• Title/Summary/Keyword: Heat exchange area

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Parameters Estimation in Longwave Radiation Formula (장파복사 모형의 매개변수 추정)

  • Cho, Hongyeon;Lee, Khil-Ha;Lee, Jungmi
    • Journal of Environmental Impact Assessment
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    • v.21 no.2
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    • pp.239-246
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    • 2012
  • Daily net radiation is essential for heat budget analysis for environmental impact assessment in the coastal zone and longwave radiation is an important element of net radiation because there is a significant exchange of radiant energy between the earth's surface and the atmosphere in the form of radiation at longer wavelengths. However, radiation data is not commonly available, and there has been no direct measurement for most areas where coastal environmental impact assessment is usually most needed. Often an empirical equation, e.g., Penman and FAO-24 formulae is used to estimate longwave radiation using temperature, humidity, and sunshine hour data but local calibration may be needed. In this study, local recalibration was performed to have best fit from a widely used longwave equation using the measured longwave radiation data in Korea Global Atmospheric Watch Center (KGAWC). The results shows recalibration can provided better performance AE=0.23($W/m^2$) and RMSE=14.73($W/m^2$). This study will contribute to improve the accuracy of the heat budget analysis in the coastal area.

A Study of Weldability for Pure Titanium by Nd:YAG Laser(III) - Weld Properties of Edge Welding - (순티타늄판의 Nd:YAG 레이저 용접성에 관한 연구(III) - 에지 용접 특성 -)

  • Kim, Jong-Do;Kil, Byung-Lea;Kwak, Myung-Sub;Song, Moo-Keun
    • Journal of Welding and Joining
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    • v.27 no.6
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    • pp.74-79
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    • 2009
  • Titanium and titanium alloy can be reproduced immediately even if oxide films($TiO_2$) break apart in sea water. Therefore, since titanium demonstrates large specific strength and outstanding resistance to stress corrosion cracking, crevice corrosion, pitting and microbiologically influenced corrosion in sea water environment, it has been widely applied to heat exchanger for ships. In particular, with excellent elongation, pure titanium may be deemed as optimal material for production of heat exchanger plate which is used with wrinkles formed for efficient heat exchange. Conventional plate type heat exchanger prevented leakage of liquid through insertion of gasket between plates and mechanical tightening by bolts and nuts, but in high temperature and high pressure environment, gasket deterioration and leakage occur, so heat exchanger for LPG re-liquefaction device etc do not use gasket but weld heat exchanger plate for use. On the other hand, since welded plate cannot be separated, it is important to obtain high quality reliable welds. In addition, for better workability and production performance, lasers that can obtain weldment with large aspect ratio and demonstrate fast welding speed even in atmospheric condition not in vacuum condition are used in producing products. So far, 1st report and 2nd report compared and analyzed embrittlement degrees by bead colors of weldment through quantitative analysis of oxygen and nitrogen and measurement of hardness as fundamental experiment for the evaluation of titanium laser welding, and evaluated the welding performance and mechanical properties of butt welding. This study welded specimens in various conditions by using laser and GTA welding machine to apply edge welding to heat exchanger, and evaluated the mechanical strength through tensile stress test. As a result of tensile test, laser weldment demonstrated tensile strength 4 times higher than GTA welds, and porosity could be controlled by increasing and decreasing slope of laser power at overlap area.

A Study on the Optimal Design and Performance Analysis of the Solid-Gas Chemical Heat Transformer (고-기 화학열변환기의 최적설계 및 성능해석에 관한 연구)

  • Choi, S.H.;Lee, S.I.;Baek, I.H.;Choi, I.S.
    • Applied Chemistry for Engineering
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    • v.8 no.5
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    • pp.729-736
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    • 1997
  • For the recovery of industrial waste heat, a chemical heat transformer based on the reversible reaction between metal chlorides and ammonia gas was designed and a pilot scale unit of 1 kW-1hr was developed. A static calculation, which determined the amount of reacting materials and operating condition of system, and dynamic simulations were performed for the optimal design. The temperature and output power of generator in the system were varying with the amount of salt and heat exchange area. Optimum conditions such as the amount of salt-graphite, apparent density and size of mechanical unit were determined by the dynamic simulation for the system. According to the operating cycle of 4 stages, experimental results of temperature and output power were well agreed with the simulation values. This chemical heat transformer is turned out to be a very promising system for recovery of industrial waste heat because of its effective feature of lifting temperature.

