Phase Changing Materials (PCM) is proving to be one of the major breakthroughs in industries as it has various applications in sustainable and renewable energy. The present study investigates the melting and solidification of phase change material (ice) in the presence of titanium oxide nanoparticles in a horizontal channel with internal heat source. The parametric study is carried out by varying the inlet velocity, heat source strength and nanoparticle volume fractions. The problem is modeled as three-dimensional laminar steady flow considering the effects of melting and solidification using Ansys Fluent. The heat sources mounted at the lower wall of the channel are specified with constant wall temperature boundary condition and the remaining walls are considered as adiabatic. The forced velocity inlet boundary condition is specified for the longitudinal velocity at the inlet and pressure outlet boundary condition is considered at the outlet of the channel. The results are analyzed by plotting the pathlines, longitudinal velocity contours, pressure and temperature contours. The results indicate that the longitudinal inlet velocity significantly affects the flow and heat transfer characteristics inside the horizontal channel. The increase in inlet velocity strengthens the melting rate and increases the heat transfer rate inside the channel. It is also found that the melting rate increases linearly with increase in the heat source intensity and nanoparticle volume fraction. © Published under licence by IOP Publishing Ltd.