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In this paper, innovative test methods including aerodynamic acceleration, PIV measurement, separate statistics of incidence and rebound information were used to systematically investigate the rebound characteristics of flaky oxide particles and angular quartz sand impacting stainless steel at high temperature. Through the statistical analysis of a large number of experimental results and the measurement of the microscopic erosion morphology of the target surface, combined with the numerical simulation of the gas-solid two-phase flow of the test section, the intrinsic relationship between the rebound behavior of the particles and their erosion behavior was systematically explored for the first time. Meanwhile, the effects of the incident parameters, particle size and accelerated airflow on the rebound characteristics of the particles were revealed. The results have important guiding significance for further understanding the physical properties of particle-wall interaction and predicting the particle erosion characteristics and erosion distribution of industrial equipment components.

Aviation and ground compressors are susceptible to the erosion of hard particles in the sandy environment, leading to lower performance and shorter service life of the equipment. Although many studies have been performed on this topic, current literature mainly focused on the steady ideal operating conditions of compressors. In this paper, particle motion behavior and erosion characteristics in the blade passage of a 3.5-stage axial compressor under actual service environment are investigated with the RANS numerical simulation method systematically. By comparing the particle trajectories, erosion rate density and other indicators, effect of particle diameter, particle mass concentration, compressor speed and inlet conditions on erosion characteristics are explored in detail. Results show that the value of erosion rate density on the blade pressure side is overall higher than the suction side. The erosion area and intensity of the rotors are generally more serious than stators, especially on the first rotor blade. With variation in particle size, particle diameter of 100 μm becomes the turning point to change the erosion trend of the blades. Moreover, the overall erosion rates increase linearly with increasing mass concentration of inhaled particles. However, its impact on the erosion position and morphology are not obvious. When the compressor speed increases from 6050 rpm to 6650 rpm, the eroded mass of R1 increases by 10.7%, and the casing erosion rate increases about 11 times. Compared with the winter condition, the overall erosion rate in summer increases by 62%. The results of this paper will provide a technology basis for the prediction on particle erosion behavior and formulation of operation and maintenance programs for aero engines and ground gas turbines under the actual service environment.

Based on the microscopic morphology and size distribution of the iron oxide scales measured in our erosion tests, 109 micro flaky particles were elaborately generated by MATLAB codes to ensure that the morphology and size distribution were basically consistent with the observations under the microscope. Furthermore, based on the nonlinear explicit dynamics software ABAQUS/explicit, the numerical simulations of the erosion mechanism of multi-particles on the blade substrate 1Cr12W1MoV in a high-parameter turbine were performed. Compared with the experimental data, the influence of the particle shape, particle size, impact velocity and particle roundness on the erosion rate was studied in detail. The results show that the shape of the particles has a great effect on the erosion rate. The impact angle corresponding to maximum erosion rate of the flaky particles is around 24°–30°. While the equivalent maximum impact angle is around 45°–60° for spherical particles. The effect of micro-cutting on erosion is greater than that of extrusion-forging for flaky particles. While the influence of micro-extrusion and forging on erosion is huger than that of micro-ploughing for spherical particles according to the morphologies results. In addition, the higher the roundness of the flaky particles, the lower the erosion rate. When the sphericity of the erodent particles entering the cascade passage reaches 0.5856 or more, the erosion rate will be greatly reduced, thereby significantly alleviating the erosion damage of the blade. The results of this paper will provide theoretical basis and technical support for further understanding of the erosion mechanism of typical blade materials in dust-laden turbines.

Supercritical heat transfer mechanisms and heat transfer correlations are firstly reviewed in present paper. The heat transfer characteristics of S-CO2 in circumferentially non-uniform heated vertical upward flow are then numerically studied and the fundamental mechanisms are discussed. The abnormal heat transfer for S-CO2 is believed to be caused by the comprehensive effect of thermophysical property variations. For S-CO2 with non-uniform heating and large mass flow rate, the enhanced heat transfer is mainly related to the large specific heat in the near wall region while the deteriorated heat transfer is dominated by the thickening viscous sublayer induced by the viscosity increase. Besides, the buoyancy effect induced by the density variation is still prominent to axial velocity distribution even in the forced convection. Finally a new correlation with higher accuracy is developed for S-CO2 circumferentially average heat transfer by introducing the correction parameters of viscosity, specific heat, axial flow-acceleration and non-uniform heat flux.

Based on the establishment of the original and improved models of the turbine blade, a thermal-fluid-solid coupling method and a finite element method were employed to analyze the internal and external flow, temperature, and thermal stress of the turbine blade. The uneven temperature field, the thermal stress distribution characteristics of the composite cooling turbine blade under the service conditions, and the effect of the thickness of the thermal barrier coating (TBC) on the temperature and thermal stress distributions were obtained. The results show that the method proposed in this paper can better predict the ablation and thermal stress damage of turbine blades. The thermal stress of the blade is closely related to the temperature gradient and local geometric structure of the blade. The inlet area of the pressure side-platform of the blade, the large curvature region of the pressure tip of the blade, and the rounding between the blade body and the platform on the back of the blade are easily damaged by thermal stress. Cooling structure optimization and thicker TBC thickness can effectively reduce the high temperature and temperature gradient on the surface and inside of the turbine blade, thereby reducing the local high thermal stress.

In this paper, the supercritical carbon dioxide power cycle used to recover the waste heat of gas turbine is investigated by means of conventional exergy analysis and advanced exergy analysis. Firstly, the thermodynamic parameters of carbon dioxide cycle in design stage are determined by single-objective optimization with net power output as objective function. Then, conventional exergy analysis is carried out on the partial heating cycle under real, unavoidable and ideal conditions. After that, advanced exergy analysis, in which the exergy destruction is divided into endogenous / exogenous part and avoidable / unavoidable part is adopted to reveal the improvement potential of the system and illustrate the interaction among the components. According to the calculation results, a total amount of 3.55MW (47.33%) exergy destruction could be reduced by the improvement of component efficiency. Endogenous exergy destruction is higher than exogenous exergy destruction in all components. Based on the results of conventional exergy analysis, the high-temperature heater should be paid attention in order to reduce exergy destruction. However, according to the results of advanced exergy analysis, the technical improvement of turbine should be emphasized due to its high endogenous-avoidable exergy destruction. Meanwhile, for the components with high unavoidable exergy destruction, external systems should be employed to exploit the underutilized energy and enhance the system performance.

