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The graphene oxide (GO) nanocoating surface was fabricated by GO nanoparticles self-assembly on plain copper surface under nucleate pool boiling. Saturated and subcooled pool boiling experiments on GO nanocoating surface with dist...
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The graphene oxide (GO) nanocoating surface was fabricated by GO nanoparticles self-assembly on plain copper surface under nucleate pool boiling. Saturated and subcooled pool boiling experiments on GO nanocoating surface with distilled water at atmospheric pressure were conducted. Saturated pool boiling performance indicated enhancements of 78% in critical heat flux (CHF) and 41% in maximum heat transfer coefficient (HTC) when compared with the plain copper surface. It was found that the enhancement was mainly attributed to the improved wettability and high thermal conductivity of GO nanocoating, as well as the increased surface roughness. Subcooled pool boiling results showed that the liquid subcooling had significant effect on heat transfer performance of GO nanocoating surface. The CHF increased linearly with the increased subcooling degree, and the maximum HTC increased almost linearly with the increased subcooling degree. The CHF reached 274 W/cm(2) at subcooling degree of 19 K, which translated an enhancement of 128% when compared with the plain copper surface. This high CHF can address the heat dissipation bottleneck in ultra high-power density electronic devices. To better understand the subcooling effect on nucleate boiling, visualization studies on bubble growth characteristics at subcooled pool boiling were investigated with a high-speed digital camera. It was shown that bubbles were smaller and grew more slowly with the increase of liquid subcooling, and microbubble jets were observed at moderate heat flux regime.
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A novel heat exchanger unit structure was adopted to improve the thermal-hydraulic performance of compressed humid air and high-temperature flue-gas in a megawatt (MW) grade humid air turbine (HAT) cycle. Staggered airfoil fin cha...
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A novel heat exchanger unit structure was adopted to improve the thermal-hydraulic performance of compressed humid air and high-temperature flue-gas in a megawatt (MW) grade humid air turbine (HAT) cycle. Staggered airfoil fin channels and rectangular straight fin channels were projected for the compressed humid air and flue-gas, respectively. A three-dimensional model of the heat exchanger unit structure was built to simulate the heat transfer and flow of flue-gas and compressed humid air under different moisture content, mass flow-rate, and inlet temperature of humid air. The thermal-hydraulic performances of staggered airfoil channels were contrasted with that of straight and zigzag channels. The results showed that the airfoil channel has the best comprehensive thermal-hydraulic performance. Heat transfer and friction factor correlations were proposed to predict thermal-hydraulic performances of the compressed humid air flowing in the airfoil channel. The effects of moisture content on the heat transfer and flow characteristics were quantitatively described using correlations. The moisture content of the humid air is the main influence factor on heat transfer performance. In present study, the results and correlations can provide guidance for the design and application of recuperator structures with airfoil fins for the MW grade HAT cycle.
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Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. Thus, to improve design and operation charact...
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Compressed air energy storage (CAES) systems usually operate under off-design conditions due to load fluctuations, environmental factors, and performance characteristics of the system. Thus, to improve design and operation characteristics, it is important to study off-design performance of CAES systems. The compression process plays an important role in CAES systems. In this paper, we discuss the methodology for modeling off design operation of a multistage compression process with intercooling of the most promising adiabatic CAES (A-CAES) system. The off-design performances under two proposed kinds of operating regulations are analyzed and compared. These two operating regulations are equal-power-ratio regulation (EPR) and optimizing variable inlet guide vane rotation angle (OVRA) (optimizing all stages simultaneously) regulation. Correlation between parameters such as total power consumption ratio, exergy efficiency, hot water temperature versus mass flow rate ratio, and back pressure is revealed in depth. Based on this research, the optimal operation laws, including pressure ratio distribution and efficiency distribution among all stages, are obtained, and it is found that the primary optimum principle is to enhance the isentropic efficiencies of low-pressure stages to approach design point. Finally, the optimized regulating law for the inlet guide vane rotation angles of the 4 stages is revealed. This study provides strong support for the design, operation, and control of CABS systems.
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A classifier trained by a normalized simulation parameter could not identify an actual fault. In order to solve this problem, improved data preprocessing is proposed which normalizes the deviation of the simulation parameter, thus...
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A classifier trained by a normalized simulation parameter could not identify an actual fault. In order to solve this problem, improved data preprocessing is proposed which normalizes the deviation of the simulation parameter, thus making preprocessed simulation data more accurate at revealing the performance of an actual gas turbine. Furthermore, an optimization deep belief network (DBN) based on a genetic algorithm is developed, which shows a good classification ability. The superiority of these two methods is validated respectively by a three-shaft gas turbine platform. It has also been found that based on the DBN optimization method, adding outlet temperature parameter T-3 to a high-pressure compressor can significantly improve diagnostic accuracy, increasing it by 10.1%. Finally, the fault experimental result validates the effectiveness of improved data preprocessing combined with an optimization DBN to diagnose faults in actual gas turbines.
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Compressed air energy storage (CAES) system with low-temperature thermal energy storage (TES) has advantages of profitability and start-up characteristics in the field of electrical energy storage, and many CAES pilot plants have ...
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Compressed air energy storage (CAES) system with low-temperature thermal energy storage (TES) has advantages of profitability and start-up characteristics in the field of electrical energy storage, and many CAES pilot plants have been built in China. However, CAES systems face challenge of different working conditions in operation process due to changing pressure of air storage, influence of components' thermal mass and other boundary conditions. In this paper, we simulated a dynamic CAES system in which part-load operation regularities of compressors and expanders, thermal inertia of components, volumetric effects of pipes and heat exchange between system and environment were taken into consideration. Based on this, exergy analysis of whole energy storage process and influence of ambient factors on multi-cycle performances have been conducted. The results Indicate detailed features of the dynamic charging and discharging processes including system performance at start-up stage and entire process, which are beneficial to a comprehensive understanding of operation process and can be a reference in design and operation of CAES plants.
