Reynolds Number Effects on the Freewheeling Behavior of a High Solidity Vertical River Kinetic Turbine

A four-bladed, squirrel-cage, and scaled vertical kinetic turbine was designed, instrumented and tested in the water tunnel facilities at the University of Manitoba. With a solidity of 1.3 and NACA0021 blade profile, the turbine is classified as a high solidity model. Results were obtained for conditions during freewheeling at various Reynolds numbers. In this study, the freewheeling tip speed ratio, which relates the ratio of maximum blade speed to the free stream velocity at no load, was divided into three regions based on the Reynolds number. At low Reynolds numbers, the tip speed ratio was lower than unity and blades were in a stall condition. At the end of the first region, there was a sharp increase of the tip speed ratio so the second region has a tip speed ratio significantly higher than unity. In this region, the tip speed ratio increases almost linearly with Reynolds number. At high Reynolds numbers, the tip speed ratio is almost independent of Reynolds number in the third region. It should be noted that the transition between these three regions is a function of the blade profile and solidity. However, the three-region behavior is applicable to turbines with different profiles and solidities.

Thermal Conductivity Prediction for Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve a higher working temperature and thus lead to a better efficiency. Yttria-Stabilized-Zirconia (YSZ), a material with low thermal conductivity, is commonly used as the TBC top coat to provide the thermal barrier effect. In this paper, an analytical model is proposed to estimate the effective thermal conductivity of the TBCs based on the microstructures. This model includes the micro structure details, such as grain size, pore size, volume fraction of pores, and the interfacial resistance. To validate the model, two sets of TBC samples were fabricated and tested for thermal conductivity and associated microstructures. The first set of samples were disk shaped YSZ-Al2O3 samples fabricated using a pressing machine. The YSZ-Al2O3 powder mixture was 0, 1, 2, 3, 4 and 5 wt% Al2O3/YSZ powder ratio. The second set of samples were fabricated by Atmospheric Plasma Spray process for two different microstructure configurations, standard (STD) and vertically cracked (VC), at two different thicknesses, 400 and 700 urn respectively. A laser flash system was used to measure the thermal conductivity of the coatings. Experiments were performed over the temperature range from 100°C to 800°C. The porosity of the YSZ samples was measured using a mercury porosimetry analyzer, POREMASTER 33 system. A Scanning Electron Microscope (SEM) was used to study the microstructure of the samples. It is observed that the microstructure and the porosity are directly linked with the thermal conductivity values. The relationship of the properties to the real microstructure determines the validity of the proposed model.

Power Generation for the Near Future

As society continues advancing into the future, more energy is required to supply the increasing population and energy demands. Unfortunately, traditional forms of energy production through the burning of carbon-based fuels are dumping harmful pollutants into the environment, resulting in detrimental, and possibly irreversible, effects on our planet. The burning of coal and fossil fuels provides energy at the least monetary cost for countries like the US, but the price being paid through their negative impact of our atmosphere is difficult to quantify. A rapid shift to clean, alternative energy sources is critical in order to reduce the amount of greenhouse gas emissions. For alternative energy sources to replace traditional energy sources that produce greenhouse gases, they must be capable of providing energy at equal or greater rates and efficiencies, while still functioning at competitive prices. The main factors hindering the pursuit of alternative sources are their high initial costs and, for some, intermittency. The creation of electrical energy from natural sources like wind, water, and solar is very desirable since it produces no greenhouse gases and makes use of renewable sources—unlike fossil fuels. However, the planning and technology required to tap into these sources and transfer energy at the rate and consistency needed to supply our society comes at a higher price than traditional methods. These high costs are a result of the large-scale implementation of the state-of-the-art technologies behind the devices required for energy cultivation and delivery from these unorthodox sources. On the other hand, as fossil fuel sources become scarcer, the rising fuel costs drive overall costs up and make traditional methods less cost effective. The growing scarcity of fossil fuels and resulting pollutants stimulate the necessity to transition away from traditional energy production methods. Currently, the most common alternative energy technologies are solar photovoltaics (PVs), concentrated solar power (CSP), wind, hydroelectric, geothermal, tidal, wave, and nuclear. Because of government intervention in countries like the US and the absence of the need to restructure the electricity transmission system (due to the similarity in geographical requirements and consistency in power outputs for nuclear and traditional plants), nuclear energy is the most cost competitive energy technology that does not produce greenhouse gases. Through the proper use of nuclear fission electricity at high efficiencies could be produced without polluting our atmosphere. However, the initial capital required to erect nuclear plants dictates a higher cost over traditional methods. Therefore, the government is providing help with the high initial costs through loan guarantees, in order to stimulate the growth of low-emission energy production. This paper analyzes the proposal for the use of nuclear power as an intermediate step before an eventual transition to greater dependence on energy from wind, water, and solar (WWS) sources. Complete dependence on WWS cannot be achieved in the near future, within 20 years, because of the unavoidable variability of these sources and the required overhaul of the electricity transmission system. Therefore, we look to nuclear power in the time being to help provide predictable power as a means to reduce carbon emissions, while the other technologies are refined and gradually implemented in order to meet energy demand on a consistent basis.

