• Title, Summary, Keyword: Heat Transfer Coefficient

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Heat Transfer Characteristics of Fin-Tube Heat Exchanger Coated with FAPO Zeolite Adsorbent at Different Operating Conditions (FAPO 제올라이트 흡착제 코팅을 통한 핀-관 열교환기 운전조건별 열전달 성능특성)

  • Jeong, Chul-Ki;Kim, Yong-Chan;Bae, Kyung-Jin;Cha, Dong-An;Kwon, Oh-Kyung
    • Journal of the Korea Society For Power System Engineering
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    • v.21 no.3
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    • pp.93-101
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    • 2017
  • In conventional adsorption chamber, adsorbent is embedded in between heat exchanger fins by wire mesh. This method impedes heat and mass transfer efficiency. So in this study, to improve the heat transfer performance of heat exchanger, a fin-tube exchanger was coated with FAPO (Ferroaluminophosphate) zeolite adsorbent. The fin-tube heat exchanger has a fin pitch of 1.8 mm with a variation of adsorbent coating thickness of about 0.1 mm, 0.15 mm and 0.2 mm. By varying cooling water temperature and chilled water temperature respecively, heat transfer rate and overall heat transfer coefficient were investigated. As a result, the heat transfer rate and overall heat transfer coefficient increase with decreasing cooling water temperature and increasing chilled water temperature. Under the basic conditions, the heat transfer rate of heat exchanger with 0.2 mm coating thickness is 11% and 43% higher than that of 0.1 mm and 0.15 mm, respectively. The overall heat transfer coefficient is $189.1W/m^2{\cdot}^{\circ}C$, it is two times lager than that of 0.1 mm.

Estimation of Overall Heat Transfer Coefficient for Single Layer Covering in Greenhouse (일중 피복온실의 관류열전달계수 산정)

  • Hwang, Young-Yun;Lee, Jong-Won;Lee, Hyun-Woo
    • Protected Horticulture and Plant Factory
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    • v.22 no.2
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    • pp.108-115
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    • 2013
  • This study was conducted to suggest a model to calculate the overall heat transfer coefficient of single layer covering for various greenhouse conditions. There was a strong correlation between cover surface temperature and inside air temperature of greenhouse. The equations to calculate the convective and radiative heat transfer coefficients proposed by Kittas were best fitted for calculation of the overall heat transfer coefficient. Because the coefficient of linear regression between the calculated and measured cover surface temperature was founded to 0.98, the slope of the straight line is 1.009 and the intercept is 0.001, the calculation model of overall heat transfer coefficient proposed by this study is acceptable. The convective heat transfer between the inner cover surface and the inside air was greater than the radiative heat transfer, and the difference increased as the wind speed rose. The convective heat transfer between the outer cover surface and the outside air was less than the radiative heat transfer for the low wind speed, but greater than for the high wind speed. The outer cover convective heat flux increased proportion to the inner cover convective heat flux linearly. The overall heat transfer coefficient increased but the cover surface temperature decreased as the wind speed increased, and the regression function was founded to be logarithmic and power function, respectively.

Experimental study on characteristics of evaporation heat transfer of $CO_2$ in horizontal micro-channel tube (수평 다채널관 내 이산화탄소의 증발 열전달 특성에 관한 실험적 연구)

  • Lee, Sang-Jae;Kim, Dae-Hoon;Choi, Jun-Young;Lee, Jae-Heon;Kwon, Young-Chul
    • Proceedings of the KSME Conference
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    • pp.2200-2205
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    • 2007
  • In order to investigate the variation on a heat transfer coefficient during evaporation of $CO_2$, basic experiment on the evaporation heat transfer characteristics in a horizontal micro-channel tube was performed. Hydraulic diameters of micro-channels were 0.68 and 1.46 mm. The experiment apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiments were conducted for various mass fluxes of 300 to 800 kg/$m^2s$, heat fluxes of 10 to 40 kW/$m^2$ and saturation temperatures of -5 to 5$^{\circ}C$. With the increase heat flux, the evaporation heat transfer coefficient increased. And the significantly change of the heat transfer coefficient was observed at any heat flux and mass flux. As the saturation temperature increased and the hydraulic diameter decreased, the heat transfer coefficient increased.

