Liquid vapor phase change for highly efficient and sustainable cooling

Liquid-vapor phase change of water is an essential and complex phenomenon germane to many natural and industrial systems. Desirable characteristics such as high latent heat, wide availability, non-toxicity, and low cost, allow water to become the ideal fluid to extract heat in many powerplant and electronic related applications. This is especially important recently as effective thermal management has become a critical bottleneck that hinders further advancements in new technologies that continue to increase in functionality and heat generation. Typically, two-phase flow boiling and evaporation are the two most widely adopted techniques to extract heat. Given their ubiquitous importance in cooling applications, understanding the underlying physics that govern both is paramount to fully maximizing their potential. In doing so, we are able to attain more efficient systems that are more cost-effective and sustainable. To gain a fundamental understanding of thermal transport during evaporation, past approaches have utilized optical, shadowgraph, and infrared (IR) imaging. Although such methods can reveal rich information, they are unable to quantify the temperature of the surrounding gas phase. To overcome this challenge, others have used a micro-thermocouple to probe the temperature distribution around or near the liquid-vapor interface of a sessile droplet. However, in these past investigations, the spatial resolution of measured temperatures near the liquid-vapor interface was limited and the sessile droplet varied in size while the temperatures were acquired. To provide a better understanding of the liquid-vapor phase change phenomenon, a platform that would overcome past difficulties encountered during the study of droplet evaporation is required. This dissertation proposes we develop such a platform by coupling a piezo-driven droplet generation mechanism to a controlled micro-thermocouple to probe microdroplet evaporation. Although evaporation provides effective means for thermal management, it is only appropriate for sub-saturation temperatures. Alternatively, two-phase flow boiling allows heat extraction at higher temperatures. The rate of heat extraction during flow boiling is greatly influenced by the surface topology. Previous studies to enhance heat transfer utilized different techniques such as inserts, surfactants, dimples, extended surfaces, ribs, vortex generators, and many more. These techniques depend on geometric modifications to induce turbulence and create additional nucleation sites to augment the heat transfer. In order to extend on these augmentation techniques, this dissertation also investigates the feasibility of microstructures in enhancing heat transfer in copper and aluminum tubes.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Mousa, Mohamed Hatem Abdelsadek Ahmed

Contributors dc:contributor

• Miljkovic, Nenad
• Jacobi, Anthony
• Elbel, Stefan
• Nawaz, Kashif

• heat transfer
• droplet evaporation
• thermocouple
• interface
• ambient evaporative cooling
• Heat transfer augmentation
• Swirl flow
• Pressure drop
• Passive heat transfer
• Active heat transfer
• Nusselt number
• Friction factor
• Twisted tape
• Insert
• Internal flow
• Boundary layer

Statement dc:rights

• Copyright 2022 Mohamed Mousa

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115862

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115862