Search Results (68)

The turbine rotor is a core component in many energy conversion systems, where it is subjected to loads such as aerodynamic and centrifugal forces that make it highly susceptible to damage. Consequently, the reliability of the turbine rotor ranks among the key aspects of concern. This paper proposes an efficient approach based on the kriging model to conduct the reliability analysis of a turbine rotor. First, a parametric model of the turbine rotor was established. This parametric model was subsequently applied in a multifactor fluid–structure interaction model used to analyze the working performance of the turbine rotor. Finally, a kriging surrogate model was built and applied using these data in combination with various reliability analysis methods to analyze the structural reliability and reliability sensitivities of the turbine rotor. Furthermore, the reliability sensitivity results indicated that the outlet pressure had the greatest impact on rotor reliability. Thus, the proposed method was shown to have practical application value in the reliability analysis of the rotor structure. Full article

This study innovatively proposes a pipeline-type pneumatic lift sediment removal device for cleaning pollutants at the bottom of fish breeding tanks and conducts hydrodynamic characteristic analysis on its core component, the pneumatic lift pipeline structure, which consists of a horizontal circular tube with multiple micro-orifices at the bottom and an upward-inclined circular tube. The pipeline has an inner diameter of 20 mm and a vertical length of 1.2 m, with the orifice at one end of the horizontal tube connected to the gas supply line. During operation, compressed gas enters the horizontal tube, generating negative liquid pressure that draws solid–liquid mixtures from the tank bottom into the pipeline, while buoyant forces propel the gas–liquid–solid mixture upward for discharge through the outlet. Under a constant gas flow rate, numerical simulations investigated efficiency variations through three operational scenarios: ① different pipeline orifice diameters, ② varying orifice quantities and spacings, and ③ adjustable pipeline bottom clearance heights. The results indicate that in scenario ①, an orifice diameter of 4 mm demonstrated optimal efficiency; in scenario ②, the eight-orifice configuration achieved peak efficiency; and scenario ③ showed that the proper adjustment of the bottom clearance height enhances pneumatic efficiency, with maximum efficiency observed at a clearance of 10 mm between sediment suction pipe and tank bottom. Full article

This study investigates the mechanism behind the cavitation-induced noise in an automotive heater core and proposes a structural solution to eliminate it. Abnormal noise during cold-start conditions in a compact passenger vehicle was traced to cavitation in the heater core of the heating, ventilation, and air conditioning (HVAC) system. Controlled bench tests, in-vehicle measurements, and computational fluid dynamics (CFD) simulations were conducted to analyze flow behavior and identify the precise location and conditions for cavitation onset. Results showed that high flow rates and low coolant pressure generated vapor bubbles near the junction of the upper tank and outlet pipe, producing distinctive impulsive noise and vibration signals. Flow visualization using a transparent pipe and accelerometer data confirmed cavitation collapse at this location. CFD analysis indicated that the original geometry created a high-velocity, low-pressure region conducive to cavitation. A redesigned outlet with a tapered transition and larger diameter significantly improved flow conditions, raising the cavitation index and eliminating cavitation events. Experimental validation confirmed the effectiveness of the modified design. These findings contribute to improving the acoustic performance and reliability of automotive HVAC systems and offer broader insights into cavitation mitigation in fluid systems. Full article

In centrifugal pump open cavitation tests, cavitation regulation valves are indispensable. During valve regulation, the irregular shape of the flow cross-section easily induces cavitation, significantly affecting the test results. This study investigates and designs a novel cavitation regulation valve. The valve core is composed of several identical valve flaps. By restricting the movement direction and distance of the valve flaps, the shape of the flow cross-section remains circular under different valve openings, ensuring optimal fluid flow conditions. This study examines the influence of the number of valve flaps on the flow state. The results indicate that, as the number of valve flaps increases, the flow cross-section approaches a circular shape, reducing the number of bubbles and improving the valve flow state. When the number of valve flaps increases to 20, the flow state shows no significant difference from a circular flow cross-section. Additionally, this study investigates the impact of the valve inlet and outlet shapes on the flow state. The findings reveal that the rounded corner structure experiences severe cavitation inside and at the rear end of the valve. The chamfered corner structure generates bubbles earlier than the initial valve structure but exhibits a stronger ability to resist pressure fluctuations. Both the chamfered inlet and chamfered outlet structures help suppress cavitation, with the chamfered outlet structure exhibiting lower-pressure fluctuations and stronger cavitation resistance. Therefore, the novel cavitation regulation valve with a circular flow cross-section can effectively enhance fluid flow conditions and suppress valve cavitation, demonstrating significant engineering application value. Full article

