Enhanced Air-Gap Control for High-Speed Plasmonic Lithography Using Solid Immersion Lens With Sharp-Ridge Nanoaperture

Recently, plasmonic nanolithography is studied by many researchers (1, 2 and 3). This presented a low-cost and high-throughput approach to maskless nanolithography technique that uses a metallic sharp-ridge nanoaperture with a high strong nanometer-sized optical spot induced by surface plasmon resonance. However, these nanometer-scale spots generated by metallic nanoapertures are formed in only the near-field region, which makes it very difficult to pattern above the photoresist surface at high-speeds.

Performance of a Turbine Driven by a Pulsed Detonation Combustor

There is longstanding government and industry interest in pressure-gain combustion for use in Brayton cycle-based engines. Theoretically, pressure-gain combustion allows heat addition with reduced entropy loss. The pulsed detonation combustor (PDC) is a device that can provide such pressure-gain combustion and possibly replace the typical steady deflagration combustor. The PDC is inherently unsteady, however, and comparisons with steady deflagration combustors must be based upon time-integrated performance variables. In this study, the radial turbine of a Garrett automotive turbocharger was coupled directly to and driven, full admission, by a hydrogen-fueled PDC fueled. Data included pulsed-cycle time histories of turbine inlet and exit temperature, pressure, velocity, mass flow, and enthalpy. The unsteady inlet flowfield showed momentary reverse flow, and thus unsteady accumulation and expulsion of mass and enthalpy within the device. The coupled turbine-driven compressor provided a time-resolved measure of turbine power. Duty cycle increased with PDC frequency. Power and cycle-average specific work increased with PDC frequency and fill fraction.

Implementation of Brackish Groundwater Desalination Using Wind-Generated Electricity as a Proxy for Energy Storage: A Case Study of the Energy-Water Nexus in Texas

With a push toward renewable electricity generation, wind power has grown substantially in recent U.S. history and technologies continue to improve. However, the intermittency associated with wind-generated electricity without storage has limited the amounts sold on the grid. Furthermore, continental wind farms have a diurnal and seasonal variability that is mismatched with demand. To increase the broader use of wind power technologies, the development of systems that can operate intermittently during off-peak hours must be considered. Utilization of wind-generated electricity for desalination of brackish groundwater presents opportunities to increase use of a low-carbon energy source and supply alternative drinking water that is much needed in some areas. As existing water supplies dwindle and population grows, cities are looking for new water sources. Desalination of brackish groundwater provides one potential water source for inland cities. However, this process is energy-intensive, and therefore potentially incongruous with goals of reducing carbon emissions. Desalination using reverse osmosis is a high-value process that does not require continuous operation and therefore could utilize variable wind power. That is, performing desalination in an intermittent way to match wind supply can help mitigate the challenges of integrating wind into the grid while transforming a low-value product (brackish water and intermittent power) into a high-value product (treated drinking water). This option represents a potentially more economic form of mitigating wind variability than current electricity storage technologies. Also, clean energy and carbon policies under consideration by the U.S. Congress could help make this integration more economically feasible due to incentives for low-carbon energy sources. West Texas is well-suited for desalination of brackish groundwater using wind power, as both resources are abundant and co-located. Utility-scale wind resource potential is found in most of the region. Additionally, brackish groundwater is found at depths less than 150 m, making west Texas a useful geographic testbed to analyze for this work, with applicability for areas with similar climates and water supply scarcity. Implementation of a wind-powered desalination project requires both economic and geographic feasibility. Capital and operating cost data for wind turbines and desalination membranes were used to perform a thermoeconomic analysis to determine the economic feasibility. The availability of wind and brackish groundwater resources were modeled using geographic information systems tools to illustrate areas where implementation of a wind-powered desalination project is economically feasible. Areas with major populations were analyzed further in the context of existing and alternative water supplies. Utilization of wind-generated electricity for desalination presents a feasible alternative to energy storage methods. Efficiency, economics, and ease of development and operation of off-peak water treatment were compared to different energy storage technologies: pumped hydro, batteries, and compressed air energy storage. Further economics of compressed air energy storage and brackish groundwater desalination were examined with a levelized lifetime cost approach. Implementation of water desalination projects using wind-generated electricity might become essential in communities with wind and brackish groundwater resources that are facing water quality and quantity issues and as desires to implement low carbon energy sources increase. This analysis assesses the economic and geographic feasibility and tradeoffs of such projects for areas in Texas.

