• 제목/요약/키워드: Counterflow

검색결과 264건 처리시간 0.02초

오블롱 셀 플레이트 열교환기에서의 R-l34a, R-407C, R-410A의 증발 열전달에 관한 실험적 연구 (Study on Evaporation Heat Transfer of R-l34a, R-407C, and R-410A in the Oblong Shell and Plate Heat Exchanger)

  • 박재홍;김영수
    • 설비공학논문집
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    • 제16권9호
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    • pp.845-854
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    • 2004
  • The evaporation heat transfer coefficient for R-l34a, R-407C (a mixture of 23wt% R-32, 25 wt% R-125, and 52 wt% R-l34a) and R-410A (a mixture of 50 wt% R-32 and 50 wt% R-125) flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the exchanger by four plates of commercial geometry with a corrugated sinusoid shape of a chevron angle of 45 degree. The effects of the mean vapor quality, mass flux, heat flux, and saturation temperature of different refrigerants on the evaporation heat transfer were explored in detail. Similar to the case of a Plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. It is found that the evaporation heat transfer coefficient in the plates is much higher than that in circular pipes. The present data show that the evaporation heat transfer coefficients of all refrigerants increase with the vapor quality. At a higher mass flux h, is higher than for the entire range of the vapor quality. Raising the imposed wall heat flux was found to slightly improve h$_{r}$, while h$_{r}$ is found to be lower at a higher refrigerant saturation temperature. A comparison of the performance of the various refrigerants reveals that R-410A has the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. Based on the present data, empirical correlations of the evaporation heat transfer coefficient were proposed.sed.

『동의수세보원(東醫壽世保元)』의 결흉(結胸) 해석 - 소양인 결흉을 중심으로 - (Interpretation of chest bind(結胸) in Donguisusebowon(東醫壽世保元) based on the chest bind disease of the Soyang pattern)

  • 장우창
    • 대한한의학원전학회지
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    • 제28권4호
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    • pp.99-119
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    • 2015
  • Objectives : This study aims to compare and analyze the contents and logic of Lee Jema's chest bind theory of the Soyang pattern with that of the traditional perspective since Shanghanlun, and to further investigate its underlying meaning and evaluate its value. Methods : Study chest bind related arguments of Lee through historical, demonstrative and positive investigation. First, contrast related texts starting from Shanghanlun, followed by reasoning based on general medical logic. Finally review clinical case studies from texts and papers for verification. Results : According to Lee, the key to diagnosis and treatment in preventing major chest bind which is a severe condition in the exterior cold pattern of the Soyang constitution, is to disperse fluid bind using GanSui(甘遂) in the water counterflow and vomiting(水逆嘔吐) stage prior to the major chest bind symptoms of stiffness and pain in the lower chest(心下硬痛), and reducing phlegm-rheum using DoJeokGangGiTang(導赤降氣湯) in the beginning stages of chest bind. HyeongBangDoJeokSan(荊防導赤散) is the main formula in treating phlegm-rheum, a causal factor to chest bind, modified according to the 'treat the three burners separately(三焦分治)' theory of the DaoChiSan(導赤散) section in WanBingHuiChun (萬病回春) to accomodate the Soyang constitution. Conclusions : If we follow Lee's diagnosis and treatment system on chest bind, it will allow us to diagnose chest bind in the earlier stages and secure safe treatment.

비정상 대향류 확산 화염의 소화 한계 확장에 대한 실험적 연구 (An Experimental Study on the Extinction Limit Extension of Unsteady Counterflow Diffusion Flames)

