• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.6
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• pp.457-463
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• 2007

Various correlations of saturated vapor density in a truncated power series form are tested and compared in this study. Saturated vapor density correlation can be expressed relating logarithmic reduced density to the reduced temperature. Five types of correlation has been investigated using saturated vapor density data for 22 pure substance refrigerants from ASHRAE (American Society of Heating, Reftigerating and Air-Conditioning Engineers, Inc.) property tables and NIST (National Institute of Standards and Technology) Chemistry Webbook. Correlations are fitted to the data points by least squares method. Data points are equally weighted. The best type of correlation among the five types is suggested. The results obtained indicate that the best correlations with 3, 4, and 5 terms yield average AAD's (Average Absolute Deviation) of 0.27%, 0.04%, and 0.02%, respectively, while widely used conventional correlations with 3, 4, and 5 terms yield those of 1.19%, 0.61%, and 0.17%. The suggested type of correlation could reduce the number of terms while improving performance.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.205-210
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• 2001

Cubic equations of state with two temperature dependent parameters are suggested and optimized using ASHRAE data for methane, propane, carbon dioxide, R-32 and R-134a. Appropriate simple functional forms are assumed for the temperature dependent parameters. The equations tested are Martin, Fuller, Harmens-Knapp, Schmidt-Wenzel. Among them modified Schmidt-Wenzel equation of state appears to be the choice for calculation of saturation properties such as vapor pressures, saturated liquid volumes, and saturated vapor volumes with an average absolute deviation of about one percent over the entire region excluding; the near cirtical.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.677-680
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• 2005

In numerical analysis on the thermal performance of the heat exchanger with phase change fluids, the numerical values of thermodynamic properties are needed. But the steam table should be modeled properly as the direct use of thermodynamic properties of the steam table is impossible. In this study the function approximation characteristics of neural networks was used in modeling the saturated vapor region of refrigerant R12. The neural network consists of one input layer with one node, two hidden layers with 10 and 20 nodes each and one output layer with 7 nodes. Input can be both saturation temperature and saturation pressure and two cases were examined. The proposed model gives percentage error of ${\pm}$0.005% for enthalpy and entropy, ${\pm}$0.02% for specific volume and ${\pm}$0.02% for saturation pressure and saturation temperature except several points. From this results neural network could be a powerful method in function approximation of saturated vapor region of R12.

• Atmosphere
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• v.33 no.5
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• pp.457-475
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• 2023

Accurately predicting localized heavy rainfall is challenging without high-resolution mesoscale cloud information in the numerical model's initial field, as precipitation intensity and amount vary significantly across regions. In the Korean Peninsula, the radar observation network covers the entire country, providing high-resolution data on hydrometeors which is suitable for data assimilation (DA). During the pre-processing stage, radar reflectivity is classified into hydrometeors (e.g., rain, snow, graupel) using the background temperature field. The mixing ratio of each hydrometeor is converted and inputted into a numerical model. Moreover, assimilating saturated water vapor mixing ratio and decomposing radar radial velocity into a three-dimensional wind vector improves the atmospheric dynamic field. This study presents radar DA experiments using a numerical prediction model to enhance the wind, water vapor, and hydrometeor mixing ratio information. The impact of radar DA on precipitation prediction is analyzed separately for each radar component. Assimilating radial velocity improves the dynamic field, while assimilating hydrometeor mixing ratio reduces the spin-up period in cloud microphysical processes, simulating initial precipitation growth. Assimilating water vapor mixing ratio further captures a moist atmospheric environment, maintaining continuous growth of hydrometeors, resulting in concentrated heavy rainfall. Overall, the radar DA experiment showed a 32.78% improvement in precipitation forecast accuracy compared to experiments without DA across four cases. Further research in related fields is necessary to improve predictions of mesoscale heavy rainfall in South Korea, mitigating its impact on human life and property.

