Abstract: A refrigeration system for cooling and drying hot moist compressed air comprises sub-cooling the liquid refrigerant from the condenser to eliminate all flash gas and render the entire evaporator effective for refrigeration purposes. The heat exchangers for the evaporator and for sub-cooling the liquid refrigerant are of a novel construction comprising a one-piece finned copper inner cylinder with the routed fin enclosed inside of an annular copper shell in which a 0.020-inch clearance exists between the annular copper shell and the fins to allow passage of a stream of air which causes the laminar flow around the routed fin construction to be agitated by eddy diffusion. The use of the novel heat exchanger in the refrigeration system along with the step of sub-cooling the liquid refrigerant produces a gain in refrigeration effect of about 23% to 30% without an increase requirement for either power or energy.