Design Construction and Test of a Subscale Ammonia Borane Reactor

Two ammonia borane (AB or NH3BH3) dehydrogenation routes, namely hydrolysis and thermolysis, have been described in the literature. The work done on design, construction and testing of a subscale AB reactor is reported herein along with a discussion on the results. In this work, an AB dehydrogenation reactor system capable of handling two grams of AB per batch was designed. Operational safety, material compatibility and manufacturability were the major design requirements. The reactor system consisted of a high pressure feeder, a cylindrical stainless steel reactor vessel, an evolved gas heat exchanger and an ammonia filter, and a hydrogen flow meter. The reactor was operated in a temperature range of 430 K to 445 K for a nominal batch reaction time of 30 minutes. Measurements of hydrogen yield rates, system storage capacity and analysis of the reaction kinetics were completed. Overall repeatability of hydrogen yields was confirmed. A few practical problems associated with byproduct formation and removal are discussed in this paper.

Design and Analysis of a High Power Density, Low Temperature Waste Heat Recovery System Using an Oil-Free Turboalternator

In this paper the authors will present the design and preliminary test results for a distributed electric generating system that uses renewable energy source for economical load-following and peak-shaving capability in an oil-free, high-speed micro-turboalternator system using compliant foil bearings and a permanent magnet alternator. Test results achieved with the prototype system operating to full speed and under power generating mode will be presented. A comparison between predicted and measured electrical output will also be presented up to a power generating level of 25 kWe at approximately 55,000 rpm. The excellent correlation between design and test provides the basis for scale up to larger power levels. Based upon the turboalternator test results a thermodynamic cycle analysis of a system using low grade waste heat water at approximately 100 C will be reviewed. The tradeoff study results for a series of environmentally friendly refrigerant working fluids will also be presented including sensitivity to vaporization and condensing temperatures. Based on the cycle and pinch point analyses predicted maximum output power was determined. Finally a preliminary turbine design for the selected R134a working fluid was completed. The results of this study show that a net output power level of greater than 40 kW is possible for approximately 240 l/m flow of water at 100C is possible.

Techno-Economic Evaluation of Pressurized Oxy-Fuel Combustion Systems

Oxy-fuel combustion coal-fired power plants can achieve significant reduction in carbon dioxide emissions, but at the cost of lowering their efficiency. Research and development are conducted to reduce the efficiency penalty and to improve their reliability. High-pressure oxy-fuel combustion has been shown to improve the overall performance by recuperating more of the fuel enthalpy into the power cycle. In our previous papers, we demonstrated how pressurized oxy-fuel combustion indeed achieves higher net efficiency than that of conventional atmospheric oxy-fuel power cycles. The system utilizes a cryogenic air separation unit, a carbon dioxide purification/compression unit, and flue gas recirculation system, adding to its cost. In this study, we perform a techno-economic feasibility study of pressurized oxy-fuel combustion power systems. A number of reports and papers have been used to develop reliable models which can predict the costs of power plant components, its operation, and carbon dioxide capture specific systems, etc. We evaluate different metrics including capital investments, cost of electricity, and CO2 avoidance costs. Based on our cost analysis, we show that the pressurized oxy-fuel power system is an effective solution in comparison to other carbon dioxide capture technologies. The higher heat recovery displaces some of the regeneration components of the feedwater system. Moreover, pressurized operating conditions lead to reduction in the size of several other critical components. Sensitivity analysis with respect to important parameters such as coal price and plant capacity is performed. The analysis suggests a guideline to operate pressurized oxy-fuel combustion power plants in a more cost-effective way.