Finite element method (FEM) was used to study the stress peak of stress S11 (Radial stress component in X-axis) on the steam turbine blade surface of four typical erosion-resistant coatings (Fe2B, CrN, Cr3C2-NiCr and Al2O3-13%TiO2). The effect of four parameters, such as impact velocity, coating thickness, Young’s modulus and Poisson’s ratio on the stress peak of stress S11 were analyzed. Results show that: the position of tensile stress peak and compressive stress peak of stress S11 are far away from the impact center point with the increase of impact velocity. When coating thickness is equal to or greater than 10μm, the magnitude of tensile stress peak of stress S11 on the four coating surfaces does not change with the coating thickness at different impact velocities. When coating thickness is equal to or greater than 2μm, the magnitude of tensile stress peak of stress S11 of four coatings show a trend of increasing first and then decreasing with the increase of Young’s modulus. Meanwhile, the larger the Poisson’s ratio, the smaller the tensile stress peak of stress S11. After optimization, When coating thickness is 2μm, Poisson’s ratio is 0.35 and Young’s modulus is 800 GPa, the Fe2B coating has the strongest erosion resistance under the same impact conditions, followed by Cr3C2-NiCr, CrN, and the Al2O3-13%TiO2 coating, Al2O3-13%TiO2 coating has the worst erosion resistance.

In this paper, the water droplet erosion (WDE) performance of typical martensitic precipitation substrate 0Cr17Ni4Cu4Nb in steam turbine final stage, laser solid solution strengthened sample, laser cladding sample and brazed stellite alloy samples have been studied based on a high-speed rotating waterjet test system. The WDE resistance of several materials from strong to weak is in sequence: Brazed stellite alloy &gt, laser cladding sample &gt, laser solid solution sample &gt, martensitic substrate. Furthermore, the WDE resistance mechanism and the failure mode of brazed stellite alloy have been revealed. It is found that the hard carbide in the stellite alloy is the starting point of crack formation and propagation. Under the continuous droplet impact, cracks grow and connect into networks, resulting in the removal of carbide precipitates and WDE damage. It is proved that the properties of the Co-based material itself is the reason for its excellent WDE resistance. And the carbides have almost no positive contribution to its anti-erodibility. These new findings are of great significance to process methods and parameter selection of steam turbine blade materials and surface strengthened layers.

In order to study the effect of initial surface roughness on water droplet erosion resistance of last stage blade substrate of steam turbine, eight 17-4PH samples were grounded and velvet polished by different mesh metallographic sandpaper to establish sample with different initial surface roughness. The water droplet erosion experiments were carried out in the highspeed jet water erosion experiment system, and the mass and micro-morphology of each sample were measured by using precision electronic balance and ultra-depth of field microscope respectively at each experimental stage, and the measurement of water erosion trace width and maximum water erosion depth were also completed at the same time. On the basis of experiments, LS-DYNA was used for numerical simulation to verify the reliability of experimental results again. Results show that the smoother the initial surface of sample, then the smaller the mass loss, the stronger its water erosion resistance. On the contrary, the rougher the initial surface of sample, the more severe the surface irregularity, the more times the water droplets concentrated at the lowest point of pit when water droplets flow laterally after impact is completed, thus accelerating the formation of initial crack and lateral expansion, the poorer the water erosion resistance of sample. At same water erosion time, the smoother the sample surface, the later the complete erosion trace appear, the narrower the water erosion trace width. However, the maximum water erosion depth of sample is not affected by the initial surface roughness. The numerical simulation results are in good agreement with the experimental results.

A novel combined supercritical carbon dioxide recompression Brayton/organic flash cycle is investigated by means of exergoeconomic analysis. The supercritical carbon dioxide recompression Brayton/organic flash cycle is a combination of a supercritical carbon dioxide recompression Brayton cycle and an organic flash cycle where the organic flash cycle absorbs waste heat from the supercritical carbon dioxide recompression Brayton cycle for power generation. Seven different organic flash cycle working fluids are examined, including n-Nonane, n-Octane, n-Heptane, n-Hexane, n-Pentane, R365mfc and R245fa. Parametric study is employed to investigate the effects of the some decision variables on the first and second law efficiencies and the total product unit cost of the supercritical carbon dioxide recompression Brayton/organic flash cycle and the supercritical carbon dioxide recompression Brayton cycle. The performances of the supercritical carbon dioxide recompression Brayton/organic flash cycle and the supercritical carbon dioxide recompression Brayton cycle are optimized and then compared from the perspective of thermodynamics and exergoeconomics. The results show that the second law efficiency and the total product unit cost of the supercritical carbon dioxide recompression Brayton/organic flash cycle are up to 6.57% higher and up to 3.75% lower than those of the supercritical carbon dioxide recompression Brayton cycle, respectively. Compared with the supercritical carbon dioxide recompression Brayton/organic Rankine cycle, the supercritical carbon dioxide recompression Brayton/organic flash cycle can obtain slightly higher second law efficiency, and comparable or slightly lower total product unit cost. It can also be concluded that the highest second law efficiency and the lowest total product unit cost for the supercritical carbon dioxide recompression Brayton/organic flash cycle are achieved when the n-Nonane is used as the organic flash cycle working fluid.

A CO2 transcritical power cycle (CDTPC) is a promising power system to utilize low temperature geothermal heat source. Many researchers mainly focus on the thermodynamic and thermo-economic performance analysis or optimization for a CDTPC, or compare the design performance of a CDTPC with that of organic Rankine cycle. The objective of this paper is to study the effects of a recuperator on the design and off-design performances of a CDTPC for low temperature geothermal plants. Detailed off-design mathematical models of the basic and regenerative CDTPCs are built to complete this study under the variable mass flow rates and temperatures of the geothermal water and the cooling water temperatures conditions by a sliding pressure operation control strategy. The results reveal that no matter how the geothermal water mass flow rate and temperature or the cooling water temperature vary, both the overall net power and overall thermal efficiency of the regenerative CDTPC system are higher than those of the basic CDTPC system. Meanwhile, a recuperator can improve the overall system performance of a CDTPC system under the both design and off-design conditions, although the recuperator might weaken the off-design behavior of some key components. In addition, a recuperator can improve off-design behaviors of the CO2 pump performance under the off-design conditions. The guidelines for the rotational speed listed in the tables for CO2 pumps might provide some reference for practical operation.

In this paper, tensile stress distribution in the surface of high-parameter steam turbine blade anti-erosion boride coatings under single particle impact was investigated using a nonlinear finite element software ABAQUS/explicit based on the actual erosion environment in power units. The results showed that the single Fe2B phase coating hardly had stable anti-erosion capability when the coating thickness was less than 20 μm under the continuous impacts. For the bilayer boride coating composed of top phase FeB and bottom phase Fe2B, the whole coating began to show the stable anti-erosion performance with top FeB phase coating thickness of 120 μm from the standpoint of maximum surface tensile stress reduction. Anti-erosion performance of single Fe2B phase boride coating was 23.15% higher than the bilayer boride coating. Besides, the optimum parameters configurations for boride coatings were studied.

