| 1. |
- Hou, Yandong, et al.
(författare)
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Effects of rolling motion on helical coil once-through steam generator thermal-hydraulic characteristics
- 2023
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 194, s. 110068-
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Tidskriftsartikel (refereegranskat)abstract
- Steam generators are essential for the safe, economical, and reliable operation of nuclear reactors. Helical Coil Once-through Steam Generators (HCOTSG) offer unique advantages over other types of steam generators for ship reactors or offshore platforms. To investigate the effect of rolling motion due to ocean conditions on the safe and economic operation of HCOTSG, a new model and a new code are developed in this paper. The program is developed and allows numerical simulation of HCOTSG under ocean conditions. The validity of the code was verified by comparing the simulation results with the design parameters of the Marine Reactor X (MRX) steam generator and the simulation results of other dedicated programs. The code was further used to perform the International Reactor Innovative and Secure (IRIS) transient operating conditions under typical rolling motions. Then, the influences of different swing directions, angles, periods, and positions of swing axes from the origin of the system operating parameters are analyzed. In the cases discussed in this paper, the following conclusions are obtained: (a) The direction of the swing significantly affects the system. The most dangerous situation is around the x-axis, and the case around the z-axis is the safest, in which the rolling situation has little effect on the system because the centripetal force is perpendicular to the tube wall, and the gravitational pressure drop is constant. (b) when the swing angle increases, except the fluctuation speed is faster, the fluctuation range of the parameters also increases. (c) when the swing period changes, the parameters’ fluctuation range also change (d) the orientation of the swing axis from the origin affects the magnitudes of the parameters’ changes (e) the distance of the swing axis from the origin affects the magnitude of the parameter variation and the farther the swing axis is from the origin, the greater the parameter fluctuation.
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| 2. |
- Hou, Yandong, et al.
(författare)
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Thermal-hydraulic characteristics of helical coiled once-through steam generators in inclining condition of ocean
- 2024
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 200
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Tidskriftsartikel (refereegranskat)abstract
- This paper develops a one-dimensional thermal–hydraulic analysis program to simulate the main thermal–hydraulic parameter changes of helical coil once-through steam generator (HCOTSG) under inlet thermal–hydraulic parameters perturbation in inclining and vertical conditions. The inclining process is divided into the process of rotating from the vertical position to the inclining position and the stable inclining process. The rotating process is regarded as swaying motion. The swaying and inclining motions are achieved by modifying the momentum equation. What's more, the code was verified through experiments on two-phase heat transfer and friction pressure drop, as well as comparisons with the design parameters of the HCOTSG of the International Reactor Innovative and Secure (IRIS) reactor. The results of the simulation indicate that the direction of incline has an obvious impact on the safety of the HCOTSG, with inclination towards the y-axis having the greatest impact. In the stable inclining process, an increase in the angle of inclining results in a rise in primary-side outlet temperature and a reduction in heat transfer, while the secondary-side pressure drop increases. Furthermore, the HCOTSG underwent testing with eight types of transient perturbations, including four sudden perturbations and four linear perturbations. Results indicated that during sudden perturbations, apart from the secondary-side pressure drop, there were no substantial differences in simulated results between the inclined and vertical states at the same time during the transition process. However, during linear perturbations, due to the slow changes in parameters, the differences between the inclined and vertical states at the same time were more distinct. Regardless of the perturbation type, the inclined state led to a deterioration in the dynamic condition of the system compared to the vertical state.
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| 3. |
- Wu, Xiuchen, et al.
(författare)
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Exposures to temperature beyond threshold disproportionately reduce vegetation growth in the northern hemisphere
- 2019
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Ingår i: National Science Review. - : Oxford University Press (OUP). - 2095-5138 .- 2053-714X. ; 6:4, s. 786-795
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Tidskriftsartikel (refereegranskat)abstract
- In recent decades, terrestrial vegetation in the northern hemisphere (NH) has been exposed to warming and more extremely high temperatures. However, the consequences of these changes for terrestrial vegetation growth remain poorly quantified and understood. By examining a satellite-based vegetation index, tree-ring measurements and land-surface model simulations, we discovered a consistent convex pattern in the responses of vegetation growth to temperature exposure (TE) for forest, shrub and grass in both the temperate (30°−50° N) and boreal (50°−70° N) NH during the period of 1982−2012. The response of vegetation growth to TE for the three vegetation types in both the temperate and boreal NH increased convergently with increasing temperature, until vegetation type-dependent temperature thresholds were reached. A TE beyond these temperature thresholds resulted in disproportionately weak positive or even strong negative responses. Vegetation growth in the boreal NH was more vulnerable to extremely high-temperature events than vegetation growth in the temporal NH. The non-linear responses discovered here provide new insights into the dynamics of northern terrestrial ecosystems in a warmer world.
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| 4. |
- Zhang, Chao, et al.
