Equilibrium and Non-Equilibrium Flows, Compressible Flows, and Choke Flows

This chapter focuses on non-equilibrium flow, compressible flow, and choke flow. A working knowledge of these flow types is required to understand how reactors behave when the coolant suddenly passes from a region of high pressure P_high to a region of low pressure P_low during a loss-of-coolant accident. The chapter describes how the mass flow rate behaves when each of these factors comes into play. Critical flow starts when the pressure gradient achieves its maximum possible value at the channel exit. In long channels, the residency time is long enough for the phases to come into thermal equilibrium. In general, temperature differences between the phases can be used to explain why the critical pressure ratio changes as a function of orifice length. The slip equilibrium model assumes that the phases in the coolant channel or orifice are in thermal equilibrium but that the critical flow rate G_critical is also a function of the slip ratio S.