The present work mainly focuses on the thermodynamic and exergoeconomic comparisons between the novel single-pressure multi-stage CDTPCs (carbon dioxide transcritical power cycles) and single-pressure single-stage CDTPC for engine waste heat recovery. A method based on exergy fuel distribution is proposed to calculate the fuel cost for the bottoming CDTPCs. Parametric analysis is conducted to study effects of the decision variables on the performances of the considered CDTPCs, which are also optimized and compared. The thermodynamic study shows that the double-stage CDTPC can produce the highest net power output of 517.27 kW for a 2928 kW engine at exhaust gas temperature of 470 °C. The exergoeconomic study reveals that the single-stage CDTPC has the lowest total unit cost when exhaust gas temperature is 300–600 °C and the double-stage CDTPC is recommended when exhaust gas temperature is 530–600 °C due to better thermodynamic and exergoeconomic performances. Meanwhile, the triple-stage CDTPC is not recommended when exhaust gas temperature is 300–600 °C considering thermodynamics and exergoeconomics. A multi-objective optimization is also conducted to obtain an optimal condition for the considered CDTPCs for the case study.

A novel dual-pressure Allam cycle integrated with the cold energy recovery of liquefied natural gas is proposed and analyzed in this paper. The feature of this system is that the cold energy of liquefied natural gas is successively utilized in two condensers with different condensing pressures, thereby reducing the heat transfer temperature difference in the condensation process and improving the system performance. The proposed system is discussed in detail based on the results of thermodynamic analysis and optimization. According to the simulation results, the largest exergy destruction belongs to the combustion chamber. Moreover, the exergy destruction in the condenser is greatly reduced owing to the dual-pressure condensation process. The system exergy efficiency first increases and then decreases with the increment of combustor temperature and main turbine inlet pressure. However, the system performance would deteriorate as the main turbine outlet pressure and bottom turbine outlet pressure increase. According to the results of single-objective optimization, the electricity efficiency and specific work of the dual-pressure Allam cycle are 15.76% and 68.75% higher than the classical Allam cycle, respectively. In addition, the exergy efficiency of the dual-pressure Allam cycle is up to 51.88%, which is improved by 1.57% compared with the single-pressure Allam cycle.

Exergoeconomic analysis is performed for a novel combined SCRB/ARC (supercritical CO2 recompression Brayton/absorption refrigeration cycle) in which the waste heat from the SCRBC is recovered by an ARC for producing cooling. Parametric analysis is conducted to investigate the effects of the decision variables on the performance of the SCRB/ARC cycle. The performances of the SCRB/ARC and SCRBC cycles are optimized and compared from the viewpoints of first law, second law and exergoeconomics. It is concluded that combining the SCRBC with an ARC can not only enhance the first and second law efficiencies of the SCRBC, but also improve the exergoeconomic performance. The results show that the largest exergy destruction rate occurs in the reactor, while the components in the ARC have less exergy destruction. The reactor and turbine are the first and second important components from exergoeconomic aspects. When optimization is based on the exergoeconomics, the first and second law efficiencies and the total product unit cost of SCRB/ARC are 26.12% higher, 2.73% higher and 2.03% lower than those of the SCRBC. The optimization study also reveals that an increase in the reactor outlet temperature can enhance both thermodynamic and exergoeconomic performances of the SCRB/ARC. For the basic design case, the SCRB/ARC can produce 71.76 MW of the cooling capacity and 6.57 MW of the cooling exergy at the expense of only 0.36 MW of power in comparison with the SCRBC.

Transcritical power cycles (TPCs) using CO 2 -based binary zeotropic mixtures for the conversion of low-grade geothermal water at 100–150 °C into power are presented and analyzed when cooling water temperature ( T cw ) is 10–30 °C in this paper. 6 refrigerants are selected as the additives into CO 2 according to 2 criteria. Performances of TPCs with 6 selected CO 2 -based mixtures are optimized by pattern search algorithm (PSA). Thermodynamic and economic analyses are conducted. The results reveal that R161/CO 2 is the best fluid for a TPC in terms of both thermal performance and economic performance while R290/CO 2 might be an unsuitable working fluid in TPC due to its lower thermal performance. When T cw = 10–20 °C, a TPC using R161/CO 2 at X R161 = 0.7 can increase net power output by 14.43–50.46% and decrease cost per net power by 27.96–48.72% compared with a TPC using CO 2 . The selected CO 2 -based mixtures can reduce CPP of a TPC compared with CO 2 although more heat transfer area is required. Meanwhile, the CO 2 -based mixtures can decrease the high operating pressure, and enlarge the condensing temperature range compared with CO 2 . In addition, the CO 2 -based mixtures except R161/CO 2 and R152a/CO 2 are not recommended for a TPC when T cw is low.

Based on the erosion rate model and the particle rebound model of blade material obtained through accelerated erosion test under high temperature, systematic numerical simulations of the complex gas-particle flows in inlet volute and cascade of a large capacity gas pressure recovery turbine are performed in this paper. The influence of inlet volute structure and cascade channel structure on the aerodynamic performance and erosion characteristics of turbine is first investigated. Results show that although mixing flows and vortex flows are formed in turbine intake volute, total pressure loss of volute is less than 0.7% because of low gas velocity. Erosion damage on the trailing edge of nozzles and rotating blades is mainly caused by high-speed cutting behavior of ash particles. The typical inlet volute structure results in an uneven erosion of first stage nozzles along circumferential direction. Nozzles located below the horizontal split are mainly eroded in blade root area, while erosion distribution of nozzles located above the horizontal split is irregular, and worse than the erosion degree of the lower half circle. Flow acceleration characteristics and cascade circumferential structure must be comprehensively considered so as to simultaneously improve the aerodynamic and anti-erosion performance of turbine.

In this paper, particle separators with different structures are designed based on main steam pipe of an ultra supercritical steam turbine. With the employment of particle rebound model established through high temperature particle rebound experiment, systematic numerical simulations on the influence of particle trap structure, steam mass flow for transporting particles on separation performance and pressure loss characteristic of separation system are carefully conducted. Besides, the effect of particle separation system on the working performance of thermal system is also analyzed. Results show that particle separation efficiency of three traps increases with the increase of amount of steam for transferring particles first, which then stabilize after a certain value is reached, while pressure loss of particle separation system is basically constant. With a small amount of transporting steam, separation efficiency of 100 μm particle in trap B can reach up to 78%, and pressure loss of the system is below 13 kPa. Effect of particle separation system on the heat rate of 1000 MW thermal system is less than 0.15%, which is well below the profits earned through the reduction of solid particle erosion to turbine blades. The result of this paper will provide new ideas for thoroughly solving erosion problem of high parameter steam turbine.

