• Solar Energy
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• v.18 no.2
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• pp.123-135
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• 1998

The effect of the thermal conductivity of a centered, square, heat-conducting body on natural convection In a square enclosure was examined numerically. Numerical simulations was carried out for Pr=0.17, $Ra=1.0{\times}10^4,\;1.0{\times}10^5,\;1.0{\times}10^6$, $K^*$=1.0, 6.6, 34.0 and t=0.5, 1.0, 2.0. The results were reported in terms of streamlines, isotherms, Nusselt number. As the results, the mean Nusselt number increases with the increasing of ${\zeta}$ at a constant Ra and $K^*$. In the case of ${\zeta}=1.0$(obstruction shape ratio), the mean Nusselt numbers were decreased as increasing of $K^*$(obstruction thermal conductivity ratio) with regardless of the Rayleigh number. When the constant obstruction size and thermal conductivity ratio, convective heat transfer effect was more enhanced at ${\zeta}=2.0$ than ${\zeta}=0.5$.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.8
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• pp.816-821
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• 2013

This paper reports numerical study results with respect to the thermal performance of various hybrid fins (HFs) and a pin fin (PF) passively cooled under natural convection state. Investigated HFs are a basic hybrid fin (BHF), a hollow hybrid fin (HHF), and a solid hybrid fin (SHF). CFD models for both HFs and the PF have been developed to explore their thermal performance under various heat dissipations. Thermal performances of fins have been analyzed by quantifying array-based heat transfer coefficients, $h_a$, and mass-based heat transfer coefficients, $h_m$, for each fin. Study results show that $h_a$ of the SHF is 23% greater than that of the PF. $h_m$ of the HHF is found to be even 140% greater than that of the PF, and the HHF is found to be 40% better than the BHF in terms of the mass-based performance, $h_{m{\cdot}}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.11
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• pp.935-942
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• 2014

A numerical analysis of the effect of the Prandtl number on the natural convection in a cold outer tilted square enclosure with an inner hot circular cylinder is presented. Several Prandtl numbers (Pr=0.1, 0.7, 7) are considered, with different angles($0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$) for the enclosure and Rayleigh numbers ($Ra=10^3$, $10^4$, $10^5$). The effect of the Prandtl number on the natural convection is analyzed using isotherms and streamline and surface-averaged Nusselt numbers. The flow and heat transfer characteristics are found to be dependent on the time for $Ra=10^5$ and Pr=0.1 at angles of $0^{\circ}$ and $45^{\circ}$. However, in the other cases, the flow and heat transfer characteristics are independent of the time.The surfaceaveraged Nusselt number increases with an increase in the Prandtl number. As the Prandtl number increases, the Nusselt number becomes larger regardless of the angle for $Ra=10^5$. In particular, the Nusselt number steeply increases when the angle is $45^{\circ}$ for $Ra=10^5$ and Pr=0.1.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.13 no.3
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• pp.148-156
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• 1984

The effect of inclination on the steady, two-dimensional, laminar natural convection in rectangular enclosures with localized heating from below has been investigated numerically. The enclosure was uniformly heated with a partial heat source at the center of the bottom wall and cooled from the upper wall while the other walls were insulated. The governing equations were solved numerically by using the ADI finite difference method with the SOR method. The computations were carrid out with air, Pr =0.733, in the Grashof number range, $1\times10^4\~3\times10^4$, for the inclination of the enclosures was varied from $0^{\circ}\;to\;90^{\circ}$. The effects of Grashof number and aspect ratio on the inclination for the transition of the flow pattern in enclosures were determined. From the results, it was found that the transition angles of the flow in the enclosures were greater in localized heating than in uniform heating from below, and that the inclination was to strongly effect on the heat transfer and the flow pattern within the enclosure.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.12
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• pp.1113-1120
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• 2013

A numerical analysis of the effect of the position of a circular cylinder in a $45^{\circ}$ tilted enclosure on natural convection in the enclosure is presented. The location of the cylinder is changed between -0.4 and 0.4. The Rayleigh number is varied between $10^3$ and $10^5$. The effect of the location of the cylinder on natural convection in the enclosure is analyzed by the isothermal line, stream line, and surface-averaged Nusselt number. The flow and heat transfer characteristics are independent of time in the range of the Rayleigh number and cylinder location that is considered in this study. The surface-averaged Nusselt number of the cylinder and enclosure increases as the cylinder gets closer to the wall of the enclosure.

• Journal of the Korean Magnetics Society
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• v.13 no.3
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• pp.127-132
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• 2003

Natural convection of a magnetic fluid is different from that of Newtonian fluids because magnetic-body force exists in addition to gravity and buoyancy. In this paper, natural convection of a magnetic fluids (W-40) in a cubic cavity was examined by experimental method. One side wall was kept at a constant temperature (25 $^{\circ}C$), and the opposite side wall was also held at a constant but lower temperature (20 $^{\circ}C$). The magnetic fields of various magnitude were applied up and down by permanent magnets. We measured temperatures at 5 points which are the most suitable places in cavity by the analysis record. The thermo-sensitive liquid crystal film (R20C5A) was utilized in order to visualize wall-temperature distributions. Several kinds of experiments were carried out in order to clarify the influence of direction and intensity of magnetic fields on the natural convection. It was found that the natural convection of a magnetic fluids could be controlled by the direction and intensity of the magnetic fields.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.04a
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• pp.278-283
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• 2002

Cooling characteristics for the three type spindles with high frequency motor are studied. For the analysis, three dimensional models are built considering heat transfer characteristics such as natural and forced convection coefficients. Unsteady-state temperature distributions and thermal deformations according to the cooling conditions are analyzed by using the finite element method.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2001.10a
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• pp.105-110
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• 2001

Unsteady-state temperature distributions for spindle system with built-in motor according to spindle type are studied. For the analysis, three dimensional model is built considering heat transfer characteristics such as natural and forced convection coefficients. Temperature distributions are analyzed by using the finite element method. Results of analysis are compared.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1737-1746
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• 1991

본 연구에서는 저온의 순수물 속의 등온 수직원기둥에 의해 야기되는 열전달 특성을 구명함에 있어서 짧은 원기둥 범주에 속하는 종횡비 0.5인 얼음 원기둥을 이용 하여 실험적으로 열전달 특성을 구명하였다. 그리고 전 유동장을 가시화 하였으며, 얼음의 융해율로써 누셀트(Nusselt)수를 측정하여 기존의 결과들과 비교검토하였다.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.10a
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• pp.969-974
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• 2002

Thermal characteristics according to the cooling methods are studied for the three type spindles with high frequency motor. For the analysis, three dimensional mode]s are built considering heat transfer characteristics such as natural and force convection coefficients. Unsteady-state temperature distributions and thermal deformations according to the cooling conditions are analyzed by using the finite element method.