Structured surfaces at the extremes of heat transfer

The formation of frost on aluminum heat exchangers imposes severe penalties on various heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems by increasing thermal resistance and pressure drop. Decreased system efficiency leads to an increase in energy usage. Incomplete and inefficient braze alloy flow decreases the strength of brazed joints in various HVAC&R systems causing refrigerant leakage. Refrigerant leakage caused a direct increase in the global warming potential and an indirect increase in energy usage. These issues are tackled using specially designed structured surfaces that allow us to control phase change phenomena and fluid flow. This thesis focuses on developing scalable and feasible surface modifications for large-scale industrial systems. We begin by developing and applying a scalable superhydrophobic coating to off-the-shelf aluminum heat exchangers and testing their performance in various conditions. We specifically utilize the phenomenon of jumping droplet condensation to extend the frosting cycle and the low surface wettability to improve defrost efficiency. We then develop a simple and highly scalable surface modification to improve brazing alloy flow in copper to copper braze joints by increasing the wettability of the joints. The techniques and insights presented in this thesis improve the technology readiness level of superhydrophobic coatings and potentially decrease refrigerant leak rates from HVAC&R equipment. The discussion presented in this thesis will also inform future work on developing practical and durable coatings for different types of heat exchangers and how to evaluate them.

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

• Boyina, Kalyan

Contributors dc:contributor

• Miljkovic, Nenad
• Wang, Sophie
• Ferreira, Placid
• Elbel, Stefan
• Cosby, Ron

• Heat Transfer
• Phase-change
• HVAC&R
• Heat Pumps
• Air cycle Machines
• Heat exchangers
• Polymer coatings
• Nanostructures
• Brazing.

Statement dc:rights

• Copyright 2022 Kalyan Boyina

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115906

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115906