This paper proposes a novel carbon dioxide transcritical power cycle combined with an absorption refrigeration cycle (CDTPC-ARC) to recover waste heat from jacket water and exhaust gas of heavy-duty ICEs. Firstly, a detailed study is conducted to investigate the effects of key operating parameters on the performance of CDTPC-ARC. Secondly, a comparative study on the proposed CDTPC-ARC and the existing CDTPC-DT (consisting of CDTPC with regenerator and CDTPC without regenerator) under the same waste heat conditions shows that CDTPC-ARC can produce approximately constant net power output ( W net ) when Tcw = 18–36 °C, while CDTPC-DT can’t operate in the transcritical power cycle when Tcw ⩾ 26.1 °C. Finally, parametric optimization is performed to achieve the maximum W net of the combined cycles by using genetic algorithms (GA). Results show that CDTPC-ARC can produce more W net and have a larger recycle efficiency compared with CDTPC-DT when Tcw > 20 °C. When Tcw = 25 °C, W net,op of CDTPC-ARC is 14.6–20.2% higher than that of CDTPC-DT and the corresponding ηrec is 9.8–25.5% higher than that of CDTPC-DT. In addition, economic performance comparison between the two cycles is performed. The results show that CDTPC-ARC has better economic performance.

Compared with the ORC (organic Rankine cycle) and the steam Rankine cycle, the CDTPC (CO2 (carbon dioxide) transcritical power cycle) shows a higher potential in converting middle-grade waste heat into useful work. In this paper, we propose a novel type of single-pressure, multi-stage CDTPC to overcome the shortcomings of the CDTPC in utilizing waste heat of exhaust gas from gas turbines or internal combustion engines. System parameter optimization is carried out in various CDTPC to achieve the maximum net power output of cycle by using the genetic algorithm(GA). A comparative study between the existing CDTPC and the proposed novel type of CDTPC with the same exhaust gas temperature Tgi (250–500 °C) at the inlet of the gas heater shows that the novel type of CDTPC can increase the net power output by 3.9–26.3% and decrease the optimum working pressure by 13.2–31.0%. If exhaust gas is non-corrosive, waste heat can be utilized more effectively by the double-stage CDTPC when 250 °C ≤ Tgi ≤ 412 °C and by the three-stage CDTPC when 412 °C

In this paper, a comparative investigation on the supercritical carbon dioxide power cycle for waste heat recovery of gas turbine is carried out. Four categories and six cycles are chosen to represent typical layout of supercritical carbon dioxide power cycle based on thorough literature reviews. The selected cycles are optimized and analyzed based on the results of single- and multi-objective optimization from the perspective of system efficiency, economic cost and configuration complexity. According to the exergy destruction analysis, several guidelines about the heat exchangers are proposed to enhance the thermal efficiency of gas turbine waste heat recovery system, including the avoiding of preheating, the utilization of partial heating layout, the employment of segmentation method and modified logarithmic mean temperature difference, the increase in the number of gas heater. The results indicate that turbine dominates the investment cost of power cycle. In conclusion, dual heated cascade cycle-II should be employed to pursue the maximized system efficiency. Otherwise, partial heating cycle is recommended due to its balanced overall performance.

In this study, the high temperature erosion mechanisms and damage characteristics of a boronized coating have been systematically studied by employing an improved high-temperature accelerated erosion test bench and impact contact theory analyses. Within the scope of the experimental parameters, the erosion rate of the boronized coating under the same erosion conditions was observed to be only one half to one-twelfth of the erosion rate of the substrate. Furthermore, the boronized coating was noted to be less sensitive to the speed of the erosion particles than the plastic substrate, thus, indicating superior and more stable erosion resistance than the base material. The boronized coating exhibited typical brittle fracture characteristics under impact by the high-speed particles. When the particle impact normal stress exceeded the critical stress for crack propagation owing to the coating defects, the surface and subsurface layers of the coating initially formed horizontal and vertical micro-cracks, followed by their gradual expansion and intersection. After destabilization, the brittle coating material was peeled layer-by-layer from the surface of the test piece. At the same incident speed, as the particle size was increased from 65 &mu, m to 226 &mu, m and 336 &mu, m, the size (width) of the erosion cracks on the coating surface increased from 1 &mu, m to 30 &mu, m and 100 &mu, m respectively. Correspondingly, the erosion damage thickness of the coating was enhanced from 15 &mu, m to 50 &mu, m. In the case of the quartz sand particle size exceeding 300 &mu, m, the dual-phase boronized coating did not provide effective protection to the substrate. Furthermore, based on the elastoplastic fracture theory, a prediction model for the erosion weight loss of the boronized coatings within the effective thickness range has been proposed in this study.

An integration system for 1000 MW S-CO2 connected-top-bottom power cycle with overlap utilization and coal-fired boiler is developed. The adaptive modification module is introduced to eliminate the non-convergence for S-CO2 superheater thermal calculation in the system iteration. Thermal-hydraulic performance in terms of thermal performance, cycle efficiency, heater configurations, heater areas and final parameter evenness are discussed. Firstly, the strong constraint effects of inlet and outlet parameters on superheater thermal calculation convergence are demonstrated and the adaptive modification module is established. Secondly, based on the detailed thermal-hydraulic analysis, different layouts are compared to identify the flow path way and the heat absorption of S-CO2 flow in different heating processes. The midpoint between the two peaks of heat flux is recommended as the start point for the cold fluid placement in cooling wall arrangement. Finally, a new layout is proposed to obtain the highest overall thermal-hydraulic performance, with a net power efficiency up to 47.57% and a total heater area of 316426.18 m2. The design sequences for S-CO2 coal-fired boiler heaters are recommended as well.

A novel combined cooling, heating and power system which consists of carbon dioxide power cycle, absorption chiller and heaters is proposed in this paper for waste heat recovery of gas turbine. In the proposed cogeneration system, the absorption chiller and heaters are driven by the residual energy of carbon dioxide power cycle and flue gas simultaneously. Detailed mathematic models are established to simulate and evaluate the system from the perspective of thermodynamics and economics. The results of parametric analysis indicate that there is an optimal value for the turbine inlet temperature, at which the exergy efficiency is maximized and the levelized cost of exergy is minimized. As the split ratio increases, the exergy efficiency and levelized cost of exergy of the proposed system first increase then decrease simultaneously. Single-objective optimization is carried out to maximize the exergy efficiency of the proposed system. The optimal results show that the exergy efficiency and levelized cost of exergy of the cogeneration system are 4.62% higher and 0.90 cent lower than that of standalone power cycle, respectively. Compared with the alternative cogeneration system in which only low-temperature flue gas or the waste heat of power cycle is used to drive the refrigeration subsystem and heating subsystem, the exergy efficiency of proposed system is enhanced by 2.89% and 1.3%, respectively. Finally, multi-objective optimization is carried out with exergy efficiency and levelized cost of exergy as objective functions. Pareto frontier is calculated and recommended point is given for the engineering practice.

