Critical multiphase flow

Abstract

Chapter 7 is devoted to the critical multiphase flow. It starts with the mathematical definition of the criticality condition, with the appropriate design of a numerical grid structure and numerical iteration strategy. Then the methods used in the modern design are presented starting from the simple models and increasing gradually the complexity. First the single phase critical flow in pipe is considered for the case with no friction energy dissipation and constant cross section. Then the general case is presented for perfect gas. Then the same ideas are extended to simple two phase cases for pipes and nozzles: subcooled critical mass flow rate in short pipes, orifices and nozzles; frozen homogeneous non-developed flow; nonhomogeneous developed flow without mass exchange; equilibrium homogeneous flow; equilibrium non-homogeneous flow; inhomogeneous developing flow in short pipes and nuzzles with infinitely fast heat exchange and with limited interfacial mass transfer. Then the modern state of the knowledge for describing critical flow is presented by considering physical details like: bubbles origination; bubble fragmentation; bubble coalescences; droplets origination. Examples follow for application of the theory of the critical flow in real scale analysis: blow down of a closed pipe and blow down of a vessel.