Thermal Enhancement in Storage Silos with Periodic Wall Heating

In this paper, unsteady natural convection problem in vertical, open-ended, porous cylinder has been numerically investigated to simulate the transient heat and mass convection in the grain storage in silos. The medium is the seat of a chemical reaction, and the enclosure lateral wall is submitted to a varying temperature profile. Time-dependent boundary temperature is presented as sinusoidal function which can approximate real weather conditions. In the case of constant temperature, a map diagram comprising several characteristic parameters such as Rayleigh number, aspect ratio, buoyancy ratio and lumped effective reaction rate of the two observed flow types, with and without fluid recirculation, was obtained. In order to approve that heat exchanges are dependent of reversal flow and control parameters, the phase diagrams connecting heat transfer ( Nu ) to the recirculation flow rate ( Q r ) are proposed. The observed relative difference between sinusoidal and constant wall temperature increases with increasing Rayleigh number ( Ra ) and dimensionless temperature amplitudes ( X A ), and it is particularly sensitive to the buoyancy ratio values ( N ) and the reaction rate ( A k ). This difference passes from 18.7 % in the only thermal case to 8.15 % in the thermo-solutal case.