Experimental Analysis of the Condenser Design in a Thermosiphon System for Cooling of Telecommunication Electronics

Abstract

Passive two-phase cooling systems are an efficient and viable alternative to conventional air-cooling schemes for thermal management of electronics due to their capability of dissipating higher power densities with lower power consumption and noise levels. This article aims to assess the performance of a novel two-phase air-cooled thermosyphon for cooling shelf-level telecommunications equipment that is designed with 18 line cards. In particular, the main objective is to investigate the effect of the condenser technology on the thermal-hydraulic performance of the cooling system. The thermosyphon consists of a multimicrochannel evaporator with 18 individual microchannel zones (one per card) connected to an air-cooled condenser via riser and downcomer tubes. The total height of the loop, from midevaporator to midcondenser, is approximately 50 cm. Two different condenser designs have been tested: a single-pass louvered-fin flat-tube condenser, and a multipass wavy-fin, circular-tube condenser. An extensive experimental campaign is performed to evaluate the performance of these two air-cooled condensers in a front-to-back airflow configuration. The experiments are carried out with R134a as the working fluid, varying filling ratios from 45% to 60%, and heat loads from 102 to 1023 W under uniform and nonuniform conditions. The influence of the air-side fan configuration is also investigated by varying the fans speed from 10 548 to 15 480 min−1 and by increasing the fan-tray height from 65 to 103 mm. The results demonstrate that the single-pass louvered-fin flat-tube condenser provides lower liquid-side frictional pressure drops and consequently higher refrigerant mass flow rate in the loop. This leads to a higher critical heat flux value, which is ideal for increasing power densities and limiting dry-out occurrence. On the other hand, the multiple-pass wavy-fin, condenser offers lower thermal resistances over a larger range of dissipated heat loads. This is mainly attributed to its lower air-side pressure drop.