The Supercritical carbon dioxide (S–CO2) Brayton cycle is considered as a promising alternative to traditional steam Rankine cycle due to its high efficiency and compactness. However, in coal-fired power system, the S–CO2 temperature at cooling wall entrance is newly recognized quite high, leading to an over-temperature crisis. A coupled model of combustion and S–CO2 heat transfer was established to predict cooling wall temperature of a 1000 MW S–CO2 Brayton coal-fired boiler. Based on the module arrangement in S–CO2 boiler, the “cold S–CO2-hot fire matching and cascaded temperature control” principle in 1D model was proposed to reduce the cooling wall temperature. Three methods were examined including the low-temperature fluid matching high heat flux burner region, the counterflow, and more cold fluid in circulation drained to match high heat flux zone. The results show that the optimal arrangement can significantly reduce the temperature in overheated region 12–44 °C and eliminate the local hot spot. In addition, the 3D model was developed to obtain the maximum wall temperature and the uneven temperature in the circumferential direction. The employment of spiral cooling wall could alleviate circumferential unevenness and reduce wall temperature. The present work can provide important guidance to design of S–CO2 Brayton coal-fired power system.

This paper proposes a novel combined cooling and power (CCP) system based on a regenerative supercritical carbon dioxide Brayton cycle (sCO2 cycle) and an ammonia-water absorption refrigeration cycle (ARC) for engine waste heat recovery. In the proposed system, the supercritical carbon dioxide Brayton cycle absorbs the waste heat of the internal combustion engine to generate power, and the absorption refrigeration cycle utilizes the low-grade energy in the supercritical carbon dioxide turbine exhaust to provide cooling. Firstly, energy and exergy analysis is performed on the combined cooling and power system. Then, detailed parametric analysis is carried out to study the effects of key parameters, such as the compressor outlet pressure, turbine inlet temperature, generator hot-end temperature difference, and evaporator temperature on the exergy efficiency and total product unit cost. Finally, the non-dominated sorting genetic algorithm II is adopted for multi-objective optimization to obtain the maximum exergy efficiency and the minimum total product unit cost. Multi-objective optimization results reveal that better thermodynamic and economic performances can be obtained by lowering the evaporator temperature. Compared with the single regenerative supercritical carbon dioxide system, the proposed system can increase the exergy efficiency by 2.29–2.54%pt (percentage point), and the thermal efficiency by 8.16–18.93%pt, but might increase the total product unit cost. Under different evaporator temperatures (−10–10 °C), the proposed system can generate 248.19–253.90 kW of net power output, accounting for 8.48–8.67% of the rated power output of the engine, and produce 70.57–168.86 kW of cooling capacity by consuming 0.445–0.532 kW of pump work. In addition, exergy destruction analyses indicate that the components in the bottoming ARC generally have less exergy destructions.

This study proposes a supercritical CO2 recompression cycle based on external oxy-coal combustion. It aims to evaluate and improve the performance of the system guided by energetic and exer...

Full three-dimensional unsteady numerical investigation on an axial air turbine in 50% partial admission is conducted. The partial admission turbines are under different unsteady loading and unloading process, as well as flow parameters, respectively. The loss coefficient and static pressure distributions at the key position are presented in detail to analyze the nonuniformity originated from partial admission. The results show that the nonuniformity decreases along flow direction and the efficiency of control stage also decreases but with the uniformity improved downstream of the rotors with increasing admitting numbers in equal partial admission degree. The reasons for efficiency decreasing are reasonably explained with windage and sector end losses presented by static entropy distributions. The periodic changes of unsteady forces in amplitude and direction are also compared and transformed in the frequency domain by FFT method. The largest circumferential exciting force factor which is remarkably larger than the corresponding axial exciting force factor decreases by 13.2% with the increase of admitting arc number. Compared with the common distribution of two symmetric admitting arcs, the maximum exciting force factor of triangle admitting arc distribution drops 11.3% with the mere efficiency decrease of 1.32%. The multiple admitting arc turbines are more conducive to be applied to submarines which concerns more about exciting force other than efficiency. Efficiency and unsteady forces are both worth being taken into consideration in the practical applications.

Reducing solid particle erosion of blades is one of the most urgent problems for high-parameter steam turbine power generation technology. Based on the erosion rate model and particle rebound model of blade materials obtained through accelerated erosion test under high temperature, erosion characteristics of flaky particles in control stage of a typical supercritical steam turbine were systemically studied using three-dimensional numerical simulation method. The erosion mechanism of hard coatings on nozzle suction surface is first revealed, and erosion resistance of boride coating with large oxide particles is validated through high-temperature erosion test. Results show that serious erosion damage of boride coating on the latter half of nozzle suction surface is caused by the combined rebounded impingement of large particles between 1000 µm and 2000 µm after their initial impingement on the nozzle pressure surface and the leading edge of rotating blade. The average particle impingement velocity can reach up to 150–180 m/s, and the impingement angle is in the range of 18°–28°. High-temperature erosion test results show that boride coating will soon broken and fall off under the continuing impact of millimeter-sized particles, which confirms that hard coatings are difficult to resist the high-intensity impingement from these large particles. Therefore, separating particles before entering the nozzle chamber with the employment of an inertial separator should be the optimal choice for improving the erosion resistance of turbine. The results of this study enrich the types of blade erosion damage and provide a new idea for reducing erosion damage of control stage blades.

The full cavitation model introduced by Singhal et al. was partly improved based on experimental results. The improved cavitation model is used to simulate cavitating flow in multiple nozzle oil jet pump for lubrication system in steam turbine. The influence of noncondensible gas on flowing characteristics of multiple nozzle oil jet pump was studied with noncondensible gas content in the range of 0.01–500 ppm. Results show that noncondensible gas has little influence on nonchoking flow while imminent choking flow and deep choking flow are greatly affected. With the increase of noncondensible gas, multiple nozzle oil jet pump enters choking flow earlier. The maximum suction flow rate per unit throat area of multiple nozzle oil jet pump remains constant with varying pressure ratios and area ratios under choking flow, which is only determined by the noncondensible gas content. It is suggested that the maximum suction flow rate per unit throat area is used for the prediction of choking flow in multiple nozzle oil jet pump. This study also provides qualitative criteria for the upper limit of water content in lubrication oil, which avoids multiple nozzle oil jet pump working under choking flow.

Reducing solid particle erosion of blades is one of the most urgent problems for supercritical steam turbine power generation technology. Based on the erosion rate models and the particle rebound models of blade materials obtained through accelerated erosion test under high temperature, systematic numerical simulations of the complex steam-particle flow in high pressure inlet flow channel and governing stage cascade of a supercritical steam turbine with four control valves was performed in this paper. The influence the typical nozzle chamber structure and partial-arc admission on the erosion characteristics of control stage blades was first investigated. Results show that erosion condition of nozzles in the same nozzle segment vary greatly along circumferential direction, while erosion damage to the leading edge of different circumferential rotating blades is uniform. Compared with four-valve opening condition, erosion weight-loss of the whole nozzle segment increases by 14% and 25% under three-valve opening condition and two-valve opening condition, respectively. Besides, under the partial-arc admission conditions, some large particles coming from the steam admission nozzle segment will collide back and forth between vanes and rotating blades in the downstream nozzle segment without steam admission, thus causing certain erosion to the trailing edge of nozzle suction side.

