Solid to liquid and liquid to vapor two phase heat transfer enhancement approaches

Fu, Wuchen

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https://hdl.handle.net/2142/121215 Copy

Description

Title

Solid to liquid and liquid to vapor two phase heat transfer enhancement approaches

Author(s)

Fu, Wuchen

Issue Date

2023-07-10

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

Miljkovic, Nenad

Doctoral Committee Chair(s)

Miljkovic, Nenad

Committee Member(s)

• Jacobi, Anthony M.
• Banerjee, Arijit
• Elbel, Stefan

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)

• Phase change material
• Pool boiling
• Heat transfer
• Refrigerant

Abstract

Phase change heat transfer, a phenomenon commonly observed in nature, plays a pivotal role in a wide range of industrial systems. Leveraging the substantial latent heat present in candidate substances, phase change heat transfer enables considerably enhanced heat transfer rate compared to single phase heat transfer. This doctoral dissertation focuses on heat transfer enhancement approaches of heat absorption process: melting, which is a solid to liquid phase I first studied solid-to-liquid phase change heat transfer enhancement approach using pressure-enhanced phase change material close-contact melting. Phase change materials show promise to address challenging problems in thermal energy storage and thermal management. A key obstacle for the application of these materials is the low thermal conductivity of common phase change materials such as ice, paraffin wax, and low melting temperature metals, which hinders their efficacy as the transient melt-front moves away from the heat source. Here, I propose a novel approach that achieves the spatial control of the melt front location using pressure-enhanced close contact melting. Termed dynamic phase change materials, our approach enables ultra-robust temperature stabilization with pure phase change materials. With paraffin wax it results in effective energy density and power density of 230 J/cm3 and 0.8 W/cm3, respectively. I demonstrate our approach to achieve effective energy density of 480 J/cm3 and power density of 1.6 W/cm3 using gallium. I use physics-based analytical and finite element models to guide and validate experiments that reveal the ability of our dynamic phase change materials to control surface temperatures at unprecedented heat fluxes approaching 3 kW/cm2. This approach uses pure and cost-effective materials, overcoming complexities and cost of composite phase change materials. I report design guidelines for developing and integrating dynamic phase change materials for thermal management and thermal energy storage applications. While pressure-enhanced melting employs external power consumption in the form of a pressure source to force liquid to exit the interface between solid phase change material and the heat source, nucleate boiling, as a more natural phenomenon, harnesses the intrinsic density difference between liquid and vapor to drive continuous expulsion of vapor from the interface between liquid and the heat source. Higher boiling heat transfer coefficient can benefit the system by more compact design, higher cooling capacity and better overall performance. To further enhance the boiling heat transfer coefficient, researchers have developed numerous methods involving modifications to both surfaces and working fluids properties. In this dissertation, I will introduce a meticulously designed and validated pool boiling testing system. I characterized boiling performances of three different refrigerants, including two low global warming potential (GWP) refrigerants, R1336mzz(E) and R1336mzz(Z). The boiling performance of these two low-GWP refrigerants on plain copper and aluminum tubes will be reported for the first time. In addition, refrigerant pool boiling enhancements will be investigated on three distinct micro-structured tubes, namely etched aluminum, Boehmite, and copper oxide structured tubes. These modifications resulted in a remarkable heat transfer coefficient enhancement ratio of up to 250% when compared to smooth tubes. To understand the mechanism behind the enhancement, I used advanced surface characterization methods, such as Scanning Electron Microscopy and Confocal Microscopy to observe the structures on modified tubing surfaces. By investigating the relationship among enhancement ratio, structure size and refrigerant properties, I proposed a design guideline for developing micro-structured surfaces for refrigerants with different properties.

Graduation Semester

2023-08

Type of Resource

Thesis

Handle URL

https://hdl.handle.net/2142/121215

Copyright and License Information

Copyright 2023 Wuchen Fu

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