Theoretical and numerical analyses of a ceramic monolith heat exchanger

팽진기,윤영환,김경환,윤건식 대한기계학회 2010 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.24 No.7

This study assessed the performance of a ceramic monolith heat exchanger, estimating heat transfer and pressure drop by numerical computation and the ε-NTU method. A heat exchanger consists of rectangular ducts for exhaust gas, a ceramic core, and rectangular ducts for air and exhaust gases, as well as air in the cross-flow direction. The numerical computations were performed for the whole domain,including the exhaust gas, ceramic core, and air. In addition, the heat exchanger was examined using a conventional ε- NTU method with several Nusselt number correlations from the literature to characterize the flow in the rectangular duct. The results of these numerical computation analyses demonstrated that the effectiveness of the heat exchanger, as demonstrated using the ε-NTU method with Stephan’s Nusselt number correlation, came closest to the results of computation with a relative error of 2%. The air-side pressure drops indicated by the results of numerical computation were 13-22% higher than those calculated using the head loss equation with the inclusion of a friction factor that was obtained from previous experiments examining heat transfer conditions.

Experimental measurement and numerical computation of the air side convective heat transfer coefficients in a plate fin-tube heat exchanger

팽진기,김경환,윤영환 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.2

The air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement and numerical computation. The heat exchanger consists of a staggered arrangement of refrigerant pipes with a diameter of 10.2 mm and a fin pitch of 3.5 mm. In the experimental study, the forced convective heat transfer was measured at Reynolds numbers of 1082, 1397, 1486, 1591 and 1649 based on the diameter of the refrigerant piping and on the maximum velocity. The average Nusselt number for the convective heat transfer coefficient was also computed for the same Reynolds number by using the commercial software STAR-CD with the standard rd k −ε turbulent model. It was found that the relative errors of the average Nusselt numbers between the experimental and numerical data were less than 6 percent in a Reynolds number range of 1082~1649. The errors between the experiment and other correlations from literature ranged from 7% to 32.4%. However, the literature correlation of Kim et al. is closest to the experimental data within a relative error of 7%.

CFD code를 활용한 전력용변압기 온도상승 예측 비교

팽진기(Jin-Gi Paneg),심재휘(Jae-Hwi Shim),정승붕(Seung-Boong Jeong) 대한전기학회 2017 대한전기학회 학술대회 논문집 Vol.2017 No.7

세라믹 열교환기의 이론해석 및 CFD시뮬레이션

팽진기(Jin Gi Paeng),윤영환(Young Hwan Yoon) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.5

A ceramic monolith heat exchanger is studied to find the performance of heat transfer and pressure drop by numerical computation and ζ-NTU method. The numerical computation was performed throughout the domain including fluid region in exhaust gas-side rectangular ducts, ceramic core and fluid region in air-side rectangular duct with the air and exhaust in cross flow direction. In addition, the heat exchanger was also analyzed to estimate the performance by conventional ζ-NTU method with several Nusselt number correlations for flow in rectangular duct from literature. By comparisons of both performances by the numerical computation and the ζ-NTU method, the effectiveness by ζ-NTU method was closest to the result by numerical computation within a relative error of 2.14% when Stephan's Nusselt number correlation was adopted to the ζ-NTU method among the several correlations.

일체형 세라믹 열교환기의 전산 열응력 해석에 관한 연구

팽진기(Jin Gi Paeng),김기철(Ki Chul Kim),윤영환(Young Hwan Yoon) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.11

The thermal stresses of a ceramic heat exchanger were analyzed numerically since the ceramic material is good in heat resistance but weak in the thermal stress. The analysis of thermal stress was conducted in the ceramic core with two boundary conditions depending on bolt jointing. The thermal stresses were computed by applying temperature and pressure distributions obtained from the numerical results of conjugate heat transfer to ANSYS WORKRBENCH. When number of bolt joining halls was reduced from 8 × 2 to 4 × 2, the maximum principal stresses decrease by 47.6~50.5% and increase in safety factors by 2.18~2.5 for ultimate tensile strength. Thus, it can be said that bolt joining halls should be minimized in ceramic heat exchanger to be efficient in reducing thermal stress. In addition, the width of particular gas flow passages were revised from 52 mm to 42 mm to reduce maximum thermal stresses since certain passages experienced high thermal stresses. From the revision, safety factors were increased by 13.8~14.1% for the boundary condition of 4 × 2 bolt joining halls, Therefore, it is suggested that thermal stress can be reduced by changing local geometry of a ceramic heat exchanger.

