Effective Dynamic Conductivity Correlation of Nanofluids in Convective Flow

Abstract

Many researchers have made desperate efforts to study for thermal characteristic of working fluid. As an idea to obtain higher thermal characteristic than that of existing pure fluid, e.g. water, the nanofluid is contrived and it expanded the research field for thermal properties and method to measure them. Nanofluid is a colloidal system consisting of nano-sized particles (dispersed phase) and a liquid (dispersed medium). Various materials of nanoparticles (e.g. Al2O3, CuO, SiO2, TiO2 and so on) have been dispersed in conventional heat transfer fluids (e.g. water and ethylene glycol). The enhanced effective thermal conductivity, one of the representative thermal characteristics, of stationary nanofluid has measured by various ways

transient hot wire, temperature oscillation and steady state parallel plate method. From these works, study of effective stationary thermal conductivity of nanofluid settles into shape pretty much and the methods carry conviction to researchers through many papers. In convective flow condition, however, it is hard to convince that we have an index of thermal conductivity for the accurate estimation. While several researchers strongly have said that the dynamic conductivity of nanofluids differs from static conductivity, they didnt give a reasonable relation between them and an obvious reason for the results. Obviously, at the real industrial field, the persuasive standard of the conductivity in convective flow condition is more useful than that in stationary condition. In this study, the dynamic conductivity of water-based nanofluids (Al2O3, Si, Cu with water) is measured in a fully developed laminar tube flow under uniformly heating and cooling conditions, and then compared with the static conductivity at the mean fluid temperature subject to convective flow conditions. Then using the Buckingham Pi theorem, one of the method for defining a function with related variables, we will make a correlation for the effective dynamic thermal conductivity to estimate conveniently.