Abstract:
Solar energy is the most important energy resource among all renewable energy resources
due to its quantitative abundance. It is easy to convert solar energy into thermal energy and this
method is most widely accepted for the utilization of this abundant renewable energy resource.
However, due to intermittent nature of solar energy availability, an energy storage system is
required to be attached with solar collectors to store energy for use when solar energy is not
available. A storage system therefore constitutes an important component of the solar energy
utilization system.
The heat energy may be stored as sensible heat or latent heat. The energy storage taking
place without the phase change is the sensible heat storage whereas in case of latent heat storage
phase change of material take place. In sensible heat storage when rocks and pebbles are packed
in container then it is known as packed or rock bed and they are most commonly used storage
system due to its low cost.
An extensive literature review was carried out on packed bed storage system.Literature
review reveals that most of the experimental work done on packed bed storage system use air as
heat transfer fluid. Keeping this in view it was proposed to investigate the behavior of storage
tank with water and oil (therminol – vp1) as heat transfer fluids. In order to investigate the
storage tank with different HTFs, an experimental set up comprising of sensible heat storage tank
containing bed elements, a heating set up, an electric pump, temperature and fluid flow
measuring devices has been designed, fabricated and commissioned. It was planned to collect
temperature data at different locations of packed bed.
Based on the experimental study it has been found that the increment in temperature is
faster when water was used as HTF as compared to oil as HTF. The temperature variations were
also observed with respect to different volume flow rate of HTFs. It was found out that
increment at low flow rate was higher due to more contact time of HTF with the storage
materials. The temperature is found to be decreased first along the axis but at the bottom part it
again start increasing due to storage of HTF in the lower plenum. Beside this, different properties
like Nusselt number, Reynolds number, Friction factor, Pressure drop across bed, Amount of
Energy stored and the efficiency of storage tank has been computed.
