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입자층(粒子層)을 이용한 열교환기(熱交換器)에서 소요동력(所要動力)에 따른 전열특성(傳熱特性)에 관(關)한 연구(硏究)
유지오,양한주,조용철,서정윤,Yoo, J.O.,Yang, H.J.,Cho, Y.C.,Seo, J.Y. 대한설비공학회 1992 설비공학 논문집 Vol.4 No.4
In order to improve the performance of heat exchanger, fluidized bed is often employed. The experiments are carried out in fluidized double pipe parallel flow heat exchanger in which finned tube is vertically immersed. And the heat transfer coefficients between the heated tube and fluidized bed of alumina beads(dp=0.41, 0.54, 0.65, 0.77mm) are calculated as a function of air fluidized velocity and pumping power. The effects of particle size, static bed height and pumping power on the heat transfer coefficients are investigated. And the heat transfer coefficients are compared with that of single phase forced convection heat exchanger. In particular, the heat transfer performance of each type heat exchanger is evaluated in relation to the pumping power.
유동층형(流動層形) 핀관(管) 열교환기(熱交換器)의 열전달특성(熱傳達特性)에 관(關)한 기초적(基礎的) 연구(硏究)
이석우,유지오,양한주,서정윤,Lee, S.W.,Yoo, J.O.,Yang, H.J.,Seo, J.Y. 대한설비공학회 1991 설비공학 논문집 Vol.3 No.3
Experiments have been conducted to measure the overall heat transfer coefficient for gas-solid fluidized double pipe heat exchanger with finned tube. The average particle diameters of alumina are used in 0.4, 0.5, 0.6 and 0.9mm. And the effects of average particle diameter, static bed height and flow velocity on overall heat transfer coefficient have been investigated. Also the heat transfer effect of fluidized bed was compared with that of single phase forced convection and that of heat exchanger with smooth tube.
충돌분류계에서 WIRE MESH를 이용한 열전달 증진에 관한 연구
금성민,김동춘,유지오,이창언,임장순,Kum, S.M.,Kim, D.C.,Yoo, J.O.,Lee, C.E.,Yim, C.S. 한국태양에너지학회 1997 한국태양에너지학회 논문집 Vol.17 No.2
본 연구는 2차원 충돌공기분류계의 포텐셜코어 영역에서 열전달증진을 목적으로 노즐출구와 전열면사이에 메쉬를 설치한후 노즐출구 속도, 메쉬와 전열면사이의 간극, 노즐출구와 전열면사이의 거리를 변화시킬 때의 열전달특성을 메쉬를 설치하지 않은 경우와 비교 검토한 것으로 메쉬를 설치했을 때에는 분류가 전열면에 충돌하면서 소분류로 분할되어 발생하는 난류에 의해 충돌영역에서 열전달성능이 좋아지며, 또한 벽면분류영역으로 진행하면서 홀과 홀사이의 밑부분에서 일어나는 가속으로 인해 열전달성능이 향상된다. 특히 메쉬와 전열면사이의 간극을 변화시켰을 경우 정체점부근에서는 간극이 클수록, 벽면분류영역에서는 간극이 작을수록 전달성능은 향상되며 U=18m/s, H/B=2, C=1인 경우에는 메쉬를 설치하지 않은 평판보다 평균 약 44%의 열전달증진 효과과 있었다. 그리고 본 실험결과를 기존의 난류촉진체를 이용한 연구결과와도 비교 검토하였다. The objective of this research was to investigate the enhancement of heat transfer by wire mesh in impinging air jet system at the potential core region. The first experiment was carried out without mesh between nozzle exit and flat plate and the second experiment was done with mesh between them. When mesh was installed in front of the plate, heat transfer has been Increased due to the acceleration between rectangular halls and divided small jet In case clearances are changed, heat transfer comes to maximum under the condition of C=1mm, irrespective of nozzle exit velocity and H/B. Also the average heat transfer enhancement rate of a flat plate with mesh has been increased about 44% at maximum under the condition of U=18m/s, H/B=2 and C=1mm, compared to the result of a flat plate without mesh.
단열벽체두께가 변화되는 밀폐공간에서 복사-자연대류열전달특성에 관한 연구
권용일(Y.I.Kwon),유지오(J.O.Yoo),권순석(S.S.Kwon) 한국태양에너지학회 1995 한국태양에너지학회 논문집 Vol.15 No.3
본 연구는 온돌공간으로 가정한 2차원 밀폐공간에서 단열벽체두께를 변화시켜 표면복사-자연대류 열전달특성에 대해 수치해석방법을 이용하여 고찰하였다. 복사열전달이 동반된 자연대류인 경우, 밑면의 평균 Nusselt수는 벽면방사율이 증가함에 따라 증가하고 벽체의 무차원두께가 감소함에 따라 증가되며 순수자연대류인 경우보다 큰 값을 나타낸다. 밑면의 평균 Nusselt수는 단열벽체의 두께를 감소시킴에 따라 복사열 전달을 동반하는 자연대류의 대류열전달량이 자연대류의 열전달량보다 다소 작은 값을 나타냈다. This study is investigated numerically on the heat transfer characteristics of surface radiation-natural convection interactions in a two dimensional enclosure assumed Ondol cavity. Mean Nusselt number of the bottom surface with surface radiation is increased by increasing wall emissivity and by decreasing dimensionless thickness of adiabatic wall and is greater than that without radiation. Mean Nusselt number of the bottom surface for convection only with surface radiation is slightly smaller than that without surface radiation with decrease dimensionless thickness of adiabatic wall.
