Publication Date


Document Type


First Advisor

Cho, Kyu Taek

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Mechanical Engineering


Nanofluids; Fluids--Thermal properties; Heat--Transmission


Improvement in heat transfer rate is one of the important demands in thermal energy systems. Conventionally, the area or geometry of heat-exchanging surfaces have been modified to enhance heat transfer rate, but adversely causing the size of system to be increased. In order to overcome this drawback and control the transport of thermal energy actively, new thermal-energy-transferring fluid called Nanofluid has been developed. Nanofluids are the emulsion solution containing nano-sized particles such as metal oxides and carbon materials in base fluids. But, one of challenging issues of nanofluids is instability leading to sedimentation of nanoparticles in the solution, and thus the nanofluids lose their thermal properties. The sedimentation is resulted from interactions among nanoparticles, and as attractive forces increase, the particle sedimentation is accelerated. In this study, extensive tests were conducted to understand key controlling parameters of the instability. Especially, effects of the size and the surface charge potential of particles in the fluid on the instability were investigated, and performance of surfactants and their sensitivity to the pH conditions were studied for three different types of surfactants. It was found that the performance of surfactant to enhance stability of nanofluids was affected significantly by chemical structure (i.e. functional group) in the surfactant and their interactions with charges in the solution and on particle surfaces. Various combinations of surfactants of different chemical structures were made and their performance were analyzed to suggest a way to enhance stability in performance of surfactants.


Advisors: Kyu Taek Cho.||Committee members: Pradip Majumdar; John Shelton.||Includes bibliographical references.||Includes illustrations.


vii, 57 pages




Northern Illinois University

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