A Study on the Heat Transfer and Pressure Drop for Two-phase Flow Boiling of FC-72 in Parallel Micro-channels

With the development of electronic equipment industry, the systems and components are pursuing high-performance and high-efficiency, and the size of system is gradually downsizing as well. Furthermore, the development of technology that can efficiently eliminate the heat generated inside a miniature system is demanded. Thermal and fluidic characteristics in micro-channels used by heat sink have been proved by many experimental studies and can be applied to various areas. This study analyzed the characteristics on heat transfer and pressure drop of FC-72 in parallel micro-channels through an experimental study. Parallel micro-channel is 450μm in width, 200μm in depth, 60mm in length, and has 15 channels. Before the experiment, the shape of the manifold, length of the channel and the flow field based on inlet condition are analyzed using CFD. The parallel micro-channel to be used in the experiment was designed based on the analysis results. The experiment is conducted at the mass flux of 100.3-408.5 kg/m2s and heat flux of 3.2-49.0 kW/m2 and the vapor quality at this time is within the range of 0.00-0.96. The total pressure drop in the channel is expressed as the sum of frictional pressure drop and the accelerational pressure drop. Since the frictional pressure drop is considerably larger than accelerational pressure drop in most cases, it is essential to precisely calculate the frictional pressure drop in order to predict the total pressure drop. Frictional pressure drop is usually calculated by using the homogeneous model and the separated flow model, the frictional pressure drop obtained from the experiment is compared to those calculated by the homogeneous model and the separated flow model. In order to accurately predict the frictional pressure drop, this study expresses the two-phase friction multiplier as the function for Reynolds number, Weber number, and Martinelli parameter to develop a new correlation that considers the inertial force, viscous force, and surface tension of fluid. The new correlation predicts well the frictional pressure drop obtained in this study within 5.5% MAE. The flow boiling heat transfer in the channel is known to occur by nucleate boiling and forced convective boiling. In the region where nucleate boiling dominates the flow, heat transfer usually occurs from the creation and breakaway of bubbles, and the flow pattern in such a region indicates mainly bubbly and slug flow. Also, the heat transfer coefficient normally depends on the heat flux, but is not affected too much by mass flux and vapor quality. In contrast, in the region where the forced convective boiling dominates, most of the flow pattern is annular flow, and the heat transfer usually occurs through the evaporation of the thin liquid film around the heating surface. The heat transfer coefficient usually depends on the mass flux and vapor quality in this region, and is nearly unrelated to the heat flux. The heat transfer mechanism in micro-channel is being reported differently by researchers. According to the result of this experiment, in the region of lower vapor quality, nucleate boiling plays a role as the main mechanism of heat transfer. The influence of nucleate boiling gradually decreases as the vapor quality increases. As the effects of forced convective boiling gradually increases, nucleate boiling and forced convective boiling occur compositively. Based on such a mechanism of heat transfer, a new correlation to predict heat transfer coefficient is developed. A new correlation obtained in this study considers the effects of both nucleate boiling and forced convective boiling, and predicts the result within 4.6% MAE.List of Tables iv List of Figures v Nomenclature viii Abstract xi 1. 서 론 1.1 연구배경 및 목적 1 1.2 연구내용 5 2. 선행 연구 및 기본 이론 2.1 유동분배 6 2.2 2상 유동 압력강하 10 2.2.1 균질 모델(Homogeneous model) 10 2.2.2 분리류 모델(Separated flow model) 12 2.3 2상 유동 비등 열전달 19 3. 실험 장치 및 방법 3.1 실험 장치 28 3.2 실험 방법 34 3.3 데이터 처리 35 4. 병렬 마이크로 채널의 설계 및 수치해석 4.1 개요 38 4.2 수치해석 39 4.3 요약 59 5. 2상 유동 압력강하 5.1 개요 60 5.2 압력강하 특성 61 5.3 새로운 마찰 압력강하 예측 상관식 74 5.4 요약 83 6. 2상 유동 비등 열전달 특성 6.1 개요 85 6.2 열전달 특성 87 6.3 새로운 열전달 계수 예측 상관식 95 6.4 요약 106 7. 결 론 108 참고문헌 11

A Study on the Performance Analysis of 1kW Class Radial InflowTurbine for Ship's WHRS by CFD

