The spiral jet mill cut size equation

• An equation for spiral jet mill cut size is derived and verified experimentally.
• Solids feed rate and gas mass flow rate are variables within the equation.
• Constants are defined for the material being micronised, mill and carrier gas.
• The equation behaviour matches previously reported data in academic literature.
• A scale up methodology and improvements in energy efficiency are proposed.

Micronisation, or fine grinding, is a key unit operation for many industries, with the spiral jet mill being popular as it is robust and reliable. Within this paper an analytical derivation for spiral jet mill cut size as a function of micronisation settings, gas thermodynamic properties and empirically derived constants for the material and mill is presented for the first time. This has been corroborated by experimental evidence and previously reported data in the academic literature and provides an insight into the interaction between aerodynamic particle classification and fine grinding. A scale up methodology is proposed for a high value material by using a small scale mill to determine the material specific constants of the high value material and a cheaper surrogate material to determine mill specific constants at increased scale.

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