• Title/Summary/Keyword: Surface heat exchange

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Numerical Investigations of Enhancement of a Convective Fin Efficiency by Convection-Radiation Gonjugate Heat Transfer (대류-복사 복합 열전달을 고려한 대류 핀효율의 향상에 관한 수치적 연구)

  • 이동렬;김호용;이재곤;박용국;김기대
    • Journal of Advanced Marine Engineering and Technology
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    • v.25 no.1
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    • pp.146-154
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    • 2001
  • In almost all real situations, there will be a radiant interchange between adjacent fins with the base surface as well as with the external environment. In the problem of this study, a rectangular fin is attached to a based. Our concern is whether the convective fin efficiency can be increased by the radiation heat exchanged between the fin and the base surface and how much. If the fin temperature toward the tip increased by the effect of radiation, the convective heat transfer increase due to the temperature difference between the ambient temperature and the surface temperature of the fin. If this true, the efficiency of the fin due to the radiation will increase. Attention is directed toward several parameters which have major roles on getting values of the fin efficiencies in several different values of parameters. Many different cases are, therefore, to be examined to have maximum fin efficiency by varying the values of each parameter.

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The Catalytic heat Exchanger of Catalytic Fins Deposited With PD Catalyst (Pd 촉매 담지핀을 이용한 촉매 열 교환기의 특성분석 실험)

  • 유상필;서용석;정남조;유인수;조성준
    • Proceedings of the Korea Society for Energy Engineering kosee Conference
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    • 2000.04a
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    • pp.209-214
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    • 2000
  • The catalytic heat exchanger, which integrates two functions of heat generation and heat exchange into one equipment, was designed and its characteristics were investigated by experiments. The surface of the fin tube was deposited with Pd catalyst. The conversion of the mixture in the catalytic heat exchanger was more significantly affected by the inlet velocity of the mixture than by the inlet temperature and equivalence ratio of the mixture. It was found that the catalytic surface area of the fin tubes should be sufficiently increased to make the combustion intensity of the catalytic heat exchanger as high as possible. Results showed that the fin tubes, placed in the triangularly staggered form, should be adjusted so that the mixture flows uniformly over all the catalytic fin surfaces.

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Numerical Study of Heat Flux and BOG in C-Type Liquefied Hydrogen Tank under Sloshing Excitation at the Saturated State (포화상태에 놓인 C-Type 액체수소 탱크의 슬로싱이 열 유속과 BOG에 미치는 변화의 수치적 분석)

  • Lee, Jin-Ho;Hwang, Se-Yun;Lee, Sung-Je;Lee, Jang Hyun
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.35 no.5
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    • pp.299-308
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    • 2022
  • This study was conducted to predict the tendency for heat exchange and boil-off gas (BOG) in a liquefied hydrogen tank under sloshing excitation. First, athe fluid domain excited by sloshing was modeled using a multiphase-thermal flow domain in which liquid hydrogen and hydrogen gas are in the saturated state. Both the the volume of fluid (VOF) and Eulerian-based multi-phase flow methods were applied to validate the accuracy of the pressure prediction. Second, it was indirectly shown that the fluid velocity prediction could be accurate by comparing the free surface and impact pressure from the computational fluid dynamics with those from the experimental results. Thereafter, the heat ingress from the external convective heat flux was reflected on the outer surfaces of the hydrogen tank. Eulerian-based multiphase-heat flow analysis was performed for a two-dimensional Type-C cylindrical hydrogen tank under rotational sloshing motion, and an inflation technique was applied to transform the fluid domain into a computational grid model. The heat exchange and heat flux in the hydrogen liquid-gas mixture were calculated throughout the analysis,, whereas the mass transfer and vaporization models were excluded to account for the pure heat exchange between the liquid and gas in the saturated state. In addition, forced convective heat transfer by sloshing on the inner wall of the tank was not reflected so that the heat exchange in the multiphase flow of liquid and gas could only be considered. Finally, the effect of sloshing on the amount of heat exchange between liquid and gas hydrogen was discussed. Considering the heat ingress into liquid hydrogen according to the presence/absence of a sloshing excitation, the amount of heat flux and BOG were discussed for each filling ratio.

