• Advances in Energy Research
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• 제4권3호
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• pp.213-221
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• 2016

The main purpose of this work is to test the validation of use of a four step reaction mechanism to simulate the laminar speed of hydrogen enriched methane flame. The laminar velocities of hydrogen-methane-air mixtures are very important in designing and predicting the progress of combustion and performance of combustion systems where hydrogen is used as fuel. In this work, laminar flame velocities of different composition of hydrogen-methane-air mixtures (from 0% to 40% hydrogen) have been calculated for variable equivalence ratios (from 0.5 to 1.5) using the flame propagation module (FSC) of the chemical kinetics software Chemkin 4.02. Our results were tested against an extended database of laminar flame speed measurements from the literature and good agreements were obtained especially for fuel lean and stoichiometric mixtures for the whole range of hydrogen blends. However, in the case of fuel rich mixtures, a slight overprediction (about 10%) is observed. Note that this overprediction decreases significantly with increasing hydrogen content. This research demonstrates that reduced chemical kinetics mechanisms can well reproduce the laminar burning velocity of methane-hydrogen-air mixtures at lean and stoichiometric mixture flame for hydrogen content in the fuel up to 40%. The use of such reduced mechanisms in complex combustion device can reduce the available computational resources and cost because the number of species is reduced.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.217-222
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• 2007

Since 1973, we attain a successful achievement of nation-wide afforestation such as a thick forest and heaped-up leaves. However, the higher of the formation density in forest, the more dangerous to be a large-scale forest fire whenever fire occurs. According to the type of forest in the country, 42% of the forest is occupied by conifer forest that are highly flammable, and the distribution of forest age is in a transition period from immature forest to mature one. And the structure is too weak to the forest fire for the occurrence and spread because there are too many scrub and shrub trees in the forest. As a matter of course, it is on the increase of the thinning-forest that can shift the forest structure from a weak on forest fire to a strong one nowaday. In other words, thinning-forest has primary purposes such as the promotion of producing forest trees, production of excellent timbers, and build-up of public forest area. Furthermore, in some reports, the reduction of ladder fuel by eliminating the vertical/horizontal fuel in a forest and ensuring spaces in the forest can decrease the occurrence of forest fire and the risk of spread of burning as by-effect. Therefore, this study is designed to clarify the relation with the risk of forest fire by an on-spat-investigation of the characteristics of forest composition on the thinning and the non-thinning area.

• 한국연초학회지
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• 제28권1호
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• pp.23-30
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• 2006

In order to improve the final product quality, tobacco industry has gradually decreased the size and number of steams in the cigarette. Especially, steams bigger than $3{\times}3$ mm($length{\times}thickness$) and $2{\times}10$ mm($width{\times}length$) are not acceptable in the process as objectionable stems. A total number of 12 samples where the $length{\times}tickness$ samples were prepared by decreasing the present sample ($3{\times}3$ mm) with 1 mm up to $1{\times}1$ mm, and the $width{\times}length$ samples were prepared by decreasing the present sample ($2{\times}10$ mm) with 2 mm up to $2{\times}6$ mm for the stems in leaf and stems in expanded cut-tobacco were prepared to apply a fire ball drop test using stems. In addition, cigarettes were produced for these stems in order to analyze the forced fire ball drop including the burning, encapsulation and unencapsulation pressure drop and a single or unspecified direction combustion. Based on the results of the test, it was evident that the fire ball drop in the stems in expanded cut-tobacco presented a lower level than that of the stems in leaf. Also, the stems in expanded cut-tobacco presented a larger swelling and higher burning for a single direction than that of the stem in leaf. In addition, it was considered that the management criteria for objectionable stems should be changed as $3{\times}3$ mm and $2{\times}8$ mm for the $length{\times}thickness$ and $width{\times}length$ sample, respectively, in both steams in leaf and expanded cut-tobacco.

