• Bulletin of the Korean Chemical Society
• /
• v.31 no.6
• /
• pp.1704-1710
• /
• 2010

The structure of a 2D grid-like copper(II) complex [Cu$(NCO)_2$(pyz)](pyz=pyrazine) (1) consists of 1D chains of Cu-pyz units connected by double end-on (EO) cyanato bridges. Each Cu(II) ion has a distorted octahedral coordination, completed by the four EO cyanato and two pyrazine ligands. Magnetic interactions through EO cyanato and pyrazine bridges in 1 are discussed on the basis of DFT broken-symmetry calculations at the B3LYP level. For model dicopper(II) complexes I (bridged by cyanato) and II (bridged by pyrazine), electronic structure calculations reproduce very well the experimental couplings for the S = 1/2 ferromagnetic and antiferromagnetic exchange-coupled 2D system: the calculated exchange parameters J are +1.25 $cm^{-1}$ and -3.07 $cm^{-1}$ for I and II, respectively. The $\sigma$ orbital interactions between the Cu $x^2-y^2$ magnetic orbitals and the nitrogen lone-pair orbitals of pyrazine are analyzed from the viewpoint of through-bond interaction. The energy splitting of 0.106 eV between two SOMOs indicates that the superexchange interaction should be antiferromagnetic in II. On the other hand, there are no bridging orbitals that efficiently connect the two copper(II) magnetic orbitals in I because the HOMOs of the basal-apical NCO bridge do not play a role in the formation of overlap interaction pathway. The energy separation in the pair of SOMOs of I is calculated to be very small (0.054 eV). This result is consistent with the occurrence of weakly ferromagnetic properties in I.

• Journal of the Korean Ceramic Society
• /
• v.53 no.6
• /
• pp.659-664
• /
• 2016

Ash deposition of heat exchange boiler, caused mainly by accumulation of particulate matter, reduces heat transfer of the boiler system. Heat and mass transfer through porous media such as ash deposits mainly depend on the microstructure of deposited ash. Therefore, in this study, we investigated microstructural and thermal properties of the ash deposited on the boiler tube. Samples for this research were obtained from the fuel economizer tube in an industrial waste incinerator. To characterize microstructures of the ash deposit samples, scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD) and BET analysis were employed. The results revealed that it had a porous structure with small particles mostly of less than a few micrometers; the contents of Ca and S were 19.3, 22.6% and 18.5, 18.7%, respectively. Also, the results showed that it consisted mainly of anhydrite ($CaSO_4$) crystals. - The thermal conductivities of the ash deposit sample obtained from the economizer tube in industrial waste incinerator were measured to be 0.63 and 0.54 W/mK at $200^{\circ}C$, which were about 100 times less than the thermal conductivity (61.32 W/mK) of the boiler tube itself, indicating that ash deposition on the boiler tube was closely related to a decrease in boiler heat transfer.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2009.09a
• /
• pp.385-395
• /
• 2009

In this study, a series of numerical analysis has been accomplished on the thermal performance and sectional efficiency of a closed-loop vertical ground heat exchanger (U-loop) in a geothermal heat pump system (GHP) considering the circulating fluid, pipe, grout and soil formation. A finite element analysis program, ABAQUS, was employed to evaluate the temperature distribution on the cross section of the U-loop system involving HDPE pipe/grout/formation and to compare sectional efficiency between the conventional U-loop and a new latticed HDPE pipe system. Especially, the latticed pipe is equipped with a thermal insulation zone in order to reduce thermal interference between the inflow pipe and the outflow pipe. Also, a thermal stress analysis was performed with the aid of ABAQUS. 3-D finite volume analysis program, FLUENT, was adapted to analyze a coupled system between fluid circulation in the pipe and heat transfer and simulate an operating process of the closed-loop vertical ground heat exchanger. In this analysis, the effect of the thermal properties of grout, rate of circulation pump, distance between the inflow pipe and the outflow pipe, and the effectiveness of the latticed HDPE pipe system are taken into account.

• The Journal of the Acoustical Society of Korea
• /
• v.35 no.6
• /
• pp.436-444
• /
• 2016

Uniformity in transducer performance is a must-have to ensure the reliable acoustic performance of a tile projector, used for active echo reduction. However, practical limitations imposed by variations in material properties and fabrication errors lead to performance variations among unit transducers, which could degrade the radiation characteristics (transmitting voltage response and directivity) of the tile projector and ultimately the echo reduction performance. In this paper we present a method to minimize these adverse effects via an appropriate placement of unit transducers within the tile projector. To this end, we perform a series of coupled acoustic-piezoelectric simulations, assuming a group of 36 unit transducers having 6 dB variations in transmitting voltage response, to analyze and compare the radiation characteristics of tile projectors under different transducer placement schemes.

• Clean Technology
• /
• v.18 no.1
• /
• pp.89-94
• /
• 2012

In this study, we investigated the activity of Pd and Pt supported on acidic Fe-ZSM5 supports for selective catalytic oxidation of ammonia ($NH_3$-SCO). Among the catalysts, Pt/Fe-ZSM5 catalyst exhibited superior $NH_3$-SCO activity to Pd/Fe-ZSM5 catalyst. We also tested Pt/Fe-ZSM5 catalysts with different Fe loading using ion-exchange method to prepare Fe-ZSM5 supports, which resulted in the increased catalytic performance with smaller Fe content: $NH_3$ was oxidized completely at low temperature ($250^{\circ}C$). The physicochemical properties of Fe-ZSM5 were investigated to figure out the relationship between the characteristics of the catalysts and the catalytic activity on $NH_3$-SCO by Inductively coupled plasma-atomic emissions spectrometer (ICP-AES), $N_2$ sorption, X-ray diffraction (XRD), temperature programmed desorption of $NH_3$ ($NH_3$-TPD) technique.

