• Title, Summary, Keyword: convection

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Computational Simulation of Heat flow phenomena in Newly Designed Heat Sinks (뉴 디자인된 히트싱크의 열 유동 현상 컴퓨터 시뮬레이션)

  • Lim Song Chul;Choi Jong Un;Kang Kae Myung
    • Korean Journal of Materials Research
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    • v.14 no.11
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    • pp.775-779
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    • 2004
  • 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.

Bifurcation to Chaotic Thermal Convection in a Horizontal Annulus (수평 환형 공간에서의 혼돈 열대류로의 분기)

  • Yoo, Joo-Sik;Kim, Yong-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.24 no.9
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    • pp.1210-1218
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    • 2000
  • Thermal convection in a horizontal annulus is considered, and the bifurcation phenomena of flows from time-periodic to chaotic convection are numerically investigated. The unsteady two-dimensional streamfunction-vorticity equation is solved with finite difference method. As Rayleigh number is increased, the steady flow bifurcates to a time-periodic flow with a fundamental frequency, and afterwards a period-tripling bifurcation occurs with further increase of the Rayleigh number. Chaotic convection is established after a period-doubling bifurcation. A periodic convection with period 4 appears after the first chaotic convection. At still higher Rayleigh numbers, chaotic flows reappear.

Influence of thermo-physical properties on solutal convection by physical vapor transport of Hg2Cl2-N2 system: Part I - solutal convection

  • Kim, Geug-Tae;Kim, Young-Joo
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.20 no.3
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    • pp.125-132
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    • 2010
  • For typical governing dimensionless parameters of Ar = 5, Pr = 1.16, Le = 0.14, Pe = 3.57, Cv = 1.02, $Gr_s=2.65{\times}10^6$, the effects of thermo physical properties such as a molecular weight, a binary diffusivity coefficient, a partial pressure of component B on solutally buoyancy-driven convection (solutal Grashof number $Gr_s=2.65{\times}10^6$) are theoretically investigated for further understanding and insight into an essence of solutal convection occurring in the vapor phase during the physical vapor transport of a $Hg_2Cl_2-N_2$ system. The solutally buoyancy-driven convection is significantly affected by any significant disparity in the molecular weight of the crystal components and the impurity gas of nitrogen. The solutal convection in a vertical orientation is found to be more suppressed than a tenth reduction of gravitational accelerations in a horizontal orientation. For crystal growth parameters under consideration, the greater uniformity in the growth rate is obtained for either solutal convection mode in a vertical orientation or thermal convection mode in horizontal geometry. The growth rate is also found to be first order exponentially decayed for $10{\leq}P_B{\leq}200$ Torr.

Lead bromide crystal growth from the melt and characterization: the effects of nonlinear thermal boundary conditions on convection during physical vapor crystal growth of mercurous bromide

  • Geug-Tae Kim;Moo Hyun Kwon
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.14 no.4
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    • pp.160-168
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    • 2004
  • We investigate the effects of solutal convection on the crystal growth rate in a horizontal configuration for diffusive-convection conditions and purely diffusion conditions achievable in a low gravity environment for a nonlinear thermal gradient. It is concluded that the solutally-driven convection due to the disparity in the molecular weights of the component A $(Hg_2Br_2)$ and B (CO) is stronger than thermally-driven convection for both the nonlinear and the linear thermal profiles, corresponding to $Gr_t= 8.5{\times}10^3,\; Gr_s = 1.05{\times}10^5$. For both solutal and thermal convection processes, the growth rates for the linear thermal profile (conducting walls) are greater than for the nonlinear case. With the temperature humps, there are found to be observed in undersaturation for diffusive-convection processes ranging from $D_{AB}$ = 0.087 to 0.87. For the vertical configurations, the diffusion mode is so much dominated that the growth rate and interfacial distribution is nearly regardless of the gravitational accelerations. Also, the diffusion mode is predominant over the convection for the gravity levels less than 0.1 $g_0$ for the horizontally oriented configuration.

