Structured surfaces at the extremes of heat transfer

Boyina, Kalyan

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

Description

Title

Structured surfaces at the extremes of heat transfer

Author(s)

Boyina, Kalyan

Issue Date

2022-07-14

Director of Research (if dissertation) or Advisor (if thesis)

• Miljkovic, Nenad
• Wang, Sophie

Doctoral Committee Chair(s)

• Miljkovic, Nenad
• Wang, Sophie

Committee Member(s)

• Ferreira, Placid
• Elbel, Stefan
• Cosby, Ron

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

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

Abstract

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.

Graduation Semester

2022-08

Type of Resource

Thesis

Copyright and License Information

Copyright 2022 Kalyan Boyina

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