A Study on the Subcooled Boiling Phenomenon of Vertical Annulus Pipe

To enhance the multi-dimensional analysis capability of a subcooled boiling two-phase flow, the population balance equations and improved heat partitioning algorithm were coupled together. Several models for the heat partitioning algorithm and the breakup & coalescence models for the population balance equation were reviewed and a detailed discussion was given to get a better understanding of the subcooled boiling flows. To implement the models, two-fluid models of CFX.12.1 was developed with the improved heat partitioning algorithms and the latest breakup & coalescence models. Improved heat partitioning algorithm included the bubble lift-off diameter model. it took into account the bubble's sliding on a heated wall after its departure from a nucleate site. Lehr et al.(2002) model was adopted as the breakup model of the population balance model. It took into account bubble's capillary pressure. Due to bubbles's capillary pressure, A very small bubbles is unlikely to breakup and the formation of very small bubbles is also unlikely. Coalescence effects due to the turbulent fluctuation, buoyancy and wake-entrainment were taken into account for bubbly flows. Among coalescence models, Luo(1993), Wang(2005), and Hibiki(2000) models were adopted for those coalescence effects. There is no inter-phase turbulent models at CFX.12.1. Inter-phase turbulent models could do a significant role at the two-phase flows. The SST(Shear Stress Transport) turbulent model was developed with the Krepper(2010)'s inter-phase turbulent model. With the improved two-fluid models and default models of CFX.12.1, the behavior of an upwards forced convective subcooled boiling flows in a vertical annular channel is simulated. Comparison of models predictions against local measurements is made for the void fraction, liquid velocity and vapour velocity covering a range of different mass, heat fluxes and inlet subcooling temperature. A lot of difference was revealed between the default model's prediction and measurement. But better agreement is achieved between the improved model's predictions and measurements.1. 서론 1.1 연구배경 1.2 연구목적 2. 본론 2.1 이상유동의 지배방정식 2.1.1 상간 질량 교환 2.1.2 상간 모멘텀 교환 2.1.3 상간 열전달 2.1.4 상간 난류 교환 2.2 비등모델 2.2.1 기존의 비등 모델 2.2.2 개선 비등 모델 2.2.3 Force balance 모델 (1) Yoeh의 방법(2008) (2) Bae의 방법(2010) 2.3 Population balance 모델 2.3.1 IAC 수송 모델 2.3.2 MUSIG 모델 (1) Breakup 모델 (2) Coalescence 모델 2.4 시뮬레이션 및 결과 2.4.1 벤치마크 실험 2.4.2 격자생성 2.4.3 기존모델의 설정 2.4.4 개선모델의 설정 2.4.5 계산결과와 분석 3. 결

복잡한 유체 유동의 시뮬레이션 및 가시화 방법론

Thesis(doctors) --서울대학교 대학원 :전기. 컴퓨터공학부,2010.2.Docto

고강도강판의 융융 아연 취화에 대한 가열속도의 효과

MasterThe aim of the study is to investigate the heating rate effect on Liquid Metal Embrittlement (LME) of galvanized Advanced High Strength steels (AHSSs) by using hot tensile tests. Three galvanized steels were heated with different rates and strained at 600 and 700 ℃ to examine the embrittlement by liquid Zn. In all steel grades, the microstructures at coating/substrate interfaces change as Fe-Zn intermetallic compounds form during heating. These intermetallic compounds have higher melting points than that of pure Zn, and thereby can prevent the substrate from contacting with the embrittling liquid metal. Hence, the embrittlement possibility is reduced with slower heating rate by more active formation of Fe-Zn intermetallics. The formation kinetics varies among the steels due to the different characteristics of inhibition layer rather than the crystal structures or compositions of the substrates. In TRansformation Induced Plasticity (TRIP) steel, it is likely that liquid metal exists at both temperature, because Fe-Zn intermetallic formation kinetics is slowest. Thus, the TRIP steel exhibits LME at both temperatures regardless of heating rates. Since Fe-Zn reaction is faster in TWining Induced Plasticity (TWIP) steel than that in the TRIP steel, LME occurs at 700 ℃, but not at 600 ℃. Although the Fe-Zn reaction in the Press Hardening Steel (PHS) is slower than that in TWIP steel and liquid metal is available at 700 ℃, the PHS is not embrittled; this is because the PHS experiences a lower tensile stress than the other steel grades due to its lower tensile strength. In overall, the heating rate plays an important role in LME by influencing the presence of a liquid Zn at high temperature. Moreover, it is proved that a sufficient tensile stress is required for LME

