Extending the operating limits in a loop heat pipe by employing a bypass line as an emergency safety device for thermal management of electronics

초록

Critical thermal load with dryout can limit the operation of a loop heat pipe (LHP). To address this issue, this study considers an auxiliary bypass line to enhance the critical thermal load of an LHP with a cylindrical evaporator. An auxiliary bypass line is installed between the liquid core and vapor space of the LHP evaporator, with two control valves attached at its beginning and end, enabling switching between normal operating mode (NOM) and bypass operating mode (BOM). The LHP features a cylindrical evaporator and condenser with a double-pipe heat exchanger, and all components-including the tubing system- are fabricated from stainless steel. A porous nickel wick structure with rectangular grooves facilitates vapor passages. The results indicate that the critical thermal load increases by more than 21 % compared with that of the NOM within the applicable thermal load range when BOM is employed. The bypass line ensures continued operation in emergencies where operation is impossible under NOM, making it a viable safety mechanism. Under favorable tilt angles (>= 30 degrees), BOM reduces the evaporator wall temperature by up to 12 %, enhancing the steady-state heat transfer performance of the LHP. However, under adverse angles, including horizontal orientation, BOM increases wall temperature by up to 27 %, deteriorating the steady-state heat transfer performance of the LHP.

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