Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 41-42). / We have performed a series of experiments to characterize the different regimes observed in drop impacts during evaporative cooling of heated surfaces. We found four regimes which were named splashing, fizzing, flat film, and marbling based on the dynamic properties of the drop impact. We found that the emergence of these regimes is primarily controlled by the Jacob number, a dimensionless group describing the ratio of sensible to latent energy absorbed during liquid-vapor phase change. Using our classification scheme, we can predict a range of useful Jacob numbers to use in the cooling of electronic components. From these Jacob numbers, we can extract the material properties of a fluid required to cool a given system. / by Catherine Helene Koveal. / S.B.

Thesis (M.S.) Massachusetts Institute of Technology. Dept. of Mechanical Engineering, 1957. / Bibliography: leaves 95-96. / by Marsbed Hablanian. / M.S.

Thesis (S.M. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 61-62). / The hydrodynamic forces on ocean vehicles increase dramatically during sharp maneuvers as compared to forward motion due to large areas of separated flow. These large forces severely limit maneuverability and reduce efficiency. Applying active flow separation control to ocean vehicles would reduce resistance during maneuvers and thereby improve maneuvering performance. In this thesis I discuss experiments in active separation control in a simpler, but still relevant, two-dimensional flow past a circular cylinder at moderate sub-critical Reynolds numbers (37,000 and 52,000 in experiment and 100 and 10,000 in simulation). The active control injects momentum into the boundary layer via the moving surfaces of two small control cylinders located near boundary layer separation and rotated by servo motors. The relationship between drag and rotation rate is found to be Reynolds number regime dependent; at Re = 100 the drag decreases linearly with rotation rate and at Re = 10,000, the relationship is non-linear. This nonlinearity appears to be due to the interaction between vortex shedding from the small control cylinders (which does not occur at Re = 100) and the main cylinder wake. Computational two-dimensional viscous simulations are consistent with the physical experiment and help to illustrate the phenomenon. Finally, the power consumed by the active control mechanism is considered and estimated to be significantly smaller than the power savings in reduced drag. / by .James Crandall Schulmeister / S.M.in Ocean Engineering

