Cooling and/or liquefying system and method

A method for cooling and/or liquefying a flow of fluid, comprising the steps of:

• providing a low-temperature refrigeration device for refrigeration at a temperature of between minus 100 degrees centigrade and minus 273 degrees centigrade, the refrigeration device comprising:
• a working circuit forming a loop and containing a working fluid;
• a cooling exchanger intended to extract heat at at least one member by heat exchange with the working fluid circulating in the working circuit, the working circuit forming a cycle comprising, in series:
• a mechanism for compressing the working fluid, a mechanism for cooling the working fluid, a mechanism for expanding the working fluid, and a mechanism for heating the working fluid, wherein the mechanism for cooling the working fluid and the heating mechanism comprise a common heat exchanger through which the working fluid passes in countercurrent in two separate passage portions of the circuit depending on whether it is cooled or heated, the device being configured to ensure an equal mass flow rate in said two passage portions in the common heat exchanger;
• a bypass duct bypassing one of the two passage portions, said bypass duct comprising a bypass valve which, when it is open, modifies the mass flow rate in one of the two passage portions;
• and
• a circulation duct for said flow of fluid to be cooled in heat exchange with the cooling exchanger of the refrigeration device, wherein the refrigeration device is configured to cool the cooling exchanger in order to cool the fluid to be cooled that is circulating in the duct, with the bypass valve closed, and when more than a given quantity of frost is present, to heat the cooling exchanger with the bypass valve open in order to evacuate impurities that have solidified in said cooling exchanger;
• cooling the cooling exchanger in order to cool the fluid circulating in the duct via the operation of the refrigeration device without opening the bypass valve;
• and
• defrosting and evacuating impurities that have solidified in said cooling exchanger during the cooling step by heating the cooling exchanger via operation of the refrigeration device with the bypass valve in an open position.