• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.2
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• pp.141-155
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• 1993

Thermodynamic properties of R-32 are calculated and its refrigeration performance is evaluated for the purpose the feasibility study of replacing R-22 with R-32. (1) Refrigeration effect of R-32 is superior to that of R-22 because heat of evaporation of R 32 is about 50% higher than that of R-22. However, COP of R-32 system is 10-30% lower than that of R-22 system. It is mainly attributed to the vapor pressore of R-32 being about 62% higher than R-22. (2) Since the pressure ratio and the specific heat ratio of R-32 system is higher than those of R -22, compressor discharging temperature rises as high as to $130-150^{\circ}C$. It may cause mechanical failure of compressor due to the breakdown of lubricant. Compressor should be improved to lower the temperature if R-32 is to replace R-22. (3) Averaged two-phase heat transfer coefficient of R-32 is about 10-20% higher than that of R-22. It may assume better heat exchanger effectiveness but not guarantee the better COP of R-32 system than R-22. (4) The high vapor pressure is the first reason to drop R-32 out of the line of R-22 alternative refrigerant. So, refrigerant mixtures based on R-32 are recommended to adjust the vapor pressure first and keep superior volumetric capacity of R-32.

• Bulletin of the Korean Chemical Society
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• v.34 no.3
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• pp.810-814
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• 2013

The thermodynamic parameters for the intercalative interaction of structurally related well known intercalators, 9-aminoacridine (9AA) and proflavine (PF) were determined by means of fluorescence quenching study. The fluorescence intensity of 9AA decreased upon intercalation to DNA, poly[$d(A-T)_2$] and poly[$d(G-C)_2$]. A van't Hoff plot was constructed from the temperature-dependence of slope of the ratio of the fluorophore in the absence and presence of a quencher molecule with respect to the quencher concentration, which is known as a Stern-Volmer plot. Consequently, the thermodynamic parameters, enthalpy and entropy change, for complex formation was calculated from the slope and y-intercept of the van't Hoff plot. The detailed thermodynamic profile has been elucidated the exothermic nature of complex formation. The complex formation of 9AA with DNA, poly[$d(A-T)_2$] and poly[$d(G-C)_2$] was energetically favorable with a similar negative Gibb's free energy. On the other hand, the entropy change appeared to be unfavorable for 9AA-poly[$d(G-C)_2$] complex formation, which was in contrast to that observed with native DNA and poly[$d(A-T)_2$] cases. The equilibrium constant for the intercalation of PF to poly[$d(G-C)_2$] was larger than that to DNA, and was the largest among sets tested despite the most unfavorable entropy change, which was compensated for by the largest favorable enthalpy. The favorable hydrogen bond contribution to the formation of the complexes was revealed from the analyzed thermodynamic data.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.1116-1124
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• 1995

Using a cycle simulation program developed by authors, some thermodynamic characteristics of an aircraft ECS under various operating conditions are studied. When the inlet temperature of cockpit and avionics bay, as well as ram air flow, is held fixed, the effect of the change of regulated bleed pressure is examined. When the regulated bleed pressure, and the cockpit and avionics bay inlet temperature are fixed, the effect of the change of ram air flow is also investigated.

• Journal of the Korean Applied Science and Technology
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• v.26 no.1
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• pp.45-50
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• 2009

Three-dimensional, statistical-mechanical formulations of problems are usually untractable analytically, and therefore they are commonly solved numerically. However, their one-dimensional counterparts are always to be solved analytically. In general analytical solutions sheds more insights to the problems than numerical solutions. Hence, solutions of one-dimensional problems may provide key properties to the problems, when they are extended to three dimensions. In this article, thermodynamic properties of one-dimensional fluid comprising molecules of rigid rods are analyzed statistical-mechanically. Molecules of rigid rods are characterized with repulsive or excluded volume effect. It is observed that this feature is well reflected in thermodynamic functions such as Helmholtz free energy. volumetric equation of state. chemical potential, entropy, etc.

• Journal of the Korean Chemical Society
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• v.43 no.3
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• pp.251-256
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• 1999

Viscosities of toluene were experimentally determined by the falling-ball method at several temperatures and pressures to investigate the pressure and temperature dependence of the viscosity of toluene. With the shear stress of the viscous flow of toluene, the shear free energy, the shear entropy, and the shear enthalpy were defined to discuss the variations of the shear thermodynamic properties with pressure. The effect of temperature and pressure on the shear thermodynamic properties obtained experimentally can be explained by means of the molecular thermal agitation due to temperature incleasing and the steric effect of the closed molecules of to Iuene due to pressure elevation.

