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High-Pressure Diesel Injection Studied by Time-Resolved X-Ray Phase-Contrast Imaging
( Kamel Fezzaa ),( Wah Keat Lee ),( Seong Kyun Cheong ),( Christopher F. Powell ),( Ming Chia Lai ),( Jin Wang ) 한국액체미립화학회 2005 한국액체미립화학회 학술강연회 논문집 Vol.2005 No.-
With high-energy and high-brilliance x-ray beams available at third-generation synchrotron sources, propagation-based phase-enhanced imaging was developed as a unique metrology technique to visualize the internal structure of high-pressure fuel-injection nozzles. We have visualized the micrometer-scale machining and finishing defects inside 200-μm fuel-injection nozzles in a 3-mm-thick steel housing using phase-enhanced x-ray imaging. Because of the phase enhancement, for the first time, this new microimaging-based metrology technique has been used to directly study the highly transient pintle motion in the nozzles in situ and in real time with 10-μs temporal resolution, which is virtually impossible by any other means. The needle motion has been shown to have the most direct effect on the fuel-jet structure and spray formation immediately outside of the nozzle. In addition, a transient computational fluid dynamics simulation of in-nozzle fuel flow is in progress to correlate the fuel jets immediately outside the orifice and the in-nozzle flow.
Short time dynamics of water coalescence on a flat water pool
Lim, Su Jin,Gim, Bopil,Fezzaa, Kamel,Weon, Byung Mook ELSEVIER 2016 CURRENT APPLIED PHYSICS Vol.16 No.12
<P>Coalescence is an important hydrodynamic event that frequently takes place in nature as well as in industry. Here we provide an experimental study on short time dynamics of water coalescence, particularly when a water droplet comes in contact with a flat water surface, by utilizing high-resolution high-penetration ultrafast X-ray microscopy. Our results demonstrate a possibility that an extreme curvature difference between a drop and a flat surface can significantly modify the hydrodynamics of water coalescence, which is unexpected in the existing theory. We suggest a plausible explanation for why coalescence can be modified by an extreme curvature difference. (C) 2016 Elsevier B.V. All rights reserved.</P>
Short time dynamics of water coalescence on a flat water pool
Su Jin Lim,Bopil Gim,Kamel Fezzaa,Byung Mook Weon 한국물리학회 2016 Current Applied Physics Vol.16 No.12
Coalescence is an important hydrodynamic event that frequently takes place in nature as well as in industry. Here we provide an experimental study on short time dynamics of water coalescence, particularly when a water droplet comes in contact with a flat water surface, by utilizing high-resolution high-penetration ultrafast X-ray microscopy. Our results demonstrate a possibility that an extreme curvature difference between a drop and a flat surface can significantly modify the hydrodynamics of water coalescence, which is unexpected in the existing theory. We suggest a plausible explanation for why coalescence can be modified by an extreme curvature difference. © 2016
Measurement of the vapor layer under a dynamic Leidenfrost drop
Lee, Gi Cheol,Noh, Hyunwoo,Kwak, Ho Jae,Kim, Tong Kyun,Park, Hyun Sun,Fezzaa, Kamel,Kim, Moo Hwan Elsevier 2018 INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER - Vol.124 No.-
<P><B>Abstract</B></P> <P>To understand the Leidenfrost phenomenon, which is the results of formation of a thin vapor layer, the progression of the vapor should be analyzed. However, due to the limitation of measuring techniques, the empirical measurement of the vapor layer under a dynamic Leidenfrost drop as a function of time has not been reported because the vapor is only tens of micrometers thick and forms within a tenth of a millisecond. Therefore, this paper presents a synchrotron X-ray imaging with the precise resolution to overcome the limitation of previous measurement technique. The liquid–vapor interfacial behavior of a drop of ethanol that is being levitated above a flat SiO<SUB>2</SUB> surface by the Leidenfrost phenomenon is analyzed depending on surface temperature. Measurements suggest that a thin (<2 μm) vapor layer develops between the surface and the drop; i.e. that the liquid does not contact the solid. The measured thickness of this vapor layer under a dynamic Leidenfrost drop was less than the thickness of the vapor layer estimated by analytical solution of a model of vapor layer thickness for a static Leidenfrost drop. The new technique presented in this study will support transient numerical simulations or an analytical solution of the vapor layer under a dynamic Leidenfrost drop, and may have applications in research on the effects of artificial surface structure on the Leidenfrost phenomenon.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The liquid–vapor interface under a dynamic Leidenfrost drop is detected. </LI> <LI> Based on the nucleation phenomenon, the liquid–solid contact is discriminated. </LI> <LI> At high temperature, a vapor layer with thickness <2 μm is inferred. </LI> <LI> The vapor layer starts to grow with a center-peak or parallel profile. </LI> <LI> The vapor-layer thickness for static theory overestimates the experimental results. </LI> </UL> </P>