EXPERIMENTAL INVESTIGATION OF LAMINAR FLOW, POOL BOILING HEAT TRANSFER, STABILITY, AND BUBBLE DYNAMICS IN NANOFLUIDS
Mechatronics Engineering, PhD Dissertation, 2017
Prof.Ali Koşar (Thesis Advisor),
Prof.İ. Kürşat Şendur, Assoc. Prof. İ. Burç Mısırlıoğlu, Prof.Pınar M. Mengüç (Özyeğin University), Prof.Khellil Sefiane (University of Edinburgh)
Date & Time: July 26th, 2017 – 15:00 PM
Place: SUNUM G111
Keywords: Nanofluid, Single- and Two-Phase Heat Transfer, Bubble Dynamics
The advances in cooling microelectromechanical systems (MEMS) have led to extensive research efforts on flow and heat transfer in miniaturized channels during the last two decades. The need for high heat removal rates in many engineering devices used in microelectronics, energy industry, transportation, and optoelectronic industries such as plasmonics and thermophotovoltaic cells led to the development of smart engineering designs and/or efficient and high performance heat transfer fluids. An increase in heat transfer rate can be achieved by either optimizing the geometry and characteristic lengths or increasing heat transfer coefficients via enhancing thermophysical properties of fluids. Geometric optimization of engineering systems is limited to the production scale, when the system goes to miniaturization. Additionally, conventional coolants such as water, ethylene glycol, oil, refrigerants, and air result in limited heat transfer rates. Thus, suspending nanoparticles of average diameters of 1-100 nm with higher thermal conductivities in conventional liquid coolants was introduced which is called “nanofluids”. The term “nano” is related to nano-size particles, while the term “fluids” stands for base liquids which these nanoparticles are dispersed. Despite being one of the most studied subjects in heat transfer, many underlying mechanisms of nanofluids are still not fully elucidated due to its complex nature. In this thesis, pressure drop, single- and two-phase heat transfer of water-based nanofluids for different nanoparticles, concentrations, microtube hydraulic diameters, and heated lengths were investigated. Additionally, bubble dynamics in pool boiling on thin platinum wire, and flow in glass minichannels was studied. Finally, a novel method for increasing the stability of nanofluids was presented.