• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.6
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• pp.669-681
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• 2012

In this paper, analytical calculations using a novel mutual inductance formula for a resonant wireless power transmission system using helical coils. The look-up table of critical variables during the mutual inductance calculation process was formulated. The calculation results for resonant frequency and insertion loss were compared with experimental results when the distance between the two helical coils in a structure where the transmission and reception is symmetrical was varied with 10 mm increments from 53 mm to 500 mm. On average, the resonant frequency showed a difference of 5.63 % between the experimental results and the calculation results. The insertion loss had an average difference 2.25 dB where the smallest difference of 0.33 dB occurred with 290 mm. It was found that the experimental results without using a balun were in greater agreement with the calculation results.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.62-67
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• 2022

Liquid hydrogen (LH₂) has a higher density than gaseous hydrogen, so it has high transport efficiency and can be stored at relatively low pressure. In order to use efficient bulk hydrogen in the industry, research for the LH₂ supply system is needed. In the high-pressure hydrogen station based on LH₂ currently being developed in Korea, a heat exchanger is used to heat up supercritical hydrogen at 700 bar and 60 K, which is pressurized by a cryogenic high-pressure pump, to gas hydrogen at 700 bar and 300 K. Accordingly, the heat exchanger used in the hydrogen station should consider the design of high-pressure tubes, miniaturization, and freezing prevention. A helical heat exchanger generates secondary flow due to the curvature characteristics of a curved tube and can be miniaturized compared to a straight one on the same heat transfer length. This paper evaluates the heat transfer performance through parametric study on the distance between coils, guide effect, and anti-icing design of helical heat exchanger. The helical heat exchanger has better heat transfer performance than the straight tube exchanger due to the influence of the secondary flow. When the distance between the coils is uniform, the heat transfer is enhanced. The guide between coils increases the heat transfer performance by increasing the heat transfer length of the shell side fluid. The freezing is observed around the inlet of distribution tube wall, and to solve this problem, an anti-icing structure and a modified operating condition are suggested.

• Journal of the Korean Chemical Society
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• v.38 no.10
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• pp.710-718
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• 1994

We suggest a statistical thermodynamic theory for the conformational transition of a synthetic alanine (Ala), ${\alpha}$-aminoisobutyric acid (Aib) alternative oligopeptide, Buo-(Ala-Aib)$_n$-oMe, where the terminal groups Buo and oMe stand for t-butoxy and methoxy, respectively. Pure Aib homo-oligomers have always been found to adopt $3_{10}$ helical conformations, while polyalanine has always $\alpha$ helical conformation. In an organic solvent (e.g. $CD_3$CN) it shows that the length for the $3_{10}$/${\alpha}$ helix transitions of Buo-(Ala-Aib)$_n$-oMe, is 8 at room temperature. In an aqueous solution oligopeptide has always coil conformation at room temperature. In an organic solution, helical structures of the oligopeptide are more stable than coil structure, so we studied the $$3_{10}/\alpha$ helix transitions, considering coiled-conformations, coiled and $3_{10}$ helical conformations, and coiled and $\alpha$ helical conformations by using the zipper model. We determined the values of parameters ($\sigma_A$, $\sigma_T$, $\xi_A$, $\xi_T$) from the relating published data; $\sigma_A$ = 0.00011, $\sigma_T$ = 0.0060, $\xi_A$ = 10.1, $\xi_T$ = 3.90. The distributions of $\alpha$ helical length can be N-2, N-3, N-4, ${\cdots}$, 3, 2, 1 (N = 2n) while those of $3_{10}$ helical length, N-1, N-2, N-3, N-4, ${\cdots}$, 3, 2, 1.

• Macromolecular Research
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• v.8 no.3
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• pp.103-115
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• 2000

The structural changes viewed from the molecular level have been investigated for the isothermal crystallization phenomena of polyethylene (PE) and the solvent-induced crystallization phenomenon of syndiotactic polystyrene (sPS) glassy sample. The data, which were collected by the time-resolved measurements of Fourier-transform infrared spectra, Raman spectra, synchrotron-sourced small-angle X-ray scattering, wide-angle X-ray scattering, and so on, were combined together to extract the detailed structural information in these phase transition phenomena. In the case of PE, the isothermal crystallization from the melt to the orthorhombic form was found to occur via the conformationally-disordered trans chain form, followed by the formation of the lamellar stacking structure of regular orthorhombic-type crystals. In the case of sPS, the amorphous chains in the glassy sample were found to enhance the mobility through the interaction with the injected solvent molecules, which act as a trigger to cause the conformational ordering from the random coil to the regular T$_2$G$_2$-type helical form. The thus created short helical segments were found to grow into longer helices, which gathered together to form the crystallites, as revealed by the organized coupling of the infrared, Raman and X-ray scattering data.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.2
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• pp.237-244
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• 2016

Helical compression springs have been widely used in industries. The springs should be verified through experiment whether the inherent characteristics of the spring can be maintained during the manufacturing process. Considerable time and expense is spent in the manufacturing process. Therefore, in this study, the structural integrity evaluation of a spring was conducted using linear static structural analysis. Verification and comparison of the experimental data were carried out using a variety of international industrial standards with the intent to prove the validity of this study. The spring model did not consider coil ends. As a result of conducting the structural analysis, the quality of the mesh was improved and the time needed to create an analytical model was reduced. The study indicated that Poisson's ratio had little influence on the result of the structural analysis. Additionally, the possibility of verifying the structural integrity evaluation by structural analysis was confirmed.

