• Title/Summary/Keyword: heat transfer characteristics

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A Study on the Greenhouse Water Curtain System: Heat Transfer Characteristics

  • 손원명;한길영
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.32 no.E
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    • pp.80-87
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    • 1990
  • Energy balance equations Were developed to describe the heat transfer mechanisms in a double layer plastic greenhouse with a water curtain system. Heat transfer variables were determined by using various temperature data measured in a conventional prototype semicircular cross-section greenhouse over a range of water temperatures and water flow rates. The heat transfer coefficient between flowing water and greenhouse air was independent of water flow rates. But the heat transfer coefficient between water surface and the stagnant air space within the double plastic layer was dependent on water flow rates. Substituting the heat transfer coefficients, determined from the energy balance equations in the heat transfer equations, demonstrated various relationships among ambient air temperature, greenhouse air temperature, water temperature, and water flow rates. The heating benefits were linearly related to not only the inside and outside air temperatures but also to the water temperature. The energy conservation effects of the water curtain system were found even initial water temperatures were considerably lower than the greenhouse setting temperatures. Sensitivity analysis for heat transfer coefficients demonstrated that the heat transfer coefficient between greenhouse air and the stagnant air within the plastic layers was the most significant coefficient in the estimation of heating effects.

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Effectiveness of a Heat Transfer Characteristics of an Auxiliary Chamber for Performance of an Air Spring (보조용기의 열전달특성이 공기스프링의 성능에 미치는 영향)

  • Jang, Ji-Seong
    • Journal of Power System Engineering
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    • v.17 no.2
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    • pp.121-127
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    • 2013
  • The air spring is used widely because of the easy change of spring constant, and, a superior vibration and shock insulation performance. Among the apparatus using the merits of that, the air spring connected an auxiliary chamber has been developed and used as a component of suspension system for an automobile and a railroad car. The purpose of this study is to suggest a design method reflecting heat transfer effect for an air spring system connected auxiliary chamber. In order to do so, this study investigates change of reaction force along with variations in heat transfer coefficient, and, analyzes an effectiveness of a heat transfer characteristics of an auxiliary chamber for external force attenuation characteristics and impedance characteristics of an air spring connected an auxiliary chamber.

Heat Transfer Characteristics of High Temperature molten salt storage for Solar Thermal Power Generation (태양열 발전에서 태양열에너지 수송을 위한 고온 축열 물질의 열절달 특성)

  • Mao, Aiming;Kim, Ki-Man;Kang, Yong-Heack;Han, Gui-Young
    • 한국신재생에너지학회:학술대회논문집
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    • 2008.05a
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    • pp.190-193
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    • 2008
  • The heat transfer characteristics of molten salt storage system for the solar thermal power generation were investigated. Temperature profiles and the heat transfer coefficients during the storage and discharge stage were obtained with the steam as the heat transfer fluid. Two kinds of inorganic salt were employed as the storage materials and coil type of heat exchanger were installed in both tanks to provide the heat transfer surfaces during the storage and discharge stage. The effects of steam flow rates, flow direction of steam in the storage tank and the initial temperature of storage and discharge tank on the heat transfer were tested.

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Influence of Refrigeration Oil on Evaporation Heat Transfer Characteristics of R-290 Inside Micro Fin Tube (마이크로 휜 증발관내 냉매 R-290의 열전달 특성에 미치는 냉동유의 영향)

