• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.433-434
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• 2006

Monosized germanium micro particles are prepared by a newly developed Pulsated Orifice Ejection Method. The obtained particles are categorized into two kinds of the microstructures as refined and coarse ones. The morphological difference is estimated to be determined by the undercooling level during nucleation. Actually, the increase in the temperature of the melt was effective in coarsening the microstructure, because the temperature of the melt intensely relates to the undercooling level. The transition temperature of coarse and refined microstructures is found to be 1300-1350K. Furthermore, a triggered nucleation could improve the crystallinity of the particles in the short separation.

• 대한기계학회논문집B
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• 제24권9호
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• pp.1239-1246
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• 2000

The objective of this work is to measure space and time resolved wall heat fluxes during nucleate pool boiling of R113/R11 mixtures using a microscale heater array in conjunction with a high speed CCD. The microscale heater array is constructed using VLSI techniques, and consists of 96 serpentine platinum resistance heaters on a transparent quartz substrate. Electronic feedback circuits are used to keep the temperature of each heater at a specified temperature and the variation in heating power required to keep the temperature constant is measured. Heat flux data around an isolated bubble are obtained with triggered CCD images. CCD images are obtained at a rate of 1000frames/second. The heat transfer variation vs. time on the heaters directly around the nucleation site is plotted and correlated with images of the bubble obtainedby using the high speed CCD. For both of the mixture(R11/R113) and pure system(pure R11, pure R113), the wall heat fluxes are presented and compared to find out the qualitative difference between pure and binary mixture nucleate boiling.

• 한국지구과학회지
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• 제35권5호
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• pp.305-312
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• 2014

A number of coated grains (spherical to elongated ones in shape) were collected from a small stream, Dijon, France. They were characterized by typical concentric lamination surrounding broken twigs, and were thus identified as concentric precipitation on plant twigs. Within carbonate coatings of the plant twigs, two morphological groups including, eukaryotic green algae (Vaucheria sp.) and cyanobacteria (Scytonema sp. and Rivularia sp.) were detected, which form carbonate crystals that are surrounding their filaments. The filaments could have triggered carbonate precipitation by photosynthetic removal of $CO_2$ causing the increase of alkalinity of the water, and by supporting their sheaths as nucleation sites. Such encrusted twigs were found from 70 meters downstream, in which temperature and pH were measured as $11.1^{\circ}C$ and 8.18, respectively. These water chemistries ($11.1^{\circ}C$ and pH 8.18), with the aid of microbial photosynthesis, were likely to provide a suitable condition for carbonate precipitation on the twigs.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2276-2296
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• 2022

This study validates the applicability of the CUPID code for simulating subcooled wall boiling under high-pressure conditions against number of DEBORA tests. In addition, a new numerical technique in which the interfacial momentum non-drag forces are calculated at the cell faces rather than the center is presented. This method reduced the numerical instability often triggered by calculating these terms at the cell center. Simulation results showed good agreement against the experimental data except for the bubble sizes in the bulk. Thus, a new model to calculate the Sauter mean diameter is proposed. Next, the effect of the relationship between the bubble departure diameter (D_dep) and the nucleation site density (N) on the performance of the Wall Heat Flux Partitioning (WHFP) model is investigated. Three correlations for D_dep and two for N are grouped into six combinations. Results by the different combinations show that despite the significant difference in the calculated D_dep, most combinations reasonably predict vapor distribution and liquid temperature. Analysis of the axial propagations of wall boiling parameters shows that the N term stabilizes the inconsistences in D_dep values by following a behavior reflective of D_dep to keep the total energy balance. Moreover, ratio of the heat flux components vary widely along the flow depending on the combinations. These results suggest that separate validation of D_dep correlations may be insufficient since its performance relies on the accompanying N correlations.