ABSTRACT
146Convective heat transfer involving liquids plays an important role in a wide range of applications, including industrial heating and cooling. This heat transfer mode can be passively enhanced by changing flow geometry, wall conditions, and/or fluid thermophysical properties. In this regard, an innovative way of enhancing the thermal conductivity of the fluid is adding solid particles of micrometer size; however, these particles tend to agglomerate. This particular problem can be overcome by using nanoparticles, and Choi (1995) and his team pioneered the use of nanoparticles dispersed in base fluids to prepare so-called nanofluids, with consequent enhancement of the thermal conductivity as compared to that of the base fluids. These days, researchers all over the world are focusing their attention on nanofluids, as they offer an immense potential for increasing heat transfer in various applications including electronic cooling. The latest research focuses on the synthesis of hybrid nanofluids, which possess physical properties that lead to high heat transfer enhancement without excessive friction increase. The aim of this book is to bring together a number of recent contributions regarding nanofluids from several researchers from all over the world. The latest research results, innovations, and methodologies are reported in the book in order to support discussion and to circulate ideas and knowledge about heat transfer enhancement in nanofluids without a preconceived opinion, either positive or negative, on this topic. This chapter presents the methodology for the preparation of nanocomposites and studies experimentally the performance of the resulting hybrid nanofluids under turbulent forced convection in a tube with and without inserts. The experiments are conducted for a range of values encountered in practical applications, and the results are thoroughly discussed taking into account the experimental data available in the literature. User-friendly Nusselt number and friction factor correlations are also proposed.
