내열 주조 합금(IN-657) 파괴 거동 해석을 위한 Ni-Cr-Nb-C 시스템 열역학 모델링

김동응 ( Dongeung Kim ) 한국주조공학회 2021 한국주조공학회지 Vol.41 No.5

다양한 합금계에 대한 계산열역학은 CALPHAD 기법으로 잘 알려져있다. 실험적으로 측정된 열역학 특성들을 활용하여 각상에 대한 Gibbs 에너지 모델 파라미터들을 구하여, 주로 실험적으로 측정되지 못한 영역에 대한 예측이나 실험 결과에 대한 열역학 해석에 활용되고 있다. 본 연구에서는 내열 주조 합금 (IN-657)이 장시간 사용 후에 일정 영역에서 파괴되는 현상의 열역학적 해석을 위해 Ni-Cr-Nb-C 사원계 시스템의 열역학 모델링을 수행하였고, Cr 함량에 따른 시스템의 안정상, 온도에 따른 상분율 및 Ni₂Cr상의 long range ordering 파라미터를 계산하였고 실험결과와 비교하였다. 계산된 열역학 물성들은 실험으로 보고된 파괴 온도 영역 및 해당 영역에서 생성된 안정상에 대한 결과를 잘 설명한다. CALPHAD 기법을 통한 열역학 모델링은 다양한 주조 합금의 열역학적 거동을 해석하고 예측하는데 유용하게 사용될 수 있을 것으로 기대된다. Computational thermodynamics for various alloy systems is well known as the CALPHAD technique. Gibbs energy model parameters for each phase are obtained from experimentally measured thermodynamic properties and are mainly used to predict areas not experimentally measured and to analyze experimental results thermodynamically. In this study, the thermodynamic modeling of the Ni-Cr-Nb-C quaternary system is conducted for a thermodynamic analysis of the phenomena by which heat-resistant cast alloys (IN-657) are destroyed in certain areas after long-term use. The stable phases in the system according to the Cr content, phase fraction depending on the temperature, and long-range ordering parameters for the Ni₂Cr phase are calculated and compared to results obtained experimentally. The calculated thermodynamic properties suitably explain the experimentally reported fracture temperature range and the results of stable phases formed in the fractured areas. Thermodynamic modeling through the CALPHD method is expected to be useful for analyzing and predicting the thermodynamic behaviors of various cast alloys.

Stable Interconnect System for Horizontal Thermoelectric Coolers by Thermodynamic‑Based Prediction

Min-Woo Jeong,이소연,Hong-Bum Park,Hoo-Jeong Lee,주영창 대한금속·재료학회 2019 ELECTRONIC MATERIALS LETTERS Vol.15 No.5

We studied the improvement of interfacial stability and contact resistance by applying Cu with high electrical conductivitybut high diffusivity to thin film type thermoelectric devices. Since the thin film device has a large surface to volume ratio, itis necessary to minimize the contact resistance occurring at the interface in order to minimize heat generation due to resistance. For the reliability of such a device, long duration phase stability is required, especially when using Cu electrodes withhigh diffusivity. The interconnect system, including Cu and the barrier materials, was selected based on a phase diagram witha thermodynamic-based calculation. The interlayer was required to improve the unstable interface to prevent the reactionof Cu and Bi2Te3. Ta and Mo, which are low diffusivity materials, were selected as candidates. Thermodynamic calculationresults showed that Ta has a stable interface with Bi2Te3,while Mo reacts with Te. The calculation was confirmed byexperiments, and it was determined that the longer the annealing process, the higher the contact resistance is when the Mointerlayer is applied, which is in accordance with the thermodynamic calculation. The thermodynamic calculations are auseful methodology when selecting materials with a stable interface with highly reactive chalcogenide materials.

Thermodynamic Analysis of Intergranular Additives in Sintered Nd-Fe-B Magnet

X. G. Cui,X. H. Wang,C. Y. Cui,G. C. Yin,C. D. Xia,X. N. Cheng,X. J. Xu 한국자기학회 2017 Journal of Magnetics Vol.22 No.2

To get deeper insight into the effect of intergranular additives in sintered Nd-Fe-B magnet and consequently improve the properties better, the interaction between additives (oxide, nitride, and carbide) and Nd-rich phase in the temperature range of 298.15-1400 K was analyzed thermodynamically. It can be found that the oxide additives became less stable than nitrides and carbides. Except for calcium oxide, almost all oxides could react with Nd from Nd-rich phase. To be different from oxide additives, the mechanism of nitrides and carbides was defined with various elements, either reaction with Nd from Nd-rich phase or not. The two different mechanisms would show different effects on the microstructure and hence properties of magnet. The thermodynamic analysis had a better agreement with the experimental information.

