In this research, subcooled flow boiling of water and water-based nanofluid in the different channels cross sections with the same hydraulic diameter is simulated. The subcooled flow boiling of water in the channels is studied by Euler – Euler model. The results of this part was matched with the experimental data very well. To study the effects of nanoparticles in the subcooled boiling flow, copper oxide nanoparticles with 40 nm in diameter were injected at the inlet to the flow. The nanofluid subcooled boiling is simulated by considering three phases, liquid, vapor and nanoparticles. The water and vapor interaction is simulated by Euler-Euler approach; and the motion of nanoparticles in the continuous fluid is modeled by Euler – Lagrange model. Water, vapor and nanoparticles were considered continuous fluid, dispersed fluid and dispersed solid, respectively. After model validation, boiling of nanofluids was modeling in different channels. Volume fraction and temperature variations is obtained along the channels. The results showed that, at low concentrations of nanoparticles (0.001 kg/s) rectangular channels and at higher concentrations (0.005 kg/s) square channels have the greatest changes in vapor volume fraction compared to pure water boiling.