Thermal performances and kinetics analyses of greenhouse hybrid drying of two-phase olive pomace: Effect of thin layer thickness

The present work is focused on the assessment of energy flow (drying efficiency, specific energy consumption, specific moisture extraction rate and moisture extraction rate) in a hybrid greenhouse dryer (solar/hot air) during the thin layer drying of two-phase olive pomace. Three layer thicknesses of the two-phase olive pomace were evaluated in this study, namely 2 cm, 4 cm and 6 cm. Moreover the drying kinetics and effective moisture diffusivity were also investigated. The moisture content of the two-phase olive pomace was reduced from 54 wt% to a value below 20 wt%., which was achieved in 14 h, 32 h and 53 h for three layers thicknesses respectively. The drying process of the two-phase olive pomace occurred in the falling rate and the Two-Term Gaussian model was found to be the most suitable drying model to describe the behavior for the three thin layer thicknesses. The average drying efficiencies of the greenhouse dryer for the three thin layer thicknesses of the two-phase olive pomace were 16.9%, 7.85% and 5.31%, respectively. The specific energy consumption (SEC) was found to be 5.7 kWh/kg, 14.2 kWh/kg and 21.3 kWh/kg for the three drying experiments, respectively, associated to an average specific moisture extraction rate (SMER) values of 0.27 kg/kWh, 0.13 kg/kWh and 0.085 kg/kWh, respectively.

Automated summary

This study focuses on evaluating the energy flow in a hybrid greenhouse dryer (solar/hot air) during the thin layer drying of two-phase olive pomace. The drying process was found to occur in the falling rate and the Two-Term Gaussian model was the most suitable to describe the behavior. The average drying efficiencies were relatively low while the specific energy consumption and specific moisture extraction rate were relatively high.