Impact of Temperature and Nanoparticle Concentration on Turbulent Forced Convective Heat Transfer of Nanofluids

Theoretical analysis of the influence of nanoparticles and temperature on the average Nusselt (Nu) number and the average heat transfer coefficient (HTC) during the turbulent flow of nanofluid in a horizontal, round tube was carried out. The Nu number is a function of the Reynolds (Re) number and the Prandtl (Pr) number, which in turn are functions of the thermophysical properties of the liquid and the flow conditions. On the other hand, the thermophysical properties of nanoliquids are primarily a function of nanoparticle concentration (NPC) and temperature. Hence, the correct determination of the value of the Nu number, and then the HTC, which is needed for engineering calculations, depends on the accuracy of determining the thermophysical properties of nanofluids. In most cases, the thermophysical properties of the nanofluids are calculated as functions of the corresponding thermophysical properties of the base liquid. Therefore, the accuracy of the calculations of the thermophysical properties of nanofluids is equally determined by the reliable correlations for the base liquids. Therefore, new correlations for the calculation of the thermophysical properties of water have been developed. The results of calculations of the thermophysical properties of the base liquid (water) and the water-Al2O3 nanofluids by use of carefully selected correlations is presented. It was established that even for small concentrations of nanoparticles, a significant intensification of heat transfer using nanofluids as compared to the base liquid is obtained for the tested temperature range.