Concentration Measurement of Lithium Bromide Aqueous Solution by Electrical Resistivity

Absorption chillers have currently become an important device in saving energy because of its effectiveness in utilizing low grade heat. Lithium bromide is widely used as absorbent in this system. But there were few outstanding concentration measurement methods in practice before. In this paper, complete electrical resistivity data of lithium bromide aqueous solution for concentration measurement was given. The electrical resistivity of lithium bromide aqueous solution was measured at concentrations of 35–70 wt% of lithium bromide and temperatures of 10–100°C. Results of this work can meet the requirement of concentration measurement of lithium bromide in absorption chillers without extracting samples.

A Demand Based Optimum Solar Panel Orientation

The clear sky and monthly clearness index models are used to evaluate the hourly and monthly insolation on unit area of a tilted surface for the entire year. The hourly power consumption of a typical municipality (for this case New York City) for typical summer and winter days are used to determine the tilt and azimuth angles of a solar panel such that the solar energy reached the panel best match the energy consumption pattern. For the example case considered, in this work New York City, the electric power consumption peaks during summers at afternoon hours, due to increase in building cooling loads. It is found that orienting the solar panel at a westward azimuth angle with a tilt angle that results in maximum annual insolation is the best orientation of the solar panel for responding to both the peak energy demand and having reasonably high overall annual power generation. Although the model is used to optimize the solar panel orientation for New York City, it can however, be used for any building at any location as long as the needed solar data and power consumption pattern are known.

Water Utilization in Data Center Infrastructure

Fresh water is one of the few resources which is scarce and has no replacement; it is also closely coupled to energy consumption. Fresh water usage for power generation and other cooling applications is well known and accounts for 40% of total freshwater withdrawal in the U. S[1]. A significant amount of energy is embedded in the consumption of water for conveyance, treatment and distribution of water. Waste water treatment plants also consume a significant amount of energy. For example, water distribution systems and water treatment plants consume 1.3MWh and 0.5MWh[2], respectively, for every million gallons of water processed. Water consumption in data centers is often overlooked due to low cost impact compared to energy and other consumables. With the current trend towards local onsite generation[3], the role of water in data centers is more crucial than ever. Apart from actual water consumption, the impact of embedded energy in water is only beginning to be considered in water end-use analyses conducted by major utilities[4]. From a data center end-use perspective, water usage can be characterized as direct, for cooling tower operation, and indirect, for power generation to operate the IT equipment and cooling infrastructure[5]. In the past, authors have proposed and implemented metrics to evaluate direct and indirect water usage using an energy-based metric. These metrics allow assessment of water consumption at various power consumption levels in the IT infrastructure and enable comparison with other energy efficiency metrics within a data center or among several data centers[6]. Water consumption in data centers is a function of power demand, outside air temperature and water quality. While power demand affects both direct and indirect water consumption, water quality and outside air conditions affect direct water consumption. Water from data center infrastructure is directly discharged in various forms such as water vapor and effluent from cooling towers. Classification of direct water consumption is one of the first steps towards optimization of water usage. Subsequently, data center processes can be managed to reduce water intake and discharge. In this paper, we analyze water consumption from data center cooling towers and propose techniques to reuse and reduce water in the data center.

Design of a New 45 kWe High-Flux Solar Simulator for High-Temperature Solar Thermal and Thermo-Chemical Research

In this paper, we present a systematic procedure to design a solar simulator for high-temperature concentrated solar thermal and thermo-chemical research. The 45 kWe simulator consists of seven identical radiation units of common focus, each comprised of a 6.5 kWe xenon arc lamp close-coupled to a precision reflector in the shape of a truncated ellipsoid. The size and shape of each reflector is optimized by a Monte Carlo ray tracing analysis to achieve multiple design objectives, including high transfer efficiency of radiation from the lamps to the common focal plane and desired flux distribution. Based on the numerical results, the final optimized design will deliver 7.5 kW over a 6-cm diameter circular disc located in the focal plane, with a peak flux approaching 3.7 MW/m2.