• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.928-938
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• 1997

The end winding is an important part in induction motor for thermal analysis. But there is little information on the heat transfer coefficient of that surfaces because of geometrical complexity. So our experimental object is to know the heat transfer coefficient of end winding and find the optimum design parameter of rotor fan. Carbon coated papers were used for a uniform heat generating surfaces which were easy to fabricate. The experiments of some parameters were performed as varying rotation speed of rotor fan. We obtained the local and average Nusselt number of the end winding surfaces by correcting radiation and conduction losses errors. The results showed that the average Nusselt number increased with rotor fan blade number and width but decreased with end winding length. However, the increasing limits existed in the case of rotor fan width and blade number. So optimum design value were obtained for rotor fan width and blade numbers.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.118-125
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• 2004

The experimental study on flow and heat transfer characteristics was conducted to investigate and to compare the performance of swirl jet by a twisted tape as a swirl generator with the performance of impinging single circular jet in fully developed flow tube. The effects of jet Reynolds number(Re=8700, 13800, 20000, 26500), dimensionless distance of nozzle-to-plate(H/d=2, 4, 6, 8) and swirl ratio(S=0.11, 0.23, 0.30) of the jet on the local and average Nusselt number have been examined. Measurements of local heat transfer rate and flow patterns on the jet impinging plate were used naphthalene sublimation technique and flow visualization technique respectively. Mean velocity and turbulence intensity of the jet along the centerline were measured. With a twisted tape in the nozzle exit, average Nusselt number at the around area of stagnation point were higher than those without the twisted tape at H/d=2, 4 and with the increase of Reynolds number. With a twisted tape in the nozzle, in the case of H/d=2, Re=26500 and S=0.11, maximum local Nusselt number at the region of y/d=0 and x/d=0.44 was obtained.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2798-2803
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• 2008

The confined slot air jet impinging normally on a moving flat surface has been investigated numerically by using commercial CFD code Ansys CFX-V11. Turbulent flows are modeled using k-w turbulence model. Two-dimensional turbulent flow is considered. Calculations were conducted for a nozzle-to-plate spacing of eight slot nozzle width, at three Reynolds number(Re=4500, 6700 and 10,000) and four surface-to-velocity ratios i.e. 0, 0.25, 0.5 and 1. Results are compared against corresponding cases for heat transfer from a stationary plate. Local Nusselt number is calculated under constant wall temperature condition. The analysis reveals that the average Nusselt number increases considerably with the jet exit Reynolds number, but decrease with the plate velocity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.529-535
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• 2005

This study experimentally examines the air-side performance of spiral finned tube heat exchangers. The effects of fin spacing, fin height, and tube alignment were investigated. Reduction of fin spacing decreased the Colburn j factor. However, the effect of fin height on the Colburn j factor was negligible. An increase of tube row decreased the Nusselt number for both staggered and in-line tube alignments. However, the decrease of the Nusselt number for the in-line tube alignment was much more significant than that of the staggered tube alignment. The average Nusselt number of the staggered tube alignment was larger than that of the in-line tube alignment by $10\%$ when the Reynolds number ranged from 300 to 1700. An empirical correlation of the Nusselt number was developed by using geometric parameters of heat exchanger and correction factors. The correction factor considered the effects of tube alignment and number of tube rows on the heat transfer. The proposed correlation yielded a mean deviation of $4\%$ from the present data.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.337-342
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• 2006

Natural convection flows in a cubical air-filled cavity that has one pair of opposing faces isothermal at different temperatures, $T_h\;and\;T_c$, respectively, the remaining four faces having a linear variation from $T_c\;to\;T_h$ are numerically simulated by a solution code(PowerCFD) using unstructured cell-centered method. Special attention is paid to three-dimensional flow and thermal characteristics according to the variation of inclination angle $\theta$ of the isothermal faces from horizontal: namely $\theta=0^{\circ},\;15^{\circ},\;30^{\circ},\;45^{\circ},\;50^{\circ},\;60^{\circ},\;75^{\circ}\;and\;90^{\circ}$. Comparisons of the average Nusselt number at the cold face are made with experimental benchmark results found in the literature. It is demonstrated that the average Nusselt number at the cold face has a maximum value around the inclination angle of $50^{\circ}$. It is also found that the code is capable of producing accurately the nature of the laminar convection in a cubical air-filled cavity with differentially heated walls.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.1
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• pp.16-24
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• 2022

