공기유속 분포와 열전달 향상조건을 고려한 발전 플랜트용 공랭식 응축기(ACC)의 성능에 관한 수치적 연구

서민성,박창용 대한설비공학회 2019 설비공학 논문집 Vol.31 No.9

The objective of this study was to carry out a simulation study to estimate the change of cooling capacity at a power plant ACC (air-cooled condenser) with the variation of air velocity distribution and heat transfer enhancement on water and air side. As the input variables at the simulation model, average air velocity and air inlet temperature were 3 m/s and 36℃, respectively. Water inlet quality and mass flux were 0.9 and 3.31 kg/m2s, respectively. Five cases of the air velocity distribution were considered in this study, and the simulation results showed that the effect of air velocity distribution on the ACC cooling capacity change was up to 2.66%. The cooling capacity increased by 1.46%, with 100% enhancement of heat transfer at the inner surface of the ACC tube and with the usage of louver fins with 3 mm fin pitch under a uniform air velocity distribution condition. However, it was predicted that a 23.4% reduction of the ACC tube length was possible to perform identical cooling capacity with the heat transfer enhancement. The effect of the heat transfer enhancement on the cooling capacity was changed with the variation of air velocity distribution. 본 연구에서는 공기 유속분포와 관 내측 및 공기 측 열전달 향상을 고려하는 경우, 발전 플랜트용 ACC 냉각용량의 변화를 시뮬레이션 모델을 통해 예측하였으며 다음과 같은 결과를 얻었다. (1) 동일한 평균 공기유속 3 m/s의 조건에서 ACC 전면에 불균일한 공기 유속분포를 고려한 ACC 냉각용량은 균일한 유속분포를 가정한 경우의 ACC 냉각용량에 비해 최대 2.66% 낮았다. (2) 동일 평균 공기유속 3 m/s 조건에서 증기 유동방향에 대해 공기의 유속이 감소하는 분포조건의 ACC 냉각용량은 공기유속이 증가하는 분포조건의 냉각용량에 비해 최대 2.96% 더 높았다. (3) ACC 관 내측에 100% 열전달 향상과 공기 측에 3 mm의 핀 피치를 갖는 루버 핀을 적용하는 경우 ACC의 냉각용량은 균일한 공기유속 조건에서 최대 1.46%, 공기유속이 증기 유동방향으로 지수적인 증가를 하는 분포조건에서 최대 3.66% 증가하는 것으로 예측되었다. 이는 관 내측에 응축이 완료된 액체가 흐르는 유동길이가 길어지며 이 영역이 냉각용량의 증가에 크게 기여하지 못하기 때문으로 분석되었다. (4) 관 내측과 공기 측의 열전달 계수를 각각 100%와 105% 증가시키는 경우 3 m/s의 균일한 공기유속 분포조건에서 열전달 촉진형상이 적용되지 않은 기준형상의 1열 핀-튜브의 길이보다 23.4% 감소된 길이의 관으로 동일한 냉각용량을 구현할 수 있을 것으로 예측되었다. (5) 열전달을 향상시키는 기술을 적용하기 위해서는 관 내측에 미소 구조를 갖도록 하거나 루버 형상을 갖는 핀을 사용하는 등의 추가적인 비용이 요구되므로, 길이 감소에 따른 비용감소 효과와 경제성을 비교한 후 기술의 적용여부를 결정해야 할 것이다.

