• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.258-261
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• 2007

Simulations of the thermally-induced residual stresses and birefringence in freely quenched plates of polycarbonate were performed by using the linear viscoelastic and photoviscoelastic constitutive equations for the mechanical and optical properties, respectively, and the first order rate equation for volume relaxation. The predictions for the birefringence showed good agreement with experimental measurements. Based on the simulation, the influences of various cooling conditions on the residual stress and birefringence in plates were investigated. The residual stress and birefringence increased with increasing initial temperature, decreasing coolant temperature and increasing heat transfer coefficient of coolants.

• 한국주조공학회지
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• 제30권5호
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• pp.167-173
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• 2010

벌크 비정질 합금의 특성상 점도가 높고, 냉각속도가 빨라 냉각되는 합금의 온도를 직접 측정하는 것은 곤란하므로, 측정에 의하여 냉각속도를 구하는 것은 매우 어렵다. 본 연구에서는 합금의 온도를 직접 측정하는 대신 금형의 온도를 측정하고, 측정된 금형의 온도를 상용 열해석 프로그램을 이용한3차원 계산 결과와 비교, 보정하는 역문제 기법을 사용하여 Cu계와 Zr계 벌크 비정질합금의 냉각속도를 예측하였다. 예측된 냉각속도는 금형온도와 시편의 두께에 따라Cu계의 경우는 284~300 K/s, Zr계는 279~289 K/s로, 초기 금형온도의 영향은 크지 않은 것으로 나타났다. 전산모사 결과와 달리 금형을 수냉한 쪽보다 가열한 쪽의 응고중 냉각속도가 빨라 조직이 더 미세한 것으로 나타났는데, 이는 응고중 금형과 주물간에 에어갭의 형성으로 열전달을 방해 받은 영향으로 사료된다.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2005년도 전력전자학술대회 논문집
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• pp.466-468
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• 2005

Recently, the demand for the development of high quality and high speed laser printer and efficient power utilizations are required. Among complicate electro-mechanic devices in laser printer, the toner fusing unit consumes above 90[%] of all electrical energy needed for printing devices. Therefore, the development of more effective energy-saving toner fusing process becomes a significant task of much great demand. Generally, there are several way to implement fusing unit, among them this paper present a new hybrid induction heating method. The proposed induction heating method enables to increase coupling coefficient between heating coil and heat roller also to Increase total energy transfer efficiency. Therefore the proposed IH inverter system provide very fast W.U.T.(Warm UP Time), also high efficiency. Through experimental result, the proposed control system is verified.

• 한국공작기계학회논문집
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• 제16권6호
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• pp.159-162
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• 2007

Recently, Pb-free solder ball technology, which is getting more significant in miniaturization of electronic equipment, and resolution of recent environmental problems, is necessary to be developed. A plastic-core solder ball is much promising in those considerations. Plastic-core solder balls have the tendency to replace the usual metal-core solder ball from low material cost and superior mechanical properties. The thermal effects, however, are important in manufacturing process, such as deposing micro-sized metal thin film on the spherical polymer surface. Furthermore plastic-core solder balls are easy to be broken due to CTE and elastic coefficient of material property from heat transfer. We propose technical computational investigations for the manufacturing design and the reliability of plastic-core solder ball from thermal stress analysis.

• 대한설비공학회지:설비저널
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• 제17권5호
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• pp.583-589
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• 1988

Condensation of water vapor into an absorbent liquid of LiBr-water solution falling over a bank of water cooled horizontal tubes was investigated theoretically. The governing conservation equation for a re-defined physical transport phenomena were solved numerically using a finite difference method. Raw parameters were used in this study, since reliable experimental data is required prior to a dimensionless parametric study. The average values of wall heat transfer coefficient and interfacial absorption rate were defined to see the system performance. Other parameters include tube diameter, streamwise coordinate (and number of tubes in row), mass flow rate, and the wall temperature. The effects of these quantities on the absorption processes and suggestions for a rational system design have been presented.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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• pp.258-263
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• 2007

The performance of louver-finned flat-tube radiators for computer CPU liquid cooling were experimentally investigated. In this study, 5 samples of louver-finned flat-tube radiators with different width size (19mm, 24mm), tube hole (1, 9) and pass number (1, 2, 5) were tested in a wind tunnel. The experiments were conducted under the different air velocity ranging from 1 to 5 m/s. The water flow rate through a pass was 1.7 LPM. Inlet temperatures of air and water were $20^{\circ}C$ and $30^{\circ}C$ respectively. The results showed that the best performance in the 24mm sample considering pressure drop and heat transfer coefficient.

• International Journal of Air-Conditioning and Refrigeration
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• 제13권3호
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• pp.158-166
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• 2005

The present study investigated experimentally and numerically the enhancement of absorption performance due to the waviness of falling film in the vertical absorber tube. The momentum, energy and mass diffusion equations were utilized to find out temperature and concentration profiles at both the interfaces of liquid solution and refrigerant vapor and the wall. Flow visualization was performed to find out the wetting characteristics of the falling film. The maximum heat transfer coefficient was obtained for the wavy flow using spring as an insert device through both numerical and experimental studies. Based on the numerical and experimental results, the maximum absorption rate was found for the wavy-flow using spring as the insert device. The differences between experimental and analytical results ranged from $5.0\;to\;25\%\;when\;Re_j>100$.

• 설비공학논문집
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• 제2권1호
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• pp.63-73
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• 1990

A numerical analysis of initial unsteady state flow and heat transfer in an enclosed cavity has been performed by the Modified QUICK Scheme. The stable QUICK Scheme which modified the coefficient always to be positive is included in this numerical analysis. The implicit method is applied to solve the unsteady state flow; between iterations the PISO (Pressure - Implicit with Splitting of Operators) algorithm is employed to correct and update the velocity and pressure fields on a staggered grid. The accuracy of the Modified QUICK Scheme is proved by applying fewer grid systems than those which Ghia et al. and Davis applied. The initial unsteady mixed convection in an enclosed cavity is analyzed using the above numerical procedure. This study focuses on the development of the large main vortex and secondary vortex in forced convection, the effects of the Rayleigh Number in natural convection and the relative direction of the forced and natural convection.

• 설비공학논문집
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• 제2권1호
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• pp.27-36
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• 1990

An experimental investigation was made to study the performance characteristics of evaporator having different fin configurations and tube inner grooves. Three different types of fin such as super slitted fin, slitted fin, plain fin, and two types of tube such as inner grooved tube, and bare tube, are tested varying the air velocity, evaporation temperature and superheat of refrigerant. Results show that in the range of air side Reynolds number $3{\times}10^3\;-\;1.5{\times}10^4$ evaporator with super slitted fin and inner grooved tube shows best performance. It is 80% higher in overall heat transfer coefficient and 2.6 times higher in pressure loss compared to that with plain fin inner grooved tube. Friction factor is found to be almost independent of evaporating temperature and degree of superheat, while Colburn j factor varies with evaporating temperature.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 1999년도 추계 학술발표회 논문집
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• pp.211-216
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• 1999

One of the problems in a refrigerator operation is the frost formation on a cold surface of the evaporator. The frost layer is formed by the sublimation of water vapor when the surface temperature is below the freezing point. This frost layer is usually porous and formed on the cold surface of the evaporator. The frost layer on the surface of a evaporator will make side effect such as thermal resistance. However, these important factors have not been used in determining the defrosting period. In this report, a prediction taking into account the change of the fin efficiency due to the growth of the frost layer.