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.
Abstract
In this paper, a typical negative Poisson’s ratio lattice structure was studied and several diagonally reinforced 3D lattice structures were designed and analysed using the finite element ...method. On this basis, the fatigue life of the unreinforced and reinforced structures was calculated using SIMULIA Fe-safe software. Meanwhile, the fatigue failure process of the lattice structure was systematically simulated and quantitatively analysed by combining the multiaxial fatigue damage model. Results show that the enhancement design from the cell structure can provide an anti-diagonal shear enhancement effect. The structure A, B, and C can decrease the maximum von Mises stress by 95.8, 97.1, and 94.66%, and increase the compressibility by 80%, 56%, and 127%, respectively. The structure A enhancement yields the best overall performance in terms of structural stress, compressibility, and negative Poisson’s ratio properties enhancement. Compared with the unreinforced structure, the lifetime distribution of the structure A reinforced structure changes in both position and level. The overall lifetime has been improved from 10
2.813
of the unreinforced structure to 10
7
of the reinforced structure. Quantitative calculation of the fatigue damage is consistent with the fatigue life prediction results, which further validate the effectiveness of the diagonal enhancement method and the enhancement structure of the negative Poisson’s ratio lattice structure.
Abstract
Hydrogen blended with natural gas is one of the best ways for large-scale hydrogen transportation; however, pipeline steels exploited for transferring natural gas have the risk of hydrogen ...embrittlement. Therefore, the hydrogen damage mechanism and resistance property of different steel pipelines should be carefully examined to select suitable materials for the task mentioned above. The common X42, X52, X70, and AISI 1020 are taken into account as research objects. Their mechanical properties and hydrogen absorption properties in a hydrogen environment are investigated to explore further factors affecting the hydrogen embrittlement of material. Dynamic slow strain rate tensile test results show that these materials exhibit varying hydrogen embrittlement sensitivity in a hydrogen environment. AISI 1020 has the highest hydrogen embrittlement susceptibility, then X70, and X42 presents the lowest one. Generally, hydrogen embrittlement behaviours are strengthened by increasing the current density. As the current density grows, the fracture mode of pipeline steels transforms from the ductile fracture to the quasi-cleavage fracture and finally turns into the cleavage fracture. The hydrogen embrittlement fracture of the tensile specimen results from the action of the HEDE and HELP in various zones. TDS test results indicates that the content of C and Mn significantly influence on the hydrogen solubility in metal materials.
Based on the actual operation parameters and temperature-dependent material properties of a gas turbine unit, composite cooling blade model and corresponding reliable boundary conditions were ...established. Transient thermal-fluid-solid coupling simulations were then comprehensively conducted to analyze the transient flow and the temperature field of the blade under startup, shutdown, and variable loads condition. Combined with the obtained transient temperature data, the non-linear finite element method was exploited to examine the effect of these transient operations on the turbine blade thermal stress characteristics. Results show that the temperature and pressure on the blade surface increase with the load level and vice versa. As the startup process progresses, the film cooling effectiveness and the heat convection of airflows inside the blade continuously grow; high-temperature areas on the pressure surface and along the trailing edge of the blade tip gradually disappear. Locally high-temperature zones with the maximum of 1280 K are generated at the air inlet and outlet of the blade platform and the leading edge of the blade tip. The high thermal stresses detected on the higher temperature side of the temperature gradient are commonly generated in places with large temperature gradients and significant geometry variations. For the startup/shutdown process, the rate of increase/decrease of the thermal stress is positively correlated with the load variation rate. A slight variation rate of the load (1.52%/min) can lead to an apparent alteration (41%) to the thermal stress. In operations under action of the variable load, although thermal stress is less sensitive to the load variation, the rising or falling rate of the exerted load still needs to be carefully controlled due to the highly leveled thermal stresses.
