Document Type

Thesis

College

College of Engineering

Department

Mechanical Engineering

Degree

MSE in Mechanical Engineering

Date Completed

4-2026

First Committee Member

Pourghasemi, Mahyar

Second Committee Member

Rahnamai, Kourosh

Third Committee Member

Mascarenhas, Brendan

Abstract

In recent years, the demand for efficient thermal management in miniaturized and high-performance electronic devices has grown rapidly. As electronic devices become more compact and powerful, their heat dissipation density increases, requiring more innovative and efficient thermal management solutions. Among the most promising solutions for localized cooling are micro-scale cold plates, which have been widely studied since their introduction in the early 1980s [1]. These devices, due to their small footprints and high surface-to-volume ratios, are highly suited for cooling microprocessors, sensors, and integrated circuits. However, one major limitation of conventional microchannel cold plates is their high pressure drop characteristic, which leads to increased pumping power and energy consumption. Thus, engineers and researchers have started to explore a variety of solutions, including fractal and other nature-inspired structures (such as tree roots, leaf veins, lung airways, and blood vessels), to design more efficient geometries that enhance heat transfer rates and minimize flow resistance within small-scale heat sinks and cold plates [2–4]. One specific design that has garnered significant interest is a tree-shaped fractal channel configuration, in which larger trunk channels bifurcate into smaller branches, enabling uniform flow distribution with low pumping power requirements [2]. Such designs are supported by constructal theory, which optimizes flow paths to reduce energy loss [5,6]. This research presents a detailed computational fluid dynamics (CFD) investigation of forced convection heat transfer in disk-shaped microscale cold plates incorporating bio-inspired fractal and wavy microchannel structures. The numerical model is first validated against reliable experimental data from the literature to ensure the accuracy of the predicted flow and thermal behavior. Following validation, systematic parametric studies are performed to examine the influence of geometric and flow parameters on the thermal-hydraulic performance of the heat sink.

The first part of the study focuses on fractal networks with straight microchannels using water and HFE-7000 dielectric fluid as working coolants. The fractal configurations are defined by varying the number of branching levels (m = 1–4) and the hydraulic diameter of the main branch (286–400 μm), with inlet Reynolds numbers ranging from 45 to 890. Cold plate performance is evaluated based on three key criteria: convective heat transfer capability, thermal resistance (maximum substrate temperature), and temperature uniformity across the heated surface. Generalized performance graphs are provided for both coolants, illustrating the optimal branching level for each design criterion across the Reynolds number range.

The second part of the study investigates fractal networks with wavy microchannels. The geometric parameters considered include channel amplitude, wavelength, and hydraulic diameter, while the branching level is maintained at m = 1 and the Reynolds number varies from 150 to 1500. Water is used as the working fluid in this section. Validated numerical simulations were performed to determine the optimal relationships between the geometrical parameters of the main and secondary branches of the wavy fractal networks, resulting in the highest Nusselt number and the lowest pumping power.

This study aims to provide a comprehensive investigation of fluid flow and heat transfer in disk-shaped cold plates featuring fractal networks of straight and wavy microchannels. The findings and results in this work provide valuable insight into the relationship between geometry, coolant type, and thermal-hydraulic behavior of disk-shaped fractal cold plates, helping guide the design of energy-efficient micro-scale cooling systems for electronics and battery systems.

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