• Journal of Advanced Marine Engineering and Technology
• /
• 제27권1호
• /
• pp.108-116
• /
• 2003

In this paper, the experimental results of condensation heat transfer were reported for the plate and shell heat exchangers(P&SHE) using R-l34a. An experimental refrigerant loop has been established to measure the condensation heat transfer coefficient of R-l34a in a vertical P&SHE. Two vertical counter flow channels were formed in the P&SHE by three plates of geometry with a corrugated trapezoid shape of a chevron angle of 45$^{\circ}$. Downflow of the condensing R-l34a in one channel releases heat to the cold up flow of water in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality of R-l34a on the measured data were explored in detail. The results indicate that at a higher vapor quality the condensation heat transfer coefficients are significantly higher. Condensation heat transfer coefficients were increased when the refrigerant mass flux was increased. A rise in the average heat flux causes an slight increase in the hr. Finally, at a higher system pressure the hr is found to be lower. Correlation is also provided for the measured heat transfer coefficients in terms of the Nusselt number.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.679-682
• /
• 2002

Energy dissipations in a general PHE flow are the compounded effects of the piled corrugate geometries and its wall pressure and temperature distributions. In addition, although the exchangers are substantial pieces of engineering equipment, they are composed of a very large number of nominally identical and small geometrical elements. In the present numerical study, the three-dimensionally complicated energy dissipation fields and those wall-shape-induced flow destabilization are investigated in the cross-corrugated passages, which result in high energy transports with comparatively low pressure drop. We revealed the critical conditions as $Re=157.3 for the wall-shape-induced flow destabilization in a general PHE element by initial value method, or shooting method, and compare its value to that of analytical solution of plane Poiseille flow, two-dimensional grooved flow and so on. We also observed the detailed variation of flow field and energy transportation with changes in time and flow variables such as Reynolds number. Lastly, we considered the flow natural frequency, or Strouhal number, with variation of hydrodynamic conditions for the best use of active control, such as forced mass flow rate pulsative flow, to enhance energy transportation.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.699-702
• /
• 2008

This paper describes the numerical simulations in the cooling of the radiator in a distribution transformer. The aim of this work is the cooling optimization of the transformer by CFD simulations. A clear understanding of the cooling pattern in a radiator which is a main heat remover in the power transformer is essential for optimizing the radiator design increasing the thermal efficiency. In this paper we study the heat transfer and fluid flow in a 3-phase 400kVA transformer. The plate radiators of this transformer become wrinkled (corrugated radiator) and there are filled with transformer oil. The oil is circulated due to the natural convection driven by buoyancy effects through radiators so that the ultimate cooling medium is the surrounding air. In the design of transformers, it is of interest to minimize the cost and size of radiators. The obtained results show the temperature and flow distributions and the possibility to optimize the transformer with 3-dimensional CFD models using FLUENT.

• 한국강구조학회 논문집
• /
• 제30권1호
• /
• pp.49-58
• /
• 2018

본 연구는 비선형 유한 요소 해석을 통해 제형의 절곡형상 웨브를 갖는 보의 수평패널 길이와 경사패널의 비 ${\beta}$에 따른 전단 거동을 파악하였다. 선행 실험연구 결과를 통해 정확도 높은 해석모델을 검증하였으며, 이를 토대로 ${\beta}$ 및 전단거동에 영향을 미치는 핵심 변수에 대한 변수해석을 실시하였다. 또한 변수해석 결과를 통해 선행연구의 제안식을 평가하였다. 분석결과 Eurocode는 다른 제안식보다 보수적으로 평가하고 있으며, 김영숙의 제안식은 Moon의 제안식에 따라 비탄성 영역에 포함 된 모델만이 경제적인 평가를 하는 것으로 판단된다.

• 대한기계학회논문집A
• /
• 제34권2호
• /
• pp.219-226
• /
• 2010

스탬핑 프로세서는 고생산성과 낮은 가격으로 인해 자동차 차제나 항공기 부품, 그리고 전자제품 등 다양한 장치에 널리 이용된다. 최근에 에너지 산업과 연관되어 연료전지 분리판, 열교환기 등에 사용되는 주름구조를 가지는 박판의 응용이 급속히 증가되고 있다. 그러나 복잡한 형상 때문에 주름구조물을 한번의 성형으로 만들기가 매우 어렵다. 따라서 본 연구에서는 다단성형공정을 이용하여 성형성을 향상시키는 방법을 제안하였다. 1 차 박판성형 후 열처리를 통하여 가공경화 부분을 제거하고 다시 성형하는 방법으로 복잡하고 실용성이 높은 박판구조물 제작이 가능하도록 하였다. 본 연구에서는 제안한 방법을 검증하기 위하여 판형 열교환기에 응용이 가능한 두께 $100{\mu}m$를 가지는 박판주름구조를 제작하고 공정변수를 연구하였다.