The rising cost of energy and global warming in recent years have highlighted the need to develop advanced energy systems to increase efficiency and to reduce emissions. The availability of energy plays an important role in the development and prosperity of a nation. In recent years, waste heat recovery, renewable energy sources, cogeneration and combined cycle power generation systems are receiving a great deal of attention. WHRS(Waste Heat Recovery System) generates electrical energy from a ship's exhaust gases. This could reduce the ship's fuel consumption and CO2 emissions. A turbine is a rotary machine that extracts energy from a fluid flow and converts it into useful work. Axial flow turbines and radial inflow turbines are the two most common types of dynamic turbines. The radial inflow turbine stage is differentiated from an axial stage by having the fluid undergo a significant radius change in passing through the rotor. In other words, in the radial stage the fluid enters the rotor in the radial inward direction and leaves in the axial direction. The flow within the rotor passage is three dimensional and complex, hence the use of numerical methods such as computational fluid dynamics(CFD) is necessary. CFD is analysis of systems involving fluid flow, heat transfer and associated phenomena by means of computer-based simulation. In this study, performance and internal flow of 100kW class radial inflow turbine were analysed. Three dimensional simulation was performed using commercial code of ANSYS CFX 12.1. The radial inflow turbine was comprised of vane nozzle with 18 blades and rotor with 13 blades. Performance analysis was made for the isentropic efficiency(total-static) and mechanical power covering a range of different massflow rate, turbine speed and area ratio of the scroll casing.목 차 Abstract iii 기호설명 v 제 1장 서론 1 1.1 연구배경 및 필요성 1 1.2 연구목적 3 제 2장 증기터빈의 이론적 접근 5 2.1 열사이클 5 2.2 터빈 기본방정식 및 이론 7 2.2.1 터보기계방정식 7 2.2.2 속도삼각형 9 2.2.3 등엔트로피 효율 11 2.3 scroll casing 설계 13 제 3장 수치해석 17 3.1 수치해석 기법 17 3.2 지배방정식 19 3.2.1 수송방정식 19 3.2.2 상태방정식 20 3.3 이산화방법 21 3.4 난류모델링 25 제 4장 100kW급 구심터빈의 성능해석 28 4.1 구심터빈 설계형상 28 4.2 질량유량 및 회전수 변화에 따른 성능해석 30 4.2.1 계산격자 및 경계조건 30 4.2.2 결과 및 고찰 32 4.3 스크롤케이싱 변화에 따른 성능해석 55 4.3.1 계산격자 및 경계조건 55 4.3.2 결과 및 고찰 56 제 5장 결론 85 참고문헌 8

The Role of M&A in Restructuring Korea's Distressed Firms

With the outbreak of the financial crisis in mid-1997, the Korean government has removed a majority of M&A-related regulations in order to facilitate M&A transactions. This was based upon the belief that M&As are one of the most efficient ways to restructⅠ. 서 론 　Ⅱ. M&A 관련 정부정책의 변화 　Ⅲ. 분석자료 　Ⅳ. 실증분석 방법 및 결과 　Ⅴ. 결 론 　참 고 문

Potential Foreign Competition and Market Structures: Empirical Analysis and Policy Implications

Opening domestic market to international trade may enhance not only actual competition but also potential competition from foreign competitors. It seems that the competition authority has focused mainly on the actual competition (measured by the current mI. 서론 II. 선행연구 　1. 국내 선행연구 　2. 해외 선행연구 III. 실증분석 　1. 실증분석모형 　2. 변수의 구축 및 분석 자료 　3. 실증분석방법 　4. 추정결과 IV. 분석의 종합 및 정책적 시사

Performance Analysis on Foreign-invested Firms in the SEZ

To attract more FDI inflows, the Korean government has designated several special economic zones (SEZs), offering various advantages and support to the FDI. There is, however, a shared acknowledgement that those efforts have gained little reward. In thisⅠ. 서 론 　Ⅱ. 기존 연구 　Ⅱ. 기존 연구 　Ⅳ. 분석 결과 　Ⅴ. 결 론 　참고문헌 　부

What Explains Firm’s Innovativeness in Korean Manufacturing?: Global Activity and Knowledge Sources

In this paper, we analyzed whether there exists positive relation between firm’s global activity and various innovation output and, if it exists, what are the major factors by which innovation outputs can be generated, focusing on the different degree ofⅠ. 연구의 배경 및 목적 Ⅱ. 선행연구 검토 Ⅲ. 데이터 및 방법론 Ⅳ. 실증분석 V. 요약 및 정책적 시사

Effect of Slow Walking Speed on Gait

Objective: To investigate the effect of slow walking speed on the gait. Method: Twenty healthy young male subjects were recruited. The temporospatial data, kinematic and kinetic data in sagittal plane at two different walking speed (2 km/hr, 4 km/hr) were obtained through three dimensional analyzer with the force plate, and compared these parameters at slow gait speed to those at normal gait speed. Results: The cadence and step length decreased significantly and double support time increased significantly (p<0.05) at slow speed compared to at normal speed. The most peak angle of hip, knee and ankle joint decreased, maximal ankle dorsiflexion angle in stance phase increased significantly at slow speed compared to at normal speed (p＜0.05). The most maximal extension and flexion moment and power in sagittal plane decreased compared to at normal speed (p＜ 0.05). Conclusion: The results of this study demonstrate that only slow walking speed without any pathology may change the temporospatial, kinematic and kinetic parameters of gait, and these results may be useful to interpret the data of gait analysis in the disabled persons with slow walking speed.ope

