Abstract:
The interest of exploiting solar energy for electrification and other household applications such
as heating and cooking is increasing due to the reason that they are clean and ecofriendly. In
doing so, energy storage mediums are integrated to maintain the energy demand with the
intermittent nature of solar energy. Phase change materials (PCMs) has shown a great energy
storage use in solar thermal applications despite their low thermal conductivity property which
makes low heat transfer during charge/discharge or energy store/release process. Studies show
embedding extended surfaces (fins) in the PCM is easier and economical among the different heat
transfer enhancement methods. But there are limited works on the problem of increasing geometric
parameters of fins, as it replaces the mass of the PCM which results in reduced latent heat storage.
This work intends to study and optimize the heat transfer rate and latent heat storage of a solar
cooking with finned heat storage system. The study was started by collecting the energy demand
for household cooking and solar irradiance assessment of the study site. Following this bench
mark, a PCM vessel and parabolic trough solar collector were designed. Numerical simulations
using CFD tool ANSYS 16.0 and experiments has been conducted to investigate the effect of fin
length and thickness on the performance of the system. Design optimization was made using
response surface methodology with central composite design for design points.
Hitec salt or molten salt with 53% KNO3, 6% NaNO3 and 41% NaNO2 by composition (with 142
°C melting temperature, 110 kJ/kg heat of fusion) is selected as suitable PCM material for the
application. The findings show that increasing fin length show better heat transfer rate than
increasing fin thickness. The thicker and longer fin with dimensions of 1.5 and 140 mm
respectively, gave 65.97% faster rate than the system without fin. In the optimization process it
was found that the fin with 0.8 mm thickness and 140 mm length gives optimized design for the
heat transfer rate and energy storage capacity. The optimized design takes 10.21 hr. for complete
solidification process and can release 2237.91kJ heat.
