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Skewed Spray Characteristics of Impinging Injector
Bimal Subedi,Inchul Lee,Min Son,Bongki Shin,Chanwoo Seo,Jaye Koo 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.12
The atomization characteristics of doublet skewed impinging injectors with a like-on-like arrangement was investigated and compared in this paper for various angle of incident and skewness fraction at various Reynolds conditions using water as a simulant. In this study, the liquid sheet formed along with its variance with skewness factor were analysed using the methods of spray image photography. The graphical relationship between factor of skewness with Reynolds number and angle of spray was derived as the result.
Reliability study on skewness of doublet impinging injectors
Bimal Subedi,손민,장석필,구자예 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.5
The atomization characteristics of skewed like-on-like impinging injectors were studied using water as a simulant. The shadowgraph technique and Laser deflection analyzer were used to understand the variances in spray mode, breakup length, and spray angles with the fraction of skewness under different angles of impingement, pressure, and Weber number. The range of reliability of performance from the perspective of the manufacturer was determined through quantitative and qualitative analyses of atomization and spray characteristics. The three different modes of spray breakup were well mixed, reflective, and transmissive. The breakup length decreased with the increase in spray angle up to a certain fraction of skewness. The spray fan angle and SMD in skewed impinging injection were directly proportional to the fraction of skewness. A large fraction of skewness provided the spray sheet with a small droplet size at the center of the spray sheet and large droplet sizes with rising radial distances toward the edge of the sheet. This paper attempts to define the maximum allowable misalignment and basic reliability limit for the design and evaluation of performance of impinging injectors in terms of fraction of skewness. Values at the perfect impingement condition were used as references for the significant reduction in the manufacturing cost of impinging injectors.
비균일 열유속 다중 열원을 가지는 박판형 Vapor Chamber의 최대 열전달량에 대한 이론적 연구
김성현,Subedi Bimal,장석필 대한기계학회 2019 大韓機械學會論文集B Vol.43 No.8
This paper describes a theoretical study of pressure distribution, temperature distribution and maximum heat transfer rate of thin-flat vapor chamber, which can be used for the cooling of multi-heat sources with different heat flux such as electronic devices. The maximum heat transfer rate is determined by capillary limitation. To consider different heat flux for the multi-heat sources, a weighting factor approach was introduced and applied to our model instead of using the same heat flux. When geometry of vapor chamber, position of heat sources and heat sinks and amount of total heat are fixed, the effect of heat flux ratio on pressure distribution and temperature distribution of the vapor chamber is investigated and the reason is explained. The maximum heat transfer rate for thin-flat vapor chamber with multi-heat sources is theoretically presented according to heat flux ratio between the heat sources when geometry of vapor chamber, position of heat sources and heat sinks are fixed. 본 연구에서는 열유속 크기가 서로 다르며(비균일 열유속) 여러 개의 열원을 가지는 전자부품들의 냉각으로 사용될 수 있는 박판형 vapor chamber의 압력 분포, 온도 분포 그리고 모세관력 제한조건에 의해 결정되는 최대 열전달량에 대해 이론적으로 연구하였다. 기존에 다중 열원의 조건으로 사용했던 균일 열유속 조건 대신 비균일 열유속 조건을 고려하기 위하여 weighting factor를 제시하고 모델에 적용하였다. 특히 vapor chamber의 형상, 열원 및 방열부의 위치, 그리고 열량이 동일한 조건 하에서 다중 열원에 주어지는 열유속 크기 비율이 vapor chamber의 압력 분포 및 온도 분포에 미치는 영향을 확인하였으며 그 이유를 설명하였다. 또한 vapor chamber의 형상, 열원 및 방열부의 위치를 고정시킨 상태에서 다중 열원에 주어지는 열유속 크기 비율에 따른 vapor chamber의 최대 열전달량을 제시하였다.
최태종,Bimal Subedi,함현준,박명수,장석필 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.8
In this review paper, we summarize important milestones in experimental studies that indicate the effects of volume fraction, nanoparticle size, operating temperature and pH on the internal forced convective heat transfer characteristics of nanofluids. In addition, many mechanisms for the enhancement of the convective heat transfer coefficient of nanofluids proposed by investigators are categorized into two dominant mechanisms. The first dominant mechanism is properties’ change of nanofluids such as thermal conductivity and viscosity. The other is the motion of nanoparticles in nanofluid flow due to Brownian motion, thermal dispersion and migration. Finally, the thermal performance criteria which can estimate whether nanofluids are useful in actual engineering systems, are summarized. Authors expect that the understanding of the convective heat transfer characteristics of nanofluids could help many thermal engineers to develop nanofluids which can be used in industrial applications.