Abstract: A method of freezing aqueous liquids which method comprises the steps of:a) introducing the aqueous liquid into a mould;b) allowing at least the aqueous liquid in contact with said mould to freeze; andc) releasing said frozen liquid from said mould; wherein said method further comprises the step of:d) pre-cooling said mould to a temperature such that the frozen aqueous liquid can be readily released from said mould as a unitary structure.

Abstract: A method of freezing aqueous liquids which method comprises the steps of:a) introducing the aqueous liquid into a mould;b) allowing at least the aqueous liquid in contact with said mould to freeze; andc) releasing said frozen liquid from said mould; wherein said method further comprises the step of:d) pre-cooling said mould to a temperature such that the frozen aqueous liquid can be readily released from said mould as a unitary structure.

Abstract: Supplementary cooling for a mechanical refrigeration plant using ammonia as a refrigerant is provided by placing a tube in the vapor space of a buffer vessel and introducing liquid nitrogen into the tube. Although ammonia solidifies at -78.degree. C. and liquid nitrogen enters the tube at -196.degree. C. no ammonia solidifies on the tube even after extended operation. The present invention also provides a method of refrigeration which comprises introducing liquid nitrogen into the heat exchanger of a refrigeration apparatus in accordance with the invention and condensing refrigerant therewith. Preferably, the refrigerant is selected from the group consisting of ammonia and fluorocarbon R22.