• 소성∙가공
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• 제31권5호
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• pp.290-295
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• 2022

Recently, the use of high-tech ceramic parts in functional electronic parts, automobile parts and semiconductor equipment parts is increasing. These ceramics materials are required to have high reproducibility, reliability, large size and complex shapes. The researchers initiated the work to develop a new shaping method called gel casting, which allows high performance ceramic materials with a complex shape to be produced. The manufacturing process parameters of gel casting include uniform mixing of the initiator, bubble removal, and slip injection. In this study, we analyzed the dispersion and gelation characteristics according to the change in the additive content of the alumina slurry in the gel casting process. The alumina slurry for gel casting was prepared by mixing a solvent, a monomer and a dispersant through a ball mill. Alumina powder and a gelation initiator were added to the mixed solution, and ball milling was performed for 24 hours. A viscosity of 6,435 cps and a stable zeta potential value were obtained under the conditions of alumina powder content of 55 vol% and dispersant 2.0 wt%. After curing for 12 hours by adding aps 0.1wt%, TEMED 0.2wt%, and Monomer 3, 5wt%, it was possible to separate from the molding cup, confirming that the gelation was completed.

• Wind and Structures
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• 제34권4호
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• pp.385-394
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• 2022

Global Warming has been driven majorly by the consumption of fossil fuels. Harnessing energy from wind is viable solution towards reducing carbon footprint created due to burning such fuels, However, wind turbines have their problems of flow separation and aerodynamic stall to tackle with. In an attempt to delay the stall angle and improve the aerodynamic characteristics of the NACA 0015 symmetrical aerofoil, lateral cylindrical ridges were attached to its suction surface, at chord positions ranging from 0.1c to 0.5c. The characteristics of the original and ridged aerofoils were obtained using simultaneous pressure readings taken in a wind tunnel, at a free stream Reynolds number of R_e = 2.81 × 10⁵ for a wide range of free stream angles of attack ranging from -45° to 45°. Depending on the ridge size, a delay in stall angle varying from 5° to 20° was achieved together with the maximum increase in lift in the post-stall phases. Additionally, efforts were made to identify the optimum position for each ridge.

• 대한설비공학회지:설비저널
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• 제16권1호
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• pp.89-102
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• 1987

Experiments have been carried out to study the atomisation characteristics of superheated liquid(water) jet injected into the atmosphere through a single-hole nozzle. In present experi-mental range, superheated liquid jet has been observed to be atomised in two-phase effluent type; that is, spray formed by the bubble nucleation in the nozzle. In case of liquid injection through a long nozzle (L/D=29.09), the critical superheat for occurrence of two-phase effluent atomisa-tion can be determined from sudden change of spray angle. Sauter mean diameter of the spray droplets decreases as the degree of superheat increases. For the short nozzle (L/D=7.27), mean diameter increases with the injection pressure, while it decreases for the long nozzle; however for the long nozzle the effect of injection pressure is not significant compared with the short nozzle. For the short nozzle the uniformity of drop size distribution increases with increasing the degree of superheat, but for the long nozzle the effect of superheat on the uniformity is not appreciable.

• 한국압력기기공학회 논문집
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• 제17권2호
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• pp.109-118
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• 2021

In the periodic surveillance material test for the spacer component of fuel channel assembly in CANDU, a microstructural characterization analysis is required in addition to the mechanical property evaluation test. In this study, detailed microstructure analysis and simple mechanical property evaluation of archive spacer parts were conducted to indirectly support the surveillance test and assist in the study of spacer material degradation. We investigated the microstructural characteristics of the spacer garter spring coil through comparative analysis with the plate material. The main microstructure characteristics of the garter spring coil X-750 are represented by the fine grain size distribution, the ordering phase distribution developed inside the matrix, the high dislocation density inside the grains, and the arrangement of coarse carbides. In addition, the yield strength of the garter spring coil X-750 was indirectly evaluated to be approximately 1 GPa. We also established an analytical method to elucidate the microstructural evolution of the radioactive spacer garter spring coil X-750 based on Canadian research experiences. Finally, we confirmed the measurement technique for helium bubble formation through TEM examination on the helium implanted X-750 material.

• Ocean Systems Engineering
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• 제12권3호
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• pp.335-358
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• 2022

Hydrodynamic field alteration around a cylindrical pier using a curved vane is numerically investigated. The curved vane with various angles ranged from 10 to 220 degree is placed at the upstream of the cylindrical pier. Laminar flow is adopted in order to perform the steady-state analysis. It is found that the flow separation leads to the formation of four bubbles depending on the value of the curved vane angle. Two bubbles are located in the region between the rear of the curved vane and the leading surface of the cylindrical pier, while the remaining two bubbles are located at the wake zone behind the cylindrical pier. Numerical analysis is performed to reveal the hydrodynamic field and influence of curved vane on the formation and evolution of the bubbles. It is found that the center and size of the bubble depend mainly on the value of the curved vane angle. It is observed that the flow velocity vector shows clearly the alteration in the flow velocity direction especially at the leading surface and rear surface of the curved vane owing to the occurrence of flow separation and flow dissipation along the circumference of the vane.