Preliminary Studies on Double-Diffusive Natural Convection During Physical Vapor Transport Crystal Growth of Hg2Br2 for the Spaceflight Experiments

  • Ha, Sung Ho;Kim, Geug Tae
    • Korean Chemical Engineering Research
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    • v.57 no.2
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    • pp.289-300
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    • 2019
  • We have conducted a preliminary numerical analysis to understand the effects of double-diffusive convection on the molar flux at the crystal region during the growth of mercurous bromide ($Hg_2Br_2$) crystals in 1 g and microgravity (${\mu}g$) conditions. It was found that the total molar fluxes decay first-order exponentially with the aspect ratio (AR, transport length-to-width), $1{\leq}AR{\leq}10$. With increasing the aspect ratio of the horizontal enclosure from AR = 1 up to Ar = 10, the convection flow field shifts to the advective-diffusion mode and the flow structures become stable. Therefore, altering the aspect ratio of the enclosure allows one to control the effect of the double diffusive natural convection. Moreover, microgravity environments less than $10^{-2}g$ make the effect of double-diffusive natural convection much reduced so that the convection mode could be switched over the advective-diffusion mode.

Experimental Study on Coefficient of Flow Convection (유수대류계수에 관한 실험적 연구)

  • 정상은;오태근;양주경;김진근
    • Proceedings of the Korea Concrete Institute Conference
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    • pp.297-302
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    • 2000
  • Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structure, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection is developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect in internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. finally a prediction model of the coefficient of flow convection is proposed using experimental results from the developed device. According to the proposed prediction model, the coefficient of flow convection increases with increase in flow velocity and decreases with increase in pipe diameter and thickness. Also, the coefficient of flow convection is largely affected by the type of pipe materials.

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The Natural Convection in Horizontal Porous Layer with Vertical or Horizontal Throughflow (수직$\cdot$수평 관통류를 갖는 수평 다공층에서 자연대류 연구)

  • Seo S. J.;Park C. K.
    • Journal of computational fluids engineering
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    • v.3 no.1
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    • pp.73-81
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    • 1998
  • The effect of vertical or horizontal throughflow on natural convection in horizontal porous layer was investigated. The computations were performed by employing Darcy-Brinkman-Forchheimer equation to consider the effect of inertia and viscous effect. The patterns of streamlines and isotherms are observed by changing the strength of throughflow. The vertical throughflow stabilizes the natural convection in porous layer. It also disturbs the developing vertical and horizontal velocity component of natural convection cell and increases the critical modified Rayleigh number. The horizontal throughflow influences the stabilization of natural convection in porous layer much more than the vertical throughflow. And it changes a stable convection into a oscillatory convection.

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Topological Optimization of Heat Dissipating Structure with Forced Convection (강제 대류를 통한 열소산 구조물의 위상최적화)

  • Yoon, Gil-Ho
    • Proceedings of the KSME Conference
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    • pp.408-409
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    • 2008
  • This paper presents a new development for topology optimization of heat-dissipating structure with forced convection. To cool down electric devices or machines, two types of convection models have been widely used: Natural convection model with a large Archimedes number and Forced convection with a small Archimedes number. Nowadays, many engineering application areas such as electrochemical conversion device or fuel cell devices adopt the forced convection to transfer generated heat. Therefore, to our knowledge, it becomes an important issue to design flow channels inside which generated heat transfer. Thus, this paper studies optimal topological designs considering fluid-heat interaction. To consider the effect of the advection in the heat transfer problem, the incompressible Navier-stokes equation is solved. This paper numerically studies the coupling phenomena and presents optimal channel design considering forced convection.

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UNIQUENESS OF IDENTIFYING THE CONVECTION TERM

  • Cheng, Jin;Gen Nakamura;Erkki Somersalo
    • Communications of the Korean Mathematical Society
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    • v.16 no.3
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    • pp.405-413
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    • 2001
  • The inverse boundary value problem for the steady state heat equation with convection term is considered in a simply connected bounded domain with smooth boundary. Taking the Dirichlet to Neumann map which maps the temperature on the boundary to the that flux on the boundary as an observation data, the global uniqueness for identifying the convection term from the Dirichlet to Neumann map is proved.

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A Quantitative Visualization of Mixed Convection in Parallel Plates Using PIV (PIV를 이용한 평행평판 내의 혼합대류의 정량적 가시화)

  • 박일용;배대석
    • Journal of the Korean Society of Marine Engineering
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    • v.28 no.3
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    • pp.509-515
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    • 2004
  • The PIV(Particle Image Velocimetry) with liquid crystal tracers is used for visualizing and analysis of the mixed convection in the parallel plates with the upper part cooled and the lower part heated. It is found that the flow pattern of mixed convection in the parallel plates can be classified into three patterns which was affected by Reynolds number. Also, the periodic nature is confirmed, and visualized in experiment.