Unsteady conjugate mathematical model for natural heat convection with change phase of pure water inside of a square container caused by external mixed heat convection of cool air and the effect of baffles attached to a freezing tunnel has been studied numerically. The coupled equations were solved by Finite Volume method with the SIMPLE algorithm. Effect of the baffles on freezing time, evolution of local dimensionless heat flux and surface temperature distribution at the container with water were studied. The results showed that the hydrodynamic and thermal boundary layer were reduced due to the baffles, this effect reduced the freezing time and homogenized the superficial temperature of the container. Additionally, the effect of the length of baffles on the heat flux and vortex shedding frequency behind the water container were assessed. (c) 2021 Elsevier Ltd and IIR. All rights reserved.