A Novel Type Of Multi-Evaporator Closed Loop Two Phase Thermo-Syphon: Thermal Performance Analysis and Fluid Flow Visualization

A novel type of multi-evaporator Closed Loop Two Phase Thermo-syphon has been designed and tested at different inclinations and heat input levels. The device consists in an aluminum tube (I.D./O.D. 3/5mm), 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, firstly evacuated and then partially filled with FC-72, 50% vol. Each turn of the evaporator zone is wrapped with five electrical wiring heaters, giving a symmetrical heat power input at all the branches of the device. 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 up to 450 fps, as shown in Fig. 1. 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 all the inclination and the heat power input tested. At the vertical orientation, the device shows promising results since it is able to dissipate up to 260 W keeping the evaporator zone below 85 °C.