FREEZING POINT DEPRESSION OF VARIOUS ICE SLURRIES

Ideal solutions with equal molar concentration have an equal freezing point. The properties that determine heat and mass transfer processes encountered in a secondary cooling cycle are however determined by the mass fraction of solutes. Generally for aqueous solutions, the more freezing point depressant added, the less efficient heat and mass transfer properties. Therefore substances with low molecular weight are expected to result in more efficient ice slurries. By calculating ice slurry properties, heat transfer and pressure drop, it was investigated if ice slurries of low molecular weight additives result in efficient ice slurries. For the substances considered, it was found that the molecular weight is a good indication for ice slurry efficiency, but is not decisive under all conditions. Ice slurries of three particular substances were found to have most promising properties: Sodium chloride, lithium chloride and potassium formate. Substances like antifreeze proteins depress the freezing point of a solution actively by interfering in the ice crystal formation. These substances have been suggested for freezing point depression in ice slurries too, but can only be used to control ice crystal size or supercooling effects, and not to depress the freezing point because of the extra temperature difference introduced with thermal hysteresis.