• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.25 no.2
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• pp.151-160
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• 1996

• Journal of Energy Engineering
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• v.22 no.2
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• pp.120-127
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• 2013

This study investigated the characteristics of heat transfer and pressure drop for cross-flow heat exchanger of premixed combustion system. The premixed burner was in front of a heat exchanger, and the number of heat exchanger modules was changed to investigate the characteristics of NOx and CO emissions with various equivalence ratios. In addition, the effectiveness, entropy generation and pressure drop were calculated by various number of heat exchanger modules and the performance of heat exchanger was analyzed by the exergy loss.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.1940-1949
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• 1995

A numerical study for a two dimensional multi-jet with crossflow of the spent fluid has been carried out. Three different distributions of mass-flow rate at 5 jet exits were assumed to see their effects upon the flow characteristics, especially in the jet-flow region. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Results show that a fully developed laminar flow exists above a certain Reynolds number whose exact value depends upon the mass flow rate distribution. AS the Reynolds number increases, the flow becomes transitional from downstream and finally a fully developed turbulent flow forms in the jet-flow region. The critical Reynolds number where the fully developed turbulent flow forms is quite dependent upon the distribution of mass-flow rate. One interesting result is that the distribution of the skin friction coefficient along the inpingement plate in the jet-flow region shows a consistent dependency on the Reynolds number, i.e. inversely proportional to the square root of the Reynolds number, regardless of flow regime.

• The KSFM Journal of Fluid Machinery
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• v.2 no.1 s.2
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• pp.96-102
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• 1999

Cross flow fans are used in various applications, especially in industrial ventilation applications and in room air conditioners, due to their superior performance characteristics. Unlike radial and/or axial fans, the design of cross flow fans have been mostly based on earlier experiences and experiments. In the present study, numerical computations of flow fields through a cross flow fan used in room air conditioner are performed to investigate the detailed flow fields and to study the effect of the blade shape on performance curves to aid better design of the fan. Despite some discrepancies between the two results, it is seen from the present study that the computational results agree quite well with the qualitative experimental results. It is also shown from the present study that by having a different shape of blade, it is possible to achieve about $15\%$ increase in flow rates. The stimulating results of the present study can be used in the design of high performance cross flow fans with the use of optimal design algorithm and experimental verifications.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.235-240
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• 2007

Performance of an air-cooled plate heat exchanger (PHE) was evaluated in this study. The PHE was manufactured in two types of single-wave and double-wave plates in parallel assembly. The heat exchanger aims to substitute open-loop cooling towers with closed-loop water circulation, which guarantees cleanliness and compactness. In this study, prototype single-wave and double-wave PHEs were designed and tested in a laboratory scale experiments. From the tests, the double-wave PHE shows approximately 50% enhanced heat transfer performance compared to the single-wave PHE. However, the double-wave PHE costs 30% additional pressure drop. For the commercialization, a wide channel design for air flow would be essential for performance and reliability.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.8
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• pp.1016-1023
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• 2012

Because heat exchanger consists of many circular tubes, the analysis of local heat transfer and pressure drop at the surrounding of circular tubes, performance and calculation of size, economics play important roles in design. In this study, This study conducted experiment and analysis in order to observe convective heat transfer coefficient LMTD (logarithm mean temperature difference) and pressure losses according to water temperature and air flow rate using a cross flow heat exchanger of staggered arrangement. This heat exchanger was composed of staggered arrangement for five rows and seven columns of tube banks, and the condition of experiment and analysis are $40{\sim}65^{\circ}C$ of water temperature and $5.0{\sim}12.3m^3/s$ of air flow rate. As a result of it, since air density decreases as water temperature and flow rate increases, Reynolds number decreases with characteristics of low flow velocity but mean heat transfer coefficient increases with air flow rate increase, heat transfer performance has been improved and pressure losses decreased. And since heat transfer rate shows about 8~12% and pressure drop around 0.01~7.5% error as the analysis result, the feasibility of this study could be evaluated.

• Proceedings of the KIEE Conference
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• 2001.07b
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• pp.620-622
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• 2001

자성체 코어의 비선형 특성을 이용하여 DC와 AC 전류를 측정하는 Zero-Flux Current Transformer는 정밀 전류 측정용으로 많이 연구되고 있다. Zero-Flux Current Transformer는 DC 대전류 측정에 합당하며 저 전류 측정에 사용될 경우 소모전류, 안정되고 첨예한 필터 제작, magnetic modulator에 의한 zero point drift, 자화 전류가 비대칭일 때 출력 등과 같은 문제가 해결되어야 한다. 그리고 상용으로 사용하기 위하여 Hand-Held Type으로 제작되어야하며 동작시의 소모전류가 작고 정확도가 우수하여야 한다. 본 연구에서는 자화 전류가 비대칭일 때 출력을 zero로 만들기 위하여 사용하는 필터와 복잡한 회로로 구성된 magnetic modulator 부분을 여러개의 peak detector를 사용하여 AC와 DC를 측정하는 클램프미터를 개발하였으며 그 특성에 대한 내용을 기술하였다.

• Proceedings of the KIEE Conference
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• 2008.07a
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• pp.721-722
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• 2008

This paper deals with comparison and analysis for rotor losses of permanent magnet synchronous generator using phase current harmonic analysis according to dc and ac load. On the basis of analytical field analysis, the rotor losses are analysed. Particularly, rated speed and ac load and the rated speed and dc load conditions are considered. This paper compared rotor losses considered dc load with rotor losses considered ac load. Although our analytical modes is low speed, the rotor losses must be considered by results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.5
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• pp.503-511
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• 2013

The humidifying supply gas is important in terms of the performance efficiency and membrane life improvement of a PEM fuel cell. A planar membrane humidifier is classified as a cross-flow and counter-flow type depending on the flow direction, and heat and mass transfer occur between the plate and the membrane. In this study, the changes in heat and mass transfer for various inlet temperatures and flow rates are compared according to the flow direction by using the sensible and latent ${\varepsilon}$-NTU method. The obtained results indicate that the counter flow shows higher heat and mass transfer performance than the cross flow at a low flow rate, and the difference in performance decreases as the flow rate increases. Furthermore, changes in the mass transfer performance decrease considerably with a nonlinear increase in the inlet temperature, and variations of the heat transfer performance are small.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.6
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• pp.347-354
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• 2009

Experimental study on a cross-flow air-cooled plate heat exchanger (PHE) was performed. Two types of PHEs were manufactured either with single-wave plates or with double-wave plates in parallel. Cooling air flows through the PHEs in a crosswise direction against internal hot water. The heat exchanger aims to substitute open-loop cooling towers with closed-loop water circulation, which guarantees cleanliness and compactness. In this study, prototype single-wave and double-wave PHEs were designed and tested in a laboratory scale experiments. From the tests, the double-wave PHE shows approximately 50% enhanced heat transfer performance compared to the single-wave PHE. However, the double-wave PHE costs 30% additional pressure drop. For the commercialization, a wide channel design for air flow would be essential for performance and reliability.