The heat extraction from the conventional channels under two-phase flow boiling conditions with water as the coolant is investigated numerically in this work. The numerical investigation was carried out by using ANSYS Fluent 2022R1 commercial software by selecting the Rensselaer Polytechnic Institute (RPI) wall heat flux partitioning approach by employing the Eulerian-Eulerian two-phase model. A three-dimensional computational domain was used for the simulation to understand the fluid boiling inside the conventional channel under steady state conditions, focusing on the effect of aspect ratio (AR) on the vapor volume fraction. The simulations were performed for a constant mass flux of 150.46 kg/m²-s with the heat flux value ranging from 10-100 kW/m² and at the inlet subcooled temperatures of 303K, 313K and 323K. The temperature of the channel bottom surface and the heat transfer coefficient (HTC) obtained numerically were compared with the experimental results and it was found that the results matched well. The volume of vapor fraction increased with the increase in heat flux for all values of inlet subcooled temperature considered in this study for all the test sections. At low inlet subcooled temperature, the volume of vapor fraction decreased with an increase in AR at all heat fluxes. However, there was no observable trend at higher heat flux and high inlet subcooled temperature.