Study on the Improvement of Exchange Bias and Magnetoresistance in Co/Cu/Co/FeMn Spin Valve by Heat Treatment (Co/Cu/Co/FeMn 스핀밸브의 자기저항 특성 향상 연구)

  • Kim, Hong-Jin;Bae, Jun-Soo;Noh, Eun-Sun;Lee, Taek-Dong;Lee, Hyuck-Mo
    • Journal of the Korean Magnetics Society
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    • v.12 no.1
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    • pp.24-29
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    • 2002
  • It was observed that exchange bias field was increased with smooth surface and better ${\gamma}$-FeMn formation. Sputtering conditions were varied for the control of the surface roughness and ${\gamma}$-FeMn formation. From the results of Cu deposition as underlayer, it was found that ${\gamma}$-FeMn formation was closely related with the thickness of underlayer. After heat treatment, exchange bias field was increased over three times. This improvement was likely that the crystallites of ${\gamma}$-FeMn were well formed. In Co/Cu/Co/FeMn spin valve structure, magnetoresistance was increased over 1.4 times through the heat treatment. This was due to the disappearance of Co/Cu intermixed dead layer and removal of defect, and this was examined by AES analysis.

Research on Performance of Large Rotor-type Heat Recovery Exchanger using CFD Analysis on Surface Corrugation (요철형상의 CFD 해석을 통한 대용량 로타형 폐열회수열교환기 성능에 관한 연구)

  • Kim, Dong-Gyu;Ha, Byeong-Yong;Kim, Kun-Oh;Kum, Jong-Soo;Jeong, Seok-Kwon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.24 no.12
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    • pp.875-880
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    • 2012
  • The field of the large volume heat exchanger for wasted heat recovery ventilation system is being expanded enormously seeing as the fact that the quantity of reducing energies are huge due to the large volume heat exchanger for wasted heat recovery system at large buildings and factories, which consume large amount of energies while it has been arising huge amount of losses in Korea because of the lack of technology. To develop large volume waste heat recovery heat exchanger, rotor type heat exchanger was simulated for the surface corrugation. Based on the simulation results produced $30,000m^3/h$ grade waste heat recovery, heat exchanger was performed for the actual experiment. In addition, performance tests exceed the capacity of a large waste heat recovery heat exchanger performance test methods proposed.

On The Variation Of The Mixed Layer Depth And The Heat Flux In The Sea Of Japan

  • Shim, Taebo;Kim, Kuh
    • 한국해양학회지
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    • v.16 no.2
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    • pp.49-56
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    • 1981
  • Annual variation of the surface mixed layer depth (MLD) in the southern part of the Sea of Japan is investigated based upon the oceanographic and meteorological data taken during 1971∼1975 by the Fisheries Research and Development Agency and the Central Meteorological Office of Korea. It is found that the variation of the MLD is strongly correlated with the heat exchange between the atmosphere and sea. The MLD and heat flux vary within ranges comparable to those in the Kuroshio region found by Bathen(1972) and Wyrtki(1965)

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Human Solar Heat Load and Thermal Comfort in an Outdoor Environment (건축외부공간에 있어서 인체의 일사열부하(日射熱負荷) 및 열적(熱的) 쾌적성(快適性)에 관한 실험적 연구)

  • Jeong, Chang-Won;Yoon, In
    • Journal of the Korean Society of Industry Convergence
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    • v.1 no.2
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    • pp.65-74
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    • 1998
  • The purpose of this paper is to investigate the mount of relief of human solar heat load and thermal comfort in outdoor environment in summer, Six different types of sites, T garden and its neighboring area in Japan, were selected as the experiment sites. The experiments were conducted from 22 to 29 August, 1994 to find the relationship between climatic conditions and human responses, Climatic conditions, subjects's thermal sensation and skin temperature were measured. Radiant heat exchange on the human body was estimated on the basis of the measured air and surface temperature and solar radiation. Thermal index Operative Temperature and New Effective Temperature was modified with the effect of the radiant heat exchange. Human thermal comfort and skin temperature is affected by the solar radiation and the sky factor in an outdoor environment. The effect of tree shade was verified on thermal comfort, The mount of relief of human solar heat load is relation to the existence of shade a solar radiation and the sky factor. The urban garden is one of the effective design element in an urban environmental planning.