(The) role of Dickkopf-1 related with epithelial-mesenchymal transition in the lip patterning of the chick embryo

치의학과/박사[한글]Dickkopf(Dkk)-1는 Dkk family중 하나로 강력한 Wnt 길항 작용을 하여 전-후방 axial patterning, 눈, 사지 혹은 체절 등의 발생 과정에서 중요한 역할을 하는 것으로 알려져 있다. 뇌와 얼굴을 포함하는 두부의 발생에서도 Dkk-1이 특별히 중요하다고 인정되고 있지만 구체적인 역할에 관하여는 아직 덜 알려져 있다.Dkk-1 및 Wnt가 조절하는 상피-간엽 전이(Epitheial-Mesenchymal Transition) 과정은 상피의E-cadherin 발현 감소에 의한 세포 사이 결합력 약화와 이에 따른 세포의 상피 특성이 사라지는 현상을 말한다. 이 전이 과정은 상처의 치유, 암의 전이 과정에서 중요할 뿐 아니라 발생 과정, 특히 상피가 없어지면서 패터닝이 일어나는 부위에서 필수적이다. 얼굴 형태에 중요하고 인간에게 가장 흔한 선천성 기형인 구순열을 일으킬 수 있는 입술의 발생 과정에서도 이 기전은 중요하게 작용할 수 있다. 얼굴 발생 초기 내측 비돌기와 상악 돌기가 서로 맞붙고 중간에 개재된 상피가 없어지면서 입술이 형성되기 때문이다. 따라서 구순열 형성의 가능한 기전으로 상피-간엽 전이 기전의 실패와 이에 작용할 수 있는 Dkk-1의 역할 가능성에 대해 연구하는 것이 본 연구의 목적이었다.닭 배아 모델에서 융합 직전의 전비돌기(frontonasal process) 표피 하부에 매식된 Dkk-1 단백질은 부분적인 구순열을 초래하였으며 상피층의 소실 지연과 관련되었다. 또 Bone morphogenetic protein의 발현 패턴 차이와 함께 상피-간엽 전이에 필수적인 E-cadherin과 Snail의 발현 변화도 확인하였다. 이러한 결과를 통해 닭 입술 형성 과정에서 얼굴 돌기를 둘러싸고 있는 상피의 소실 과정에는 상피-간엽 전이 현상이 포함되어 있으며, Wnt 길항제인 Dkk-1의 조절이 중간 개재 상피의 운명에 아주 중요하다는 것을 확인할 수 있었다. 앞으로 이러한 상피-간엽 전이 현상과 인간 구순열 발생의 연관성 및 치료 가능성 등에 대한 폭넓은 연구가 필요할 것으로 예상된다. [영문]Dkk-1, the most extensively studied Dkk family member, is a potent Wnt antagonist. In vertebrate embryos, Dkk-1 is correlated with head development that has been postulated to involve inhibition of Wnt signaling. The purpose of this study is to identify function of Dkk-1 related with epithelial-mesenchymal transition (EMT) in the lip patterning of chik embryos. By analyzing the developmental pattern of chicken embryos after Dkk-1 treated, Wnt signal including Dkk-1 is involved in the developments of the lip, especially during the fusion process of facing epithelium of the facial prominences. When beads soaked with Dkk-1 were implanted into the subepithelial mesenchyme of the frontal mass, the embryos showed the absence or delayed epithelial fusion and disintegration to make the mesenchymal bridging. Frequently, it resulted in the partial cleft between the maxillary and globular process, but the final phenotype of the embryos failed to show the cleft lip/primary palate, possibly associated with the lack of continuous Dkk-1 protein action. Western blot and immunohistochemical analysis revealed that overexpression of Dkk-1 caused the down-regulation of Snail, which is the downstream of Wnt signal pathway to control the E-cadherin. And E-cadherin, which is a well known transmembrane gycoprotein and mediates epithelial cell-to-cell adhesion, was shown to be upregulated from RT-PCR analysis. In addition, the components of Bmp signaling pathways like Bmp4 and MSX-1 were influenced by the exogenous Dkk-1 protein at the epithelium or mesenchyme of the fusing prominences. Taken together, Dkk-1 as a component of Wnt signaling pathway is essential for the fate of the epithelium to have the developmental fusion and disintegration to make EMT at the maxillary process and frontonasal mass.ope

