IHTC14-22863 MECHANISM AND MODELING OF REWETTING INITIATION OF HOT DRY SURFACE IN SATURATED AND SUBCOOLED FILM BOILING

ABSTRACT The behavior of rewetting on a high superheated and dry surface, focusing on rewetting temperature just as collapse of saturated and subcooled film boiling was investigated experimentally and analytically. Saturated and subcooled pool film-boiling experiments were conducted by using a Silicon wafer with 20 mm length, 20 mm width and 0.5 mm thickness and pure water at atmospheric condition. Saturated and subcooled impingement jet experiments were also preformed. Then, the model analysis of rewetting initiation of a hot dry surface in saturated and subcooled film boiling was constructed by using hydrodynamics instability on liquid-vapor interface (Rayleigh-Taylor instability) and a heat conduction model (rewetting model under a falling film). Some physical parameters on Rayleigh-Taylor instability, for example released period of bubble from vapor film on a heater, generated volume rate of vapor and so on, were estimated by using Two-Phase Boundary Layer theory of saturated and subcooled film boiling. The present analytical results also showed that as the liquid subcooling was high, MHF temperature was higher. Namely, the predictions agreed with the present experimental results and Dhir-Purohit's correlation. In addition, the present model of MHF temperature was developed by taking into account the dependence on thermal conductivity of wall of the MHFtemperature

Clustering of Lyman Break Galaxies at z=4 and 5 in The Subaru Deep Field: Luminosity Dependence of The Correlation Function Slope

We explored the clustering properties of Lyman Break Galaxies (LBGs) at z=4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z=4 and 5. More luminous LBGs have a steeper correlation function. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions for LBGs predicted by this mock catalog were found to be almost consistent with the observation. Moreover, the overall correlation functions of LBGs were reproduced reasonably well. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark haloes had steeper and larger-amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the slope of the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity-dependence of the angular correlation function, if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs (abridged).Comment: 16 pages, 17 figures, Accepted for publication in ApJ, Full resolution version is available at http://zone.mtk.nao.ac.jp/~kashik/sdf/acf/sdf_lbgacf.pd