The New Jersey Institute of Technology's
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Title:	Electric-field-driven processes in multiphase fluid systems
Author:	Lei, Qian
View Online:	njit-etd2021-093 (xxxv, 191 pages ~ 13.1 MB pdf)
Department:	Department of Chemical and Materials Engineering
Degree:	Doctor of Philosophy
Program:	Chemical Engineering
Document Type:	Dissertation
Advisory Committee:	Khusid, Boris (Committee chair) Sirkar, Kamalesh K. (Committee member) Armenante, Piero M. (Committee member) Basuray, S. (Committee member) Zhang, Wen (Committee member) Kondic, Lou (Committee member)
Date:	2021-12
Keywords:	Boiling processes Colloidal suspensions Columnar and cellular pattern Electric field Low gravity Positively and negatively polarized particles
Availability:	Unrestricted
Abstract:	Advantages of using electric fields in miniaturized apparatuses for a wide range of applications are revealed by numerous experimental and theoretical studies over the last several decades as it offers a simple and efficient method for manipulation of multiphase fluid systems. This approach is considered to be especially beneficial for control of boiling processes and colloidal suspensions considered in the presented work. Boiling. Today's trends for enhancing boiling heat transfer in terrestrial and space applications focus on removal of bubbles to prevent formation of a vapor layer over the surface at a high overheat. In contrast, this dissertation presents a new boiling regime that employs a vapor-air bubble residing on a small heater for minutes and driving cold water over the surface to provide high heat flux. Single-bubble boiling of water was investigated under normal gravity and low gravity in parabolic flights. Experiments demonstrated a negligible effect of gravity level on the rate of heat transfer from the heater. Due to self-adjustment of the bubble size, the heat flux provided by boiling rose linearly up with increasing heater temperature and was not affected by a gradually rising water temperature. The fast response and stable operation of single-bubble boiling over a broad range of temperatures pave the way for development of new devices to control heat transfer by forming surface domains with distinct thermal properties and wettability. Suspensions. The response of polarized particles suspended in a host fluid to an external electric field is widely employed in various applications through the ability to vary reversibly the suspension structure and viscosity (often referred to as electrorheological effect). It has been known for centuries that the application of a strong electric field to a suspension of polarized particles will cause the particles to form head-to-tail chains along the field direction gradually coalescing into thick columns. A new phenomenon in suspensions of polarized particles was discovered by Kumar, et al. 2005; Agarwal, et al. 2009. They found that under certain conditions chains formed by particles in an alternating current (AC) electric field rearrange in the plane perpendicular to the field direction into a cellular pattern of particle-free domains surrounded by particle-rich walls. The main goal of our study was to find key variables affecting the formation of these structures in a suspension of polarized particles subjected to external alternating (AC) and direct (DC) current fields. Experiments were conducted on suspensions of positively and negatively polarized particles. As expected, the application of a strong AC field caused the particles in all tested suspensions to form chains along the field direction. However, rearrangement of chains into a cellular structure was achieved only in suspensions of negatively polarized particles. By accounting solely for dipole-dipole interaction between polarized particles exposed to an electric field, current theories fail to describe the formation of a cellular structure since they predict that the field effects should depend on the square of the particle polarizability and therefore be the same for negatively and positively polarized particles. Based on our findings, it is suggested that the formation of a cellular structure by negatively polarized particles is driven by weak multi-particle repulsion. Presented results demonstrate that the coupling of AC and DC fields provides a powerful technique for control, manipulation and assembly of polarized particle in various applications.