Food freezer

A food freezer comprising:

• an enclosure;
• conveyor means for supporting food products within said enclosure and carrying said food products therethrough;
• mechanical refrigeration means for freezing said food products as they are carried through said enclosure, said mechanical refrigeration means comprising:
• a first heat transfer fluid;
• a first closed refrigeration circuit containing said heat transfer fluid, comprising a first evaporator disposed within said enclosure, a first condenser disposed outside of said enclosure, means to effect flow of said first heat transfer fluid through said first evaporator and said first condenser, and a compressor to compress fluid entering said first condenser;
• means to effect heat transfer from said food products to said first heat transfer fluid in said first evaporator so as to evaporate fluid therein without direct contact between said food products and said first heat transfer fluid, comprising a gas within said enclosure and blower/fan means for effecting gas flow over said first evaporator and said food products within said enclosure;
• a second closed refrigeration circuit comprising a second heat transfer fluid, a second evaporator disposed in thermal communications with said first condenser, a second condenser, and means to convey a second heat transfer fluid through said second refrigeration circuit so as to effect transfer of heat from said first heat transfer fluid to said second heat transfer fluid;
• and
• means tor emove heat from said second condenser;
• wherein said first heat transfer fluid consists essentially of CO.sub.2 and is maintained at pressures of between 60.4 psig and 120 psig while in said first evaporator.