Refrigeration device and method

A device for low-temperature refrigeration between −100° C. and −273° C. comprising a working circuit containing a working fluid, the device being capable of extract heat from at least one component by heat exchange with the working fluid circulating in the working circuit, the working circuit comprising in series:

• first and second centrifugal compressors arranged in series for isentropic or substantially isentropic compression of the fluid;
• first and second electric drive motors for correspondingly driving the first and second centrifugal compressors, the first electric drive motor and the first centrifugal compressor forming a first compression stage, the second electric drive motor and the second centrifugal compressor forming a second compression stage;
• a cooling exchanger for isobaric or substantially isobaric cooling of the fluid;
• a turbine coupled to the motor of the first compressor for isentropic or substantially isentropic expansion of the fluid, wherein:
• each of the centrifugal compressors has an optimum specific speed that is determined by maximizing its energy efficiency;
• the first centrifugal compressor has a defined volume flow rate (Q1) and a defined mechanical power (P1);
• the second centrifugal compressor has a defined volume flow rate (Q2) and a defined mechanical power (P2);
• the first electric drive motor has a rotary speed w1 in radians per second;
• the second electric drive motor has a rotary speed w2 in radians per second;
• a ratio Q1:Q2 is between 1.1 and 2.5;
• a ratio P1:P2 is between 1.1 and 2.5;
• and
• a ratio w1:w2 is between 0.5 and 1.5.