Abstract:
Considering the size and relevance of coffee industry to the Ethiopian economy this work
presents the design, prototype development, analytical and numerical simulation as well as
experimental investigation on an active solar coffee dryer. The solar collector and dryer system
configuration has been optimized for minimal pressure drop by incorporating guide vanes and
minimizing flow separation tendency using numerical simulation on ANSYS. The effect of air mass
flow rate on optimal depth of collector, temperature rise and pressure drop were characterized
including the effect of variation in solar insolation using CFD approach. By comparing different dryer
configurations based on pressure drop and air flow uniformity, a new dryer configuration prototype
was developed. In addition, thermal performance of the solar air heater was evaluated experimentally
at three different airflow rates on a collector with corrugated absorber plate and another collector
with flat absorber plate. High collector outlet temperature and efficiency were observed in a collector
with corrugated absorber plate. The effect of depth of grain, moisture content on wet basis, airflow
rate and humidity of air were explored for parametric sensitivity vis-à-vis drying time. Within 5
hours, coffee bean dried from 29% moisture content to 12.3% on a clear sunny day and within 7hours
from 19% moisture content to 11.1% on a partially overcast day. Average thermal efficiency of the
dryer was found to be 50.5% for clear sunshine day and 36.9% for partial overcast day. A good
agreement has been observed between the experimental results and the CFD temperature rise
predicted output with a deviation of 7.5%. Analytically predicted drying time compared with
experimentally measured drying time within a 12.9% deviation. The cost -to-benefit analysis with a
comparative assessment on traditional mode of coffee drying has been done and the payback period is
found to be 1.03 years with significant benefits..
