Solution of the Riemann Problem for Water with Phase Transition: Influence of the Equation of State

We address the solution of the Riemann problem for water in the diphasic domain. We compare the solution obtained with the IAPWS equation of state (EOS) with the solution obtained with a modified stiffened gas EOS for pure liquid water, a tabulated EOS for the diphasic domain and a modified perfect gas EOS for pure steam. Since our interest is phase transition, we limit ourselves to temperatures below 623 K. We obtain convex isentropes which do not cross each other, so that the Riemann problem can be solved easily and its solution is unique. We analyze the effect of the EOS which has been selected. We give examples which are useful to understand the depressurization process in a tube.