High-performance control valves are essential components in power plants. High-parameter control valves are specialized valves for controlling high-pressure, high-flow, high-temperature, and highly corrosive media. Control valve performance is critical for the stable operation of power plants. The multi-stage counter-flow passage is a common structure in pressure-reducing control valves, effectively mitigating cavitation and erosion on the valve walls. However, in practice, vibration issues in multi-stage passage valves are particularly pronounced. This study employs FSI (fluid–structure interaction) to simulate the vibration characteristics of multi-stage passages. Flow field data for the multi-stage passage are obtained through FLUENT software. A time-frequency analysis of the lift coefficient in the multi-stage passage flow field was performed. The vibration characteristics of the valve core’s inlet and outlet surfaces were studied using Transient Structural software. The results show that when high-pressure fluid passes through the valve core’s passage, it undergoes buffering, steering, and rotating motions, leading to a gradual pressure drop and generating resistance and lift. These phenomena are primarily caused by vortex shedding in the flow field, with the dominant frequency observed to be approximately 5400 Hz. Additionally, as the valve core progresses through the P1 phase at the inlet and the P2 phase at the outlet, the vibration intensity gradually decreases, reaching a minimum in the sixth phase, before increasing and peaking in the final stage. Analysis of the flow field characteristics within the valve core passage reveals the significant impact of vortex shedding on the valve core’s vibration and lift. Phase analysis of the valve core’s vibration intensity further clarifies its behavioral changes at different operational stages. These findings help optimize the design of multi-stage buffering valve cores, improving their performance and stability. Full article

To address the challenges of insufficient model generalization, high false alarm rates due to the scarcity of leakage data, and frequent minor leakage alarms in traditional weak leakage (the leakage amount is less than 1%) detection methods for gas transmission pipelines, this paper proposes a real-time weak leakage detection framework for natural gas pipelines based on the combination of the generalized likelihood ratio (GLR) and ensemble learning. Compared to traditional methods, the core innovations of this study include the following: (1) For the first time, GLR statistics are integrated with an ensemble learning strategy to construct a dynamic detection model for pipeline operating states through multi-sensor collaboration, significantly enhancing the model’s robustness in noisy environments by fusing pressure data from the pipeline inlet and outlet, as well as outlet flow data. (2) An adaptive threshold selection mechanism that dynamically optimizes alarm thresholds using the distribution characteristics of GLR statistics is designed, overcoming the sensitivity limitations of traditional fixed thresholds in complex operating conditions. (3) An ensemble decision module is developed based on a voting strategy, effectively reducing the high false alarm rates associated with single models. The model’s leakage detection capability under normal and noisy pipeline conditions was validated using a self-built gas pipeline leakage test platform. The results show that the proposed method can achieve the precise detection of pipeline leakage rates as small as 0.5% under normal and low-noise conditions while reducing the false alarm rate to zero. It can also detect leakage rates of 1.5% under strong noise interference. These findings validate its practical value in complex industrial scenarios. This study provides a high-sensitivity, low-false-alarm, intelligent solution for pipeline safety monitoring, which is particularly suitable for early warning of weak leaks in long-distance pipelines. Full article

