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Influence of Gas Desorption in a Safety Relief Valve Undergoing Cavitation
Marcos Lema,Anne Gosset,Fernando López Peña 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4
In this study, the characterization of the flow through a safety relief valve (SRV) is performed in presence of cavitation and gas desorption. For this purpose, a transparent safety relief valve model is used on an experimental facility in which the flow conditions (mass flow rate, fluid temperature, and pressure upstream and downstream the valve) are accurately monitored. For six different valve openings, the characteristic curves of the valve are measured while flow visualization is performed on the transparent model. The results show that choked flow conditions are reached for the six valve openings used in this study, and with a remarkable repeatability. In order to take into consideration the gas saturation level of the working fluid, the vacuum system used to adjust the pressure downstream the valve is also used for gas desorption by storing the liquid under vacuum conditions, a process known as vacuum degasification. In saturated liquids the evolved gas bubbles modify the flow properties, such as the speed of sound, and this may have an influence in the cavitation inception and the occurrence of choked flow. This study proves that gas saturated water in standard conditions (atmospheric pressure and 293 K) has the same behavior that fully deaerated water, both under the same cavitating conditions. It is thus not necessary to take the saturation level of the liquid into account when in standard conditions.
Sana, H.,Rauw, G.,Sung, H.,Gosset, E.,Vreux, J.-M. Blackwell Publishing Ltd 2007 MONTHLY NOTICES- ROYAL ASTRONOMICAL SOCIETY Vol.377 No.3
<P>ABSTRACT</P><P>We discuss the properties of the X-ray sources with faint optical counterparts in the very young open cluster NGC 6231. From their positions in the Hertzsprung–Russell diagram, we find that the bulk of these objects probably consists of low-mass pre-main-sequence (PMS) stars with masses in the range 0.3–3.0 M<SUB>⊙</SUB>. The age distribution of these objects indicates that low-mass star formation in NGC 6231 started more than 10 Myr ago and culminated in a starburst-like event about 1–4 Myr ago when the bulk of the low-mass PMS stars as well as the massive cluster members formed. We find no evidence for a spatial age gradient that could point towards a sequential star formation process. Only a few X-ray sources have counterparts with a reddening exceeding the average value of the cluster or with infrared colours indicating the presence of a moderate near-IR excess. The X-ray spectra of the brightest PMS sources are best fitted by rather hard thermal plasma models and a significant fraction of these sources display flares in their light curve. The X-ray brightest flaring sources have decay times between 2 and 16 ks. The X-ray selected PMS stars in NGC 6231 have log <I>L</I><SUB>X</SUB>/<I>L</I><SUB>bol</SUB> values that increase strongly with decreasing bolometric luminosity and can reach a saturation level (log <I>L</I><SUB>X</SUB>/<I>L</I><SUB>bol</SUB>∼−2.4) for non-flaring sources and even more extreme values during flares.</P>