2-Dimensional transient mixed-convection in a horizontal rectangular enclosed cavity heated from a lower solid block is numerically studied. The enclosure simulates the thermal reservoir for the storage and shipment of biomaterials. The lower solid block containing the thermal biomass that has adiabatic sides and bottom wall, is coupled along the top wall with a hollow cavity of aspect ratio (H/L = 0.5), whose side and top walls are assumed to be surrounded by a phase change material and has been assigned constant temperature of 273K. Initially, the temperature of the biomaterials is raised to 283K; the upper cavity is filled with quiescent air and uniform temperature at time zero. Laminar airflow is assumed with a fan in middle of the cavity. The basic characteristics and flow structures during the transition of natural-convection-dominated flow to forced-convection-dominated flow are determined. The problem is solved for the range of mixed-convection regime and the fluid flow structure and heat transfer is found to be dependent on mixed-convection as determined by the buoyancy parameter Gr/Re2. As anticipated, the forced-convection-dominated flow is found to be more effective in cooling of the thermal biomass than the natural-convection-dominated flow. This study shows that using the assisted forced convection results in an increase in the cooling performance of the biomaterial container in the natural-convection-dominated type mixed-convection flow. Examining the area averaged Surface Nusselt number along the coupled wall with time and the rate of heat transfer from the thermal biomass during the Quasi-steady stage validates the above hypothesis.

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