Experimental investigation on the start-up characteristics of single loop thermosyphon for motorized spindle bearing-shaft system cooling

Single loop thermosyphon (SLTP) is a promising method for handling the thermal dissipation problem of motorized spindle bearing-shaft system. The SLTP used for motorized spindle shaft cooling is with different structure from that of the existing SLTP. Therefore, it is necessary to conduct comprehensive study for its working mechanism. A visualization and thermal characterization experiment was carried out to research the effect of different heat load (Q) and liquid filling ratio (FR) on the start-up characteristics of the SLTP in this paper. The results show that the heat transfer in the SLTP with high FR at low heat load is intermittent boiling. The working fluid oscillates at the boiling incipience due to the U-shape structure of evaporator section, and temperature of the evaporator wall has an overshoot because of subcooled fluid and “interfacial vaporization heat sink effect”. At high heat load, the SLTP with high FR will translate from natural convection to nucleate boiling when starting, while liquid in the storage pool will be pushed into condenser section by vapor because of the excessive liquid level. However, the SLTP with low FR will not boil at low heat load, it forms a circulation mode of natural convection and condensation. With the increase of heat load, the heat transfer mechanism of the SLTP with low FR develops into nucleate boiling, and the liquid film returning from condenser section will be boiling when flows through evaporator section. In present experiment, the SLTP with 30% FR has the best start-up and flow performance.