Créé le : 30/06/2015
Pinho J., Rambaud P., Buchlin JM., Chabane S. - 01/03/2014 - RC - 5th symposium of VKI / Phd Research, Brussels - Mars 2014…
Previous experiments were conducted and reported in two di erent safety relief valves. It was noticed that in presence of cavitation, the mass flux tends to be reduced due to the two-phase mixture compressibility. The first goal of this study is to propose a mathematical model capable of predicting the mass flux of a valve experiencing cavitation at initial high subcooling conditions. An extension of the actual recommended sizing equations of IEC 60534-2-3 is proposed, including a formulation of the semi-critical region, based on the hypothesis that compressibility of a two-phase mixture may be considered as an ellipse. It is verified that at chocking flow conditions, the critical section is partially filled by vapor as the fluid velocity equals the local speed of sound.
In the second part of the research, optical measurement techniques are applied to characterize a challenging two-phase flow through a transparent model of a safety relief valve. Results of f-PIV show the existence of a submerged jet just downstream the geometrical section, with two non-symmetric shear layers at its sides. Under cavitation conditions, it is confirmed that vapor bubbles are formed in the shear layers, characterized by a higher vorticity content. Finally, the phenomenon of mass flow limitation is reproduced and interaction between cavitation and flow topology is highlighted and understood for the first time.
Contact :
Saïd Chabane
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