EXPERIMENTAL INVESTIGATION OF POOL BOILING HEAT TRANSFER IN NANOFLUIDS AROUND SPHERICAL SURFACES

In this study, the pool boiling heat transfer around spherical surfaces with high temperature quenched by nanofluids at saturated conditions and under atmospheric pressure was experimentally investigated. In the experiments, pure water-based silica, alumina, titania and copper oxide nanofluids with three different volumetric particle concentrations (0.01, 0.05 and 0.1%) were used. After the spherical test specimen made up off brass material was heated at high temperatures, it was suddenly plunged into the nanofluid suspensions at saturated conditions. Using the temperature-time data of the specimen, the cooling curves were drawn and the boiling curves were obtained. The experimental results showed that the cooling performance of test specimen depended on the type of nanofluids and nanoparticle concentration. In the first quenching tests, although the cooling trend were nearly identical to that in pure water, it was observed that the cooling time was considerably shortened with the repetition tests in nanofluids. This effect enhanced with the nanoparticle concentrations. For silica nanofluids, especially, the film boiling region vanished during the repetition tests and the critical heat flux dramatically increased. The experimental results also showed that a considerable change in nucleate pool boiling heat transfer was not observed for all nanofluids. Consequently, it was determined that the nanoparticles deposited on the test surface after the quenching tests by nanofluids increased the wettability and thus caused the increment in critical heat flux.