복부대동맥류의 직경비에 따른 정상유동 및 맥동유동에 관한 수치적 연구

모정하,박상규,Moh, Jeong-Hah,Park, Sang-Kyu 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.7

The objective of the present study was to investigate the characteristics of flow and wall shear stress under steady and pulsatile flow in the aneurysm. The numerical simulation using the software were carried out for the diameter ratios ranging from 1.5 to 3.0, Reynolds number ranging from 900 to 1800 and Womersley number, 15.47. For steady flow, it was shown that a recirculating vortex occupied the entire bulge with its core located closer to the distal end of the bulge and the strength of vortex increased with increase of the Reynolds number and diameter ratio. The position of a maximum wall shear stress was the distal end of the aneurysm regardless of the Reynolds number and diameter ratios. For the pulsatile flow, a recirculating flow at the bulge was developed and disappeared for one period and the strength of vortex increased with the diameter ratio. The maximum values of the wall shear stress increased in proportion to the diameter ratio. However, the position of a maximum wall shear stress was the distal end of the aneurysm regardless of the diameter ratios.

원형관 및 납작관-평판휜 형상의 밀집형 열교환기에 대한 대류열전달 상관관계식

모정하(Jeong-Hah Moh) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.3

본 연구에서는 열의 수가 세 개인 원형관 및 종횡비가 고려된 납작관-평판휜 형상의 밀집형 열교환기 내 공기의 유동 및 열전달 특성을 RNG k-ε 난류모델을 적용하여 수치적으로 해석하였다. 수치조건의 범위는 원형관인 경우 1,000<ReDh<10,000이며, 납작관인 경우 1,000<ReDh<10,000 및 3.06<AR<5.44이다. 마찰인자는 ?=CRe<SUP>m</SUP>Dh의 형태로, Colburn j 계수는 j=Cre<SUP>m</SUP>Dh 형태로 상관관계식을 제시하였다. 이러한 상관관계식은 향후 원형관 및 납작관-평판휜 형상의 열교환기 설계시에 기본적인 자료로 충분히 활용될 수 있을 것으로 판단된다. Aspect-ratio-based numerical analysis is carried out to investigate the air-side convective heat transfer characteristics in compact heat exchangers with circular tubes and flat tubes-plate fins. The RNG k-ε model is adopted for turbulence analysis. The numerical analysis is carried out for aspect ratios ranging from 3.06 to 5.44 and for Reynolds numbers ranging from 1,000 to 10,000. The calculated results indicate a correlation between the friction factor and Colburn j factor in the compact heat exchanger system for the range of aspect ratios under consideration. The results obtained for circular tubes and flat tubes-plate fins in this study can be utilized to realize the optimal design of an air conditioning system.

입구영향 및 주름높이의 변화를 고려한 판형열교환기의 유동 및 열전달 특성

모정하(Jeong Hah Moh) 대한기계학회 2010 大韓機械學會論文集B Vol.34 No.11

본 연구에서는 입구영향과 주름높이가 고려된 판형열교환기의 유동 및 열전달특성을 수치적으로 해석하였다. 여러 개의 단위셀을 연결한 다중셀에 입구부와 출구부가 부착된 모델을 기본으로 입구부의 길이변화(Lcell∼5Lcell)에 따른 모델과 P/H비 변화(2≤P/H≤4)에 따른 모델에 대하여 수치해석을 수행하였다. 수치조건은 쉐브론각 15°, 주름피치 24㎜이며, 1,000≤Re≤10,000이다. 마찰인자는 f=CRe<SUP>m</SUP> 의 형태로, Colburn j 계수는 j=CRe<SUP>m</SUP>의 형태로 상관관계식을 제시하였다. 이러한 상관관계식은 향후 판형열교환기 설계시에 기초자료로 활용될 수 있을 것으로 판단된다. Numerical analysis has been carried out to investigate the heat transfer characteristics of a plate heat exchanger. The multi-cell models with inlet part and outlet part are used for performing numerical simulation. The plate heat exchanger is characterized by chevron angle of 15°, corrugation pitch of 24㎜ and corrugation height 6~12㎜. The length of the inlet-part considered in the analysis ranges from 24.8 to 124㎜ and Reynolds numbers range from 1,000 to 10,000. The correlations such as friction factor and Colburn factor are compared with previous experimental data. The results can be utilized for designing the plate heat exchanger.

주름높이의 변화를 고려한 판형열교환기의 완전발달유동 및 열전달 수치해석

모정하(Jeong Hah Moh) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.1

본 연구에서는 주름높이가 고려된 판형열교환기의 완전발달유동 및 열전달특성을 수치적으로 해석하였다. 여러 개의 단위셀(5개 또는 7개)을 연결한 다중셀에 입구부와 출구부가 부착된 모델을 기본으로 P/H비 변화(2.0≤P/H≤4.0)에 따른 모델에 대하여 수치해석을 수행하였다. 작동유체는 물이며, 수치조건은 쉐브론각 20˚, 300≤Re≤1,500이다. 그리고 마찰인자는 f=CRe<SUP>m</SUP> 의 형태로, Colburn 계수는 j=CRe<SUP>m</SUP>의 형태로 상관관계식을 제시하였다. 수치해석 결과 완전발달유동은 세 번째 셀부터 시작되었으며, 누셀트수는 P/H비가 작을수록 큰 값을 나타냈다. Numerical analysis has been carried out to investigate the fully developed flow and heat transfer characteristics of a plate heat exchanger. Multi-cell models with an inlet part and outlet part are used to perform the numerical simulation. The plate heat exchanger is characterized by a chevron angle of 20˚ and a P/H ratio of 2.0~4.0. The working fluid is water and the Reynolds numbers range from 300 to 1,500. The correlation is given in the form of f=CRe<SUP>m</SUP> for the friction factor and j=CRe<SUP>m</SUP> for the Colburn factor. It is found that the fully developed flow starts from the third cell and the Nusselt number increases with decreasing P/H ratios.