Thermodynamic assessment of carbazole-based organic polycyclic compounds for hydrogen storage applications via a computational approach

Shin, Byeong Soo,Yoon, Chang Won,Kwak, Sang Kyu,Kang, Jeong Won Elsevier 2018 International journal of hydrogen energy Vol.43 No.27

<P><B>Abstract</B></P> <P>Liquid organic hydrogen carriers (LOHCs) are promising candidates for storage and transport of renewable energy due to their reversible reaction characteristics. For the proper assessment of candidate molecules, various thermochemical properties are required, and significant experimental efforts are necessary. In this work, we suggest a systematic method for the estimation of thermochemical properties for LOHC candidate molecules combining Density Functional Theory (DFT) calculations, Conductor-like Screening Model (COSMO) and Molecular Dynamics (MD) simulations. We applied the suggested method for the assessment of previously reported LOHC materials. Based on the analysis, new candidates of carbazole-derivative compounds (<I>N</I>-acetylcarbazole, <I>N</I>-phenylcarbazole, <I>N</I>-benzoylcarbazole, and 4-methyl-4H-benzocarbazole) are suggested, and their properties are estimated and reviewed. Calculation results show that these candidates can provide high theoretical hydrogen uptake capacities above 6 wt% and optimal heats of dehydrogenation in the liquid phase. Analysis on the stereoisomerism showed that the structure-selectivity toward less stable stereoisomers of the hydrogen-rich form is preferable for the dehydrogenation process.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The existing LOHCs were re-evaluated in terms of thermodynamics. </LI> <LI> A new types of carbazole-derivative compounds are proposed as LOHCs. </LI> <LI> All proposed candidates satisfy the thermodynamic standards. </LI> <LI> Unstable isomers of hydrogen-rich form showed thermal efficient for dehydrogenation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

열역학적 사이클의 제2법칙 효율의 정의에 대한 기본 연구

박경근(Kyoung Kuhn Park) 대한설비공학회 2012 설비공학 논문집 Vol.24 No.11

A general concept on the definition of the second law efficiencies of thermodynamic cycles is introduced. The efficiency is defined to be proportional to the entropy generation divided by the maximum possible entropy generation. This way of definition of the cycle efficiency is clear and concise and, moreover, follows faithfully the concept of the second law of thermodynamics. This definition is applied to heat engine, refrigerator and heat pump. The second law efficiencies of heat engine and refrigeration cycles are derived, which are the same as the existing ones, respectively. The second law efficiency of heat pump, however, finds to be different from the existing one. Discussion is given about the difference and its cause.

THERMODYNAMIC ANALYSIS OF SINGLE- AND DOUBLE-EFFECT ABSORPTION REFRIGERATION SYSTEMS FOR COOLING ETHANOL FERMENTATION PROCESS

HUGO VALENÇA DE ARAÚJO,JOSÉ VICENTE HALLAK D'ANGELO 대한설비공학회 2014 International Journal Of Air-Conditioning and Refr Vol.22 No.4

Alcoholic fermentation is one of the most important stages in industrial ethanol productionprocess, involving a biochemical and exothermic reaction. Sometimes cooling towers are notcapable of supplying a cold utility with a temperature low enough to maintain the fermentativemedium temperature in a desirable range. Absorption Refrigeration Systems (ARS) appears to bea good alternative to obtain the necessary refrigeration for the fermentation process. The aim ofthe present paper was to carry out a thermodynamic analysis of ARS, evaluating their performancethrough the First and Second Laws of Thermodynamics. ARS with different con¯gurationswere studied (single-effect and double-effect with series, parallel and reverse parallel flows), all ofthem operating with water/lithium bromide mixture as working pair, under different operatingconditions in order to satisfy the cooling load required by an industrial alcoholic fermentationprocess. Another objective of this paper was to investigate the risk of LiBr crystallization, whichcan result in scaling formation, with the aid of the solid–liquid phase equilibrium curve of H2O/LiBr mixture. Among the double-effect con¯gurations studied, it was observed that series flow presents the more signi¯cant crystallization risk, which represents a limit to improve its First andSecond Law performances. It was veri¯ed that the Second Law performance for the single-anddouble-effect ARS analyzed are similar, but their First Law performance are considerably different. This is due to the amount and quality of the heat consumed in the first effect generators ofthese systems. For a base case studied, First Law performance measured by coefficient of performance(COP) of double-effect ARS is 72% greater than the one for single-effect, while forSecond Law performance, measured by exergetic efficiency, an increase of 5% was observed.