• Journal of Advanced Navigation Technology
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• v.21 no.4
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• pp.371-376
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• 2017

In this paper, we propose a magnetic resonant WPT(wireless power transfer) scenario using a large coil resonating at 6.78 MHz, and compare the characteristics through a three-dimensional electromagnetic field simulation and a magnetic resonant WPT equivalent circuit. The magnetic resonant WPT equivalent circuit proposed in this paper considers the parasitic capacitance generated between the coils in addition to the conventional equivalent circuit. Based on this analysis, we fabricated the magnetic resonant WPT coil and compared it with simulation prediction. As a result of comparison, the transfer characteristics and the resonance frequency shift can be predicted. Error proposed characteristics of equivalent circuit for the magnetic resonant WPT and the measured values are estimated to be ${\Delta}{\mid}S11{\mid}=1.31dB$ and ${\Delta}{\mid}S21{\mid}=1.21dB$, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.8
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• pp.783-789
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• 2012

In this study, turbulent flow and heat transfer characteristics in a helically coiled tube have been numerically investigated. Helically coiled tubes are commonly used in heat exchange systems to enhance the heat transfer rate. Accordingly, they have been widely studied experimentally; however, most studies have focused on the pressure drop and heat transfer correlations. The centrifugal force caused by a helical tube increases the wall shear stress and heat transfer rate on the outer side of the helical tube while decreasing those on the inner side of the tube. Therefore, this study quantitatively shows the variation of the local Nusselt number and friction factor along the circumference at the wall of a helical tube by varying the coil diameter and Reynolds number. It is seen that the local heat transfer rate and wall shear stress greatly decrease near the inner side of the tube, which can affect the safety of the tube materials. Moreover, this study verifies the previous experimental correlations for the friction factor and Nusselt number, and it shows that the correlation between the two in a straight tube can be applied to a helical tube. It is expected that the results of this study can be used as important data for the safety evaluation of heat exchangers and steam generators.

• Journal of Environmental Science International
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• v.7 no.1
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• pp.62-66
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• 1998

Toxic Mastoparan B(MP-B) which is purified from the venom of the hornet Vespa basalis is a cationic amphlphilic tetradecapeptide. MP-B and Its Ala-substituted analogues were synthesized by solld phase method and the toxic peptide-membrane interactions were examined by circular dichroism(CD) spectra, fluorescence spectra, and leakage abilities in phospholipid membranes. In the presence of phospholipid vesicles, synthetic MP-B and its analogues formed amphiphilic -helical structures, but in the buffer soletion, those exhibited random coil conformation as measured by CD. Fluorescence spectra of MP-B and its analogues which indicated the binding affinity of peptide on phospholipid vesicles showed that the replacement of Lys at position 2 and 11 with Ala caused a remarkable effect in the blue shalt and that at position 2, in the leakage ability of the peptide.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.130-132
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• 1997

In this paper, we propose a new type of tubular linear induction motor(TLIM) with two-dimensional motion. The proposed motor consists of four short primary LIMs arranged on a same circumference and a common secondary. By adopting independently energized ring-windings to the primary, we can expect the reduction of coil-end region and the freedom of alternating current supply. The secondary conductor is capable of producing anyone of rotary, linear, and helical motions by controlling the phase of supply currents in each primary winding. From the 3-D finite element analysis and the experiment, we derive the feeding conditions to increase the subsidiary rotary-force and an optimal arrangement of primary currents to reduce the number of slot.

• Nuclear Engineering and Technology
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• v.38 no.8
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• pp.753-762
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• 2006

In this paper, works related to enhancement of the CHF are reviewed in terms of fundamental mechanisms and practical applications. Studies on CHF enhancement in forced convection are divided into two categories, CHF enhancement of internal flow in tubes and enhancement of CHF in the nuclear fuel bundle. Methods of enhancing the CHF of internal flows in tubes include enhancement of the swirl flow using twisted tapes, a helical coil, and a grooved surface; promotion of flow mixing using a hypervapotron; altering the characteristics of the heated surface using porous coatings and nano-fluids; and changing the surface tension of the fluid using additives such as surfactants. In the fuel bundle, mixing vanes or wire wrapped rods can be employed to enhance the CHF by changing the flow distributions. These methods can be applied to practical heat exchange systems such as nuclear reactors, fossil boilers, fusion reactors, etc.