• 제목/요약/키워드: pool boiling

검색결과 224건 처리시간 0.029초

Low-fin 촉진 표면에서 임계 열유속까지의 분무 냉각 열전달 특성 (Heat Transfer Characteristics of Spray Cooling up to Critical Heat Flux on a Low-fin Enhanced Surface)

  • 이요한;강동규;정동수
    • 설비공학논문집
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    • 제25권9호
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    • pp.522-528
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    • 2013
  • Spray cooling is a technology of increasing interest for electronic cooling and other high heat flux applications. In this study, heat transfer coefficients (HTCs) and critical heat fluxes (CHFs) were measured on a smooth square flat copper heater of $9.53{\times}9.53$ mm at $36^{\circ}C$ in a pool, with a smooth flat surface, and 26 fpi. Low-fin surfaces were used to see the change in HTCs and CHFs according to the surface characteristics, and FC-72 was used as the working fluid. FC-72 fluid had a significant influence on the heat transfer characteristics of the spray over the cooling surface. HTCs were taken from 10 $kW/m^2$ to critical heat flux, for all surfaces. Test results with Low-fin showed that the CHFs of all the enhanced surface were greatly improved. It can be said that the surface form affects the heat transfer coefficient and critical heat flux.

설비공학 분야의 최근 연구 동향 : 2016년 학회지 논문에 대한 종합적 고찰 (Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2016)

  • 이대영;김사량;김현정;김동선;박준석;임병찬
    • 설비공학논문집
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    • 제29권6호
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    • pp.327-340
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    • 2017
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2016. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of flow, heat and mass transfer, the reduction of pollutant exhaust gas, cooling and heating, the renewable energy system and the flow around buildings. CFD schemes were used more for all research areas. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results of the long-term performance variation of the plate-type enthalpy exchange element made of paper, design optimization of an extruded-type cooling structure for reducing the weight of LED street lights, and hot plate welding of thermoplastic elastomer packing. In the area of pool boiling and condensing, the heat transfer characteristics of a finned-tube heat exchanger in a PCM (phase change material) thermal energy storage system, influence of flow boiling heat transfer on fouling phenomenon in nanofluids, and PCM at the simultaneous charging and discharging condition were studied. In the area of industrial heat exchangers, one-dimensional flow network model and porous-media model, and R245fa in a plate-shell heat exchanger were studied. (3) Various studies were published in the categories of refrigeration cycle, alternative refrigeration/energy system, system control. In the refrigeration cycle category, subjects include mobile cold storage heat exchanger, compressor reliability, indirect refrigeration system with $CO_2$ as secondary fluid, heat pump for fuel-cell vehicle, heat recovery from hybrid drier and heat exchangers with two-port and flat tubes. In the alternative refrigeration/energy system category, subjects include membrane module for dehumidification refrigeration, desiccant-assisted low-temperature drying, regenerative evaporative cooler and ejector-assisted multi-stage evaporation. In the system control category, subjects include multi-refrigeration system control, emergency cooling of data center and variable-speed compressor control. (4) In building mechanical system research fields, fifteenth studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, renewable energies, etc. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which could be help for improving the energy efficiency of the buildings. (5) The field of architectural environment was mostly focused on indoor environment and building energy. The main researches of indoor environment were related to the analyses of indoor thermal environments controlled by portable cooler, the effects of outdoor wind pressure in airflow at high-rise buildings, window air tightness related to the filling piece shapes, stack effect in core type's office building and the development of a movable drawer-type light shelf with adjustable depth of the reflector. The subjects of building energy were worked on the energy consumption analysis in office building, the prediction of exit air temperature of horizontal geothermal heat exchanger, LS-SVM based modeling of hot water supply load for district heating system, the energy saving effect of ERV system using night purge control method and the effect of strengthened insulation level to the building heating and cooling load.

