• 소성∙가공
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• 제33권5호
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• pp.309-314
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• 2024

Supersonic aircraft and missiles often encounter damage issues due to high-speed collisions with small objects such as ice particles and water droplets. This can significantly impact the safety and performance of these vehicles, making the assessment and development of collision testing crucial. Existing collision testing methods have relied on equipment such as gas guns, which utilize high pressure. However, most accelerators for projectiles are large-scale devices designed for weaponry and high-pressure gases, rendering them inaccessible and unsuitable for laboratory use. Therefore, there is a need for research into easily accessible and economically efficient testing devices at the laboratory level. An impact tester can launch a projectile with a velocity of 100 m/s using low-pressure compressed air at approximately 10 bar. The velocity of the impact tester projectile is determined by the pressure within the chamber, friction, and the length of the barrel. In this study, computational fluid dynamics was utilized to define friction coefficients that match experimental results based on projectile weight, enabling accurate prediction of velocity. The resulting data provides practical and effective insights for the design of impact testers, utilizing the defined friction coefficients to understand and predict complex physical phenomena.

• 한국조리학회지
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• 제20권3호
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• pp.13-21
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• 2014

본 연구에서는 순환형 감압건조 및 초고압 추출공정을 이용하여 전통적인 기존 추출공정과 비교함으로써 복합 추출공정에 의한 감귤의 항산화 활성 증진을 확인하고자 연구를 수행하였다. 건조공정을 거친 후 초고압 처리 추출물의 수율이 20.41~28.19%로 높은 추출 수율을 나타내어 건조전 열수추출공정(17.21%)과 비교하여 약 1.6배의 높은 추출수율을 나타내었다. 순환형 감압건조와 초고압 공정을 병행하였을 시 총 폴리페놀과 플라보노이드 함량이 순환형 감압건조공정을 거치지 않은 것보다 다소 증가되는 것으로 보아 활성성분의 용출이 증진된 것으로 보인다. DPPH radical 소거 활성은 15분 초고압 처리한 추출물이 48.21%로 높은 활성을 나타내었다. 전처리 공정에 따른 감귤 시료의 주사전자현미경(SEM)을 통해 순환형 감압건조 후 초고압 추출이 감귤 내부 조직까지 영향을 주어 세포벽이 깨어지면서 조직 및 구조가 변화한 것으로 판단되며, 이를 통해 수율 및 활성 성분의 용출 증가가 이루어 진 것으로 사료된다. 따라서, 감귤의 건조 및 초고압 추출공정의 최적화를 통한 활성물질의 추출 극대화를 통해 추출수율을 향상시킬 것으로 판단된다.

• 대한기계학회논문집B
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• 제32권2호
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• pp.83-91
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• 2008

A three-dimensional computation was conducted to understand effects of the low Reynolds number on the performance in a low-speed axial compressor at the design condition. The low Reynolds number can originates from the change of the air density because it decreases along the altitude in the troposphere. The performance of the axial compressor such as the static pressure rise was diminished by the separation on the suction surface with full span and the boundary layer on the hub, which were caused by the low Reynolds number. The total pressure loss at the low Reynolds number was found to be greater than that at the reference Reynolds number at the region from the hub to 85% span. Total pressure loss was scrutinized through three major loss categories in a subsonic axial compressor such as the profile loss, the tip leakage loss and the endwall loss using Denton#s loss model, and the effects of the low Reynolds number on the performance were analyzed in detail.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.138-141
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• 2007

A three-dimensional computation was conducted to understand effects of the low Reynolds number on the performance in a low-speed axial compressor at the design condition. The low Reynolds number can originates from the change of the air density became it decreases along the altitude in the troposphere. The performance of the axial compressor such as the static pressure rise wag diminished by the separation on the suction surface and the boundary layer on the hub, which were caused by the low Reynolds number. The total pressure loss at the low Reynolds number was found to be greater than that at the reference Reynolds number at the region from the hub to 90% span. Total pressure loss was scrutinized through three major loss categories in a subsonic axial compressor such as profile loss, tip leakage loss and endwall loss using Denton's loss model, and effects of the low Reynolds number on the performance were analyzed in detail.

