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.

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.

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.

Sports Engineering Program at UCD

The University of Colorado Denver (UCD) has taken the leadership role with the first Sports Engineering Program in the United States. Sports Engineering is an exciting new area of emphasis for graduate degrees in engineering. This educational program is offered through cooperation between the downtown Denver College of Engineering and Applied Science and the Anschutz Medical Campus, both part of the University of Colorado Denver. This program is showing great promise for high enrollments and exciting research opportunities working with the sports equipment manufacturers, the athletes, and the sports medicine community.

Numerical Study of Cavitation Characteristics of Profiles for Use in Marine Current Turbines

Kinetic energy in the oceans offers an important and promising source of renewable energy which can be exploited by marine current turbines (MCT). One of the key issues related with design of MCT’s is the cavitation inception along turbine blades. Cavitation occurrence in MCT’s blades generates erosion and poor power performance with similar effect in the hydraulic turbine case. In this work, a numerical investigation using the vorticity–stream function code XFOIL in order to study cavitation characteristics in NACA 4 series profiles was performed. The study was developed systematically starting from NACA 4415 profiles and varying independently camber percentage, camber position and thickness. Other study carried out was the effect of trailing edge deflection in the cavitation bucket. Results show a symmetrical increment in cavitation free zone for profiles with increasing thickness. Also for camber increment, the cavitation free zone is incremented, especially at high angles of attack. For variation of camber percentage, increasing camber produces the cavitation bucket moves to high lift zone which suggest that the profile could cavitate at low and negative Cl in wide range of cavitation numbers. Finally the effect of trailing edge deflection produces a slight increment in cavitation free zone which is similar to the effect of camber increment. Also, the trailing edge deflection shows that a same Cl can be achieved with lower angle of attack and lower pressure coefficient compared with the standard profile, constituting a desired behavior from the cavitation point of view. Finally, local dimensionless correlations were developed which can be used for parametric studies of cavitation performance of MCT’s in the design stage.

Exploring the Water/Energy Nexus: Developing a Unified Approach to Water and Energy Issues in California

Metropolitan Water District (Metropolitan) is a public agency charged with providing its service area with adequate and sufficient supplies of high quality water. Metropolitan was incorporated in 1928 by an Act of the California Legislature to serve its 13 original founding Member Agencies. Today, Metropolitan provides water to 26 cities and water agencies serving more than 19 million people in six counties in Southern California. On average Metropolitan delivers 1.7 billion gallons of water per day. California, the third-largest state in the U.S. by land area, has a diverse geography including foggy coastal areas, alpine mountain ranges, hot and arid deserts, and a fertile central valley. California is also the most populous state, exceeding 37 million people in 2010. California’s large population drives the interlinked demands for water and energy in the state. The water-energy nexus in California is highlighted by the fact that two-thirds of the population resides in Southern California while two-thirds of the state’s precipitation occurs in Northern California. Separating Southern California from the rest of the state is a series of east-west trending mountain ranges. Water conveyance projects have been constructed to address this north-south water imbalance and to also import supplies from the Colorado River, hundreds of miles east of Southern California population centers. The movement of water on this scale requires significant energy resources. The California Energy Commission (CEC) estimates that water-related energy use consumes 19% of the state’s electricity and 30% of its natural gas usage every year, and demand is growing. Energy management is a critical concern to Metropolitan and other California water agencies. These issues drive water and energy leaders to jointly manage energy and water use to ensure long-term mutual benefits.