Analysis of helium cryogenic cycle for the cooling of cold neutron source

A reverse Brayton cycle with advance refrigeration of liquid nitrogen and four cycles with advance expander refrigeration were designed to provide 17.5 K cold source for H₂ system of cold neutron source (CNS) project. Based on thermodynamic and exergetic computation for the different cycle modes, thermodynamic parameters, exergy loss, exergy efficiency and cycle capability were obtained and analysed respectively. The results show that the capabilities and exergy efficiencies of the cycles with liquid nitrogen and prepositive parallel connected expander are greater than those of others; for the cycle modes with advance expander refrigeration, parallel connection mode is superior to series connection mode, and prepositive mode is superior to postpositive mode. The main exergy loss of cycle occurs in the compressor, expander and exchanger, so there are three ways to improve exergy efficiency of cycle: (1) reducing the mass rate of helium by improving cycle; (2) improving isoenthopic efficiency of the expander and isothermal efficiency of the compressor; (3) improving distribution of temperature, pressure, temperature difference and refrigerant in the exchanger. These results provide numerical basis of the design of helium cryogenic cooling system of CNS for China advanced research reactor (CARR).