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Experimental Study on the Determination of Heat Transfer Coefficient for the KURT (KURT 내 열전달계수 결정에 관한 실험적 연구)

  • Yoon, Chan-Hoon;Kwon, Sang-Ki;Kim, Jin
    • Tunnel and Underground Space
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    • v.19 no.6
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    • pp.507-516
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    • 2009
  • In cases of high-level radioactive waste repositories, heat load is apparent by radioactive waste decay. The safety of a waste repository would be influenced by changing circumstances caused by heat transfer through rock. Thus, a ventilation system is necessary to secure the waste repository. The first priority for building an appropriate ventilation system is completing a computer simulation research with thermal rock properties and a heat transfer coefficient. In this study, the heat transfer coefficient in KURT was calculated using the measurement of inner circumstance factors that include dry bulb and wet bulb temperature, rock surface temperature, and barometric pressure. The heater that is 2 m in length and 5 kw in capacity heats the inside of rock in the research module by $90^{\circ}C$. As a result of determining the heat transfer coefficient in the heating section, the changes of heat transfer coefficient were found to be a maximum of 7.9%. The average heat transfer coefficient is approximately 4.533 w/$m^2{\cdot}K$.

An Analysis of Heat Transfer Coefficient of Soil Surface in Closed Ecosystems Using CFD (CFD를 이용한 폐쇄생태계 내 토양표면의 열전달계수 분석)

  • Roh, Sang-Mok;Nam, Sang-Woon
    • Korean Journal of Agricultural Science
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    • v.33 no.1
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    • pp.85-95
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    • 2006
  • A model experiment has been performed to get the heat transfer coefficient on the soil surface in the closed ecosystem. The heat flux on the soil surface was measured and the heat transfer coefficient was derived in the following two cases with 5-stepped control of inside air current speed. One case was that heat flowed from air to soil and the other case was that heat flowed from soil to air. Three dimensional CFD model has been set to simulate thermal environment in the closed ecosystem including soil layers. The standard $k-{\varepsilon}$ model of the CFD program was chosen for turbulence model and heating wire buried in the soil layers was set as heat source option to simulate the case when the temperature of soil surface was higher than that of inside air in the closed ecosystem. Between one case that heat flowed from air to soil and the other case that heat flowed from soil to air, there were big differences in the temperature distribution of soil layers and the heat transfer coefficient of the soil surface. The increasing rate of heat transfer coefficient on each case according to the increase of inside air current speed was similar to each other and it respectively increased linearly. But the heat transfer coefficient on the case that heat flowed from soil to air was much bigger than that of the other case. The model was validated by comparing simulated values of CFD model with measured values of the model experiment. Simulated and measured temperature of inside air and soil layers, and heat transfer coefficient of the soil surface were well accorded and the range of corrected $R^2$ was 0.664 to 0.875. The developed CFD model was well simulated in parts of the temperature of inside air and soil layers, the distribution of the inside air current speed, and heat transfer coefficient of the soil surface were able to be quantitatively analyzed by using this model. Therefore, the model would be applied and used for analysis of heat transfer coefficient between air and surface in various agricultural facilities.

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Evaporation Heat Transfer Characteristics of $CO_2$ in a Horizontal Tube

  • Son Chang-Hyo;Kim Dae-Hui;Choi Sun-Muk;Kim Young-Ryul;Oh Hoo-Kyu
    • International Journal of Air-Conditioning and Refrigeration
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    • v.13 no.4
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    • pp.167-174
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    • 2005
  • The evaporation heat transfer coefficient of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500kg/m^2s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has greater effect on nucleate boiling than convective boiling. The evaporation heat transfer coefficient of $CO_2$ is highly dependent on the vapor quality, heat flux and saturation temperature. The evaporation heat transfer coefficient of $CO_2$ is very larger than that of R-22 and R-134a. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the correlation of Jung et al. But the existing correlations failed to predict the evaporation heat transfer coefficient of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

Study on Condensation Heat Transfer and Pressure Drop Characteristics of R-22 in Brazed Plate Heat Exchanger (R-22를 사용한 용접형 판형 열교환기의 응축열전달 및 압력강하 특성에 관한 연구)

