Abstract Summary (Max 250 words)
Power input for two phase gas-liquid processes in stirred tanks is usually predicted using empirical correlations with no well-adopted mechanistic models. Accurate prediction of gassed power is critical to ensuring correct power input for industrial processes such as gas-liquid mass transfer. A new mechanistic model is proposed for the ratio of gassed to ungassed power (PG/PU) based on the dimensionless numbers Ae (Aeration Number) and Fr (Froude Number). The model uses a local force balance to establish maximum gas cavity size, a local mass balance to determine equilibrium gas cavity size at a given gas flow rate and proposes a direct theoretical relationship between the gas cavity size and PG/PU. To evaluate the predictive accuracy of the model, power measurements were performed in an air/water system for Rushton, Smith, and R135 Gasfoil impellers in cylindrical vessels across three scales (24”, 34”, 48”). The model was then fitted to the data with impeller specific coefficients, covering Aeration numbers from 0 to 0.7 and Froude numbers from 0.1 to 3.0. The model correctly captures key observed behaviours across all three scales and is shown to be more accurate than available empirical models. Detailed results and correlation for the Rushton impeller are presented. The mechanistic basis improves robustness and furthers understanding of the mechanisms behind gassed power input for different impellers. By improving prediction of gassed power, the model allows for better and more robust industrial designs, ensuring the desired power input is delivered to processes that rely on it.
