The effects of liraglutide on cardiometabolic parameters

양호동,문신제 대한내과학회 2020 대한내과학회 추계학술대회 Vol.2020 No.1

압전 액츄에이터를 이용한 열전냉각 시스템 성능 향상에 관한 연구

양호동,윤희성,오율권 한국안전학회 2009 한국안전학회지 Vol.24 No.6

This study investigated on enhancement of thermoelectric cooling system performance by piezoelectric actuator. The thermoelectric cooling system consisted of the thermoelectric module, a heat sink and a cooling fan, respectively. Also, the piezoelectric actuator was applied to improve the performance of thermoelectric cooling system and investigate the heat transfer phenomenon. The temperature distribution of test section was measured to investigate cooling characteristics of thermoelectric cooling system. The flow phenomenon of test section was visualized using visualization device. When the piezoelectric actuator was applied to the heat transfer process of thermoelectric cooling system, acoustic streaming was occurred in test section. The acoustic streaming was occurred forced convection flow, and was regularly formed the temperature distribution in test section. The results clearly show that the acoustic streaming is one of the prime effects to enhance the convection heat transfer and can enhance the performance of thermoelectric cooling system.

화재모델링을 이용한 목표 대상물의 열적 손상에 대한 정량적 위험성 평가방법의 고찰

양호동,한호식,황철홍,김성찬 한국화재소방학회 2016 한국화재소방학회논문지 Vol.30 No.5

The quantitative risk assessment methods for thermal failure in targets were studied using fire modeling. To this end,Fire Dynamics Simulator (FDS), as a representative fire model, was used and the probabilities related to thermal damageto an electrical cable were evaluated according to the change in fire area inside a specific compartment. ‘The maximumprobability of exceeding the damage thresholds’ adopted in a conservative point of view and ‘the probability of failure’including the time to damage were compared. The probability of failure suggested in the present study could evaluate thequantitative fire risk more realistically, compared to the maximum probability of exceeding the damage thresholds withthe assumption that thermal damage occurred the instant the target reached its minimum failure criteria in terms of thesurface temperature and heat flux. 화재모델링을 이용한 목표 대상물의 열적 손상에 대한 정량적 위험성 평가방법이 검토되었다. 이를 위해 대표적인 화재모델로서 FDS가 사용되었으며, 특정 구획 내에서 화원 면적 변화에 따른 전기 케이블의 열적 손상과 관련된 확률이평가되었다. 보수적 관점에서 적용되고 있는 ‘최대 손상임계 초과확률’과 손상시간의 정보가 포함된 ‘손상확률’이 체계적으로 비교되었다. 목표 대상물이 표면온도 및 열유속에 대한 최소 손상기준에 도달하는 순간에 열적 손상이 발생된다는가정이 적용된 최대 손상임계 초과확률에 비해 본 연구에서 제안된 손상확률은 정량적 화재 위험성을 보다 현실적으로평가할 수 있음을 확인하였다.

초음파 진동 가진시 발생하는 압력분포가 열전달 촉진에 미치는 영향에 관한 연구

양호동,유성림,오율권 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.1

본 연구에서는 실험적으로 구한 열전달 계수 향상비와 수치해석을 통해 계산된 음향장에서의 압력분포 결과를 조사하여 비교해 보았다. 상변화 물질로는 끓는점이 300℃인 파라핀을 사용하였으며, 용융용기 내에는 고정된 40㎑의 주파수를 발생시킬 수 있는 두 개의 초음파 진동자가 부착되어 있다. 액상파라핀 영역에서의 유동현상을 가시화하기 위해 입자영상추적계(PIV)를 사용하였으며, 초음파 강도의 변화가 열전달에 미치는 영향을 조사해보기 위하여 초음파 강도를 70W에서 340W까지 변화시켜 보았다. 또한, 액상파라핀내의 압력을 계산하기 위해 결합형 유한요소-경계요소법을 적용한 수치해석 방법을 통해 그 결과를 계산 해 보았다. 실험결과, 초음파 강도가 증가할수록 열전달 계수가 증가하였으며, 340W의 초음파 강도가 주어졌을 때 약 27.8%의 열전달이 향상되는 것을 확인할 수 있었다. 수치해석 결과에서는 초음파 강도가 340W일 때 약 60%의 압력이 증가된 것을 확인할 수 있었으며, 결국 초음파 진동자 부근에서 높은 압력분포는 매질내에서 불완전한 유통을 파괴할 수 있는 강한 유통을 형성한다. 즉, 액상영역에서의 급격한 압력변동은 열전달을 촉진하며 이는 압력분포 결과와 열전달 향상비의 결과가 일치하는 것으로 확인할 수 있다. The objectives of this work are to investigate that the augmentation ratio of heat transfer coefficient was experimentally measured and was compared with the acoustic pressure distributions in acoustic fields obtained by numerical analysis. Liquid paraffin with a boiling point of 300℃ was selected as a medium. Two ultrasonic transducers are installed at the melting cavity and was applied the fixed ultrasonic frequency of 40㎑. A particle image velocimetry (PIV) was used for the visualization of flow field inside the liquid region of the paraffin. And ultrasonic intensities were varied from 70W to 340W in order to investigate the effect of the ultrasonic vibrations strength on heat transfer. Also, a coupled finite element-boundary element method (FE-BEM) was applied to calculate the acoustic pressure in the liquid paraffin. From the experimental and numerical results, the heat transfer coefficient is increased with increase in the ultrasonic intensities. The largest augmentation of heat transfer (about 27.8%) is measured at the ultrasonic intensity of 340W. The results of numerical analysis obtain that acoustic pressure is increased by 60% at the ultrasonic intensity of 340W. In the end, the higher acoustic pressure distribution near two ultrasonic transducers develops more intensive flow destroying the flow instability. That is, the intensive acoustic pressure variation augments heat transfer as the profile of acoustic pressure variation is consistent with that of augmentation of heat transfer.