플라스틱 공기가열기와 트랜치가 장착된 백연 방지형 냉각탑

구태준(TaeJun Gu),전종환(Jonghwan Jeon),임동욱(Dongwook Yim) 대한설비공학회 2016 대한설비공학회 학술발표대회논문집 Vol.2016 No.6

고성능 비행체 엔진을 위한 분출냉각의 연구동향

황기영(Ki-Young Hwang),김유일(You-Il Kim) 한국항공우주학회 2011 韓國航空宇宙學會誌 Vol.39 No.10

분출냉각은 높은 압력과 온도의 가혹한 환경에서 운용되는 고성능 액체로켓과 공기흡입 엔진을 위한 가장 효과적인 냉각방법이다. 분출냉각이 적용되는 경우, 연소기 라이너와 터빈 블레이드/베인은 다공질 벽면을 통과하는 냉각재(공기 또는 연료)뿐만 아니라 차단막으로 작용하는 벽면을 빠져나온 냉각재에 의해 냉각된다. 이러한 냉각기술의 실용화는 가용한 다공질 재료의 부재로 인해 제한을 받아왔다. 그러나 금속결합 기술의 발전으로 확산접합과 식각된 얇은 금속판으로 제작한 Lamilloy^®와 같은 다층 기공 구조물이 개발되었다. 그리고 또한 경량 세라믹 매트릭스 복합재료가 개발됨에 따라 분출냉각은 근래 고성능 엔진 냉각을 위한 유망 기술로 여겨지고 있다. 본 논문에서는 분출냉각의 최근 연구동향 및 가스터빈, 액체로켓 및 극초음속 비행체 엔진에 이의 적용사례를 고찰하였다. Transpiration cooling is the most effective cooling technique for the high-performance liquid rockets and air-breathing engines operating in aggressive environments with higher pressures and temperatures. When applying transpiration cooling, combustor liners and turbine blades/vanes are cooled by the coolant(air or fuel) passing through their porous walls and also the exit coolant acting as an insulating film. Practical implementation of the cooling technique has been hampered by the limitations of available porous materials. But advances in metal-joining techniques have led to the development of multi-laminate porous structures such as Lamilloy^® fabricated from several diffusion-bonded, etched metal thin sheets. And also with the availability of lightweight, ceramic matrix composites(CMC), transpiration cooling now seems to be a promising technique for high-performance engine cooling. This paper reviews recent research activities of transpiration cooling and its applications to gas turbines, liquid rockets, and the engines for hypersonic vehicles.

분출냉각 소재를 위한 고온 공기 공급 시스템 개발과 시험결과

이정민(Jungmin Lee),나재정(Jaejeong Na) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12

개발된 분출냉각 소재의 고온 조건에서 시험평가를 수행하기 위해 고온 공기 공급시스템이 개발되었다. 이 고온 공기 공급시스템은 아크-플라즈마 발생기로부터 공급되는 초고온 공기에 찬 공기를 혼합하여 구성하였다. 장치의 성능 시험과 시험조건 설정 시험을 통해 유질을 평가하고 장치의 성능을 확인하였다. 고온 시험은 분출냉각 소재에 약 1500K의 고온 공기를 공급하고 약 600K의 냉각 공기를 공급하여 분출냉각 소재의 우수한 냉각특성을 확인하였다. In order to test and evaluate designed transpiration cooling materials in hot flow condition, a hot air supply system was developed. It realized to mix very hot air from an arc-plasma generator with cold air. In a performance test and the test to set test condition, a flow quality was evaluated and performance of the system was confirmed. Hot testes were executed as main hot air about 1500K and coolant about 600K were supplied to a transpiration cooling material. As the result, cooling characteristics of the transpiration cooling material was confirmed.

물-공기 직접접촉식 공기조화장치의 성능해석

유성연,권화길,김광영 대한설비공학회 2004 설비공학 논문집 Vol.16 No.2

Performance of the water/air direct contact air conditioning system, in which heat and mass are directly transferred between air and water droplet, is simulated using semi-empirical method. Direct contact system improves transport efficiency compared to conventional indirect contact system. In this study, correlations for which represent the capacity of direct contact system are derived as a function of air and water flowrate from the experimental data. Cooling and heating performance of the water/air direct contact air conditioning system are evaluated using these correlations.

