ARTICLE IN PRESS JID: JTICE [m5G;May 3, 2017;6:51] Journal of the Taiwan Institute of Chemical Engineers 000 (2017) 1–9 Contents lists available at ScienceDirect Journal of the Taiwan Institute of Chemical Engineers journal homepage: www.elsevier.com/locate/jtice Thermophysical and rheological properties of water-based graphene quantum dots nanofluids Ahmad Amiri a,∗ , Mehdi Shanbedi b,∗ , Hossein Dashti c a Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, Malaysia b Department of Chemical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran c Department of Chemical Engineering, School of Chemical and Petroleum Engineering, Curtin University, WA, Australia a r t i c l e i n f o Article history: Received 18 January 2017 Revised 6 April 2017 Accepted 7 April 2017 Available online xxx Keywords: Graphene quantum dots Nanofluid Stability Viscosity Density Thermal conductivity a b s t r a c t Application of the suspended solid particles in the base fluids is one of the novel methods to increase the thermal performance of heat transfer fluids. However, the major problems with this technique are the short time colloidal stability, low thermal conductivity of additive as well as significant negative ef- fects on rheological properties once loading nanoparticles. The present study explores, for the first time, the impacts of graphene quantum dot (GQD) on the colloidal stability and thermophysical properties of water-based GQD suspensions as a new generation of heat transfer fluid. To this end, amine-treated GQD (A-GQD) were synthesized with a novel method. Surface functionality groups on A-GQD were analyzed by XPS. Atomic-force microscopy (AFM), UV–vis spectrometry, zeta potential and average particle size techniques have been used in order to measure and evaluate the colloidal stability, size and thickness of A-GQD. After applying A-GQD as an additive, colloidal stability results indicate no sedimentation after a 30-day period. In addition, all the thermophysical properties e.g. thermal conductivity, density and viscos- ity were measured experimentally. The viscosity of the water-based A-GQD samples was tested at various shear rates, concentrations and temperatures. Further, it has shown that by loading A-GODs in the water, the increasing rate of the density and viscosity is not significant. Interestingly, the water-based A-GQD nanofluids at very low concentration significantly increase the thermal conductivity in comparison with that of pure water. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. 1. Introduction The poor thermal conductivity of conventional heat transfer flu- ids such as air, deionized (DI) water, ethylene glycol (EG) and en- gine oil is one of the biggest problems in high heat transfer ap- plication in mechanical equipment and engineering processes. The addition of ultrafine solids particles suspended in the base fluid could enhance the thermal conductivity of fluids [1–5]. The early studies indicated that the low dispersion stability of suspended particles with sizes in the range of millimeters or micrometers could have an adverse influence on the effective thermal conduc- tivity. Their poor stability suspension leads to abrasion and channel clogging [6]. However, recently it was found that nanosized parti- cles (1–100 nm) suspensions in a common fluid can result in more stable and high thermal conductivity as well as improved rheologi- cal properties [7,8]. The term of ‘‘nanofluid’’ was first used by Choi in 1995 [9]. Several studies have shown an increased interest in ∗ Corresponding authors. E-mail addresses: ahm.amiri@gmail.com (A. Amiri), mehdi.shanbedi@stu- mail.um.ac.ir (M. Shanbedi). nanofluids in order to improve heat transfer, stability and thermo- physical properties performance [10,11]. Several types of additives have been identified in the research community: metals, metal oxides e.g. titanium oxide (TiO 2 ), aluminum oxide (Al 2 O 3 ) and carbon-based nanostructures e.g. carbon nanotubes, graphene. The main problem of metal- and metal oxide-based nanoparticles is their sedimentation in the common base fluid. Carbon-based nanostructures are capable to be functionalized covalently and non-covalently to change from a hydrophobic structure to hydrophilic one. Recently, re- searchers have shown an increased interest in development of different carbon-based nanostructures to prepare nanofluids like single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, graphene, graphene nanoplatelets and graphene oxide [12–16]. Graphene as a single atomic plane of graphite has high electrical and thermal conductivity, high specific surface area (SSA), high fracture strength and highly ordered graphitic carbon those attract lots of attention for the application in processes with high heat flux such as coolant technology [17]. The thermal conductivity of graphene has been measured to be in the range of 2000–5350 W/m K at room temperature [18–23]. The http://dx.doi.org/10.1016/j.jtice.2017.04.005 1876-1070/© 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Please cite this article as: A. Amiri et al., Thermophysical and rheological properties of water-based graphene quantum dots nanofluids, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.04.005