• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2296-2302
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• 2005

This study is focused on the comparison of heat transfer performance of two thermosyphons having 60 straight and helical internal grooves. Distilled water has been used as working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, the inclination angle and operating temperature were used as experimental parameters. The heat flux and heat transfer coefficient are estimated from experimental results. The conclusions of this study may be summarized as follows; Liquid fill charge ratio, inclination angle and geometric shape of grooves were very important factors for the operation of thermosyphon. The optimum liquid fill charge ratio for the best heat flux were $30\%$. The heat transfer performance of helically grooved tube was higher than that of straight grooved tube in low inclination angle (less than $30^{\circ}$), but the results were opposite in high inclination angle (more than $30^{\circ}$). As far as optimum inclination angle concerns, range of $25^{\circ}\~30^{\circ}$ for a helically grooved tube and about $40^{\circ}$ for a straight grooved tube are suggested angles for the best results.

• Nuclear Engineering and Technology
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• v.52 no.5
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• pp.908-917
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• 2020

Corrosion of structural materials presents a critical challenge in the use of lead-bismuth eutectic (LBE) as a nuclear coolant in an accelerator-driven system. By forming a protective layer on the steel surfaces, corrosion of steels in LBE cooled reactors can be mitigated. The amount of oxygen concentration required to create a continuous and stable oxide layer on steel surfaces is related to the oxidation process. So far, there is no oxidation experiment in fuel assemblies (FA), let alone specific oxidation detail information. This information can be, however, obtained by numerical simulation. In the present study, a new coupling method is developed to implement a coupling between the oxygen mass transfer model and the commercial computational fluid dynamics (CFD) software ANSYS-CFX. The coupling approach is verified. Using the coupling tool, we study the oxidation process of the FA and investigate the effects of different inlet parameters, such as temperature, flow rate on the mass transfer process.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1075-1080
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• 2006

Purpose of this study is proposal of estimating method about window thermal performance that based on KS F 2278 'Test method of thermal resistance for windows and doors' due to material composition of PVC frame window. First step of this study is research of present state about material composition of PVC frame window. Second is selection of main effective elements about window thermal resistance. For example, composition of Glazing, Frame area ratio of total window area, frame width, opening type, area of heat transfer and so on. Third is multiple regression analysis about thermal performance of PVC frame window due to main effective elements. It produces equations of multiple regression analysis due to opening type. Case of sliding window is $Y=0.149+0.034X_g+0.248X_{far}$, 4track sliding is $Y=0.584+0.175X_g+1.355X_{far}-0.008X_{fw}$, Tilt & Turn window is $Y=-0.161+0.076X_g+0.576X_{far}+0.0008X_{fw}$.

• Journal of the Korean Wood Science and Technology
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• v.47 no.1
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• pp.66-79
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• 2019

The aim of the study is to use the by-products sawdust, formed during sawing and mandarin peel which are agricultural by products. The boards were manufactured by mixing the sawdust and mandarin peel at different mixing ratio and density. In terms of changes in surface temperature of ceramics, we could found that the velocity was fast in the early time of heat transfer until 10 minutes and after that the velocity increased but not very fast. At the elapsed time of 30 minutes, the surface temperature of ceramics increased with the carbonization temperature and rate of mandarin peel addition did not influence the surface temperature. Far - infrared emissivity had no constant tendency in rate of mandarin peel addition, it decreased with increase of carbonization temperature.

• ETRI Journal
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• v.45 no.2
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• pp.254-266
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• 2023

This paper investigates the effect of hardware impairments (HIs) and imperfect channel state information (ICSI) on a SWIPT-assisted adaptive nonorthogonal multiple access (NOMA)/orthogonal multiple access (OMA) system over independent and nonidentical Rayleigh fading channels. In the NOMA mode, the energy-constrained near users act as a relay to improve the performance for the far users. The OMA transmission mode is adopted to avoid a complete outage when NOMA is infeasible. The best user selection scheme is considered to maximize the energy harvested and avoid error propagation. To characterize the performance of the proposed systems, closed-form and asymptotic expressions of the outage probability for both near and far users are studied. Moreover, exact and approximate expressions of the ergodic rate for near and far users are investigated. Simulation results are provided to verify our theoretical analysis and confirm the superiority of the proposed NOMA/OMA scheme in comparison with the conventional NOMA and OMA protocol with/without HIs and ICSI.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.135-145
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• 2004

