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권영철(Young Chel Kweon),장근선(Keun Sun Chang),권정태(Jeong-Tae Kwon),김무환(Moo Hwan Kim) 대한설비공학회 2000 설비공학 논문집 Vol.12 No.11
In order to investigate the effects of an electric field on EHD (Electro-hydrodynamic) nucleate boiling heat transfer characteristics in a nonuniform electric field under saturated pool boiling, the basic study has been performed experimentally. In the present study, the working fluid is R-113 and the plate-wire electrode system is used to generate a steep electric field gradient. Boiling parameters are investigated by using a high speed camera. The electric field distribution around a wire is obtained to understand the effect of an electric field on bubble departure/movement. The experimental results show EHD effects are much more considerable when the applied voltage increases. Bubbles depart away from the heated wire in radial direction. It is confirmed that the mechanisms of EHD nucleate boiling are closely connected with the dynamic behavior of bubbles. The boiling parameters are significantly changed by the electric field strength. With increasing applied voltages, the bubble size decreases and the nucleation site density, bubble velocity and bubble frequency increase.
디지털 스크롤 압축기를 적용한 시스템 에어컨의 냉난방특성에 대한 실험적 연구
전용호(Young Ho Jun),김대훈(Dae Hun Kim),권영철(Young Chel Kweon),장근선(Keun Sun Chang),이윤수(Yun Su Lee),문제명(Je Myung Moon),윤백(Youn Baek),홍주태(Ju Tae Hong) 대한설비공학회 2003 설비공학 논문집 Vol.15 No.6
In order to investigate the cooling and heating characteristics of a variable-capacity system A/C applying a digital scroll compressor, the cooling and heating capacities and COP are measured by the psychrometric calorimeter. The capacity of the system is controlled by the digital scroll compressor, which is operated by controling PWM valve and the loading vs. unloading time. In the case of unloading compared that of loading, the consumption power of the compressor is about 11% and the capacity variation of the system A/C is within about 1%. When the system A/C is operated under the cooling and heating standard conditions, COP is nearly uniform but cooling capacity and heating capacity increase at minimum, rated and maximum modes. The system A/C applying the digital scroll compressor is effective for the range with high load or the width of large load variation. When the auxiliary heater is on, at the cold region, the system A/C produces the excellent heating capacity.
디지털 스크롤 압축기를 이용한 시스템 에어컨의 냉난방특성
전용호(Young Ho Jun),김대훈(Dae Hun Kim),권영철(Young Chel Kweon),이윤수(Yun Su Lee),문제명(Je Myung Moon),홍주태(Ju Tae Hong) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
In order to investigate the cooling and heating characteristics of a variable-capacity system A/C using<br/> a digital scroll compressor, the cooling and heating capacities and EER are measured by the<br/> psychrometric calorimeter. The capacity of the system is controlled by the digital scroll compressor,<br/> which is operated by controling PWM valve and the loading vs. unloading time. When the system A/C<br/> is operated under the cooling and heating standard conditions, EER is nearly uniform but cooling<br/> capacity and heating capacity increase at minimum, rated and maximum modes. When the auxiliary<br/> heater is on, at the cold region, the system A/C produces the excellent heating capacity.
박성관(Seong Kwan Park),권영철(Young Chel Kweon),김도완(Do Wan Kim) 대한기계학회 2002 대한기계학회 춘추학술대회 Vol.2002 No.5
An efficient finite element method is introduced for two dimensional viscous incompressible flows using the vorticity formulation. The objective of this paper is the treatment of how to make the vorticity boundary condition instead of pressure in the primitive variable case. We construct the linear finite element approximation for the solution of Navier-Stokes and Stokes flows. We can analyze not only regular domain but also irregular domain, using this formulation.
초음파에 의한 평판에서의 임계열유속 증진에 대한 실험적 연구
김대훈(Dae Hun Kim),권영철(Young Chel Kweon),정지환(Ji Hwan Jeong) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
Augmentation of CHF by ultrasonic is experimentally studied under subcooling pool boiling<br/> condition. Experiment is carried out for downward-facing plate with and without the ultrasonic. The<br/> working fluid is distilled water. Experimental apparatus is composed of a bath, power supply, test<br/> section, ultrasonic generator, DAQ system. Experiment is performed with the subcooling temperature of<br/> 5℃, 20℃, 40℃ and the inclined angle of 0°, 10°, 20°, 45°, 90. From the experimental results, it is<br/> found that ultrasonic effect enhances CHF of the downward-facing plate. As increasing the degree of<br/> subcooling, the rate of CHF increase is enhanced. As increasing the inclined angle, the rate of CHF<br/> increase decreases. Also, we can see that the heat transfer mechanism of CHF augmentation is closely<br/> connected with the dynamic behavior of bubble generation and departure.
Ji Hwan Jeong(정지환),Young Chel Kweon(권영철),Hyun Jung Kim(김현정) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
The experimental measurements show that the heat transfer performance of heaters submerged in a water pool was enhanced when ultrasonic vibration is applied to the water pool. The increase rate in CHF values varied depending on inclination angle of heated surface with the maximum when horizontal downward facing. The experimental conditions inside the water pool with and without ultrasonic vibration were analysed using FLUENT. Steam bubbles are not simulated using FLUENT due to its limitation. Based on the examination results, it can be concluded that an ultrasonic vibration enhances fluid mixing around heater itself and thus provides heated surface with fresh water. This has an effect of lowering liquid temperature adjacent to heater surface, and in turn, leads to a heat transfer augmentation.