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Characteristics of Sensible Heat and Latent Heat Fluxes over the East Sea Related with Yeongdong Heavy Snowfall Events (영동대설 사례와 관련된 동해상의 현열속과 잠열속 분포 특성)

  • Kim, Ji-Eon;Kwon, Tae-Yong;Lee, Bang-Yong
    • Ocean and Polar Research
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    • v.27 no.3
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    • pp.237-250
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    • 2005
  • To investigate the air mass modification related with Yeongdong Heavy snowfall events, we examined sensible and latent heat fluxes on the East Sea, the energy exchange between atmosphere and ocean in this study. Sensible and latent heats were calculated by a bulk aerodynamic method, in which NCEP/NCAR reanalysis data and NOAA/AVHRR weekly SST data with high resolution were used. Among winter precipitation events in the Yeongdong region, 19 heavy precipitation events $(1995{\sim}2001)$ were selected and classified into three types (mountain, cold-coastal, and warm types). Mountain-type precipitation shows highly positive anomalies of sensible and latent heats over the southwestern part of the East Set When separating them into the two components due to variability of wind and temperature/ specific Humidity, it is shown that the wind components are dominant. Cold-coastal-type precipitation also shows strong positive anomalies of sensible and latent heats over the northern part and over the central-northern part of the East Sea, respectively. It is shown that the sensible heat anomalies are caused mostly by the decrease of surface air temperature. So it can be explained that cold-coastal-type precipitation is closely related with the air mass modification due to cold air advection over warm ocean surface. But in warm-type precipitation, negative anomalies are found in the sensible and latent heat distributions. From this result, it may be postulated that warm-type precipitation is affected by the internal process of the atmosphere rather than the atmosphere-ocean interaction.

Ion Exchange Capacity and Phase Separation of Alkali Borosilicate Glass by Substituting $Al_2O_3$ (산화알루미늄의 치환에 따른 붕규산 유리의 분상 미 이온교환성에 관한 연구)

  • 김병호;유영문
    • Journal of the Korean Ceramic Society
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    • v.21 no.1
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    • pp.41-50
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    • 1984
  • The ion-exchange porous glasses were prepared by heat treating and subsequently acid treating the (95-y) $SiO_2$.$yB_2O_3$.$5Na_2O+xAl_2O_3$ glasses with y=55, 45, 35, 25. mole% and x=0, 2, 5, 9 mole% It was then investigated how the cation exchange capacity was affected by the phase separation in these glasses. For that matter such quantities as alkali extraction amount pore volume and specific surface area of the glasses were measured. The phase separation in these glasses was in general suppressed by the addition of $Al_2O_3$ maximally around the composition of 5 mole% $Al_2O_3$ This may be because the micro-phase separation prevailed in the glass of that composition over the macro-phase separation increasing thereby the specific surface area as well as the residual amount Al of after acid-treatment and accordingly the cation exchange capacity. The maximum values of the cation exchange capacity was observed to be about 150meq/100g for the glasses of (40-50) $SiO_2$ (55~45)$yB_2O_3$. $5Na_2O+5Al_2O_3$.

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An Analytical Study on the Heat Transfer Characteristics of MF Evaporation Tubes Attached with a Fin (핀이 부착된 MF증발관의 열전달 특성에 대한 해석적 연구)

  • Park, Yong-Seok;Seong, Hong-Seok;Suh, Jeong-Se
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.20 no.1
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    • pp.48-56
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    • 2021
  • In this study, the heat transfer process around the finned channel tubes is numerically examined. Serially arranged tubes of an evaporator were used for heat exchange. The numerical analysis results confirmed that the vortex generated at the rear of the channel pipe was caused by the fin. Furthermore, it was also confirmed that the temperature difference was large between the inlet and outlet ends of the fin. The temperature of the location where the fin was attached to the channel pipe was found to be close to the surface temperature of the channel wall. However, the temperature rose rapidly closer to the ambient air temperature of 350 K towards the fin end, located at a distance of 0.035 m; it was found to have a significant influence on the heat transfer around the fin-attached channel tube. The wider the vertical flow path, the lower the total heat transfer coefficient. However, the overall heat transfer coefficient increased as the horizontal flow path narrowed. The increment is attributed to an increase in the heat transfer amount due to increased heat transfer surface.