Control valves are used as flow regulators for steam turbines, which operate under wide ranges of valve openings and pressure ratios. The inherent throttling action and complex 3D flow in control valves result in vibration and intolerable noise at small and medium valve openings. The vibration and noise clearly are firmly with the flow pattern. Experiments and numerical simulation are the primary means of determining the mechanisms. In this paper, a phenomenon of sound mutation in control valve was experimentally observed by continuously changing the pressure ratio. This phenomenon is explained for the first time. Different noise and pressure fluctuations can appear even under the same condition, depending on the process of changing the pressure ratio. A method of continuously changing the pressure ratio was used in the unsteady numerical simulation to reveal the mechanism. The results show that sound mutation occurs due to the change of annular flow and core flow. The annular flow has a lower noise and a more stable flow pattern than the core flow. Sound mutation can be used as a simple way of determining the ranges of the core flow and the annular flow.

In this paper, high temperature erosion tests are performed on four typical anti-erosion coatings for high-parameter steam turbine blades using pneumatic accelerated erosion method to simulate the actual erosion environment in power units. With the employment of scanning electron microscope, energy-dispersive X-ray spectroscopy, glancing-angle X-ray diffraction, and Vickers indentation testing techniques, detailed microscopic analysis of samples is conducted to reveal the underlying causes affecting the anti-erosion performance of coatings. Results show that, under the solid particle erosion at high temperature, boride coatings with more compact structure and higher hardness have stronger anti-erosion ability, whose erosion rate is only 30–50% that of HVOF Cr3C2 coatings under the same erosion condition. Boride coatings composed of duplex phase (FeB and Fe2B) have lower anti-erosion damage capability than that of boride coatings composed of single Fe2B phase. Under high-speed large incidence angle impingement, the surface layer of FeB cracks easily and rapidly propagates to the subsurface layer Fe2B phase under the sustained impingement from particles, resulting in the flaking off and failure of coatings. Single Fe2B phase boride coatings have smaller hardness gradient in the depth direction and higher fracture toughness than boride coatings composed of duplex phase, so that exhibit more stable excellent erosion resistance under different erosion parameters. Therefore, single Fe2B phase boride coatings should be used as the preferred wear resistant coating for turbine blades solid particle erosion problem.

Combining an improved particle image velocimetry technique with a far-field microscope, a high-resolution quantitative measurement of the transient secondary flow field in an annular turbine cascade is conducted through moving the laser light sheet to follow the primary flow. The measuring results revealed the transient behavior and strong unsteadiness of the secondary flow in a cascade for the first time. It is confirmed that the suction side leg of the horseshoe vortex rotates around the passage vortex along the rotating direction of passage vortex. In the secondary flow of cascade, the formation, development and decay of Hopf bifurcations caused by the competition between the tensile deformation and the dissipation, have become a major behavior of vortex evolution. Driven by the interaction between the passage vortex and the suction side leg of the horseshoe vortex as well as the transverse pressure gradient, the passage vortex was pushed to the suction surface and ultimately formed the wall vortex. Furthermore, the strength of secondary vortex was enhanced with the increase of aerodynamic parameters, though the scale of vortex was gradually shrinking and the limit cycle concentrated at the core of vortex. However, no change happened to the location of vortex core and the structure of vortex. The computational fluid dynamics results revealed that the results using the SST k- ω model was the closest to the experiment results in the topological structure, the evolution process of secondary flow and the magnitude estimation, followed by those with the RNG k- ɛ model. The results with standard k- ɛ model were clearly inconsistent with the experimental results.

Supercritical carbon dioxide is widely used in power plant and refrigeration system as working fluid. In this paper, a novel combined cooling and power system consists of supercritical carbon dioxide recompression Brayton cycle and transcritical carbon dioxide refrigeration cycle is proposed. In the novel system, the working fluid through the recompressor in supercritical carbon dioxide recompression Brayton cycle is partially replaced by the refrigeration compressor outlet working fluid in transcritical carbon dioxide refrigeration cycle. Mathematical models are established to simulate the combined system under steady-state conditions and the simulated results show that the reactor dominates the exergy destruction followed by the cooler and high temperature recuperator. Effects of five parameters, including turbine discharge pressure, cooler outlet temperature, evaporation temperature, cooling capacity and mass flow fraction are evaluated. The performances of the proposed combined system and the separation system are optimized and then compared from the perspective of thermodynamics. The calculated results show that the combined system’s comparative advantage over separation system will increase with increasing cooling capacity and decreasing evaporation temperature. The exergy efficiency of combined system is up to 2.45% and 5.87% higher than separation system when evaporation temperature is 273.15 K and 253.15 K, respectively. In order to balance the contradiction between the investment and system performance, the multi-objective optimization is conducted with exergy efficiency (to be maximized) and annual cost per heat consumption (to be minimized) as objective functions at different evaporation temperature. Non-dominated sorting generic algorithm-II is employed and Pareto frontier solution for the proposed system is given. Suggestions for engineering practice are provided based on the distributions of some key parameters on Pareto frontier solution.

The actual industrial erosion caused by the impingement of particles swarming from different perspectives is often different from the single-angle impingement of solid particle in the erosion test. In order to predict the erosion problems in practical engineering more reasonably, a series of elevated temperature erosion tests were conducted to study the surface ripple and enduring erosion behavior of heat-resistance stainless steel suffering from the single-angle impingement or multiangle alternative impingement of angular particles. The test results indicated that the surface of target materials with good ductility produced large-scaled transverse ripples and small-scaled longitudinal ripples after experienced a long-time single-angle impingement of angular solid particles under a 773–873-K high-temperature environment. The longitudinal ripples could accelerate the emergence and development of large-scaled transverse ripples. Initial erosion scars caused the differentiation of material deformability and plastic flow in the different locations of concave–convex scars, which further drove the evolution of the surface morphology from disordered scars to coherent ripples under the sustained attack of high-velocity particles. The more dimples the eroded surface of target material produced, it was easier for the target materials to produce coherent ripple. However, the interactions among the erosion behaviors with different attack angles made initial concave–convex scars difficult to evolve to coherent ripples under the multiangle alternative erosion. Further statistical results of erosion tests indicated that it can basically satisfy the practical engineering need by taking the erosion rate of initial surface layer as the erosion rate of the target material within the whole life cycle.

