The effect of surface roughness and surface finish on two-phase and single-phase heat transfer and pressure drop characteristics

Efficient thermal management is essential in modern thermal systems where compact, high-performance heat exchangers needs to dissipate large heat loads. With rising power densities and the demand for energy-efficient systems, research has focused on enhancing boiling performance through surface structuring while simultaneously improving air-side heat transfer by innovative geometric modifications. This dissertation systematically investigates structured surface fabrication strategies including laser texturing, chemical etching, sintering, and electrodeposition and evaluates their effects on pool boiling, flow boiling, and air-side convective heat transfer performance. A physics-based design framework was established to link fluid properties, operating conditions, and nucleation theory to optimize surface morphologies for pool boiling application. Using laser texturing, surfaces with tailored cavities and patterned geometries were fabricated to control nucleation site density and capillary liquid transport. Experimental pool boiling studies demonstrated significant enhancements, with checkerboard structures achieving up to 56% improvement in critical heat flux (CHF) and ~730% increase in heat transfer coefficient (HTC) relative to smooth copper surface. Pool boiling investigations of circular and hexagonal patterns revealed that geometry and feature size strongly influence bubble dynamics, liquid replenishment, and vapor removal. Flow boiling experiments using chemically etched and sintered copper tubes further demonstrated the benefits of structured surfaces. While etched tubes enhanced HTC with negligible pressure drop penalties, sintered wick tubes provided up to 76% HTC augmentation with pressure drop penalties reaching as high as 60%. Performance factor analysis in flow boiling confirmed that thermal benefits outweighed hydraulic penalties under most conditions. The studies on air-side heat exchangers showed that electrodeposition created surface roughness that disrupted laminar sublayers and promoted mixing which enhanced overall HTC up to 23% with only modest increases in pressure drop. These results demonstrated that structured surfaces can be systematically designed to enhance boiling and convective heat transfer performance. The findings highlights the relationship between surface morphologies and heat transfer characteristics and provide guidelines in the development of high-performance heat exchangers for two-phase and single-phase applications.

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

• Roni, Md Rakibul Hasan

Contributors dc:contributor

• Miljkovic, Nenad
• Bradshaw, Craig
• Wang, Sophie
• Nawaz, Kashif

• Laser texturing
• chemical etching
• sintering
• electrodeposition
• structured surfaces
• pool boiling
• flow boiling

Statement dc:rights

• Copyright 2025 Md Rakibul Hasan Roni

Language dc:language

en

Handle dc:identifier

https://hdl.handle.net/2142/132756

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/132756