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Geng Chen,Youping Tu,Cong Wang,Yi Cheng,Han Jiang,Hongyang Zhou,Hua Jin 대한전기학회 2018 Journal of Electrical Engineering & Technology Vol.13 No.6
Fluoronitriles-CO₂ gas mixtures are promising alternatives to SF6 in environmentallyfriendly gas-insulated transmission lines (GILs). Insulating gas heat transfer characteristics are of major significance for the current-carrying capacity design and operational state monitoring of GILs. In this paper, a three-dimensional calculation model was established for a GIL using the thermal-fluid coupled finite element method. The calculated results showed close agreement with experimentally measured data. The temperature distribution of a GIL filled with the Fluoronitriles-CO₂ mixture was obtained and compared with those of GILs filled with CO₂ and SF6. Furthermore, the effects of the mixture ratio of the component gases and the gas pressure on the temperature rise and current-carrying capacity of the GIL were analyzed. Results indicated that the heat transfer performance of the Fluoronitriles-CO₂ gas mixture was better than that of CO₂ but worse than that of SF₆. When compared with SF6, use of the Fluoronitriles-CO₂ gas mixture caused a reduction in the GIL’s current-carrying capacity. In addition, increasing the Fluoronitriles gas component ratio or increasing the pressure of the insulating gas mixture could improve the heat dissipation and current-carrying capacity of the GIL. These research results can be used to design environmentally-friendly GILs containing Fluoronitriles-CO₂ gas mixtures.
Wanfu Guo,Youping Yi,Shiquan Huang,Hailin He,Jie Fang 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.1
Large 2219 Al–Cu alloy transition rings are extensively utilised in launch vehicles. However, coarse-grained structures andagglomerated Al2Cusecond-phase particles considerably decrease the ductility of large 2219 Al–Cu alloy rings manufacturedusing the conventional hot rolling process. In this study, 10%–40% warm rolling deformation was applied to elucidatethe evolution of grain structures, characteristics of the Al2Cusecond-phase particles, and the influencing mechanisms ofductility. The results indicate that increased warm rolling deformation can facilitate dynamic recrystallisation and yield moresub-grains, which leads to the appearance of numerous finer and more equiaxed recrystallised grains after solution heattreatment; however, the homogeneity of the grain structure is decreased. With increased warm rolling deformation, Al2Cusecond-phase particles are more dispersed and more completely fragmented; furthermore, the dispersed and fragmentedAl2Cuparticles are more thoroughly dissolved during solution heat treatment. By the combined action of grain structuresand second-phase particles, the main fracture mode transitions from intergranular fracture into transcrystalline fracture. Thisresults in elongation in the axial and circumferential directions increasing steadily with increased warm rolling deformation;elongation in the radial direction initially increases, and finally decreases due to the appearance of glide planes. Samples thatexperience a warm rolling deformation of 30% exhibit the best overall elongation.
Jianwu Huang,Youping Yi,Shiquan Huang,Fei Dong,Wanfu Guo,Dengliang Tong,Hailin He 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.5
2219 Al–Cu alloy transition rings are widely used in launch vehicles. However, the coarse and agglomerated second-phaseAl2Cuparticles significantly deteriorate the mechanical properties and ductility of 2219 Al–Cu alloy rings manufactured bytraditional thermal deformation processes. In this study, cryogenic deformation (− 190 °C) is applied for the manufacturingof 2219 Al–Cu alloy rings to alleviate this problem. The effects on the evolution of second-phase Al2Cuparticles and themechanical properties of the T8-aged samples were examined in comparison with the results of room-temperature (25 °C)and conventional thermal deformation at 480 °C. The results indicate that cryogenic deformation can effectively producehigh-density dislocations and strongly crush coarse particles, promoting the dissolution of Al2Cuparticles and improving theirdistribution in the Al matrix when combined with subsequent solution treatment and rolling processes. As the deformationtemperature was decreased from 480 to −190 °C, the area fraction of the coarse particles was decreased from 1.55 to 0.47%,while their mean size was decreased from 11.8 to 8.3 μm. Correspondingly, the uniformity and density of the precipitatesafter T8 aging were improved. Thus, the mechanical properties of the T8-aged samples were improved with decreasingdeformation temperatures; the average ultimate tensile strength, yield strength, and elongation were increased by 20 MPa,22 MPa, and 3.1% at room temperature.