• Journal of the Korean Society of Propulsion Engineers
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• v.19 no.1
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• pp.61-67
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• 2015

The cooling of hot exhaust gas is an important issue for the construction of combustor test facility. Water spray is an effective method for exhaust gas cooling due to its large latent heat in process of evaporation. In this study, 1-D analysis has been performed based on continuity, energy conservation, and saturated vapor property to understand water spray cooling of combustion gas. In the exhaust duct of combustor test facility, the injected water decreases combustion gas temperature, and evaporates in the combustion gas. However, some of the injected water is collected in the sump due to condensation. The evaporation of water helps combustion gas cooling, but causes pressure increase inside the exhaust duct due to increase of vapor pressure. These phenomena has been analyzed by 1-D modeling in this study. From 1-D analysis, the adequate mass flow rate of water spray to cool combustion gas and to avoid excessive pressure rise inside the exhaust duct has been decided.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.183-188
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• 2005

The effect of heat conduction resistance on laminar film condensation of the pure saturated vapor in forced flow over a flat plate has been investigated as boundary layer solutions. A efficient numerical methods for water are proposed for its solution. The momentum and energy balance equations are reduced to a nonlinear system of ordinary differential equations with four parameters: the Prandtl number, Pr, Modified Jacob number, $Ja^{\ast}/Pr$, defined by an overall temperature difference, a property ratio $\sqrt{P_l{\mu}_l/P_v{\mu}_v}$ and the conjugate parameter ${\zeta}$. The similarity and simplified solutions obtained reveal the effects of the conjugate parameter.

• Journal of Mechanical Science and Technology
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• v.15 no.9
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• pp.1339-1345
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• 2001

Laminar film condensation of a saturated pure vapor in forced flow over a flat plate is analyzed as boundary layer solutions. Similarity solutions for some real fluids are presented as a function of modified Jakob number (C$\_$pι/ ΔΤ/Prh$\_$fg/) with property ratio (No Abstract.see full/text) and Pγ as parameters and compared with approximate solutions which were obtained from energy and momentum equations without convection and inertia terms in liquid flow. Approximate solutions agree well with the similarity solutions when the values of modified Jakob number are less then 0.1 near 1 atmospheric pressure.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.303-311
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• 2005

The problem of conjugate laminar film condensation of the pure saturated vapor in forced flow over a flat plate has been investigated as boundary layer solutions. A simple and efficient numerical method is proposed for its solution. The interfacial temperature is obtained as a root of 3rd order polynomial for laminar film condensation, and it is presented as a function of the conjugate parameter. The momentum and energy balance equations are reduced to a nonlinear system of ordinary differential equations with four parameters: the Prandtl number, Pr, Jacob number, $Ja^{\ast}$, defined by an overall temperature difference, a property ratio R and the conjugate parameter ${\zeta}$. The approximate solutions thus obtained reveal the effects of the conjugate parameter.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.224-224
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• 2012

For decades, carbon fiber has expanded their application fields from reinforced composites to energy storage and transfer technologies such as electrodes for super-capacitors and lithium ion batteries and gas diffusion layers for proton exchange membrane fuel cell. Especially in fuel cell, water repellency of gas diffusion layer has become very important property for preventing flooding which is induced by condensed water could damage the fuel cell performance. In this work, we fabricated superhydrophobic network of carbon fiber with high aspect ratio hair-like nanostructure by preferential oxygen plasma etching. Superhydrophobic carbon fiber surfaces were achieved by hydrophobic material coating with a siloxane-based hydrocarbon film, which increased the water contact angle from $147^{\circ}$ to $163^{\circ}$ and decreased the contact angle hysteresis from $71^{\circ}$ to below $5^{\circ}$, sufficient to cause droplet roll-off from the surface in millimeter scale water droplet deposition test. Also, we have explored that the condensation behavior (nucleation and growth) of water droplet on the superhydrophobic carbon fiber were significantly retarded due to the high-aspect-ratio nanostructures under super-saturated vapor conditions. It is implied that superhydrophobic carbon fiber can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell. Moreover, such nanostructuring of carbon-based materials can be extended to carbon fiber, carbon black or carbon films for applications as a cathode in lithium batteries or carbon fiber composites.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.6
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• pp.345-352
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• 2010

In this study, external condensation heat transfer coefficients(HTCs) of R134a and R1234yf are measured on a plain, low fin, and Turbo-C tubes at the saturated vapor temperature of $39^{\circ}C$ with the wall subcooling of $3{\sim}8^{\circ}C$. R1234yf is a new alternative refrigerant of low greenhouse warming potential for replacing R134a which is one of the greenhouse gases controlled by Kyoto protocol and is used extensively in mobile air-conditioners. Test results show that the external condensation HTCs of R1234yf are very similar to those of R134a for all three surfaces tested. For the application of condensation heat transfer correlations to the design of condensers charged with R1234yf, thorough property measurements are needed for R1234yf in the near future.