• International Journal of Air-Conditioning and Refrigeration
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• 제13권2호
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• pp.99-106
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• 2005

Falling film heat transfer has been widely used in many applications in which heat and mass transfer occur simultaneously, such as evaporative coolers, cooling towers, absorption chillers, etc. In such cases, it is desirable that the falling film spreads widely on the surface to form a thin liquid film to enlarge contact surface and to reduce the thermal resistance across the film and/or the flow resistance to the vapor stream over the film. In this respect, hydrophilic treatment of the surface has been tried to improve the surface wettability by decreasing the contact angle between the liquid and the surface. However, the hydrophilic treatment was found not very effective to increase the surface wettedness of inclined surfaces, since the liquid flow forms rivulet patterns instead of a thin film as it flows down the inclined surface and accelerates gradually by the gravity. In this work, a novel method is suggested to improve the surface wettedness enormously. In this work, the surface is treated to have a thin hydrophilic porous layer on the surface. With this treatment, the liquid can spread widely on the surface by the capillary force resulting from the porous structure. In addition to this, the liquid can be held within the porous structure to improve surface wettedness regardless of the surface inclination. The experiment on the evaporative cooling of inclined surfaces has been conducted to verify the effectiveness of the surface treatment. It is measured that the latent heat transfer increases almost by $80\%$ at the hydrophilic porous layer coated surface as compared with the untreated surface.

• 한국태양에너지학회 논문집
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• 제33권6호
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• pp.47-53
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• 2013

In order to reduce the energy consumption of the building, much effort is being made. The problems are that excessive solar radiation in summer and the heat loss in winter by the increase of window area. To prevent this problems, government limited the window area ratio or the performance of windows in new buildings. In order to reduce energy consumption of the existing buildings, the window film insulation is spotlight because the window film insulation was simple to installation. This study confirmed the performance of the window film insulation and affect to heating & cooling load of buildings. The impact of the window film insulation coating was confirmed by experiment. And this study confirmed the annual heating & cooling load by simulation. As a results, the surface temperature of coated window was higher than the surface temperature of existing window. The window film insulation was increased surface temperature of window. And this study confirmed that the increased surface temperature was slightly affected the room air temperature through experiment of the insulation box. The results of the heating and cooling load by simulation, this study confirmed that the case of coated window film insulation decreased cooling load in summer and increased heating load in winter. Also the annual total heating & cooling load was increased a little in the case of coated the window film insulation.

• 한국전산유체공학회지
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• 제7권3호
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• pp.9-16
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• 2002

Most of modem aerospace gas turbines must be operated at a gas temperature which is several hundreds of degrees higher than the melting temperatures of the materials used in their construction. Complicated cooling schemes need to be employed in the combustor walls and in the high pressure turbine stages. Internal passages are cast or machined into the hot sections of aero-gas turbine engines and air from the compressor is used for cooling. In many cases, the cooling system is engineered to utilize jets of high velocity air, which impinge on the internal surfaces of the components. They are categorized as 'Impinging Cooling Method' and 'Vortex Cooling Method'. Specially, research of new cooling system(Vortex Cooling Method) that overcomes inefficiency of film cooling and limitation of space. The focus of new cooling system that improves greatly cooling efficiency using less amount of cooling air on surface heat transfer elevation. Therefore, in this study, a numerical analysis has been peformed for characteristics of flow and heat transfer in the swirl chamber and compared with the flow measurements by LDV. Especially, for understanding high heat transfer efficiency in the vicinity of wall, we considered flow structure, vortex mechanism and heat transfer characteristics with variation of the Reynolds number.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2010년도 제35회 추계학술대회논문집
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• pp.642-647
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• 2010

막냉각은 고온의 연소가스에 장시간 노출되어 있는 공기흡입식 추진기관의 연소실 내벽을 열적으로 보호하기 위해 사용하고 있으며, 슬롯형 냉각라이너를 이용한 막냉각 방법은 냉각특성을 향상시키기 위해 오랫동안 연구되어 왔다. 본 논문에서는 다중 슬롯형 냉각라이너의 연소영역과 냉각영역에서의 기체역학적 유동 및 열전달 계산에 대한 연구결과를 기술하였다.

• 한국추진공학회지
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• 제14권1호
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• pp.20-28
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• 2010

스크램제트 연소기 내 파일런 분사기의 연료-공기 혼합특성을 살펴보았으며, 공력가열로부터 파일런을 보호하기 위한 막냉각의 효과를 조사하였다. 수치연구를 위하여 3차원 Navier-Stokes 방정식과 $k-{\omega}$ SST 난류 모델을 이용하였다. 연료인 수소와 공기를 냉각 유체로 고려하였다. 파일런 분사기를 이용하는 경우 침투거리가 증대되고, 혼합률도 주목할 만큼 증대되었으나, 공력가열에 의한 파일런의 전방 표면 과열을 확인하였다. 파일런 전방에 파일런 표면에 평행한 냉각 제트를 분사하는 막냉각을 이용하면 파일런 표면의 과열을 막을 수 있음을 확인하였다.

