The effect of air flow rate on single-layer drying characteristics of Arabica coffee

This study was intended to evaluate the behavior of Arabica Coffee (Coffea arabica L.) bean during the single-layer drying process under several levels of drying air velocity. The research was carried out at the Processing Laboratory of Agricultural Engineering Department, Hasanuddin University - Indonesia, during the period of February to May 2011. Sample used was an Arabica Coffee, Line S-795 variety, obtained from a coffee farmer in Enrekang Regency - South Sulawesi. The main equipment applied was a tray dryer, Model EH-TD-300 Eunha Fluid Science. The dryer was constructed to flow the drying-air parallel with the crop-layer. Three different levels of air velocity (0.5, 1.2, and 1.8 m/s) under constant drying temperature of 47oC were exercised in this research. The moisture ratio was determined for each drying run and fitted to several existing thin-layer drying models. Research results indicated that among the models, Hii et al. model (2008) is the best one, R2 reached up to 0.99, to represent the behavior of the Arabica Coffee during the single-layer drying process. It was also observed that increasing air velocity from 0.5 m/s to 1.8 m/s failed to considerably improve the drying rate, although the paired t-test indicated that their moisture ratios were statistically different. The curves of the moisture contents (dry-basis) resulting from the three levels of air velocity across elapsed drying time were very much overlapping, especially at the elapsed drying time greater than 10 hours