DIAGNOSTICS OF PLASMA INDUCED IN Nd:YAG LASER WELDING OF ALUMINUM ALLOY

  • Kim, Jong-Do;Lee, Myeong-Hoon;Kim, Young-Sik;Seiji Katayama;Akira Matsunawa
    • 대한용접접합학회:학술대회논문집
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    • 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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    • pp.612-619
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    • 2002
  • The dynamic behavior of Al-Mg alloys plasma was very unstable and this instability was closely related to the unstable motion of keyhole during laser irradiation. The keyhole fluctuated both in size and shape and its fluctuation period was about 440 ${\mu}{\textrm}{m}$. This instability has been estimated to be caused by the evaporation phenomena of metals with different boiling point and latent heats of vaporization. Therefore, the authors have conducted the spectroscopic diagnostics of plasma induced in the pulsed YAG laser welding of Al-Mg alloys in air and argon atmospheres. In the air environment, the identified spectra were atomic lines of Al, Mg, Cr, Mn, Cu, Fe and Zn, and singly ionized Mg line, as well as strong molecular spectrum of AlO, MgO and AIH. It was confirmed that the resonant lines of Al and Mg were strongly self-absorbed, in particular in the vicinity of pool surface. The self-absorption of atomic Mg line was more eminent in alloys containing higher Mg. These facts showed that the laser-induced plasma was relatively a low temperature and high density metallic vapor. The intensities of molecular spectra of AlO and MgO were different each other depending on the power density of laser beam. Under the low power density irradiation condition, the MgO band spectra were predominant in intensity, while the AlO spectra became much stronger in higher power density. In argon atmosphere the band spectra of MgO and AlO completely vanished, but AlH molecular spectra was detected clearly. The hydrogen source was presumably the hydrogen solved in the base Metal, absorbed water on the surface oxide layer or H$_2$ and $H_2O$ in the shielding gas. The temporal change in spectral line intensities was quite similar to the fluctuation of keyhole. The time average plasma temperature at 1 mm high above the surface of A5083 alloy was determined by the Boltzmann plot method of atomic Cr lines of different excitation energy. The obtained electron temperature was 3, 280$\pm$150 K which was about 500 K higher than the boiling point of pure aluminum. The electron number density was determined by measuring the relative intensities of the spectra1lines of atomic and singly ionized Magnesium, and the obtained value was 1.85 x 1019 1/㎥.

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수치해석을 이용한 마스트집합체 내 핵연료 집합체의 열수력적 안전성 연구 (Numerical study on the thermal-hydraulic safety of the fuel assembly in the Mast assembly)

  • 김영수;윤병조;김휘융;전재영
    • 에너지공학
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    • 제24권1호
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    • pp.149-163
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    • 2015
  • 본 연구에서는 전산유체역학(Computational Fluid Dynamics, CFD) 해석코드를 사용하여 마스트집합체의 열수력적 안전성에 대한 연구를 수행하였다. 이를 위해 자연대류 벤치마크 문제를 선정하여 CFD 코드의 물리모델을 선정 및 해석 능력을 검증하고 이를 이용하여 마스트집합체에 대한 자연대류 열전달 해석을 수행하였다. 본 연구에서는 Betts et al.의 사각 수직공동에서 난류 자연대류 실험결과를 대상으로 CFD 해석을 수행하여 자연대류 조건에 적용하기 위한 난류 모델로 표준 $k-{\omega}$ 모델을 선정하였다. 이렇게 도출된 난류모델을 CFD코드에 적용하여 Bates et al.에 의해 수행된 PNL(Pacific Northwest Laboratory)의 $2{\times}6$ 번들 실험과 이에 대한 Kwon et al.의 MATRA, Fluent 코드의 해석과 비교 계산을 수행하여 CFD코드의 부수로조건 자연대류 열전달 해석 능력을 검증하였다. 최종적으로 도출된 $k-{\omega}$ 난류 모델을 사용하여 마스트집합체 및 핵연료 집합체에 대한 자연대류 해석을 수행하였다. 해석 결과 수조 내부 및 부수로 내에서 안정적인 자연대류 유동이 발생함을 확인하였으며, 본 유동 조건에서 핵비등이탈비를 계산함으로써 열수력적 안전성을 정량적으로 평가하였다.