음향장 내의 상변화 열전달 촉진에 관한 연구

양호동,나기대,오율권 한국에너지학회 2004 에너지공학 Vol.13 No.2

본 연구에서는 초음파 진동의 가진에 의하여 유도되어진 음향장 내에서의 열전달 결과를 실험과 수치적 해법을 통해 조사해 보았다. 초음파 가진시 용기 바닥면에서 자유표면으로 향하는 강한 유체흐름, 즉 ?음향흐름?은 입자영상추적계(PIV)를 통하여 가시화 하였다. 또한, 음향흐름이 존재하는 상태에서 실험을 통해 구해진 열전달 향상비와 수치적 해법에 의해 구하여진 음압분포를 비교하여 보았으며, 수치적 해법을 위하여 결합형 유한요소-경계요소법(Coupled FE-BEM)을 적용하였다. 실험을 통한 연구결과와 수치적 해법을 통한 연구결과에서 우리는 매질내에서 초음파 진동의 가진으로 인해 발생하는 음압 변동이 열전달의 증감과 밀접한 관련이 있음을 확인할 수 있다.

초음파 가진시 물의 비등열전달 과정에서 형성되는 압력장 해석을 위한 수치해석적 연구

양호동,오율권 朝鮮大學校 機械技術硏究所 2005 機械技術硏究 Vol.8 No.2

본 연구에서는 물을 가열하는 동안, 초음파 진동에 의해 형성된 음압이 비등 열전달 과정에 미치는 영향을 알아보기 위해 수치해석적 방법을 이용하여 조사해 보았다. 수치해석은 40㎑의 초음파 진동을 진동판 밑변에 부착된 1개의 초음파 진동자에 가진하는 것으로 하였고, 해석 모델은 진동판 밑면을 유한요소법을 이용하여 모델링한 후, 해석 모델에 경계요소법을 적용하여 음장내의 음압을 해석하는 결합형 유한요소-경계요소법(coupled FE-BEM)을 적용하였다. 또한, 초음파 가진으로 인해 형성되는 음압이 열전달 촉진에 영향을 미치는 중요한 요인의 하나로 작용하고 있기 때문에, 비등 과정에서의 열전달 계수를 초음파 진동을 가진한 경우와 가진하지 않은 경우로 나누어 측정하고 음압과 열전달 촉진과의 관계를 살펴보았으며, 실험결과, 초음파 진동자 부근에서의 열전달 촉진 형성 결과와 음압의 형성 결과가 유사한 형태를 보이는 것을 확인할 수 있었다. The present study was numerically investigated that the acoustic pressure caused by ultrasonic vibration has an effect on boiling heat transfer in the water. For the numerical work, a coupled finite element-boundary element method(FE-BEM) was used to calculate the acoustic pressure in the water. In case of the numerical model, the modeling of vibrating plate installed an ultrasonic transducer was performed by the finite element modeling. And then, finite element modeling data consisted element and node number was converted to the boundary element data by SVS(Structural Vibration Simulator). Also, the local heat transfer coefficient was experimentally measured and was compared with the acoustic pressure distributions in order to investigate the relationship between acoustic pressure and enhancement of heat transfer. The results of this study reveal that the acoustic pressure is some of the facts enhanced heat transfer as the profile of acoustic pressure variation is consistent with that of enhancement of heat transfer.