In this study, we analyzed changes in flow characteristics and energy-dissipation characteristics due to changes in hydrogen temperature and inlet/outlet differential pressure in a check valve, which affect the storage safety and reliability of high-pressure hydrogen refueling systems. The effects of flow separation and recirculation flow generation at the back end of the valve were investigated, and the pressure, flow rate, pressure coefficient, and energy dissipation at the core part (where the hydrogen inflow is blocked) and the outlet part (where the hydrogen is discharged) were numerically analyzed. The hydrogen-inlet temperature (T_in) was selected as 233 K, 293 K, and 363 K, and the differential pressure (∆P) was selected in the range of 2 to 10 MPa in 2 MPa steps. To ensure the reliability of the numerical results, mesh dependence was performed, and the effect of the mesh geometry on the results was less than 2%. The numerical simulation results showed that the hydrogen introduced into the core part is discharged into the discharge part, and the pressure decreases by up to 6% and the velocity increases by up to 16% at the 95 mm position of the L-shaped curved tube. In addition, for the hydrogen-inlet temperature of 233 K in the L-shaped curved tube, the flow velocity decreases by up to 60% and the pressure coefficient increases at the 2.3 mm point in the Y-axis direction, indicating that the main flow area is biased towards the bottom of the valve due to the constriction of the veins caused by flow separation. The TDR results showed that the hydrogen discharge to the discharge region increased by 96% at 95 mm compared to 90 mm, and the turbulent kinetic energy of the hydrogen was dissipated, resulting in a temperature increase of up to 4.5 K. The exergy destruction was maximized in the core region where flow separation occurs, indicating that the pressure, velocity, and TDR changes due to flow separation and recombination have a significant impact on the energy loss of the flow in the check valve. Full article

To investigate the impact of airfoil angle of attack on the output performance of a valveless piezoelectric pump with airfoil baffles, this study conducted comprehensive performance tests and full-flow field simulations of piezoelectric pumps across a range of angles. At a driving voltage of 100 V and with a Clark Y airfoil set at an angle of 0°, the piezoelectric pump reached a peak output flow rate of 200.7 mL/min. An increase in the angle of attack corresponded to a decline in both the maximum output flow rate and the maximum back pressure of the pump. Flow field simulation results demonstrated that an increased airfoil angle of attack led to a gradual increase in entropy production within the piezoelectric pump. Turbulent dissipation and wall entropy production were found to be more pronounced compared to viscous entropy production. High turbulent dissipation was primarily observed at the pump chamber inlet, the trailing edges of the airfoils in both the inlet and outlet pipes, and the outlet bend. As the angle of attack increased, the complexity of the vortex core structures within the flow field escalated as well. Regions with significant wall entropy production were notably concentrated at the outlet bend. Full article

With the rapid advancement of modern industries, pressure vessels and piping have become increasingly integral to sectors such as energy, petrochemicals, and process industries. To grasp the research and application status in the field of pressure vessel and piping safety, 670 publications in the Web of Science core database from 2008 to 2024 were taken as data samples in this paper. The knowledge mapping tools were used to carry out co-occurrence analysis, keyword burst detection, and co-citation analysis. The results show that the research in this field presents a multidisciplinary and cross-disciplinary state, involving multiple disciplines such as Nuclear Science and Technology, Engineering Mechanics, and Energy and Fuels. The “International Journal of Hydrogen Energy”, “International Journal of Pressure Vessels and Piping”, and “Nuclear Engineering and Design” are the primary publication outlets in this domain. The study identifies three major research hotspots: (1) the safety performance of pressure vessels and piping, (2) structural integrity, failure mechanisms, and stress analysis, and (3) numerical simulation and thermal–hydraulic analysis under various operating conditions. The current challenges can be summarized into three aspects: (1) addressing the safety risks brought by new technologies and materials, (2) promoting innovation and the application of detection and monitoring technologies, and (3) strengthening the building capacity for accident prevention and emergency management. Specific to China, the current challenges include the safety and management of aging equipment, the effective detection of circumferential weld cracks, the refinement of risk assessment models, and the advancement of smart technology applications. These findings offer valuable insights for advancing safety practices and guiding future research in this multidisciplinary field. Full article

