Quick freezing plant - using evaporation of sprayed cryogenic liquid and augmentation of mass-flow by recirculation

摘要

The objects to be frozen, e.g. foodstuffs are placed on a conveyor belt within a thermally insulated chamber and after spraying with e.g. liquid nitrogen, pass through a constricted section of the chamber forming a tunnel. From the plenum at the down end of this tunnel the gases are dran off by an extractor fan and recirculated into the tunnel through longitudinal pipes so that the objects are cooled by evaporation of the liquid followed by cooling by a stream of gas mixture between that produced by initial contact evaporation and that which has been recirculated. The objects are loaded onto and unloaded from the main conveyor by narrow transverse conveyors each split into an internal section and an external section in a narrow side tunnel opening into the chamber through a port with a gas curtain cold seal formed by jets of part of the output from the above fan. By recirculation the maximum cooling effect is obtained for a given input of expensive cryogenic liquid.