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2003. / Includes bibliographical references (p. 115-120). / by Justin Matthew Verdirame. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 107-115). / Heat transfer at the scales of atoms plays an important role in many applications such as thermoelectric energy conversion and thermal management of microelectronic devices. While nanoengineering offers unique opportunities to manipulate heat to our advantages, it also imposes challenges on the fundamental understanding of nanoscale heat transfer. As the characteristic lengths of the system size become comparable to the mean free paths of heat carriers, macroscopic theories based on heat diffusion are no longer valid due to size effects. Atomistic level simulation can provide powerful insights into the microscopic processes governing heat conduction, and is the focus of this thesis. In this thesis, we first introduce atomistic techniques to investigate phonon transport in bulk crystals. We start with normal mode analysis within the classical molecular dynamics framework to estimate the spectral phonon transport properties. Although it can provide the detailed phonon properties adequately, classical molecular dynamics with empirical potentials do not always yield accurate predictions. Then, we move to first-principles density functional theory (DFT) to compute mode-dependent phonon properties. Such simulations can well reproduce experimental values of phonon dispersion and thermal conductivity with no adjustable parameters, establishing confidence that such an approach can provide reliable information about the microscopic processes. These detailed calculations not only unveil which phonon modes are responsible for heat conduction in bulk crystals, but also expand our fundamental understanding of phonon transport, such as the importance of optical phonons. Next, we study thermal transport across single and multiple interfaces via the atomistic Green's function method, especially the impact of interface roughness on phonon transmission across a single interface and coherent phonon transport in superlattices. Both the DFT and Green's function techniques provide fundamental parameters that then can be used to understand mesoscale transport. This paves the way for multiscale modeling from first-principles. Through these multiscale modeling efforts, we are able to obtain a comprehensive understanding of heat transfer from the atomistic to the macroscale, with important implications for energy applications. Complementary to the theoretical work, we measure the interface thermal conductance using ultrafast time-domain thermoreflectance experiments, examining thermal transport across solid-liquid interfaces modified by self-assembled monolayers. We find that an extra molecular layer can enhance the thermal transport across solid-liquid interfaces. In summary, theoretical, computational and theoretical approaches have been applied to study heat transfer at the atomistic level. The findings from this thesis have improved our fundamental understanding of phonon transport properties with important implications for energy applications and beyond, and build a foundation for multiscale simulation of phonon heat conduction at the mesoscale. / by Zhiting Tian. / Ph. D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2017. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 44). / Flow chemistry is an emerging approach to chemical synthesis in which chemical processes are performed on reactants as they continuously flow through reactors. In order to drive such flows, low flow rate, high pressure pumps are used. The standard pump in use is the displacement pump. However, it tends to be expensive and produces a discontinuous flow. The goal of this investigation is to prototype a miniature multistage centrifugal pump and assess whether or not such pumps can perform in flow chemistry applications in the place of displacement pumps. This thesis explores the design features implemented in the development of this pump and how they contributed to its performance as pertaining to use in flow chemistry. Specifically, the pump was designed to be comprised of modularly stackable pump stages and to be thermochemically stable, operating without the use of dynamic seals. Ultimately, the device designed succeeded in being modularly stackable and in operating without dynamic seals. However, the target pressure rise per stage was not fully met. Moreover, testing of the pump revealed a high sensitivity in flow rate to changes in generated pressure head. Thus, it is not yet deemed a viable alternative to the current standard of displacement pumps. / by Brian Yue. / S.B.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1993. / GRSN 642876 / Chart, 61 x 94 cm. folded to 23 x 20 cm., in pocket following text. / Includes bibliographical references (leaves 251-256). / by Don J. Lee. / M.S.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 140-142). / This thesis presents the design, modeling, fabrication and experimental validation of an active precision fixturing system called the Hybrid Positioning Fixture (HPF). The HPF uses the principles of exact constraint, combined with principles and means of Nanomanipulation to fixture components with tens of nanometer accuracy and repeatability. Achieving this level of performance requires addressing three fundamental limitations of precision fixtures; (1) Elimination of stiction via integrated compliance, (2) Integration of sensors and actuators to enable correction of systematic and time variable alignment errors, and (3) Improvement of fixture contacts' stability and longevity via hard coatings. Conceptual and analytic models are developed for the integration of compliant elements, sensors and actuators within the fixture. The validity of these concepts/models is tested via a prototype HPF. Analytic models and design rules are provided to guide designers in the use of thin coatings for precision fixture contacts. These are based upon non-linear finite element analysis. The effects of hard and soft interlayer, which reduce coating stresses and improve coating adherence, are also analyzed. The performance of the HPF is measured in two modes, passive (constant voltage supplied to piezoelectric actuators) and active (actuators supplied with different input voltages). The HPF is shown to be capable of 3 [sigma], passive repeatability of 100nm in x, y, and repeatability of 2 [mu] radian in [theta]x, [theta]y and [theta]z. Active tests indicate that the HPF is capable of accuracy of better than 5nm. / (cont.) The fixture is shown to have a load capacity of 450 N and stiffness of 7N/[mu]m. The combination of nanometer-level accuracy, repeatability and high load capacity make the HPF suitable for a range of current and emerging applications such as photonics packaging, mask to wafer alignment, nanomanufacturing, nano-scale research experiments and automated transfer lines. / by Kartik Mangudi Varadarajan. / S.M.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1996. / Includes bibliographical references (p. 103-104). / by Murat Erentürk. / M.S.

Thesis (M.S.) Massachusetts Institute of Technology. Dept. of Mechanical Engineering, 1947. / Bibliography: leaves A1-A2. / by Charles Oliver Smith. / M.S.