  • Park, Cheol-Min;An, Young-Tae;Lee, Wook-Hyun;Kim, Jeung-Hoon;Kim, Jong-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.7
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    • pp.938-944
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    • 2000
  • Recently, micro fin tube is widely used to heat exchanger for high performance. And, as the alternative refrigerants for R-22, hydrocarbons such as R-290, R-600 and R-600a are very promising because of their low GWP and ODP. Thus, R-290 was used as working fluid in this study. Most design of heat exchanger had been based on heat transfer characteristics of pure refrigerant although refrigerant oil exists in the refrigeration cycles. So, the influence of oil on heat transfer characteristics have to be considered for investigating exact evaporation heat transfer characteristics. But, this is an unresolved problem of refrigeration heat transfer. Therefore the influence of the refrigeration oil to the evaporation heat transfer characteristics of R-290 were conducted in a horizontal micro tin tube. The mineral oil was used as refrigeration oil. The experimental apparatus consisted of a basic refrigeration cycle and a system for oil concentration measurement. Test conditions are as the follows; evaporation temperature $5^{\circ}C$, mass velocity 100 $kg/m^2s$, heat flux 10 $kW/m^2$, oil concentration 0, 1.3, 3.3, 5.7 wt.%, and quality $0.07{\sim}1.0$. When refrigeration oil was entered, oil foaming was observed at the low quality region. And, very small bubbles were observed as quality was increased. Pressure drop and heat transfer coefficient increased as the concentration of refrigeration oil increased to 5 wt.%.. The performance index of heat exchanger was the highest near 3.3 wt.%.

Development of a Particle Bed Heat Exchanger (IV) -An Experimental Study on Heat Transfer Characteristics of Fixed Bed Heat Exchanger (입자층(粒子層)을 이용(利用)한 열교환기(熱交換器) 개발(開發)에 관(關)한 연구(硏究)(IV) -고정층(固定層) 열교환기(熱交換器)의 전열특성(傳熱特性)에 대한 실험적(實驗的) 연구(硏究))

  • Yang, H.J.;Seo, J.Y.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.2 no.3
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    • pp.234-242
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    • 1990
  • In this study, heat transfer characteristics of vertical fixed bed with air flowing through were experimentally investigated. The experiments were conducted for cases where heat was transfer steady state conditions from an immersed cylindrical heated to the surrounding fixed ved of steel balls. Based on the experimental data, the optimum conditions for heat transfer augmentation have been determined and shows in empirical forms. For the same power loss, comparison of heat transfer effect between the fixed bed and single phase forced convection device indicates that both miniaturization of heat exchange device and heat transfer augmentation at low flow velocity are possible by application of the fixed bed to heat exchangers. The present results could provide a useful design information for the heat exchangers where fixed beds are used.

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Characteristics of Absorption and Heat Transfer for Film Falling along a Vertical Inner Tube (2nd. Report, Characteristics of Heat Transfer) (수직관내(垂直管內)를 흘러내리는 액막식(液膜式) 흡수기(吸收器)의 흡수(吸收) 및 열전달특성(熱傳達特性)(제(第)2보(報) 열전달특성(熱傳達特性)))

  • Ohm, K.C.;Rie, D.H.;Choi, G.G.;Kasiwagi, Takao;Seo, J.Y.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.5 no.4
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    • pp.257-264
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    • 1993
  • This is the second report of a three part study on the absorption and heat transfer characteristics of absorber, the correlation of refrigerating capacity and heating capacity. The 2nd report deals with the heat transfer characteristics of a vertical falling film type absorber of inner copper tube. The solute is LiBr-Water solution(60wt%) and the solvent is water vapor. The film Reynoles numbers are varied in the range of 35~130. The states of LiBr solution at the top of absorber are supercooled liquid and superheated liquid. The results are summarized as follows ; Heat transfer results reveal that for the absorption of falling film, the state of LiBr solution appears to be influential in determining the heat transfer. Thus, for the state of supercooled liquid, heat transfer coefficient decreases with increasing the film Reynolds number, but in the condition of superheated liquid, it increases conversely. The mass transfer coefficients that were presented in the 1st.report and heat transfer coefficients of this paper are presented as the dimensionless correlation. The optimum water flowrate which brings about maximum value of heat flux in the film exists, and that increases with increasing the cooling water temperature.

