ABSTRACT
A numerical study is carried out to predict the transient response of a packed bed
thermal storage system containing a phase change material (PCM) as a packing material. A
vertical cylindrical heat storage packed bed containing PCM encapsulated in spherical pebbles
with air as a working fluid is investigated. Three different PCMs in addition to rock grains are
tested. The present problem is modeled using two dimensional axisymmertric time-dependent
coupled partial differential equations for energy conservation of the working fluid and the
PCM. The energy equation for the working fluid is transformed by finite difference
approximation and solved by Alternating Direction Implicit scheme (ADI) while the PCM
energy equations are solved using fully explicit schemes. The temperature distributions for
both the working fluid and PCM and the liquid mass fraction of the PCM are predicted in
radial and axial directions for both charging and recovery modes at different operating
parameters.
The present predictions are compared with previous experimental data to check the
validity of the present model. Also, the influence of the flowing fluid mass flow rate, inlet fluid
temperature, heat storage volume and the PCM thermophysical properties are investigated.
An enhancement in the thermal energy stored with a maximum value of about 500% is
predicted when using beds containing PCMs instead of using rock grains. |
