VC-20-006 -- CFD Study of Hydraulic Shock in Two-Phase Anhydrous Ammonia (RP-1569)

Condensation-induced hydraulic shock (CIHS) is a safetyissue that requires the accurate prediction of pipe rupture riskdue to the formation of a hydraulic shock. The prediction ofhydraulic shock formation depends on accurate modeling ofslug formation for given conditions of vapor flow rate, liquidheight, liquid subcooling, and piping geometry. This paperpresents results from the detailed three-dimensional (3-D)computational fluid dynamics (CFD) modeling of this problemapplied to twelve different cases from the experimental studyof Martin et al. (2007) with different liquid levels, vapor injectionrates, and saturation conditions. The results show aremarkable match to experimental results in terms of slugformation, slug propagation, and also in terms of shock formationtimes and shock amplitudes. The results yield rich informationabout the mechanisms associated with the formation ofinterfacial waves as a function of vapor flow rates and liquidlevel. It also reveals the necessity of condensation to trigger theformation of a slug and the possible modes of condensation(such as interfacial/wall condensation) that result in thepropulsion of the slug eventually resulting in the hydraulicshock. This is the first time such a complex problem has beensuccessfully simulated using a 3-D compressible multiphaseCFD model, demonstrating the utility of such a tool to increasethe operational safety of industrial refrigeration systems.