Freeze concentration with supersonic radiation under constant freezing rate - Effect of kind and concentration of solutes

In freezing water which contains solutes, the solutes are removed from the frozen phase and concentrated in the unfrozen liquid phase, and strong agit ation of the freezing interface is very effective. We used a supersonic rad iation method instead of propeller agitation. The experiments of freeze concentration with/without supersonic radiation w ere carried out under a constant freezing rate (40 mm/h), using two concent rations (0.5, 5.0 kg/m(3)) of three aqueous solutions (sodium chloride, L-p henyl alanine and saccharose). Under this freezing rate, freezing without s upersonic radiation could not concentrate solutes, but freezing with supers onic radiation could greatly do, and decreased the average distribution fac tor under 0.4. The distribution factors at a late stage of freezing are muc h smaller than those at an early stage, because the turbulence of solution by supersonic cavitation and the agitating intensity per unit unfrozen volu me increases. Therefore the solutes are not easily caught on the freezing i nterface as the freezing interface approaches the supersonic radiation horn . The low mass concentration solution is concentrated more than high concen tration solution. For a constant mass concentration solution, the solutes o f large molecular weight are more easily separated and concentrated than th ose of small molecular weight.