수직 상향유동 배관에서 비뉴톤유체에 의한 2상류의 유동특성 (The Characteristics of Two Phase Flow by Non-Newtonian Fluid for Vertical Up-ward in a Tube)

  • 차경옥;김재근;최경석
    • 한국가스학회지
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    • 제2권4호
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    • pp.53-59
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    • 1998
  • 기-액 2상유동장에서 유동양식은 압력강하, 보이드율분포, 유동장의 기하학적 형상과 밀접한 관계가 있다. 한편 원유수송, 비등이 발생하는 유동, 펌프에서 발생하는 케비테션 현상, 그리고 화학 반응로와 같은 상변화 장치 등의 2상유동에서 고분자물질에 의한 저항감소 현상의 적용이 가능할 것으로 예상된다. 그러나 2상유동장에서 고분자물질에 의한 저항감소에 관한 연구는 매우 미비하다. 그래서 본 연구는 2상유동장에 합성고분자물질(A611p)에 의한 저항감 소율을 실험을 통하여 계측 및 분석하였다. 본 연구에서는 고분자물질의 농도를 증가시킬수록 국부보이드율의 최고치가 관의 중심에서 관의 벽쪽으로 이동하며 2상유동의 유동양식이 변화됨을 규명하였다. 그래서 저항감소율과 유동양식과 밀접한 관계가 있음을 예측할 수 있었다.

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ROLE OF PASSIVE SAFETY FEATURES IN PREVENTION AND MITIGATION OF SEVERE PLANT CONDITIONS IN INDIAN ADVANCED HEAVY WATER REACTOR

  • Jain, Vikas;Nayak, A.K.;Dhiman, M.;Kulkarni, P.P.;Vijayan, P.K.;Vaze, K.K.
    • Nuclear Engineering and Technology
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    • 제45권5호
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    • pp.625-636
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    • 2013
  • Pressing demands of economic competitiveness, the need for large-scale deployment, minimizing the need of human intervention, and experience from the past events and incidents at operating reactors have guided the evolution and innovations in reactor technologies. Indian innovative reactor 'AHWR' is a pressure-tube type natural circulation based boiling water reactor that is designed to meet such requirements, which essentially reflect the needs of next generation reactors. The reactor employs various passive features to prevent and mitigate accidental conditions, like a slightly negative void reactivity coefficient, passive poison injection to scram the reactor in event of failure of the wired shutdown systems, a large elevated pool of water as a heat sink inside the containment, passive decay heat removal based on natural circulation and passive valves, passive ECC injection, etc. It is designed to meet the fundamental safety requirements of safe shutdown, safe decay heat removal and confinement of activity with no impact in public domain, and hence, no need for emergency planning under all conceivable scenarios. This paper examines the role of the various passive safety systems in prevention and mitigation of severe plant conditions that may arise in event of multiple failures. For the purpose of demonstration of the effectiveness of its passive features, postulated scenarios on the lines of three major severe accidents in the history of nuclear power reactors are considered, namely; the Three Mile Island (TMI), Chernobyl and Fukushima accidents. Severe plant conditions along the lines of these scenarios are postulated to the extent conceivable in the reactor under consideration and analyzed using best estimate system thermal-hydraulics code RELAP5/Mod3.2. It is found that the various passive systems incorporated enable the reactor to tolerate the postulated accident conditions without causing severe plant conditions and core degradation.

Critical Heat Flux in Uniformly Heated Vertical Annulus Under a Wide Range of Pressures 0.57 to 15.0 MPa

  • Chun, Se-Young;Chung, Heung-June;Hong, Sung-Deok;Yang, Sun-Kyu;Chung, Moon-Ki
    • Nuclear Engineering and Technology
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    • 제32권2호
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    • pp.128-141
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    • 2000
  • The critical heat flux (CHF)experiments have been carried out in a wide range of pressures for an internally heated vertical annulus. The experimental conditions covered ranges of pressures from 0.57 to 15.01 MPa, mass fluxes of 0 kg/$m^2$s and from 200 to 650 kg/$m^2$s, and inlet subcoolings from 85 to 413 kJ/kg. The characteristics of the present data and the effect of pressure on CHF are discussed. Most of the CHFs were identified to dryout of the liquid film in the annular or annular-mist flow. For the mass flux of 200 kg/$m^2$s, there were the indications that the CHF occurred at the transition from annular to annular-mist How in the pressure range of 3~10 MPa. For the mass fluxes of 550 and 650 kg/$m^2$s, the CHFs had a maximum value at a pressure of 2~3 MPa, and the pressure at the maximum CHF values had a trend moving toward the pressure at the peak value of pool boiling CHF as the mass flux decreased. The CHF data under a zero mass flux condition indicate that both the effects of pressure and inlet subcooling on the CHF were smaller, compared with those on the CHF with net water upward flow.