  • 이은도;이기호;오광철;이의주;신현동
    • 대한기계학회논문집B
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    • 제29권3호
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    • pp.390-401
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    • 2005
  • In this study, extinction limit extension of unsteady $(CH_{4}+N_{2})$/air diffusion flames was investigated experimentally. A spatially locked flame in an opposing jet burner was perturbed by linear velocity variation, and time-dependent flame luminosity, transient maximum flame temperature and OH radical were measured over time with the high speed camera, Rayleigh scattering method and OH laser-induced fluorescence, respectively. Unsteady flames survive at strain rates that are much higher than the extinction limit of steady flames, and unsteady extinction limits extend as the slope of the strain rate increases or the initial strain rate decreases. We verified the validity of the equivalent strain rate concept by comparing the course of unsteady extinction process and steady extinction process, and it was found that the equivalent strain rate concept represents well the unsteady effect of a convective-diffusive zone. To investigate the reason of the unsteady extinction limit extension, we subtracted the time lag of the convective-diffusive zone by using the equivalent strain concept. Then the modified unsteady extinction limits become smaller than the original unsteady extinction limits, however, the modified unsteady extinction limits are still larger than the steady extinction limits. These results suggest that there exist the unsteady behavior of a diffusive-reactive zone near the extinction limit due to the chemical non-equilibrium states associated with unsteady flames.

H2/Air 비예혼합화염의 화염신장율에 따른 NO 생성경로의 상세해석 (Detailed Analysis of NO Formation Routes with Strain Rate in H2/Air Nonpremixed Flames)

  • 김종현;황철홍;이창언
    • 대한기계학회논문집B
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    • 제32권8호
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    • pp.604-611
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    • 2008
  • Detailed analysis of NO formation routes and its contributions with strain rate in hydrogen/air flames were numerically investigated. LiG detailed reaction mechanism has been used for calculation, which is compared with experimental data in literature. It shows good agreement with experiment for both temperature and NO mole fraction. Three routes have been found important for NO formation in hydrogen flames. These are the Thermal route, NNH route and $N_2O$ route. Strain rate were varied to discuss the $EI_{NO}$ reduction trend in hydrogen nonpremixed flames, which are analyzed by each NO formation routes. As a result, as the strain rate increase, $EI_{NO}$ decrease sharply until strain rate $100s^{-1}$ and decrease slowly until strain rate $310s^{-1}$ again, after that $EI_{NO}$ keeps nearly constant. It can be identified that $EI_{NO}$ trend with the strain rate is well explained by a combination of variation of production rate of above Thermal, NNH and $N_2O$ route. Also result of Thermal-Mech. that includes only thermal NO reaction is compared with those of Full-Mech. As a result, It can be identified that there was difference between the two results of calculation. It is attributed to result that Thermal-mech did not consider contributions of NNH and $N_2O$ route. From these result, we can conclude that NOx emission characteristics of hydrogen nonpremixed flames should consider contributions of above three routes simultaneously.

인화귀원(引火歸原)의 병기론 연구 (Pathological Mechanistic Study of Conducting Fire Back to Its Origin)

  • 조원준;김영목
    • 동의생리병리학회지
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    • 제21권4호
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    • pp.795-802
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    • 2007
  • The fire not to back to its origin(火不歸原) is said that source yang(元陽) of sea of qi(氣海) rises because fire(火) of lower energizer(下焦) can't return to its origin. Successive medical men regarded the cause of it as yang deficiency(陽虛) or yin deficiency(陰虛) generally, but Jangseoksun(張錫純) presented eight kinds of cause, they are syndrome of upcast yang(戴陽證), deficiency of qi(氣虛), yin deficiency, yin and yang deficiency(陰陽虛), thoroughfare qi ascending counterflow(衝氣上衝), heart fire(心火), yang deficiency with cold fluid retention(寒飮) in middle energizer(中焦寒飮), yang deficiency with sunken cold locked in(沈寒錮冷). The method of conducting fire back to its origin may be the treatment of fire not to back to its origin as an interpretation of the phrase in a broad sense, but it is limited to yang deficiency with sunken cold locked in besides syndrome of upcast yang as the treatment based on pathological conditions. By this standpoint Eunsuryong(殷壽龍) used conducting fire back to its origin to remove hidden cold(伏寒) and make rising false fire(假火) settle. The meaning of conducting fire back to its origin is not just raise yang qi(陽氣) but break sunken cold locked in by using the drugs like Buja(附子), Yukgye(肉桂). Jakyak(芍藥) can concentrate yang qi on the life gate(命門) by converging it, Sukjihwang(熟地黃) can supply yin essence(陰精) and check the intense nature of tonifing yang(補陽) drugs. So if we want to use the method of conducting fire back to its origin, we should confirm the symptoms of sunken cold locked in and yang deficiency not to misdiagnose yin deficiency.