• 설비공학논문집
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• 제7권3호
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• pp.512-520
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• 1995

This study investigates the simultanceous heat and mass transfer between a falling desiccant film and air in cross flow at the interface. The application of this work is the optimization of falling film evaporators for use in potential hybrid air conditioning systems. The specific geometry considered is liquid TEG films falling along the vertical cooled surfaces of a channel with air in cross flow. The equations to describe the coupled heat and mass transfer between a falling desiccant film and air in cross flow for a falling film evaporator have been presented and solved numerically. The effects of important design and operating variables on the evaporator performance predicted by the parametric numerical analysis and suggestions for performance improvements of the evaporator are presented.

• 한국추진공학회지
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• 제7권2호
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• pp.15-22
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• 2003

본 연구에서는 2차원 압축성 Navier-Stokes 방정식을 사용하여 $30^{\cire}$ 경사진 터빈익의 냉각구를 통한 유출계수를 예측하였다. 내/외부 유동이 유출계수에 미치는 영향을 알아보기 위하여 외부유동만 존재하는 경우, 내부유동만 존재하는 경우 그리고 내/외부 유동이 없는 3가지 경우에 대하여 수치해석을 수행하였으며. 실험결과와 비교하였다. 본 연구의 수치해석결과는 유출계수를 잘 예측하였으며, 외부유동은 유출계수를 감소시키고, 내부유동은 냉각구내에서의 전압손실과 경계층의 영향을 감소시켜 특정 구간에서 유출계수를 증가시킨다는 것을 알았다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2002년도 춘계 학술대회논문집
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• pp.71-78
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• 2002

All modem, aerospace gas turbines must operate with hot stage gas temperature several hundreds of degrees hotter than the melting temperatures of the materials used in their construction. Complicated cooling schemes need to be employed in the combustor walls and In the high pressure turbine stages. Internal passages are cast or machined into the hot sections of aero-gas turbine engines and air from the compressor is used for cooling. In many cases, the cooling system is engineered to utilize jets of high velocity air, which impinge on the internal surfaces of the components. They are divided by Impinging cooling method and Vortex cooling method. Specially, Research of new cooling system(Vortex cooling method) that overcome inefficiency of film cooling and limitation of space. The focus of new cooling system that improve greatly cooling efficiency using quantity's cooling air which is less is set in surface heat transfer elevation. Therefore, In this study, the numerical analysis have been performed for characteristic of flow and thermal in the swirl chamber and compared with the flow field measurement by LDV. especially, for understanding of high heat transfer efficiency in vicinity of wall. we considered flow structure and mechanism of vortex and heat transfer characteristic in variation of Reynolds number.

• 설비공학논문집
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• 제18권9호
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• pp.714-721
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• 2006

In evaporative cooling applications, the evaporation water is supplied usually sufficiently larger than the amount evaporated to enlarge contact surface between the water and the air. Especially in indirect evaporative coolers, however, if the evaporation water flow rate is excessively large, the evaporative cooling effect is not used for heat absorption from the hot fluid but spent to the sensible cooling of the evaporation water itself. This would result in a decrease in the cooling performance of the indirect evaporative cooler. In this study, the effects of the evaporation water flow rate on the cooling performance are investigated theoretically. The cooling process in an indirect evaporative cooler is modeled into a set of linear differential equations and solved to obtain the exact solutions to the temperatures of the hot fluid, the moist air, and the evaporation water. Based on the exact solutions, it is analyzed how much the cooling performance is affected by the evaporation water flow rate. The results show that the decrease in the cooling effectiveness is substantial even for a small flow rate of the evaporation water and the relative decrease is more serious for a high-performance evaporative cooler.

• 대한기계학회논문집B
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• 제37권3호
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• pp.267-273
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• 2013

막충진재(film fill)를 갖는 냉각탑용 팬의 효율적인 운전조건을 제시하기 위하여, Merkel의 이론을 바탕으로 한 종전의 최적 총연간비용 모델을 사용하여 입구 물온도와 열부하에 따른 최소팬동력을 구하는 프로그램이 새로이 개발되었으며, 냉각탑의 설계 맵이 본 연구로부터 제시되었다. 전형적인 예들을 통하여 본 프로그램의 타당성이 입증되었다. 주어진 열부하에서 이들 팬동력(z 축)-공기질량플럭스(x 축, 최소팬동력 존재)-입구물온도(y 축, 최소팬동력의 최대값 존재)의 3차원 그래프는 말안장 형상으로 나타났다. 최소팬동력들은 열부하에 따라 증가하였다. 따라서, '고온수 유입과 저유량의 공기로 작동' 될 때가 항상 최소팬동력 조건이 아니며, '주어진 입구물온도에 대하여 최소팬동력에 대응하는 최적의 공기질량플럭스가 (열부하와 무관하게) 존재한다'는 사실이 본 연구결과로부터 밝혀졌다.