1 DISPERSION STABILITY AND RHEOLOGICAL CHARACTERISTICS OF WATER AND ETHYLENE GLYCOL BASED ZINC OXIDE NANOFLUIDS Adnan QAMAR 1 , Attique ARSHAD 1 , Zahid ANWAR 1* , Rabia SHAUKAT 1 , Muhammad AMJAD 1 , Shahid IMRAN 1 , Luqman RAZZAQ 1 , Muhammad ALI 2 , Theodosios KORAKIANITIS 3 *1 Department of Mechanical, Mechatronics, and Manufacturing Engineering Department, New- Campus, University of Engineering & Technology Lahore, Pakistan 2 Department of Mechanical Engineering, University of Engineering & Technology, Taxila, Pakistan 3 Parks College of Engineering, Aviation & Technology, Saint Louis University, United States *Corresponding author; E-mail: zahida@kth.se With advancement of nanoscience, “nanofluids” are becoming quite popular among thermal engineers. High thermal conductivity, relatively less settling speed, and higher surface area of nanoparticles are a few key promoting properties. The last two decades have seen dramatic progress towards using nanoparticles in industrial applications. However, the stability and rheological characteristics of prepared nanofluids have serious effects on their transport characteristics, but unfortunately, this has not found proper attention from researchers. In this study, stability and rheological characteristics of ZnO nanoparticles within deionized water, ethylene glycol, and their blends have been extensively tested. Stability was observed using UV-vis spectroscopy, while the viscosity was measured with the help of a rheometer. The data was collected with 0.011-0.044 wt. % loading of nanoparticles, while experiments were conducted within 15-55 o C temperature range. Better stability was recorded when nanofluids were prepared with pure ethylene glycol. Experiments showed that the viscosity increased with particle loading, whereas the effect of surfactants appeared to be insignificant. Research results were used to assess predictions of different viscosity models. Experimental data was overpredicted by Einstein, Brinkman, and Batchelor’s models. Key words: Ethylene glycol, Deionized water, Nanoparticles, Nanofluid, Stability, Viscosity, Zinc oxide 1. Introduction High-tech industries like microelectronics, transportation, manufacturing, and defense are facing a huge challenge in the field of cooling. The heat dissipation quest is rapidly increasing in microelectronics. Heat transfer intensification is needed to fulfill the demands of modern high-tech electronic devices [1]. Thermophysical properties of the working medium have a significant impact on fluid flow and thermal characteristics [2]. Nanofluids (NFs), a new kind of heat transfer medium and consisting of dilute dispersion of nanometer-sized metallic and non-metallic particles in engine oil, ethylene glycol (EG), deionized water (DIW) and distilled water (DW), have gained significant