• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.1-20
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• 1998

Processing of thin films by chemical vapor deposition (CVD) is accompanied by chemical reactions, in which the rigorous kinetic analysis is difficult to achieve. In these conditions, thermodynamic calculation leads to better understanding of the CVD process and helps to optimise the experimental parameters to obtain a desired product. A CVD phase diagram has been used as guide lines for the process. By determining the effect of each process variable on the driving force for deposition, the thermodynamic limit for the substrate temperature that diamond can deposit is calculated in the C-H system by assuming that the limit is defined by the CVD diamond phase diagram. The addition of iso-supersaturation ratio lines to the CVD phase diagram in the Si-Cl-H system provides additional information about the effects of CVD process variables.

• Advances in aircraft and spacecraft science
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• v.8 no.1
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• pp.1-15
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• 2021

Mars exploration demands aerodynamic computations for a proper design of missions of spacecraft carrying instruments and astronauts to Mars. Both Computational Fluid Dynamics (CFD) and Direct Simulation Monte Carlo (DSMC) method play a key role for this purpose. To the author's knowledge, the altitude separating the fields of applicability of CFD and DSMC in Mars atmosphere entry is not yet clearly defined. The limitations in using DSMC at low altitudes are due to technical limitations of the computer. The limitations in using CFD at high altitudes are due to thermodynamic non-equilibrium. Here, this problem is studied in Mars atmosphere entry, considering the Mars Pathfinder capsule in the altitude interval 40-80 km, by means of a DSMC code. Non-equilibrium is quantified by the relative differences between translational temperature and: rotational (θt-r), vibrational (θt-v), overall (θt-ov) temperatures, anisotropy is quantified by the relative difference between the translational temperature component along x and those along y (θx-y) and along z (θx-z). The results showed that θt-r, θt-v, θx-y, θx-z are almost equivalent. The altitude of 45 km should be the limit altitude for a proper use of a CFD code and the altitude of 40 km should be the limit altitude for a reasonable use of a DSMC code.

• Journal of The Korean Astronomical Society
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• v.49 no.1
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• pp.1-8
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• 2016

The aim of this study is to describe the physical processes taking place in the solar photosphere. Based on 3D hydrodynamic simulations including a detailed radiation transfer scheme, we investigate thermodynamic structures and radiation fields in solar surface convection. As a starting model, the initial stratification in the outer envelope calculated using the solar calibrations in the context of the standard stellar theory. When the numerical fluid becomes thermally relaxed, the thermodynamic structure of the steady-state turbulent flow was explicitly collected. Particularly, a non-grey radiative transfer incorporating the opacity distribution function was considered in our calculations. In addition, we evaluate the classical approximations that are usually adopted in the onedimensional stellar structure models. We numerically reconfirm that radiation fields are well represented by the asymptotic characteristics of the Eddington approximation (the diffusion limit and the streaming limit). However, this classical approximation underestimates radiation energy in the shallow layers near the surface, which implies that a reliable treatment of the non-grey line opacities is crucial for the accurate description of the photospheric convection phenomenon.

• Journal of the Korean Chemical Society
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• v.40 no.6
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• pp.409-414
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• 1996

The limit of applicability of Navier-Stokes equation to stationary plane shock-waves is examined by using the principle of minimum entropy production of linear irreversible thermodynamics. In order to obtain analytic results, the equation is linearized near the equilibrium of downstream. Results show that the solution of Navier-Stokes equation which fits the boundary condition of far downstream flow is consistent with the thermodynamic requirement within the first order when the solution is expanded around the M=1, where M is the Mach number of upstream speed.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.1
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• pp.80-83
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• 1999

Processing of thin films by chemical vapor deposition(CVD) is accompanied by chemical reactions, in which the rigorous kinetic analysis is difficult to achieve. In these conditions, thermodynamic calculation leads to better understanding of the CVD process and helps to optimise the experimental parameters to obtain a desired product. A CVD phase diagram has been used as guide lines for the process. By determining the effect of each process variable on the driving force for deposition, the thermodynamic limit of the substrate temperature for a diamond deposition is calculated in the C-H system by assuming that the limit is defined by the CVD diamond phase diagram. The addition of iso-supersaturation ratio lines to the CVD phase diagram in the Si-Cl-H system provides additional information about the effects of CVD porcess variables.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.77-86
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• 1992

