Abstract
The capture of solute into freezing part is difficult due to vigorous agitation of the freezing interface during the freezing of solution. We have been studying the applicability of supersonic radiation to the agitating method, and found that the freeze concentration efficiency of solutes is improved greatly by this radiation. In this paper, the effect of the freezing rate on the freeze concentration characteristics is examined. We modified the experimental apparatus where the distance between a supersonic transducer and freezing interface can keep constant (40 mm). Freezing columns (55 mm inner diameter and 320 mm height) made of stainless steel were descended in a refrigerator (-16.5°C) at some prescribed rates (20, 40, 80, 120 mm/h) with/without supersonic radiation (54 W). This means freezing rate can be maintained almost prescribed constant values. From these experiments, it was found that the solute could hardly be concentrated in unfrozen part and the distribution factors of solutes were about 1.0 for all freezing rates without supersonic radiation. On the other hand, with supersonic radiation the distribution factors were much smaller than 1.0 at slower freezing rate (20, 40 mm/h) and were small up to 0.5 at faster freezing rate (80, 120 mm/h).
