Gas balance control in flash freezing systems

Claim 1

In an apparatus for flash freezing of articles comprising a hollow housing structure defining a substantially thermally isolated process chamber, means including a conveyor operating in said chamber for transporting articles in succession along a process path leading into, through and out of said chamber, means for contacting a cryogenic liquid with each article at a certain region along said process path to flash said liquid at least partially to gas for freshly generating refrigerant gas within said chamber, means defining a plenum chamber adjacent to said process path upstream of cryogenic liquid contact region, pumping means having a suction inlet communicating with a first portion of said process path upstream of said cryogenic liquid contact region for receiving said freshly generated refrigerant gas, said pumping means having a discharge outlet upstream of said first portion and communicating with a second portion of said process path through said plenum chamber to develop a high-velocity stream traveling along a recirculation flow path through said chamber from said discharge outlet, through said plenum chamber to said suction inlet, the improvement which comprises passage means in said plenum chamber between said first and second portions of said process path and communicating with said suction inlet, a control element adjacent said passage means, and means for adjusting the position of said control element relative to said passage means, whereby when said control element completely closes said passage means, the circulating gas travels along said entire recirculation path, and when said control element is spaced from said passage means at least some of said circulating gas travels along a shortened path through said passage means, said suction inlet and said discharge outlet.