04. Boiling and Multi-Phase Flow

Recently, the use of boiling cooling has been considered for emergency cooling in nuclear power plants and for cooling of large power devices. For these purposes, it is necessary to improve the Critical Heat Flux(CHF). It is known that the use of honeycomb porous structure enables higher CHF to be achieved in a large heater size. We have fabricated porous plates by the electrodeposition method. In this method, porous metal is deposited on the electrode surface by immersing electrodes in acidic solution and energizing. We used electrodeposited porous plates in saturated pool boiling of water. As a result, the CHF was improved to 3.7 MW/m2 by using them. The experimental results showed that the difference in the porous structure, such as thickness and existence ratio of macro-channels, greatly affected to the CHF. In the range of 0.4~2 mm porous plate thickness, the CHF was improved with increasing thickness. The porous plate with near-zero macro-channels showed higher CHF compared to porous plates with a very high ratio of macro-channels. Furthermore, we measured absorption ability of each porous plate. As a result, we found that CHF tended to be improved as the dynamic water absorption ability increased. In summary, these results suggest that the dynamic water absorption characteristic, which depend on the porous structure, have significant influences on the improvement of CHF. In this presentation, we discuss these factors evaluated experimentally and the specific CHF improvement mechanism.