냉각 공기 유동 최적화를 통한 공력 성능 향상에 관한 수치적 연구

송봉하(Bongha Song),이규익(Kyuik Lee),하종백(Jongpaek Ha) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11

These days, the fuel economy of road vehicles is getting important all over the world due to the several reasons such as the depletion of fossil fuel, high fuel cost, and stringent regulation of toxic exhaust gas from conventional internal engine combustion. Therefore, all auto makers have been requested to develop a vehicle with high fuel efficiency as a demand of times. In this view point, aerodynamics is well known as a big potential which can contribute considerably to solve these demands from customers. Total drag of road vehicle is mainly composed of three parts, exterior skin effect from upper body, underbody effect, and engine room’s flow recirculation effect driven by engine cooling air flow. Especially, drag increment from engine cooling air flow needs to be minimized for better aerodynamic performance through the optimization of front-end styling. However, P/T cooling performance has also to be considered carefully because there is a trade-off relationship between aerodynamics and engine cooling performance. In this research, the drag impact on cooling air flow was studied using CFD analysis. Aerodynamics friendly cooling air flow system is completed by the optimization of front grille inlet opening, cooling air outlet, and CRFM sealing, which is represented by baffle and gap seal. The analysis results showed that grille inlet opening could be closed by reducing the leakage of cooling air flow from grille inlet to heat exchanger. Finally, the closing of noneffective grille inlet opening driven by the optimization of CRFM sealing using baffle and gap seal gave us dramatic aerodynamic saving effect, and therefore it will help the fuel economy. The size of cooling air outlet also showed that the bigger the size, the better the aerodynamic performance.

차량 저항 특성을 이용한 Air baffle의 냉각성능 향상에 대한 연구

임태훈(Taehun Lim),장윤혁(Younhyuck Chang),조용석(Yongseok Cho) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11

A quantity and distribution of air flow are key factors for vehicle cooling performance. But it is getting hard to have enough quantity of air flow and good air distribution because engine room compartments come to get closed with one another. Normally, there are two solutions to increase air flow available for the cooling. First one is to increase Fan motor capacity which includes additional electric power consumption and affect negatively on fuel-economy. Second one is to prevent air leakage from the quantity of air flow entered into vehicle inside. Air baffle (Air leakage protection part) is very effective to implement air flow management with low investment and short period for development. This work presents the vehicle cooling performance with separate air baffle designs by using CFD and actual vehicle tests and help to design cooling system without costly changes to achieve the required vehicle target.

공기조화, 냉동 분야의 최근 연구 동향

한화택(Hwataik Han),신동신(Dong Sin Shin),최창호(Chang-Ho Choi),이대영(Dae-Young Lee),김서영(Seo Young Kim),권용일(Yong-Il Kwon) 대한설비공학회 2008 설비공학 논문집 Vol.20 No.6

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2006 has been accomplished. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environments. The conclusions are as follows. (1) The research trends of fluid engineering have been surveyed as groups of general fluid flow, fluid machinery and piping, etc. New research topics include micro heat exchanger and siphon cooling device using nano-fluid. Traditional CFD and flow visualization methods were still popular and widely used in research and development. Studies about diffusers and com￢pressors were performed in fluid machinery. Characteristics of flow and heat transfer and pip￢ing optimization were studied in piping systems. (2) The papers on heat transfer have been categorized into heat transfer characteristics, heat exchangers, heat pipes, and two-phase heat transfer. The topics on heat transfer characteristics in general include thermal transport in a cryo-charnber, a LCD panel, a dryer, and heat generating electronics. Heat exchangers investigated include pin-tube type, plate type, ventilation air-to-air type, and heat transfer enhancing tubes. The research on a reversible loop heat pipe, the influence of NCG charging mass on heat transport capacity, and the chilling start-up characteristics in a heat pipe were reported. In two-phase heat transfer area, the studies on frost growth, ice slurry formation and liquid spray cooling were presented. The studies on the boiling of R-290 and the application of carbon nanotubes to enhance boiling were noticeable in this research area. (3) Many studies on refrigeration and air conditioning systems were presented on the practical issues of the performance and reliability enhancement. The air conditioning system with multi indoor units caught attention in several research works. The issues on the refrigerant charge and the control algorithm were treated. The systems with alternative refrigerants were also studied. Carbon dioxide, hydrocarbons and their mixtures were considered and the heat transfer correlations were proposed. (4) Due to high oil prices, energy consumption have been attentioned in mechanical building systems. Research works have been reviewed in this field by grouping into the research on heat and cold sources, air conditioning and cleaning research, ventilation and fire research including tunnel ventilation, and piping system research. The papers involve the promotion of efficient or effective use of energy, which helps to save energy and results in reduced environmental pollution and operating cost. (5) Studies on indoor air quality took a great portion in the field of building environments. Various other subjects such as indoor thermal comfort were also investigated through computer simulation, case study, and field experiment. Studies on energy include not only optimization study and economic analysis of building equipments but also usability of renewable energy in geothermal and solar systems.

