Date of Award

2020-01-01

Degree Name

Master of Science

Department

Mechanical Engineering

Advisor(s)

Md. Mahamudur Rahman

Abstract

Developing efficient heat dissipation technologies is of critical importance towards the development and the commercialization of next-generation compact and high-performance electronic devices, cooling systems, power generation systems and chemical processing units, as well as retrofitting the existing thermal management schemes. As such, phase change heat transfer systems, more specifically boiling heat transfer systems, have attracted significant attention due to their ability to extract a large amount of latent energy stored within the fluid. Pool boiling is an efficient mode of phase change heat transfer processes accompanied by nucleation of vapor bubbles from liquid on to the hot surfaces, bubble growth, and departure from the heated surface in a stagnant liquid. Noticeably, boiling becomes vigorous and more effective at higher power as vapor production increases with increasing the surface temperature. However, if the applied power from the industrial systems exceeds the upper governing limit of a heat transfer surface, which is also termed as the critical heat flux (CHF) limit, a drastic increase in surface temperature occurs leading to system failure. This occurs due to the formation of a stable vapor film on the heated surface that creates insulation effect in between the hot surface and coolant. It is therefore essential to design and develop advanced thermal management schemes to further increase the surface maximum heat transfer capability (CHF) limit.

Motivated by these goals, in the last decades, several researchers have explored solutions to enhance the limits of boiling heat transfer. By manipulating the solid-liquid-vapor interface using these structures, more than 100% increase in boiling heat transfer has been realized. The reasons of this significant enhancement are typically attributed to the surface roughness, wettability, and capillary wicking. Several engineered surfaces have been considered, including hydrophilic porous layers, nanowires, nanorods, oxide nanostructures, micropillars, hoodoos, micro-ridges, hierarchical structures and many others. However, this massive heat transfer enhancement has only been demonstrated on flat surfaces, whereas, in reality, vast majorities of industrial heat transfer surfaces are of tubular geometries. Additionally, the boiling mechanism is significantly different between flat surface and tubular surface. For instance, different from flat surface, local heat transfer on a tubular surface is primarily governed by the liquid convection in the bubble layer around the tube and evaporation under the sliding bubbles. Thus, it is important to experimentally demonstrate the heat transfer enhancement on these curved surfaces utilizing the advanced micro/nano-structures for the industrial applications. Moreover, these reported enhancements are limited to atmospheric pressure boiling conditions as opposed to the high-pressure environment in industrial applications. Additionally, several CHF correlations for engineered surfaces have been reported by the scientists in the last one decade; still, there is no general agreement on the enhancement mechanisms. Again, these models were developed for the planar surfaces at atmospheric boiling conditions. In this regard, this Thesis aims to design and develop a high-pressure high heat flux pool boiling test facility for micro/nano-engineered rods using water as the working fluid and capable of operating up to 20 bar pressure.

Language

en

Provenance

Received from ProQuest

File Size

93 pages

File Format

application/pdf

Rights Holder

Omar Hernandez Hernandez Rodriguez

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