• Journal of Mechanical Science and Technology
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• v.17 no.6
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• pp.935-944
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• 2003

Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface had a minor effect.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.177-179
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• 2012

We present Spitzer IRS spectroscopy of $CO_2$ ice toward 19 young stellar objects (YSOs) with luminosity lower than $1L_{\odot}$. Pure $CO_2$ ice forms only at elevated temperatures, T > 20 K, and thus at higher luminosities. Current internal luminosities of YSOs with L < $1L_{\odot}$ do not provide such conditions out to radii of typical envelopes. Significant amounts of pure $CO_2$ ice would signify a higher past luminosity. We analyze $15.2{\mu}m$ $CO_2$ ice bending mode absorption lines in comparison to the laboratory data. We decompose pure $CO_2$ ice from 12 out of 19 young low luminosity sources. The presence of the pure $CO_2$ ice component indicates high dust temperature and hence high luminosity in the past. The sum of all the ice components (total $CO_2$ ice amount) can be explained by a long period of low luminosity stage between episodic accretion bursts as predicted in an episodic accretion scenario. Chemical modeling shows that the episodic accretion scenario explains the observed total $CO_2$ ice amount best.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.2
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• pp.225-233
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• 1995

Experiments were performed to investigate the heat transfer characteristics of nonazeotropic mixture R-22+R-114 in a heat pump system. The ranges of parameter, such as heat flux, mass flow rate, and quality were $8,141{\sim}32,564W/m^2$, 24~58kg/h, and 0~1, respectively. The overall compositions of the mixtures were 50 and 100 per-cent of R-22 by weight for R-22+R-114 mixture. The results indicated that there were distinct different heat transfer phenomena between the pure substance and the mixture. In case of pure refrigerant the heat transfer rates for cooling were strongly dependent upon quality of the refrigerant. Overall evaporating heat transfer coefficients for the mixture were somewhat lower than pure R-22 values in the forced convective boiling region. For a given flow rate, the heat transfer coefficient at the circumferential tube wall(top, side, and bottom of the test tube) for R-22/R-114(50/50wt%)mixture, however, was higher than for pure R-22 at side and bottom of the tube. Furthermore, a prediction for the evaporating heat transfer coefficient of the mixtures was developed based on the method of Yoshida et.al.'s. The resulting correlation yielded a good agreement with the data for the refrigerant mixtures.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1239-1246
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• 2000

The objective of this work is to measure space and time resolved wall heat fluxes during nucleate pool boiling of R113/R11 mixtures using a microscale heater array in conjunction with a high speed CCD. The microscale heater array is constructed using VLSI techniques, and consists of 96 serpentine platinum resistance heaters on a transparent quartz substrate. Electronic feedback circuits are used to keep the temperature of each heater at a specified temperature and the variation in heating power required to keep the temperature constant is measured. Heat flux data around an isolated bubble are obtained with triggered CCD images. CCD images are obtained at a rate of 1000frames/second. The heat transfer variation vs. time on the heaters directly around the nucleation site is plotted and correlated with images of the bubble obtainedby using the high speed CCD. For both of the mixture(R11/R113) and pure system(pure R11, pure R113), the wall heat fluxes are presented and compared to find out the qualitative difference between pure and binary mixture nucleate boiling.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.2
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• pp.144-151
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• 2003

An experimental study was carried out in a uniformly heated horizontal tube to examine heat transfer characteristics of pure refrigerants, R134a and R123, and their mixtures during flow boiling. The flow pattern was also observed through tubular sight glasses with an internal diameter of 10 mm located at the inlet and outlet of the test section. Tests were run at a pressure of 0.6 MPa and in the heat flux ranges of 5~100 kW/$m^2$, vapor Quality 0~100 percent and mass velocity of 150-600 kg/$m^2$s. The observed flow patterns were compared to the flow pattern map of Kattan et al., which predicted well the present data over the entire range of mass velocity employed in this study. Heat transfer coefficients of the mixture were less than the interpolated values between pure fluids both in the low quality region where the nucleate boiling is dominant and in the high quality region where the convective evaporation is dominant.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.2
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• pp.254-266
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• 1996

Boiling heat transfer coefficients of pure refrigerants(R22, R32, R125, R134a, R290, and R600a) and refrigerant mixtures(R32/R134a and R290/R600a) are measured experimentally and compared with several correlations. Convective boiling term of Chen's correlation predicts experimental data for pure refrigerants fairly well(root-mean-square error of 12.1% for the quality range over 0.2). An analysis of convective boiling heat transfer of refrigerant mixtures is performed for an annular flow to study degradation of heat transfer. Annular flow is the subject of this analysis because a great portion of the evaporator in refrigeration or air conditioning system is known to be in the annular flow regime. Mass transfer effect due to composition difference between liquid and vapor phases, which is considered as a driving force for mass transfer at interface, is included in this analysis. Correction factor $C_F$ is introduced to the correlation for the pure substances through annular flow analysis to apply the correlation to the mixtures. The flow boiling heat transfer coefficients are calculated using the correlation considering nucleate boilling effect in the low quality region and mass transfer effect for nonzazeotropic refrigerant mixtures.