Based on experiments and numerical simulation, the influence of the inlet flow channel of a steam turbine on the solid particle erosion of nozzle segments was investigated systematically. The results indicate that the upstream channels of the nozzle segment, such as the regulating valve, nozzle chamber and connection pipe, concentrate the solid particle erosion to a small number of nozzles or local regions of the nozzle, which greatly reduces the time for nozzle damage. Compared with the present erosion situation, measures adopted to distribute particles at the inlet of a nozzle chamber uniformly can double the service life of a nozzle segment, while the service life can be increased by eight to ten times through measures to distribute particles uniformly at the inlet of a nozzle segment. This article shows that the service life of a nozzle segment can be doubled through substituting a nozzle chamber with a tangential steam intake for one with a normal steam intake. Moreover, a boride layer with 0.04 mm effective thickness or a CrN layer with 0.01 mm effective thickness can further double the service life of a nozzle segment. In addition, a pocket-trap arranged in the particle-aggregated area after an elbow can reduce the weight loss at nozzle sites with the most serious erosion by over 85%. These investigations are of great significance to the long-term, safe and high-efficiency running of a steam turbine.

In this article, a new particle tracking model is established through high temperature erosion modeling test. Based on the model, steam-particle flows in the governing stage cascade of a supercritical steam turbine are systematically investigated and the influence of oblique stator on the aerodynamic performance and erosion characteristics of governing stage blades is carefully studied. Results show that with the increase of nozzle oblique angle, the maximum load position gradually moves toward nozzle trailing edge. Consequently, secondary flow loss of nozzle cascade gradually decreases. Compared with the prototype structure of governing stage, stage efficiency increases by 0.8%, 0.35%, and 0.44%, respectively, when nozzle oblique angle increases to 15°, 30°, and 45°. Meanwhile, erosion at the trailing edge of nozzle pressure side and leading edge of rotor suction side gradually decreases, while erosion of rotor pressure surface increases. The maximum erosion position of nozzle pressure surface and rotor suction surface keeps constant, but the maximum erosion position of rotor pressure surface gradually moves forward. Comprehensive analysis shows that when nozzle oblique angle reaches 30°, erosion of nozzle trailing edge reduces by 14%, and stage efficiency increases by 0.35%; erosion resistance and aerodynamic performance of governing stage can be both well considered.

Impingement on blade surface by fine particles with high velocity is commonly seen in steam turbines, gas turbines and compressors, which affect the service life and reliability of the equipment. Study on particles’ rebound characteristics is of great significance to reduce the blade erosion and to control particle trajectory. Based on the nonlinear explicit dynamics analysis software ANSYS/LS-DYNA, the impacts of fine spherical particles with different diameters (20 to 500μm) on a typical martensitic stainless steel (AISI 403) target with high velocity (50 to 250m/s) have been systematically studied. The influences of incident velocities, impact angles, particles sizes on its rebound characteristics, relative impact depth, and relative dissipated energy have been analyzed. Results show that velocity restitution coefficient e decreased with the impact angle β1, the incident velocity V1, and the particle size dp. However, the role of particle size on the velocity restitution coefficient seemed to be far less than that of the other two factors. Both of particle’s tangential and normal velocity coefficient of restitution declined with the increasing impact angle in most cases. However, when the incident velocity V1 = 200m / s and the impact angle β1 > 45°, the tangential velocity restitution coefficient et of 100 μm and 200 μm particles increased with the increase in the impact angle β1. The reason might be that the relative impact depth drel was located a zone ranged from 0.1515 to 0.1677, where the tangential rebound behavior could be enhanced. Most of the variation of the tangential and normal velocity restitution coefficient along β1 decreased with the increase in the particle diameter. However, when V1 = 200m/s and β1 > 15°, the tangential reflected velocity of the larger particles was enhanced gradually. In addition, the values of the relative impact depth drel increased with the increasing impact angle and incident velocity, and it increased with the increasing particle diameter in most cases. The relative dissipated energy of particles steadily increased with the impact angle and incident velocity, respectively. Particle diameter had little effect on energy dissipation in comparison with the impact angle and incident velocity.Copyright © 2015 by ASME

Cavitation characteristics of oil jet pumps with multiple nozzles were studied using high frequency response pressure transducers with Mobile DTE Light Oil in experiment, which has an environment the same as that in the lubrication system of the steam turbine in a power plant. The influence of working oil pressure, pressure ratio, and area ratio on cavitation characteristics were studied with the area ratio ranging from 4 to 9, and the working oil pressure ranging from 1.8 to 2.8 MPa. Results show that the cavitation erosion on the throat surface is caused by the intense shear layer of high-speed jet in the throat, which leads to the collapse of vortex cavitation bubbles near the throat surface in an oil jet pump with multiple nozzles. What is more, the vortex cavitation is difficult to eradicate in an oil jet pump with multiple nozzles for the lubrication system of a steam turbine. However, there is a working point with low cavitation intensity, which is also the high efficiency point that ensures both relative safety and high efficiency. This study provides quantitative relation for the determination of working oil pressure, area ratio, and pressure ratio of an oil jet pump with multiple nozzles, which is significant for engineering.

The efficiency of the multiple nozzle oil jet pump was systematically investigated using the Mobile DTE Light Oil based on the similarity theory in experiment. The experimental condition is the same as that for the multiple nozzle oil jet pump in lubrication system of steam turbine in the power plant. Thus, the influence of the area ratio and the pressure ratio on the efficiency and the pressure ratio interval of variable conditions with stable efficiency was studied in the area ratio range of 4∼9. Results show that there is a fixed relationship between the area ratio and the pressure ratio, which leads to the high efficiency of multiple nozzle oil jet pump. However, the high efficiency value and the pressure ratio interval of variable conditions with stable efficiency show different tendencies with the changing area ratio of multiple nozzle oil jet pump. In the area ratio range of 4∼9, the pressure ratio with the high efficiency value increases by 0.03 with the decrement of 1 for the area ratio. When the area ratio is larger than 6.3, the high efficiency value increases by 1% absolutely with the area ratio decreasing by 1, but remains almost unchanged for the area ratio less than 6.3. Furthermore, the increasing area ratio widens the pressure ratio interval of variable conditions with stable efficiency. The increase of the area ratio by 1 leads to the increment of 9.7% relatively for the pressure ratio interval of variable conditions with stable efficiency. This study provides the quantitative criteria for the determination of the area ratio and the pressure ratio of multiple nozzle oil jet pump, which keeps the high and stable efficiency simultaneously. Apparently, this study has significant engineering contribution.Copyright © 2014 by ASME

