Stokes shape factor for lactose crystals

The alpha-lactose crystal has a tomahawk shape which needs to be accounted for when designing settling equipment. A shape factor can be used to achieve this. A variety of shape factors have been used for lactose crystals in the literature. This paper sets out to experimentally determine a shape factor for lactose. Large undamaged tomahawk shaped lactose crystals were grown in a lactose agar gel and then recovered for use in settling experiments. Typical industry produced crystals were also tested for comparison. Settling experiments enabled the calculation of a Stokes settling diameter, the diameter of a sphere with the same density and settling velocity as the tomahawk shaped lactose crystal. Using crystal mass to calculate equivalent particle volume and Stokes diameter, the Stokes shape factor for lactose gel-grown crystals was calculated to be 0.99. A Stokes height factor (B_St) was formulated which, when multiplied by the height of the lactose crystal, gives the Stokes settling diameter. The lactose B_St value was determined to be 0.595 ± 0.007 and 0.643 ± 0.008 for gel-grown and plant-grown lactose crystals, respectively.