Optimization Design of an Axial-Flow Fan Used in Local Ventilation in Mining Industry

In a world where the increasing demand on developing energy-efficient systems is probably the most stringent design constraint, the trend in engineering research in recent years has been to optimize the existing technologies rather than to implement new ones. The present work addresses a robust axial-type fan design technique developed using an optimization technique. A fan is indispensable equipment for primary and local ventilation in mining industries. We always pursue the fan with high working efficiency and low noise. In this paper, an optimization method is developed to improve the pneumatic properties of the fan based on the blade element theory. A new type of fan used in local ventilation is designed with the help of computer. It is shown that the new design enhanced the efficient up to 88%. Numerical analysis is also conducted to validate the optimization design results.

Progressive Clearance Labyrinth Seal for Turbo-Machinery Applications

Turbomachinery sealing is a challenging problem due to the varying clearances caused by thermal transients, vibrations, bearing lift-off etc. Leakage reduction has significant benefits in improving engine efficiency and reducing emissions. Conventional labyrinth seals have to be assembled with large clearances to avoid rubbing during large rotor transients. This results in large leakage and lower efficiency. In this paper, we propose a novel Progressive Clearance Labyrinth Seal that is capable of providing passive fluidic feedback forces that balance at a small tip-clearance. A modified packing ring is supported on flexures and employs progressively tighter teeth from the upstream to the downstream direction. When the tip-clearance reduces below the equilibrium clearance, fluidic feedback forces cause the packing ring to open. Conversely, when the tip-clearance increases above the equilibrium clearance, the fluidic feedback forces cause the packing ring to close. Due to this self-correcting behavior, the seal provides high differential pressure capability, low leakage and non-contact operation even in the presence of large rotor transients. Theoretical models for the feedback phenomenon have been developed and validated by experimental results.

Polymer Heat Exchangers: An Enabling Technology for Water and Energy Savings

Polymer heat exchangers (PHXs), using thermally-enhanced composites, constitute a “disruptive” thermal technology that can lead to significant water and energy savings in the thermoelectric energy sector. This paper reviews current trends in electricity generation, water use, and the inextricable relationship between the two trends in order to identify the possible role of PHXs in seawater cooling applications. The use of once-through seawater cooling as a replacement for freshwater recirculating systems is identified as a viable way to reduce the use of freshwater and to increase power plant efficiency. The widespread use of seawater as a coolant can be made possible by the favorable qualities of thermally-enhanced polymer composites: good corrosion resistance, higher thermal conductivities, higher strengths, low embodied energy and good manufacturability. The authors use several seawater cooling case studies to explore the potential water and energy savings made possible by the use of PHX technology. The results from three case studies suggest that heat exchangers made with thermally enhanced polymer composites require less energy input over their lifetime than corrosion resistant metals, which generally have much higher embodied energy than polymers and polymers composites. Also, the use of seawater can significantly reduce the use of freshwater as a coolant, given the inordinate amounts of water required for even a 1MW heat exchanger.