A computational study of combined thermal and solutal convection (double diffusive convection) in a sealed crystal growth reactor is presented, based on a two-dimensional numerical analysis of the nonlinear and strongly coupled partial differential equations and their associated boundary conditions. The average Nusselt numbers for the source regions are greater than those at the crystal regions for 9.73 × 10³ ≤ Gr_t ≤ 6.22 × 10⁵. The average Nusselt numbers for the source regions varies linearly and increases directly with the thermal Grashof number form 9.73 × 10³ ≤ Gr_t ≤ 6.22 × 10⁵ for aspect ratio, Ar (transport length-to-width) = 1 and 2. Additionally, the average Nusselt numbers for the crystal regions at Ar = 1 are much greater than those at Ar = 2. Also, the occurrence of one unicellular flow structure is caused by both the thermal and solutal convection, which is inherent during the physical vapor transport of Hg₂Br₂. When the aspect ratio of the enclosure increases, the fluid movement is hindered and results in the decrease of thermal buoyancy force.

• Journal of the Korean Solar Energy Society
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• v.25 no.4
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• pp.101-110
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• 2005

An experimental study of heat transfer of submerged water jet impinging normally on a flat plate is presented. Heat transfer measurements obtained with Reverse cone type nozzle(Rcone) were compared to those obtained with Cone type nozzle(Cone) and Square edged type nozzle(Vert) of the same diameter(D=8mm) for different jet velocities in the range of $3{\sim}7m/s(Re_D=30000{\sim}70000)$ and various nozzle-to target spacings($H/D=2{\sim}10$). The local Nusselt number profiles exhibited a sharp drop for $r/D{\leq}0.5$ and 2nd, 3rd peaks revealed at r/D=2, 3 respectively, followed by a slower decrease there after. The peaks were weakened with increasing the nozzle-to target spacing and decreasing the jet velocity. The stagnation Nusselt number of the Reverse cone type nozzle was larger than those of the other two nozzles for H/D=2. 10, but Cone type nozzle had the highest value for $H/D=4{\sim}8$. Also average Nusselt number of the Reverse cone type nozzle was higher than those of the other two nozzles at $H/D=2{\sim}10$, except for $V_o=7ms$ of H/D=6.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.1
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• pp.61-68
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• 1991

The purpose of this study is to investigate the heat transfer characteristics and the flow structure in the case of rectangular air jet impinging vertically on the flat heating surface. The maximum value of Nusselt number at stagnation point is observed at H/B=10. It is found that this trend has been caused by the effect of stretching of large scale vortex in the stagnation region. For potential core region the Nusselt number distribution in the downstream of the stagnation point decreases gradually and begins to increase at about X/B=3. From the flow visualization it could be seen that small eddy produced from the nozzle edge grows in large scale and that large scale eddy disturbed the thermal boundary layer on the heating plate. The local average Nusselt number becomes maximum at X/B=0.5 regardless of H/B variation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1105-1114
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• 1997

The heat transfer characteristics of free surface water jet impinging normally against a flat uniform heat flux surface were investigated. This deals with the effect of three nozzle configurations (Cone type, Reverse cone type, Vertical circular type) on the local and the average heat transfer. Heat transfer measurements were made for water jet issuing from a nozzle of which exit diameter 8 mm. The experimental conditions investigated are Reynolds number range of 27000 ~ 70000( $V_{O}$=3 ~ 8 m/s), nozzle-to-target plate distances H/D=2 ~ 10, and radial distance from the stagnation point r/D ~ = 0 ~ 7.42. For all jet velocities of H/D=2, the local Nusselt number decreased monotonically with increasing radial distance. However, for H/D from 4 to 10, and for the jet velocity $V_{O}$.geq.7 m/s for Cone type nozzle and $V_{O}$.geq.6 m/s for the other type nozzles, the Nusselt number distributions exhibited secondary peaks at r/D=3 ~ 3.5. For Reverse cone type nozzle and Vertical circular nozzle, the maximum stagnation point heat transfer and the maximum average heat transfer occurs at H/D=8. But for the Cone type nozzle, the maximum stagnation and average heat transfer occurs at H/D=10, 4, respectively. From the optimum nozzle-to-target plate distance, the stagnation and the average heat transfer reveal the following ranking: Reverse cone type nozzle, Vertical circular type nozzle, Cone type nozzle.ozzle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.461-472
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• 1995

The interaction of laminar mixed convection and surface radiation in a two-dimensional channel with an array of rectangular blocks is analyzed numerically. Three blocks are maintained at high temperature and the other bottom and top horizontal walls are insulated. Discrete ordinate method(DOM) is introduced to analyze the radiative heat transfer. The effects of the variations of Reynolds number and channel specifications on the heat transfer characteristics are investigated. The average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number and dimensionless geometric parameters such as the block spacing, height and channel spacing. For the conditions considered in this study, average Nusselt numbers along the block surfaces are strongly influenced by the channel spacing and Reynolds number but weakly influenced by the block spacing and block height.