The pump turbine, as the core equipment of a pumped storage power plant, is most likely to operate in the hump zone between condition changes, which has a great impact on the stable operation of the power plant, and the high sedimentation of a natural river will lead to wear and tear in the overflow components of the equipment. Therefore, this paper is based on the Euler–Lagrange model, and seeks to investigate the distribution of vortices in the hump zone of the pump turbine and its effect on the movement of sand particles. The study shows that as the flow rate increases, the strip vortex in the straight cone section of the draft tube becomes elongated, and the cluster vortex in the elbow tube section gradually decreases. The strip vortex encourages the sand particles to move along its surface, while the cluster vortex hinders the movement of the sand particles. The accumulation areas of the sand particles in the straight cone section and the elbow tube section increase axially and laterally, respectively. The blade vortex in the runner gradually occupies the flow channel as the flow rate increases, and the blade vortex near the pressure surface encourages the sand particles to move towards the suction surface, resulting in the serious accumulation of sand particles on the suction surface. As the flow rate increases, the number of blades where sand particles accumulate increases and the accumulation area moves towards the cover plate and the outlet. The flow separation vortex in the double-row cascade decreases as the flow rate increases, which drives the sand movement in the middle and lower sections of the vanes. The area of sand accumulation in the stay vane decreases with increasing flow rate, but the area of sand accumulation between the guide vanes increases and then decreases. The vortex on the wall surface of the volute gradually decreases with the flow rate, and the vortex zone at the outlet first decreases, then disappears, and finally reappears. The vortex at the wall surface suppresses the sand movement, and its sand accumulation area changes from elongated to lumpy and finally to elongated due to the increase in flow. The results of the study provide an important theoretical reference for reducing the wear of pump turbine overflow components. Full article

The swivel system of a hydraulic excavator is susceptible to pressure impact during start and stop, which significantly impacts the service life of the excavator. In this investigation into how varying speeds affect the dynamic characteristics of a swing motor’s buffer relief valve (BRV), the AMESim simulation model of the whole swing motor was established, and its validity was confirmed through experimental testing. The pressure overshoot rate and start–stop impact time of the BRV of a swing motor at 1000 rpm, 1500 rpm, and 2000 rpm, under different spring stiffnesses, were analyzed. Based on the mathematical model of the BRV, the influence of the main structural parameters of the BRV on its dynamic characteristics were analyzed using an AMESim simulation model of the whole swing motor. The results show that an increase in the rotational speed of the electric motor, while maintaining a constant spring stiffness, affects the pressure overshoot rates of both the buffer relief valve of the swing motor inlet (BRVSMI) and the buffer relief valve of the swing motor outlet (BRVSMO); specifically, when the set pressure is established at 20 MPa, the pressure overshoot rate is observed to be higher, and the start–stop impact time exceeds 25 MPa. During the start phase of the swing motor, the start impact time for the BRVSMI remains relatively constant at approximately 2.5 s, with the pressure overshoot rate stabilizing at around 0.8. Conversely, in the stop phase of swing motor, both the stop impact time and the pressure overshoot rate of the BRVSMO exhibit variability in their response to the structural parameters of the BRV. Under conditions of comparatively high pressure, it is recommended to increase the diameter of the spool damping hole, the mass of the valve core, and the viscous damping coefficient, while simultaneously reducing the guide rod diameter of the buffer plunger, as these modifications can effectively enhance the start–stop impact time and mitigate the pressure overshoot rate. Full article

The emulsion pump’s flow loss directly affects its performance and efficiency. However, the annular plunger chamber leakage and valve core hysteresis are challenging to avoid during operation. This study systematically investigated the impact of the annular gap in the plunger cavity on emulsion pump performance. Using theoretical analysis and computational fluid dynamics methods, it explored the mechanism of the port valve hysteresis during discharge. The simulation results show that the leakage of the annular gap is proportional to the gap thickness and the inlet pressure and inversely proportional to the dynamic viscosity of the emulsion. With the increase of plunger eccentricity, the leakage increases slowly. The increase in the outlet diameter of the port valve will lead to more significant hysteresis of the valve core. The change of outlet pressure has little effect on the hysteresis and flow of the spool, and the response speed of the wing-guided bevel discharge valve is faster than that of the ordinary poppet valve. Considering the above factors, the flow distribution process of the emulsion pump can be accurately analyzed, providing a reference for pump optimization. Full article