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Study on the influence of flow blockage in severe accident scenario of CAP1400 reactor

  • Pengcheng Gao;Bin Zhang ;Jishen Li ;Fan Miao ;Shaowei Tang ;Sheng Cao;Hao Yang ;Jianqiang Shan
    • Nuclear Engineering and Technology
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    • v.55 no.3
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    • pp.999-1008
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    • 2023
  • Deformed fuel rods can cause a partial blockage of the flow area in a subchannel. Such flow blockage will influence the core coolant flow and further the core heat transfer during the reflooding phase and subsequent severe accidents. Nevertheless, most of the system analysis codes simulate the accident process based on the assumed flow blockage ratio, resulting in inconsistencies between simulated results and actual conditions. This paper aims to study the influence of flow blockage in severe accident scenario of the CAP1400 reactor. First, the flow blockage model of ISAA code is improved based on the FRTMB module. Then, the ISAA-FRTMB coupling system is adopted to model and calculate the QUENCH-LOCA-0 experiment. The correctness and validity of the flow blockage model are verified by comparing the peak cladding temperature. Finally, the DVI Line-SBLOCA accident is induced to analyze the influence of flow blockage on subsequent CAP1400 reactor core heat transfer and core degradation. From the results of the DVI Line-SBLOCA accident analysis, it can be concluded that the blockage ratio is in the range of 40%-60%, and the position of severe blockage is the same as that of cladding rupture. The blockage reduces the circulation area of the core coolant, which in turn impacts the heat exchange between the core and the coolant, leading to the early failure and collapse of some core assemblies and accelerating the core degradation process.

Effect of Greenhouse Cooling and Transplant Quality Using Geothermal Heat Pump System (지열-열펌프 시스템의 온실냉방 및 육묘 효과)

  • Lee, Jae-Han;Lee, Yong-Beom;Kwon, Joon-Kook;Kang, Nam-Jun;Kim, Hak-Joo;Choi, Young-Hah;Park, Jin-Myeon;Rhee, Han-Cheol
    • Journal of Bio-Environment Control
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    • v.15 no.3
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    • pp.211-216
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    • 2006
  • This study was carried out to investigate the effect of greenhouse cooling by a geothermal heat pump system on greenhouse temperature and growth of vegetable transplants in summer season. Greenhouse air temperature in day time was $3-4^{\circ}C$ lower in fog plus shading system than in shading, while in night time that was $5-7^{\circ}C$ lower in geothermal heat pump (GHP) plus shading system compared to shading or fogplus shading. system. Plant height of cucumber, tomato and hot pepper transplants was shortened in GHP plus shading compared to shading or fog plus shading system. And Leaf area and dry weight were slightly decreased in GHP plus shading compared to the other systems. Therefore, healthy transplant index on cucumber, tomato and hot pepper was higher in GHP plusshading than in shading or fogplusshading system.

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 (설비공학 분야의 최근 연구 동향 : 2016년 학회지 논문에 대한 종합적 고찰)

  • Lee, Dae-Young;Kim, Sa Ryang;Kim, Hyun-Jung;Kim, Dong-Seon;Park, Jun-Seok;Ihm, Pyeong Chan
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.29 no.6
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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.

Development of $20\;Nm^3$/hr Hydrogen Generator for Hydrogen Fueling Station (수소스테이션용 $20\;Nm^3$/hr급 수소제조장치 개발)

  • Oh, Young-Sam;Baek, Young-Soon
    • Transactions of the Korean hydrogen and new energy society
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    • v.17 no.3
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    • pp.263-271
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    • 2006
  • In this study, $20\;Nm^3/hr$ scale compact hydrogen generator which can be apply to the hydrogen station was manufactured and tested. The design of $20\;Nm^3/hr$ scale compact hydrogen generator was upgraded on the base of $5\;Nm^3/hr$ scale plate hydrogen generator concept stacking the plate reactors. Ideas for improving system efficiency such as heat recovery from the exhaust, exhaust duct which is especially design for plate type reactor, reinforcement of insulation, enlargement of heat exchange area of reactor, introduction of desulphurizer reactor and PROX rector in a compact design etc. were applied. From the performance test, we can learn that the $20\;Nm^3/hr$ scale compact hydrogen generator can be operated steadily at 100% road condition and the methane conversion of over 94%(at S/C=3.75) was obtained. This result shows that the concept of plate type hydrogen generator can be scale-up to the $20\;Nm^3/hr$ scale and fit for hydrogen generator for on site hydrogen station application.

