In: Advances in Nanotechnology. Volume 11 ISBN: 978-1-62948-732-8 Editors: Zacharie Bartul and Jérôme Trenor © 2014 Nova Science Publishers, Inc. Chapter 8 RHEOLOGICAL PROPERTIES OF P ARAFFIN-BASED CO 3 O 4 NANO-FERROFLUID Alireza Fazlali, 1,* Saba Lashkarara 1 and Amir H. Mohammadi 2,3,  1 Department of Chemical Engineering, Faculty of Engineering, Arak University, Arak, Iran 2 Institut de Recherche en Génie Chimique et Pétrolier (IRGCP), Paris Cedex, France 3 Thermodynamics Research Unit, School of Engineering, University of KwaZulu-Natal, Howard College Campus, Durban, South Africa ABSTRACT The rheological properties of Co 3 O 4 ferrofluid (F.F.) nanoparticles in paraffin base have been investigated for wide concentration range. For preparing this ferrofluid, ball mill and ultrasonic bath were used. The experimental results show that these magnetic fluids show approximately Newtonian behavior in very low concentrations, whereas they seem to act as a non-Newtonian fluid by increasing concentration. The viscosity of this ferrofluid is falling with shear rate increasing, especially for high concentrations; thus this phenomenon shows shear thinning behavior. The viscosity of the ferrofluid is increasing with claiming up in the Co 3 O 4 nanoparticles concentrations in a constant shear rate. The experimental data have been compared with some existing models. Keywords: Co 3 O 4 ; nanoparticle; ferrofluid; viscosity; nanoparticle interaction; model. 1. INTRODUCTION A magnetic fluid (ferrofluid or F.F.) is a stable suspension of magnetic nanoparticles such as Fe 3 O 4 [1], CoFe 2 O 4 [2], Mn–Zn [3], Co–Zn [4], Lithium ferrite [5] in a base liquid. The base liquid can be polar or nonpolar compound [6]. In order to avoid nanoparticles  Corresponding authors: Alireza Fazlali, Email: a-fazlali@araku.ac.ir & Amir H. Mohammadi, E-mail: a.h.m@irgcp.fr Complimentary Contributor Copy