다양한 작동 조건에서 환경제어장치용 공기 사이클 냉각 시스템의 성능 평가

백승윤,김경수,안성민,권세진 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.4

본 논문에서는 램 공기로 구동하는 공기 사이클 냉각 시스템의 성능 시험평가 내용을 소개한다. 역브레이튼 사이클로 구동되는 공기 사이클 기계는 구심 터빈, 원심 압축기, 에어포일 베어링 등으로 구성된다. 이 시스템은 마하 수 0.3 ~ 0.8, 고도 0 ~ 9,000 m 의 비행 조건에서 열 교환기를 통해 2kW 이상의 냉동 용량을 공급하도록 설계되었다. ACM 의 성능은 간접적 방법에 의해 다양한 비행조건에서 실험적으로 평가한다. 시험 평가는 지상 시험 설비에서 ACM 의 입구 조건 및 가열기의 열량을 변화시켜서 수행하였다. 고도 성능의 예측은 지상 시험 데이터에 기초하여 차원 해석과 상사에 의해 추정하는 방법을 이용한다. 시험 결과로부터 개발 대상 ACM 은 설계 조건에서 2 kW 이상의 냉동 용량을 가지며, 주어진 고온 조건에서 전 시험 영역에 걸쳐 적절한 냉각 성능을 제공한다. In this paper, an introduction to the performance test of air cycle cooling system driven by captured ram air. The air cycle machine operating on a reverse bootstrap cycle consists of a radial turbine, a centrifugal compressor and air foil bearings. The system is designed to provide cooling capacity over 2 kW through heat exchanger in the flight condition of Mach 0.3 to 0.8 and 0 to 9,000 m altitude. The performance of the ACM is evaluated experimentally in a variety of flight conditions, by indirect method. Test and evaluation was carried out in a ground test facility by changing inlet conditions of the ACM and heat load of the heater. The altitude performance is estimated by dimensional analysis and similarity based on the ground test data. From the experimental results ACM has cooling capacity of over 2 kW in the design condition, and the developed ACM offers acceptable cooling performance in the whole test range at the given hot day condition.

원통형 배터리팩 열 관리를 위한 공기 냉각과 액침 냉각 비교 연구

김진섭,김슬아,신동환,김우경,문선영,정융,손상호 대한기계학회 2023 大韓機械學會論文集B Vol.47 No.10

The thermal performance of immersion cooling for the thermal management of a cylindrical battery pack was investigated compared with that of the conventional air cooling. The cylindrical battery pack comprising 126 battery cells has a nominal voltage of 25.2 V and nominal capacity of 54 Ah. The battery pack is located in the housing of 330 mm × 234 mm × 100 mm, and a dielectric working fluid (3M Novec 7200) flows into the bottom and out from the top of it. Charging and discharging currents were fixed at 0.75 C (40.5 A), and the flow rate of the working fluid was maintained at 1.715 kg/min. During three consecutive cycles of charging and discharging, immersion cooling exhibited superior thermal performance than air cooling by decreasing the maximum cell temperature by 18.1°C and temperature difference between cells by 84%.