• 동력기계공학회지
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• 제13권4호
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• pp.5-10
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• 2009

Urea-SCR system, the selective catalytic reduction using urea as reducing agent, is a powerful technique to reduce nitrogen oxides(NOx) emitted from diesel engines. However, a tank of urea(32.5 wt%)-water solution can be frozen in low ambient temperature levels of below $-11^{\circ}C$. The purpose of this study is to understand freezing and melting phenomena of the urea-water solution, and its can be applied to get the urea-water solution from frozen it within 5 minutes after cold start. Factors considered were the type of heater and the urea tank shape. From the results, it was found that melting volume of cartridge heater B during 5 minutes of heating period was 83ml when supplying electric power of 150W. Horizontal heater B, which was put in the narrow bottom space of the tank T1, had fast melting characteristics.

• 한국응용과학기술학회지
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• 제22권2호
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• pp.168-174
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• 2005

Aluminum tri-butoxide was mixed with the water/ethanol solution and then chloroplatinic acid was added to the solution. The solution was dried at $100^{\circ}C$ for 15hrs to remove the solvent and water then it was calcined at $500^{\circ}C$. The catalyst was activated with a gas mixture. During the activation, the temperature was increased from $150^{\circ}C$ to $500^{\circ}C$. The necessary amount of urea was dissolved in 50mL water and injected. Aqueous urea solution was then mixed with the feed gas stream. At low temperatures, nitrogen containing compounds of urea decomposition are used as reductants in the reducton of $NO_X$. However at high temperatures the nitrogen containing compounds are oxidized to NO and $NO_2$ by oxygen instead of being used in the reduction. The activity of the catalyst was dependent on urea concentration in the feed stream when there was not adequate water vapor in the feed. The maximum conversion was shifted from $250^{\circ}C$ to $150^{\circ}C$ when water concentration was increased from 2 to 17%. It seems that the maximum temperature shifts to lower temperatures because the hydrolysis rate of HNCO increases with water, resulting in higher amounts of $NH_3$.

• 대한기계학회논문집B
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• 제38권1호
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• pp.41-48
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• 2014

Urea-SCR 시스템은 주로 열해리와 증발시간의 부족으로 인해 발생하는 암모니아 슬립 현상과 관련된 몇 가지 문제점들을 가지고 있으며, 이러한 문제점들은 분사된 요소수용액의 불균일한 분포를 초래한다. 따라서 본 연구에서는, 배기가스와 요소수용액 사이의 증발 및 혼합특성을 강화시키기 위해 인젝터 장착 각도 그리고 믹서의 장착 및 설치 각도와 같은 다양한 매개변수들을 바꾸며 전산해석 연구를 수행하였다. 그 결과, 이와 같은 매개변수들이 배기가스와 요소수용액의 증발 및 혼합특성에 상당한 영향을 미친다는 것을 알 수 있었으며, 이 매개변수들의 최적화가 요구된다. 또한, 본 논문은 Urea-SCR 분사 시스템의 DeNOx 성능을 증가시키고 암모니아 슬립을 감소시키기 위한 최적 설계 시 유용한 기준을 제안할 것이다.

• 대한화학회지
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• 제24권3호
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• pp.209-217
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• 1980

요소 1,3-디메틸요소(DMU), 아세트아미드, 프로피온아미드의 상대점도와 삼투계수를 dimethylsulfoxide(DMSO), 메탄올, 에탄올 및 물용액에서 $25^{\circ}$C와 $45^{\circ}$C에서 각각 측정하였다. 수용액에서 각 용질의 점도증가량은 분몰랄부피가 증가하면서 증가하였으나 물아니 용액에서는 오히려 감소하였다. 또한 요소의 점도 증가량은 수용액에서는 DMU보다 작았으나, 물아닌 용액에서는 DMU보다 컸다. 그러나 아미드류는 어느 용매에서나 거의 같은 점도증가량을 나타내었다. 요소수용액에서 삼투계수는 DMU 수용액보다 컸으며, 물아닌 용액에서 요소용액은 DMU보다 Raoult의 법칙에서 크게 벗어났다. 이러한 사실로부터 요소는 DMSO 용액에서 자체회합을 크게 일으키고 있으며 알코올용액에서는 DMU보다는 큰 정도의 용매-용질상호작용, 수용액에서는 용매구조를 파괴하고 있음을 알았다. 아세트아미드나 프로피온아미드는 수용액이나 DMSO 용액에서보다 알코올용액에서 더 크게 용매구조를 파괴하고 있음을 알았다.