The health management of the reciprocating compressor is crucial for its long term steady operation and safety. Online condition monitoring technology for the reciprocating compressor is almost ...mature, whereas the fault diagnosis technologies are still insufficient to meet the need. Therefore, in this paper, a novel fault detection method for the reciprocating compressor based on digital image processing and artificial neural network (ANN) was proposed. This method is implemented to the sectionalized pressure–volume (p–V) curves, which are obtained by dividing a working cycle in the cylinder into four thermal processes, including expansion, suction, compression and discharge. Hit-or-miss transform is adopted to extract the comprehensive gradients of expansion and compression curves, and vertical projection transform is applied to extract the vertical projection features. Finally, all of the features are fed to an ANN to do classification. To validate the proposed method, a seeded fault testing was conducted to collect real running data. The results showed that the new approach shows a good performance, with a high classification accuracy of 97.9%.
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.
•A propane and iso-butane pre-cooled mixed refrigerant liquefaction process.•C3&C4-MR process has advantages over the widely used C3-MR process in terms of operating costs.•Energy consumption and ...exergy analysis are performed.•The guidance and recommendations for mixed refrigerant ratio are summarized.•Compare C3&C4 and R410a as pre-coolants respectively and obtain the best ratio of propane and iso-butane.
The development of a small skid-mounted natural gas liquefaction plant can economically, environmentally-friendly, and efficiently collect natural gas in mountainous areas where are not easy to lay pipelines. A propane and iso-butane pre-cooled mixed refrigerant liquefaction process (C3&C4-MR) is proposed in this paper. Compared with the propane pre-cooled mixed refrigerant liquefaction process, the improved liquefaction process can reduce system energy consumption and increase exergy efficiency greatly. Genetic algorithm is applied to optimize energy consumption of C3&C4-MR process. The optimized specific energy consumption STotal is 0.301 kW·h/kg, which is 18.0% lower than the optimized C3-MR process. And compared with the optimized R410a pre-cooled mixed refrigerant liquefaction process, STotal of C3&C4-MR process is 5.64% lower than that of R410a-MR process. Besides, mixed propane and isobutane as pre-coolant is easier to obtain from the feed gas. By analyzing the temperature sensitivity of mixed refrigerant and calculating the unit compression power consumption of a single refrigerant, the guidance and recommendations for mixed refrigerant ratio are summarized. Due to the property of iso-butane, the optimal percentage of iso-butane in the pre-coolant was analyzed. In conclusion, C3&C4-MR process is energy-saving and advanced in terms of system operating costs to recycle scattered natural gas in remote areas.
Liquid piston hydrogen compressors (LPHCs) are promising used in hydrogen refueling stations. Piston braking is crucial to LPHCs since the solid piston works under a high stroke frequency, which may ...result in piston collision. The on-off valve in the previous studies requires complicated control program to ensure the piston positions at dead centers. In this paper, a novel LPHC with a double buffer structure and an improved hydraulic driving system are proposed. A simulation involving the flow through the buffer aperture confirms the braking effect of the proposed design. Some parameters affecting piston braking are studied. A light piston can produce a lower velocity pulsation and lower peak pressure in the buffer chamber. The minimal piston displacement decreases with an increase in the bottom throttle diameter, while the maximal piston displacement increases with an increase in the top throttle diameter. The results also show that the slight pulsation of the piston velocity is attributed to the spool insertion, the piston reverse motion, and the opening of valves. This study can provide a technical reference for the optimization of LPHCs.
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•A liquid piston compressor is proposed for hydrogen refueling stations.•Double buffer structure facilitates piston braking and avoids collision.•Reducing piston mass declines the pulsation amplitude of piston velocity.•Adjusting throttle diameters can change the positions of dead centers.
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.
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•Conducted experimental and numerical studies on the rebound characteristics of the particles.•Studied the effects of particle parameters and accelerated airflow.•Revealed relationship between particle rebound behavior and erosion behavior.•Established rebound models for different non-spherical particles.
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