• The Korean Journal of Ceramics
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• v.5 no.3
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• pp.288-295
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• 1999

Partial conductivities contributed by electron holes, oxygen ions, and protons were caluclated in $SrZr_{0.95}Y_{0.05}O_{2.975}$, using the reported formulae derived from the defect chemistry of HTPCs. Required parameters were obtained from the graphical analysis of total conductivity variation against partial pressure of water vapor and oxygen. Predicted overall conductivities showed a reasonable agreement with experimental measurements. The conductivity of the material showed a linear increase with square root of the water vapor pressure. This increase was due to proton conduction in an almost pure ionic conductivity. The calculation of partial conductivities at $800^{\circ}C$ resulted in an almost pure ionic conductivity at $P_{02}=10^{-10}$ atm and a predominant hole conductivity at $P_{02}=10^{-10}$ atm. Pure proton conduction was not expected at this temperature, contrary to the earlier reports. Discussions were made in relation with reported thermodynamic data and defect structure of the material. It was shown that from the total conductivity dependence on water vapor pressure, the pure ionic conductivity at low oxygen partial pressures could be separated into protonic and oxygen ionic conductivity in $ZrO_2$-based HTPCs.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.91-100
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• 1996

Experimental results for forced convection condensation of non-azeotropic refrigerant mixtures inside a horizontal smooth tube are presented. The mixtures of R-22+R-134a and pure refrigerants R-22 and R-134a are used as the test fluids and a double pipe heat exchanger of 7.5mm ID and 4800mm long inside tube is used. The range of parameters are 100-300kg/h of mass flow rate, 0-1.0 of quality, and 0, 33, 50, 67, and 100 weight percent of R-22 mass fraction in the mixtures. The heat flux, vapor pressure, vapor temperature and tube wall temperature were measured. Using the data, the local and average heat transfer coefficients for the condensation have been obtained. In the same given experimental conditions, the liquid heat transfer coefficients for NARMs were considerally lower than that of the pure refrigerant of R-22 and R-134a. Local heat transfer characteristics for NARMs were different from pure refrigerant R-22 and R-134a. In some regions, local heat transfer coefficients for NARMs were increased in the following order ; Bottom$\rightarrow$Top$\rightarrow$Side. The condensation heat transfer coefficients for NARMs increased with mass velocity, heat flux, and quality, but were considerably lower than that of pure refigerant R-22 and R-134a.

• The Journal of Korean Academic Society of Nursing Education
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• v.8 no.1
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• pp.38-50
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• 2002

The purpose of this study is to identify the relationship among injury prevention practices, health locus of control, and response patterns to HLOC of the elderly. Subjects were 121 healthy elderly. The data had been collected from November 5 to 18 in 2001 and analyzed with descriptive statistics, t-test, ANOVA, Pearson's correlation and stepwise multiple regression. Health locus of control and injury prevention practices were measured by using MHLC scale and an instrument created by the researcher on the basis of the results of literature review respectively. The results of this study were as follows: The mean score of injury prevention practices was 2.80 and the mean scores for the health locus of control were internal health locus of control : 17.25, external health locus of control : 16.09, and chance health locus of control : 14.26. The response patterns of the HLOC identified were six types; pure internal, pure powerful others, pure chance, double external, believers in control, and complex control. The 'pure internal' was the largest group(35.5%), and the 'believers in control' was the next(31.4%). The relationship between internal health locus of control and the injury prevention practices of the elderly revealed a significant correlation(r=.215, p=.018). The relationship between external health locus of control and the injury prevention practices of the elderly revealed a significant correlation (r= .208, p=.022). There was significant difference between response patterns of the health locus of control and injury prevention practices(F=2.393, p=.042). There were significant differences between injury prevention practices and general characteristic factors, which were education, family type, administration of medication, injury experience, ADL, and self-directed search for health information. Self-directed search for health information, injury experience, and education explained 16.7% of the variance for injury prevention practices. The above results may be used as the basic data for seeking more efficient way of improving safety of the elderly.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.7 no.1
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• pp.21-29
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• 1993

In this paper, we studied the 50% flashover voltage of lightening impulse which affect the most serious damages on the insulation of the electric power network system. Also its V -t characteristics and corona process phenomena of pure $SF_6, N_2, SF_6-N_2$mixtures under the circumstances of nonuniform field gap are researched. Comparing the characteristics of pure $SF_6$ with that of $SF_6, N_2$mixtures, we discussed that breakdown processes and $SF_6, N_2$ mixture's application to economics.As a results, 50% flashover voltage of $SF_6$ 50% - $N_2$ 50% for impulse voltage is higher then that of 80% of pure SF6, measured data and calculated data by equal area law are almost equal from the points of view of V-t characteristics. Therefore, it has been known that $SF_6$ 50% - $N_2$ 50% mixtures can be used as an economic constitution gas of pure $SF_6$, it is verified that corona processes from Lichtenberg figure.