Effects of rheology and mantle temperature structure on edge-driven convection: Implications for partial melting and dynamic topography

Kim, Dae-Hee,So, Byung-Dal Elsevier 2020 Physics of the earth and planetary interiors Vol.303 No.-

<P><B>Abstract</B></P> <P>Edge-driven convection, which affects partial melting, intraplate volcanism, and dynamic topography, is small-scale convection that occurs along a lithospheric keel with a sharp contrast in lithospheric thickness. Various factors, including Rayleigh number, lateral mantle temperature heterogeneity, and geometry of the keel, influence the edge-driven convection, and the correlation between edge-driven convection and surface expressions (dynamic topography and volcanism) is complicated. We performed a finite element study to quantify the effects of these factors on dynamic topography and partial melting. We found that the dynamic topography is more prominent when a strong edge-driven convection cell develops, which corresponds to homogeneous mantle temperatures and the absence of mantle wind. In contrast, the development of edge-driven convection cells and dynamic topography near the lithospheric keel are hindered when the mantle temperature is strongly heterogeneous (laterally varying ~280 K). This indicates that a large lateral contrast in mantle temperature results in a strong mantle wind that may prevent the development of edge-driven convection cells. An increase in the Rayleigh number results in more vigorous convection and enhances partial melting. Our study shows that the location of volcanic activity at craton edges and passive margins can be reproduced in models with weakly heterogeneous mantle temperature for given mantle viscosity. The existence of a strong mantle wind (e.g., related to subducting slabs or mantle plumes) may inhibit the formation of an edge-driven convection cell and its related partial melt near a lithospheric keel. However, mantle conditions with weak temperature heterogeneity (<~14 K) or high mantle viscosity (>17×10<SUP>19</SUP> Pa∙s), which corresponds to the Rayleigh number of 1.8×10<SUP>6</SUP>, do not induce partial melts despite the development of edge-driven convection cells. Our model parametrized the condition and location of edge-driven convection cells and partial melts, which can contribute to understanding anomalous intraplate volcanisms, such as in Jeju Island south of the Korean Peninsula and the Tanzania Craton near the East African Rift.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Small lateral thermal heterogeneity causes localized edge-driven convention. </LI> <LI> Topography increases and decreases due to upwelling and downwelling of EDC, respectively. </LI> <LI> Thermal heterogeneity has promoting and suppressing effects on partial melting at lithospheric edge. </LI> <LI> Strong mantle wind prevents the localization of mantle partial melting near lithospheric edge. </LI> <LI> Strict range of thermal heterogeneity is needed for partial melting at lithospheric edge. </LI> </UL> </P>

A Study on the Convective Cooling Performance of the Secondary Battery in Electric Vehicle

이동렬(Dong-Ryul Lee) Korean Society for Precision Engineering 2018 한국정밀공학회지 Vol.35 No.12

This study is to investigate convection cooling performance of the Secondary Battery of Electric Vehicle without heat sink. Research is focused on the comparative study on cooling between forced convection and natural convection cooling. Selected local locations for various temperature distributions had shown in the flow domain. Final temperature on the cell surface has been compared by forced convection with natural convection. According to the results of velocity and temperature distributions in the fluid domain, Buoyancy appear by density difference in the natural convection. Apparent vortex was detected in the fluid domain for forced convection. According to calculations of convective heat transfer coefficient between cell and atmosphere in the battery pack, average value of more 70-78% heat transfer coefficient increased by forced convection than natural convection. Average temperature value of the cell surface decreased up to 46.50% by forced convection. Due to vortex by air, cooling performance of forced convection is excellent. In addition, cooling on edge of the battery is better than heat source location.

