• Title/Summary/Keyword: Heat convection

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Studies on the Focusing Solar Agricultural Crop Dryer - Part1. Heat Efficiency of Aluminum-laminated Aeryl Film Solar Heater - (농산물(農産物) 건조용(乾燥用) 곡면집광식(曲面集光式) 태양열(太陽熱) 이용(利用) 장치(裝置)에 관한 연구(硏究) - 제1보(第1報). 알루미늄-아크릴 필림을 이용(利用)한 태양열(太陽熱) 집열장치(集熱裝置)의 열이용(熱利用) 효율(?率) -)

  • Chun, Jae-Kun;Mok, Chul-Kyoon;Kim, Hyun-Uk
    • Korean Journal of Food Science and Technology
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    • v.11 no.1
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    • pp.8-12
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    • 1979
  • A cylindrical solar energy focusing collector constructed using aluminum-laminated film plastered on the acrylic plate and examined its performances under the Korean local weather conditions. The reflector surface of this collector· evidenced the reflectivity of 66.1%,which was satisfactory value that could be applicable to the solar collector for its low price and at·availability. Collector efficiency measured at the heat exchanger fluid in absorber-copper pipe black colored was 73% and the resulting natural convection of the heat transfer media (water) was recorded up to 2.82 cm/sec. The overall efficiency of the solar heater in operation was 28.6% and it was correlated with the solar energy input and the temperature elevation difference gained.

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Focusing effect of a Metallic Layer according to the Cooling Condition and Height in a Severe Accident (중대사고시 금속용융물층의 냉각 조건과 높이가 열속 집중 현상에 미치는 영향)

  • Moon, Je-Young;Chung, Bum-Jin
    • Journal of Energy Engineering
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    • v.24 no.1
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    • pp.78-87
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    • 2015
  • Focusing effect of a metallic layer in a severe accident depending on the aspect ratios and cooling conditions of top plate and side wall was investigated. Experiments were carried out for Rayleigh numbers and aspect ratio in the range of $8.49{\times}10^7{\sim}5.43{\times}10^9$, 0.135~0.541 respectively. In order to achieve high Rayleigh numbers, the heat transfer experiments were replaced by mass transfer experiments based on the heat and mass transfer analogy. A sulfuric acid-copper sulfate ($H_2SO4-CuSO_4$) electroplating system was adopted as the mass transfer system. The experimental results agreed well with the Rayleigh-Benard natural convection correlations of Dropkin and Somerscales and Globe and Dropkin. When compared with the standard Rayleigh-Benard problem, the cooling by the side wall is even higher than the top. For a shorter height, the interaction between the heated and cooled plumes increases due to decrease of the height. Thus, the heat transfer increases.

A Study on the Thermoacoustic Oscillation of an Air Column (기주의 열음향진동에 관한 연구)

  • 권영필;이병호
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.253-261
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    • 1987
  • Thermoacoustic oscillation of an air column induced by heated wires is investigated analytically and experimentally. Acoustic power generation from a single heater wire is estimated based on the result of heat transfer analysis and expressed in terms of the efficiency factor indicating the conversion efficiency from heat to acoustic energy. It is shown that the efficiency factor becomes maximum when the wire radius is the order of the coustic boundary layer thickness and the flow velocity is close to the thermal diffusion velocity. Onset condition of the column oscillation is obtained by equating the acoustic power generation at the heater to the power loss due to thermoviscous dissipation at the tube wall and the convection and radiationloss at the open ends of the tube. In estimating the acoustic power generation, the heater is treated as a stretched single wire by correcting the flow velocity to take into account the interactions between adjacent heater wires. Experiment is performed by using a spiral heater of 1mm diameter in an air column of 37mm diameter. The heat input to drive the oscillation is measured and compared with the theoretical prediction. A good agreement is found between the theory and experiment, which is regarded as a substantial verification of the present analysis.

