• Journal of Fisheries and Marine Sciences Education
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• v.26 no.4
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• pp.894-901
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• 2014

This study concerns the performance of condensation heat transfer in two-phase loop thermosyphons. In the present work, R134a has been used as the working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, heat flux and wind speed of condensation have been used as the experimental parameters. The results show that the filling rate of working fluid and heat flux are very important factors for the operation of two-phase loop thermosyphons. The optimum liquid fill charge ratio for the best condensation heat transfer rate was 80%.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.3
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• pp.528-537
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• 1989

The objective of this paper is to investigate effects of the specific heat and the diameter of suspending particles on the heat transfer coefficient of two phase turbulent flow with suspension of solid particles in a circular tube with constant heat flux. Heat transfer coefficients of two phase turbulent flow in pipe with suspension of graphite powder were measured with variations of particle sizes and solid-gas loading ratio. Measured data were compared with predictions by numerical analysis in which the turbulece models are closed on the first order level. Results show that heat transfer coefficient increases with increasing the solid-gas loading ratio and the specific heat of suspending material, however, it decreases as the average diameter of particles decreases below $24{\mu}m$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.231-239
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• 2002

Experiments on the single phase cooling heat transfer and pressure drop with microfin tubes were performed using water as a test fluid. Experimental data were obtained in the range of Reynolds number 3000 ~40000 and Prandtl number 4-6. The data of microfin tubes presented the characteristics of rough surface tube in pressure drop and heat transfer Experimental data were compared with the heat transfer and friction factor correlations of smooth tubes. Heat transfer enhancements of microfin tubes were lower than pressure drop penalty factors. The helix angle is more significant parameter in both of the pressure drop and heat transfer than the relative roughness. The correlations of Nusselt number and friction factor were suggested for the tested microfin tubes. Maximum deviations between correlations and experimental data were within $\pm15$% for Nusselt number and $\pm10$% for friction factor.

• Journal of Power System Engineering
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• v.17 no.4
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• pp.45-50
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• 2013

This paper presents the comparison of heat transfer and pressure drop of various secondary refrigerants (single-phase and two-phase) in the indirect refrigeration system. The main results were summarized as follows: In case of heat transfer, it is useful to use secondary refrigerants in low evaporating temperature region and the heat transfer coefficient of single-phase is larger than two-phase secondary refrigerants. In case of pressure drop, it is useful to use secondary refrigerants in high evaporating temperature region and the pressure drop of two-phase is smaller than single-phase secondary refrigerant. Also, $CO_2$ is the best useful because pressure drop of $CO_2$ among the secondary refrigerants is the smallest.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.9
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• pp.477-483
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• 2013

A numerical analysis of solid-liquid phase change was performed on a heat transfer module which consisted of circulating water path (BRINE), heat transfer plate (HTP) and phase change material (PCM) layers, such as high temperature PCM (HPCM, $78{\sim}79^{\circ}C$) and low temperature PCM (LPCM, $28{\sim}29^{\circ}C$). There were five arrangements, consisting of BRINE, HTP, LPCM and HPCM layers in the heat transfer module. The time and heat transfer rate for melting/solidification was compared to their arrangements, against each other. As results, the numerical time without convection was longer than the experimental one for melting/solidification. Moreover, the melting/solidification with the BRINE I-LPCM-BRINE II-HPCM arrangement was faster(10 hours) than the others; HPCM-BRINE-LPCM, BRINE I-HPCM-LPCM-BRINE II one.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.45 no.4
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• pp.146-153
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• 2008

In this paper, a integrated phase-locked loop(PLL) as a clock multiphase generator for a high speed serial link is designed. The designed PLL keeps the same bandwidth and damping factor by using programmable current mirror in the whole operation frequency range. Also, the close-loop transfer function and VCO's phase-noise transfer function of the designed PLL are obtained with circuit netlists. The self impedance on board-mounted chip is calculated according to sizes and positions of decoupling capacitors. Especially, the detailed self-impedance analysis is carried out between frequency ranges represented the maximum gain in the close-loop transfer function and the maximum gain in the VCO's phase noise transfer function. We shows PLL's jitter characteristics by decoupling capacitor's sizes and positions from this result. The designed PLL has the wide operating range of 0.4GHz to 2GHz in operating voltage of 1.8V and it is designed 0.18-um CMOS process. The reference clock is 100MHz and PLL power consumption is 17.28mW in 1.2GHz.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.297-303
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• 2000

Natural convection heat transfer have been paid attention because it can be applied to various areas such as cooling of nuclear reactor, heat storing system and so on. Among such applications, the melting process of phase change material(PCM) has been actively studied. However most researches have focused on phase change heat transfer in natural melting. Therefore, In this paper, ultrasonic vibration was adopted to increase the melting rate. In addition, general relationship and corelationship between melting with ultrasonic vibration and melting without ultrasonic vibration have been established during the melting of PCM.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.71-76
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• 2000

This experimental study was conducted to figure out the drag reduction and convective heat transfer in vertical downward two-phase flow with polymer additives. The drag reduction effect were analyzed by using the difference of the pressure drop between the flow with polymer additives and without it. Experimental results show that the pressure drop with polymer additives is less than the pressure drop without polymer in vertical downward two-phase flow. And the convective heat transfer has decreased with increasing the polymer concentration in vertical downward two-phase flow.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.724-727
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• 2002

2,7-dibromo-9, 9-dialkyl-substituted-fluorene derivatives were prepared by the alkylation of 2,7-dibromofluorene with various alkyl groups under two-phase phase transfer catalysis (PTC) conditions, as monomers for synthesizing poly(dialkylfluorene)s. Tetra-nbutylammonium hydrogen sulfate (TBAHS) was used as a phase transfer catalyst to enhance nucleophilic substitution. In addition, NaOH in water (25M) was used as a base to generate anions. Compared to conventional alkylation using butyllithium(BuLi), the reaction using the PTC technique attained high selectivity and substantial conversion of reactants, due to the enhanced reaction rate, while the reaction was carried out under moderate conditions. An approximately 90% yield was obtained from the reaction and the reaction time was remarkably reduced. 2,7-dibromo-9,9-dihexyl-fluorene, 2,7-dibromo-9,9-dioctyl-fluorene, and 2,7-dibromo-9,9-di(2-ethylhexyl)-fluorene were effectively synthesized by phase transfer catalytic reaction.

• The Journal of the Acoustical Society of Korea
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• v.18 no.2E
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• pp.31-38
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• 1999

This paper focuses on extracting formants from transfer function, derived from linear prediction analysis of speech signal. The second derivative of the log magnitude spectrum of the transfer function, the first and third derivatives of the phase spectrum of the transfer function in the z-plane are discussed. Their resolutions of detecting formants are analyzed and some comparisons are given. Theoretical analyses and experimental results show that the third derivative of the phase spectrum decays more rapidly around the formant locations than the first derivative of the phase spectrum and the second derivative of the log magnitude spectrum. Compared with the second derivative of the log spectrum and the first derivative of the phase spectrum, the third derivative of the phase spectrum has higher resolution in frequency domain and provides more accurate formant extraction.