Numerical analysis of Poiseuille-Rayleigh-Bénard convection in supercritical carbon dioxide

Wang Zhipeng,Xu Hong,Chen Chong,Hong Gang,Song Zhenguo,Zhang Yaoli 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.9

The supercritical carbon dioxide (SeCO2) Brayton cycle is an important energy conversion technology for the fourth generation of nuclear energy. Since the printed circuit heat exchanger (PCHE) used in the SeCO2 Brayton cycle has narrow channels, Rayleigh-Benard (RB) convection is likely to exist in the tiny channels. However, there are very few studies on RB convection in supercritical fluids. Current research on RB convection mainly focuses on conventional fluids such as water and air that meet the Boussinesq assumption. It is necessary to study non-Boussinesq fluids. PRB convection refers to RB convection that is affected by horizontal incoming flow. In this paper, the computational fluid dynamics simulation method is used to study the PRB convection phenomenon of non-Boussinesq fluid-supercritical carbon dioxide. The result shows that the inlet Reynolds number (Re) of the horizontal incoming flow significantly affects the PRB convection. When the inlet Re remains unchanged, with the increase of Rayleigh number (Ra), the steady-state convective pattern of the fluid layer is shown in order: horizontal flow, local traveling wave, traveling wave convection. If Ra remains unchanged, as the inlet Re increases, three convection patterns of traveling wave convection, local traveling wave, and horizontal flow will appear in sequence. To characterize the relationship between traveling wave convection and horizontal incoming flow, this paper proposes the relationship between critical Reynolds number and relative Rayleigh number (r).

자연대류와 강제대류에서 펠티에 소자를 이용한 내부터널 구조를 가지는 히트싱크에 관한 연구

이민(Lee, Min),김태완(Kim, Tae-Wan) 한국산학기술학회 2014 한국산학기술학회논문지 Vol.15 No.7

펠티에 소자는 전자부품이나 장비에서 발생하는 열을 냉각하기 위한 방법으로 많이 사용되고, 히트싱크는 이러한 열을 외부로 방출하기 위한 방법으로 많이 사용되고 있다. 본 연구에서는 내부터널의 형상을 가지는 히트싱크에 대한 냉각 및 히팅성능을 자연대류와 강제대류 상태에서 열전달 특성에 대하여 고찰하였다. 또한, 시간에 따른 히트싱크의 열전달 특성 및 온도분포의 변화에 따른 실험을 수행하였고, 자연대류와 강제대류에 따른 히트싱크의 열전달 특성, 온도분포의 변화를 실험을 통해 비교 연구 하였다. 냉각 실험에서 A형상 및 B형상 냉각 핀 히트싱크는 자연대류보다는 강제대류에서 온도가 더 감소하는 것을 알 수가 있었고, 강제대류와 자연대류에서 A, B형상 모두 -15℃까지 떨어지는 것을 알 수 있었다. 전압이 증가 할수록 강제대류와 자연대류 상태에서 A, B형상 냉각 핀 히트싱크 모두 온도가 감소하였다. 히팅실험에서 A형상 및 B형상 냉각 핀 히트싱크는 자연대류보다는 강제대류에서 온도가 더 증가하는 것을 알 수가 있었고, 강제대류와 자연대류에 서 전압이 13V일 때, A형상 냉각 핀 히트싱크는 전압이 150℃, 강제대류에서 B형상 냉각 핀 히트싱크는 145℃까지 증가 하였다. 전압이 증가할수록 강제대류와 자연대류 상태에서 A, B형상 냉각 핀 히트싱크 모두 온도가 증가하였다. The Peltier Module has been used to dissipate the heat from electronic devices and electronic components. In this module, a heat sink is used to release the operating heat into the air outside. This study addressed the heat transfer characteristics for a heat sink with an inner tunnel. Under forced and natural convection conditions, the heat transfer characteristics were different. Therefore, the cooling and heating performances were studied for the heat sink, which has an inner tunnel. The heat transfer conditions were also evaluated by performing an experimental test, which investigated the heat transfer characteristics related to the variance in time and temperature distribution. Experiments on the heat transfer characteristics of the heat sink were conducted based on the forced and natural convection and temperature distribution changes. In the cooling experiment, the A- and B-shaped cooling pin heat sinks decreased the temperature of the forced convection than the temperature of natural convection. In the forced and natural convection, the A- and B-shaped decreased to a minimum of -15°C. Under the forced and natural convection conditions, A- and B-shaped cooling pin heat sinks decreased the temperature when the voltage was increased. In the heating experiment, the A- and B-shaped cooling pin heat sinks increased the temperature of the forced convection than the temperature of natural convection. In forced convection, when the voltage was 15°C, the temperature of the A-shaped cooling pin heat sink increased to 150℃, and the temperature of the B-shaped cooling pin heat sink increased to 145℃. Under forced and natural convection conditions, the A- and B-shaped cooling pin heat sinks showed an increase in temperature with increasing voltage.