Numerical Simulation of Standing Column Well Ground Heat Pump System Part 1: Validation of the Numerical Model (단일심정 지열히트펌프의 수치적 모델링 Part I: 수치해석 모델 검증)

  • Park, Du-Hee;Kim, Kwang-Kyun;Kwak, Dong-Yeop;Chang, Jae-Hoon;Park, Si-Sam
    • Journal of the Korean Geotechnical Society
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    • v.26 no.2
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    • pp.33-43
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    • 2010
  • Geothermal energy is gaining wide attention as a highly efficient renewable energy and being increasingly used for heating/cooling systems of buildings. The standing column well (SCW) is especially efficient, cost-effective, and suitable for Korean geological and hydrological conditions. However, a numerical model that simulates the SCW has not yet been developed and applied in Korea. This paper describes the development of the SCW numerical model using a finite-volume analysis program. The model, through hydro-thermal coupled analyses, simulates heat transfer through advection, convection, and conduction. The accuracy of the model was verified through comparisons with field data measured at SCWs in the U.S. and Korea. Comparisons indicated that the SCW numerical model can closely predict the performance of a SCW. The numerical model was used to perform a comprehensive parametric study in the companion paper.

An Application of Equivalent Heat Source for Thermal Analysis of Pavement Process (포장시 열영향 해석을 위한 등가열원의 적용성)

  • Lee, Wan-Hoon;Yoo, Byoung-Chan;Chung, Heung-Jin
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.3A
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    • pp.391-399
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    • 2008
  • Because of relatively high temperature, over $240^{\circ}C$, of asphalt for steel deck bridge during pavement procedure, the temperature of deck could rise over $100^{\circ}C$ and undesirable excessive displacement and thermal stress could occur. In this study, in order to estimate the thermal effect of pavement process and to find the optimal pavement process, a new thermal analysis technique with Equivalent Heat Source (EHS) is proposed and its applicability to the practical pavement of steel bridge is studied. EHS is developed to simulate the high temperature pavement materials and its thermal effect such as conduction and convection which cannot be explain easily in general structural analysis program for bridge design. To verify the applicability of new analysis technique with EHS, thermal analyses of steel deck bridge with uplift and curved bridge with various pavement procedures are presented.

A study on thermal fluid analysis in X-ray tube for non-fire alarm (비화재보를 위한 X-ray tube 내 열 유동해석에 관한 연구)

  • Yun, Dong-Min;Jeon, Yong-Han
    • Design & Manufacturing
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    • v.16 no.2
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    • pp.33-38
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    • 2022
  • Currently, Korea is an aging society, and it is expected to enter a super-aging society in about 4 years. Accordingly, many X-ray technologies are being developed. In X-rays, 99% of X-rays are converted into heat energy and 1% into light energy (X-rays). 99% of the thermal energy raises the temperature of the anode and its surroundings, and the cooling system is an important factor as overheating can affect the deterioration of X-ray quality and shortened lifespan. There is a method of forced air cooling using natural convection. Therefore, in this study, when X-rays were taken 5 times, Flow analysis was performed on heat removal according to temperature rise and cooling time for the heat generated at the anode of the X-ray tube (input power 60kW, 75kW, 90kW). Based on one-shot, the most rapid temperature rise section increased by more than 57% to 0.03 seconds, A constant temperature rises from 0.03 seconds to 0.1 seconds, It is judged that the temperature rises by about 8.2% or more at one time. After one-shot cooling, the cooling drops sharply from about 60% to 0.03 seconds, It is judged that the temperature has cooled by more than 86% compared to the temperature before shooting. One-shot is cooled by more than 86% with cooling time after 0.1 seconds, As the input power of the anode increases, the cooling temperature gradually increases. Since the tungsten of the anode target inside the X-ray tube may be damaged by thermal shock caused by a rapid temperature rise, an improvement method for removing thermal energy is required when using a high-input power supply.

Experiments on Natural Convection on the Outer Surface of a Vertical Pipe by Using Fluids with High Pr Number (높은 Pr 수의 유체를 사용한 수직 원형관 외부의 자연대류 실험)

  • Kang, Gyeong-Uk;Chung, Bum-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.35 no.1
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    • pp.33-42
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    • 2011
  • In this study, we investigated the natural convection on the outer surface of a vertical pipe by performing mass transfer experiments using fluids with high Pr number using the concept of analogy between heat and mass transfer. A cupric acid-copper sulfate electroplating system was adopted as the mass transfer system. Tests were performed for $Ra_H$ numbers from $1.4{\times}10^9$ to $4{\times}10^{13}$, Pr numbers from 2,094 to 4,173, and diameters from 0.005 m to 0.035 m. The test results for laminar flow conditions were in good agreement with the correlations reported by King, Jakob and Linke, McAdam, and Bottemanne, and those for turbulent conditions with the correlations presented by Fouad for a vertical plate and also proved the dependence on Pr numbers. The obtained correlations were $Nu_H=0.55Ra^{0.25}_H$ for laminar and $Nu_H=0.12Ra^{0.28}_HPr^{0.1}$ for turbulent. The transition between laminar and turbulent occurs at $Ra_H$ of about $10^{12}$.

