• Journal of Power System Engineering
• /
• v.16 no.6
• /
• pp.11-18
• /
• 2012

대형 상용 엔진에서 발생하는 유효 도시 마력의 약 4~15%는 마찰 손실을 통해서 사라지며 마찰 손실 중 약 40~55%는 엔진 실린더와 피스톤 사이의 마찰에 의하여 발생하여, 엔진 전체에서 발생하는 마찰 손실 중 가장 많은 부분을 차지하고 있다. 이 연구에서는 엔진 실린더 라이너의 온도 분포 개선을 통해 라이너를 따라 유막을 형성하고 있는 윤활유의 적정 점성을 유지시키는 방법을 제시하고자 한다. 피스톤-라이너에서 발생하는 마찰 특성은 피스톤의 행정 위치에 따라서 접촉 마찰과 유막에 의한 마찰로 구분되며 이에 따라 요구되는 윤활유의 점성 특성 또한 달라진다. 먼저 해석 모델을 통하여 실린더 라이너 내부 온도 분포 특성을 확인한 후 피스톤 마찰 특성을 고려한 적정 온도 분포를 고찰하며 실린더 라이너에 열저항 코팅을 통해서 이를 구현하였다. 또한 실린더-피스톤 간의 마찰/윤활 해석을 통하여 열저항 코팅의 마찰 개선효과를 확인하였다.

• Journal of the Korea Concrete Institute
• /
• v.27 no.3
• /
• pp.265-272
• /
• 2015

In this study, a method to reduce temperature rise due to hydration in mass concrete is investigated. It is to use retarder (glucose) for reducing heat of hydration and to use calcium silicate hydrate (C-S-H) for compensating the retardation effect due to its role as a nucleation seed. For this purpose, the temperature rise of cement paste due to hydration was measured and the effect of using both C-S-H and glucose on setting and 28-day compressive strength of mortar specimens was investigated. According to the experimental results, using C-S-H and glucose caused the reduction in the maximum temperature but accelerated the time to reach the maximum temperature compared to that of retarded cement paste using glucose. In addition, using C-S-H and glucose did not show significant effect on 28-day compressive strength of mortar specimens, indicating that the method shown in this study can be a successful alternative to control maximum temperature rise in mass concrete.

• Journal of the Korean Ceramic Society
• /
• v.42 no.3 s.274
• /
• pp.198-204
• /
• 2005

Fluosilicate salts based hydration heat reducer(SWP-HR), used in this study, is composed of fluosilicate salts, soluble silica, aromatic polymer condensate and nitrate salt based inorganic compound with latent heat property. Effects of SWP-HR addition on the hydration heat and anti-crack property of cement mortar were investigated. Adiabatic hydration temperature and drying shrinkage length of SWP-HR added cement mortar had a tendency to decrease compared to those of cement mortar without SWP-HR addition. Also, it was confirmed through crack pattern experiment of plate-form specimen for elucidating crack-reducing characteristic that anti-crack property of SWP-HR added cement mortar was improved.

• Journal of Korean Society of Disaster and Security
• /
• v.11 no.2
• /
• pp.69-74
• /
• 2018

Fog to which environmental impacts are sensitive has a danger to the safety of citizens due to the difficulty in predicting the specific area/time zone. Therefore, we propose a white smoke fog reduction technique using a fog removal device that can remove fog particles directly through dry air and anionic condensation nucleus instead of conventional passive countermeasures. In this study, to verify the effect of reducing fog and the effect of temperature on the white smoke fog which is frequently occurred in the detention basin. As a result, the visible distance of 100m or more was secured within 30 seconds, and it was confirmed that the fog reduction effect is more effective. Also, the lower the temperature, the larger the amount of white smoke fog was. However, the effect of reducing the white smoke fog by temperature was insignificant. Through this experiment, it was possible to verify the reduction effect of the white smoke fog generated in the detention basin through fog removal device.

• Clean Technology
• /
• v.16 no.4
• /
• pp.265-271
• /
• 2010

The deactivated diesel oxidation catalyst(DOC) was remanufactured by ultrasonic wave treatment with various solutions, followed by active component re-impregnation. The catalytic performance and surface properties of remanufactured DOC were studied at various remanufacturing conditions. The proper ultrasonic-wave cleaning time at various solutions and optimal re-impregnation amounts of active component for the best catalytic performance were investigated. The catalytic performance tests on the conversions of CO and THC(total hydrocarbon) were also carried out at various temperatures by catalytic reaction test unit using bypass gas from the diesel engine dynamo system. It was found that the catalytic performance of DOC remanufactured with the high-temperature air washing, ultrasonic wave cleaning at acidic/basic solutions and active component re-impregnation method was recovered to 90% level of its activity compared to that of the fresh DOC, which was caused by removing the deactivating materials from the surface of the DOC through the analyses of catalyst performance test and their characterization by Optical microscope, EDX, ICP, TGA, and porosimeter.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.40 no.10
• /
• pp.637-644
• /
• 2016

