Impact of heat exchanger surface wettability on condensation, frosting, and defrosting performance under practical testing conditions

Condensation and frost accumulation on aluminum heat exchangers present major challenges for heating, ventilation, air conditioning, and refrigeration (HVAC&R) systems. Both phenomena increase thermal resistance and airflow restriction, which diminish heat transfer, lower system capacity, and drive up energy consumption. In air-source heat pumps (ASHPs) and electric vehicle heat pumps (EV HPs), frosting under cold and humid conditions is particularly problematic, as it forces frequent defrosting cycles that restore performance only at the expense of significant efficiency losses. Reducing the impact of condensation and frost on system operation is therefore critical to lowering energy demands and improving reliability across residential, commercial, and transportation applications. One promising strategy to address these challenges is through surface engineering, where coatings and treatments are designed to alter wettability and control droplet dynamics, frost nucleation, and ice adhesion. Prior studies have mainly concentrated on hydrophobic and hydrophilic coatings applied to flat samples or simplified heat exchanger models. While such work has offered important insights, it falls short of representing the behavior of full-scale commercial finned-tube and microchannel heat exchangers, where geometry, coating robustness, and operating environment strongly influence overall performance. Furthermore, newer approaches, such as superhydrophobic, superhydrophilic, quasi-liquid surfaces, and slippery liquid-infused porous surfaces, have shown promise in laboratory studies but remain insufficiently explored in system-level evaluations. This dissertation investigates a broad set of engineered surface modifications applied to aluminum heat exchangers and examines their performance under controlled condensation, frosting, and defrosting conditions. By systematically comparing hydrophobic, superhydrophobic, hydrophilic, superhydrophilic, quasi-liquid, and slippery liquid-infused porous surface modifications on full-scale heat exchanger platforms, this work demonstrates how surface wettability influences water harvesting efficiency, refrigeration performance, and heating system operation. The approaches and insights presented here contribute to advancing the readiness of functional coatings and provide guidance for developing next-generation HVAC&R systems that are more energy-efficient, sustainable, and resilient.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Ghaddar, Dalia

Contributors dc:contributor

• Miljkovic, Nenad
• Wang, Sophie
• Cai, Lili
• Wang, Pingfeng

• Water harvesting
• Low-energy
• Non-wetting
• Dropwise condensation
• Filmwise condensation
• Heat transfer
• Mass transfer
• Heat pump, Heating mode, Frost formation, Defrosting, Coatings

Statement dc:rights

• Copyright 2025 Dalia Ghaddar

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132748

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132748