• 대한기계학회논문집B
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• 제22권4호
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• pp.542-550
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• 1998

A direct contact heat exchanger using particle-suspended gas as a heat transfer medium is analyzed with an extended emphasis on the radiation, i. e., considering the radiation by both gas and particles. While the Runge-Kutta method is used for a numerical analysis of the momentum and energy equations, the finite volume method is utilized to solve the radiative transfer equation. Present study shows a notable effect by the gas radiation in addition to the particle radiation, especially when changing the chamber length as well as the gas and particle mass flow rate. When the gas and particle mass flow rate is raised, the gas temperature in the particle heater still increases as the gas absorption coefficient increases, which is different from the results for the small scale heat exchanger.

• 한국가시화정보학회지
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• 제13권1호
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• pp.30-34
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• 2015

This study concerns flow and heat transfer characteristics of FC-72 condensing flow in a micro-channel. A computational model of condensing flow with a hydraulic diameter of 1 mm is constructed using the FLUENT computational fluid dynamics code. The computed void fraction contour plots are presented for different mass velocities. The smooth-annular, wavy-annular, transition and slug flows are observed with the model, which are quite similar to those observed in a micro-channel experiment. The computed two-phase condensing heat transfer coefficient is compared with previous empirical correlation for two-phase condensation heat transfer in micro-channels.

• 전력전자학회논문지
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• 제25권5호
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• pp.404-411
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• 2020

Inductive power transfer (IPT) systems for electric vehicles generally require zero phase angle (ZPA) frequency tracking control to achieve high efficiency. Current sensors are used for ZPA frequency tracking control. However, the use of current sensors causes several problems, such as switching noise, degrading control performance, and control complexity. To solve these problems, this study proposes ZPA frequency tracking control without current sensors. Such control enables ZPA frequency tracking without real-time control and achieves stable zero voltage switching operation closed to ZPA frequency within all coupling coefficient and load ranges. The validity of the proposed control algorithm is verified on LCCL-S topology with a 3.3 kW rating IPT experimental test bed. Simulation verification is also performed.

• Bulletin of the Korean Chemical Society
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• 제22권9호
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• pp.958-962
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• 2001

The chiral amine auxiliary mediated stereoselective alkylation reactions of glycinamides 1-6 and 15-17 using phase transfer catalyst (PTC) for liquid-solid extraction are described. The secondary N-(diphenylmethylene) glycinamides 1, 2 and 3 give better selectivities and yields than tertiary N-(diphenylmethylene) glycinamides 4, 5 and 6. Alkylation of the glycinamide 1 and 2 using 18-Crown-6 as a PTC in toluene at $-40^{\circ}C$ gives best selectivities and yields. Alkylations of N-(4-chlorophenylmethylene)glycinamides 15, 16 and 17 under same PTC conditions give $\alpha$, $\alpha-disubstituted$ amino acid derivatives 18, 19 and 20 with low diastereoselectivities.

• 대한방사성의약품학회지
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• 제7권2호
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• pp.141-146
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• 2021

With increasing interest in fluorinated compounds, nucleophilic fluorination reaction has been generally used for synthesizing fluorine-containing chemicals. However, alkali metal fluorides (MFs) generally have low solubility and reactivity in organic solvent. To overcome these problems, various phase transfer catalysts (PTCs) have been investigated. Calix-arene is known as to capture the metal cation(M⁺), and therefore in this review, we would like to introduce several kinds of calix-arene based PTCs, such as bis-tert-alcohol-functionalized crown-6-calix[4]arene (BACCA), oligo-ethylene glycol linked bis-triethyleneglycol crown-5-calix[4]arene (BTC5A), and ionic liquid functionalized calix-arene based catalyst, as well as ion-pair receptor crown-6-calix[4]arene-capped calix[4]pyrrole.

• 천문학논총
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• 제23권2호
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• pp.25-29
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• 2008

Scattering of incident light by the interstellar dust is usually approximated by Henyey-Greenstein scattering phase function. Recently, Draine (2003) proposed a new analytic phase function with two parameters. We describe an algorithm to generate random numbers distributed according to the Draine’s function, and compare two phase functions. It is also derived exact solutions of two parameters for given values ${\langle}cos{\theta}{\rangle}$ and ${\langle}cos^2{\theta}{\rangle}$. It is found that Henyey-Greenstein function with g = ${\langle}cos{\theta}{\rangle}$ provides a good approximation for ${\lambda}\;>\;2000{\AA}$. At shorter wavelengths, more realistic phase function may be needed for radiative transfer models.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.246-251
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• 2001

Solid-liquid phase change (i.e. melting or solidification) occurs in a number of situations of practical interest. Some common examples include the melting of edible oil, metallurgical process such as casting and welding, and materials science applications such as crystal growth. Therefore, due to the practical importance of the subject, there have been a large number of experimental and numerical studies of problems involving phase change during the past few decades. Also, this study presented the effective way to enhance phase change heat transfer.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 ITC-CSCC -1
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• pp.237-240
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• 2000

We have proposed a simple method based on IIR filters for realizing sound image localization. How-ever the nonlinearity of phase characteristics of the IIR filters, which are used for sound image localization, cause decrease of the localization accuracy. In this paper we investigate the influence of phase characteristics on the sound localization. Head-related transfer functions (HRTFs) of a dummy-head are approximated by the IIR filter. We carried out sound image localization experiment with 2-loudspeaker reproduction using the approximated HRTFs. Then the errors which obtained from experiments were compared with the theoretical values which were estimated from the phase shifts of the IIR filters. As a result there was little influence of the nonlinear phase characteristics of the IIR fitters in the localization on the horizontal plane.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2943-2948
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• 2010

Silica monolith powders were prepared by a new procedure where ground powders of proper size distribution were obtained without sieving. An initiator was attached to this ground monolith and polystyrene was bound by reversible addition-fragmentation chain transfer polymerization to give a new stationary phase. The separation efficiency of this phase was found better than that of the polystyrene bound phase based on conventional silica particles and that of the C18 bound silica monolith powders.

• Journal of Advanced Marine Engineering and Technology
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• 제20권3호
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• pp.162-170
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• 1996

A numerical study on the Stefan problem occurred in cryosurgery is performed. Crank-Nicholson type finite difference algorithm based on the enthaly method is adapted to solve the phase change problem in this study. As it is a moving boundary problem, special emphasis is put on the estimation of the freezing front location. Two cases selected here are freezings of human tissue by disk type cryoprobe and by hemispherical one. In both cases, the heat flows are considered to be one dimensional. The calculated results using enthalpy method are compared with those using the program TRUMP and with Neumann's solution. These results agree guite well with each other. While it is pretty difficult to get accurate freezing front location by TRUMP due to the so- called "phase change knee" occured during the phase change, the algorithm based on the enthalpy method is proved to be very powerful to cope with this kind of problem.f problem.