2003 Volume 29 Issue 4 Pages 471-476
The freezing concentration efficiencies of water-NaCl and water-glucose systems were investigated over a wide range of freezing rate in cylindrical freezing columns (50 or 55 mm inner diameter). The effect of supersonic radiation on the concentration efficiency was also examined.
As a result, freezing without supersonic radiation could hardly concentrate solutes at freezing rates above 5 mm/h, while of slower freezing rates below 3 mm/h the concentration efficiency increased. Supersonic radiation remarkably improved the freezing concentration efficiency, and slower freezing rate increased this efficiency. The dissolved oxygen concentration (namely, the dissolved air concentration) of solution also influenced this efficiency. When the dissolved oxygen concentration was higher than 7 mg/L, solutes could sufficiently be concentrated by the generation of cavitation, even at 40 mm/h (fast freezing rate). On the other hand, when the dissolved oxygen concentration was below 7 mg/L, where cavitation is hardly generated, solutes could be concentrated by vibration with supersonic radiation at freezing rates below 15 mm/h.
