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Abstract
Nucleate pool boiling heat transfer in microcapillary grooves with different microcavity distribution is investigated experimentally. Using de-ionized water as a working fluid, the influence of the diameters and distributions of the microcavities on the nucleate pool boiling heat transfer characteristics of a microcapillary-grooved plate are obtained at different liquid levels in an evaporator. The investigations show that the existence of cavities apparently increases the bubble numbers on the surfaces of the microcapillary grooves, especially for the cavities with smaller diameters. However, the existence of the cavities also increase the flow resistance of the liquid driven by the capillary force in the microcapillary grooves. The optimum distance between the neighboring cavities is about 3.1 times the diameter of the cavity. The boiling heat transfer coefficients of the microcapillary grooves with the structured surfaces of the cavities are compared with the predictions of experimental correlation for conventional microcapillary grooves. The results indicate that the nucleate boiling heat transfer in microcapillary grooves is much enhanced by manufacturing microcavities on the surfaces, and the boiling heat transfer coefficients of the microcapillary grooves with microcavities of L/D = 3.1 is about five times higher than those predicted by the correlation of convective boiling heat transfer.
ACKNOWLEDGMENTS
The authors would like to acknowledge Dr. Takei's Lab of Nihon University and the National Science Foundation (Grant 201050976062).