(författare)
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Heaving motion effect on the transient thermodynamic characteristics of helical coil once-through steam generators in mixed ocean conditions
- 2024
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- Based on the finite difference method, the fixed boundary method, and a staggered grid method, this paper develops a one-dimensional thermal–hydraulic analysis code to simulate the effects of heave motion and more complex oceanic motions, namely heaving coupled with inclination and heaving coupled with swaying, on the thermal–hydraulic parameters of the International Reactor Innovative and Secure (IRIS) reactor's helical coil once-through steam generator (HCOTSG). The oceanic conditions were achieved by modifying the momentum equation. The validity and accuracy of the code were obtained by comparing the results with the design parameters of HCOTSG for two types of marine nuclear reactors, the SMART reactor and the IRIS reactor, and with the calculations of some similar international prediction programs. The simulation results indicate that (1) when only heave motion is considered, increasing the amplitude and reducing the period both result in a greater magnitude and a faster rate of change in the HCOTSG parameters. (2) When the combined motion of inclining and heaving is present, the dynamic performance of the composite motion inclining towards the positive x-axis deteriorates the most severely, while its thermodynamic conditions improve slightly. In this direction, the inclining angle has little influence on the thermal–hydraulic characteristics of HCOTSG. (3) When the combined motion of heaving and swaying is present, the dynamic performance is more severely affected under swaying motion towards the negative y-axis, despite a slight improvement in thermodynamic conditions. In this direction, as the swaying angle increases, the trend of parameter variation under swaying is similar but with a greater magnitude of change. The deterioration in dynamic performance becomes more severe, although there are small improvements in thermodynamic conditions. With the swaying period increasing, the maximum and minimum values of the secondary side pressure drop show little change. Additionally, the average thermodynamic conditions exhibit little variation.
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| 5. |
- Dong, Haoxuan, et al.
(författare)
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Flexible Eco-cruising Strategy for Connected and Automated Vehicles with Efficient Driving Lane Planning and Speed Optimization
- 2024
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Ingår i: IEEE Transactions on Transportation Electrification. - 2332-7782. ; 10:1, s. 1530-1540
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Tidskriftsartikel (refereegranskat)abstract
- Eco-cruising control of vehicles is a potential approach for improving vehicle energy efficiency and reducing travel time. However, many eco-cruising studies merely focused on vehicle longitudinal speed optimization but overlooked the lane change maneuvers, which may impair the benefits of eco-cruising when the vehicle encounters the slowly moving preceding vehicle. This study proposes a flexible eco-cruising strategy (FECS) with efficient driving lane planning and speed optimization capabilities simultaneously for connected and automated vehicles. The FECS is designed with a hierarchical control framework, where the first layer uses the Dijkstra algorithm to plan an efficient driving lane sequence considering the long-term effect of the preceding vehicles, then guides the second layer to optimize the vehicle’s speed for saving energy using trigonometric speed profile. The optimized driving trajectory is implemented in the third layer by regulating the speed and yaw angle for guaranteeing safe inter-vehicle distance when uncertainties are present. Finally, stochastic simulation with randomized traffic flows and typical case analysis based on real-world traffic data are conducted to demonstrate the performance of the FECS. The results manifest FECS’s capability of lowering driving costs in moderate-flow and free-flow traffic. However, we note that the benefits are less pronounced in congested-flow traffic.
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| 6. |
- Hou, Yandong, et al.
(författare)
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A review on the external cooling of the pressure vessel lower head in nuclear power plant
- 2023
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Ingår i: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 410
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Forskningsöversikt (refereegranskat)abstract
- At the beginning of the new century, since nuclear energy received widespread attention due to its economy and environmental protection, the nuclear industry has developed rapidly. However, there are still some issues challenging the safety of nuclear power plants (NPPs) especially at extreme conditions. During a hypothetical severe accident in a light water reactor, the core fuel will be disrupted and melt-down resulting from the absence of coolant, and finally forms a high-temperature molten pool at the lower head of reactor pressure vessel (RPV), which threaten the integrity of RPV, one of the most important barriers to prevent radioactive fission product releasing to the environment. In this regard, the decay heat removal of the molten pool plays an essential role in the strategy of in-vessel retention (IVR)-external reactor vessel cooling (ERVC) to arrest the molten corium inside the RPV, as shown in Fig. 1.This paper examines the research work about experimental investigation, theoretical analysis, and numerical simulation conducted for ERVC and summarizes the different approaches proposed by scholars to strengthen ERVC capabilities. Those approaches are the replacement of the cooling work materials, the application of nanofluids, surface modification, and other methods. Finally, it concludes the deficiencies of the current study and the direction of future efforts.
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| 7. |
- Hou, Yandong, et al.