LSM-ESB composite cathode via spinel cobalt oxide nano particle decoration

본 발명은 코발트 산화물 나노 입자의 함침에 의해 촉매 활성이 현저히 향상된 코발트 산화물 나노 입자가 함침된 LSM-ESB 계열 복합 공기극 및 그 제조 방법에 관한 것이다. 본 발명의 일 실시 예의 코발트 산화물 나노 입자가 함침된 LSM-ESB 계열 복합 공기극은, LSM-ESB 복합층; 및 상기 LSM-ESB 복합층에 함침된 스피넬 구조의 코발트 산화물 나노 입자를 포함하는 코발트 산화물 나노 입자를 포함하여 구성될 수 있다

Gold Rhombic Dodecahedra with Controllable Sizes: Synthesis and Their Tunable Optical Properties

In this poster, we present the synthesis of Au rhombic dodecahedra with controllable sizes and uniform in size and shape, in high yield via seed-mediated growth. In brief, uniform single-crystalline Au nanospheres with the diameter of 10-nm were prepared and then were allowed to grow into Au rhombic dodecahedra by reduction of HAuCl4 with N,N-dimethylformamide and water in the presence of poly (vinyl pyrrolidone) and trisodium citrate. It was found that the concentration of trisodium citrate played a key role to form Au rhombic dodecahedra by its selective capping on the {110} facets of Au. Size of the Au rhombic dodecahedra could be easily controlled in the range from 30 nm to 120 nm by adjusting the number of the Au seed, the concentration of HAuCl4 added in the growth solution, the reaction time, or these combinations

ELECTROLYTE MATERIAL FOR SOLID OXIDE FUEL CELL, MANUFACTURING METHOD THEREOF, AND SOLID OXIDE FUEL CELL COMPRISING SAME

본 발명의 일실시예는, 산화 비스무트에 어븀(Er), 이트륨(Y) 및 지르코늄(Zr)이 도핑된 것을 특징으로 하는, 고체산화물 연료전지용 전해질 소재, 이의 제조방법 및 이를 포함하는 전해질 및 연료전지를 제공한다. 본 발명에 따르면 높은 이온전도도를 가지며, 700℃ 이하의 온도에서 장시간 연료전지를 구동하여도 이온전도도의 저감이나 사면체 플로우라이트 구조로의 상변이가 발생하지 않아 내구성이 우수한 고체산화물 연료전지용 소재, 이의 제조방법 및 이를 포함하는 전해질 및 연료전지를 제공할 수 있다

Synthesis and Electrochemical Activity of Sodium Titanium Phosphate for Sodium Ion Battery

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Yielding and Work Hardening Behaviors of ¡+£ and ¡’+£ Lamellar Structures in an Fe-10Mn-3Al-0.5Mo-0.2C Alloy

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크기와 형태가 제어된 다양한 금속 나노입자의 합성 및 응용

학위논문(박사) - 한국과학기술원 : 생명화학공학과, 2012.8, [ xviii, 190 p. ]Controlling the size and shape of metal nanoparticles has been one of the most interesting research topics over the past decade, because the several properties of metal nanoparticles can be finely and widely tuned by controlling their size and shape. Thanks to these tunable properties, metal nanoparticles have been widely applied in various fields such as electronics, sensing, imaging, and biomedicine as well as catalysis. In this re-gard, tremendous efforts have been devoted to the synthesis of metal nanocrystals with different sizes and shapes, in order to study their growth mechanisms and to study their size- and shape-dependent properties as well as to fine-tune or enhance the properties. However, growth mechanisms for metal nanoparticles with dif-ferent shapes are still unclear and high-level synthetic control is also necessary. For this dissertation, I synthe-sized various metal nanoparticles with different sizes and shapes for the following purposes: i) to understand their formation mechanisms in order to facilitate better control over the size and shape of metal nanoparti-cles, ii) to study size- and shape-dependent properties of them, iii) to apply them to several applications. Chapter 1 introduces basic knowledge in this field that includes what is metal nanoparticle, shape- and size-dependent properties of metal nanoparticles, and how to control the size and shape of metal nanoparticles. Chapter 2-4 describe experimental results for this dissertation. More specifically, Chapter 2 presents shape evolution of Au nanoparticles. We found that rhombic dodecahedral Au nanoparticles in the early stage of the reaction transformed into Au octahedra with the other shapes. By stopping the reaction at certain times, Au nanoparticles with different shapes such as rhombic dodecahedral, truncated rhombic dodecahedral, rhombic cuboctahedral, truncated octahedral, and octahedral could be obtained. Their strong scattering ability arisen from the localized surface p...한국과학기술원 : 생명화학공학과