Numerical simulation of two phase flow in high pressure and low pressure evaporator pipes in recovery boiler

In this study, a numerical simulation of evaporation in two phase flow of water has been performed considering energy and mass transfer during phase change based on the VOF (volume offluid) model in CFD software Fluent 6.3, with a UDF (user defined function) as an evaporation, and unsteady solution is considered in several times. The operating conditions are specified at high pressure (HP), 99.7 bar and low pressure (LP), 10.5 bar in saturation conditions of water flow in temperature, 583 K and 450 K, respectively. Also, the physical properties of water are determined by inlet temperature and pressure system in saturation conditions. Two phase properties such as void fraction, distribution of wall temperature, heat transfer coefficient and heat flux are also investigated in this study. The simulations are carried out on upward water flow in a two dimensional vertical tube with constant temperature of wall heating surface condition. The pressure-implicit with splitting of operators (PISO) pressure-velocity coupling scheme is used to improve the efficiency of calculation. The flow is considered as turbulent based on the RNG k-ε model.