• Journal of Korean Society for Atmospheric Environment
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• 제19권E1호
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• pp.1-9
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• 2003

The soil concentrations of polychlorinated biphenyls (PCBs) were measured at 12 sites in Ansung, Kyonggi province, Korea. Correlation coefficient (r) between total PCBs and organic matter content (OM) was significant (r=0.562, p< 0.05). It suggests that organic matter may be a key factor of soil absorption of PCBs. The PCB concentrations of low chlorinated congeners with high vapor pressure were relatively abundant in air but high chlorinated congeners with low vapor pressure were mainly dominated by soil. The results indicated the influence of physicochemical properties of PCBs such as vapor pressure, octanol - air partition coefficient ( $K_{OA}$ ). The calculated soil/air fugacity quotients suggested that the soil may be a source of heavier molecular PCBs (>penta-CBs) to the atmosphere, where lighter molecular PCBs appear to be affected by a movement from air to soil, especially tetra-CBs. Therefore, PCB homologs with low vapor pressure might have been influenced by revolatilization from soil.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2572-2592
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• 1996

A low-Reynolds-number second moment turbulence closure was developed with the aid of DNS data. Model coefficients of nonlinear return to isotropy term were derived by use of Cayley-Hamilton theorem and two component turbulence limit condition as the functions of invariances of anisotropy and turbulent Reynolds number. Launder and Tselepidakis' cubic mean pressure strain model was modified to fit the predicted pressure-strain components to the DNS data. Two component turbulence limit condition was the precondition to be satisfied in developing the second moment turbulence closure for the realizable Reynolds stress prediction. But the satisfactions of Reynolds stress level and pressure-strain level of each component were compromised because the satisfaction of both levels was impossible.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.195-200
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• 2001

An experimental study on critical heat flux (CHF) has been performed for water flow in a uniformly heated vertical 3 by 3 rod bundle under low flow and a wide range of pressure conditions. The objective of this study is to investigate the parametric trends of CHF with 3 by 3 rod bundle test section where three unheated rods exist. The general trends of the CHF are coincident with previous understandings. At low flow and system pressure above 3 MPa, some critical qualities are larger than 1.0 due to counter-current flow in test sections. Since there is a supply of water to the heated section from unheated section, the maximum CHFs at system pressure between 2 and 4 MPa are not shown.

• 한국안전학회지
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• 제24권5호
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• pp.21-27
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• 2009

Effective way of cooking oil fire extinguishment is using water mist system which has cooling and smothering effects. Low pressure water mist system has advantage because it is compatible with existing sprinkler systems. To increase the effectiveness of low pressure water mist system, additives can be used which increase the momentum of water particle and the chemical effect. In this experiment, aqueous film forming form(AFFF) agent is used as additive and the effect of additive concentration and water pressure are experimented. For the extinguishment of cooking oil fire such as soybean and olive oils, AFFF agent is effective and can decrease the fire extinguishing time and water consumption.

• Transactions on Electrical and Electronic Materials
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• 제3권2호
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• pp.24-27
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• 2002

The NdBaCuO superconductor samples were zone-melted in low oxygen partial pressure (1%O$_2$+99%Ar). The zone-melting temperature was decreased about 12$0^{\circ}C$ film 1,06$0^{\circ}C$, the zone-melting temperature in air. Thus the loss of liquid phase (BaCuO$_2$ and CuO) was reduced during: the zone-melting process. The content of non-superconducting phase Nd422 in zone-melted NdBaCuO samples was clearly decreased and, therefore, the substitution of Nd for Ba was occurred. The superconductivity of zone-melted Nd$_{1+x}$Ba$_{2-x}$Cu$_3$O$_{y}$ prepared under low oxygen partial pressure was distinctively improved.d.d.d.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 정기총회 및 추계학술대회 논문집 학회본부
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• pp.261-263
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• 1993

The effects of the magnetic field and gas pressure on the etching characteristics were investigated in the axial magnetic field enhanced RIE system. This system has many advantages compared with the conventional RIE system ; the capability of operating at low pressure, low self-bias voltage, high electron density and high etch rate in the low pressure, but also has disadvantages such as the nonconformity of plasma density which intensifies as the magnitude of magnetic field increases. To overcome this problem we made some grooved anode and tried to find the optimal pressure and B-field strength.