| 摘要 |
The present invention provides a cryogenic freezer (10) and method using a freezing chamber (12) within which articles are cooled under the direct application of a cryogen, causing the cryogen to vaporise into a cryogenic vapor. The freezing chamber (12) has inlet (14) and outlet (16) plenums through which articles to be frozen are passed into and from the freezing chamber (12), respectively. The liquid cryogen is introduced from a make-up tank (20) into the freezing chamber (12) and into direct contact with the articles to be frozen. Conduits connect the inlet and outlet plenums (14,16) to a blower (34) that draws air from outside the freezing chamber (12) and the cryogenic vapor from inside the freezing chamber (12) to prevent air from entering the freezing chamber. The cryogenic vapor is drawn from an outlet (44) in the freezing chamber (12) to a recovery unit (42) to be compressed, purified and liquefied. The resulting liquid cryogen is then fed back to the make-up tank (20). In order to prevent air from being processed by the recovery unit (42) along with the cryogenic vapor, the cryogenic vapor is drawn from the freezing chamber (12) at a level thereof that is as low as possible and such that the mass flow rate of the cryogenic vapor drawn from the freezing chamber (12) is equal to that of the liquid cryogen upon its entry into the freezing chamber (12). <IMAGE> |