열-구조 연성해석에 의한 알루미늄 6061 마찰교반용접 특성 변수 연구

박찬우,팽진기,옥주선 한국항공우주학회 2011 한국항공우주학회 학술발표회 논문집 Vol.2011 No.11

마찰교반용접(FSW)과정에서의 모재의 변형과 온도분포를 연구하기 위해 A fully coupled thermomechanical model 을 적용하였다. 본 연구의 주요변수는 용접 툴의 회전속도이며, 다른 주요변수에 따른 영향을 3 차원해석 결과로 나타내었다. 본 해석 결과, 최대온도가 용접모재의 용융점이하에서 나타남을 알 수 있다. 본 수치 모델에서는 용접모재의 leading side 에서 높은 온도구배가 발생하며, 회전 각속도가 증가할수록 최대 온도가 증가함을 알 수 있다. 본 연구는 ABAQUS Ver.6.7 로 시뮬레이션을 수행하였다. 또한 마찰교반용(FSW)과정에서의 대 변형은 ALE(Arbitrary Lagrangian-Eulerian) finite element formulation 을 사용하였으며, Mass scaling 을 사용하여 해석 시간을 줄일 수 있었다. A fully coupled thermo-mechanical model is adopted to study the temperature distribution and the material deformation in friction stir welding (FSW) process. Rotational speed is most important parameter in this research. Three dimensional analysis results under different process parameters were presented. Results indicate that the maximum temperature is lower than the melting point of the welding material. The higher temperature gradient occurs in the leading side of the workpiece. The maximum temperature can be increased with increasing the tool angular velocity, rpm in the current numerical modeling. In this research ABAQUS Ver.6.7 is used to analyze a fully coupled thermo-mechanical model. ALE(Arbitrary Lagrangian-Eulerian) finite element formulation is used for the large deformation in FSW process and the Mass scaling is used for analysis time efficiency.

Comparison between numerical computations and measurements by LDV for fluid flow in rectangular duct systems

김경환,팽진기,윤영환 대한기계학회 2008 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.22 No.9

Fluid flows in rectangular duct systems are measured by using the laser-Doppler velocity meter and computed by commercial software of Star-CD for comparisons between flows. Three rectangular systems are investigated in this study: a rectangular duct with a 90 degree bent elbow, a rectangular duct with two branches, and a rectangular duct in the middle of which a circular cylinder is located. These investigations show that the numerical solutions satisfactorily predict design factors: for example, the K -factor for an elbowed duct, the distribution ratio of flow rates into each branch from a main duct, and the Nusselt number around the circular duct. However, there are some disagreements in the velocity profile and turbulent kinetic energy at each cross section of the duct systems.

평판 핀 튜브 열교환기의 공기측 강제대류 열전달 계수에 대한 실험 및 수치계산

윤영환,팽진기,윤건식 대한설비공학회 2006 설비공학 논문집 Vol.18 No.9

Air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement and numerical computation. The heat exchanger consists of staggered arrangement of refrigerant pipes of 10.2mm diameter and the pitch of fins is 3.5mm. In the experimental study, the forced convective heat transfer is measured at Reynolds number of 1082, 1397, 1486, 1591 and 1649 based on diameter of refrigerant piping and mean velocity. Average Nusselt number for the convective heat transfer coefficient is alsocomputed for the same Reynolds number by commercial software of STAR-CD with standard turbulent model. It is found that the relative errors of average Nusselt numbers between experimental and numerical data are less than 6 percentage in Reynolds number of 1082∼1649. The errors between experiment and other correlations are ranged from 7% to 32.4%. But the correlation of Kim at al is closest to the experimental data within 7% of the relative error.

이중진공관형 태양열 집열기의 연간 집열효율에 관한 연구

김기철(Kim Ki-Chul),팽진기(Paeng Ji-Gi),윤영환(Yoon Young-Hwan) 한국태양에너지학회 2008 한국태양에너지학회 논문집 Vol.28 No.4

The Storage efficiency of concentric evacuated tube solar collector is tested for one year from January 1st to December 31st under the real sun condition. The testing equipment is operated continuously for three days without cooling the storage tank. Daily storage efficiency is obtained from dividing stored energy in the storage tank by solar insolation on the solar collector for each day. Daily averaged temperature of the storage tank is lowest in January and highest in August. Monthly averaged storage efficiency is also lowest in November and highest in June. Therefore, it can be said that the storage temperature and the storage efficiency are roughly proportional to outdoor temperature. Furthermore, the daily storage efficiency is reversely proportional to (Ts - Ta)/Ic, where Ts and Ta are daily averaged storage temperature and outdoor temperature from sunrise to sunset, and Ic is total insolation on the solar collector for a day.

연료전지용 소형 금속 열교환기의 성능에 대한 실험 및 이론적 연구

윤영환(Yoon,Young-Hwan),팽진기(Paeng,Jin-Gi) 한국태양에너지학회 2011 한국태양에너지학회 논문집 Vol.31 No.4

This study assessed the performance of a compact heat exchanger with staggered tube banks for recuperation of high temperature exhaust thermal energy for SOFC fuel cell system. The compact heat exchanger in this study is two pass system which consists of 315×202.5×48.5㎣ and 132 tubes of 6.0㎜Φ for each heat exchanger. From experiments of the 2 pass heat exchanger system, air temperature was increased from 50~85℃ to 402~482℃ while gas temperature was decreased from 600℃ to 305~402℃ according to mass flow rates of 3.9~7.8 g/s. The experimental heat transfer rates of the heat exchanger were compared with CFD numerical solutions with the conventional ζ-NTU method. From the comparisons, the following conclusions were obtained. For the heat exchanger system, the relative errors of heat transfer rate by CFD solution were from 7.1 to 27%, and those by ζ-NTU method were from 0.6% to 21% compared with experimental data. From the comparisons, it can be said that both of CFD and ζ-NTU method almost simulated to experimental data except specific conditions. Pressure drops through air tubes and gas passages were calculated with both of the CFD computation and head loss equations. The differences between them were from 14 to 22%.