• Title/Summary/Keyword: 표면 열유속

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Effects of Micro-fin Structure on Spray Cooling Heat Transfer in Forced Convection and Nucleate Boiling Region (강제대류 및 핵비등영역에 있어서 마이크로 휜 형상이 분무냉각 열전달에 미치는 영향)

  • Kim, Yeung-Chan
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.34 no.11
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    • pp.983-990
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    • 2010
  • In the present study, spray cooling heat transfer was experimentally investigated for the case in which water is sprayed onto the surfaces of micro-fins in forced convection and nucleate boiling regions. The experimental results show that an increase in the droplet flow rate improves heat transfer due to forced convection and nucleate boiling in the both case of smooth surface and surfaces of micro-fins. However, the effect of subcooling for fixed droplet flow rate is very weak. Micro-fins surfaces enhance the spray cooling heat transfer significantly. In the dilute spray region, the micro-fin structure has a significant effect on the spray cooling heat transfer. However, this effect is weak in the dense spray region. A previously determined correlation between the Nusselt number and Reynolds number shows good agreement with the present experimental data for a smooth surface.

Evaluation of Thermal Properties for the Far Infrared Therapy After Microvascular Anastomosis for the Treatment of Circulatory Diseases (미세혈관 문합 후 순환계 질환 개선을 위한 원적외선 치료기의 열적 특성 평가)

  • Yang, Young-Kyu;Oh, Seung-Hyun;Kim, Cheol-Woong
    • Transactions of the KSME C: Technology and Education
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    • v.1 no.2
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    • pp.179-186
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    • 2013
  • Far-infrared radiation therapies are becoming more popular for blood circulation disorders, cardiovascular disease, skin diseases, inhibit cancer cell, etc replacing conventional operations. In this research, thermal characteristics of heating part in panel radiators, which is effective on the blood circulation disorders were experimentally analyzed. The heating line supplies heat energy to insulation coatings with heat flux of $150mW/m^2$ in normal status and as a result the coatings reached 20% of the heating line temperature. In other words, the insulation itself could increase surface temperature of heating plates by 20% and raise thermal time constant promote blood circulation effect. We also found that space arrangement of the heating lines was an important factor in designing heating parts and both coefficient of heat conduction and density of the heating plate should be also considered for superimpose of thermal diffusion.

Characteristics of Membrane Permeability on the Separation of Solid in a Liquid Livestock Manure (축분액비의 고액분리에 있어서 분리막의 투과특성)

  • 황명구;차기철;이명규
    • Journal of Animal Environmental Science
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    • v.6 no.3
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    • pp.175-184
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    • 2000
  • A lab-scale MF membrane reactor was installed to investigate the membrane permeability, characteristics of membrane fouling at each conditions, and quality of permeate (liquid livestock manure) in the separation of solid-matters using membrane. Experiment was divided three filtration type such as follows; continuous filtration, gravity filtration, and intermittent filtration. As a result of experiment, flux 1 LMH was maintained for 7days, and trans-membrane pressure(TMP) was increased gradually under 10cmHg, but it was increased immediately after 10cmHg, respectively. However, the flux was increased, the Tmax was decreased exponential more and more. During the pure-flux test, most of the fouling of membrane was reversible. At the gravity filtration, permeate could be obtained as 1.75 LMH for 3.5days without any other electronic pressure. As an investigation of membrane surface, this study could be decided that the reason of fouling at the lower flux (Run 1 and 2) was attached matters in membrane surface, but at the higher flux (Run 4-6) was concentration polarization.

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Pressure drop and heat transfer characteristics of a flat-plate solar collector with heat transfer enhancement device (열전달 향상 장치에 따른 평판형 태양열 집열기의 압력강하 및 열전달 특성)

