Abstract: A method and apparatus to refrigerate air in a compartment wherein liquid CO.sub.2 is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in a gas fired heater to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor through pneumatically driven fan motors into a secondary heat exchanger. Orifices in inlets to the fan motors and solenoid valves in flow lines to the fan motors keep the vapor pressurized while the heater supplies sufficient heat to prevent solidification when the CO.sub.2 vapor expands through the motors. CO.sub.2 vapor is routed from the second heat exchanger to chill surfaces in a dehumidifier to condense moisture from a stream of air before it flows to the heat exchangers.

Abstract: A method and apparatus to refrigerate air in a compartment wherein liquid CO.sub.2 is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in a gas fired heater to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor through pneumatically driven fan motors into a secondary heat exchanger. Orifices in inlets to the fan motors and solenoid valves in flow lines to the fan motors keep the vapor pressurized while the heater supplies sufficient heat to prevent solidification when the CO.sub.2 vapor expands through the motors. CO.sub.2 vapor is routed from the second heat exchanger to chill surfaces in a dehumidifier to condense moisture from a stream of air before it flows to the heat exchangers.

Abstract: A method and apparatus to refrigerate air in a compartment wherein liquid CO.sub.2 is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in a gas fired heater to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor through pneumatically driven fan motors into a secondary heat exchanger. Orifices in inlets to the fan motors and solenoid valves in flow lines to the fan motors keep the vapor pressurized while the heater supplies sufficient heat to prevent solidification when the CO.sub.2 vapor expands through the motors. CO.sub.2 vapor is routed from the second heat exchanger to chill surfaces in a dehumidifier to condense moisture from a stream of air before it flows to the heat exchangers.

Abstract: A method and apparatus to refrigerate air in a compartment wherein liquid CO.sub.2 is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in a gas fired heater to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor through pneumatically driven fan motors into a secondary heat exchanger. Orifices in inlets to the fan motors and solenoid valves in flow lines to the fan motors keep the vapor pressurized while the heater supplies sufficient heat to prevent solidification when the CO.sub.2 vapor expands through the motors. CO.sub.2 vapor is routed from the second heat exchanger to chill surfaces in a dehumidifier to condense moisture from a stream of air before it flows to the heat exchangers.

Abstract: A method and apparatus to refrigerate air in a compartment wherein liquid CO2 is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in a gas fired heater to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor through pneumatically driven fan motors into a secondary heat exchanger. Orifices in inlets to the fan motors and solenoid valves in flow lines to the fan motors keep the vapor pressurized while the heater supplies sufficient heat to prevent solidification when the CO2 vapor expands through the motors. CO2 vapor is routed from the second heat exchanger to chill surface in a dehumidifer to condense moisture from a stream of air before it flows to the heat exchangers.

Abstract: A method and apparatus to refrigerate air in a compartment wherein liquid dioxide is delivered through a first primary heat exchanger such that sufficient heat is absorbed to evaporate the liquid carbon dioxide to form pressurized vapor. The pressurized vapor is heated in an external heat exchanger to prevent solidification of the pressurized carbon dioxide when it is depressurized to provide isentropic expansion of the vapor into a secondary heat exchanger. Pneumatically driven motors are driven by the pressurized carbon dioxide vapor to move air across the heat exchangers. Orifices in inlets to the motors and solenoid valves in flow lines to the motors keep the vapor pressurized while the external heat exchanger supplies sufficient heat to prevent solidification when it expands through the motors.

Abstract: Freezing apparatus in which food is quickly frozen comprising five coils, two joined in series to form a first set and two joined in series to form a second set, the exhaust of the two sets being delivered to the fifth coil in a pre-cooling chamber where food is introduced by a conveyor to the freeze tunnel. Each of the five coils is positioned in a separate chamber in the tunnel and thermal couple sensors deliver signals which are compared to a set-point signal in proportional controllers to control the flow of liquid nitrogen to each set of coils. Flow from the first and second sets of coils is vented to atmosphere and heater apparatus adjacent the fifth coil is energized when the temperature of nitrogen vapor discharged from the fifth coil is less than a predetermined value which results when formation of ice on the surface of the fifth coil reduces exchange of the heat between air circulated over the fifth coil and nitrogen vapor flowing therethrough.