Study on the convective heat transfer behaviour of laminar nanofluids flow

Nanofluids are engineered colloids of nanoparticles dispersed homogenously within base fluids. The term nanofluids refers to a mixture composed of a continuous phase, usually a saturated liquid, and a dispersed phase constituted of extremely fine metallic particles of size below 100 nm called nanoparticles. Due to the presence of nanoparticles, the thermophysical and transport properties of base fluids are subject to change. The nanofluids are considered the next-generation heat transfer fluids because of the new possibilities compared to pure fluids. Existing technologies for industrial applications, such as: microelectronics, vehicle thermal management (engine cooling) and heat exchangers seem to be insufficient and nanofluids, as reported in several studies, might offer a better alternative for proper heat transfer. The main purpose of this study is to investigate numerically the potential for replacing nanofluids in a single-phase flow for a conventional straight tube and a straight microtube under the constant temperature and constant heat flux conditions, separately. Nanofluids with a wide range of process parameters had been studied by varying three different types of base fluids including water, ethylene glycol and oil with five different type of nanoparticles viz. Al2O3, TiO2, CuO, SiO2 and ZnO. During the present investigation, six different combinations of the geometries, based fluids and nanoparticle concentrations were considered. The thermophysical properties of the nanofluids were obtained from the literature. The mathematical modeling was done using single-phase approach (SPH) were the flow was assumed as a steady incompressible flow and the continuity, momentum and energy equations are solved using the effective properties of the nanofluids. In addition to the single-phase model (SPH), the single-phase dispersion model (SPD) was also used for effectiveness of the computed results. The governing equations of mass, momentum and energy were solved using finite volume approach/method. To ensure the accuracy and consistency of computational results, various uniform grids were tested. An extensive number of numerical simulations were performed to determine the Nusselt number (Nu) of laminar nanofluids. For validation purposes, the present results of the Nusselt number were compared with the literature computational and experimental results. The results showed that the Nusselt number increases with increase in Reynolds number (Re) for all the nanofluids considered. In the case of the straight tube with 𝝓𝒃=𝟒%, the Nu increases 16% for Al2O3-water as comparted to water, 12% for Al2O3-EG as compared to EG and 8% for Al2O3-oil as compared to oil. The investigation concludes with the proposition of heat transfer correlations for the flow of nanofluids in conventional straight tube and straight microtube over a wide range of process conditions: 25