Abstract:
The main energy source of developing countries for cooking comes from biomass. Like most
developing countries, Ethiopia is also dependent on using traditional fuels. More than 98% of its
household energy comes from biomass and less than 2% from electricity and petroleum
collectively [9]. The biomass energy is mainly used to bake the country’s common food type called
“Injera” and its stew [41]. Solar energy is also can be used as energy source for baking process
but, it requires efficient collection and working fluids with high heat transfer characteristic. The
fluids used on the design of solar thermal injera baking process were shell Thermia oil B and
steam. Shell Thermia oil B have low thermal property this could increase the time required for the
baking process and the size of the components. Steam was also used as working fluid but, during
operation the pressure on the pipes would develop up to 40 bar and due to condensation of the
steam corrosion could happen on the wall of pipe. this reduces the life of the system
The main objective of this research was to study the performance of solar thermal Injera baking
system using nanofluid as heat transfer. Nanofluid used was Cu/shell Thermia oil B with a volume
concentration of 4% of nanoparticle. Thermo-physical property for nanofluid was calculated using
theoretical models obtained from the literature. Phase change material was integrated into the
system to allow night-time baking. Nitrate salt (40%KNO3-60%NaNO3) was used as energy
storage material due to its highest melting temperature (2220𝐶). Parabolic trough collector used
to collect heat from solar radiation using heat transfer fluid and amount of heat collected was
transported to the Injera baking pan and storage material through the piping system. The Pump
was used to circulate the fluid through the system. Part of fluid was stored below the pan to control
temperature fluctuation on the surface of the pan and keep the system at steady condition during
baking.
CFD simulation was done to determine the heat-up time and charging time for baking pan and
PCM respectively. Also, the performance of heat transfer fluid for nanofluid and shell Thermia oil
B was compared based on the simulation results. Simulations show that heat up time for the baking
pan was enhanced by 43.6% using nanofluid and maximum temperature on the surface of the pan
was registered 1950 C. The use of nanofluid reduced charging time for PCM by-30.6%.