대류와 복사 열원에 대한 특수방화복의 열보호 성능시험 비교

김해형,유승준,박평규,김영수,홍승태 한국화재소방학회 2017 한국화재소방학회논문지 Vol.31 No.2

The test methods using convection (flame) and radiation heat sources were compared to evaluate the thermal protectiveperformance of the firefighter’s protective clothing. In particular, the influence of the outer shell, mid-layer, and liningconstituting the firefighter’s protective clothing on the thermal protective performance was compared for convection andradiation heat sources. Tests for the thermal protective performance were carried out according to KS K ISO 9151(convection), KS K ISO 6942 (radiation), and KS K ISO 17492 (convection and radiation). When tested under the sameincident heat flux conditions (80 kW/m2), the heat transfer index (t12 and t24) for the radiation heat source was higher thanthat for the convection heat source. This means that radiation has a lesser effect than convection. For the convection heatsource, the lining had the greatest effect on the thermal protective performance, followed by the mid-layer and the outer shell. On the other hand, for the radiation heat source, the effect on the thermal protective performance was great in the order oflining, outer shell, and mid-layer. Convection and radiation have fundamentally different mechanisms of heat transfer, anddifferent heat sources can lead to different thermal protective performance results depending on the material composition. Therefore, to evaluate the thermal protective performance of the firefighter’s protective clothing, it is important to test not onlythe convection heat source, but also the radiation heat source. 소방용 특수방화복의 열보호 성능 평가를 위해 대류와 복사 열원을 이용한 시험방법을 비교하였다. 특히 특수방화복을 구성하는 겉감, 중간층, 안감이 각각 열보호 성능에 미치는 영향을 대류와 복사 열원에 대해 비교하였다. 대류 열원에 대한 열보호 성능시험은 KS K ISO 9151, 복사 열원에 대한 시험은 KS K ISO 6942 그리고 대류와 복사열원을 함께 사용하는 시험은 KS K ISO 17492의 방법에 따라 수행하였다. 같은 입사 열유속 조건(80 kW/m2)에서시험했을 때 대류 열원에 비해 복사 열원에 대한 열전달지수(t12, t24) 값이 보다 크게 나왔다. 이는 대류에 비해 복사에 의한 영향이 느리게 나타났음을 의미한다. 대류 열원에 대해서는 안감이 열보호 성능에 가장 크게 영향을 미쳤고이어서 중간층, 겉감 순서였다. 그러나 복사 열원에 대해서는 안감, 겉감, 중간층 순서로 열보호 성능에 미치는 영향이 컸다. 대류와 복사는 열전달 메카니즘이 근본적으로 다르며, 열원이 달라지면 재질 구성에 따라 열보호 성능 결과가 다르게 나올 수 있다. 따라서 특수방화복의 열보호 성능을 평가하기 위해서는 대류 열원 뿐만 아니라 복사 열원에대한 시험도 중요함을 확인하였다.