  • Ahn, Sung-Hoo;Shin, Jee-Young;Son, Young-Seok
    • Journal of Advanced Marine Engineering and Technology
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    • v.37 no.5
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    • pp.453-460
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    • 2013
  • The surface roughness and heat transfer enhancement devices are known to increase the performance of a flat plate soar collector. This study includes the experiments on the effect of the several heat transfer enhancement devices inserted in duct to simulate the flat-plate solar collector. Experiment was basically at a constant heat flux on the upper duct wall. Inserted heat transfer enhancement devices are Chamfered rib $10^{\circ}$, Chamfered rib $20^{\circ}$, Rib & Groove and Rib & Dimple. Reynolds number is in the range of 2,300 to 22,000 which corresponds to turbulent regime. With the heat transfer enhancement devices, heat transfer would increase by the secondary flow and the increase of the heat transfer area. Pressure drop also increases with the insertion of the enhancement devices. Rib & Dimple model is the best in heat transfer enhancement, however, Chamfered rib $10^{\circ}$ model is the lowest in the pressure drop. Considering the heat transfer enhancement simultaneously with low pressure drop increase, performance factor was the best for the Chamfered rib $10^{\circ}$.

The Effect of Impact Velocity on Droplet-wall Collision Heat Transfer Above the Leidenfrost Point Temperature (Leidenfrost 지점 온도 이상에서 액적-벽면 충돌 열전달에 대한 충돌 속도의 영향)

  • Park, Jun-seok;Kim, Hyungdae;Bae, Sung-won;Kim, Kyung Doo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.39 no.7
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    • pp.567-578
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    • 2015
  • Single droplet-wall collision heat transfer characteristics on a heated plate above Leidenfrost temperature were experimentally investigated considering the effects of impact velocity. The collision characteristics of the droplet impinged on the heated wall and the changes in temperature distribution were simultaneously measured using synchronized high-speed video and infrared cameras. The surface heat flux distribution was obtained by solving the three-dimensional transient heat conduction equation for the heated substrate using the measured surface temperature data as the boundary condition for the collision surface. As the normal impact velocity increased, heat transfer effectiveness increased because of an increase in the maximum spreading diameter and a decrease in the vapor film thickness between the droplet and heated wall. For We < 30, droplets stably rebounded from a heated wall without breakup. However, the droplets broke up into small droplets for We > 30. The tendency of the heat transfer to increase with increasing impact velocity was degraded by the transition from the rebounding region to the breakup region; this was resulted from the reduction in the effective heat transfer area enlargement due to the breakup phenomenon.

Investigation of Convective Heat Transfer Characteristics of Aqueous SiO2 Nanofluids under Laminar Flow Conditions (층류유동 조건에서 SiO2 나노유체의 대류 열전달 특성에 대한 연구)

  • Park, Hyun-Ah;Park, Ji-Hyun;Jeong, Rag-Gyo;Kang, Seok-Won
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.17 no.9
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    • pp.1-11
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    • 2016
  • The effect of the migration of nanoparticles near the wall of a channel on the convective heat transfer in a laminar flow of $SiO_2$ nanoparticle suspensions (nanofluids) under constant wall heat flux boundary conditions was numerically and experimentally investigated in this study. The dynamic thermal conductivity of the aqueous $SiO_2$ nanofluids was measured using T-type thermocouples attached to the outer surface of a stainless steel circular tube (with a length of 1 m and diameter of 1.75 mm). The nanofluids used in this study were synthesized by dispersing $SiO_2$ spherical nanoparticles with a diameter of 24 nm in de-ionized water (DIW). The enhancement of the thermal conductivity of the nanofluids (e.g., an increase of up to 7.9 %) was demonstrated by comparing the temperature profiles in the flow of the nanofluids with that in the flow of the basefluids (i.e., DIW). However, this trend was not demonstrated in the computational analysis, because the numerical models were based on continuum assumptions and flow features involving nanoparticles in a stable colloidal solution. Thus, to explore the non-continuum effects, such as the modification of the morphology caused by nanoparticle-wall interactions on the heat exchanging surfaces (e.g., the isolated and dispersed precipitation of the nanoparticles), additional experiments were performed using DIW right after the measurements using the nanofluids.

