• 한국유체기계학회 논문집
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• 제18권6호
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• pp.19-26
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• 2015

The present paper presented and applied an exergy analysis method to evaluate the magnitudes and the locations of exergy losses in the conventional desuperheating and depressurizing process of high pressure and temperature steam delivery system. In addition, for the reduction of exergy losses occurred in conventional process, the present study proposed new alternative processes in which the pressure reducing valve and the desuperheater of conventional process are substituted with steam turbine and heat exchanger, and their effects on exergy loss reduction and exergy efficiency improvement are theoretically investigated and compared. From the present analysis results, the total exergy loss caused in conventional desuperheating and depressurizing process accounted for 66.5% of exergy input and 85% of the total exergy loss was due to the mixing between steam and cold water(e.g desuperheating). However, it was shown from the present analysis results that the present alternative processes can additionally reduce exergy loss by maximum 92.7% of the total exergy loss in conventional process, and can also produce additional and useful energy, the electricity of 220.6 kWh and the heat of 54.3 MJ/hr.

• Korean Chemical Engineering Research
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• 제55권6호
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• pp.807-815
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• 2017

본 연구에서는 회전증발에서 건조 온도에 따른 파클리탁셀의 잔류 펜탄 제거 효율에 대해 조사하였으며 건조 공정에 대한 동역학 및 열역학적 해석을 수행하였다. 모든 온도(25, 30, 35, 40, $45^{\circ}C$)에서 건조 초기에 많은 양의 잔류용매가 제거되었으며 건조 온도가 증가할수록 건조 효율은 증가하였다. 동역학적 해석을 위해 실험데이터 값을 다섯 종류의 건조 모델식(Newton, Page, Modified Page, Henderson and Pabis, Geometric)에 적용하였으며, 이 중 Henderson and Pabis 모델이 큰 결정계수 값과 작은 평균평방근편차 RMSD 값을 가져 가장 적합함을 확인하였다. 또한 열역학적 해석을 수행한 결과, 회전증발에서의 활성화 에너지 $E_a$는 4.9815 kJ/mol이었으며, 표준 Gibbs 자유에너지 변화(${\Delta}G^0$)는 음수 값인 반면 표준 엔탈피 변화(${\Delta}H^0$)와 표준 엔트로피 변화(${\Delta}S^0$)는 양수 값을 나타내어 건조 공정이 자발적 흡열반응이며 비가역적으로 수행됨을 알 수 있었다.

• 설비공학논문집
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• 제12권4호
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• pp.363-370
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• 2000

Experiments have been peformed, using pure refrigerant R134a and a zeotropic refrigerant mixture R290/R600a(60%/40%) and their performances have been analyzed by the first and second laws(exergy method) of thermodynamics. From the experimental results, variations of compressor speed and air temperature have a great effect on the performance of the system. The sum of exergy losses in compressor and evaporator is about 60% of total exergy loss, using refrigerant R134a, so it is necessary to improve the performance of compressor and evaporator. According to the experimental results using refrigerant mixture of R290/R600a(60%/40%), the exergy losses in heat exchange processes are decreased but the exergy loss in throttling process is increased. The performance of the system has been improved by 20∼30% compared with that of R134a and exergy losses have been also reduced.

• 열처리공학회지
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• 제7권4호
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• pp.233-243
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• 1994

Constitutive relation of thermoelasto-plastic material undergoing phase transformation during quenching process were developed on the basic of continuum thermodynamics. The metallic structure, temperature and residual stresses distributions were numerically calculated by the finite element technique. The metallic structure were defined by transformation from austenite to pearlite and characterized as a fuction of thermal history and mixture rule of phase. On the distribution of thermal stress along the radial direction, axial and tangential stresses are compressive in the surface, and tential in the inner part. Radial stress is tensile in the whole body. The reversion of residual stress takes plase at 11.5~15.5mm from the center.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.172-175
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• 2003

Run-Out-Table is the region between EDT and CT. Hot killed strip is cooled by air and water in ROT. In this procedure, phase transformation and shape deformation occur due to temperature drop. Because of un-ideal cooling condition, deformation of strip and non-uniform phase distribution come into existence. This phenomenon affects the strip property and lead th the existence of residual stress. And it exerts effects on the Coiling process, Coil Cooling process, and Un-coiling process. Through these process, the residual stresses of strip are more larger and unbalance of these stresses become more severe. Finite element (FE) based models for the analysises of non-steady state heat transfer and elastoplastic deformation are described in this investigation. The analysises of thermodynamics and phase transformation kinetics are suggested also. Using the ROT simulation result coiling process and coil cooling process simulations are carried out.