초음파의 영향을 받는 하향 평판의 과냉 조건에서의 CHF 증진에 관한 실험적 연구
김대훈 ( Dae Hun Kim ),전용호 ( Young Ho Jun ),권영철 ( Young Chel Kweon ),정지환 ( Ji Hwan Jeong ),권정태 ( Jeong Tae Kwon ),이윤수 ( Yun Su Lee ) 한국공업화학회 2003 공업화학 Vol.14 No.2
본 연구는 초음파의 영향을 받는 과냉 풀비등 조건에서의 CHF 열전달 촉진 현상을 이해하기 위해 수행되었으며, 이를 위해 초음파가 가해졌을때와 가해지지 않았을 때의 중류수를 작동유체로 하는 하향평판에서의 CHF가 조사되었다. 실험장치는 수조, 전원공급장치, 시험부, 초음파발생장치(40kH_z), 데이터획득장치 등으로 구성되었으며, 0˚, 10˚, 20˚, 45˚, 90˚의 6가지 시편의 경사 각도와 5℃, 20℃, 40℃의 3가지 과냉도에 대해 실험이 수행되었다. 실험으로부터, 과냉 풀비등 내에 담겨 있는 하향평판의 CHF 열전달이 초음파에 의해 향상됨을 확인하였다. 과냉도에 따른 CHF 증가율은 과냉도가 높아질수록 향상되었고 시편의 경사각도 변화에 따른 CHF 증가율은 경사각도가 증가할수록 감소하였다. 본 실험의 결과로 초음파가 기포의 성장 띤 이탈과정에 큰 영향을 주고 있음을 알 수 있었다. Augmentation of CHF (critical heat flux) by ultrasonic was experimentally studied under subcooled pool boiling condition. Experiment was carried out on a downward-facing plate with and without the ultrasonification. The working fluid was distilled water. Experimental apparatus was composed of a bath, power supply, test section, ultrasonic generator, and DAQ system. Experiment was performed at the subcooling temperature of 5℃, 20℃, 40℃ with the plate at the inclined angles 0˚, 10˚, 20˚, 45˚, 90˚. From the experimental results, it was found that ultrasonic effect enhanced CHF in the downward-facing plate. As the degree of subcooling increased the rate of CHF was enhanced. As the inclined angle increased, the rate of CHF decreased. The heat transfer mechanism of CHF augmentation was found to be closely connected with the dynamic behavior of bobble generation and departure.
이윤수(Yun Su Lee),전용호(Young Ho Jun),김대훈(Dae Hun Kim),권영철(Young Chel Kweon),권정태(Jeong Tae Kwon),정지환(Ji Hwan Jeong) 한국공업화학회 2002 공업화학 Vol.13 No.6
본 연구는 전기장에 의한 마이크로핀 관 내부 비등열전달 현상을 이해하기 위해 수행되었으며, 이를 위해 전기장이 인가되지 않았을 때와 전기장이 인가되었을 때의 R-22를 작동유체로 하는 마이크로핀관의 열전달계수 및 압력강하를 조사하였다. 실험변수들로 시험부 입구건도, 질량유속, 열유속, DC 고전압을 선정하였고, 시험부내 증발온도는 5 ℃로 고정시키고 실험을 수행하였다. 냉매의 질량유량은 50 kg/㎡s, 75 kg/㎡s, 100 kg/㎡s, 125kg/㎡s, 열유속은 3 kW/㎡, 5 kW/㎡, 그리고 건도 0에서 0.5까지의 영역에서 DC 고전압(3.5 kV)을 인가하였다. 본 실험을 통하여, 전기장에 의해 관내유동 비등열전달이 향상됨을 관찰하였으며, 동일 DC 고전압하의 열전달특성은 저질량유속, 저열유속, 저건도영역에서 더 우수하였다. 또한 전기장이 인가된 경우에 압력강하도 전기장이 가해지지 않은 경우보다 크게 관찰되었다. Heat transfer coefficients and pressure drops were measured experimentally during the R-22 flow boiling within a micro fin tube, both presence and absence of the EHD effect. Experimental apparatus was composed of a refrigerant loop, a hot water loop, a coolant water loop, and a EHD test section. The DC high voltage(3.5 kV) was applied to the wire electrode which generates the high electric field, while the copper tube was grounded. Experiments were performed with the refrigerant saturation temperature of about 5 ℃, the mass flux of about 50∼125 kg/㎡s, heat flux of about 3∼5 kW/㎡, and inlet quality from 0 to 0.5. From the experimental results, it was found that EHD effect enhanced the boiling heat transfer of the micro fin tube, since the dynamic behavior of bubbles and refrigerant flow were modified by the electric field. Under the same DC high voltage, the heat transfer characteristics are much better at low mass flux, heat flux and quality. Pressure drop results showed that the EHD effect may increase the pressure drop substantially.