• Journal of the Korean Electrochemical Society
• /
• v.18 no.4
• /
• pp.137-142
• /
• 2015

$Mn_{1+X}Co_{2-X}O_4$ solid solutions with various Mn/Co ratios were synthesized by a combustion method, and used as cathode catalysts for lithium/air secondary battery. Their electrochemical and physicochemical properties were investigated. The morphology was examined by transmission electron microscopy (TEM), and the crystallinity was confirmed by X-ray diffraction (XRD) analyses. For the measurement of electrochemical properties, charge and discharge measurements were carried out at a constant current density of $0.2mA/cm^2$, monitoring the voltage change. Electrochemical impedance spectroscopy (EIS) analyses were also employed to examine the change in charge transfer resistance during charge-discharge process. $Mn_{1+X}Co_{2-X}O_4$ solid solutions showed enhanced cycleability as a cathode of Li/air secondary battery, and the performance was found to be strongly dependent on Mn/Co ratio. Among synthesized catalysts, $Mn_{1.5}Co_{1.5}O_4$ exhibited the best performance and cycleability, due to high charge transfer rate.

• Journal of Trauma and Injury
• /
• v.26 no.4
• /
• pp.261-265
• /
• 2013

Purpose: The aim of this study is to evaluate the transfer pattern of multiple trauma patients after acute phase management and to determine whether the time between the surgeon's decision and the actual transfer correlates with the patient's insurance type. Methods: Three hundred ninety-two(392) multiple trauma patients visited the emergency room from January 2011 to April 2013. Among the 143 patients who were admitted by a trauma surgeon, 47 were transferred to another hospital after acute phase management. The age, gender, trauma mechanism, Revised trauma score (RTS), Injury severity score (ISS), insurance type, length of ICU stay and hospital stay were analyzed through a retrospective chart review. Results: The mean age was 47.7 years, and traffic accident was the most common mechanism(26, 55.3%). The mean RTS and ISS were 6.93 and 22.7, respectively. Twenty-five patients(53%) were covered by National health insurance, and 20 patients(42.6%) were covered by automobile insurance. Patients were transferred to primary (4.3%), secondary(80.9%), tertiary(4.3%) and care(10.6%) hospitals. The mean time from transfer decision to actual transfer was significantly longer for patients who were covered by automobile insurance than it was for patients who were covered by national health insurance (p=0.038). Conclusion: An appropriate transfer system at the end of acute phase care is essential for managing trauma centers with limited staffing and facilities. In addition, the mean time from transfer decision to actual transfer seemed to be definitely related to the type of insurance covering the patient.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.4
• /
• pp.579-588
• /
• 1997

The heat transfer and flow measurements from a convex curved surface to a circular impinging jet have been made. The flow at the nozzle exit has a fully developed velocity profile. The jet Reynolds number (Re) ranges from 11,000 to 50,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the dimensionless surface curvature (d/D) from 0.034 to 0.089. The results show that the stagnation point Nusselt number (N $u_{st}$ ) increases with increasing value of d/D. The maximum Nusselt number at the stagnation point occurs at L/d .ident. 6 to 8 for all Re's and d/D's tested. For larger L/d, N $u_{st}$ dependency on Re is stronger due to an increase of turbulence in the approaching jet as a result of the more active exchange of momentum with a surrounding air. The local Nusselt number decreases monotonically from its maximum value at the stagnation point. However, for L/d=2 and Re=23,000, and for L/d.leq.4 and Re=50,000, the stream wise Nusselt number distributions exhibit secondary maxima at r/d .ident. 2.2. The formation of the secondary maxima is attributed to an increase in the turbulence level resulting from the transition from a laminar to a turbulent boundary layer.ndary layer.

• Bulletin of the Korean Chemical Society
• /
• v.22 no.2
• /
• pp.219-227
• /
• 2001

The silver colloidal effects on the excited-state structure and intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABA) in aqueous cyclodextrin (CD) solutions have been investigated by UV-VIS absorption, steady-state and time-resolved fluorescence, and transient Raman spectroscopy. As the concentration of silver colloids increases, the ratio of the ICT emission to the normal emission (Ia /Ib) of DMABA in the aqueous $\alpha-CD$ solutions are greatly decreased while the Ia /Ib values in the aqueous B-CD solutions are significantly enhanced. It is also noteworthy that the ICT emission maxima are red-shifted by 15-40 nm upon addition of silver colloids, implying that DMABA encapsulated in $\alpha-CD$ or B-CD cavity is exposed to more polar environment. The transient resonance Raman spectra of DMABA in silver colloidal solutions demonstrate that DMABA in the excited-state is desorbed from silver colloidal surfaces as demonstrated by the disappearance of νs (CO2-)(1380 cm-1 ) with appearance of ν(C-OH)(1280 cm -1) band, respectively. Thus, in the aqueous B-CD solutions the carboxylic acid group of DMABA in the excited-state can be readily hydrogen-bonded with the secondary hydroxyl group of B-CD while in aqueous and $\alpha-CD$ solutions the carboxylic acid group of DMABA has the hydrogen-bonding interaction with water. Consequently, in the aqueous B-CD solutions the enhancement of the Ia /Ia value arises from the intermolecular hydrogen-bonding interaction between DMABA and the secondary hydroxyl group of B-CD as well as the lower polarity of the rim of the B-CD cavity compared to bulk water. This is also supported by the increase of the association constant for DMABA/ B-CD complex in the presence of silver colloids.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.26 no.6
• /
• pp.437-445
• /
• 2021

This paper proposes an operating frequency design method that limits the voltage applied to aload-side converter during the initial operation of a loosely coupled resonant dual-active bridge (LCR-DAB) converter and an initial operating strategy that applies it. The LCR-DAB converter uses two wireless power transfer coils instead of the high-frequency transformer of the general DAB converter. The wireless power coil has a physical distance of several tens of millimeter or more between the two coils; thus, the LCR-DAB converter is a bidirectional isolated power conversion system that can easily achieve high insulation performance. However, for the initial operation of the LCR-DAB, if the power-side converter is operated at the resonance frequency while the load-side converter is not operating, then a very high voltage due to resonance is applied to the load-side converter, thereby causing damage to the converter. Therefore, a method that can stably charge the DC link voltage of the secondary-side converter during the initial operation is needed. This paper proposes a method to initially charge the secondary-side DC link by operating the primary-side converter at a frequency with limited voltage gain rather than at a steady-state operating frequency. The validity of the proposed frequency design method and initial operating sequence is verified through simulation and experimentation of the 1 KW LCR-DAB converter.

