Aerodynamic performance measurements of a fully scaled, film-coated, turbine stage

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1999.Includes bibliographical references (p. 147-148).The MIT Blowdown Turbine short duration test facility was used to experimentally measure the aerodynamic performance of a film-cooled turbine stage. Turbine torque, speed, mass flow, temperature, and pressure were measured and used to calculate efficiency. Pressure ratio, corrected speed, and coolant mass flow were varied parametrically over a range of conditions and compared to a baseline. No distinct trend was seen in the pressure ratio tests. Efficiency increased approximately 2.2% with a corrected speed increase of 20%. This trend is a result of a corresponding decrease in blade loading. An efficiency decrease of 2% was shown for a two-fold increase in coolant mass flow. A preliminary comparison to a previous uncooled test series showed a 2% decrease in efficiency with a 12% coolant-to-mainstream mass flow ratio. To complete these tests, an uncooled turbine configuration was modified to a film-cooled configuration. A solid blade and nozzle guide vane set was machined via electro-discharge machining, laser drilling, and laser welding to provide film-cooling holes and manifold channels. The effective area (CdA) of the film-cooling holes was measured and part-to-part variations quantified. A coolant feed system was constructed to provide coolant flow to the turbine. Flow to the rotor blades, nozzle guide vanes, and tip casing was metered and controlled independently. Thick walled, squared edged, choked orifices were used. A set of experiments were performed to show that supersaturated coolant flow could be adequately controlled by this method.by Christopher M. Spadaccini.S.M

Polytope Sector-Based Synthesis and Analysis of Microstructural Architectures With Tunable Thermal Conductivity and Expansion

The aim of this paper is to (1) introduce an approach, called polytope sector-based synthesis (PSS), for synthesizing 2D or 3D microstructural architectures that exhibit a desired bulk-property directionality (e.g., isotropic, cubic, orthotropic, etc.), and (2) provide general analytical methods that can be used to rapidly optimize the geometric parameters of these architectures such that they achieve a desired combination of bulk thermal conductivity and thermal expansion properties. Although the methods introduced can be applied to general beam-based microstructural architectures, we demonstrate their utility in the context of an architecture that can be tuned to achieve a large range of extreme thermal expansion coefficients—positive, zero, and negative. The material-property-combination region that can be achieved by this architecture is determined within an Ashby-material-property plot of thermal expansion versus thermal conductivity using the analytical methods introduced. These methods are verified using finite-element analysis (FEA) and both 2D and 3D versions of the design have been fabricated using projection microstereolithography.United States. Defense Advanced Research Projects Agency. Materials with Controlled Microstructural Architectures Progra

One-step volumetric additive manufacturing of complex polymer structures.

Two limitations of additive manufacturing methods that arise from layer-based fabrication are slow speed and geometric constraints (which include poor surface quality). Both limitations are overcome in the work reported here, introducing a new volumetric additive fabrication paradigm that produces photopolymer structures with complex nonperiodic three-dimensional geometries on a time scale of seconds. We implement this approach using holographic patterning of light fields, demonstrate the fabrication of a variety of structures, and study the properties of the light patterns and photosensitive resins required for this fabrication approach. The results indicate that low-absorbing resins containing ~0.1% photoinitiator, illuminated at modest powers (~10 to 100 mW), may be successfully used to build full structures in ~1 to 10 s

Lightweight Mechanical Metamaterials with Tunable Negative Thermal Expansion

Ice floating on water is a great manifestation of negative thermal expansion (NTE) in nature. The limited examples of natural materials possessing NTE have stimulated research on engineered structures. Previous studies on NTE structures were mostly focused on theoretical design with limited experimental demonstration in two-dimensional planar geometries. In this work, aided with multimaterial projection microstereolithography, we experimentally fabricate lightweight multimaterial lattices that exhibit significant negative thermal expansion in three directions and over a temperature range of 170 degrees. Such NTE is induced by the structural interaction of material components with distinct thermal expansion coefficients. The NTE can be tuned over a large range by varying the thermal expansion coefficient difference between constituent beams and geometrical arrangements. Our experimental results match qualitatively with a simple scaling law and quantitatively with computational models.United States. Defense Advanced Research Projects Agency. Materials with Controlled Microstructural Architectures ProgramLawrence Livermore National Laboratory (Award DE-AC52-07NA27344 (LLNL-JRNL-697779))SUTD-MIT Postdoctoral Progra

Field responsive mechanical metamaterials.

