This study seeks to design the aerodynamic features a first stage vane for a 100 MW class supercritical CO2 Brayton cycle turbomachine. For a turbine inlet temperature of 1350 K, the recuperated configuration is found to provide the highest cycle efficiency, and the corresponding cycle parameters are then used to design the turbine stages. A 6-stage turbine is selected and the first stage is designed following a one-dimensional mean line approach. Initial mean line turbomachine parameters (work coefficient and flow coefficient) are selected to provide high thermodynamic efficiency and simple radial equilibrium equation principles. Turning loss correlations are utilized to define and optimize hub and casing velocity triangle parameters. Typical turbomachinery characteristic parameters are used to compare the carbon dioxide turbine with typical air combustion turbines. Detailed aerodynamic analysis is performed on a complete three-dimensional model of the vane flow field using a commercial computational fluid dynamics code, STAR-CCM+. Actual properties of the working fluid are input to the model from the REFPROP database provided by the US National Institute of Standards and Technology (NIST). The detailed flow field is computed, from which aerodynamic loss coefficients are calculated. The computer model confirms that the design is successful in turning supercritical carbon dioxide at the prescribed angle and pressure. However, results of the real fluid simulation show that aerodynamic losses caused the stage efficiency to be about 4% below the design target.

In order to maintain viability as a future power-generating technology, concentrating solar power (CSP) must reduce its levelized cost of electricity (LCOE). The cost of CSP is assessed with the System Advisor Model (SAM) from the National Renewable Energy Laboratory (NREL). The performance of an integrally geared compressor-expander recuperated recompression cycle with supercritical carbon dioxide (sCO2) as the working fluid is modeled. A comparison of the cycle model to the integrated SAM cycle performance is made. The cycle model incorporates innovative cycle control methods to improve the range of efficiency, including inventory control. The SAM model is modified to accommodate the predicted cycle performance. The ultimate goal of minimizing the LCOE is targeted through multiple approaches, including the cost of the power block, the impact of system scale, the sizing of the thermal system relative to the power block system, the operating approach for changes in ambient temperature and availability of sunlight. Through reduced power block cost and a detailed cycle model, the LCOE is modeled to be 5.98 ȼ/kWh, achieving targeted techno-economic performance. The LCOE of the CSP system is compared to the cost of hybrid solar and fossil-fired systems. An analysis is made on the efficacy of a fossil backup system with CSP and how that relates to potential future costs of carbon dioxide emissions.

Siemens has developed a novel approach for measuring the process gas temperature leaving the power turbine in their heavy industrial gas turbine engines using active acoustic tomography. Siemens has deployed this measurement technique on two test engines of different power ranges and different combustion and exhaust duct configurations. These engine tests have demonstrated that this technology is effective and robust. All working parts are outside the heat effective zone so, unlike the traditional intrusive point temperature measurement method, sensors are easily replaceable during engine operation. Bulk exhaust temperature is used in performance testing of industrial gas turbine engines and is a critical measurement for power production. Temperature distribution information in the exhaust plane is valuable for safe engine operation and can be used to prevent lifetime reduction due to hotspots or to monitor the burner flames. Siemens used broadband sound sources for the previously reported acoustic pyrometer experiments. This paper extends this work utilizing sparse time-frequency encoded sources to improve the robustness of time of flight estimation in the high noise area of the turbine exhaust. The goal is to achieve a higher signal to noise ratio between the emitted and received signals by focusing the acoustic energy into narrow time-frequency bins that are little affected by turbine noise. Different acoustic patterns are tested and compared to the previously used broadband source both in laboratory experiments and a turbine test bed. The patterns are evaluated regarding their noise robustness, sound pressure levels and narrow autocorrelation which are important for accurate time of flight estimation in high noise environments.

No abstract

This paper focuses on unconventional thermodynamic cycles and their applications in alternative energy. It looks into these promising advancements, beginning with the exploration of trends in cost, efficiency, and the adoption of various sources of power. By studying historical trends, conventional means of obtaining energy are seen to be currently increasing in efficiency in smaller and smaller increments. The second part of our study is the application of alternative configurations of the Brayton cycle. In particular, this paper analyzes a closed-cycle turbine with supercritical carbon dioxide as the working fluid. Beginning with a simple cycle calculation, this study adapts the cycle and explores the benefit of recuperated and combined cycle systems. A parametric study was also created, comparing the efficiency versus the specific power of each cycle. Consideration of supercritical carbon dioxide as the working fluid in turbomachine cycles may demonstrate an economic advantage in the global market. This paper provides a perspective on the feasibility of these developments for realistic applications in industry. Also important to feasibility, it assesses trends in the cost of power generated by each cycle and energy source. With this information, choices may be made on which cycle is more economically promising in today’s market. The results of this study provide a clear indication of relative efficiencies. These efficiencies, in turn, determines the optimal design direction for a particular supercritical carbon dioxide cycle. In addition, the results provide insight into the effect of this technology on the cost and efficiency of concentrated solar power production.

The recent volatility in oil prices has fueled uncertainty about the world’s ability to meet future demands. Furthermore, the growing concern over the negative environmental impacts produced by emissions has resulted in worldwide efforts for developing renewable jet-fuel alternatives. This has led current military and civilian fuel specifications to allow the use of Fischer-Tropsch (FT) and Hydroprocessed fuels (HEFA) in blends up to 50% in volume with regular Jet-A/JP-8. On the other hand, physical properties, and the broad chemical composition, including trace elements in those fuels, may result in engine performance issues found only after extensive operation. This may result in higher maintenance and operation costs. This study presents the coking depositions of several renewable fuels after being stressed in a fixed bed reactor. This was done in an effort to assess the effects (if any) on the thermal stability of renewable fuels interacting with materials representative of state of the art aircraft systems (steel, aluminum, titanium tubing) and to determine whether the use of renewable fuels enhances thermal stability when blended, up to 50%, with oil-derived fuels.

The goal of this study is to design and assess the effectiveness of a micro-channel recuperator using supercritical carbon dioxide as a working fluid. A one-dimensional thermal analysis is performed for a micro-channel recuperator suitable for a Brayton cycle with a nominal 100 MW class turbomachine. The impact of supercritical carbon dioxide properties near the critical point on the thermal performance of the recuperator is studied in detail. The cycle parameters are first obtained from an overall cycle analysis. Two adjacent flow passages with square cross-section in counter-flow configuration are considered for this analysis along with appropriate symmetry. The high pressure of SCO2 is also addressed and the structural stresses on the micro-channel walls are analyzed. Only the axial temperature variations in the hot stream and the cold stream are considered in the one-dimensional analysis. Each channel is discretized in the axial direction. Axial conduction through the wall is included in the energy balance. Of particular interest in this analysis is the variation of transport properties of the CO2 working fluid as thermodynamic conditions approach the critical point. These property variations are provided to the computer code through the REFPROP database. Over the length of the heat exchanger local changes in Reynolds number, Nusselt number, and heat transfer coefficient are charted. From the results of the heat transfer calculations, the log mean temperature difference and heat exchange effectiveness of the heat exchanger is calculated. Using the code to produce multiple results, the optimum heat exchanger design is found. Recommendations on the manufacturing method of a micro-channel recuperator are made.

No abstract