  • Jeon, Chang-Deok;Gwon, O-Gap;Lee, Jin-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.2
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    • pp.171-179
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    • 2001
  • Experimental study has been carried out on the characteristics of pressure drop and heat transfer of brazed plate heat exchangers using R-22. Data are presented for the following range of variables: the mass flux (40∼90kg/$m^2$s), chevron angle ($20^{\circ}$, $35^{\circ}$, $45^{\circ}$) and inlet pressure of the refrigerant (1.4 and 1.6MPa). For both subcooled and two-phase flow, as chevron angle increases, pressure drop and heat transfer coefficient decrease. Condensation heat transfer coefficient and pressure drop were compared with the previously proposed correlations. Among therm, Traviss correlation agreed with experimental results within -40%∼-84% for heat transfer coefficient and -59%∼62% for pressure drop.

Development of a Particle Bed Heat Exchanger(I) -An Experimental Study on Heat Transfer Characteristics of Fluidized Bed Heat Exchanger with Double Pipe (Counterflow) (입자층(粒子層)을 이용(利用)한 열교환기(熱交換器) 개발(開發)에 관(關)한 연구(硏究)(I) - 유동층형(流動層形) 이중관식(二重管式) 열교환기(熱交換器)의 전열특성(傳熱特性)에 대한 실험적(實驗的) 연구(硏究) (대향류식(對向流式)))

  • Lim, J.G.;Yoo, J.O.;Yang, H.J.;Seo, J.Y.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.2 no.2
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    • pp.119-126
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    • 1990
  • In this study, the overall heat transfer coefficients are calculated on fluidized bed double pipe heat exchanger and single phase double pipe heat exchanger at the same condition. The effect of the particle size, its material, fluidizing velocity and static bed height on overall heat transfer coefficient has been investigated. The main conclusions obtained from the experiment are as follows. 1. The overall heat transfer coefficient of the fluidized bed heat exchanger is higher than that of single phase forced convective heat exchanger (maximum 2.3 times) 2. The value of the overall heat transfer coefficient increase with an increase in static bed height and decrease with an increase in particle size. 3. For the same particle size, the particle of low density can obtain higher overall heat transfer coefficient than that of high density.

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Experimental study of Heat Transfer and Pressure Drop Characteristics for the Welded Plate Heat Exchanger (용접형 판형 열교환기의 열전달 및 압력강하 특성에 관한 실험적 연구)

  • Jeong, Jong-Yun;Kim, Sung-Soo;Kang, Yong-Tae
    • Proceedings of the SAREK Conference
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    • pp.419-424
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    • 2008
  • Heat transfer and pressure drop characteristics of welded plate heat exchanger are studied to apply it for the solution heat exchanger of 210RT absorption system. This study quantifies the effect of mass flow rate and strong solution concentration on the heat transfer coefficient and pressure drop in the plate heat exchanger. The concentration of weak solution is fixed at 55% and the strong solution varies 55%, 57%, and 59% in mass. The results show that the overall heat transfer coefficient and pressure drop increase linearly with increasing Reynolds number. It is also found that the heat transfer coefficient of hot side increases with increasing the concentration of strong solution while the strong solution concentration has no effect on heat transfer coefficient of cold side.

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Experimental Study on Heat Transfer Characteristics of Evaporation using Propylene Refrigerant (프로필렌 냉매의 증발열전달 특성에 관한 실험적 연구)

  • 이호생;김재돌;정석권;윤정인
    • Journal of the Korean Society of Marine Engineering
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    • v.28 no.5
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    • pp.754-761
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    • 2004
  • In this paper, evaporating heat transfer characteristics in the refrigeration and air-conditioning facilities were studied using the environmentally friendly refrigerants R-1270 (Propylene). R-290 (Propane). R-600a (Iso-butane) and HCFC refrigerant R-22 The test tube was surrounded by an annulus with water flowing counter to the refrigerant. The tube is copper. with an outside diameter of 12.7mm and the wall thickness of 1.315mm. The test results showed that the local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to that of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficient increased with the increase of the mass velocity and it showed the higher values in hydrocarbon refrigerants than R-22 Comparing the heat transfer coefficient of experimental results with that of other correlations. the presented results had agood agreement with the Kandlikar's correlation. This results form the investigation can be used in the design of heat transfer exchangers using hydrocarbons as the refrigerant for the air-conditioning systems.