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비등 열전달 시스템의 안정성 향상을 위한 탄소나노튜브 코팅의 열전달 및 내구성에 대한 연구 (A Study on the Heat Transfer and Durability of Carbon Nano Coating for the Safety Improvement of a Pool Boiling System)

  • 전용한;김영훈;김남진
    • 대한안전경영과학회지
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    • 제19권1호
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    • pp.211-217
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    • 2017
  • In this study, we investigated to the heat transfer performance of coating nano-structure with various shapes and patterns on the heat transfer surface. As a result of the measurement of the 3D nano shape, it was confirmed that the roughness generally increases when the adhesive is sprayed on the coating surface and finished durability experiment. In the case of TEOS adhesive, the roughness increased by $0.074{\mu}m$, $0.012{\mu}m$ and $0.015{\mu}m$, and the contact angle decreased $12.64^{\circ}$, $1.31^{\circ}$, $9.84^{\circ}$ at the coating time of 120 seconds, 180 seconds and 240 seconds, respectively. In the case of PVA adhesive, the roughness increased by $0.069{\mu}m$, $0.056{\mu}m$ and $0.03{\mu}m$, and the contact angle decreased $2.85^{\circ}$, $4.82^{\circ}$, $6.96^{\circ}$ at the coating time of 120 seconds, 180 seconds and 240 seconds, respectively. In the case of DGEBF adhesive, the roughness increased by $0.042{\mu}m$, $0.053{\mu}m$ and $0{\mu}m$, and the contact angle decreased $0.81^{\circ}$ at the coating time of 120 seconds, increased $4.82^{\circ}$, $6.96^{\circ}$ at the coating time of 180 seconds and 240 seconds, respectively. As a result, the durability tends to decrease as more nano-structures are deposited, and 3D nano shapes, contact angles and SEM photographs showed that the performance of the PVA adhesive was superior among the three adhesives.

설비공학 분야의 최근 연구 동향 : 2013년 학회지 논문에 대한 종합적 고찰 (Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2013)

  • 이대영;김사량;김현정;김동선;박준석;임병찬
    • 설비공학논문집
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    • 제26권12호
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    • pp.605-619
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    • 2014
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2013. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and relative parts including orifices, dampers and ducts, fuel cells and power plants, cooling and air-conditioning, heat and mass transfer, two phase flow, and the flow around buildings and structures. Research issues dealing with home appliances, flows around buildings, nuclear power plant, and manufacturing processes are newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for general analytical model for desiccant wheels, the effects of water absorption on the thermal conductivity of insulation materials, thermal properties of Octadecane/xGnP shape-stabilized phase change materials and $CO_2$ and $CO_2$-Hydrate mixture, effect of ground source heat pump system, the heat flux meter location for the performance test of a refrigerator vacuum insulation panel, a parallel flow evaporator for a heat pump dryer, the condensation risk assessment of vacuum multi-layer glass and triple glass, optimization of a forced convection type PCM refrigeration module, surface temperature sensor using fluorescent nanoporous thin film. In the area of pool boiling and condensing heat transfer, researches on ammonia inside horizontal smooth small tube, R1234yf on various enhanced surfaces, HFC32/HFC152a on a plain surface, spray cooling up to critical heat flux on a low-fin enhanced surface were actively carried out. In the area of industrial heat exchangers, researches on a fin tube type adsorber, the mass-transfer kinetics of a fin-tube-type adsorption bed, fin-and-tube heat exchangers having sine wave fins and oval tubes, louvered fin heat exchanger were performed. (3) In the field of refrigeration, studies are categorized into three groups namely refrigeration cycle, refrigerant and modeling and control. In the category of refrigeration cycle, studies were focused on the enhancement or optimization of experimental or commercial systems including a R410a VRF(Various Refrigerant Flow) heat pump, a R134a 2-stage screw heat pump and a R134a double-heat source automotive air-conditioner system. In the category of refrigerant, studies were carried out for the application of alternative refrigerants or refrigeration technologies including $CO_2$ water heaters, a R1234yf automotive air-conditioner, a R436b water cooler and a thermoelectric refrigerator. In the category of modeling and control, theoretical and experimental studies were carried out to predict the performance of various thermal and control systems including the long-term energy analysis of a geo-thermal heat pump system coupled to cast-in-place energy piles, the dynamic simulation of a water heater-coupled hybrid heat pump and the numerical simulation of an integral optimum regulating controller for a system heat pump. (4) In building mechanical system research fields, twenty one studies were conducted to achieve effective design of the mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, and renewable energies in the buildings. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment is mostly focused on indoor environment and building energy. The main researches of indoor environment are related to infiltration, ventilation, leak flow and airtightness performance in residential building. The subjects of building energy are worked on energy saving, operation method and optimum operation of building energy systems. The remained studies are related to the special facility such as cleanroom, internet data center and biosafety laboratory. water supply and drain system, defining standard input variables of BIM (Building Information Modeling) for facility management system, estimating capability and providing operation guidelines of subway station as shelter for refuge and evaluation of pollutant emissions from furniture-like products.

