Performance tests of industrial prototype subcooling helium heat exchangers for the Large Hadron Collider

The superconducting magnets of the Large Hadron Collider (LHC) will be cooled at 1.9 K by distributed cooling loops working with saturated two-phase helium, and supplied with cold supercritical helium. In order to minimize the vapor fraction produced in the final expansion, counter-flow heat exchangers will be needed. Such heat exchangers, of compact design, featuring low-pressure drop and handling very low-pressure vapor, are non-standard products, may be of various designs, and built according to various technologies. In order to qualify potential suppliers for the 250-unit series production, CERN has procured 5 g/s prototype subcooling helium heat exchangers from four industrial companies, based on different construction principles, and tested them in collaboration with CEA Grenoble where a dedicated test station has been built. After reviewing the common functional specification, as well as the main design features of the prototypes and test station, comparative performance results are presented, and conclusions drawn as concerns future series production for the LHC