[Retracted]Evaluation of Early Suppression-Fast Response (ESFR) Sprinklers in Facilities and Residences for Elderly People ([논문철회]노인관련시설에서 조기반응형 스프링클러헤드의 유용성)

  • Choi, Young-Sang;Gong, Ye-Rin;Kong, Ha-Sung
    • Fire Science and Engineering
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    • v.29 no.4
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    • pp.15-20
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    • 2015
  • This study compared, through a fire simulation, temperature changes of the smoke layer and the air layer, and height fluctuations of the smoke layer, according to the sprinkler head installation and non-installation, and the sprinkler head types in elderly-care facilities. When a standard response sprinkler worked, the radiant heat exceeded the conditions for the occurrence of flashover. However the ESFR sprinkler prevented flashover. When the early response head worked, inhabitants were not damaged by radiant heat because the maximum value of the heat flux remained $2,293W/m^2$, which is less then the burn hazard criterion of $4,000W/m^2$. The highest temperature of the room when fire occurred exceeded the safety standard in all of the smoke layer and the air layer, but the highest temperature was kept below the safety standard after it fell down rapidly. Because the height of the smoke layer was maintained above 1.1 m when the early response sprinkler worked, the falling of the smoking layer was much more delayed than in the case where the standard response sprinkler was used.

Characteristics of Wall Pressure over Wall with Permeable Coating (침투성 코팅 처리된 벽면 주위의 벽 압력 특성)

  • Song, Woo-Seog;Shin, Seung-Yeol;Lee, Seung-Bae
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.11
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    • pp.1055-1063
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    • 2012
  • Fluctuating wall pressures were measured using an array of 16 piezoelectric transducers beneath a turbulent boundary layer. The coating used in this experiment was an open-cell, urethane-type foam with a porosity of approximately 50 ppi. The ultimate objective of the coating is to provide a mechanical filter to reduce the wall pressure fluctuations. The boundary layer on the flat plate was measured by using a hot wire probe, and the CPM method was used to determine the skin friction coefficient. The wall pressure autospectra and streamwise wavenumber-frequency spectra were compared to assess the attenuation of the wall pressure field by the coating. The coating is shown to attenuate the convective wall pressure energy. However, the relatively rough surface of the coating in this investigation resulted in a higher mean wall shear stress, thicker boundary layer, and higher low-frequency wall pressure spectral levels compared to a smooth wall.

Measurement of Average Pool Boiling Heat Transfer Coefficient on Near-Horizontal Tube (수평 가까운 튜브 표면의 평균 풀비등 열전달계수의 측정)

  • Kang, Myeong-Gie
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.1
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    • pp.81-88
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    • 2014
  • An experimental study is performed to obtain an average heat transfer coefficient around the perimeter of a near horizontal tube. For the test a stainless steel tube of 50.8 mm diameter submerged in water at atmospheric pressure is used. Both subcooled and saturated pool boiling conditions are considered and the inclination angle of the tube is changed from the horizontal position to $9^{\circ}$ in steps of $3^{\circ}$. In saturated water, the local boiling heat transfer coefficient at the azimuthal angle of $90^{\circ}$ from the tube bottom can be regarded as the average of the coefficients regardless of the tube inclination angles. However, when the water is subcooled the location for the average heat transfer coefficient depends on the inclination angle and the heat flux. It is explained that the major mechanisms changing the heat transfer are closely related with the intensity of the liquid agitation and the generation of big size bubbles through bubble coalescence.

Residual Stress Distribution on the Fillet Weldment used by Finite Element Method (유한요소법을 이용한 필렛용접 이음부의 잔류응력분포)

  • Kim, Hyun Sung;Woo, Sang Ik;Jung, Kyoung Sup
    • Journal of Korean Society of Steel Construction
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    • v.12 no.2 s.45
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    • pp.197-207
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    • 2000
  • A transient heat transfer analysis and thermo-elastic analysis have been performed for the residual stress distribution on the fillet weldment used by finite element method. Specimen is fabricated single-pass fillet welding. This computation was performed for conditions including surface heat flux and temperature dependent thermo-physical properties using by heat input as parameter. Also, cut-off temperature of residual stress estimation by thermo-elastic analysis is determined. The fillet weldment were measured to determined their residual stress distributions for using hole-drilling method. As result, it was found that large tensile residual stress is about material yield strength, and the numerical simulation results for finite element method similar to residual stresses by hole-drilling method and other exiting research. Also, cut-off temperature is effectively determined by temperature which calculated maximum thermal stress equal to material yield strength.

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