Controlled nucleation during freezing step of freeze drying cycle using pressure differential ice crystals distribution from condensed frost
A method of controlling and enhancing the nucleation of product in a freeze dryer, wherein the product is maintained at a predetermined temperature and pressure in a chamber of the freeze dryer, and a predetermined volume of condensed frost is created on an inner surface of a condenser chamber separate from the product chamber and connected thereto by a vapor port. The condenser chamber has a predetermined pressure that is greater than that of the product chamber. The opening of the vapor port into the product chamber creates gas turbulence that breaks down the condensed frost into ice crystals that rapidly enter the product chamber for even distribution therein to create uniform and rapid nucleation of the product in different areas of the product chamber.
1. A method of controlling and enhancing the nucleation of product in a freeze dryer, comprising:
maintaining the product at a predetermined temperature and pressure in a chamber of the freeze dryer;
creating a predetermined volume of condensed frost on an inner surface of a condenser chamber separate from the product chamber and connected thereto by a vapor port, the condenser chamber having a predetermined pressure that is greater than that of the product chamber; and
opening the vapor port into the product chamber to create gas turbulence that breaks down the condensed frost into ice crystals that rapidly enter the product chamber for even distribution therein to create uniform and rapid nucleation of the product in different areas of the product chamber.
2. The method of claim 1 wherein the vapor port has an isolation valve between the product chamber and the condenser chamber to open or close vapor flow therebetween.
3. The method of claim 1 wherein a vacuum pump is connected to the condenser chamber for selectively reducing the pressure within the product chamber and the condenser chamber when the isolation valve is opened.
4. The method of claim 1 wherein the pressure within the product chamber is about 50 Torr and the pressure within the condenser chamber is about atmospheric when the vapor port is opened into the product chamber.
5. The method of claim 4 wherein the temperature of the product is about −5.0° C. and the temperature of the condenser chamber is less than 0° C. when the vapor port is opened into the product chamber.
6. The method of claim 1 wherein a predetermined moisturized back fill gas is introduced into the condenser chamber to produce the condensed frost.
7. The method of claim 6 wherein the condenser chamber has a release valve which is opened to enable the moisturized back fill gas to be introduced into the condenser chamber to produce the condensed frost.
8. The method of claim 6 wherein the back fill gas is filtered ambient atmospheric air and has a moisture content of about 50-80% by volume.
9. The method of claim 6 wherein the back fill gas is nitrogen or argon with moisture added thereto.
10. The method of claim 1 wherein the inner surface of the condenser chamber is defined by a plurality of inner walls.
11. The method of claim 10 wherein the inner walls are in a coil configuration to maximize the size of the inner surface.