• 태양에너지
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• 제18권1호
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• pp.81-89
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• 1998

In this paper an experimental was done to design combustion chambers which is required radiation strength of high temperature generator of absorption rigerator. Partiqularly, in combustion chamber radiative mediums were set and basic experiments were done according to its size by radiation strength and effects of heat transfer promotion. The results are as follows : 1) When radiative mediums were set in small combustion furnace burning nonframely radiative heat transfer was effected. 2) In case that area ratio($A/A_o$) of radiative medium is 0.82 or over, temperature fluctuation effects of furnace inside were not nearly. 3) In experimental boundary heat transfer effects were 1.8 times by setting up radiative medium. Specially, $q/{\Delta}T$ values of furnace inside were uniformed nearly by setting up radiative mediums.

• 한국표면공학회지
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• 제53권2호
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• pp.59-66
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• 2020

Effects of Na₂SiO₃ concentration added into 0.1 M NaOH + 0.05 M NaF solution on the formation behavior and properties of PEO films on AZ91 Mg alloy were investigated under 1200 Hz of alternating current (AC) by voltage-time curves, in-situ observation of arc generation behavior and measurements of film thickness, surface roughness and micro vickers hardness. In the absence of Na₂SiO₃ in the 0.1 M NaOH + 0.05 M NaF solution, about 4 ㎛ thick PEO film was formed within 1 min and then PEO film did not grow but white spots were formed by local burning. Addition of Na₂SiO₃ up to 0.2 M caused more increased formation voltage and growth of PEO film with uniform generation of arcs. Addition of Na₂SiO₃ from 0.2 M to 0.4 M showed nearly the same voltage-time behavior and uniform arc generation. Addition of Na₂SiO₃ more than 0.5 M resulted in a decrease of formation voltage and non-uniform arc generation due to local burning. PEO film growth rate increased with increasing added Na₂SiO₃ concentration but maximum PEO film thickness was limited by local burning if added Na₂SiO₃ concentration is higher than 0.5 M. Surface roughness of PEO film increased with increasing added Na₂SiO₃ concentration and appeared to be proportional to the PEO film thickness. PEO film hardness increased with increasing added Na₂SiO₃ concentration and reached a steady-state value of about 930 H_V at more than 0.5 M of added Na₂SiO₃ concentration.

• 한국식품과학회지
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• 제15권4호
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• pp.392-398
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• 1983

식품 압출성형기 (Food Extruder)의 기계적 성질과 제품 특성을 이해하기 위하여 다목적 Pilot plant 용 Single-Screw Extruder를 제작하고 corn grits를 사용한 Extrusion-cooking process의 기계적 성질과 제품 특성을 조사 하였다. Start-up 기간에서 스크류우 회전속도에 따른 열 발생속도를 측정하여 다음과 같은 결론을 얻었다. Start-up 기간에서의 열 발생속도는 스크류우 회전속도 및 원료사입속도에 직접적인 영향을 받았다. 추정된 바렐내부에서의 반죽의 점도는 스크류우 회전속도에 크게 영향을 받았으며 이 점도의 변화로 바렐내부에서의 가열 용융반응이 진행되는 정도를 예측할 수 있었다. Start-up 기간에서의 팽화율은 주로 바렐내부의 온도와 열용융 반응이 일어난 정도에 의존하였다. Corn Grits가 호화되는 바렐온도와 탄화가 일어나는 온도는 회전속도에 따른 체재시간에 크게 영향을 받았다.

• 한국산림과학회지
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• 제79권3호
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• pp.255-259
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• 1990