• 설비공학논문집
• /
• 제16권9호
• /
• pp.845-854
• /
• 2004

The evaporation heat transfer coefficient for R-l34a, R-407C (a mixture of 23wt% R-32, 25 wt% R-125, and 52 wt% R-l34a) and R-410A (a mixture of 50 wt% R-32 and 50 wt% R-125) flowing in the oblong shell and plate heat exchanger were investigated experimentally in this study. Four vertical counterflow channels were formed in the exchanger by four plates of commercial geometry with a corrugated sinusoid shape of a chevron angle of 45 degree. The effects of the mean vapor quality, mass flux, heat flux, and saturation temperature of different refrigerants on the evaporation heat transfer were explored in detail. Similar to the case of a Plate heat exchanger, even at a very low Reynolds number, the flow in the oblong shell and plate heat exchanger remains turbulent. It is found that the evaporation heat transfer coefficient in the plates is much higher than that in circular pipes. The present data show that the evaporation heat transfer coefficients of all refrigerants increase with the vapor quality. At a higher mass flux h, is higher than for the entire range of the vapor quality. Raising the imposed wall heat flux was found to slightly improve h$_{r}$, while h$_{r}$ is found to be lower at a higher refrigerant saturation temperature. A comparison of the performance of the various refrigerants reveals that R-410A has the highest heat transfer performance followed by R-l34a, and R-407C had the lowest performance of the refrigerants tested. Based on the present data, empirical correlations of the evaporation heat transfer coefficient were proposed.sed.

• 대한기계학회논문집B
• /
• 제25권10호
• /
• pp.1318-1326
• /
• 2001

The evaporation heat transfer coefficient and pressure drop for refrigerant R-22 flowing in the plate and shell heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were farmed in the exchanger by three plates of commercial geometry with a corrugated trapezoid shape of a chevron angel of 45 ° Upflow boiling of refrigerant R-22 in one channel receives heat from the hot downf1ow of water in the other channel. The effects of the mean vapor quality, mass flux, heat flux and pressure of R-22 on the evaporation heat transfer and pressure drop were explored. The quality change of R-22 between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.05. The present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux, the evaporation heat transfer coefficient and pressure drop are higher for the entire range of the vapor quality Raising the imposed wall heat flux was found to slightly improve the heat transfer, while at a higher refrigerant pressure, both the heat transfer and pressure drop are slightly lower.

• 한국건축시공학회지
• /
• 제21권6호
• /
• pp.605-615
• /
• 2021

최근 공사 기간 단축과 인건비 절감을 위해 거푸집을 탈형하지 않는 비탈형 보거푸집의 필요성이 RC구조물에서 강조 되고 있다. 본 연구의 목적은 새로 개발된 비탈형 보 거푸집인 SY Beam의 콘크리트 타설시 변형성능을 평가하는 것이다. SY Beam의 표준 단면 형상은 MIDAS GEN 프로그램을 통해, 다양한 두께의 강판 데크 구조 모델링을 수행하여 결정하였다. 그 결과, SY Beam의 단면치수는 폭과 높이가 각각 400mm와 450mm로 결정하였다. 강판두께 0.8, 1.0, 1.2mm를 변수로 하여 총 3 개의 SY Beam 실험체를 제작하였다. 실제 현장에서 콘크리트를 타설할 때 작용하는 하중 조건을 반영하였다. 콘크리트 타설시 SY Beam 단면의 수직 및 수평 변위를 측정하였다. 그 결과, 수직 변위는 두께가 증가할수록 감소하는 경향을 보였다. 수직변위와 수평변위를 모두 고려할 때, 강판두께 1.2mm의 경우가 가장 안전하고 즉시 현장 적용이 가능하다. 향후, 제작성, 시공성, 경제성을 확보하기 위해 최적의 강판두께를 도출하여야 하며, 1.05, 1.1, 1.15mm 에 대한 추가의 해석 및 실험연구가 필요하다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회A
• /
• pp.384-388
• /
• 2007

Aerodynamic characteristics of Coleoptera species of Epilachna quadricollis and Allomyrina dichotoma are experimentally and numerically investigated. Using digital high speed camera and smoke wire technique, we visualized the continuous wing kinematics and the flight motion of free-flying coleoptera. The experimental visualization shows that the elytra flapped concurrently with the main wing both in the downstroke and upstroke motions. The wing motion of Epilachna quadricollis was captured and analyzed frame by frame to identify the kinematics of the wings and to implement it in the movement of a model wing (thin plate) in the simulation. The two-dimensional simulation of Epilachna quadricollis hovering flight was performed by assuming the wing cross section shape as a thin plate, even though most of insect's wings are made of curved corrugated membrane. The effect of Reynolds number are investigated by the simulation. Meanwhile, in order to investigate the role and effect of elytra, the flow visualization of Allomyrina dichotoma was carried on using smoke wire visualization technique. Here, we confirmed that the vortex generated by elytra due to its movement is strongly influence the vortex dynamic generated by hind wings.

• 한국전산유체공학회지
• /
• 제19권1호
• /
• pp.47-56
• /
• 2014

Since a typical plate heat exchanger is made up of a huge number of unitary cells, it may be impossible to predict the aero-thermal performance of the full scale heat exchanger through three-dimensional numerical simulation due to the enormous amount of computing resources and time required. In the present study, a simple flow-network model using the friction factor correlation and a thermal-network model based on the effectiveness-number of transfer units (${\varepsilon}$-NTU) method has been developed. The complicated flow pattern inside the cross-corrugated heat exchanger has been modeled into flow and thermal networks. Using this model, the heat transfer between neighboring streams can be considered, and the pressure drop and the heat transfer rate of full-scale heat exchanger matrix are calculated. In the calculation, the aero-thermal performance of each unitary cell of the heat exchanger matrix was evaluated using correlations of the Fanning friction factor f and the Nusselt number Nu, which were calculated by unitary-cell CFD model.