INTERNATIONAL JOURNAL OF MULTIDISCIPLINARY SCIENCES AND ENGINEERING, VOL. 6, NO. 1, JANUARY 2015 [ISSN: 2045-7057] www.ijmse.org 15 Effect of Surface Wettability and Spreading on Nanofluids Boiling Heat Transfer Osita Sunday Nnyigide 1 and Kyu Hyun 2 1,2 Department of Chemical Engineering, Pusan National University, South Korea Abstract– Surface wettability is one of the mechanisms responsible for the enhancement of pool boiling heat transfer. This work investigates the effect of surface wettability and spreading on nanofluids pool boiling heat transfer. Water, ethylene glycol, water-ethylene-glycol base fluids and nanofluids containing TiO 2 in different concentrations were studied on polished stainless steel substrate in an environmental chamber at 20, 25, 50, 70 and 80 0 C respectively. Keywords– Contact Angle, Pool Boiling and Surface Wettability I. INTRODUCTION ooling challenges is one of the top technical problems facing high-tech industries such as microelectronics, nuclear power plants, and automobiles. Until the evolution of nanofluids technology, conventional methods to increase heat flux rates included extended surfaces such as fins and micro-channels and increasing flow rates or pumping power, etc. However, current design solutions already push available technology to its limits. New technologies and new advanced fluids with potential to improve flow and thermal characteristics are of critical importance. Studies of thermal conductivity of suspensions as enhanced heat transfer fluids have been confined to mm-sized particles but the major challenge has been the rapid settling of these particles in fluids. Nanofluids are promising to meet these challenges. Pool boiling is a type of boiling where the fluid is stationary at the beginning with respect to the heating surface. Example of pool boiling can be imagined traditionally when using a gas cooker to boil water in a kettle. The degree to which water makes and retains contact with the surface of the kettle affects the rate of boiling and heat transfer. In the field of engineering, a more suitable illustration is seen in liquid cooled high-end computers. The ability of a liquid to make and retain contact easily with a heater surface is paramount in improving efficiency of heat transfer system. Understanding the surface wettability of cooling fluids and method of enhancement at little or no cost is of great importance in engineering and technology. Coolants with high wettability would spread quickly on the heating surface depending on its surface chemistry and the chemical composition of the liquid. A hydrophobic surface tends to avoid or minimize contact with liquids while a hydrophilic surface promotes contact, causing the liquid to spread easily. II. EXPERIMENT METHODOLOGY All nanofluids used were produced by evaporation and inert-gas condensation processing, and then dispersed in base fluid by mechanical agitation.Water, ethylene and water- ethylene-glycol WEG, were used as base fluids. Spherical morphology nanoparticles of titanium dioxide were used. Particle size was determined by Malvern Nanosizer at 20 0 C. Distilled water was used throughout the experiment. Fig. 1: Malvern nanosizer for particle size measurement and bimolecular characterization A) Contact Angle Measurement Sessile drop fitting method was used because it can be applied to Young-Laplace equation for quick calculation of interfacial tension since the needle diameter and density of the drop are known. For static contact angles greater than 30 0 , interfacial tension was calculated separately to get reliable results. Time-dependent static contact angle was measured other than advancing or receding contact angle. Time-dependent static contact angle enables understanding of settling effects of nanoparticles and alteration of liquid composition which was achieved by adding ethylene glycol to water. The Interfacial tension and time-dependent static contact angle were measured using a goniometer (KRUSS GmbH). Time-dependent static contact angle was created by dispensing the liquid/nanofluid unto a solid substrate (i.e., polished steel). A screw driven syringe pump suspended on the DSA was used to infuse liquid onto the surface through a 1.83 mm ID microneedle. A series of digital still photographs were captured by the Nikon D50 camera with a sigma macro lens. Contact angles were then measured from the digital images using the sessile drop fitting method. Measurements C