Control valve is an accident prone equipment in high-parameter steam turbine, and its safety directly influences the economy and safety of the unit. In this study, a control valve of a 600 MW subcritical unit used in the power plant was investigated to reveal the mechanism of flow induced vibration of the control valve. It is found that the intermittent vibration of the control valve is a fluid-solid interaction phenomenon, which occurs in middle-opening and transonic flow condition. The phenomenon is a variable damping and nonlinear vibration for the valve stem system. The experimental results show that as the valve head tilts to different positions, the pressure fluctuation at the valve seat changes significantly at the same time. Unsteady numerical simulation is conducted when valve head is in the center and tilts toward three different directions with the same angle. The results indicate that the separation point between the high jet flow and valve head is changing with time. The thick boundary layer caused by transonic flow and the moving high-pressure region induced by impinging jet flow are the two main reasons for the flow pattern alternation. The average unbalanced force of fluid acting on valve head varies as the flow pattern alternates. And its direction is from center to the narrower side of the annular channel in the oblique section when valve head is tilted.Copyright © 2014 by ASME

Reducing solid particle erosion (SPE) of blades is one of the most urgent problems for supercritical steam turbine power generation technology. Based on the erosion rate models and the particle rebound models of blade materials obtained through the accelerated erosion test under high temperature, erosion characteristics of the first reheat stage blades in a supercritical steam turbine was simulated and analyzed by three-dimension numerical simulation method in this paper. The influence of operating conditions, particle size distribution in the inlet of nozzle and axial clearance between vanes and rotating blades on the erosion distribution of cascade were explored quantitatively. Results show that: the erosion damage of the first-reheat stage stator is mainly caused by suction surface impingement from oxide particles. In designed loading condition, small and median size of particles mainly eroded the trailing edge (TE) of nozzle pressure surface, while large particles mainly impinge the leading edge (LE) of rotating blades and the TE of vane suction surface, and erosion increase along the blade height. When the turbine is running under part-load condition, particle impingement angle on stator pressure surface is basically unchanged, while impingement velocity slightly reduced. However, the amount of particles that impinge the stator TE suction side after their first-time impingement on rotor LE increase rapidly, leading to the more severe erosion damage of stator suction surface. The particle size distribution in the inlet of nozzle has a significant effect on the erosion simulation of first reheat stage blades, and the size distribution sampled in one unit may not be used to other units. When axial clearance changes, the erosion weight loss of vane pressure surface near TE is basically held constant, while the erosion weight loss in vane suction surface near TE decreases with the increase of axial clearance. For the supercritical 600MW unit simulated in this article, the anti-SPE performance and the unit efficiency can be balanced well when the axial clearance increases to 13mm. The results in this paper will provide a technology basis for reducing oxide particle erosion in the first reheat stage blades of supercritical steam turbine.Copyright © 2014 by ASME

A novel thermodynamic system is proposed to recover the waste heat of an internal combustion engine (ICE) by integrating the transcritical carbon dioxide (CO2) refrigeration cycle with the supercritical CO2power cycle, and eight kinds of integration schemes are developed. The key parameters of the system are optimized through a genetic algorithm to achieve optimum matching with different variables and schemes, as well as the maximum net power output (Wnet). The results indicate that replacing a single-turbine scheme with a double-turbine scheme can significantly enhance the net power output (Wnet) and lower the inlet pressure of the power turbine (P4). With the same exhaust parameters of ICE, the maximumWnetof the double-turbines scheme is 40%–50% higher than that of the single-turbine scheme. Replacing a single-stage compression scheme with a double-stage compression scheme can also lower the value ofP4, while it could not always significantly enhance the value ofWnet. Except for the power consumption of air conditioning, the net power output of this thermodynamic system can reach up to 13%–35% of the engine power when it is used to recover the exhaust heat of internal combustion engines.

Reducing the solid particle erosion (SPE) of blades is one of the most important problems for high-parameter steam turbine. Based on the erosion rate models and the particle rebound models of blade materials obtained through the accelerated erosion test under high temperature, a lot of three dimension numerical simulations were conducted in this paper. The influence of particle size on the impingement point distribution on the nozzle surface and the erosion characteristics of control stage nozzle in a supercritical steam turbine were analyzed quantitatively. The size range of the oxide scale particles participating in the erosion damage were extended to 500μm, and some special anti-erosion measures corresponding to different size particles were proposed to reduce the erosion of nozzle. Results show that the erosion of pressure surface in the trailing edge of nozzle is mainly from the high-intensity impingement of particles smaller than 160μm, especially those with the size range from 20μm to 60μm. For the impingement of these small particles, optimizing the profile and cascade structure as well as coating the hard coating on the surface of nozzle can improve the erosion resistance of nozzle. However, these small particles do not impinge the nozzle trailing edge suction surface. The severe erosion damage of suction surface of nozzle was from the impingement again of the particles with the size range from 200μm to 500μm after rebounding from nozzle pressure surface. It is very difficult to resist the erosion damage of these large particles for the hard coating, and separating large particles from main steam before entering the nozzle chamber should be a good choice for improving the erosion resistance of turbine. These studies will provide a technical basis for selecting anti-erosion measures of control stage nozzle.Copyright © 2013 by ASME

This paper experimentally examines the influence of coating thickness, test temperature, coating hardness, and defects on the erosion resistance of boride coatings, ion plating CrN coatings, and thermal spraying coatings. The results demonstrate that the erosion rate of coating can be reduced effectively by improving coating hardness and thickness with the absence of the cracks of coating during the coating process. In comparison with thermal spraying coatings, boride coatings and ion plating CrN coatings are more suitable for protecting steam turbine blades from solid particle erosion due to higher erosion resistance. However, blades cannot be protected effectively when coating is thinner than a critical value θcrit. Based on our results, it is recommended that the protective coating for the steam turbine blade should be thicker than 0.02 mm. In addition, the effect of temperature on erosion resistance of the coating is strongly dependent on the properties of transition layer between coating and substrate material. For the coating without pinholes or pores in the transition layer, the variation in erosion rate with temperature is consistent with that of uncoated substrate material. However, the erosion rate of coating descends with the elevation of test temperature when a lot of pinholes or pores are produced in the transition layer.

Through-flow capability and flow stability of some steam turbine control valves were studied by experimental investigation and numerical simulation. Based on the analysis of thermodynamic process in control valve, the relationship of flow coefficient, area ratio of valve outlet section to seat diameter section, pressure ratio and total pressure loss coefficient was deduced, and the expression of polytropic exponent was obtained. The relative deviations between formula results and experimental results are within 3%. Both expressions can be used for design and optimization to determine control valve parameters quantitatively. The results of 3D numerical simulation indicate that the topological structure of flow fields in all control valves is similar. The results of valve stability show that the airflow force acted on the valve disc depends on the vortex strength of flow around valve stem bush and valve disc, the asymmetric transonic impinging jet under the valve disc and the diffusing action. The valve operates steadily when the inlet and outlet Mach number are less than 0.15. As the unload degree is about 85%, stem vibrates at the operating conditions when pressure ratio is less than 0.8 and opening ratio is from 10% to 18%. A multihole annular orifice can make flow steady at all operating conditions.Copyright © 2008 by ASME