• Coupled systems mechanics
• /
• v.9 no.3
• /
• pp.237-264
• /
• 2020

This article investigates the static behaviour of functionally graded (FG) plates sometimes declared as advanced composite plates by using a simple and accurate quasi-3D and 2D hyperbolic higher-order shear deformation theories. The properties of functionally graded materials (FGMs) are assumed to vary continuously through the thickness direction according to exponential law distribution (E-FGM). The kinematics of the present theories is modeled with an undetermined integral component and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate; therefore, it does not require the shear correction factor. The fundamental governing differential equations and boundary conditions of exponentially graded plates are derived by employing the static version of principle of virtual work. Analytical solutions for bending of EG plates subjected to sinusoidal distributed load are obtained for simply supported boundary conditions using Navier'is solution procedure developed in the double Fourier trigonometric series. The results for the displacements and stresses of geometrically different EG plates are presented and compared with 3D exact solution and with other quasi-3D and 2D higher-order shear deformation theories to verify the accuracy of the present theory.

• Journal of Advanced Marine Engineering and Technology
• /
• v.37 no.5
• /
• pp.533-540
• /
• 2013

Prime movers in engine rooms inherently are much affected by the adjustment of their governors for the steady state and transient properties, consequently requiring that marine engineers shall be well familiar with the way to manage governor dials for normal operation. The hydro-mechanical governors basically have different control characteristics and adjustment parameters of stability from digital governors. The former include compensation mechanism using dash pot while the control algorithm of the latter is usually based on the PID action. This study is for configuring a simulation module to let trainees practice how to adjust dials for stability on hydraulic governors in the view that the practice by real governors and engines is time consuming and high cost for operation. The governor module includes the adjusting points such as speed set, speed droop, needle valve and compensation pointer with engine module of $2^{nd}$ order coupled. The results of simulation showed satisfactory responses as a training tool for the adjustment of control parameters.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.20 no.12
• /
• pp.781-788
• /
• 2008

A dynamic model has been developed to simulate dynamic operation of a real double-effect absorption chiller. Dynamic behavior of working fluids in main components was modeled in first-order nonlinear differential equations based on heat and mass balances. Mass transport mechanisms among the main components were modeled by valve throttling, 'U' tube overflow and solution sub-cooling. The nonlinear dynamic equations coupled with the subroutines to calculate thermodynamic properties of working fluids were solved by a numerical method. The dynamic performance of the model was compared with the test data of a commercial medium chiller. The model showed a good agreement with the test data except for the first 5,000 seconds during which different flow rates of the weak solution caused some discrepancy. It was found that the chiller dynamics is governed by the inlet temperatures of the cooling water and the chilled water when the heat input to the chiller is relatively constant.

• Proceedings of the SAREK Conference
• /
• 2008.11a
• /
• pp.39-44
• /
• 2008

The heat exchange between the Borehole Heat Exchanger(BHE) and the surrounding ground depends directly on ground thermal conductivity k at the certain site. The k is thus a key parameter in designing BHE and coupled geothermal heat pump systems. Currently, although a thermal hydraulic response test(TRT) is mostly used in practice, the thermal hydraulic TRT needs additional power and is generally time-consuming. A new, simple wireless P/T probe for a hi-speed k determination was introduced in this paper. This technique using a wireless P/T probe is less time-consuming and requires no external source of energy for measurement and predicts local thermal properties by measuring soil temperatures along the depth. Measured temperature data along the depth was analyzed. In order to verify the new technique for the determination of ground thermal conductivity, ground thermal conductivity k that calculated from the measured temperature data using a wireless P/T probe was compared with one obtained from conventional hydraulic TRT. When comparing the average k of two methods, the relative error was approximately 10%. As a result, the electronic TRT can replace the conventional hydraulic TRT method after carrying out the additional research on a lot of sites.

• Journal of Ginseng Research
• /
• v.39 no.4
• /
• pp.338-344
• /
• 2015

Background: Ginseng (the roots of Panax ginseng Meyer) is a well-known traditional Oriental medicine and is now widely used as a health food. It contains several types of ginsenosides, which are considered the major active medicinal components of ginseng. It has recently been reported that the qualitative and quantitative properties of ginsenosides found in ginseng may differ, depending on cultivation regions, ages, species, and so on. Therefore, it is necessary to study these variations with respect to cultivation ages and regions. Methods: In this study, 3-6-yr-old roots of P. ginseng were collected from three different cultivation regions. The contents of five ginsenosides (Rb1, Rd, Rc, Re, and Rgl) were measured by rapid resolution liquid chromatography coupled with quadruple-time-of-flight mass spectrometry. The Kruskal-Wallis Rank sum test and multiple t test were used for comparative analysis of the data to evaluate the dynamic changes in the accumulation of these ginsenosides affected by cultivation regions and ages. Results: The content and composition of ginsenosides varied significantly among specimens collected from different cultivation regions and having different cultivation ages. For all samples, the content of Rg1 and Re ginsenosides increases with age and this rate of increase is different for each sample. The contents of Rb1, Rc, and Rd varied with cultivation ages in samples from different cultivation regions; especially, Rb1 from a 6-yr-old root showed approximately twofold variation among the samples from three cultivation regions. Furthermore, the content of Rb1 highly correlated with that of Rd (r = 0.89 across all locations and ages). Conclusion: In our study, only the contents of ginsenosides Rg1 and Re were affected by the root age. Ginsenosides Rb1, Rc, and Rd varied widely with ages in samples from different cultivation regions.