Dean's Flow of Aqueous Solution of Poly (ethylene oxide)
Kim, Chong Youp,Kim, Yong Hak,Yi, Mu Kwon 한국화학공학회 1996 NICE Vol.14 No.2
In this research the flow of Newtonian and drag reducing fluids through a helical tube, i.e., Dean's flow, was experimentally studied. The primary concern was to investigate the effect of added polymer on the secondary motion caused by the centrifugal force. The polymer chosen in this study was polyethylene oxide) with the molecular weights of 300,000, 900,000 and 4,000,000 and the solvent was distilled water. The concentration range was 0 to 100 wppm. The Dean number investigated was in the range of 10 to 2,0,000. In the case of distilled water, the experimental data were in good agreement with the literature. In the case of polymer solutions, it was found that the secondary motion was suppressed as the concentration and molecular weight increased. However, if the molecular weight or concentration exceeded certain values, the effects were saturated. The results were also analyzed from the view point of drag reduction phenomena.
Grain Refinement and Thermal Stability of 2219 Aluminum Alloy in the Warm Deformation Process
Xianchang Mao,Youping Yi,Shiquan Huang,Wanfu Guo,Hailin He 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.11
2219 Al alloy is an important material for manufacturing launch vehicles, and its grain structure has a substantial effecton the performance of storage tank transition rings. In this work, warm compression tests (100–350 °C) of 2219 Al alloywere carried out, a grain refinement model of warm deformation was established, and the evolution and thermal stability ofthe static recrystallized grain size D were analyzed. The results showed that static recrystallization is the main mechanismof grain refinement, and that the nucleation rate and grain refining effects were significantly improved by decreasing thedeformation temperatures (T). The established model was found to be accurate, and the predicted and experimental valuesexhibited high degrees of coincidence. When T and the amount of deformation (Δd) were respectively 150 °C and 70%, thevalue of D was reduced from 60 μm to 21 μm. Additionally, when the solution treatment time was increased from 0 to 4 h,there was a slight change in the values of D (high thermal stability) when T was lower than 250 °C and Δd was greater than20%, but they significantly increased when Δd was less than 10%.
Zhiwu Zhang,Youping Yi,Wen You,Shiquan Huang,Yonglin Guo,Hailin He 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.6
To investigate the quenching sensitivity of the 2195 Al–Li alloy rolled sheet and guide the design of the quenching process,the time–temperature-property (TTP) curves of this material were researched through interrupted quenching experiments. The differential scanning calorimetry (DSC) and transmission electron microscope (TEM) were used to characterize theevolution of precipitates during isothermal treatment. The results of this essay demonstrated that the nose temperature of 2195Al–Li alloy is around 370 °C and the temperature range of quenching sensitivity is 340 °C to 400 °C. The microstructureobservation revealed that the T1particles precipitate and grow rapidly at the temperature from 340 to 400 °C, which is dueto the high nucleation rate of phase and fast solute diffusion kinetics, especially at the nose temperature. The needle-shapedθ′/θ″ and T1particles grow up quickly as the isothermal preservation time prolonged, leading to the decrease of the supersaturatedsolid solution of the matrix. This will reduce the number of the age-induced precipitate and weaken the subsequentage hardening effect. Therefore, the rate of cooling should be increased in the quenching sensitivity range (340–400 °C) toinhibit the precipitation of the second phase and obtain excellent mechanical properties. While in other temperature ranges,the cooling rate should be decreased appropriately to reduce residual stress. The appropriate average cooling rate is recommendedto be around 13 °C s−1 at the temperature from 340 to 400 °C.
Chenguang Wang,Youping Yi,Shiquan Huang,Fei Dong,Hailin He,Ke Huang,Yanzhen Jia 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.12
Cryogenic forming, a new technology used to manufacture aluminum alloy thin-walled parts, has attracted much attentionin recent years. This work presents an experimental and theoretical study of 2024-O aluminum alloy sheet forming limit atcryogenic temperatures and provides an effective method for accurate prediction of forming limit curves (FLCs) at cryogenictemperatures. Uniaxial tensile experiments at different temperatures were carried out between 20 °C and − 196 °C to obtainthe constitutive equation of the material at cryogenic temperatures. The Marciniak–Kuczynski (M–K) model was used topredict FLCs at cryogenic and room temperatures. The constitutive equation and yield functions are used in the model. Theeffects of different yield criteria (Mises, Hill-48, Barlat89, Gotoh, and Yld2000-2d) on the prediction results of FLC areanalyzed. These prediction results were verified by the Nakazima test, and it was found that the Yld2000-2d yield criterion isthe most accurate for FLC prediction. Finally, the M–K model is combined with this criterion to predict the FLC at differenttemperatures. It was found that the lower the temperature, the higher the FLC curve and the better the sheet formability, andthe increase is more obvious at extremely low temperatures.