Seminer - Dr. Sinan Eren Yalçın
29.07.2019
Pressure Drop and Heat Transfer Characteristics of Nanofluids in Horizontal Microtubes under Thermally Developing Flow Conditions
Sinan Eren YALÇIN, Ph.D.
Assistant Prof. Dr. Isik University, Mechanical Engineering Department
eren.sinan.yalcin@gmail.com
Abstract. This study presents pressure drop and heat transfer characteristics of water based nanofluids with TiO2 and Al2O3 nanoparticles of various mass fractions in horizontal smooth hypodermic microtubes with an outer diameter of 717 m and an inner diameter of 502 m over a wide variety of Reynolds numbers under hydrodynamically fully developed and thermally developing conditions. For this purpose, TiO2 and Al2O3 nanoparticles of 20 nm average solid diameters were added to deionized water to prepare nanofluids with different mass fractions, and prepared nanofluids were characterized by standard methods such as Dynamic Light Scattering (DLS), Scanning Electron Microscopy (SEM), and zeta potential measurements. Pressure drops, friction factors, single-phase heat transfer coefficients, and Nusselt numbers of the nanofluids were compared to the base fluid (water) and each other. Experimental friction factor coefficients were predicted within ±10% and are in good agreement with existing analytical predictions, while experimental heat transfer coefficients were predicted within ±15% with existing correlations for single phase flow. Results show that there is no considerable heat transfer enhancement for Re<1000. A consistent enhancement in heat transfer was observed (for average heat transfer coefficient up to 25%), once Reynolds number goes beyond 1500. At low Reynolds numbers, flow is mainly laminar. As Reynolds number increases, flow starts to transition to turbulent flow, and as a result, heat transfer enhancement becomes detectable, which is due to enhanced mixing of nanoparticles at higher Reynolds numbers. While the stability of nanofluids is preserved after the experiments, a gradual agglomeration of nanoparticles in nanofluids might occur with time and might be accelerated with their repetitive use in the experimental setup and at elevated temperatures. Therefore, methods for improving their stability should be developed so that implementation of nanofluids to commercial products such as refrigerators and heat exchangers would be possible.
About the Speaker. Sinan Eren Yalçın obtained his bachelor degree from Istanbul Technical University Marine Engineering Department in 2003. Then he obtained his MSc degree in 2006 from Istanbul Technical University Mechanical Engineering Department, Thermofluids Division. During the master studies he was also teaching assistant at Thermodynamics and Heat Transfer Division of the same university. Then he joined Old Dominion University Mechanical and Aerospace Engineering Department for his Ph.D. studies. He completed his Ph.D. in 2011, his research topic was flow and particle motion in micro/nanofluidic systems under electric field. Then, he joined RWHT Aachen University Chair of Technical Thermodynamics for 1.5 years as a postdoctoral research associate. His research topic was diffusion coefficient measurements via microfluidic flow systems. Later on, he joined Sabanci University Micro Flow and Thermal Systems Lab as a postdoctoral research associate for 2 years. His research topic was nanofluid heat transfer enhancement. Then, he worked in industry. 1 year at Tofas Automotive Company Engine Systems Design Department as a Research and Development Engineer, and 2 years at General Electric Aviation as a Thermal System Design Lead Engineer. Currently, he is Assistant Professor at Isik University Mechanical Engineering Department.
