Abstract: A method and apparatus of refrigerating a heat load in which heat is indirectly exchanged between the heat load and a cryogenic refrigerant so that the heat load cools. Further heat is then indirectly exchanged between the heat load and the mechanical refrigerant. The mechanical refrigerant is subjected to refrigeration cycle in which the mechanical refrigerant is compressed, cooled, condensed, expanded and evaporated. Other heat is indirectly exchanged between the cryogenic refrigerant and the mechanical refrigerant. The cryogenic refrigerant is subjected to its heat exchange with the mechanical refrigerant after having exchanged heat with the heat load. The mechanical refrigerant is subjected to the indirect heat exchange with the cryogenic refrigerant between condensation and expansion of the mechanical refrigerant within the refrigeration cycle.

Abstract: A gas injection apparatus for injecting a gas into a liquid comprising a baffle plate, a re-circulation chamber, and a discharge nozzle. The discharge nozzle is oriented normally to the baffle plate so that a liquid stream composed of the liquid is directed against the baffle plate and produces an oppositely directed flow towards the outer peripheral edge of the baffle plate. The oppositely directed flow has a sheet-like turbulent flow regime located adjacent to the plate and a circulating flow regime located above the turbulent flow regime and bounded by a re-circulation chamber. The gas is mixed into the liquid so that smaller bubbles are entrained in the turbulent flow regime and are discharged with the liquid flowing in the turbulent flow regime from the outer peripheral edge of the baffle plate. Larger bubbles flow into the circulating flow regime to break up into smaller bubbles which are entrained in the turbulent flow regime swept out of the apparatus.