Understanding the CO₂ displacement mechanism in ultra-low-permeability reservoirs is essential for improving oil recovery. In this research, a series of displacement experiments were conducted on sandstone core samples from the Chang 6 reservoir in the Huaziping area using a multifunctional core displacement apparatus and Nuclear Magnetic Resonance (NMR) technology. The experiments were designed under conditions of constant pressure, variable pressure, and constant effective confining stress to simulate various reservoir scenarios. The results indicated that the distribution characteristics of the pore structure in the rock samples significantly influenced the CO₂ displacement efficiency. Specifically, under identical conditions, rock cores with a higher macropore ratio exhibited a significantly enhanced recovery rate, reaching 68.21%, which represents a maximum increase of 31.97% compared to cores with a lower macropore ratio. Though fractures can facilitate CO₂ flowing through pores, the confining pressure applied during displacement caused a partial closure of fractures, resulting in reduced rock permeability. Based on the oil-to-gas ratio and oil recovery in the outlet section of the fractured rock samples, the CO₂ displacement process exhibited five stages of no gas, a small amount of gas, gas breakthrough, large gas channeling, and gas fluctuation. Although the displacement stage of different cores varies, the breakthrough stage consistently occurs within the range of 2 PV. These insights not only enhance our understanding of CO₂ displacement mechanisms in low-permeability reservoirs but also provide actionable data to inform the development of more effective CO₂-EOR strategies, significantly impacting industrial practices. Full article

Uniform air distribution is the basic condition for the stable operation of circulating fluidized beds and closely related to the hole layout of nozzles and the air outlet conditions. In this paper, CAD modeling software is used to establish different opening types for nozzles and the corresponding gasifier models, and Fluent simulation software for numerical simulations (k-ε model) is introduced to the hydrodynamic behavior of the upper opening, the side opening and the combined opening types of nozzles, as well as the corresponding single-nozzle fluidized bed gasifiers. The flow field distribution under the above opening modes is obtained, including the velocity distribution, static pressure distribution, and total pressure distribution, and the influence of the boundary conditions, including the inlet gas velocity and outlet pressure, on the flow field distribution inside the nozzle and in the single-nozzle fluidized bed gasifier is also investigated. The simulation results show that the suitable optimal operating conditions for the coal gasifier can be achieved with an inlet velocity of 30 m/s and an outlet pressure of 25 kPaG. Under the above conditions, the local fluidization dead zone at the elbow and top of the nozzle is narrower, the uniformity of the wind velocity can be improved, the pressure drop of the inner core tube of the nozzle is gentle, and the pressure distribution tends to be stable. Theoretically, the anti-slag performance of the nozzle is improved, which will enhance the stability and reliability of the operation of the gasification unit. Full article

LVR-15 is a light-water-tank-type research reactor placed in a stainless-steel vessel under a shielding cover located in the Research Centre Rez (CVR) near Prague. It is operated at a steady-state power of up to 10 MWt under atmospheric pressure and is cooled by forced circulation. In 2011, the fuel was replaced, going from high-enriched uranium (HEU) to low-enriched uranium (LEU). After 2017, the State Office for Nuclear Safety (SUJB) asked CVR to evaluate the LVR-15 under Design Extended Conditions B (DEC-B). For this reason, a new model was developed in the MELCOR code, which allows for modelling the progression of a severe accident (SA) in light-water nuclear power plants and estimating the behaviour of the reactor under SA conditions. The model was built by collecting information about the LVR-15. Since the research reactor can have different core configurations according to the location of the core components, the core configuration with the most fuel (hottest campaign K221) was selected. Then, to create the radial nodalisation, the details of the core components were obtained and grouped in five radial rings and 27 axial levels. The simulation was run with the boundary conditions collected from campaign K221, and the results were compared with the reference values of the campaign with a negligible percentage of error. For the coolant inlet and outlet temperature, the reference values were 318.18 K and 323.5 K, respectively, while for the simulation, the steady state reached 319 K for the inlet temperature and 324 K for the outlet temperature. Additionally, the cladding temperature of the hottest assembly was compared with the reference value (353.72 K) and the steady-state simulation results (362 K). In future work, different transients leading to severe accidents will be simulated. When simulating the LVR-15 reactor with MELCOR, specific attention is required for the aluminium-cladded fuel assemblies, as the model requires some assumptions to cope with the phenomenological limitations. Full article