Enthalpy control for CO2 refrigeration system

A method of controlling the heat transfer rate through a wall of a tube in a compartment comprising the steps of:

• delivering liquid carbon dioxide into the tube;
• moving fluid in the compartment in heat exchange relation with the tube such that heat is absorbed by the carbon dioxide to form pressurized carbon dioxide vapor in the tube;
• heating the pressurized carbon dioxide vapor;
• delivering the heated carbon dioxide vapor to drive a motor driven fan to move fluid in the compartment in heat exchange relation with the tube;
• and controlling the flow of heated vapor to the motor to prevent solidification of the carbon dioxide as it depressurizes upon reaching the pneumatic motor chambers.

A method of controlling temperature in a compartment comprising the steps of:

• circulating liquid carbon dioxide through a primary coil such that heat is absorbed by the carbon dioxide;
• changing the enthalpy of carbon dioxide exhausted from the primary coil to assure that it is in a vapor phase;
• delivering the carbon dioxide vapor through a pneumatic motor arranged to drive a fan;
• and circulating carbon dioxide from the pneumatic motor through a secondary coil, the primary and secondary coils being positioned such that the fan driven by the pneumatic motor moves air in heat exchange relation with the coils.

Temperature control apparatus comprising, a coil;

• means to deliver fluid through said coil;
• means to move air across the coil;
• first sensor means to sense temperature of carbon dioxide exhausted from the coil;
• second sensor means to sense the temperature of the surface of the coil;
• means to generate a signal when the temperature of carbon dioxide exhausted from the coil is less than a predetermined temperature;
• means energized by said signal to heat surfaces of the coil to melt ice thereon;
• and means energized by said second sensor to terminate heating of the surfaces of the coil.

Apparatus to control temperature in a cargo compartment of a trailer comprising:

• a source of liquefied carbon dioxide carried by the trailer;
• evaporator means positioned in heat exchange relation with air in the compartment;
• first conduit means connecting said evaporator means and the source of liquid carbon dioxide;
• heat exchanger means;
• second conduit means connecting the heat exchanger means with said evaporator means;
• a pneumatically operated motor;
• fan means driven by said motor arranged to cause air in the compartment to circulate over surfaces of the evaporator means, said heat exchanger means being adapted to deliver carbon dioxide from said evaporator means to said motor in a temperature range to prevent solidification of carbon dioxide as it becomes depressurized in said motor.