CA기반의 다방향 보행자 시뮬레이션 모형개발 (Multi-directional Pedestrian Model Based on Cellular Automata)

  • 이준;배윤경;정진혁
    • 한국도로학회논문집
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    • 제12권4호
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    • pp.11-16
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    • 2010
  • 보행교통류를 주제로 다양한 연구들이 진행되었지만 초기의 보행연구는 차량의 교통류이론을 그대로 적용하여 해석하기도 하였다. 최근 보행교통류에 대한 다양한 모형들이 제시되고 있으며, 특히 CA모형은 보행교통류를 위한 시뮬레이션 모형으로 빈번하게 사용되고 있다. 대표적인 CA 모형으로 가스입자의 움직임을 이용하여 양방향의 보행교통류를 설명하기도 하였는데 초기에는 정방형의 Gas-lattice 모형이 제안되었으며 이후에 정육방 Gas-lattice 모형을 이용하여 보행자의 움직임과 회피를 묘사하기도 하였다. 하지만 이러한 모형들은 보행자의 움직임을 편의임의보행으로 가정하였기 때문에 단일방향으로의 움직임만을 설명할 수 있었다. 본 연구에서 제시된 MLPM(the Multi-Layer Pedestrian Model)은 어떤 공간에서 복수개의 기종점을 가진 경우에도 현실적인 보행자의 움직임을 설명할 수 있는 모형이다.

초임계 영역내 $CO_2$ 냉각 열전달과 압력강하 분석 (Analysis of Heat Transfer and Pressure Drop During Gas Cooling Process of Carbon Dioxide in Transcritical Region)

  • 손창효;이동건;정시영;김영률;오후규
    • Journal of Advanced Marine Engineering and Technology
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    • 제28권1호
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    • pp.65-74
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    • 2004
  • The heat transfer coefficient and pressure drop of $CO_2$(R-744) during gas cooling Process of carbon dioxide in a horizontal tube were investigated experimentally and theoretically. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop consist of a receiver. a variable-speed pump. a mass flowmeter, an evaporator. and a gas cooler(test section). The main components of the water loop consist of a variable-speed Pump. an constant temperature bath. and a flowmeter. The gas cooler is a counterflow heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus The test section consists of smooth, horizontal stainless steel tube of 9.53 mm outer diameter and 7.75 mm inner diameter. The length of test section is 6 m. The refrigerant mass fluxes were 200 ~ 300 kg/($m^2{\cdot}s$) and the inlet pressure of the gas cooler varied from 7.5 MPa to 8.5 MPa. The main results were summarized as follows : The predicted correlation can evaluated the R-744 exit temperature from the gas cooler within ${\pm}10%$ for most of the experimental data, given only the inlet conditions. The predicted gas cooley capacity using log mean temperature difference showed relatively food agreement with gas cooler capacity within ${\pm}5%$. The pressure drop predicted by Blasius estimated the pressure drop on the $CO_2$ side within ${\pm}4.3%$. The predicted heat transfer coefficients using Gnielinski's correlation evaluated the heat transfer coefficients on the $CO_2$ side well within the range of experimental error. The predicted heat transfer coefficients using Gao and Honda's correlation estimated the heat transfer coefficients on the coolant side well within ${\pm}10\;%$. Therefore. The predicted equation's usefulness is demonstrated by analyzing data obtained in experiments.