설비공학 분야의 최근 연구 동향: 2014년 학회지 논문에 대한 종합적 고찰 (Recent Progress in Air-Conditioning and Refrigeration Research: A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2014)

  • 이대영;김사량;김현정;김동선;박준석;임병찬
    • 설비공학논문집
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    • 제27권7호
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    • pp.380-394
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    • 2015
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2014. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of heat and mass transfer, cooling and heating, and air-conditioning, the flow inside building rooms, and smoke control on fire. Research issues dealing with duct and pipe were reduced, but flows inside building rooms, and smoke controls were newly added in thermal and fluid engineering research area. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results for thermal contact resistance measurement of metal interface, a fan coil with an oval-type heat exchanger, fouling characteristics of plate heat exchangers, effect of rib pitch in a two wall divergent channel, semi-empirical analysis in vertical mesoscale tubes, an integrated drying machine, microscale surface wrinkles, brazed plate heat exchangers, numerical analysis in printed circuit heat exchanger. In the area of pool boiling and condensing, non-uniform air flow, PCM applied thermal storage wall system, a new wavy cylindrical shape capsule, and HFC32/HFC152a mixtures on enhanced tubes, were actively studied. In the area of industrial heat exchangers, researches on solar water storage tank, effective design on the inserting part of refrigerator door gasket, impact of different boundary conditions in generating g-function, various construction of SCW type ground heat exchanger and a heat pump for closed cooling water heat recovery were performed. (3) In the field of refrigeration, various studies were carried out in the categories of refrigeration cycle, alternative refrigeration and modelling and controls including energy recoveries from industrial boilers and vehicles, improvement of dehumidification systems, novel defrost systems, fault diagnosis and optimum controls for heat pump systems. It is particularly notable that a substantial number of studies were dedicated for the development of air-conditioning and power recovery systems for electric vehicles in this year. (4) In building mechanical system research fields, seventeen studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, and renewable energies, piping in the buildings. Proposed designs, performance performance tests using numerical methods and experiments provide useful information and key data which can improve the energy efficiency of the buildings. (5) The field of architectural environment was mostly focused on indoor environment and building energy. The main researches of indoor environment were related to the evaluation of work noise in tunnel construction and the simulation and development of a light-shelf system. The subjects of building energy were worked on the energy saving of office building applied with window blind and phase change material(PCM), a method of existing building energy simulation using energy audit data, the estimation of thermal consumption unit of apartment building and its case studies, dynamic window performance, a writing method of energy consumption report and energy estimation of apartment building using district heating system. The remained studies were related to the improvement of architectural engineering education system for plant engineering industry, estimating cooling and heating degree days for variable base temperature, a prediction method of underground temperature, the comfort control algorithm of car air conditioner, the smoke control performance evaluation of high-rise building, evaluation of thermal energy systems of bio safety laboratory and a development of measuring device of solar heat gain coefficient of fenestration system.