The purpose of this study is to understand the characteristics of unburned carbon (UBC) and NOx emissions for pulverized coal when air staging combustion is applied. A two-staged drop tube furnace capable of applying air staging combustion was designed and installed. The combustion of sub-bituminous (Tanito) has been investigated. UBC and the NOx concentration were measured under various temperatures and stoichiometric ratios in unstaged and staged combustion. As a result, UBC decreased and the NOx concentration increased with an increase in stoichiometric ratio and temperature. In particular, the NOx reduction mechanism was activated when the temperature in the fuel rich zone increased. Both UBC and the NOx concentration decreased as the temperature increased in the fuel rich zone. A high NOx reduction effect was obtained, compared to the UBC increase, when the air staging technique was applied.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.249-252
• /
• 2008

In recent large-scale structures, as mass concrete type structure is frequently applied to the building, temperature crack due to hydration heat needs to be considered. Since a volume change is internally or externally restricted in a mold after placing concrete, temperature crack of mass concrete takes place. By this reason, the reduction method to control this crack is required. In this study, low heat mixture and hydration heat difference is used to execute the analysis of hydration heat, considering the changes of heat transfer coefficient according to curing conditions and block placement of mass concrete. For the analytical modelling, original portland cement and concrete of low heat mixture are placed in the upper and lower payer, respectively. A convection boundary condition is fixed because mass concrete of block placement is characterized by the difference of mold form and curing condition. Through the analysis results considering the changes of low heat mixture, block placement, and heat transfer coefficient, we check out the temperature and stress distribution and analyze the temperature crack reduction effect.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.14 no.5
• /
• pp.2075-2080
• /
• 2013

A Coolant core for Range Extender engine has been developed using CFD technique. Coolant by-pass has been added to the improved model to reduce temperature near and between exhaust valve. Due to the increased coolant flow-rate both around the second cylinder block and between exhaust valves, improved model shows no significant stagnant flow compared with base model. Finally, the improved model shows improved heat transfer coefficients near exhaust valves, and 5% reduced pressure-drop through the coolant core. Reduced pressure-drop may increase the fuel efficiency by reducing the load of a coolant pump.

• Journal of Food Hygiene and Safety
• /
• v.36 no.6
• /
• pp.510-519
• /
• 2021

The purpose of this study was to investigate the effect of the microbial reduction and quality maintenance of the physical and chemical pretreatment of Allium monanthum. For physical treatment, handwash, bubble wash and ultrasonication were conducted at 50℃ and 60℃ for 1, 3 and 5 minutes, respectively, and for chemical treatment the sample was immersed in fumaric acid and acetic acid of 1.5% and 2% concentrations for 1, 3 and 5 minutes, respectively. As a result of the microorganism and quality analysis, 3 minutes of bubble wash was the most effective physical pretreatment in reducing fungi although the effect on reducing total viable bacterial was small. Furthermore, 5 minutes of ultrasonication at 60℃ significantly reduced microorganisms, but also resulted in the reduction of the a value of chromaticity, which cause the green color to fade. With chemical pretreatment, it was found that treating with fumaric acid was more effective in reducing the total viable bacteria and fungi than acetic acid. The result shows that 1.5% concentration of fumaric acid is the most effective with 3 minutes of treatment time. The quality of Allium monanthum were compared in the combination of the two most effective microorganism reduction pretreatments: 3 minutes of bubble wash (B3) and 3 minutes in 1.5% fumaric acid (F153). As a result of analyzing the quality characteristics over 9 days of storage at 4℃ after the treatments, it was revealed that the BF treatment is more effective in reducing fungi than the total viable bacteria. The results shows that the BF treatment is more effective in reducing total viable bacteria, whereas the F153 treatment is more effective in reducing fungi. Also, it was found that the 𝚫E value in BF was the lowest, whereas F153 treatment showed the green color faded. The maximum cohesiveness changed more significantly in the green stems than in the roots. On the 9th day of storage, the hardness of the green stem was found to be maintained at the highest level (P<0.05) after F153 treatment, whereas that of the roots decreased (P<0.05) since the 6th day after the bubble wash. Considering the reduction of microorganisms and the quality maintenance of Allium monanthum, the most effective pretreatment methods were 3 minutes in 1.5% fumaric acid for reducing microorganisms and maintaining color and maximum cohesiveness, and the combined process could also be effective if the expiration period is within 3 days.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
• /
• 2005.11a
• /
• pp.289-291
• /
• 2005

본 연구는 페러데이 효과(Faraday Effect)를 이용한 GIS용 광 CT의 개발을 위하여 출력신호의 정밀성과 안정성 향상을 위한 신호분석 시스템에 대해 검토하였다. 기존 광 CT의 Verdet 상수 의존도와 온도에 따른 특성 및 노이즈에 대한 정밀성을 개선하기 위해 신호처리 시스템 이용하여 신호를 균일화시키고 온도 보상 프로그래밍을 이용하여 온도 특성에 따른 오차를 저감시키고자 한다. 또한 신호 계측부와 신호 처리부를 분리하여 신호 처리부를 프로그래밍 시켜 실시간으로 광 CT 특성을 모니터링 할 수 있는 시스템을 연구 검토하였다.