• 한국식품저장유통학회지
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• 제31권1호
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• pp.64-79
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• 2024

The rise in popularity of vegetarian and plant-based diets has led to extensive research into plant-based whipped creams. Whipped cream is an oil-in-water emulsion that creates foam through whipping, stabilizing the foam with proteins and fats. Pea protein is an excellent emulsifier and foaming agent among plant-based proteins, but its application in whipped cream is currently limited. The objective of this study was to investigate the quality characteristics of plant-based whipped cream made with ultrasonicated pea protein. The whipped creams were evaluated based on their quality characteristics. A commercially available dairy whipped cream (CON) was used as a control. Plant-based creams were evaluated using pea protein solution, cocoa butter, and canola oil to produce un-ultrasonicated pea protein whipped cream (PP) and ultrasonicated pea protein whipped cream (UPP) at 360 W for 6 min. UPP significantly reduced whipping time and foam drainage compared with CON and PP, resulting in significantly increased overrun, fat destabilization, and hardness. Optical microscopy showed that UPP had smaller fat globules and bubble size than PP. The fat globules of UPP and CON were mostly below 5 ㎛, whereas those of PP were distributed at 5-20 ㎛. Finally, ultrasonication significantly improved the overrun, foam drainage, fat destabilization, and hardness of UPP, which are significant quality characteristics of whipped creams. Therefore, ultrasonicated plant-based pea protein whipped cream is believed to be a viable alternative to dairy whipped cream.

• 대한기계학회논문집B
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• 제38권10호
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• pp.865-871
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• 2014

본 연구는 벤츄리 시스템을 미세기포 생성을 위한 공기공급 장치로 개발하는데 그 목표를 두고 수행하였다. 이를 위해 상용유동해석 프로그램인 ANSYS CFX-15를 사용한 전산 유동해석을 통해 기하학적 형상변화가 벤츄리 관 내 유동특성들에 미치는 영향을 규명하였다 그리고 공급공기를 공급하는 공기 공급관의 위치, 크기, 개수 등을 변수로 2-유체 유동 해석을 수행하여 이들 설계 값들이 공기 공급 특성에 미치는 효과를 규명하였다. 최종적으로 직경 비 ${\beta}=0.75$의 벤츄리 확대관이 시작되는 위치에 공기 공급 구멍을 설치할 경우 가장 많은 공기가 벤츄리 관으로 유입되는 것을 확인할 수 있었으며, 유입공기 공급구멍 개수 및 직경과 벤츄리 관 내 공급되는 공기량 사이에는 선형적인 관계가 성립됨을 확인하였다.

• 한국분말재료학회지
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• 제27권1호
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• pp.37-43
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• 2020

The Fe-22wt.%Cr-6wt.%Al foams were fabricated via the powder alloying process in this study. The structural characteristics, microstructure, and mechanical properties of Fe-Cr-Al foams with different average pore sizes were investigated. Result of the structural analysis shows that the average pore sizes were measured as 474 ㎛ (450 foam) and 1220 ㎛ (1200 foam). Regardless of the pore size, Fe-Cr-Al foams had a Weaire-Phelan bubble structure, and α-ferrite was the major constituent phase. Tensile and compressive tests were conducted with an initial strain rate of 10^-3/s. Tensile yield strengths were 3.4 MPa (450 foam) and 1.4 MPa (1200 foam). Note that the total elongation of 1200 foam was higher than that of 450 foam. Furthermore, their compressive yield strengths were 2.5 MPa (450 foam) and 1.1 MPa (1200 foam), respectively. Different compressive deformation behaviors according to the pore sizes of the Fe-Cr-Al foams were characterized: strain hardening for the 450 foam and constant flow stress after a slight stress drop for the 1200 foam. The effect of structural characteristics on the mechanical properties was also discussed.

• 센서학회지
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• 제8권4호
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• pp.320-326
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• 1999

센서의 감지막 표면에 흡착되어 있는 이물질을 세척하기 위해 노즐 원리를 도입하여 소형 카트리지를 제작하였다. 세척용 노즐구조는 유동 해석 프로그램(CFD-ACE)의 검증을 통하여 소형 카트리지에 적합하도록 설계하였다. 미세가공기술을 이용하여 제작된 카트리지의 전체 크기는 약 $2.6\;cm{\times}1.5\;cm$이고 세척용 노즐의 크기는 $0.2\;mm{\times}600\;mm$이며, 측정에 필요한 시료의 양은 약 $20\;{\mu}l$이다. REFET과 의사기준전극을 이용한 차동증폭법을 사용하여 기준전극을 소형화하였다. 또한, 미세채널에서 기포로 인한 센서의 오동작을 감지하기 위해 채널 양단에 금속전극을 증착하였다. 제작된 카트리지에 pH-ISFET를 장착하여 노즐에 의한 세척효과를 조사하였다.

• 한국세라믹학회지
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• 제53권6호
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• pp.604-609
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• 2016

This study reports on wet-foam stability with respect to porous ceramics from a particle-stabilized colloidal suspension that is achieved through the addition of polymethyl methacrylate (PMMA) using a wet process. To stabilize the wet foam, an initial colloidal suspension of $Al_2O_3$ was partially hydrophobized by the surfactant propyl gallate (2 wt.%) and $SiO_2$ was added as a stabilizer. The influence of the PMMA content on the bubble size, pore size, and pore distribution in terms of the contact angle, surface tension, adsorption free energy, and Laplace pressure are described in this paper. The results show a wet-foam stability of more than 83%, which corresponds to a particle free energy of $2.7{\times}10^{-12}J$ and a pressure difference of 61.1 mPa for colloidal particles with 20 wt.% of PMMA beads. It was possible to control the uniform distribution of the open/closed pores by increasing the PMMA content and by adding thick struts, leading to the achievement of a higher-stability wet foam for use in porous ceramics.