Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. / Includes bibliographical references (leaves 55-57). / Laser interactions with metals involve absorption of photon energy by electrons, energy coupling between electrons and the lattice, and energy transport by diffusion of electrons and lattice vibrations. During picosecond laser irradiation of metal films, electrons and the lattice are not in thermal equilibrium. On the other hand, rapid laser heating produces a large degree of superheating and undercooling during melting and solidification. First, this work investigates experimentally non-equilibrium heating processes during intense picosecond laser heating of metal films. Results show excellent agreement with predictions of the two-step radiation heating model. Second, this work develops a general model to characterize both non-equilibrium energy deposition and phase change processes. The predictions show that the non-equilibrium heating processes significantly increase the laser melting threshold, enlarge the thermal-affected region, reduce the lattice temperature rise, prolong the phase change duration, and reduce the solidification speed. These results are important for materials processing using ultrashort pulsed lasers. / by Long-Sheng Kuo. / S.M.

Thesis: Nav. E., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 123-124). / Previous research has shown that porous, hydrophobic surfaces exhibit a dramatic reduction in critical heat flux (CHF), the amount of heat over a surface area required to initiate film boiling. Film boiling is characterized by the presence of a vapor layer which remains as long as the surface temperature stays above the Leidenfrost point. This vapor layer has poor heat transfer characteristics but has the potential to reduce drag by acting as a buffer between the solid surface and the liquid. The goals of this research were to quantify the drag reduction due to film boiling, examine the durability of the coating and explore the feasibility of this concept for application to a torpedo. A torpedo was chosen due to its high speed and reduced emphasis on durability, since it is only used operationally once. A hydrophobic coating was created in the laboratory using a layer-by-layer (LBL) process and its performance was compared to that of a commercial hydrophobic coating. Drop tests of uncoated and hydrophobic aluminum torpedo models were conducted in a custom-built apparatus housing a water column and a furnace, and recorded with a high-speed video camera in order to measure position versus time. Terminal velocity was extrapolated from the data and used to calculate drag coefficients. The data from this set of experiments showed that film boiling increased average terminal velocity by 23%, which corresponded to a 32% reduction in the drag coefficient. / by Ian J. Campbell. / Nav. E. / S.M.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 69-70). / Boiling is a widely used heat transfer process in industry that allows for high heat transfer with a small temperature gradient. In this study the effects of two homologous series of surfactants (trimethylammonium bromide (TAB) and methylglucamine (MEGA)) on the boiling curve of water were explored. Heat transfer vs. temperature plots were obtained for five surfactants for various concentrations under the cricical micelle concentration (CMC). Plots of temperature vs concentration for specific heat fluxes showed the lowering of the superheat that improves heat transfer when surfactants were added, resulting in an overall left shift of the boiling curve. The shifting that occurs at low concentrations of surfactant seem correlated with the diffusion coefficients of the different surfactants. The large shifting that occurs at larger concentrations is correlated with the hydrophobic tail length of each of the surfactants. This supports the hypothesis that the lowering of the dynamic surface tension, which correlates with the diffusion coefficient, is responsible for part of the lowering of the superheat. The fact that the larger shifting is correlated with the hydrophobic tail length supports the hypothesis that part of the shifting occurs due to the surfactants adsorbing onto the surface, making it more hydrophobic, increasing the contact angle, and decreasing the nucleation energy. The results of this work add to the understanding of the effects surfactants have on the boiling of water and give engineers more tools to adjust heat. / by Darci Janelle Reed. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015. / Cataloged from PDF version of thesis. / Includes bibliographical references (page 18). / Heat build-up in prosthetic sockets is a significant problem experienced by many amputees in America, with no central solution in sight. Heat and discomfort accounts for over 70% of problems experienced by lower limb amputees in America. Although there have been advances in prosthetics in the active-power knees and ankles, not even cybernetics can improve the comfort of the prosthesis if there is still a socket. The materials in prosthetic sockets are not conductive enough to relieve the heat inside of the socket. The purpose of this study is to model the temperature variance and heat transfer of an amputee's residual limb and design ways to improve current prosthetic socket technologies. With the addition of small holes, or perforations, in the socket, there will be an increase in the heat transfer by convection, while still maintaining the strength of a carbon fiber prosthesis. Through the use of discrete approximation modeling, the transient temperature inside of the socket layers can be identified and improved through design patterns cut into the socket. Increased heat transfer can be observed as the perforations in the socket become larger, although the larger the holes, the larger the stresses are in the prosthesis. Non-intrusive designs were developed for sockets before and after they are made to increase convection surface area. More modeling needs to be done in 3-dimensional polar coordinates. / by Luis Carbajal. / S.B.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005. / Includes bibliographical references (p. 51-56). / It is widely recognized that fluid shearing forces acting on endothelial cells (ECs) have a profound effect on EC morphology, structure and function. Recent investigations in vivo have indicated the presence of a thick endothelial surface layer, also called the glycocalyx, with an estimated thickness on the scale of 0.5 pm, which restricts the flow of plasma and can exclude red blood cells and some macromolecular solutes. Based on our current understanding of signal transduction, we expect that the glycocalyx plays an essential role as a possible mechanotransducer of fluid shear stress to the actin cytoskeleton of the endothelial cells. We examined whether removing the glycocalyx can affect shear-induced cellular response, e.g. cell migration speed and wound edge healing. More specifically, we compared the two major components of the glycosaminoglycans in the glycocalyx, which are heparan sulfate GAGs and chondroitin sulafte GAGs. Our results showed that the removal of heparan sulfate GAGs has a much greater impact on the shear induced response compared to chondroitin sulfate GAGs, and the short term crawling speed response is highly suppressed in the first case. Therefore, it is highly possible that heparan sulfate GAGs is involved in the shear-induced signaling pathway. / by Yu Yao. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1997. / Includes bibliographical references (leaves 230-241). / by Upendra V. Ummenthala. / Ph.D.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1998. / Includes bibliographical references (leaf 105). / by David C. Roberts. / M.S.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1934. / MIT Institute Archives copy bound with: Thompson, Ransom S. and Sylvester, Edmund Q. Current trend in automotive engine design (1934). MICROFICHE COPY AVAILABLE. / by Lorimer C. West. / B.S.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1987. / Bibliography: leaves 136-139. / by Nazareth Sarkis Bedrossian. / M.S.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006. / Includes bibliographical references (leaves 49-50). / InFocus is a worldwide leader in the digital display market. Despite its success in sales, the company posted a net loss in profit in year 2005. The major reasons are its high operating cost and high inventory level. After reviewing its reverse logistics system, we found that current policy to process the returned product does not reap the maximum amount of profit from returns. We proposed to add a new channel to process the product returns. An optimum inventory policy was also developed to maximize the profit. An alternative distribution channel of the service parts was suggested which can cut down the inventory level and reduce the operating cost. / by Yi Wu. / M.Eng.