이중관 내부 나노유체의 강제대류에 관한 수치적 연구 (Numerical Study of Forced Convection Nanofluid in Double Pipe)

  • 임윤승;최훈기
    • 융합정보논문지
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    • 제9권12호
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    • pp.147-156
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    • 2019
  • 동심 이중관에서 기본유체 물과 나노입자 산화알미늄의 혼합인 나노유체를 적용한 대향유동을 유한체적법의 수치적 방법으로 열전달 특성을 규명하였다. 고온유체는 내부 원형관으로 흐르며 열을 외부 환형관으로 흐르는 저온유체로 전달한다. 고온유체와 저온유체의 체적유량 및 나노입자의 체적농도를 변수로 두어 열전달 및 유동 특성을 조사했다. 결과는 나노입자의 체적농도와 체적유량의 증가함에 따라 열전달 성능이 증가함을 보였다. 외부와 내부 관 모두에서 나노유체인 경우가 기본유체보다 나노입자의 체적농도가 8%일 때 나노유체가 열전달 성능이 최대 17% 증가하는 것을 확인했다. 또한 기본유체에 비해 환형관의 대류열전달 계수는 최대 31% 증가함을 보였으며 열교환기의 유용도는 약 20%가 상승함을 확인하였다. 하지만 나노입자의 체적농도가 8%일때 마찰인자가 최대 136% 커지는 것을 확인하였다.

에틸렌 확산화염 내 질소 혼합이 매연 생성 특성에 미치는 영향 (Effect of N2 Diluent on Soot Formation Characteristics in Ethylene Diffusion Flames)

  • 김준수
    • 해양환경안전학회지
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    • 제29권4호
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    • pp.356-362
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    • 2023
  • 기후 변화에 따른 위험성은 전 세계적으로 오랜 기간 강조되고 있으며, 이를 극복하기 위한 노력은 해운분야에서도 국제해사 기구를 중심으로 이어지고 있다. 연소과정에서 발생한 매연을 제어하기 위하여 매연 생성 특성에 관한 연구는 필수적이다. 본 연구에서는 에틸렌 가스를 기반으로 한 대향류 확산화염에서 불활성 기체인 질소를 혼합하여 화염온도, 화염형태, 매연 생성 관련된 화학종의 상태변화를 확인하기 위해 광소멸법과 화학반응 수치해석을 수행하였다. 연구 결과. 질소의 혼합비율이 증가함에 따라 화염온도 감소와 매연체적분율 감소로 이루어졌다. 매연 입자가 분포하는 구간도 감소하였으며, 30% 이상 혼합비율이 높아지면 체적분율 감소율이 감소하였다. 매연 성장에 관여하는 화학종들의 몰분율도 감소하였다. HACA 반응 관련 화학종은 탄화수소 연료 비율에 따라 영향을 받으나, 홀수탄소 경로 관련 화학종은 탄화수소 연료 비율뿐만 아니라 화염온도 영향을 받는 것을 확인하였다.

도로터널에서 자연풍에 의한 미세물분무의 화재제어 특성에 관한 수치해석 연구 (A Numerical Study on the Fire Suppression Characteristics of a Water Mist with Natural Wind in a Road Tunnel)

  • 황철홍;김한수;이창언;장영남;신현준
    • 한국화재소방학회논문지
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    • 제22권3호
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    • pp.221-227
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    • 2008
  • 본 연구에서는 FDS 코드를 이용하여 외부 자연풍에 의한 터널 내의 미세물분무 소화특성을 검토하였으며, 상세반응이 고려된 1차원 대향류 비예혼합화염을 이용하여 화염내부에서 미세물분무의 냉각 및 화학반응효과에 의한 소화현상을 규명하였다. 연구결과로서, 외부 자연풍의 유속 증가에 따라 고온 연기층의 분포 및 분무 특성의 큰 변화가 발생됨을 확인하였다. 외부 자연풍이 없는 경우에는 분무입자 직경이 작을수록 소화성능이 좋지만, 풍속이 증가함에 따라 입자직경이 클수록 소화성능이 좋아짐을 알 수 있었다. 자연풍은 입자의 화염면 침투를 방해할 뿐 아니라. 충분한 산소의 공급으로 화제 억제를 방해할 것으로 예측된다. 또한 자연풍이 존재하는 조건의 화염은 화염 신장효과에 의해 밀폐된 공간에서의 화염 보다 작은 양의 $H_2O$침투에 의해서도 소화될 수 있으며, $H_2O$의 화학반응에 의한 소화효과는 외부 자연풍의 유속에 크게 영향을 받지 않음을 확인하였다.