Evaporative cooling system with natural refrigerant at -50 ℃ and 100 m underground

Abstract

The cooling systems of the future tracking detectors of both ATLAS and CMS experiments at the Large Hadron Collider (LHC) at CERN will be entirely based on CO2 refrigeration technology. The system is a booster refrigeration system, composed of a two stage primary part with standard R744 equipment and a low temperature secondary loop i.e. pumped oil free CO2 is cooling the tracking detectors and condensed in the low stage evaporator. The primary refrigeration sub-system installed on surface provides cold R744 (close to triple point temperature of -53°C) to the CO2 pumped loops installed 100 m underground and rejects the heat exchanged. The process must be reliable and remain stable regardless the amount of heat exchanged, which is expected to vary throughout the lifetime of the detectors. This paper reviews alternative concepts in the design of evaporative cooling systems using natural refrigerants capable of overcoming the technical challenges.