해륙풍 원리를 효과적으로 이해하기 위한 대류실험상자의 개발 및 적용

서혜리,박일우 한국현장과학교육학회 2017 현장과학교육 Vol.11 No.2

The purpose of this study is to improve and present the convection experiment box to understand the principle of the land and sea breeze effectively and to apply it to science lessons. Based on a survey of teachers' perceptions of convection experiments, we have improved the convection experiment box in three aspects: the structure of the convection box, the visualization of the convection flow, and the application of the inquiry functions. For the verification of the revised experiment, 84 fifth graders of four classes in Seoul were applied to two classes for experimental group and two classes for comparative group to evaluate the usefulness of the improved convection experiment box and the effectiveness of teaching and learning of convection. The results showed that the students’understanding level of the land and sea breeze in the experimental group was significantly higher than that in the comparative one. Both teachers who observed the lessons and the students responded to the questionnaire asking the usefulness of the improved convection experiment box that the improved experiment box was more effective than that in the current 2009 revised textbook. The improved experiment box can help students understand better the land and see breeze principle. Also, teachers expect that this improved experiment box can increase students interest and use inquiry skills as well as be utilized with ease in the lessons. 본 연구는 해륙풍 원리를 효과적으로 이해할 수 있도록 대류실험상자를 개선하여 제작하고, 이를 수업에 적용하는 데에 목적이 있다. 연구를 위해 대류실험에 대한 교사들의 인식을 조사하고, 이를 바탕으로 대류실험상자의 구조, 대류 흐름의 시각화, 탐구 기능의 활용의 3가지 측면에서 대류실험상자를 개선하였다. 개선된 실험의 효과를 검증하기 위해 서울 소재 초등학교 5학년 4개 학급 총 84명을 각각 2개의 실험반과 비교반으로 선정하였고, 해륙풍 관련 개념 검사와 실험에 대한 설문조사를 실시하였다. 학생들에게 적용한 결과, 실험반의 해륙풍 관련 개념의 이해 정도가 비교반에 비해 유의하게 높았다. 개선된 대류실험상자에 대한 평가를 묻는 설문 조사에서 학생들은 해륙풍 원리 이해에 효과적인 것으로 조사되었다. 참관 교사들은 학생들의 흥미, 탐구 기능 활용 정도, 준비의 편리성 등의 측면에서 개선된 실험이 효과적이라고 응답하였다.

뉴 디자인된 히트싱크의 열 유동 현상 컴퓨터 시뮬레이션

임송철,최종운,강계명,Lim Song Chul,Choi Jong Un,Kang Kae Myung 한국재료학회 2004 한국재료학회지 Vol.14 No.11

For improvement of heat dissipation performance, heat analysis is conducted on the newly designed heat sinks under two convection conditions by using computational fluid dynamics(CFD). Three types of heat sink, plate, wave and top vented wave, are used, and convection conditions are the variations of gravity direction at natural convection and of fan location at forced convection. The results of analysis showed that the heat resistances of top vented wave heat sink were $0.17^{\circ}C$/W(forced convection) and $0.48^{\circ}C$/W(natural convection). In the case of natural convection, gravity direction affected heat flow change, and protection against heat performance was superior in case of z-axis gravity direction. Under the forced convection, all the heat sinks revealed superior thermal characteristics in the fan position of z-axis rather than y-axis. In this study, it was observed that the top vented wave type heat sink showed the best ability of heat radiation comparing with the others.

대류실험 장치의 개발 및 활용

김태규 한국물리학회 2018 새물리 Vol.68 No.1

A convectional experiment apparatus has been developed so that convective experiments can be performed normally in the science class. The apparatus is composed of a convection box, a light source box, the object, and a smoke box with an incense stick. The reproducibility of convective experiments was ensured by them controlling the variables and quantifying the measured values. The characteristics of the smoke flowing from the incense stick depended on the size of convection box, the spacing of objects, and the height, position and depth of the ember of the incense stick. Those characteristics were also affected by the flow speed of rising smoke and the differences between the surface temperature of the objects and the temperature inside the convection box. Changes in those characteristics and in the direction of smoke flow, in particular a reversal of direction, with changing surface temperature of the objects were continuously measured. The experimental convection device developed in this study can be utilized in experiments related to convection. 대류실험을 교육 현장에서 정상적으로 실시할 수 있도록 대류실험 장치를 개발하였다. 장치는 크기를 변화시킬 수 있는 대류상자, 대류상자 내부를 비추는 광원상자, 표면 온도를 변화시킬 수 있는 물체 및 선향 연기의 유량 및 유속을 조절할 수 있는 선향 연기 상자로 구성되어 있다. 변인의 통제 및 측정값의 계량화로 정량적인 실험을 수행하여, 대류실험의 재연성을 확보하였다. 선향 연기 흐름의 기울어짐은 대류상자의 가로, 세로 및 높이, 선향 불씨의 높이, 위치 및 깊이에 의존하였다. 또한 상승하는 선향 연기의 유속 뿐 만 아니라 물체와 대류상자 내부의 온도차도 선향 연기 흐름의 기울어짐에 영향을 주었다. 물체의 표면 온도의 변화에 따라서, 선향 연기 흐름의 기울어짐이 변하고 선향 연기 흐름의 방향이 역전되는 과정을 연속적으로 측정하였다. 본 연구에서 개발된 대류실험 장치를 대류와 관련된 실험에서도 활용할 수 있다.