This paper discusses the thermodynamic study on the suction cooling-steam injected gas turbine cycle. The aim of this study is to improve the thermal efficiency and the specific output by steam injection produced by the waste heat from the waste heat recovery boiler and by cooling compressor inlet air by an ammonia absorption-type suction cooling system. The operating region of this newly devised cycle depends upon the pinch point limit and the outlet temperature of refrigerator. The higher steam injection ratio and the lower the evaporating temperature of refrigerant allow the higher thermal efficiency and the specific output. The optimum pressure ratios and the steam injection ratios for the maximum thermal efficiency and the specific output can be found. It is evident that this cycle considered as one of the most effective methods which can obtain the higher thermal efficiency and the specific output comparing with the conventional simple cycle and steam injected gas turbine cycle.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.4
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• pp.529-545
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• 2013

Strong restrictions on emissions from marine power plants (particularly $SO_x$, $NO_x$) will probably be adopted in the near future. In this paper, a combined solid oxide fuel cell (SOFC) and gas turbine fuelled by natural gas is proposed as an attractive option to limit the environmental impact of the marine sector. It includes a study of a heat-recovery system for 18 MW SOFC fuelled by natural gas, to provide the electric power demand onboard commercial vessels. Feasible heat-recovery systems are investigated, taking into account different operating conditions of the combined system. Two types of SOFC are considered, tubular and planar SOFCs, operated with either natural gas or hydrogen fuels. This paper includes a detailed thermodynamic analysis for the combined system. Mass and energy balances are performed, not only for the whole plant but also for each individual component, in order to evaluate the thermal efficiency of the combined cycle. In addition, the effect of using natural gas as a fuel on the fuel cell voltage and performance is investigated. It is found that a high overall efficiency approaching 70% may be achieved with an optimum configuration using SOFC system under pressure. The hybrid system would also reduce emissions, fuel consumption, and improve the total system efficiency.

• International Journal of Automotive Technology
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• v.2 no.4
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• pp.147-155
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• 2001

Analysis of the thermodynamic cycle of IC engine from the point of view of economy and emissions was carried out. From this analysis potential capability of engine development was derived. This potential capability is lean-burn engine, fuelled with homogeneous mixture with $\lambda \geq$ 1.4. Several different modes of fuelling were proposed and tested on one-cylinder test engine from the point of view of extending lean operating limit of the engine, emissions and fuel economy. Among them were: fuelling with evaporated preheated gasoline, with gas (LPG evaporated) and with liquid butane. From these modes, fuelling with liquid butane injected to inlet port was selected and finally tested. This novel system of fuelling offered better than standard engine performances and emissions at lean operating limit. These results were validated on full-scale two-cylinder engine.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 1999.02a
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• pp.198-201
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• 1999

An optimal cooling method for HTS(high Tc superconductor) current leads has been analytically sought to minimize the required refrigerator power. The binary current lead is a series combination of a normal metal conductor at the warmer part and an HTS at the colder part. The lead is cooled by direct contacts with a two-stage cryocooler at the joint and at the cold end. It is clearly proven that there exists unique optimal values for the joint temperature and the current density to minimize the refrigerator power per unit current. the actual power input to the cryocooler in the optimal conditions is compared with its thermodynamic limit, and some significant issues in practical design are presented with a useful graphical method.

• Korean Journal of Materials Research
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• v.15 no.1
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• pp.47-53
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• 2005

The E.M.F. of the galvanic cell with fused salt was measured to determine the activities of zinc at 720-860 K over the entire composition range of liquid Zn-In and Zn-Sn alloys. The cell used was as follows: $$(-)W{\mid}Zn(pure){\mid}Zn^{2+}(KCl-LiCl){\mid}Zn(in\;Zn-In\;or\;Zn-Sn\;alloy){\mid}W(+)$$ The activities of zinc in the alloys showed positive deviation from Raoult's law over the entire composition range. The activity of cadmium and some thermodynamic functions such as Gibbs free energy, enthalpy and entropy were derived from the results by the thermodynamic relationship. The comparison of the results and the literature data was made. The liquid Zn-In and Zn-Sn alloys are found to be close tn the regular solution. The concentration fluctuations in long wavelength limit, $S_{cc}(o)$, in the liquid alloy were calculated from the experimental results.