• International Journal of Industrial Entomology and Biomaterials
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• 제26권2호
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• pp.113-118
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• 2013

In this study, silk sericin films were prepared using different extraction methods, and the molecular conformation of sericin was examined using Fourier-transform infrared spectroscopy with attenuated total reflection geometry. Additionally, the effect of the film side (air-facing side or plate-facing side) on the molecular conformation of the sericin films was investigated. Interestingly, the molecular conformation of the sericin film depended on the film side. The molecular conformation of air-facing side of the sericin film was significantly influenced by extraction solution and time. The ${\beta}$-sheet crystallization and the crystallinity index of the sericin film markedly increased with an increase in the extraction time in hot water. The order of the crystallinity indices for the sericin films obtained with different extraction solutions was as follows: citric acid solution > urea solution >> hot water. In contrast, no remarkable differences were observed in the molecular conformation of the plate-facing side of the sericin film after extraction in hot water for different time periods. Urea and citric acid solution extractions showed remarkably higher crystallinity indices for sericin than those obtained after hot water extraction. However, no significant differences were observed in the crystallinity index of sericin between urea and citric acid solution extraction in plate-facing side of the film.

• Asian-Australasian Journal of Animal Sciences
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• 제4권1호
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• pp.91-97
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• 1991

Twenty five 75% Holstein Friesian cross bred bullocks fed rice straw (Oryza sativa) of long form, were fed with the following five treatments. 1. Rice straw, untreated (RS) 2. RS + water (1:1), stored for 24 hours (WRS) 3. RS (100 kg) + urea solution (4 kg urea/100 litre water) and dried (USRS) 4. RS (100 kg) + urea solution (as in 3) stored in wet condition for 24 hours (UWRS) 5. RS (100 kg) + urea solution (as in 3) stored in pit for 21 days (UTRS). Potential digestibility of treatments of RS was evaluated by monitoring (in vitro) Simulating Rumen like Fermentation (SRLF). The results indicated that Dry Matter Intake (DMI), digestibility of nutrients, N utilization were of the order UTRS > UWRS > USRS > WRS and RS (p < 0.05 to p < 0.01). SRLF index was high (255.84) for UTRS and least (145.58) for USRS. It was intermediary (199.66) for UWRS. The acetyl content (AC) of UTRS with higher hemicellulose (HCE) digestibility (80.8%) was low compared to UWRS, USRS, RS and WRS. The acetate content was of the order UTRS < UWRS < USRS < WRS and RS thereby indicating that reduction in acetyl content was an index of positive response of urea-treatment of RS. In addition, the ratio of HCE/AC in faeces of UTRS was 0.87 as against the ratios (2.26-2.48) observed in other treatments recording reduction in AC due to urea-treatment. Among the treatments, USRS only supplemented N while UTRS in addition to utilization N, increased the digestibility of structural carbohydrates. Reduction in treatment time from 21 days to 1 day (UWRS) resulted in improvements similar to those of UTRS.