A numerical study on the buoyancy effect around slanted-pin fins mounted on a vertical plate (Part-II: Laminar mixed convection)

Oh, Yeong Woong,Choi, Yoon Suk,Ha, Man Yeong,Min, June Kee Elsevier 2019 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.132 No.-

<P><B>Abstract</B></P> <P>This paper presents a numerical study on the mixed convection heat transfer of slanted-pin fins mounted on a vertical heated wall for the laminar flow regime, which is an extension of the authors’ accompanying study (Oh et al. 2018) on the natural convection. Using the ideal gas assumption for the air, three-dimensional governing equations for fluid flow and heat transfer were calculated by imposing a periodic boundary condition in the horizontal lateral direction with the SIMPLE algorithm. The discrete ordinate method was also included to calculate the effect of radiation. The effects of the fin-inclination angle were investigated in a modified Richardson number range of 500–2500 by varying the Reynolds number at a fixed Grashof number. It was found that as the forced convection increases, the fin-inclination angle showing the best heat transfer performance changes from negative to positive fin angles. The critical Richardson number for this transition and the corresponding flow and heat-transfer characteristics in the mixed convection regime are summarized.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The aero-thermal performance of slanted-pins on a vertical wall are examined. </LI> <LI> The mixed convection heat transfer is studied numerically. </LI> <LI> The modified Richardson number is varied in a laminar flow regime. </LI> <LI> The fin-inclination angle showing the best performance is captured. </LI> <LI> Differences from the forced- and natural- convection results are assessed. </LI> </UL> </P>

Differences in the Tropical Convective Activities at the Opposite Phases of the Quasi-Biennial Oscillation

이진행,강민지,전혜영 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.3

Differences in convective activities in the tropical region (30°S–30°N, 180°E–180°W) during different phases of the quasibiennial oscillation (QBO) are investigated over 32 years (1979–2010) using five metrics representing tropical convection: (i) precipitation and (ii) outgoing longwave radiation from observations and (iii) convective available potential energy (CAPE), (iv) deep convective heating rate, and (v) convective cloud top pressure from reanalysis data. The easterly (QBOE) and westerly (QBOW) phases of the QBO are defined using the zonal wind anomaly from the monthly climatology at 50 hPa. During the QBOE (QBOW), the convective activities are intensified (weakened) over the Maritime Continent and weakened (intensified) over the equatorial eastern and central Pacific. Therefore, the zonal mean values of the five metrics averaged over chronically convective regions show stronger convective activities during the QBOE than during the QBOW, while the opposite is true for the whole tropical region. Composite analyses are also performed during the neutral, El Niño, and La Niña periods. In the neutral period, the convective activities during QBOE are stronger than during QBOWexcept in the equatorial region (10°S–10°N). The convective activities over the Maritime Continent (central and eastern Pacific) are enhanced when La Niña and the QBOE (El Niño and the QBOW) occur simultaneously. All metrics show similar pattern to one another, implying that the metrics from reanalysis data represent the variations in the convective activities with respect to the QBO reasonably well. Among the five metrics, the CAPE is most sensitive to the QBO phase, likely because the virtual temperature in the upper troposphere is modulated by anomalous meridional circulations induced by different QBO phases.