Typically, mechanical metamaterial properties are programmed and set when the architecture is designed and constructed, and do not change in response to shifting environmental conditions or application requirements. We present a new class of architected materials called field responsive mechanical metamaterials (FRMMs) that exhibit dynamic control and on-the-fly tunability enabled by careful design and selection of both material composition and architecture. To demonstrate the FRMM concept, we print complex structures composed of polymeric tubes infilled with magnetorheological fluid suspensions. Modulating remotely applied magnetic fields results in rapid, reversible, and sizable changes of the effective stiffness of our metamaterial motifs

Microcapsules for carbon capture from power plants

Microencapsulation has typically been applied to small volume, high value applications like pharmaceuticals and cosmetics. However, the efficient separations and reactions afforded by microcapsules can also be applied to large-scale problems like clean energy. This research focuses on developing microcapsules for energy applications, particularly carbon capture and storage. Please click Additional Files below to see the full abstract

Ultralight, ultrastiff mechanical metamaterials

The mechanical properties of ordinary materials degrade substantially with reduced density because their structural elements bend under applied load. We report a class of microarchitected materials that maintain a nearly constant stiffness per unit mass density, even at ultralow density. This performance derives from a network of nearly isotropic microscale unit cells with high structural connectivity and nanoscale features, whose structural members are designed to carry loads in tension or compression. Production of these microlattices, with polymers, metals, or ceramics as constituent materials, is made possible by projection microstereolithography (an additive micromanufacturing technique) combined with nanoscale coating and postprocessing. We found that these materials exhibit ultrastiff properties across more than three orders of magnitude in density, regardless of the constituent material

Evaluation of the Influenza A Replicon for Transient Expression of Recombinant Proteins in Mammalian Cells

Recombinant protein expression in mammalian cells has become a very important technique over the last twenty years. It is mainly used for production of complex proteins for biopharmaceutical applications. Transient recombinant protein expression is a possible strategy to produce high quality material for preclinical trials within days. Viral replicon based expression systems have been established over the years and are ideal for transient protein expression. In this study we describe the evaluation of an influenza A replicon for the expression of recombinant proteins. We investigated transfection and expression levels in HEK-293 cells with EGFP and firefly luciferase as reporter proteins. Furthermore, we studied the influence of different influenza non-coding regions and temperature optima for protein expression as well. Additionally, we exploited the viral replication machinery for the expression of an antiviral protein, the human monoclonal anti-HIV-gp41 antibody 3D6. Finally we could demonstrate that the expression of a single secreted protein, an antibody light chain, by the influenza replicon, resulted in fivefold higher expression levels compared to the usually used CMV promoter based expression. We emphasize that the influenza A replicon system is feasible for high level expression of complex proteins in mammalian cells

Combustion systems for power-microelectromechanical systems applications

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, June 2004."February 2004."Includes bibliographical references (p. 261-270).As part of an effort to develop a micro-scale gas turbine engine for power generation and micro-propulsion applications, this thesis presents the design, fabrication, experimental testing, and modeling of the combustion system. Two fundamentally different combustion systems are presented; an advanced homogenous gas-phase microcombustor and a heterogeneous catalytic microcombustor. An advanced gas-phase microcombustor consisting of a primary and dilution-zone configuration is discussed and compared to a single-zone combustor arrangement. The device was micromachined from silicon using Deep Reactive Ion Etching (DRIE) and aligned fusion wafer bonding. The maximum power density achieved in the 191 mm³ device approached 1400 MW/m³ with hydrogen-air mixtures. Exit gas temperatures in excess of 1600 K and efficiencies over 90% were attained. For the same equivalence ratio and overall efficiency, the dual-zone microcombustor reached power densities nearly double that of the single zone configuration. With more practical hydrocarbon fuels such as propane and ethylene, the device performed poorly due to significantly longer reaction time-scales and inadequate fuel-air mixing achieving maximum power densities of only 150 MW/m³. Unlike large-scale combustors, the performance of the gas-phase microcombustors was more severely limited by heat transfer and chemical kinetics constraints. Using all available gas-phase microcombustor data, an empirically-based design tool was developed, important design trades identified, and recommendations for future designs presented. Surface catalysis was identified as a possible means of obtaining higher power densities with storable hydrocarbon fuels by increasing reaction rates. Microcombustors with a similar(cont.) geometry to the gas-phase devices were fitted with platinum coated foam materials of various porosity and surface area. For near stoichiometric propane-air mixtures, exit gas temperatures approaching 1100 K were achieved at mass flow rates in excess of 0.35 g/s. This corresponds to a power density of approximately 1200 MW/m³; an 8.5-fold increase over the maximum power density achieved for gas-phase propane-air combustion. Low order models including simple time-scale analyses and a one-dimensional steady-state plug flow reactor model, were developed to elucidate the underlying physics and to identify important design parameters. High power density catalytic microcombustors were found to be limited by the diffusion of fuel species to the active surface, while substrate porosity and surface area-to-volume ratio were the dominant design variables. Experiments and modeling suggest that with adequate thermal management, power densities in excess of 1500 MW/m³ and efficiencies over 90% are possible within the microengine pressure loss constraint and the material limits of the catalyst. A materials characterization study of the catalyst and its substrate revealed that metal diffusion and catalyst agglomeration were likely failure modes.by Christopher M. Spadaccini.Ph.D