Thermodynamic Modeling and Performance Optimization of a Solar-Assisted Vapor Absorption Refrigeration System (SAVARS)

Boris Huirem,Pradeepta Kumar Sahoo 대한설비공학회 2020 International Journal Of Air-Conditioning and Refr Vol.28 No.1

A thermodynamic steady-state model for a single-effect lithium bromide–water (LiBr-H2O)-based vapor absorption refrigeration system of 17.5 kW capacities has been presented using the first and second laws of thermodynamics. The mass, energy and exergy balance equations in each component of the vapor absorption cycle have been fitted into a computer program to carry out the calculation using the thermo-physical properties of the working fluid. The performance parameters such as coefficient of performance (COP), exergy coefficient of performance (ECOP), total exergy destruction (TED), etc. have been evaluated considering different temperatures in generator and evaporator, different LiBr concentrations in the weak and strong LiBr-H2O solution and different solution heat exchanger effectiveness. The model evaluated the optimum performance parameters like COP, ECOP, TED, etc. of the vapor absorption system by using Design Expert-12 software for an application like on-farm cooling or transit storage of fruits and vegetables.

Effect of Compression Ratio on the Combustion Characteristics of a Thermodynamics-Based Homogeneous Charge Compression Ignition Engine

Sung Bin Han 한국에너지학회 2015 에너지공학 Vol.24 No.3

Off-design performance analysis of a closed-cycle ocean thermal energy conversion system with solar thermal preheating and superheating

Aydin, H.,Lee, H.S.,Kim, H.J.,Shin, S.K.,Park, K. Pergamon Press 2014 RENEWABLE ENERGY Vol.72 No.-

This article reports the off-design performance analysis of a closed-cycle ocean thermal energy conversion (OTEC) system when a solar thermal collector is integrated as an add-on preheater or superheater. Design-point analysis of a simple OTEC system was numerically conducted to generate a gross power of 100 kW, representing a base OTEC system. In order to improve the power output of the OTEC system, two ways of utilizing solar energy are considered in this study: (1) preheating of surface seawater to increase its input temperature to the cycle and (2) direct superheating of the working fluid before it enters a turbine. Obtained results reveal that both preheating and superheating cases increase the net power generation by 20-25% from the design-point. However, the preheating case demands immense heat load on the solar collector due to the huge thermal mass of the seawater, being less efficient thermodynamically. The superheating case increases the thermal efficiency of the system from 1.9% to around 3%, about a 60% improvement, suggesting that this should be a better approach in improving the OTEC system. This research provides thermodynamic insight on the potential advantages and challenges of adding a solar thermal collection component to OTEC power plants.

3-화학종 대체 혼합물을 이용한 케로신의 열역학적·전달 상태량 예측

조미옥(Miok Joh),김성구(Seong-Ku Kim),최환석(Hwan-Seok Choi) 한국항공우주학회 2013 韓國航空宇宙學會誌 Vol.41 No.11

한국형발사체(KSLV-Ⅱ) 각 단 엔진의 연료로 사용되는 케로신(Jet A-1)은 추력실 재생냉각 및 연료 막냉각 과정에서 냉각유체로도 기능하게 된다. 본 연구에서는 Jet A-1의 열물리적 특성을 재현하기 위한 대체 혼합물 모델을 선정하고, SUPERTRAPP(NIST SRD4)을 이용하여 초임계압 영역을 포함하는 고압 영역에서 모델 연료의 열역학적·전달 상태량을 예측하였다. 측정값과의 비교 결과 액체로켓 엔진 추력실의 복합 열전달 해석 수행 시 Jet A-1 상태량을 추출하기 위한 데이터베이스로 활용 가능한 것으로 판단되며, 향후 연소 시험 결과와의 비교를 통하여 케로신 대체 모델의 상태량 정보를 이용한 재생냉각 추력실의 연소·냉각 성능 통합 해석 결과를 지속적으로 검증해 나갈 계획이다. Kerosene(Jet A-1), one of the propellants for each stage’s engine of the Korea Space Launch Vehicle-Ⅱ(KSLV-Ⅱ), functions as coolant at the same time as it flows inside the cooling jacket of the combustion chambers and is injected through the film cooling holes. A physical surrogate mixture model to reproduce the thermophysical characteristics of Jet A-1 has been selected and the thermodynamic/transport properties of the model fuel under high pressure including supercritical conditions have been estimated using SUPERTRAPP(NIST SRD4). Comparisons with the measured properties suggest that proposed database can be used to extract properties of Jet A-1 for conjugate heat transfer analysis of liquid propellant rocket engine thrust chambers. Predicted combustion/cooling performance of regeneratively cooled thrust chambers shall be validated through comparisons with upcoming firing test results.