Design and evaluation of heat transfer fluids for direct immersion cooling of electronic systems

Comprehensive molecular design was used to identify new heat transfer fluids for direct immersion phase change cooling of electronic systems. Four group contribution methods for thermophysical properties relevant to heat transfer were critically evaluated and new group contributions were regressed for organosilicon compounds. 52 new heat transfer fluids were identified via computer-aided molecular design and figure of merit analysis. Among these 52 fluids, 9 fluids were selected for experimental evaluation and their thermophysical properties were experimentally measured to validate the group contribution estimates. Two of the 9 fluids (C6H11F3 and C5H6F6O) were synthesized in this work. Pool boiling experiments showed that the new fluids identified in this work have superior heat transfer properties than existing coolant HFE 7200. The radiative forcing and global warming potential of new fluids, calculated via a new group contribution method developed in this work and FT-IR analysis, were found to be significantly lower than those of current coolants. The approach of increasing the thermal conductivity of heat transfer fluids by dispersing nanoparticles was also investigated. A model for the thermal conductivity of nanoparticle dispersions (nanofluids) was developed that incorporates the effect of size on the intrinsic thermal conductivity of nanoparticles. The model was successfully applied to a variety of nanoparticle-fluid systems. Rheological properties of nanofluids were also investigated and it was concluded that the addition of nanoparticles to heat transfer fluids may not be beneficial for electronics cooling due to significantly larger increase in viscosity relative to increase in thermal conductivity.PhDCommittee Chair: Teja, Amyn; Committee Member: Hess, Dennis; Committee Member: Joshi, Yogendra; Committee Member: Liotta, Charles; Committee Member: Realff, Matthe

Devotion to a Goddess in contemporary India

Revering human beings as holy and divine entities is a fairly commonplace phenomenon in Hindu India. In the Hindu scheme of things, divinity can manifest itself in different forms, in different places, at different times. Hindus commonly attribute divine powers to stones, rocks, rivers and mountains; certain kinds of birds and animals are often understood to possess sacred qualities; and occasionally human beings too fit into the category of that which is considered sacred, divine and therefore worthy of worship and veneration. This paper deals with one such divinised individual in contemporary India. Her name is Mata Amritanandamayi, which, according to her biography, means Mother of Immortal Bliss. She is popularly known as Amma, Ammachi, or Mata, all of which mean mother. In the rest of this paper I shall refer to her as the Mata. Devotees describe her as an avatar-guru, a guru, spiritual guide or teacher, who is also an incarnation, avatar, of god. My attempt here is to analyse the concept of the avatar-guru, a relatively recent phenomenon in popular Hinduism. I do this using two more conventional Hindu categories, firstly, that of the sannyasi or renouncer, and secondly, that of the avatar or divine incarnation. The avatarguru, I argue here, represents an interesting amalgamation of these two categories, and successfully resolves a crucial contradiction in the role of the renouncer in Hindu traditions. After analysing the phenomenon of the avatar-guru, I go on to explore the miraculous experiences that devotees of the Mata claim to have had after entering her fold. My research on Mata Amritanandamayi is based on an extended period of fieldwork in India and in London among followers of this avatar-guru. I should perhaps clarify at the outset that I conducted this research very much as an outsider to the belief system I encountered in the field. I was at no point inclined towards becoming a devotee of the Mata myself. As an outsider my research had its limitations since I could only seek to understand, never directly undergo, many of the experiences my informants spoke to me about. Equally however, it had important strengths as well, since as an outsider I took very little for granted but sought to question and probe every aspect of the devotional world that I encountered

Linear stability analysis of particle-laden planar jet in the dilute suspension limit

Particle laden flows are commonly seen in many industrial applications such as fluidized beds in process industry, air laden with abrasive particles in abrasive machining and particle laden plumes in chemical industries. In the present work, we perform local analysis of a particle laden planar jet in the dilute suspension regime. Unladen parallel planar jets have been extensive studied using normal modes and is shown to have two unstable modes namely sinuous and varicose modes. Sinuous modes are found to be more unstable compared to the varicose modes. In the present study, we investigate the effect of particles on the stability of planar jets. Addition of particles at low Stokes numbers (St) (fine particles) results in higher growth rates than that of the unladen jet. In the intermediate Stokes number regime, addition of particles have a stabilizing effect on both the sinuous and the varicose modes. Interestingly for St~10, the unstable varicose mode is completely damped. Increasing the Stokes number by increasing the particle size, both sinuous and varicose modes show increasing growth rates, while increasing density ratio has a stabilizing effect on the flow. For non uniform particle loading, additional modes apart from the sinuous and varicose modes are observed. These modes suggests occurrence of compositional instability with an increased particle accumulation in the shear layer that is an order of magnitude higher compared to that of the sinuous and varicose modes

Fused filament fabrication 3D printing using low-melting alloys.

Fused Filament Fabrication (FFF) 3D printing technology has been a popular method of creating prototypes using plastics in the timeliest and most affordable manner for electronic, automotive, and biomedical applications. 3D printing of metals and alloys using FFF technology could provide low-cost alternatives and solutions to the Laser-Powder Bed Fusion Process (L-PBF) and Binder Jetting processes (BJ). In current work, low melting alloys have been used as a starting material and evaluated for FFF 3D printing using two methodologies. In the first methodology, Sn60Bi40 alloy in the form of wire was used as the feedstock for FFF extrusion and process parameters for the fabrication of 2D and 3D geometries were developed. In the second methodology, low melting alloys of Sn42Bi58, Sn60Bi40 and Sn89Sb7.5 were cast onto 3-D printed molds to fabricate metal structures. The influence of mold cooling temperature on the cast specimens of Sn60Bi40 alloy was evaluated. The fabricated specimens were evaluated for its part formability, mechanical properties, and microstructure. A prototype was fabricated using the FFF 3D printing methodology and a souvenir was cast using the FFF 3D casting methodology to show case the applicability of the FFF metal 3D printing process

A branch, price, and cut approach to solving the maximum weighted independent set problem

The maximum weight-independent set problem (MWISP) is one of the most well-known and well-studied NP-hard problems in the field of combinatorial optimization. In the first part of the dissertation, I explore efficient branch-and-price (B&P) approaches to solve MWISP exactly. B&P is a useful integer-programming tool for solving NP-hard optimization problems. Specifically, I look at vertex- and edge-disjoint decompositions of the underlying graph. MWISPâÂÂs on the resulting subgraphs are less challenging, on average, to solve. I use the B&P framework to solve MWISP on the original graph G using these specially constructed subproblems to generate columns. I demonstrate that vertex-disjoint partitioning scheme gives an effective approach for relatively sparse graphs. I also show that the edge-disjoint approach is less effective than the vertex-disjoint scheme because the associated DWD reformulation of the latter entails a slow rate of convergence. In the second part of the dissertation, I address convergence properties associated with Dantzig-Wolfe Decomposition (DWD). I discuss prevalent methods for improving the rate of convergence of DWD. I also implement specific methods in application to the edge-disjoint B&P scheme and show that these methods improve the rate of convergence. In the third part of the dissertation, I focus on identifying new cut-generation methods within the B&P framework. Such methods have not been explored in the literature. I present two new methodologies for generating generic cutting planes within the B&P framework. These techniques are not limited to MWISP and can be used in general applications of B&P. The first methodology generates cuts by identifying faces (facets) of subproblem polytopes and lifting associated inequalities; the second methodology computes Lift-and-Project (L&P) cuts within B&P. I successfully demonstrate the feasibility of both approaches and present preliminary computational tests of each