Differential air flow system for promoting bottom-up freezing of blood plasma in compressed bags

A method for freezing an individual bag or a plurality of bags containing biological fluid, favoring bottom-up ice-growth, comprising the following steps:

• providing a controlled temperature chamber;
• placing an air flow system into the controlled temperature chamber;
• placing a bag or a case containing the bag on a support;
• compressing the bag or case against the support;
• driving air inside the controlled temperature chamber to obtain a differential air flow for freezing the bag, wherein the differential air flow is obtained by blowing air on the bottom of the bag or case such that a velocity of the air on the bottom of the bag or case is higher than a velocity of the air on the top of the bag or case, allowing bottom-up ice-growth;
• wherein a heat transfer coefficient on the top of the bag is less than 5 W/(m2° C.) and a heat transfer coefficient on the bottom of the bag is higher than 20 W/(m2° C.), and wherein the air flow has a velocity in a range from 1 m/s to 10 m/s.