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Gang Yang,Xutao Zhao,Desheng Zhang,Linlin Geng,Xueqi Yang,Xiongfa Gao 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.11
The large vertical centrifugal pump is the core power equipment for longdistance water division and large-scale irrigation projects. The power of the matching motor can reach 40 MW. In view of reducing the operating energy consumption of this kind of pump, the efficiency under the design condition was taken as the optimization objective, and a matching optimization on hydraulic components was proposed in this research. The optimization process was divided into two stages. The first stage focused on improving the configuration of the vane diffuser. In the second stage, the Plackett-Burman test design was used to screen out the optimization design variables of the vane diffuser and the volute, the optimal Latin hypercube sampling method was adopted to generate 106 sample cases, and an automatic numerical simulation optimization platform was built. Then, different approximate models were employed to construct the relationship between the optimization design variables and the objective function, and their fitting accuracy and robustness were compared. Finally, the optimal design parameters were determined by particle swarm optimization, and entropy production theory was used to analyze the internal flow pattern of the model before and after optimization. Results showed that D 3 , b 4 , β 3 , and S 8 have the greatest impact on the hydraulic efficiency of the pump. The multilayer backpropagation neural network has a higher fitting accuracy and better robustness compared with the other three approximate models. The efficiency of the optimized model under the design condition is increased by 4.22 %, reaching 90.82 %. Reducing the number of layers and vanes of the diffuser and improving the matching of hydraulic components can dramatically improve the hydraulic performance and hump characteristics of large vertical centrifugal pumps. Entropy production theory is a reliable approach to visualizing flow loss. The turbulent flow dissipation in the vane diffuser can be reduced the most after optimization.
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Xueqi Guo,Yuheng Zeng,Zhi Zhang,Yuqing Huang,Mingdun Liao,Qing Yang,Zhixue Wang,Minyong Du,Denggao Guan,Baojie Yan,Jichun Ye 한국물리학회 2019 Current Applied Physics Vol.19 No.7
The junction properties of tunnel silicon oxide (SiOx) passivated contact (TOPCon) with n-type poly-Si on p-type c-Si wafer are characterized using current-voltage (J-V) and capacitance-voltage (C-V) measurements. The dark J-V curves show a standard diode characteristic with a turn-on voltage of ∼0.63 V, indicating a p-n junction is formed. While the C-V curve displays an irregular shape with features of 1) a slow C increase with the decrease of the magnitude of reverse bias voltage, being used to estimate the built-in potential (Vbi), 2) a significant increase at a given positive bias voltage, corresponding to the geometric capacitance crossing the ultrathin SiOx, and 3) a sharp decrease to negative values, resulting from the charge tunneling through the SiOx layer. The C of depleting layer deviates from the normal linear curve in the 1/C2-V plot, which is caused by the diffusion of P dopants from the n-type poly-Si into the p-type c-Si wafer as confirmed by the electrochemical capacitance-voltage measurements. However, the 1/C2+γ-V plots with γ > 0 leads to linear curves with a proper γ and the Vbi can still be estimated. We find that the Vbi is the range of 0.75–0.85 V, increases with the increase of the doping ratio during the poly-Si fabrication process, and correlates with the passivation quality as measured by the reverse saturated current and implied open circuit voltage extracted from transient photoconductivity decay.
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Diagentic features of illite in Upper Triassic Chang-7 tight oil sandstones, Ordos Basin
Ai Wang,Dakang Zhong,Haihua Zhu,Lele Guo,Yangjinfeng Jiang,Xueqi Yang,Rui Xie 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.2
The Upper Triassic Chang-7 tight oil sandstones are the main tight clastic reservoirs in the Ordos Basin, central China. Illite is one of the most important cements affecting porosity and permeability of the tight oil sandstones, and this study focuses on different types of illitization and its relative formation time. The Chang-7 tight sandstones are mainly fine-grained lithic arkose and feldspar lithic sandstones, rich in mica and illite (hydrous mica). They are formed in distal delta front to semi-deep and deep lake facies, mainly deposited in a low energy environment. Porosity and permeability are very low (average porosity 8.58% and permeability 0.20 mD). The illite has many morphological characteristics and is multiphase, incorporating six types of illitization: hydrous mica, mica, and smectite illitization at the eodiagenetic stage, and kaolinite and K-feldspar illitization, and neoformation illite particles, at the mesodiagenetic stage. These different types of illitization are mainly controlled by sedimentary environment and provenance. Quartz overgrowth and diagenetic illites appear to be locally mutually exclusive, competing for detrital grain surfaces, but neoformation illite particles appear to form on the quartz overgrowth. The systematic study of Upper Triassic Chang-7 tight oil sandstones carried out here, enhances our understanding of illitization and the diagenetic model of the Ordos Basin, and contributes to reducing the exploration risk of continental tight sandstone reservoirs.
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Ai Wang,Dakang Zhong,Haihua Zhu,Lele Guo,Zhuopei Li,Yangjinfeng Jiang,Xueqi Yang,Rui Xie,Xiaowei Zheng 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.3
The seventh oil layer of the Upper Triassic Yanchang Formation (Chang-7) tight oil sandstone reservoirs is a major exploration target. A significant amount of hydrocarbons has been discovered in these reservoirs in the southwestern Ordos basin in China. The Chang-7 tight sandstones are characterised as tight with low porosity, low permeability, and strong heterogeneity. This study investigates the sedimentary facies, diagenesis, and their impact on the reservoir quality of the Chang-7 tight oil sandstones. The sandstones were deposited in a deltaic-lacustrine depositional system. Three major depositional facies are identified consisting of delta front fed by braided rivers and meandering rivers, and slump turbidite fans. The depositional environment exerts a key control on reservoir quality. The distinct low-energy sedimentary environment produced fine to very fine-grained sandstones with high matrix and mica contents, characterised by low initial porosity and permeability. Diagenesis mainly comprised mechanical compaction and cementation by quartz, carbonate minerals and various clay minerals. The reservoir properties of the Chang-7 sandstones are generally poor, with porosity of 1.4–20.7% (average porosity 8.6%) and permeability of 0.001–116.7 mD (average 0.2 mD), which are attributed to significant compaction and cementation. Mechanical compaction was more important than cementation for reducing porosity, whereas secondary dissolution porosity was significant for the Chang-7 tight oil sandstones due to closer proximity to the underlying Chang-73 source rocks.
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