10종(種)의 침엽수재(針葉樹材)와 10(種)의 활엽수재(闊葉樹材)에 있어서의 상대적(相對的) 연소도(燃燒度)를 측정(測定) 조사(調査)하기 위하여 변재(邊材) 판일재(板日材)의 산소지수(酸素指數)를 ASTM D 2863-77에 의거 Up and Down 법(法)을 통하여 구하였다. 산소지수(酸素指數)는 침엽수재(針葉樹材)의 경우 스트로부스잣나무가 21.0으로 그리고 잎갈나무가 28.2로 각각 초소치(最小値) 및 최대치(最大値)를 나타냈으며 활엽수재(闊葉樹材)의 경우 사시나무가 20.7로 초소치(最小値)를 그리고 상수리나무가 27.6으로 최대치(最大値)를 나타냈다. 따라서, 연소(燃燒)가 용이한 재료(材料)일수록 낮은 산소지수치(酸素指數値)를 지닌다는 사실(事實)에 근거하여 볼 때 침엽수재(針葉樹材)와 활엽수재(闊葉樹材)별로 잎갈나무와 상수리나무가 연소성(燃燒性)이 가장 낮으며 스트로부스잣나무와 사시나무가 연소성(燃燒性)이 가장 큰 소재(素材)임을 구명할 수 있었다.

• 한국재료학회지
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• 제20권4호
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• pp.181-186
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• 2010

Since it was developed by Joseph Aspdin, cement has been a common construction materials up to the present time. However, there are trace constituents in cement clinker. One of the trace constituents included in cement clinker, chromium, has become prominent and highly noticed lately as a social issue both inside and outside of this country because it affects the human body negatively. The aim of the present study was to investigate the concentration of water-soluble hexavalent chromium in cement clinker by using industrial by-products. For that reason, raw materials were prepared to add different $SiO_2$, $Al_2O_3$, and $Fe_2O_3$ sources. After the raw materials such as the limestone, the sand and the clay, iron ore was pulverized and mixed, and the raw meal was burnt at about $1450^{\circ}C$ in a furnace with an oxidizing atmosphere. The part in the raw materials of the clinker was substituted with slag, sludge, etc. and this was used to manufacturing cement clinker. To investigate the water-soluble hexavalent chromium content in clinker, raw meal was prepared by changing the modulus, the type, and the content of clinker materials and tested concentrations of hexavalent chromium in the clinkers. To determine $Cr^{+6}$ formation of the clinker, tests were done with raw meals adding chromium by using different industrial by-products. Consequently because the chromium was to be included in the raw materials of the clinker, production of Portland cement clinker was included with the chromium. Also, the chromium was converted into hexavalent chromium in the burning process.

• 대한한의학회지
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• 제41권3호
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• pp.173-179
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• 2020

양명열증(陽明熱證)으로 변증(辨證)된 안면홍조형 주사피부염 환자 1례에게 백호탕(白虎湯)을 투여한 결과, 약 1~2주 후 안면홍조가 호전되었음을 확인하였으며, 주증상에 동반되었던 열감 및 기타 제반증상 역시 전반적으로 호전되는 모습을 보였다.

• 한국추진공학회지
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• 제1권2호
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• pp.74-83
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• 1997

본 연구에서는 원통형 연소실에서 발생하는 고주파 연소불안정을 연소응답함수와 n-$\tau$ 음향 불안정 해석방법을 사용하여 예측하였다. 열역학적 변수들과 속도는 시간 평균성분 및 변화성분으로 분리하여 선형으로 전개하였으며, 유동은 비회전류로 가정하여 속도 포텐샬 함수를 위한 지배방정식으로 수식화하였다. 연소응답의 계산에는 화염면 상, 하류에서의 연소실반응과 화염면에서의 연속조건이 적용되었다. 연소응답은 압력간섭계수 n과 감응시간지연 $\tau$로 변환되어 중립불안정한계를 결정하였다. LOX-RP1 추진제 조합의 원통형 연소실에서 연소압력 및 추진제 혼합비의 변화는 연소 음향반응과 중립불안정에 영향을 주지 않으나, 긴 거주시간에 의한 화염면 발생의 지연과 화염면 하류에서의 공간은 고주파 연소불안정의 발생에 강한 영향을 주는 것으로 예측되었다. 결과적으로 연소의 음향응답에는 추진제의 거주시간, 연소실 형상조건과 노즐에 의한 감쇠효과가 중요한 파라메터인 것으로 나타났다.