Multi-Evaporator Closed Loop Thermosyphon

A novel type of multi-evaporator Closed-Loop Two-Phase Thermosyphon has been designed and tested at different inclinations and heat input levels. The device consists in an aluminum tube (I.D./O.D. 3/5 mm), bended into a planar serpentine with five U-turns in the heated zone, with a 50 mm transparent section for the purpose of visualization. The tube is closed in a loop, evacuated and partially filled with FC-72, 50% vol. Each turn is equipped with an electric wiring heater and the peculiar location of the heating sections causes the fluid to circulate regularly in a preferential direction. The condenser zone is embedded into a heat-sink and cooled by fans blowing air at 20 °C. Sixteen T-type thermocouples are located on the external tube wall in the evaporator and condenser zones, while the fluid pressure is measured in the condenser zone adjacent to the transparent tube. The flow pattern is recorded by means of a high-speed camera, the device operational limits (start-up and dry-out heating levels at the different inclinations) are detected and the overall thermal performance is calculated for different inclination angles and heat power inputs. Thanks to the fluid flow motion stabilization in a preferential direction due to the peculiar position of the heating elements, in vertical position the device is able to dissipate heat fluxes higher than 57% with respect to the CHF limit for FC-72, keeping also the temperatures at the evaporator zone lower than 80 °C.