• 한국군사과학기술학회지
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• 제19권4호
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• pp.483-491
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• 2016

A simple aerodynamic calculation program for high Mach number flow is developed by combining the modified Newtonian method with Tannehill's curve fits for the thermodynamic properties of air in equilibrium state. Aerodynamic characteristics for a parabolic nose are predicted and compared with CFD(Computational Fluid Dynamics) analysis results. Comparison shows good agreements, and the developed program is expected to be a practical tool for slender body aerodynamic calculation for high Mach number flow.

• 에너지공학
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• 제24권3호
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• pp.61-66
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• 2015

Homogeneous charge compression ignition (HCCI) engine combines the combustion characteristics of a compression ignition engine and a spark ignition engine. HCCI engines take advantage of the high compression ratio and heat release rate and thus exhibit high efficiency found in compression ignition engines. In modern research, simulation has be come a powerful tool as it saves time and also economical when compared to experimental study. Engine simulation has been developed to predict the performance of a homogeneous charge compression ignition engine. The effects of compression ratio, cylinder pressure, rate of pressure rise, flame temperature, rate of heat release, and mass fraction burned were simulated. The simulation and analysis show several meaningful results. The objective of the present study is to develop a combustion characteristics model for a homogeneous charge compression ignition engine running with isooctane as a fuel and effect of compression ratio.

• 한국재료학회지
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• 제23권8호
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• pp.462-468
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• 2013

We study and describe-from the point of view of the interactions of the adsorbed particles-three types of the adsorption isotherms, namely, Langmuir type adsorption isotherms, phase transition type adsorption isotherms, and adsorption limited type adsorption isotherms, which are observed by experiments. By introducing and using a one dimensional statistical occupancy model, we derived analytical adsorption isotherms for the no force, the attractive force, and the repulsive force exerted on the other adsorbed particles. Our derived adsorption isotherms qualitatively pretty well agree with the experimental results of the adsorption isotherms. To specify each adsorption type, Langmuir type adsorption is a phenomenon that occurs with no forces between the adsorbed particles, phase transition type adsorption is a phenomenon that occurs with the strong attractive forces between the adsorbed particles, and adsorption limited type adsorption is a phenomenon that occurs with the repulsive forces between the adsorbed particles. The theoretical analysis-only using fundamental thermodynamics and occupancy statistics though-qualitatively quite well explains the experimental results.

• International Journal of Fluid Machinery and Systems
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• 제1권1호
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• pp.121-139
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• 2008

For mechanical drive steam turbines, the investigation results of corrosion fatigue phenomena in the transient zone are introduced, including basic phenomena on expansion line and actual design and damage experience. These results were analyzed from the standpoint of stress intensity during the start of cracking. In order to resolve such problems, preventive coating and blade design methods against fouling and corrosive environments are developed. Detailed evaluation test results are given for coating performance using a unique test procedure simulating fouling phenomena and washing conditions. Finally, the results of the successful modification of internals and on-line washing results on site are introduced.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.430-434
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• 2001

To perform the integrity evaluation of RPV more realistically, it is necessary to evaluate the metallurgical microstructure and residual stress considering more real phenomena such as multi-pass welding process and PWHT. Accordingly, firstly, this paper proposes the integrated assessment methodology systematically developed for residual stress on weldment of RPV by using thermodynamics, diffusion theory, finite element method and validation experiment. Also, the residual stress on circumferential weldment of reactor pressure vessel is calculated considering multi-pass welding process by the commercial finite element package, ABAQUS.