## 3 Results and Discussion
### Operating Conditions and Energy Performance
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dryer Type** & \begin{tabular}{c} **Solid Mass Flow Rate** \\ **on a Dry Basis (kg h\({}^{-1}\))** \\ \end{tabular} & \begin{tabular}{c} **Air Temperature** \\ **at Dryer Inlet (\({}^{\circ}\)C)** \\ \end{tabular} & \
\begin{tabular}{c} **Wet Cassava Grits** \\ **Moisture Content** \\ **(kg kg\({}^{-1}\))** \\ \end{tabular} &
\begin{tabular}{c} **Dried Cassava** \\ **Grits Moisture** \\ **Content (kg kg\({}^{-1}\))** \\ \end{tabular} \\ \hline Fixed-bed & \(45.0\)\({}^{\text{a}}\)\(\pm\) 2.6 & \(85.2\)\({}^{\text{a}}\)\(\pm\) 1.2 & \(0.87\)\({}^{\text{a}}\)\(\pm\) 0.01 & \(0.15\)\({}^{\text{a}}\)\(\pm\) 0.02 \\ Pneumatic & \(35.9\)\({}^{\text{b}}\)\(\pm\) 7.1 & \(226.8\)\({}^{\text{b}}\)\(\pm\) 14.5 & \(0.86\)\({}^{\text{a}}\)\(\pm\) 0.05 & \(0.14\)\({}^{\text{a}}\)\(\pm\) 0.02 \\ \hline \hline \end{tabular}  
Means with no common superscript letter are significantly different by [PERSON]’s Least Significant Difference test at 5% level of significance (\(\alpha\) = 0.05).  
\end{table} 
Table 2: Operating conditions of a fixed-bed dryer and of a pneumatic dryer used to process cassava in Ghana. For both dryers, the same method for mechanically dewatering the cassava mash was used; thus, similar moisture content of the wet cassava grits was obtained. Usually between 20% and 30% of the water can be removed by mechanical means [9] and is an important step for energy saving as it consumes substantially less energy than drying with hot air [11]. The values of \(X_{\text{ws}}\) shown in Table 2 were within the range reported by [PERSON] et al., [54], for wet cassava grits being dried on pneumatic dryers. However, it is important to notice that pneumatic dryers are more frequently used for solids with a moisture content below 0.70 kg kg\({}^{-1}\)[55]. Nevertheless, moisture content was reduced to a level that is accepted for most markets [56; 5] and considered stable for long term storage [57]. Table 3 shows the energy performance indices obtained from the fixed-bed dryer and the pneumatic dryer. Regarding the heat input rate, it was significantly higher for the fixed-bed dryer, despite its lower drying air temperature. This is explained by its higher air mass flow rate; 3498 \(\pm\) 12 kg h\({}^{-1}\) compared to 533 \(\pm\) 4 kg h\({}^{-1}\) at the pneumatic dryer. Regarding the evaporation rate, Table 3 shows it was higher in the fixed-bed dryer than in the pneumatic dryer, despite its lower drying air temperature. Water evaporation rate is driven by material properties, material moisture and material quantity, plus the heat input to the dryer and the level of interaction between the material and the drying medium [30]. The fixed-bed dryer had a greater amount of material and a higher heat input rate, explaining its higher evaporation rate. Regarding specific heat consumption, Table 3 shows it was higher at the fixed-bed dryer, despite its higher evaporation rate. Specific heat consumption of pneumatic dryers in general ranges from 3000 kJ kg\({}^{-1}\)[9] to 9000 kJ kg\({}^{-1}\)[58] and for cassava drying with pneumatic dryers [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [54] reported values ranging from 3620 kJ kg\({}^{-1}\) to 5750 kJ kg\({}^{-1}\). Energy efficiency, shown in Table 3, accordingly, was superior for the pneumatic dryer. In general, the energy efficiency of pneumatic dryers usually ranges from 40% to 75% [59], and for pneumatic drying of cassava [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [54] reported values ranging from 43% to 69%. In general, the energy performance of convective dryers is dictated by the heat transfer between solid and the hot air [30], the better the contact between them, the better the energy performance [60]. The superior energy performance of the pneumatic dryer can be explained by the fact that in this dryer the material is suspended in the air, allowing for optimum solid-hot air contact, and thus efficient heat transfer [29].