식물 유래 카다놀을 포함하는 항균 방오 소재의 합성 및 분석, 그리고 수처리 막 및 코팅 소재로의 응용

학위논문 (박사)-- 서울대학교 대학원 : 화학생물공학부, 2016. 2. 이종찬.This study presents synthesis and characterization of antibacterial and antifouling polymers containing plant-based cardanol moiety, and their applications for water treatment and coating applications. Firstly, polymers containing a renewable cardanol moiety were prepared via radical polymerization of 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) and methyl methacrylate (MMA), where HCPM was synthesized by a reaction of cardanol with glycidyl methacrylate in the presence of a base catalyst. Incorporation of the cardanol moiety into PMMA was found to increase the thermal and mechanical stability of the brittle PMMA. When the cardanol based polymers were irradiated with UV light, the mechanical stability increased further because cross-linked networks were formed between the double bonds in the cardanol moieties. Cross-linked polymer films containing the cardanol moiety exhibited high gloss and transparency to visible light. Cardanol-containing polymers with and without the cross-linked networks and other cardanol-based polymers such as poly(cardanyl acrylate) and poly(2-acetoxy-3-cardanylpropyl methacrylate) all showed high antibacterial activity against Escherichia coli (E. coli), indicating that the disappearance of double bonds and/or the structure changes of connecting groups do not diminish the intrinsic bactericidal properties of the cardanol moieties. Secondly, a series of copolymers [PCD#s, where # is the weight percentage of dopamine methacrylamide (DMA) in polymers] containing mussel-inspired hydrophilic dopamine and plant-based hydrophobic cardanol moieties was prepared via radical polymerization using DMA and 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) as the monomers. PCD#s were used as coating materials to prevent flux decline of the membranes caused by the adhesion of biofoulants and oil-foulants. Polysulfone (PSf) ultrafiltration membranes coated with PCD#s showed higher biofouling resistance than the bare PSf membrane, and the bactericidal properties of the membranes increased upon increasing the content of HCPM units in the PCD#s. Serendipitously, the PSf membranes coated with the more or less amphiphilic PCD54 and PCD74, having the optimum amount of both hydrophilic DMA and hydrophobic HCPM moieties, showed noticeably higher oil-fouling resistance than the more hydrophilic PCD91-coated membrane, the more hydrophobic PCD0-coated membrane, and the bare PSf membrane. Therefore, multifunctional coating materials having biofouling- and oil-fouling-resistant and bactericidal properties could be prepared from the monomers containing mussel-inspired dopamine and plant-based cardanol groups. Finally, A new series of ABA-triblock copolymers (PHCPMF#s, where # is the number of repeating unit of HCPM at each side of the A block) containing perfluoropolyether (PFPE) as B block and cardanol based polymer as A block was prepared via atom transfer radical polymerization using modified PFPE as macroinitiator (Br-PFPE-Br) and 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) as a monomer. Stable PHCPMF# films were prepared on the silicon wafer using spin coating method, followed by UV irradiation to form a crosslinked structure. Cross-linked PHCPMF# (C-PHCPMF#) films showed bactericidal properties much better than the bare PMMA, and bacterial adhesion resistance of the films increased with decreasing the content of HCPM units in the PHCPMF#s. Moreover, bacterial adhesion resistance of the PHCPMF# films closely correlated with low surface energy and water contact angle hysteresis (CAH). Additionally, C-PHCPMF# films showed excellent cell viability on their surfaces but still didnt show any cytotoxicity due to the biocompatible property of the PFPE block. Therefore, PHCPMF#s are new ABA-triblock copolymers with PFPE and cardanol moieties, and they can be used as multifunctional coating materials having bactericidal properties, bacterial adhesion resistance, and biocompatibility in a variety of coating application.Chapter1 Introduction 1 1.1. Polymers from renewable resources 2 1.2. Antifouling and antibacterial polymers 4 1.3. Motivation 7 1.4. References 9 Chapter2 Synthesis and Characterization of Self-Cross-Linkable and Bactericidal Methacrylate Polymers Having Renewable Cardanol Moieties for Surface Coating Applications 15 2.1. Introduction 16 2.2. Experimental 18 2.3. Results and Discussion 33 2.4. Conclusion 44 2.5. References 45 Chapter3 Mussel-Inspired Dopamine- and Plant-Based Cardanol-Containing Polymer Coatings for Multifunctional Filtration Membranes 67 3.1. Introduction 68 3.2. Experimental 71 3.3. Results and Discussion 83 3.4. Conclusion 99 3.5. References 101 Chapter4 Antibacterial and Biocompatible ABA-Triblock Copolymers Containing Perfluoropolyether and Plant-Based Cardanol for Versatile Coating Applications 119 4.1. Introduction 120 4.2. Experimental 124 4.3. Results and Discussion 133 4.4. Conclusion 144 4.5. References 146 Abstract in Korean 166Docto