AUGMENTED BOILING ON COPPER GRAPHITE COMPOSITE SURFACE

An experimental study is conducted to determine the nucleate pool boiling heat transfer performance of a copper-graphite (Cu-Gr) composite surface in Freon 113. The composite medium consists of ultra-high thermal conductivity graphite fibers of 0.0008-0.010 mm diameter being consolidated in a copper matrix (50% area fraction). It has high thermal conductivity along the fiber directions, several times those in the other two directions. The heating surface is constructed with a Gr-Cu composite plate of 25 mm diameter and 10 mm thick. The boiling heat flux in the nucleate regime is compared to isotropic pure copper used as the heating surface. It is disclosed that the boiling heat transfer coefficients on the composite surface are higher than those on the copper surface by a factor of over 6 to 3, respectively at lower and higher values of superheating. Hence, the composite surface may serve as a high heat flux boiling surface with the merits of no extra pressure drop, no fouling and low cost.