Patent 4227381 Issued on October 14, 1980. Estimated Expiration Date: March 13, 1999. Estimated Expiration Date is calculated based on simple USPTO term provisions. It does not account for terminal disclaimers, term adjustments, failure to pay maintenance fees, or other factors which might affect the term of a patent.
A batch freezing apparatus has a fan or blower to continuously circulate air through the freezing chamber and back again through a recycle conduit. A cold gas such as from a liquid nitrogen supply tank is added to the recirculating air to lower the temperature in the system in a controlled manner to provide rapid freezing. The freezing chamber is capable of rotation so the material being frozen in cylinderical containers can be rotated against and freeze upon the inner surface of the container during the freezing process. The apparatus is especially suitable for freezing bull semen.
Linde BF-4 Biological Freezing System, Union Carbide Cryogenic Products