Influence of particle properties on convective heat transfer of nanofluids

Abstract

An experimental study is performed in order to examine how particle properties such as size and thermal conductivity affect the convection heat transfer of nanofluids. For this purpose, we prepare and study self-synthesized water-based nanofluids with different kinds of particles: polystyrene, SiO 2 , Al 2 O 3 and micelles. Concentrations of the nanofluids vary in the range of 0.1-1.8 vol-% and particle sizes between 8-58 nm. Full-scale convective heat transfer experiments are carried out using an annular tube heat exchanger with the Reynolds numbers varying in the range of 1000-11000. The pressure losses are also taken into account in the analysis in order to assess the feasibility of the nanofluids for practical forced convection heat transfer applications. The fluids are thoroughly characterized: viscosities, thermal conductivities, densities, particle size distributions, shapes and zeta potentials are all determined experimentally. In many previous studies, anomalous enhancement in convective heat transfer is observed based on comparison of the Nusselt numbers with equal Reynolds numbers. Also in this work, the nanofluids exhibit Nusselt numbers higher than water when compared on this basis. However, this comparison neglects the impact of differences in the Prandtl numbers, and therefore the altered thermal properties of nanofluids are not properly taken into account. In this study, no difference in Nusselt numbers is observed when the Prandtl number is properly considered in the analysis. All nanofluids performed as the Gnielinski correlation predicts, and the widely reported anomalous convective heat transfer enhancement was not observed with any nanoparticle types. Instead, we show that the convection heat transfer behavior of nanofluids can be explained through the altered thermal properties alone. However, addition of any type of nanoparticles was observed to change the fluid properties in an unfavorable manner: the viscosity increases significantly, while only moderate enhancement in the thermal conductivity is obtained. The more viscous nanofluids reach lower Reynolds numbers than water with equal pumping powers resulting in lower heat transfer coefficients. However, the increase in viscosity, and therefore also the deterioration of the convective heat transfer, is less pronounced for the nanofluids with smaller particle size indicating that small particle size is preferable for convective heat transfer applications.

Interplant heat exchanger network synthesis using nanofluids for interplant heat exchange

“…the values correspond to turbulent flow. The information is obtained from Duangthongsuk and Wongwises (2010) relating to nanofluids T iO 2 0.6% and T iO 2 1.0% , from Esfe et al 2014 Mikkola et al (2018)) have shown that the overall heat transfer efficiency (heat transfer and pressure losses are both accounted for) in forced convection heat transfer decreases when the concentration of particles increases. Therefore, we have choses mostly relatively low concentration fluids, and added as a reference one fluid having a higher concentration (SiO 2 4.0% ).…”

“…Many studies have demonstrated that the addition of the nanosized particles can cause considerable enhancement in convective heat transfer performance of the base fluid. However, an adverse effect of the particles is that they increase the viscosity of the fluid, thus enhancing the needed pumping power (Mikkola et al, 2018). In most of the nanofluid studies the overall benefit, accounting for both heat transfer and the pressure loss enhancement, has not been properly investigated.…”

Nanouptake - An European Network on Nanofluid Research

“…The Prandtl number of a nanofluid is therewith -except for extraordinary low concentrations of nanoparticles -always different than the one of its base fluid. In a joined effort, experimental data of five different experiments from independent research teams [5][6][7][8][9][10] are compiled. These experiments are: All of these experiments have two results in common:…”

A comprehensive thermo-hydraulic analysis and optimization of turbulent TiO2/W-EG nano-fluid flow inside double-pipe heat exchangers with helical coil inserts

“…The use of nanoparticles by engineers and researchers, to convert conventional fluids into nano-fluids, has been expanded dramatically in all aspects of the energy and heat transfer fields [16][17][18]. The addition of nanoparticles (such as Al 2 O 3 , TiO 2 and CuO) with high thermal conductivity to the heat transfer fluids can improve thermo-physical properties [19]. Several studies have been carried out on the application of different types of nano-fluids in HEs.…”