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Heat Transfer Characteristics of Direct Contact Heat Exchanger Using Solar Energy (태양열이용 직접접촉 열교환기내의 열전달 특성연구)

  • 강용혁;전명석;윤환기;천원기
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
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    • 1995.05a
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    • pp.78-81
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    • 1995
  • In the present study, the spray column type of direct contact heat exchangers are studied experimentally to analyze heat transfer characteristics for solar energy utilization. These experiments are carried out in the line of solar heating system, major results are as follows ; 1) the flow and aspect of working fluid drop for maxium heat transfer 2) efficiency and volumetric heat transfer coefficient of D. C. H. X. with a heavier working fluid are higher than those of D. C. H. X. with a lighter working fluid

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A study on the temperature distribution characteristics in the tube modules of a heat recovery steam generator ith the change of heat transfer modeling (배열회수 보일러 전열관군에서 열전달 모델링에 따른 온도 분포 특성 연구)

  • Ha, Ji Soo
    • Journal of Energy Engineering
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    • v.24 no.2
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    • pp.103-109
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    • 2015
  • A heat recovery steam generator consists of inlet expansion duct and heat transfer tube bank modules. For the enhancement of heat transfer in the tube bank modules, the flow should be uniform before the 1st heat transfer tube bank module. The present study has been carried out to analyze the flow characteristics in the inlet expansion duct of a heat recovery steam generator by using numerical flow analysis. The aim of the present study is to establish the proper heat transfer mechanism in the heat transfer tube bank modules by the comparison of the heat transfer models, the case with the constant heat loss per unit volume and the case with heat loss by using inner and outer convective heat transfer coefficient of heat transfer tube. From the present research, it could be seen that the heat transfer mechanism with using inner and outer convective heat transfer coefficient derives more proper temperature distribution results and the acceptance criteria of the temperature distribution within ${\pm}10^{\circ}C$ before SCR is satisfied with using this heat transfer mechanism.

The Numerical Study on the Cobustion Characteristics and the Heat Transfer Characteristics of Heat Exchanger for Condensing Gas Boiler (응축형 가스보일러 연소기의 연소특성 및 열교환기의 열전달특성에 관한 수치적 연구)

  • Kim, S.C.;Kum, S.M.;Lee, C.E.
    • Proceedings of the KSME Conference
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    • 2001.06d
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    • pp.71-78
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    • 2001
  • It was numerically studied that characteristics of fluid flow and heat transfer in a tube with disk and annular baffle for heat exchanger of condensing boiler. Using a finite volume technique and CFD code, STAR-CD, the governing equations were solved and the temperature and flow fields were investigated. The interval between tube and annular baffle, height and diameter of baffle were selected as important design parameters, and the effects of these parameters on heat transfer and fluid flow were studied. As a result, in the case of with interval, the pressure was decreased but heat transfer was increased. Also heat transfer was slowly increased as the size of disk and annular baffle were increased and the distance between baffles were decreased.

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Numerical Analysis on Heat Transfer Characteristics and Pressure Drop in Plate Heat Exchanger (판형열교환기의 열전달특성 및 압력강하에 관한 해석적 연구)

  • Kim, K.R.;Kim, I.G.;Yim, C.S.
    • Journal of the Korean Solar Energy Society
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    • v.22 no.2
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    • pp.19-26
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    • 2002
  • This study aims at numerically analyzing on heat transfer the characteristics and pressure drop of plate heat exchanger(PHE) using the Phoenics 3.1 VR Editor for the standard k-$\varepsilon$ model. Computations have been carried out for a range of chevron angle from $30^{\circ}$ to $60^{\circ}$, inlet velocity from 0.03m/s to 0.63m/s and the height of corrugation from 0.0045m to 0.0060m. The results show that both of heat transfer performance and pressure drop increase as chevron angle increases. This is because higher troughs produce higher turbulence and a higher heat transfer coefficient in the liquids flowing between the plates. As inlet velocity from 0.03m/s to 0.63m/s increases, heat transfer performance and pressure drop increase parabolically. As the height of corrugation increases, both of heat transfer performance and pressure drop decrease with the decrease of velocity. And the pressure drop decreases and the friction factor increases as the height of corrugation increases.