*3.3. Suspension Freeze Crystallization Results*

Experimental and calculated data are presented in the Supplementary Material (Tables S6–S9). Related sub-cooling degrees for both freezing times were found to vary within a range between 0.02 and 0.12.

Figures 10 and 11 show the ice yield and distribution coefficients obtained by the suspension FC experiments as function of sub-cooling degree. The ice crystal yield shows a linear dependence on sub-cooling temperature, and its value increases as the degree of sub-cooling increases. Nevertheless, the distribution coefficient is rather independent of sub-cooling degree and the values vary in a range between 0.11 and 0.36.

**Figure 10.** Ice yield and distribution coefficient of suspension freeze crystallization as a function of sub-cooling degree.

**Figure 11.** Ice yield and distribution coefficient of suspension freeze crystallization as a function of sub-cooling degree.

#### **4. Discussion**

Based on the comparison between static layer FC and suspension FC methods, the following observations are presented.

For the same freezing time and approximately the same sub-cooling temperature, ice crystal yields obtained by suspension freeze crystallization are around four-to-eight times higher than yields obtained by static layer freeze crystallization. This is as a result of the higher consumption of cooling energy and larger cooling surface area needed for the suspension crystallization experiments. In this case, the cooling area for suspension FC experiments was around nine times higher than the cooling area for static layer FC experiments.

From Figures 8–11, it is apparent that the difference between ice crystal yields obtained from the two types of aqueous solutions is greater in the case of suspension crystallization than in the case of layer crystallization. Moreover, the average value of the distribution coefficient is higher for static layer freeze crystallization, which indicates a lower ice purity than in case of suspension crystallization. These observations suggest that the mother liquor remained entrapped within the ice layer formed by the layer FC method. The distribution coefficient of static layer crystallization also shows a tendency to increase with higher undercooling and supersaturation, while for suspension crystallization the case is observed to display the opposite behavior.

For both freeze crystallization methods, the values of overall ice growth rate or freezing capacity (defined as kilogram of ice per unit of time and employed cooling surface area) are in the range of 10−4–10−<sup>3</sup> kg/m2s. Furthermore, layer FC progressed with somewhat faster freezing kinetics, as the values of overall growth rates of layer FC are noticeably higher when compared to those obtained by suspension FC. Nevertheless, for both FC methods, the overall growth rate decreased for the more concentrated solutions of 6 wt.% [DBNH][OAc], which means that [DBNH][OAc] decreased the ice-growth kinetics.