알루미늄 캐스팅 타이어 몰드 주조시 트레드 부에 발생하는 열변형 예측에 관한 연구

양호동,오율권 朝鮮大學校 機械技術硏究所 2007 機械技術硏究 Vol.10 No.2

In this study, the thermal deformation inside the aluminum casting tire mold was analyzed using the numerical analysis method and was investigated using the experimental method. The metal casting device used for manufacturing the tire mold products for automobiles in the actual industrial field was selected as an analysis model, and AI-Mg system alloy (AC7A) widely used for metal casting was selected as the mold material. For the numerical analysis, "COMSOL Multiphysics", the commercial code based on the finite element analysis (FEA), was used in order to predict the thermal deformation of the AC7 A including temperature, displacement and stress distribution. Also, in order to verify the results calculated by the numerical analysis, the experiment for temperature measurement inside the tire mold was performed using the K-type thermocouple under the same condition of numerical analysis method. In detail, the displacement inside the AC7 A tire mold was closely related to the temperature difference. The displacement for 15 minutes in the metal casting device appeared to be larger at the center parts of tire mold (tread part) than on its sides, and the one calculated for the time until it was completely cooled at atmosphere temperature after it was removed from the metal casting device appeared to be larger on the measurement points of 1, 4 and 7 near the atmosphere than on other points. Moreover, the stress inside the AC7A tire mold appeared to be larger at the center parts of tire mold (tread part) because of the shrinkage caused by the cooling speed difference for the initial 15 minutes, and larger on the measurement points 2, 5 and 8 when the mold was removed from the metal casting device because of slow cooling speed. From these numerical analysis conditions and results, when the temperature distribution calculated by the numerical analysis and the one actually measured by the experiment were compared with each other, it appeared that there was a slight temperature difference between them because of the latent heat of the AC7A during the phase change process but th6eir cooling patterns were almost similar results.

저기압 고산소 환경에서 화염 전파특성에 관한 실험적 연구

양호동,권행준,박설현 한국화재소방학회 2016 한국화재소방학회논문지 Vol.30 No.6

The characteristics of flame spread under similar atmospheric conditions to those inside the first stage of launch vehicleswere investigated to provide fundamental knowledge to prevent fires and explosions of vehicles during launchingoperations. To this end, the rate of flame spread on the solid fuel was measured at elevated oxygen concentrations andreduced atmospheric pressures. A 0.18 mm diameter optical fiber was used as a solid fuel. The experimental results indicatedthat elevated oxygen concentrations can increase the rate of flame spread while increasing the atmospheric pressuresto 1 atm can lead to decreases in the rate of flame spread. The increases in the rate of flame spread with pressure isdue mainly to reductions in the convective heat loss that are clarified through an analysis of the pressure dependence onthe convective heat transfer coefficient. 발사체의 지상 운영과정이나 발사과정에서 일어날 수 있는 화재와 폭발사고 예방을 위해 1단 동체 내부에 형성될 수있는 연소 환경에서 화염의 전파특성을 고찰해 보았다. 이를 위해 1단 동체 내부에 형성될 수 있는 고산소-저기압 환경을 연소챔버 내에 조성하고 고체연료를 점화시켜 화염 전파율을 측정하였다. 고체연료로는 두께가 0.18 mm인 광섬유를사용하였다. 주어진 조건에서 산소농도가 증가함에 따라 광섬유를 따라 전파하는 화염의 속도는 급격히 증가하였지만 챔버 내의 압력이 대기압에 가까질 수록 화염의 전파속도는 감소하였다. 압력 증가에 따른 화염전파율의 감소의 원인을 파악하기 위해 대류열전달계수와 화염전파율의 압력 상관성 분석해 보았으며, 이를 통해 압력이 낮아질수록 대류 열손실이줄어들어 화염전파율이 증가하는 것을 확인하였다.

초음파에 의한 상변화 물질의 용융촉진 과정 분석 및 가시화

양호동(Ho-Dong Yang),오율권(Yool-Kwon Oh) 한국트라이볼로지학회 2005 한국트라이볼로지학회 학술대회 Vol.2005 No.6

This study analyzed the melting process of solid-liquid phase change material (PCM) and applied the visualization to investigation of heat transfer by ultrasonic vibrations. For heating condition, we considered the constant heat flux condition and investigated the melting process of a PCM from a heated vertical wall for the following; one without ultrasonic vibrations (natural melting) and the other with ultrasonic vibrations. in the present study, heat flow was measured in the absence of and in the presnece of acoustic streaming. This streaming produced by ultrasonic vibrations was visualized by a particle image veiocimetry (PIV) and a thermal infrared camera. Ther experimental results revealed that acoustic streaming could accelerate the melting process as much as 2.5 times, compared to the rate of the melting without ultrasonic vibrations. Also, temperature and Nusselt numbers over time provided conclusive evidence of the important role of acoustic streaming on the melting phenomena of the PCM.

유해물질 제거를 위한 국소배기장치 후드의 흡입력 증가에 관한 연구

양호동(Ho-Dong Yang),김영선(Young-Sun Kim),오율권(Yool-Kwon Oh) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5

This study investigates on the inhalation force improvements of hood consisted one of the local ventilation systems attached the new device named as gas-guidance-device for removed a pollution source. The numerical method applying finite element method is calculated the velocity and pressure distributions of a moving fluid at the beginning and the inside of a hood with and without the gas-guidance-device in hood. And, the experimental study is measured the wind velocity using the anemometer at the same condition of numerical study. Also, the optimum shape of gas-guidance-device which is suitable for hood shape derived from the numerical and experimental results. The results of this study is supplied the important data to an industrial field for control of a pollution source in the engineering aspect. Moreover, the introduced technique of hood attached the gas-guidance-device is very useful to remove the harmful materials such as dust and waste happened in the manufacturing factory.