• 한국분무공학회지
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• 제27권1호
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• pp.11-17
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• 2022

In upcoming Post Stage-V and Tier 5 regulations of construction machineries, nitrogen oxide (NOx) emissions are strictly limited in cold start conditions. In response to this, a method of improving NOx conversion efficiency has been applied by installing an electric heating catalyst (EHC) in front of conventional urea-SCR systems so that the evaporation and thermal decomposition of urea-water solution can be promoted in cold start conditions. In this strategy, the evaporation and thermal decomposition of urea-water solution and corresponding NOx conversion efficiency are governed by temperature conditions inside the EHC. Therefore, characterizing the temperature distribution in the EHC under various operating conditions is crucial for the optimized operation and control of the EHC in Urea-SCR systems. In this study, a 1-D modeling analysis was performed to predict the heater surface temperature distribution in EHC under various operating conditions. The reliability of prediction results was verified by comparing them with measurement results obtained using an infrared (IR) camera. Based on 1-D analysis results, the effects of various EHC operation parameters on the heater surface temperature distribution were analyzed and discussed.

• 한국염색가공학회지
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• 제11권3호
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• pp.49-57
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• 1999

The effect of padding solution for the microwave heat dyeing of polyester fabric was studied variously. The dyeing property of polyester fabric varied with the kinds of added chemicals in the padding solution. Polyester fabrics impregnated in aqueous urea solution and aqueous sodium chloride solution for 10 minutes and then dyed for 7 minutes by microwave apparatus(2450 MHz, 700 W) under optimum conditions give good exhaustion. An aqueous solution of urea and a sodium chloride solution was more effective than water as padding solution for microwave heating dyeing. The K/S values of dyed polyester fabric by microwave were significantly affected by the type of solvent added in padding media and its concentration. Added solvents, n-hexane, acetone and dimethyl formamide were also more effective than water as padding media for the microwave heating dyeing. It is assumed that the effect of used solvents on dyeing property of polyester fabrics depends on the solubility parameter difference between solvent and polyester fabric.

• 대한기계학회논문집B
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• 제40권1호
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• pp.1-7
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• 2016

환원제를 이용하여 배기가스 내의 NOx를 질소로 환원시키는 요소수 SCR 시스템은 다른 후처리 장치들 중에서 가장 효율적인 장치로 알려져 있다. 차량에 적용되는 SCR 장치는 32.5wt%의 공융혼합물을 이용한다. 이러한 혼합물의 가장 큰 장점 중의 하나는 $-11.7^{\circ}C$에서 얼기 때문에 추운 환경에서 응고를 피할 수 있다는 것이다. 한편, 이러한 추운 환경에서 시동시 필요한 수용액을 충분히 공급하기 위해서는 고체상을 가열해야 한다. 따라서 본 연구에서는 Fluent 상용코드를 이용하여 3차원 비정상 전산해석을 통한 냉각수 및 전기가열 방식에 따른 고체상 요소수의 시간에 따른 액상비 및 온도분포와 같은 해동 및 열전달 특성을 고찰하였다. 본 연구를 통하여 전기히터 가열 방식이 냉각수 방식보다 효율적임을 확인하였다.

• Journal of Plant Biology
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• 제5권2호
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• pp.6-12
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• 1962

For the comparison with the previous paper (4) the present report deals with the absorption and metabolism of urea and other nitrogen ions in barley seedling absorbed through root. 1. The amount of nitrate in barley treated with urea reach it peak on the 8th day. NO3 on the 4th, NH4 on the 6th or 8th, respectively. 2. The ammonia content in urea group reaches its peak on the 6th day but other groups on the 4th day. The present data in the urea group show to shorten 4 days compared with that of the previous paper(4). 3. the content of total amide from the present data aare gradully increased on all of the groups during this experiment. These are agreement with the result of the previous paper (4). 4. the alcohol solution nitrogen in the urea gorup shows the similar tendency to the NaNO3 group but reaches it peak 2 days later than in the (NH4)2SO4 group. 5. The content of total nitrogen in the urea series has the lowest amount at the beginning while the richest from the 4th day after. These would be explained on that the absorption of urea is delayed and the PH in the urea solution does not change, so called "physiological neutrality". The author should like express his sincere thanks to Prof. M.J.Lee of Seoul National University for his valuable advices.e advices.