• 열처리공학회지
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• 제11권2호
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• pp.99-110
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• 1998

The effects of pre-heat treatment(Q/T) on microstructure and hardness of SCM435 structural steel nitrided by micro-pulse plasma was investigated. The quenching and tempering temperatures for obtaining matrix hardness of SCM435 steel on range of HRC30 to HRC40 desired for machine parts were about $860^{\circ}C$ and $500^{\circ}C$ respectively. The case depth of SCM435 nitrided at $480^{\circ}C$ for 5 hours was independent of pre-heat treatment condition and was approximately $150{\mu}m$. However, hardness and compactness of nitrified layer on Q/T treated specimen were more heigher than annealed specimen. The case depth increased linearly with the increase of nitriding temperature, however, the hardness of nitrified layer decreased with the temperature. Phase mixture of ${\gamma}^{\prime}$-phase($Fe_4N$) and ${\varepsilon}$-phase($Fe_3N$) were detected by XRD analysis in the nitrified layer formed at optimum nitriding condition, and only single ${\gamma}^{\prime}$-phase was detected in the nitrified layer formed at higher nitriding temperature such as $540^{\circ}C$. The optimum nitriding temperature was approximately $480^{\circ}C$ which is lower than tempering temperature for preventing softening behavior of SCM435 matrix during nitriding process and the surface hardness of nitrified layer obtained by optimum preheat treatment condition was about Hv930.

• KSBB Journal
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• 제26권3호
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• pp.193-198
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• 2011

Polyester was prepared through the esterification reaction between watsepaper liquefied by ethylene glycol and carboxylic acid. Liquefaction was carried out at the previously determined condition of 100 minutes, $160^{\circ}C$, and 3% sulfuric acid, and the hydroxyl value of the liquefied product was 411 mg KOH/g. In order to remove bubbles produced during the curing step, the method to introduce a slight nitrogen stream into reaction vessel and/or the method to preheat a polyester film at $85^{\circ}C$ before curing step were used alone or in combination. But if curing temperature was $130^{\circ}C$, simple method to cure a film for 5 hours at $130^{\circ}C$ without using both methods was found to be most effective. The polyesters prepared with various carboxylic acids showed significant different physical properties, and maleic acid was best among them. Also, the effect of reaction time and temperature, C/H (carboxyl group/hydroxyl group) ratio, and type of additive on the crosslinkage of polyester was investigated. Lithium hydroxide or citric acid as additive was used to enhance the crosslinkage of polyester and citric acid was proved to be much more effective than lithium hydroxide. The effect of reaction temperature on the crosslinkage was marginal, but the crosslinkage decreased above $130^{\circ}C$. The crosslinkage was 86% when the polyester was prepared at an optimum condition such as $130^{\circ}C$ and 15 minutes of reaction condition, 1.5 of C/H ratio, $130^{\circ}C$ and 5 hours of curing condition, and 10% addition of citric acid.

• 에너지공학
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• 제14권4호
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• pp.268-276
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• 2005

액체연료(중유)공급량 기준 20kg/hr규모의 반응로에서 증기분무 내부 혼합식 노즐을 이용하여 잔사유의 연소실험을 수행하였다. 본 실험에서 사용한 감압 잔사유는 점도가 높고 황함량, 잔류탄소와 금속성분의 함량도 높았다. 잔사유의 착화를 위해서는 반응로를 일정온도까지 예열하여야 했으며 이는 LPG를 이용하였다. 잔사유 공급량을 변화시키면서 축방향 및 반경방향의 로내 가스 온도, 주요 가스농도 및 채집된 고체 입자를 분석하였다. 잔사유의 주반응영역은 버너 팁으로부터 약 1 m 근방에서 형성되었으며 이는 축방향 가스 온도, 농도 분포 및 입자의 크기로부터 확인할 수 있었고, 반응로의 하류에서는 완전 확립된 온도분포를 보여주고 있었다. 고체 입자의 SEM 분석으로부터 잔류 탄소입자는 기공이 많은 형태를 띠고 있었다.

• 에너지공학
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• 제12권3호
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• pp.223-230
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• 2003

본 연구에서는 제철소의 슬러지 소각로 배가스의 냉각을 위한 열교환기에서의 가스측 파울링 현상의 측정 및 분석에 대한 연구를 수행하였다. 소각로 배가스는 열교환기의 수직 전열관을 통과하면서 냉각되며 동시에 연소용 공기를 예열한다. 이러한 열교환기의 파울링은 주로 열교환기 입구에 발생하여, 본 연구에서는 열교환기의 입구 형태와 비슷한 형상의 오염다공판을 사용하여 슬러지 소각로 배가스의 파울링 현상을 측정하였으며, 부착분진에 대한 특성분석을 수행하였다. 분석 결과, 분진 부착율은 온도와 분진성분 및 분진크기에 영향을 받으며, 또한 오염다공판의 위치에 따라 부착형태가 다르게 나타났다. 또한 전산 해석을 통하여 오염다공판의 구멍 크기에 따라 분진부착율이 변하는 것을 알 수 있었다. 그리고 오염다공판을 사용하여 다관식 원통형 열교환기의 입구에서의 파울링 특성을 측정할 수 있음을 확인하였다.

• 대한기계학회논문집B
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• 제26권4호
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• pp.555-560
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• 2002

Numerical simulations of freely propagating flames burning stoichiometric CH$_4$/O$_2$/$N_2$mixtures are performed at atmospheric pressure in order to understand the effect of the $O_2$enrichment level on CH$_4$/Air flame. A chemical kinetic mechanism is employed, the adopted scheme involving 54 gas-phase species and 632 forward reactions. The calculated flame speeds are compared with the experiments for the flames established at several $O_2$enrichment level, the results of which is in excellent agreement. As a result of the increased $O_2$enrichment level from 0.21 to 1, the mole fraction of CO in the burred gas is increased. The flame speed and the temperature in the burned gas are also increased, but the thickness of the flame is severely shrunken in the preheat region. The maximum of the calculated EINO is obtained around 0.6 and 0.7 of the $O_2$enrichment level in cases of flames for fuel-lean mixtures.