Studies on Downstream Stator With Rotor Re-Staggering and Forward Sweeping in a Subsonic Axial Compressor Stage

The present numerical work studies the flow field in subsonic axial compressor stator passages for: (a) preceding rotor sweep (b) preceding rotor re-staggering (three stagger angle changes: 0°, +3° and +5°); and (c) stator sweeping (two 20° forward sweep schemes). The following are the motives for the study: at the off-design conditions, compressor rotors are re-staggered to alleviate the stage mismatching by adjusting the rows to the operating flow incidence. Fundamental to this is the understanding of the effects of rotor re-staggering on the downstream component. Secondly, sweeping the rotor stages alters the axial distance between the successive rotor-stator stages and necessitates that the stator vanes must also be swept. To the best of the author’s knowledge, stator sweeping to suit such scenarios has not been reported. The computational model for the study utilizes well resolved hexahedral grids. A commercial CFD package ANSYS® CFX 11.0 was used with standard k-ω turbulence model for the simulations. CFD results were well validated with experiments. The following observations were made: (1) When the rotor passage is closed by re-staggering, with the same mass flow rate and the same stator passage area, stators were subjected to negative incidences. (2) Effect of stator sweeping on the upstream rotor flow field is insignificant. Comparison of total pressure rise carried by the downstream stators suggests that an appropriate redesign of stator is essential to match with the swept rotors. (3) While sweeping the stator is not recommended, axial sweeping is preferable over true sweeping when it is necessary.

Energy Efficient Strategies and Renewable Energy Technologies for Desalination

Energy is often the most significant factor in the affordability and sustainability of treating various different source waters with reverse osmosis membrane facilities. More than 33% of the cost to produce water using reverse osmosis (RO) technology is attributed to electrical demands. The largest energy-consuming component of the overall treatment are the high pressure pumps required to feed water to the process. Because of the high energy burden and production of greenhouse gas (GHG) emissions, renewable energy is being increasingly considered for desalination projects. The selection of the appropriate renewable energy resource depends on several factors, including plant size, feed water salinity, remoteness, availability of grid electricity, technical infrastructure, and the type and potential of the local renewable energy resource. The cost of desalination with renewable energy resources, as opposed to desalination with conventional energy sources, can be an important alternative to consider when reduced environmental impact and lower gas emissions are required. Considering the proposed climate protection targets that have been set and the strong environmental drivers for lowered energy usage, future water desalination and advanced water treatment systems around the world could be increasingly powered by renewable energy resources. In addition to renewables, energy optimization/minimization is deemed critical to desalting resource management. Methods employed include enhanced system design, high efficiency pumping, energy recovery devices and use of advanced membrane materials.

Passive Morphing Airfoil With Honeycombs

A passive morphing may improve the aerodynamic characteristics through structural shape change by aerodynamic loads during the flight, resulting in improving fuel efficiency. The passive morphing structure should have a capability to be highly deformed while maintaining a sufficient stiffness in bending. Honeycombs may be good for controlling both stiffness and flexibility. This paper investigates a honeycomb airfoil’s static deformations through the fluid-structure interaction using computational fluid dynamics and structural finite element analysis. The structural performance will be investigated with varying honeycomb geometries including regular, auxetic and chiral meso-structures.

Thermal Performance Evaluation of Seawater Cooling Towers

Seawater has been used for long time as a cooling fluid in heat exchangers to reduce fresh water usage in industry and power plants. The thermophysical properties of seawater are different from those of fresh water due to the salt content or salinity. This difference is sufficient to affect the heat and mass transfer processes which in turn change the thermal performance. Thermal design of fresh water cooling towers is described in detail in many textbooks and handbooks. However, only a rule of thumb is frequently used for designing of seawater cooling towers. This rule recommends degrading the tower performance by approximately 1% for every 10,000 ppm of salts in the feed water. In this paper, the thermal performance of seawater cooling towers is presented using a detailed model of counterflow wet cooling towers which takes into consideration the coupled simultaneous heat and mass transfer processes and uses state-of-the-art seawater properties from the literature. The model governing equations are solved numerically and the validity of this model is checked using new experimental data that has been measured using a bench top counterflow seawater cooling tower. The effect of the variation of seawater salinity as well as other operating conditions on the effectiveness and Merkel number is investigated.