Numerical modeling of two-phase flow in the NaCl-H2O system: Introduction of a numerical method and benchmarking

In order to facilitate modeling of fluid flow processes in seafloor hydrothermal systems, we introduce a numerical scheme called FISHES that is capable of simulating two‐phase fluid flow in the NaCl‐H2O system. We discuss the equations governing fluid flow, the thermodynamic relations between various quantities employed, and the coupling of these elements together in a time marching scheme. The thermodynamic relations are expressed in terms of equations of state compiled from lookup tables. These are based on previously published formulations for the density and enthalpy of NaCl‐H2O fluid in regions of phase space that are relevant to the study of seafloor hydrothermal systems. We show that the thermodynamic quantities vary both smoothly and physically in P‐T‐X space. In particular, vapor salinity values near the vapor‐liquid‐halite coexistence surface are in agreement with recently measured values. We compare code output from an approximately one‐dimensional scenario to the analytic solution of the classical one‐dimensional thermal advection‐diffusion equation and find that the numerical output and analytic solution are in agreement. The numerical code is also benchmarked against previously published results for the Elder problem and for the problem of fluid extraction from a one‐dimensional, two‐phase horizontal pipe. We find that the results using FISHES are in agreement with previously published results. Finally, we show that results from a one‐dimensional vertical salt pipe simulation agree with an analytic solution.