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 (설비공학 분야의 최근 연구 동향 : 2013년 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.26 no.12
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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.

Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2012 (설비공학 분야의 최근 연구 동향 : 2012년 학회지 논문에 대한 종합적 고찰)

  • Han, Hwataik;Lee, Dae-Young;Kim, Sa Ryang;Kim, Hyun-Jung;Choi, Jong Min;Park, Jun-Seok;Kim, Sumin
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.25 no.6
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    • pp.346-361
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    • 2013
  • This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2012. 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. The conclusions are as follows : (1) The research works on thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and valves, fuel cells and power plants, ground-coupled heat pumps, and general heat and mass transfer systems. Research issues are mainly focused on new and renewable energy systems, such as fuel cells, ocean thermal energy conversion power plants, and ground-coupled heat pump systems. (2) Research works on the 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 natural convection in a square enclosure with two hot circular cylinders, non-uniform grooved tube considering tube expansion, single-tube annular baffle system, broadcasting LED light with ion wind generator, mechanical property and microstructure of SA213 P92 boiler pipe steel, and flat plate using multiple tripping wires. In the area of pool boiling and condensing heat transfer, researches on the design of a micro-channel heat exchanger for a heat pump, numerical simulation of a heat pump evaporator considering the pressure drop in the distributor and capillary tubes, critical heat flux on a thermoexcel-E enhanced surface, and the performance of a fin-and-tube condenser with non-uniform air distribution and different tube types were actively carried out. In the area of industrial heat exchangers, researches on a plate heat exchanger type dehumidifier, fin-tube heat exchanger, an electric circuit transient analogy model in a vertical closed loop ground heat exchanger, heat transfer characteristics of a double skin window for plant factory, a regenerative heat exchanger depending on its porous structure, and various types of plate heat exchangers were performed. (3) In the field of refrigeration, various studies were executed to improve refrigeration system performance, and to evaluate the applicability of alternative refrigerants and new components. Various topics were presented in the area of refrigeration cycle. Research issues mainly focused on the enhancement of the system performance. In the alternative refrigerant area, studies on CO2, R32/R152a mixture, and R1234yf were performed. Studies on the design and performance analysis of various compressors and evaporator were executed. (4) In building mechanical system research fields, twenty-nine studies were conducted to achieve effective design of mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, renewable energy systems, and lighting systems in buildings. New designs and performance tests using numerical methods and experiments provide useful information and key data, which can improve the energy efficiency of buildings. (5) In the fields of the architectural environment, studies for various purposes, such as indoor environment, building energy, and renewable energy were performed. In particular, building energy-related researches and renewable energy systems have been mainly studied, reflecting interests in global climate change, and efforts to reduce building energy consumption by government and architectural specialists. In addition, many researches have been conducted regarding indoor environments.

Recent Tectonism in the Korean Peninsula and Sea Floor Spreading (한반도(韓半島)의 신기(新期) 지형운동(地穀運動)에 관(關)하여)

  • Park, Byong Kwon;Kim, Suh Woon
    • Economic and Environmental Geology
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    • v.4 no.1
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    • pp.39-43
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    • 1971
  • The Korean Peninsula is located between the tectonically stable Asian Continent and the tectonically active Japanese islands. The east coast of Korea shows evidence of uplift whereas the west coast shows evidence of submergence. However, radiocarbon dates indicate that the rate of submergence of the west coast of Korea is slower than the tectonically stable east coast of North America. Therefore, both east and west coasts of Korea might have been uplifted during the last post-glacial period. This uplift may result the spreading line of the from compressional strain produced along East Sea of Korea (Japan Sea) and/or the conversion hinge line of the Pacific mantle convection current plunging beneath the Asian continent. This downturn is supposed to be located in the Japan Trench. High heat flow near the east coast of Korea produces the differential strain. This strain accelerates the compressional strain of the peninsula. The Sea Floor Spreading Theory can explain the tectonism of the Korean Peninsula in Recent time. Baek-Doo Mt. and Han-Ra Mt., dormant volcanoes, may be an evidence of westward movement of the Korean Peninsula.

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