Experimental and numerical study of the transient performance of a packed bed
thermal storage system was carried out. Experiments were carried out to measure the
transient temperature distributions inside a cylindrical packed bed with air as a working
fluid. The packing was composed of rock grains of irregular sizes ranging between 14
and 20 mm. The bed container was constructed from a PVC cylinder with 1 m overall
height and 0.15 m inside diameter. Measurements of the bed temperature were
conducted at different axial and radial positions and at different operating parameters.
The present problem was modeled using two time-dependent coupled partial
differential equations of the energy conservation of air and solid phases. The fluid
energy equation was transformed by finite difference approximation and solved by
Alternating Direction Implicit scheme (ADI) while the solid energy equation was
solved using fully explicit scheme. The solution provides predictions for the
dimensionless temperature distributions for both fluid and solid phases within the
packed bed in the radial as well as in the axial direction for both charging and recovery
modes at different operating parameters. The influence of aspect ratio, the flowing air
velocity, the inlet air temperature, bed size and bed thermal capacity are also
investigated.
Three correlations were obtained from the present results for the bed charging
duration, effectiveness, and the storage efficiency as functions of the different
operating and design parameters.