비대칭 엇갈림 배열로 구성된 납작관-평판휜 형상의 밀집형 열교환기에 대한 대류열전달 특성 해석

모정하(Jeong-Hah Moh),이상호(Sang-Ho Lee) 대한기계학회 2009 大韓機械學會論文集B Vol.33 No.5

Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in compact heat exchanger with flat tubes and continuous plate fins having a symmetric and non-symm etric staggered arrangements. Simulation results such as air velocity and temperature distributions are presented, and heat transfer coefficients are compared with previous experimental results. In order to investigate the flow and heat transfer features by periodic boundary conditions, the three blocks were used. Predicted heat transfer coefficients between the three blocks are similar while there are relatively differences, compared with the experimental data. From the calculated results a correlation for Colburn j factor in the compact heat exchanger system is suggested. The predicted results in this study can be applied to the optimal design of air conditioning system.

경사진 원형관에서 표면장력과 중력에 의한 비뉴턴 유체(멱법칙 모델)의 유동 및 변위

모정하(Jeong Hah Moh),Y. I. Cho 대한기계학회 2014 大韓機械學會論文集B Vol.38 No.1

본 논문은 경사진 원형관에서 표면장력과 중력으로 구동되는 비뉴턴 유체(멱법칙 모델)의 유동 및 변위를 이론적으로 연구한 것이다. 그리고 표면장력에 의하여 연속적으로 원형관 내로 유입되는 비뉴턴 유체의 변위를 기술하기 위한 지배방정식을 처음으로 개발하였다. 뉴턴의 운동방정식으로부터 유도된 식은 2계 비선형이며 비제차인 형태의 상미분 방정식이다. 지배방정식의 해를 수평관에서 변위를 시간의 함수로 기술한 식 및 실험과 비교한 결과 정량적으로 동일한 일치를 보였다. 여기에 더하여 정상상태인 힘의 균형식의 결과에 대해서도 정확한 일치로 나타남을 확인할 수 있었다. This paper presents the theoretical analysis of a flow driven by surface tension and gravity in an inclined circular tube. A governing equation is developed for describing the displacement of a non-Newtonian fluid(Power-law model) that continuously flows into a circular tube owing to surface tension, which represents a second-order, nonlinear, non-homogeneous, and ordinary differential form. It was found that quantitatively, the theoretical predictions of the governing equation were in excellent agreement with the solutions of the equation for horizontal tubes and the past experimental data. In addition, the predictions compared very well with the results of the force balance equation for steady.

종횡비에 따른 납작관-평판휜 형상의 밀집형 열교환기 내 공기 측 대류열전달특성에 대한 수치해석

모정하(Jeong-Hah Moh) 대한기계학회 2008 大韓機械學會論文集B Vol.32 No.9

Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in a compact heat exchanger with flat tubes and continuous plate fins according to the aspect ratio. RNG k-ε model is applied for turbulence analysis. Simulation results such as air velocity and temperature distributions are presented, and heat transfer coefficients are compared with previous correlations for circular tubes. The numerical conditions are considered for the aspect ratios ranging from 3.06 to 5.44 and Reynolds number ranging from 1000 to 10,000. The results showed that heat transfer coefficients decreased with the increase of aspect ratio. From the calculated results a correlation of Colburn j factor for the considered aspect ratio in the compact heat exchanger system is suggested. The predicted results in this study can be applied to the optimal design of air conditioning system.

밀집형 열교환기 내 공기 측 대류열전달특성

모정하(Jeong-Hah Moh),이상호(Sang Ho Lee) 대한설비공학회 2009 대한설비공학회 학술발표대회논문집 Vol.2009 No.-

Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in compact heat exchangers with continuous plate fins. Simulation results such as air flow and temperature distributions are presented, and heat transfer characteristics are compared for various inlet conditions. Results from various turbulence models are also compared for applicability. There is large difference between the local heat transfer coefficient distributions along the cylinder wall for circular tubes. Colburn j factors from the calculated results of circular and flat tubes in the heat exchangers are compared for various Reynolds number. The predicted results in this study can be applied to the optimal design of air conditioning system. with compact heat exchanger.

원형관-평판휜 형상의 밀집형 열교환기 내 공기 측대류열전달특성에 대한 수치해석

모정하(Jeong-Hah Moh),이상호(Sang-Ho Lee) 대한기계학회 2007 大韓機械學會論文集B Vol.31 No.12

Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in a compact heat exchanger with circular tubes and continuous plate fins. Simulation results such as air velocity and temperature distributions are presented, and heat transfer coefficients are compared with previous experimental correlations. Three models of standard and RNG k-ε, and Reynolds stress are applied for turbulence model applicability. Predicted heat transfer coefficient from the models of standard and RNG k-ε are very close to those of the heat transfer correlations while there are relatively large difference, more than 17 percentage in the result from the Reynolds stress model. From the calculated results a correlation for Colburn j factor in the compact heat exchanger system is suggested.

셸-튜브형 잠열 축열조내의 온도성층에 관한 연구

권영만(Young - Man Kwon),김경우(Kyong - Woo Kim),모정하(Jeong - Hah Moh) 대한설비공학회 2000 대한설비공학회 학술발표대회논문집 Vol.2000 No.-