Intermittent versus fully-developed boiling in a closed two-phase thermosyphon

We present experimental results and theoretical considerations on the low-pressure boiling mechanisms in a closed two-phase thermosyphon and, in particular, on the transition between intermittent-boiling and fully-developed boiling. We classify the boiling regimes on the basis of the frequency of bubble nucleation and the ratio of bubble diameter to device diameter. A criterion for the intermittent/fully-developed boiling frontier is based on the ratio of the bubble-nucleation waiting time and the bubble growth time. From this criterion we obtain a correlation between power throughput, working-fluid pressure and nucleation critical superheat. Experimental data on operating conditions, temperatures, and nucleation frequencies are in good agreement with the proposed correlation.