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This study presents a computational model in terms of capillary wetting and flow occurring in open rectangular microgrooves heat sink. This specific microgrooves heat sink, used at inclined angle position applications, is characte...
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This study presents a computational model in terms of capillary wetting and flow occurring in open rectangular microgrooves heat sink. This specific microgrooves heat sink, used at inclined angle position applications, is characterized by high heat transfer coefficient. Based on classical conservation equations and the generalized relationships of liquid thickness and geometric structures of microgrooves, the radius of curvature, wetting cross-sectional area and average flow rate along with the wetting length (axial direction) are numerically solved. A range of parameters including inclined angles, microgrooves dimensions and contact angles are considered in this computational model. The calculated values are verified by the experimental data. The standard error of calculated values compared with the experimental data is 2.7 x 10(-4) and 1.405 x 10(-8) when calculating the radius of curvature and wetting cross-sectional area.
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The performance of a thermal energy storage system strongly influences the overall efficiency of a central solar power plant. Therefore, low-cost and high-efficiency thermal energy storage technologies have attracted considerable ...
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The performance of a thermal energy storage system strongly influences the overall efficiency of a central solar power plant. Therefore, low-cost and high-efficiency thermal energy storage technologies have attracted considerable attention in recent years. A thermal energy storage concept using a spray-type packed bed is proposed in the present study. In addition, a small-scale semi-transparent spray-type packed bed thermal storage system was set up, using thermal oil as a transfer fluid and spherical particles as the storage media inside the packed bed. An experimental study on the liquid holdup and heat storage characteristics of the proposed spray-type packed bed system was conducted. The results indicate that the total liquid holdup increases as the volume flow rate increases, and the static liquid holdup inside the packed bed shows no relationship with the flow rate or height of the packed bed. Herein, a comparison of the unit cost for different thermal energy storage technologies is presented.
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Designing the primary airfoils for the outboard part of wind turbine blades is a complicated problem of balancing structural, aerodynamic, and acoustic requirements. This paper presents an optimization method for the overall perfo...
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Designing the primary airfoils for the outboard part of wind turbine blades is a complicated problem of balancing structural, aerodynamic, and acoustic requirements. This paper presents an optimization method for the overall performance of outboard wind turbine airfoils. Based on the complex flow characteristics of the rotor blades and the varying requirements along the span of a blade, the design principles of outboard airfoils were investigated. The requirements for improving the structural performance and reducing the aerodynamic noise were combined with the following aerodynamic design considerations: high efficiency, low extreme loads, stability, and a wide operating region. Thus, this paper proposes a new mathematical model for overall airfoil optimization using the airfoil performance evaluation indicators. Then, an integrated optimization design platform is established for outboard airfoils. Through 2 design cases, new airfoils with desirable aerodynamic characteristics and improved overall performance were obtained. Comparisons between the new airfoils and reference airfoils based on numerical predictions indicate that the proposed method with the newly established mathematical model can effectively balance the complex requirements of the airfoil and improve its overall performance. More notably, the design cases also indicate that the established optimization design method can be used to address special designs of outboard airfoils for different blade requirements.
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Sensor faults can cause incorrect estimations of gas path fault amplitudes in gas turbines. In this paper, an unscented Kalman-filter (UKF)-based simultaneous diagnostic scheme for gas-turbine gas path and sensor faults is propose...
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Sensor faults can cause incorrect estimations of gas path fault amplitudes in gas turbines. In this paper, an unscented Kalman-filter (UKF)-based simultaneous diagnostic scheme for gas-turbine gas path and sensor faults is proposed. A fault detection and isolation (FDI) system based on the UKF method avoids the requirement to establish different hypothetical models for hierarchical multiple-model-based FDI. Moreover, a fault identification module based on the weighted sum of squared residuals from a bank of filters is proposed to confirm the actual fault. The corresponding fault amplitude is then estimated to adaptively update the related parameters of the fault-diagnosis system according to the actual determined fault. Finally, several simulation case studies are conducted, based on a three-shaft gas turbine. The simulation results show that when two faults coincide, the proposed scheme not only has diagnostic accuracies of 97.3% and 93% for sensor faults and gas path faults, respectively, but also estimates the fault magnitude to a high degree of accuracy.
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Performance analysis and optimization for a three-shaft, recuperated gas turbine with power turbine variable area nozzle (VAN) is conducted in this paper. A modified recuperator simulation model is obtained from recuperator experi...
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Performance analysis and optimization for a three-shaft, recuperated gas turbine with power turbine variable area nozzle (VAN) is conducted in this paper. A modified recuperator simulation model is obtained from recuperator experiment. A gas turbine performance simulation program is established. The influence of power turbine shaft speed on engine performance is studied and optimized control of power turbine shaft speed is proposed. Comparative performance analysis proves VAN angle control improves engine performance, but leads to less compressor surge margin and increased risk of over temperature. The optimized control of VAN angle wider different safety operation temperature limits and ambient temperature is investigated. Power turbine shaft speed barely influences the optimized control of VAN angle, but temperature limits and ambient temperature greatly do. By decoupling power turbine shaft speed and VAN angle, an optimized control strategy for power turbine shaft speed and VAN angle is proposed, which brings 6.37%, 15.88%, 47.80% increases in output power, and 10.84%, 25.59%, 64.97% increase in thermal efficiency when relative high-pressure shaft speed is 0.95, 0.90 and 0.85, respectively. Maximum thermal efficiency could be achieved at part-load conditions rather than design-point if temperature limit is relaxed.
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