Rheology and Efficacy Analysis of Nanofluids

Abstract

Cooling has become a major challenge for system design and performance in the fast growing technology. This development is pushing the conventional cooling methods to its limitation and there is an ever increasing call for new cooling methods to cope with current technologies. One of the possible ways of satisfying this demand is by introducing nanofluids as heat transfer fluids. Nanofluids are colloidal suspension of nanoparticles with enhanced thermal conductivity engineered for heat transfer application. Understanding the thermophysical property of nanofluids is crucial for their practical applications. The main objective of the present study is to investigate the viability of nanofluids for heat transfer applications. The applicability of Pump-probe technique for measurement of nanoscale thermal transport in nanofluids was investigated. Stable nanofluids of Copper, Zirconia, Silicon Carbide and Yttria in water and ethylene glycol basefluids were prepared by the conventional two step method without addition of surfactants. Particle size and zeta potential characterization of the nanofluids were carried out by electro-acoustic and DLS techniques. Yttria based nanofluids were found promising for their stability and dielectric properties. The viscosity of yttria nanolfuids increased with concentration almost linearly and showed an increment of around 3% at 0.1 vol% to 45 % at 5 vol% of particle. This increment was found beyond the prediction of Einstein or Batchelor theoretical models. The effective viscosity of these nanofluids showed non-linear dependence on temperature and this was due to particle-particle interaction which is observed from the higher orders fitting values of Arrhenius model. Theoretical analyses for the efficacy of Yttria and copper nanofluids are made for laminar and turbulent flow regimes. In laminar flow regimes, Yttria nanofluids showed promising results above 37oC and a maximum of 16% increase in efficiency was gained at working temperatures of 100oC. Similarly, Copper nanofluids were found viable for temperatures above 50oC with an efficiency gain of 7.5% maximum. In case of turbulent flow applications, Yttria nanofluids remain better coolants for temperature above 45oC despite of Copper nanofluids incompetence in the experimental range of temperature.

Date of Award	2011
Original language	American English
Supervisor	Youssef Shatilla (Supervisor)