid mass transfer at the free surface. This study quantifies mass transfer under surface‑evaporation conditions in large stirred tanks, where the removal of volatile components becomes extremely time‑consuming. A practical measurement approach was established by analyzing the dissolution of a volatile species from the gas phase into the liquid, monitored via transient gas‑phase pressure. The volumetric mass transfer coefficient (kLa) was obtained directly from pressure‑decay profiles. To enhance transfer, a gate‑type impeller was installed so that its blades intersected the free surface, promoting surface renewal and interfacial turbulence. Performance was evaluated using kLa and the power consumption per unit liquid volume. Scale‑up behavior was examined using vessels with diameters from 0.3 to 2.2 m. Importantly, by formulating a dimensionless correlation that explicitly accounts for the increase in gas–liquid interfacial area, we demonstrate a predictive method for scale‑up that consistently captures observed trends across the examined scales. These findings provide a practical basis for the design and scale‑up of vacuum‑operated mixing systems handling viscous fluids.
