Low pressure boiling instabilities in a T-type thermosyphon

Experiments were performed to characterize the boiling instabilities in a copper–water T-type thermosyphon consisting of a horizontal square cross-section evaporator embedded into a heat spreading plate with an extended condenser tube. Steady heating was applied from heaters in the plate and removed using a water jacket on the condenser tube. The unsteady heat transfer out of the condenser was compared to temperature fluctuations measured in the heated plate and on the thermosyphon for different condenser inclination angles. There was a delay in the onset of boiling and intermittent boiling with prolonged quiescent periods that caused very large variations in heat transfer rate and evaporator temperature for nominal heat fluxes of 0.43–4.3 W/cm2 (for a saturation pressure of 1.44–10.6 kPa) when the condenser angle was 22.5° or greater from the horizontal. The effect of the delayed onset of boiling and the intermittent boiling increased with inclination angle up to 60°. Neither delayed onset of boiling or prolonged quiescent periods were observed when the condenser angle was 8° or 15°, except at very low heat transfer rates; however, there was substantial variability in the evaporator performance.