DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO_2 COOLING LINES

摘要

Evaporative CO_2 cooling is under design for several new silicon particle detectors at CERN. In general therncooling lines inside the detectors are long (up to 25 m) and have small diameters (1 to 3 mm). Heat loadsrntypical vary from 50 to 350 watt per cooling line. The individual cooling lines are manifolded and operate inrnparallel with each other.rnThe long and small diameter cooling lines cause relative high pressure drops. These pressure drops causerntemperature gradients which must be minimized to meet the strict temperature requirements of siliconrndetectors. The parallel operations of the several cooling lines which are operating with different heat loadsrnrequire a careful design of the flow distribution to ensure a good heat transfer in all the channels.rnThis paper describes the ongoing developments at CERN concerning the understanding of a proper designrnfor long evaporative channels. A simulation program called CoBra is built to investigate the theoreticalrnaspects. Test results on long evaporators under development for the Atlas-IBL and CMS-pixel experiments atrnCERN are presented and compared with the simulation model.