PhD Disseratation Defense: Abdolali Khalili Sadaghiani22-05-2019
MICRO/NANO-ENGINEERED TECHNIQUES FOR ENHANCED POOL BOILING HEAT TRANSFER
Abdolali Khalili Sadaghiani
Mechatronics Engineering, PhD Dissertation, 2019
Prof. Dr. Ali Koşar.(Thesis Advisor), Prof. Dr. Kürşat Şendur,
Assoc. Prof.Burç Mısırlıoğlu, Prof. Dr.Pınar Mengüç, Prof. Dr.Hyun Sun Park
Date & Time: June 17th, 2019 – 11 AM
Place: Collaboration space – 1002A
Keywords: Surface modification, Fundamental and application, MEMS techniques, Biocoating, Graphene, Biphilic surfaces, pHEMA coating, Surface wettability, Artificial cavities, Boiling heat transfer, Critical heat flux
Environmental aspects such as water treatment as well as military applications and thermal management emphasize on the need for next generation cooling technologies based on boiling heat transfer. Micro/nano enhanced surfaces have shown a great potential for the performance enhancement in the systems involving boiling phenomena. The lack of fully understanding the mechanisms responsible for the enhancement on these surfaces and scalability of these technologies for large and complex geometries over the wide range of materials are two main issues. The goals of this dissertation are to understand the fundamentals of pool boiling heat transfer (BHT) and critical heat flux (CHF) mechanisms on engineered surfaces, to develop new techniques for surface alteration for BHT and CHF enhancement, and to proposed novel, facile and scalable surfaces modification techniques for related industries.
Part 1: Fundamental
For artificial cavities it was shown that CHF occurrence on the hydrophilic surfaces is mainly due to hydrodynamic instability, while dry-out is the dominant CHF mechanism on the hydrophobic surfaces. The obtained results imply that although the increase in hole diameter enhances CHF for all the fabricated samples, the effect of pitch size depends on surface wettability such that CHF increases and decreases with pitch size on the hydrophobic and hydrophilic surfaces, respectively.
For biphilic surfaces, a novel and facile process flow for the fabrication of biphilic surfaces was proposed. It was shown that boiling heat transfer coefficient and CHF increased with A*=AHydrophobic/Ahydrophilic up to 0.6249. Surfaces with A*>0.6249 demonstrated a decreasing trend in CHF and heat transfer coefficient enhancement, which is caused by earlier interaction of nucleated bubbles, thereby triggering the generation of vapor blanket at lower wall superheat temperatures.
Pool boiling on pHEMA coated surfaces with thicknesses of 50, 100 and 200 nm were used to study the effect of surface porosity and inclination angle on heat transfer and bubble departure process. According to obtained results, combination of the effects of the interaction between active nucleation sites, the increase in bubble generation frequency, and the increase in bubble interactions were presented as the reasons behind the enhancement in heat transfer on coated surfaces.
Part 2: Novel techniques
Pool boiling experiments conducted on 3D foam-like graphene coated surfaces to show the effect of graphene coating thickness on the pool boiling heat transfer performance. According to the obtained results, 3D structure of the coating has a significant effect on pool boiling heat transfer mechanism. Factors such as pore shape and mechanical resonance of the 3D structure could be possible reasons for bubbling behavior in developed nucleate boiling.
A novel coating, crenarchaeon Sulfolobus solfataricus P2 biocoatings, were proposed for the performance enhancement of heating and cooling devices, thermofluidic systems, batteries, and micro- and nanofluidic devices. Pool boiling experiments were performed on biocoated surfaces with thicknesses of 1 and 2µm. The obtained results indicated that biocoated surfaces enhance boiling heat transfer by providing numerous nucleation site densities and by increasing bubble interaction on the superheated surface.