NUCLEATE POOL BOILING HEAT-TRANSFER IN A HIGHLY WETTING LIQUID ON MICRO-GRAPHITE-FIBER COMPOSITE SURFACES

This paper presents results of an experimental study on heat transfer enhancement in nucleate pool boiling of a highly wetting liquid, penta ne. on graphite fiber composite surfaces. Two kinds of composites are investigated: graphite-copper (Gr-Cu) consisting of graphite fibers in a copper matrix and graphite-aluminum (Gr-Al) consisting of graphite fibers in an aluminum matrix. Micro-graphite fibers of 8-10 mu m in di ameter are embedded in the matrices with fibers being arranged perpend icular to the boiling surface. The highly wetting liquid has a nominal contact angle of between 2 and 4 degrees of most known surfaces. Pool boiling heat transfer performances of the graphite composites are com pared with those of pure metal surfaces in the hysteresis region, whic h is commonly encountered within boiling startup periods, and the deve loped boiling region in which the overall performance is determined. I t is revealed that the presence of graphite fibers reduces hysteresis effects in the startup region and also enhances overall performance in the developed region. In the hysteresis region, hysteresis temperatur es are reduced more on the Gr-Al surface than on the Gr-Cu surface. In the developed boiling region, however; the heat transfer performance is enhanced more on the Gr-Cu surface than on the Gr-Al surface. (C) 1 998 Elsevier Science Ltd. All rights reserved.