• Korean Chemical Engineering Research
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• v.61 no.1
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• pp.116-122
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• 2023

We study the relationship of entropy with the properties of molecules and also with the macroscopic specifications of the system, i.e., component and phase. Understanding different viewpoints of classical mechanics and quantum mechanics for the indistinguishability of molecules belonging to the same component, we discuss a few thermodynamic systems in which the properties of molecules are to be consistent with the component as a macroscopic term of classifying the molecules. With a clear definition of thermodynamic microstate, the drawback of the Boltzmann statistics caused by the distinguishability of molecules is avoided, and the Gibbs paradox of entropy consequently disappears. Corresponding to the characteristics of fluid and solid phases, we investigated the effects of the indistinguishability and the symmetry number of molecules and the number of microstates realized in time on the partition function and the entropy. In particular, we show that crystalline solid can be regarded as a system which does not satisfy the ergodic hypothesis.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.10
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• pp.56-60
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• 2006

It is essential to predict thermodynamic properties of combustion gas with respect to a propellant mixture ratio for the development of a gas generator for a liquid rocket engine. The present study shows the temperature measurement of exit combustion gas as a function of a mixture ratio through the series of combustion tests of a fuel-rich gas generator with liquid oxygen and Jet A-1. The measurements of dynamic and static pressures, and combustion gas temperatures allowed the estimation of thermodynamic properties like a specific heat ratio, a gas constant, and a constant pressure specific heat of the combustion gas. The comparison of the experimental results with predictions made by interpolation parameters obtained from the modification of the chemical equilibrium code indicates that the interpolation method calibrated using the temperature measurements can be utilized as an effective tool for the initial design of a fuel-rich gas generator.

• 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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.7 s.262
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• pp.596-603
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• 2007

As increasing interest for soot emission. etc in combustion systems, various studies are being carried out for the reduction and measurement techniques of soot. Especially, laser induced incandescence is the useful measurement technique which has distinguished spatial and temporal resolution for primary particle size, volume fraction and aggregated particle size etc. Time resolved laser induced incandescence is the technique for measuring primary particle size that is decided to solve the signal decay rate which is related to the cooling behavior of heated particle by pulsed laser. The cooling behavior of heated particle is able to represent the heat and mass transfer model which are involved constants of soot property for surround gas temperature on the our previous work. In this study, it is applied to the time-dependence thermodynamic properties for soot temperature instead of constants of soot property for surround gas temperature and compared two different model results.

• Preventive Nutrition and Food Science
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• v.22 no.1
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• pp.56-61
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• 2017

Rheological properties of waxy barley flour (WBF) dispersions mixed with various gums (carboxyl methyl celluleose, guar gum, gum arabic, konjac gum, locust bean gum, tara gum, and xanthan gum) at different gum concentrations were examined in steady and dynamic shear. WBF-gum mixture samples showed a clear trend of shear-thinning behavior and had a non-Newtonian nature with yield stress. Rheological tests indicated that the flow and dynamic rheological parameter (apparent viscosity, consistency index, yield stress, storage modulus, and loss modulus) values of WBF dispersions mixed with gums, except for gum arabic, were significantly higher than those of WBF with no gum, and also increased with an increase in gum concentration. In particular, konjac gum at 0.6% among other gums showed the highest rheological parameter values. Tan ${\delta}$ values of WBF-xanthan gum mixtures were lower than those of other gums, showing that there is a more pronounced synergistic effect on the elastic properties of WBF in the presence of xanthan gum. Such synergistic effect was hypothesized by considering thermodynamic compatibility between xanthan gum and WBF. These rheological results suggest that in the WBF-gum mixture systems, the addition of gums modified the flow and viscoelastic properties of WBF, and that these modifications were dependent on the type of gum and gum concentration.

• Journal of Powder Materials
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• v.11 no.5
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• pp.421-426
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• 2004

The microstructure and mechanical property of hot-pressed $Al_2O_3/Cu$ composites with a different temperature for atmosphere changing from H$_{2}$ to Ar have been studied. When atmosphere-changed from H$_{2}$ to Ar gas at 145$0^{\circ}C$, the hot-pressed composite was characterized by inhomogeneous microstructure and low fracture strength. On the contrary, when atmosphere-changed at low temperature of 110$0^{\circ}C$ the composite showed more homogeneous microstructure, higher fracture strength and smaller deviation in strength. Based on the thermodynamic consideration and microstructural analysis, it was interpreted that the Cu wetting behavior relating to the formation of CuAlO$_{2}$ is probably responsible for strong dependence of microstructure on atmosphere changing temperature. The reason for a strong sensitivity of fracture strength and especially of its deviation to atmosphere changing temperature was explained by the microstructural inhomogeneity and by the role of CuAlO$_{2}$ phase on the interfacial bonding strength.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.294-296
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• 2017

In this study heat transfer characteristics of kerosene at supercritical condition was predicted. And a sample heat transfer calculation was performed using this result. The prediction was done by assuming kerosene as a mixture of a number of pure substances, and combining the thermodynamic properties of them, using NIST SUPERTRAPP. A regeneratively cooled supersonic combustor will be desinged using the resultant thermophysical property data of supercritical kerosene. Comparing with the combustion test results of the regenerative cooling combustor, the predicted thermophysical property data will be verified.

• Korean Journal of Materials Research
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• v.29 no.3
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• pp.189-195
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• 2019

The effect of C, Mn, and Al additions on the tensile and Charpy impact properties of austenitic high-manganese steels for cryogenic applications is investigated in terms of the deformation mechanism dependent on stacking fault energy and austenite stability. The addition of the alloying elements usually increases the stacking fault energy, which is calculated using a modified thermodynamic model. Although the yield strength of austenitic high-manganese steels is increased by the addition of the alloying elements, the tensile strength is significantly affected by the deformation mechanism associated with stacking fault energy because of grain size refinement caused by deformation twinning and mobile dislocations generated during deformation-induced martensite transformation. None of the austenitic high-manganese steels exhibit clear ductile-brittle transition behavior, but their absorbed energy gradually decreases with lowering test temperature, regardless of the alloying elements. However, the combined addition of Mn and Al to the austenitic high-manganese steels suppresses the decrease in absorbed energy with a decreasing temperature by enhancing austenite stability.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.696-701
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• 2001

The performance and the internal flow of the impeller of the centrifugal chiller compressor with refrigerant R12 as working fluid were studied numerically, using CFD code, CFX-Tascflow, which is commercially available. In this numerical study, the thermodynamic and transport properties of the refrigerant gas were generated by the property program of NIST and linked with main program to extend the capability of the code to refrigerant gases. Numerical study was applied to several mass flow rates near the design mass flow rate at constant rotating speed. Overall performance and flow characteristics of the impeller at impeller exit were investigated. The results were physically reasonable and showed good agreement with experimental measurement at the design flow rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.6
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• pp.832-839
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• 1998

The potential work is defined as the maximum available work extractable from a composite system. It is important concept to understand the behavior of a composite system because it is a property of the composite system and shows the possible room for the system to change its state by itself. To explain this concept quantitatively, the behavior of a composite system composed of two simple ideal gas systems is analyzed. The potential work of the composite system is estimated, the various reversible processes from a given state to the equilibrium state and the processes on which potential works are constant are shown on the T-P and S-V planes. Such an effort will be necessary to understand and characteristics of composite systems as well as helpful for a deeper comprehension of the energy conversion principles.