An experimental study is conducted to investigate the flow and heat transfer characteristics of a multi-tube inserted impinging jet. Four different multi-tube devices are tested for various nozzle-to-plate distance. Flow visualization by smoke-wire method and velocity measurements using a hot-wire anemometer are applied to analyze the flow characteristics of the multi-tube insert impinging jet. The local heat transfer coefficients of the multi-tube inserted impinging jet on the impingement surface are measured and the results are compared to those of the conventional jet. In multi-tube inserted system the multi-tube length plays an important role in the flow and heat transfer characteristics of the jet flow. With multi-tube insert of I3d4 and I6d4 which has relatively longer tube length than the multi-tube-exit of I3d1 and I6d1, the flow maintains its increased velocity far downstream due to interaction between adjacent flows. For the small H/D of 4, the local heat transfer coefficients of multi-tube inserted impinging jet are much higher than those of the conventional jet because the flow has higher velocity and turbulent intensity by the use of the multi-tube device. At large gap distance of H/D=12, also higher heat transfer rates are obtained by installing multi-tube insert except multi-tube insert of I3d1.

• Information Systems Review
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• v.11 no.1
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• pp.69-83
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• 2009

In a global software development project, knowledge transfer between a corporate headquarter and offshore development sites is considered to be important for effective software development. This article presents empirical research that investigates factors influencing knowledge transfer in global software development. The factors evaluated in this study are: 1) quality of communication infrastructure, 2) quality of partnership and 3) types of governance mechanism. Questionnaires were collected from offshore development sites in Mauritius. While the quality of both the partnership and communication infrastructure were found to be determinants to knowledge transfer, hierarchical governance had a negative impact on knowledge transfer. Although the results are similar to the previous studies done within an organizational boundary, implications of the results are far different due to the geographical distance among offshore locations. Future research is called for to investigate the relationships between governance type and knowledge transfer.

• Journal of Microbiology and Biotechnology
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• v.9 no.6
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• pp.695-703
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• 1999

We have studied the stereospecificities of various pyridoxal 5'-phosphate (PLP) dependent enzymes for the hydrogen transfer between the C-4' of a bound coenzyme and the C-2 of a substrate in the transamination catalyzed by the enzymes. Stereospecificities reflect the structures of enzyme active-sites, in particular the geometrical relationship between the coenzyme-substrate Schiff base and the active site base participating in an $\alpha$-hydrogen abstraction. The PLP enzymes studied so far catalyze only a si-face specific (pro-S) hydrogen transfer. This stereochemical finding suggests that the PLP enzymes have the same topological active-site structures, and that the PLP enzymes have evolved divergently from a common ancestral protein. However, we found that o-amino acid aminotransferase, branched chain L-amino acid aminotransferase, and 4-amino-4-deoxychorismate lyase, which have significant sequence homology with one another, catalyze a re-face specific (pro-R) hydrogen transfer. We also showed that PLP-dependent amino acid racemases, which have no sequence homology with any aminotransferases, catalyze a non-stereospecific hydrogen transfer: the hydrogen transfer occurs on both faces of the planar intermediate. Crystallographical studies have shown that the catalytic base is situated on the re-face of the C-4' of the bound coenzyme in o-amino acid aminotransferase and branched chain L-amino acid aminotransferase, whereas the catalytic base is situated on the si-face in other aminotransferases (such as L-aspartate aminotransferase) catalyzing the si-face hydrogen transfer. Thus, we have clarified the stereospecificities of PLP enzymes in relation with the primary structures and three-dimensional structures of the enzymes. The characteristic stereospecificities of these enzymes for the hydrogen transfer suggest the convergent evolution of PLP enzymes.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.100-103
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• 2002

The recent machine tools are requested so high-quality processing and productivity increasing. Therefore it is so necessary to develop technology far high-speed and high-precision. This thesis touches on the development of high speed and intellectual line center. At first, the line center is necessary that strong structure, compact structure and light weight design far high-speed processing and transfer. So. It is necessary that examination of new materials and structures for light-weight and control devices for precision processing. So. It is going to make mention of the process of 1st model production for the above-mentioned base on test model production and evaluation.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.4
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• pp.129-135
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• 2002

The present article deals with the measurement and the numerical calculations far the temperature distribution near the facing of the lockup clutch. The rotating telemetry system is Introduced for the estimation inside high-speed torque converter For the numerical calculation, the effect of the convective heat transfer is considered as well as the conduction to the solid. The estimation shows that the oil temperature near facing rapidly rises as the lockup clutch is engaged. The numerical results shows good agreements with the experimental values for the maximum temperature near the facing of the lockup clutch.