Award Date
8-1-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Mechanical Engineering
First Committee Member
Jeremy Cho
Second Committee Member
Hui Zhao
Third Committee Member
Kwang Kim
Fourth Committee Member
Melissa Morris
Fifth Committee Member
Zhange Feng
Number of Pages
202
Abstract
Boiling processes play a substantial role in numerous commercial and industrial sectors, including electronic components, avionics, power plants, cooling systems, and water purification centers, for thermal management. The efficient heat transfer mechanism and high latent heat of evaporation inherent in water contribute significantly to bubble formation during boiling. Despite being widely employed as a heat transfer process, enhancing boiling presents challenges due to its non-equilibrium, dynamic, and unpredictable nature. One effective method to improve boiling heat transfer is through the use of surfactants. When added and dissolved in water, surfactants modify the liquid-solid and liquid-vapor interfacial properties, thereby altering boiling behavior, including bubble size, nucleation site density, departure frequency, and non-coalescence. Previous studies have indicated that surfactants are most effective in boiling water near the critical micelle concentration (CMC), a property in equilibrium that depends on the type of surfactant. However, conventional wisdom studies have primarily investigated a limited number of surfactants across narrow molar concentration ranges. The work presented in this dissertation broadens the scope by examining a wide array of ionic and nonionic surfactants over a wide concentration range. Surprisingly, we have discovered an optimal concentration range that operates independently of the critical micelle concentration (CMC). Our findings unveil that the effectiveness of surfactant-enhanced boiling is governed by two opposing factors: the dynamic adsorption of surfactants to interfaces and the increase of liquid dynamic viscosity at exceedingly high surfactant concentrations. Furthermore, this dissertation illustrates that dynamic adsorption operates as a diffusion transport-limited behavior, contending within a limited time window of a bubble lifetime and the timescale of diffusion necessary for surfactant adsorption to interfaces. With the right interplay between these two timescales, changes in boiling behavior are synchronous, quantified through the heat transfer coefficient (HTC) and the critical heat flux (CHF). This phenomenon unveils an HTC-CHF trade-off behavior, regardless of the surfactant type. Furthermore, we evaluate whether ionic liquid-based surfactants (ILBSs) of different chain lengths could break in the HTC-CHF trade-off behavior, as reported in recent literature. Overall, the results presented in this dissertation challenge conventional wisdom in the field, providing a fresh, practical perspective on how surfactants enhance the efficiency of boiling systems with the right amount of surfactant additives in the fluid. We also established general correlations to predict changes in aqueous surfactant boiling heat transfer. This novel scientific approach is applicable for any type of surfactant across a wide range of systems that rely on a boiling process to optimize heat transfer, particularly in energy-centric applications using surfactants, thus offering a new practical method to predict changes in aqueous surfactant.
Keywords
Boiling; Critical micelle concentration; Diffusion; Heat transfer; Surfactant; Two-phase flow
Disciplines
Mechanical Engineering
File Format
File Size
21600KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Mata Arenales, Mario, "The Role of Surfactant Adsorption in Boiling Dynamics" (2024). UNLV Theses, Dissertations, Professional Papers, and Capstones. 5137.
https://digitalscholarship.unlv.edu/thesesdissertations/5137
Rights
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