In this study, a 2-D simulation of forced boiling of a fluid flow inside a boiler raiser. The fluid enters the raisin in saturated state. The raiser is under constant heat flux. The simulated 2-D two-phase flow simulation process is presented in a vertical tube with a constant flux boundary condition. To simulate the application of Fluent version 18, and also to validate the results, the results were compared with the experimental results. The simulation error rate was about 3%. The effect of thermal flux intensity on the heat transfer coefficient of heat transfer and the wall temperature and fluid pressure were investigated. The simulation results showed that with the thermal thermochemistry increasing in the tube wall, the heat transfer coefficient h has a downward trend. This is due to an increase in the volume fraction of water vapor and, consequently, to a decrease in the thermal conductivity of the vapor relative to the fluid in the liquid water. Also, in higher thermal flasks, the heat transfer coefficient h (due to rapid fluctuations in the thermo physical properties of the liquid and vapor fluid, as well as the emergence of the dynamic instability of vortices) increases.In this study, a 2-D simulation of forced boiling of a fluid flow inside a boiler raiser. The fluid enters the raisin in saturated state. The raiser is under constant heat flux. The simulated 2-D two-phase flow simulation process is presented in a vertical tube with a constant flux boundary condition. To simulate the application of Fluent version 18, and also to validate the results, the results were compared with the experimental results. The simulation error rate was about 3%. The effect of thermal flux intensity on the heat transfer coefficient of heat transfer and the wall temperature and fluid pressure were investigated. The simulation results showed that with the thermal thermochemistry increasing in the tube wall, the heat transfer coefficient h has a downward trend. This is due to an increase in the volume fraction of water vapor and, consequently, to a decrease in the thermal conductivity of the vapor relative to the fluid in the liquid water. Also, in higher thermal flasks, the heat transfer coefficient h (due to rapid fluctuations in the thermo physical properties of the liquid and vapor fluid, as well as the emergence of the dynamic instability of vortices) increases.