• Transactions of the Korean hydrogen and new energy society
• /
• v.34 no.3
• /
• pp.283-291
• /
• 2023

The physical properties were analyzed for four gas diffusion layers, and gas diffusion electrodes (GDEs) for the cathode of high-temperature polymer electrolyte membrane fuel cell were fabricated through bar coating with three binder to carbon (B/C) ratios. Among them, The GDE from JNT30-A6P showed a significant change in secondary pore volume at a B/C ratio of 0.31, which had the largest pore volume among all GDEs. In the polarization curve, JNT30-A6P GDE showed the best membrane electrode assembly (MEA) performance with a peak power density of 384 mW/cm² at a a B/C ratio of 0.31. From the distribution of relaxation time analysis, the peak 1 corresponding to mass transfer resistance of oxygen reduction reaction (ORR) was significantly reduced in the JNT30-A6P GDE. This is the result that when the binder content decreased, the volume of the secondary pore increased, and the mass transfer resistance of ORR decreased, which played an essential role in the MEA performance.

• 한국연소학회:학술대회논문집
• /
• 2005.10a
• /
• pp.170-178
• /
• 2005

Multi-hole type oxygen combustion burner was developed for industrial gasification and smelting furnace. We investigated characteristics of flame, radiation transfer, and soot emission in the convectional oxygen burner with respect to the feeding condition of fuel and oxygen. Regarding the results of the conventional burner, we designed new burners which have larger fuel consumption rate and radiation heat transfer. We changed the size and hole number and shape of the exit plane of the burner. In addition, the performance of the burner was tested with respect to the feeding condition of the fuel and air: Normal Diffusion flame(NDF) and Inverse Diffusion Flame(IDF). We investigated the flame configuration, radiation heat transfer, and soot formation by using a CCD camera, heat flux meter, and Laser Induced Incadescence(LII), respectively. The stable operating condition was obtained by the flame configuration and the flame of the burner which has dented exit plane was more stable in whole operating conditions. The characteristics of radiative heat transfer were sensitive to the feeding condition of reactants and the flame of 75% primary oxygen and 25% secondary oxygen of the IDF case shows maximum radiation heat transfer. The soot volume fraction of the flame was measured in the axial direction of the flame and the amount of soot volume fraction is proportion to the radiation heat transfer. As a result, we can get the optimal operating condition of the newly designed burner which enhances the characteristics of flame stabilization and radiation heat transfer.

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

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.22-29
• /
• 2001

The present study investigates the effects of various rib arrangements and rotating on heat/mass transfer in the cooling passage of gas turbine blades. The cooling passage has very complex flow structure, because of the rib turbulator and rotating effect. Experiments and numerical calculation are conducted to investigate the complex flow structures and heat transfer characteristics; the numerical computation is performed using a commercial code, FLUENT ver.5, to calculate the flow structures and the experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. For the rotating duct tests, the test duct, which is the cross section of is $20mm\times40mm$ (the hydraulic diameter, $D_h$, of 26.7 mm, has two-pass with $180^{\circ}$ turning and the rectangular ribs on the wall. The rib angle of attack is $70^{\circ}$ and the maximum radius of rotation is $21.63D_h$. The partition wall has 10 mm thickness, which is 0.5 times to the channel width, and the distance between the tip of the partition wall and the outer wall of the turning region is 26.7 mm $(1D_h)$. The turning effect of duct flow makes the very complex flow structure including Dean type vortex and high turbulence, so that the heat/mass transfer increases in the turning region and at the entrance of the second pass. The Coriolis effect deflects the flow to the trailing surface, resulting in enhancement of the heat/mass transfer on the trailing surface and reduction on the leading surface in the first pass. However, the opposite phenomena are observed in the second pass. The each rib arrangement makes different secondary flow patterns. The complex heat/mass transfer characteristics are observed by the combined effects of the rib arrangements, duct rotation and flow turning.

• Transactions of Materials Processing
• /
• v.19 no.1
• /
• pp.25-31
• /
• 2010

To achieve desired microstructure and mechanical property of a manufacturing product, heat treatment process is applied as a secondary process after forging. Especially, quenching process is used for improving strength, hardness, and wear resistance since phase transformation occurs owing to rapid heat transfer from the surface of the specimen. In the present paper, a study on surface temperature measurement for water quenching of eutectoid steel was investigated. In order to determine the temperature history in experiments, three different measuring schemes were used by varying installation techniques of K-type thermocouples. Depending on the measured temperature distribution at the surface of the specimen, convective heat transfer coefficients were numerically determined as a function of temperature by the inverse finite element analysis considering the latent heat generation due to phase transformation. Based on the inversely determined convective heat transfer coefficient, temperature, phase, and hardness distributions in the specimen after water quenching were numerically predicted. By comparing the experimental and computational hardness distribution at three different locations in the specimen, the best temperature measuring scheme was determined. This work clearly demonstrates the effect of temperature measurement on the final mechanical property in terms of hardness distribution.