Study on Pool-Nucleate Boiling Heat Transfer Characteristics by Using Artificial Cavities

Pool boiling heat transfer experiments were performed by using the well-controlled/defined heat transfer surface for water. Uni-size and -shape artificial cavities were created on the mirror-finished silicon plate by utilizing the MEMS technology. Experimental results agreed well with what were predicted by the traditional boiling theory. The mirror-finished surface showed only the tendency of natural circulation heat transfer. The artificial-cavity heat transfer surface followed the pool-nucleate boiling trend. The onset of the pool-nucleate boiling was well predicted by the traditional pool-nucleate boiling theory. These results indicated that the artificial cavities behave just like natural cavities. The results indicated the artificial cavities are quite useful and promising to examine the true features of complicated boiling that have been overshadowed by complicatedness. From recorded high speed video pictures, the coalescence of bubbles that were growing on the cavities were classified into four categories; the normal lift (no coalescence), the vertical coalescence, the declining coalescence and the horizontal coalescence. As the cavity interval was increased, the horizontal coalescence decreases to zero, the vertical coalescence also decreases, and on the contrary to these, vertical coalescence and normal lift increase. The cavity interval 3 mm (S/Lc ≅ 1.2) seemed to be the border whether the horizontal coalescence occurs or not. (authors)