• 설비공학논문집
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• 제5권2호
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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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• 제34권3호
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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.

• 대한기계학회논문집
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• 제19권4호
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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.

• 한국응용과학기술학회지
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• 제26권1호
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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.

• 대한화학회지
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• 제43권3호
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• pp.251-256
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• 1999

여러 온도와 압력에서 톨루엔의 점성도를 공낙하법에 의하여 결정하고 톨루엔의 점성도에 대한 온도 및 압력 의존성을 연구하였다. 톨루엔의 점성 흐름에 관한 엇갈림 변형력으로부터 엇갈림 자유 에너지, 엇갈림 엔트로피, 엇갈림 엔탈피 등을 정의하여 압력 변화에 따르는 열역학적 성질의 변화를 고찰하였다. 실험적으로 결정된 엇갈림 자유 에너지, 엇갈림 엔트로피, 엇갈림 엔탈피 등을 온도 상승에 의한 톨루엔 분자들의 열운동 효과와 압력 증가에 의한 밀도 증가 및 분자의 입체 효과에 의하여 설명하였다.

• Macromolecular Research
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• 제8권2호
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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.

• 한국세라믹학회지
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• 제45권5호
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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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• 제2권1호
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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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• 제55권7호
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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.

• 대한화학회지
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• 제7권4호
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• pp.264-270
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• 1963

前報에서 誘導한 置換基效果 一般關係式은 溶媒組成에 따르는 常數, Y를 potential energy 項에 代置함으로서 solvolysis 反應에 適用할 수가 있다. 新方程式, $\Delta{\Delta}H^\neq=a'Y+b\Delta{\Delta}S^\neq$, 의 適用性은 文獻에 報告된 35個反應에 對한 直線關係를 調査해 봄으로서 檢討하였다. 結果로 平均 相關係數 0.977을 얻었고, 따라서 이 方程式이 solvolysis反應에 一般的으로 適用됨을 밝혔고, 또 Grunwald-Winstein의 式이 지니는 몇몇 難點을 解決할 수가 있음을 알 수 있었다. enthalypy-entopy 直線效果는 外部 enthalpy와 外部 entropy에 限한 것이며, 嚴格히 말해서 外部 enthalpy entropy 直線效果임을 强調하였다.