A cycle simulation of the S.I. engine and it's verification test (S.I. 엔진의 사이클 시뮬레이션 및 이의 확인 실험)

  • 목희수;김승수
    • Journal of the korean Society of Automotive Engineers
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    • v.10 no.6
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    • pp.72-84
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    • 1988
  • Engine performance is one of the main objectives specified at the beginning of a new engine design project. The cycle simulation for SI engine is based on the zero-dimensional gas exchange model and a heat release expression by Viebe. This program also requires minimum input data and takes only a short time to run. Heat transfer from cylinder transfer formula. The flow coefficient (effective area) is calculated from valve lift using the standard flow coefficient curve and engine friction is calculated from the Millington and Hartles' engine friction formula. The chemical species considered in burned gas are 6 species CO, CO, H$_{2}$, H$_{2}$O, $O_{2}$, N$_{2}$ and the cylinder pressure, homogeneous cylinder temperature, gas composition and burned fraction are calculated at each crank angle through the cycle. To check the validity and accuracy, experimental study was done with 3 engines for measuring cylinder pressure, indicated mean effective pressure, brake mean effective pressure and air flow rate, etc. Despite its simple assumptions, cycle simulation showes excellent breathing and performance correlation when compared with data of tested engines, and have been proved useful in engine design.

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Performance test of scale-up $20Nm^3/hr$ scale hydrogen generator for hydrogen station (수소스테이션용 $20Nm^3/hr$급 수소제조장치 스케일-업 및 성능시험)

  • Oh, Young-Sang;Baek, Young-Soon
    • 한국신재생에너지학회:학술대회논문집
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    • 2006.06a
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    • pp.37-42
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    • 2006
  • In this study, $20Nm^3/hr$ scale compact hydrogen generator which can be apply to the hydrogen station was tested for hydrogen station application. $20Nm^3/hr$ scale compact hydrogen generator was developed by upgrading concept of stacking plate reactor from former $20Nm^3/hr$ scale plate hydrogen generator. concepts for improving system efficiency and performance include such as idea of heat recovery from the exhaust, exhaust duct which is especially design for plate type reactor reinforcement of insulation, enlargement of heat exchange area of reactor, introduction of desulphurizer reactor and PROX rector in a compact design, introduction of back fire protection structure of plate burner and so on, We can learn that final prototype of scale-up $20Nm^3/hr$ scale compact hydrogen generator can be operated steadily in 100% road at which over 94% of methane conversion(S/C=3.75) was obtained. In case of making up the weak point, we expect that it is possible to apply to hydrogen station by way of showing an example.

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Synthesisand Electrochemical Behaviors of Hybrid Carbon (ACF/Graphene) as Supports by Microwaves-irradiation Method for Polymer Exchange Membrane Fuel Cells (PEMFC) (마이크로웨이브를 이용한 고분자 전해질 연료전지용 복합 탄소 촉매 지지체 (ACF/Graphene)의 합성과 전기화학적 거동)

  • Cho, Yongil;Jeon, Yukwon;Park, Dae-Hwan;Juon, So-Me;Kim, Tae-Eon;Oh, Kyeongseok;Shul, Yong-Gun
    • Transactions of the Korean hydrogen and new energy society
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    • v.24 no.2
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    • pp.142-149
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    • 2013
  • Carbon materials are mainly used as catalyst supports for polymer exchange membrane fuel cell (PEMFC). Catalyst supports are required specific characteristics of the carbon materials, such as large surface area and high electrical conductivity. Attempted were to improve electrical conductivity and to maintain high surface area of carbon materials using a microwave treatment. Microwave treatment, as a relatively new technique, takes short reaction time and reduce the consumption of the gases used for carbon treatment compared to a traditional heat treatment. Hybrid carbon (ACF/Graphene) as catalyst supports by microwave-irradiation method for PEMFC increase the cell performance because of increased electrical conductivity resulting in triple-phase contact and reduced the interfacial resistance. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-Ray Diffraction (XRD) were employed to analyze carbon materials. The performance of microwave-treated carbon materials was evaluated by measuring current-voltage (I-V) characteristics and electrode impedance.