Q1: Crystal size in a continuous crystalliser depends upon the

ANS:D - all (a), (b) and (c).

Rate of Heat Transfer: Heat transfer affects the temperature distribution within the crystallizer. Temperature influences solubility; generally, as temperature decreases, solubility decreases, causing the solution to become supersaturated. However, the rate of heat transfer primarily affects the rate of supersaturation rather than directly determining crystal size. Faster heat transfer rates might lead to faster cooling of the solution, potentially creating higher supersaturation levels, which in turn could influence crystal size.

1. Degree of Turbulence: Turbulence within the crystallizer affects mixing and mass transfer rates. Higher turbulence can enhance mass transfer, promoting the transport of solute to nucleation sites. This can impact crystal size indirectly by influencing the rate of supersaturation. More turbulence might lead to more effective mixing, faster dissipation of supersaturation, and consequently, larger crystal sizes due to lower supersaturation levels.
2. Degree of Supersaturation: Supersaturation is the driving force for crystallization. It represents the excess concentration of solute in a solution beyond its equilibrium solubility. Higher degrees of supersaturation generally result in the formation of smaller crystals. When the solution is highly supersaturated, nucleation occurs rapidly, leading to the formation of numerous small crystals. Conversely, lower degrees of supersaturation favor the growth of larger crystals.

While all these factors can influence crystal size indirectly by affecting the rate of supersaturation or crystal growth kinetics, the primary determinant of crystal size in a continuous crystallizer is the degree of supersaturation. Therefore, while factors like heat transfer and turbulence play important roles in the crystallization process, they do not directly determine crystal size in the same way that the degree of supersaturation does.