• Macromolecular Research
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• v.8 no.2
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• pp.66-72
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• 2000

Cis-Polybutadiene (cis-PBD) and the three polyethylenes (PE's) having different branch content were mixed to investigate crystallinity, thermodynamic interaction parameter(c), and diluents effect. Crys-tallinty of PE's decreased with increasing content of amorphous cis-PBD because of a decrease in both the degree of annealing and kinetics of diffusion of the crystallizable polymer content. The thermodynamic interaction parameter(c) for the three blend systems approximately equals to zero near the melting point. These systems were determined to be miscible on a molecular scale near or above the crystalline melting point of the crystalline PE's. From the measurement of T$\sub$m/ vs. T$\sub$c/ behavior, all the three blends showed a straight line for a plot of T$\sub$m/ vs. T$\sub$c/. This result means that the melting behavior of PE is mainly due to a diluent effect of cis-PBD component.

• Journal of the Korean Ceramic Society
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• v.45 no.5
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• pp.280-284
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• 2008

In order to investigate residence time effect on the growth of ZrC film, the ZrC films grew with various system total pressure (P) and total flow rate (Q) by low pressure chemical vapor deposition because residence time is function of system total pressure and total flow rate. Thermodynamic calculations predict that the decomposition of source gases ($ZrCl_4$ and $CH_4$) would be low as increasing the residence time. Thermodynamic calculations results were proved by investigating deposition rate with various residence time. Deposition rate decreased with residence time of source gas increased. Besides, depletion effect accelerated diminution of deposition rate at high residence time. On the other hands, the deposition rated was increased as decreasing the residence time because fast moving of intermediate gas species decrease the depletion effect. The crystal structure was not changed with residence time. However, the largest size of faceted grain showed up to specific residence time and the size of grain was decreased whether residence time increase or not.

• International Journal of Automotive Technology
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• v.2 no.1
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• pp.1-7
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• 2001

This paper presents further investigation into the effect of over-expansion cycle in a spark-ignition engine. On the basis of the results obtained in previous studies, several combinations of late-closing (LC) of intake valve and expansion ratio were tested using a single-cylinder production engine. A large volume of intake capacity was inserted into the intake manifold to simulate multi-cylinder engines. With the large capacity volume, LC can decrease the pumping loss and then increase the mechanical efficiency. Increasing the expansion ratio from 11 to 23.9 with LC application can produce about 13% improvement of thermal efficiency which was suggested to be caused by the increased cycle efficiency. The decrease of compression ratio from 11 to 5.5 gives little effect on the thermal efficiency if the expansion ratio could be kept constant. Thus, the expansion ratio is revealed to be a determining factor for cycle efficiency, while compression ratio is no more important, which suggests the usefulness of controlling the intake charge with intake valve closure timing. These were successfully explained by simple thermodynamic calculation and thus the mechanism could be verified by the estimation.

• Nuclear Engineering and Technology
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• v.55 no.7
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• pp.2556-2566
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• 2023

A first-principle approach within the framework of density functional theory was employed to study the effect of vacancy defects and fission products (FPs) doping on the mechanical, electronic, and thermodynamic properties of uranium monocarbide (UC). Firstly, the calculated vacancy formation energies confirm that the C vacancy is more stable than the U vacancy. The solution energies indicate that FPs prefer to occupying in U site rather than in C site. Zr, Mo, Th, and Pu atoms tend to directly replace U atom and dissolve into the UC lattice. Besides, the results of the mechanical properties show that U vacancy reduces the compressive and deformation resistance of UC while C vacancy has little effect. The doping of all FPs except He has a repairing effect on the mechanical properties of U_1-xC. In addition, significant modifications are observed in the phonon dispersion curves and partial phonon density of states (PhDOS) of UC_1-x, Zr_xU_1-xC, Mo_xU_1-xC, and Rh_xU_1-xC, including narrow frequency gaps and overlapping phonon modes, which increase the phonon scattering and lead to deterioration of thermal expansion coefficient (α_V) and heat capacity (C_p) of UC predicted by the quasi harmonic approximation (QHA) method.

• Journal of the Korean Chemical Society
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• v.7 no.4
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• pp.264-270
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• 1963

The general equation for the substituent effect test, which was derived in the previous paper, has been extended to correlate thermodynamic parameters of solvolysis reaction by modifying the potential energy term to represent the effect of changes in solvent composition. The linear fits of the new equation, $\Delta{\Delta}H^\neq=a'Y+b\Delta{\Delta}S^\neq$, were tested with 35 examples from literature and average correlation coefficient of 0.977 was obtained. Examination of results showed that the equation is generally applicable to solvolysis reaction and helps elucidate some the difficulties experienced with the Grunwald-Winsteln equation. It has been stressed that the linear enthalpy-entropy effect exists only between the external enthalpy and entropy of activation, and therefore strictly it is the linear external enthalpy-entropy effect.