충돌분류계에서 WIRE MESH를 이용한 열전달 증진에 관한 연구
금성민(S.M.Kum),김동춘(D.C.Kim),유지오(J.O.Yoo),이창언(C.E.Lee),임장순(C.S.Yim) 한국태양에너지학회 1997 한국태양에너지학회 논문집 Vol.17 No.1
본 연구는 2차원 충돌공기분류계의 포텐셜코어 영역에서 열전달증진을 목적으로 노즐출구와 전열면사이에 메쉬를 설치한후 노즐출구 속도, 메쉬와 전열면사이의 간극, 노즐출구와 전열면사이의 거리를 변화시킬 때의 열전달특성을 메쉬를 설치하지 않은 경우와 비교 검토한 것으로 메쉬를 설치했을 때에는 분류가 전열면에 충돌하면서 소분류로 분할되어 발생하는 난류에 의해 충돌영역에서 열전달성능이 좋아지며, 또한 벽면분류영역으로 진행하면서 홀과 홀사이의 밑부분에서 일나는 가속으로 인해 열전달성능이 향상된다. 특히 메쉬와 전열면사이의 간극을 변화시켰을 경우 정체점부근에서는 간극이 클수록, 벽면분류영역에서는 간극이 작을수록 전달성능은 향상되며 U=18m/s, H/B=s, C=1인 경우에는 메쉬를 설치하지 않은 평판보다 평균 약 44%의 열전달증진 효과과 있었다. 그리고 본 실험결과를 기존의 난류촉진체를 이용한 연구결과와도 비교 검토하였다. The objective of this research was to investigate the enhancement of heat transfer by wire mesh in impinging air jet system at the potential core region.<br/> The first experiment was carried out without mesh between nozzle exit and flat plate and the second experiment was done with mesh between them.<br/> When mesh was installed in front of the plate, heat transfer has been increased due to the acceleration between rectangular halls and divided small jet<br/> In case clearances are changed, heat transfer comes to maximum under the condition of C= 1mm, irrespective of nozzle exit velocity and H/B.<br/> Also the average heat transfer enhancement rate of a flat plate with mesh has been increased about 44% at maximum under the condition of U=18m/s, H/B=2 and C=l mm, compared to the result of a flat plate without mesh.
최규영 ( Kyu Young Choi ),안석진 ( Seok Jin Ahn ),김현근 ( Hyun Keun Kim ),이세한 ( Se Han Lee ),유창민 ( Chang Min Yu ),조재현 ( Jae Hyun Cho ),유지원 ( Ji Won Yoo ),서승오 ( Seong O Suh ),김은실 ( Eun Sil Kim ),정준오 ( Jun Oh J 대한내과학회 2010 대한내과학회지 Vol.78 No.2
Background/Aims: The most common type of syncope in young adults is neurocardiogenic in origin, which is not related to organic problems and has a benign nature. Therefore, there have been few reports regarding syncope in young Korean adults. Here, we examined the causes of syncope and its clinical characteristics in young combat and auxiliary police in Korea. Methods: We performed a retrospective study of the medical records of 193 combat and auxiliary police in Korea admitted to the National Police Hospital for syncope or presyncope between January 2004 and December 2007. Results: The subjects` mean age was 21±1.2 years, and there were 2.8±2.9 episodes of syncope (mean±SEM). The first syncope occurred after enlistment in the police in 102 patients (52.8%). Basic diagnostic studies showed two cases of elevated creatine phosphokinase and one case of anemia to be related to syncope. Syncope-related traumatic injuries occurred in 38 patients (19.7%), and syncope was more prevalent in the summer. Head-up tilt test was performed in 175 of the 193 patients, and 123 showed a positive response. Other evaluations, including brain magnetic resonance imaging, electroencephalography, and echocardiography, were not helpful for diagnosis. Syncope was neurocardiogenic in origin in the majority of cases. Other causes of syncope were exhaustion (n=2), hyperventilation syndrome (n=2), Meniere`s disease (n=1), anemia (n=1), and psychiatric problems (n=5). The causes of syncope could not be identified in 59 patients (30.5%). Conclusions: Neurocardiogenic syncope was the most common type in our study population. More than half of our patients experienced their first episode after enlisting with the police. Further studies in these groups are necessary. (Korean J Med 78:198-206, 2010)