• Journal of Welding and Joining
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• 제32권3호
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• pp.95-101
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• 2014

Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view, this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure $P_2$, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal, tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of $P_1$, $P_2$ and upset distance(${\delta}$).

• 분석과학
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• 제29권6호
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• pp.269-276
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• 2016

고산리 유적은 우리나라 최초 토기로 알려진 고산리식 토기가 출토된 초기 신석기시대 유적이다. 이 연구에서는 고산리 유적의 형성 및 점유에 대한 절대연대 편년을 위하여 유적 내 표준 퇴적층에서 채취된 시료를 대상으로 OSL 연대측정을 수행하였다. 각 퇴적층의 고고선량은 $220^{\circ}C$ 열전처리 온도의 단일시료재현법을 적용하여 산출되었으며, 최종적으로 유적의 퇴적환경을 고려하여 maximum age model을 적용하여 결정하였다. 산출된 고고선량을 연간선량율로 나누어 고산리 유적 퇴적층의 OSL 연대를 결정하였다. 각 퇴적층의 OSL 연대와 14C 연대를 종합한 결과, 고산리 유적은 신석기인들에 의해 기원전 9천년 이후에 형성된 이후 고산리식 토기를 포함하는 신석기시대 초기 유적에서부터 다양한 시기의 다양한 유구가 존재해 오다가 기원전 4천년 중반에 폐기되어 현재에 이르렀다고 추론된다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
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• pp.63-72
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• 2003

In order to reduce NOx emissions in the 20kW class microturbine under development, the low NOx characteristics, as being an application to the lean premixed combustion technology, have been investigated. The study has been conducted at the conditions of high temperature and high pressure. Theair from a compressor with the pressure of 2.5bar, 3.0bar, 3.5bar was supplied to the combustor with the temperature 560K through the air preheat-treatment. The sampling exhaust gas was measured at the immediate exit of the combustor. For the effect of temperature on NO and CO emissions, though NOx were increased, CO was decreased with increasing inlet air temperature. With increasing inlet air pressure, NOx were increased and CO was decreased also. NOx were decreased, but CO was increased with increasing inlet air mass flow rate. The test has been performed on the equivalent ratio of 0.10 to 0.16 in the lean region. NOx were increased with increasing equivalent ratio, but CO was decreased as an influence of flame temperature. CFD work with an appropriate combustion model predicated a complicated swirling flow pattern in the combustor, and also produced a numerical value of NOx and CO emissions which was to be compared with the experimental one. As the results of this study, NOx are expected to be reduced to less than 42ppm at 15% O2 when operated at the design condition of the 20kW class microturbine.

• Journal of Biosystems Engineering
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• 제25권3호
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• pp.187-194
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• 2000

One of effective utilization technique of rice husk is known to carbonize it for using as the culture materials. A series of study on the production of carbonized rice husk by a cyclone combustor shows that the carbonized rice husk produced have a strong alkalinity. Therefore, carbonized rice husk produced by a cyclone combustor is required to neutralize with proper normality. This work is the third part of a series on the production of carbonized rice husk by a cyclone combustor. In this work, the development of neutralization process was carried out in the range of experimental conditions recommended in the previous study. Those include the preheat temperature of combustion chamber of T1b=1273∼1373K, equivalence ratio =1.68∼2.17, auxiliary gas flow rates Qg=5.15∼6.43$\ell$/min. The injection technique of dilute acid was employed for neutralization. At the lower position of the outside of combustor, a dilute nitric acid selected as neutralization liquid was injected to the carbonized rice husk exhausted from the combustion chamber. The normalities of dilute nitric acid were varied to 0.01, 0.03 and 0.05N, respectively. The injection flow rates of the solution were changes from 1.7∼4$\ell$/min. The required carbonized and neutralized rice husk could be obtained at the dilute nitric acid with normality of 0.3N and flow rate of dilute nitric acid of 2∼3.5$\ell$/min. However, the carbonized and neutralized rice husks of about 10∼20% were destroyed by spray with high injection pressure.

• 한국식품조리과학회지
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• 제15권4호
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• pp.370-376
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• 1999

고춧가루 공장에서 폐기물로 발생되는 고추씨를 매운맛을 지닌 향신 조미 물질로서의 효과적인 활용하기 위하여 실험하였다. 고추씨는 열수추출하였으며 추출시 추출온도와 시간 및 소금, 당, 인산염과 유기산등의 첨가 영향을 검토하였다. 또한 추출전 10$0^{\circ}C$에서의 증자나 215$^{\circ}C$와 33$0^{\circ}C$에서의 볶음의 영향도 검토하였다. 그 결과 고추씨를 증자 또는 볶음하여 추출한 경우에 수율은 증가하였지만 탁도는 감소하였으며 매운 향미는 비가열처리구에서 높았다. 고추씨를 7$0^{\circ}C$-10$0^{\circ}C$에서 10-60분간 열수추출하였을 때 8$0^{\circ}C$에서 30분간 추출한 시료가 비교적 높은 27%의 수율을 나타내었으며 매운맛도 높았다. 한편, 소금, 당, 인산염과 유기산을 첨가하여 8$0^{\circ}C$에서 30분간 추출한 수율은 0.5% NaCl이 27.21%, 0.2% $Na_2$HPO$_4$은 29.21%로 대조구보다 약간 증가하였으며 매운 향미에는 큰 영향이 없었다.