Abstract:
In many countries of the world, the use of solar thermal systems in the agricultural area to
conserve vegetables, fruits, coffee and other crops has shown to be practical, economical and
responsible approach environmentally. Post-harvest drying of coffee is one of the main
preservation techniques employed to enhance processing, storage quality, nutritional value,
and market control. For these purposes, an efficient type of solar dryer is designed to dry
Coffee. The modeling techniques are very important to develop analyses and predict the
performance of a solar drying system. This paper presents study of computational fluid
dynamics (CFD) based thermal efficiency analysis to determine heat transfer characteristics
of solar air heater and drying chamber. Autodesk inventor professional is used to model the
proposed design and Computational Fluid Dynamics code ANSYS FLUENT is used to
simulate fluid flow and heat transfer. The design parameters considered in the analysis are
solar collector without and with jet impingement, 6,8,10 mm jet diameters are used for jet
impingement, 300 K ambient temperature, 0.02 – 0.05 kg/s mass flow rate, 500-800 W/m2
of
solar radiation of selected site and distribution of heated air in drying chamber by using
front and back header.
The simulation results revels that the collector outlet temperature, Nusselt number, and
thermal efficiency is more in D=6 mm jet diameter for mass flow rate of 0.05 and 600 W/m2
solar radiation. The V-corrugated collector without jet plate has maximum efficiency of 64.3
%, and the maximum efficiency of 72.3% can be seen at jet diameter of 6 mm. The
temperature distribution obtained was satisfactory due to the high uniformity inside the
chamber by placing the front and back header in the drying chamber. For Loading rate of 50
kg coffee average drying rate is 4.12 kgH2O/hr with drying efficiency of 38.5 %. Validation of
results compared with previously performed experimental data from literature and found to
be in good agreement. Collector efficiency predicted output with a deviation 8 %.
Improvement in thermal efficiency of solar air heater is observed by using jet
impingement on corrugate absorber plate. Solar collector with high performance and drying
chamber with good air flow distribution can improve the drying uniformity.