(författare)
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Numerical study on surface corrosion deposition of fuel elements and its influence on flow heat transfer
- 2024
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Ingår i: Annals of Nuclear Energy. - : Elsevier BV. - 0306-4549 .- 1873-2100. ; 201
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Tidskriftsartikel (refereegranskat)abstract
- Corrosion of pressurized water reactors (PWR) in nuclear power plants can lead to serious safety hazards. This study aims to analyze the deposition of corrosion products using FLUENT software. Deposition models and thermal resistance models were developed, and the effects of deposits on the reactor's thermal–hydraulic characteristics were evaluated. Additionally, the impact of various parameters on deposition and thermal–hydraulic characteristics was examined. Results show that deposits accumulate extensively in the inlet section of the fuel cladding, while appearing as spot deposits in the outlet section. For deposit thicknesses below 30 μm, the surface temperature of the cladding gradually increases. However, when the thickness exceeds 30 μm, the surface temperature rapidly rises. Furthermore, the study reveals that the deposition amount decreases with increasing inlet flow velocity, exhibits an upward trend with higher inlet temperature, and increases with a higher wall heat flux density. This research provides important insights for understanding core deposition and thermal–hydraulic characteristics in nuclear reactor systems. It offers valuable guidance for enhancing safety and operational efficiency in nuclear power plants.
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| 8. |
- Jiang, Huanxiang, et al.
(författare)
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Appropriate Molecular Interaction Enabling Perfect Balance Between Induced Crystallinity and Phase Separation for Efficient Photovoltaic Blends
- 2020
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society. - 1944-8244 .- 1944-8252. ; 12:23, s. 26286-26292
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Tidskriftsartikel (refereegranskat)abstract
- Fluorination is a promising modification method to adjust the photophysical profiles of organic semiconductors. Notably, the fluorine modification on donor or acceptor materials could impact the molecular interaction, which is strongly related to the morphology of bulk heterojunction (BHJ) blends and the resultant device performance. Therefore, it is essential to investigate how the molecular interaction affects the morphology of BHJ films. In this study, a new fluorinated polymer PBDB-PSF is synthesized to investigate the molecular interaction in both nonfluorinated (ITIC) and fluorinated (IT-4F) systems. The results reveal that the F-F interaction in the PBDB-PSF:IT-4F system could effectively induce the crystallization of IT-4F while retaining the ideal phase separation scale, resulting in outstanding charge transport. On the contrary, poor morphology can be observed in the PBDB-PSF:ITIC system because of the unbalanced molecular interaction. As a consequence, the PBDB-PSF:IT-4F device delivers an excellent power conversion efficiency of 13.63%, which greatly exceeds that of the PBDB-PSF:ITIC device (9.84%). These results highlight manipulating the micromorphology with regard to molecular interaction.
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| 9. |
- Liu, Wenlong, et al.
(författare)
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On the calculation of electric diffusion coefficient of radiation belt electrons with in situ electric field measurements by THEMIS
- 2016
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 43:3, s. 1023-1030
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Tidskriftsartikel (refereegranskat)abstract
- Based on 7years' observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS), we investigate the statistical distribution of electric field Pc5 ULF wave power under different geomagnetic activities and calculate the radial diffusion coefficient due to electric field, , for outer radiation belt electrons. A simple empirical expression of is also derived. Subsequently, we compare to previous D-LL models and find similar Kp dependence with the model, which is also based on in situ electric field measurements. The absolute value of is constantly higher than , probably due to the limited orbital coverage of CRRES. The differences between and the commonly used and models are significant, especially in Kp dependence and energy dependence. Possible reasons for these differences and their implications are discussed. The diffusion coefficient provided in this paper, which also has energy dependence, will be an important contributor to quantify the radial diffusion process of radiation belt electrons.
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| 10. |
- Wang, Weichao, et al.
(författare)
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Remarkably enhanced hybrid piezo/triboelectric nanogenerator via rational modulation of piezoelectric and dielectric properties for self-powered electronics
- 2020
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 116:2
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Tidskriftsartikel (refereegranskat)abstract
- The hybridization of different materials for energy scavenging techniques based on piezoelectric and triboelectric effects has been studied widely for various applications of nanogenerators. However, there are few reports utilizing the same oxide matrix materials with appropriate doping to simultaneously enhance the piezoelectric and triboelectric outputs. Herein, a hybrid nanogenerator (HG) consisting of a piezoelectric nanogenerator (PENG) and a triboelectric nanogenerator (TENG) was constructed using (Ba0.838Ca0.162)(Ti0.9072Zr0.092)O3 (BCZTO)/polydimethylsiloxane (PDMS) as a piezoelectric layer and Ba(Ti0.8Zr0.2)O3 (BZTO)/PDMS as a triboelectric layer. For the PENG, how the electrical output was related to the BCZTO ratio in the BCZTO/PDMS composite films was systematically investigated. For the TENG, remarkably enhanced output performance is attributed to the ferroelectric polarization and large permittivity of the BZTO/PDMS. The Kelvin probe force microscopy measurements show that the poled BZTO/PDMS composite film with a 20 wt. % mass ratio of BZTO has the highest surface charge potential, in line with the macroscopic electrical outputs of the TENG. Interestingly, the output performance of the PENG in the HG is significantly enhanced compared to the PENG acting alone, which is also verified by COMSOL simulation. After rectification, the HG can produce a maximum output voltage of 390 V and a current density of 47 mA/m2. This work not only provides a feasible solution to enhance the output performance of the HG but also offers an effective approach to develop a small, portable power source with promising application in self-powered electronics.
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