## 3 Results and Discussion
### Costs Comparison  
Table 5 shows the differences in the components of the operating costs, using the fixed-bed dryer as a reference. Regarding fuel consumption, the fixed-bed dryer used \(5.3\pm 0.3\) kg h\({}^{-1}\), while the pneumatic dryer used \(2.8\pm 0.5\) kg h\({}^{-1}\), the difference being significant by the LSD test at 5% level of significance. Both dryers had similar heating units, therefore, the greater fuel consumption of the fixed-bed dryer can be explained by its higher heat input rate. To produce 1 kg of dried solid the fixed-bed dryer consumed \(0.11\pm 0.01\) kg and the pneumatic dryer consumed \(0.07\pm 0.02\) kg, being significantly different by the LSD test at 5% level of significance. Considering the cost of the diesel, to produce 1 kg of dried cassava grit, USD 0.14 was spent when the fixed-bed dryer was used and USD 0.08 was spent when the pneumatic dryer was used. Regarding the electric power consumption, the fixed-bed dryer used \(1.3\pm 0.1\) kW while the pneumatic dryer used \(2.3\pm 0.2\) kW, this difference is significant by the LSD test at 5% level of significance. While the fixed-bed dryer had only one 5.2 kW motor powering the fan, the pneumatic dryer had two, a 4.0 kW motor powering the feeder and another 7.5 kW motor powering the fan, explaining the higher electric power consumption observed in this dryer. As noted, the air mass flow rate in the fixed-bed dryer was significantly higher, but the motor powering the fan was of a smaller size. That is because, in the pneumatic dryers, the airflow has not only to remove the evaporated moisture but has also to provide the required hydrodynamic condition needed to transport the material. According to [PERSON] et al. [68], in general, fuel to supply the dryer with heat is the main component of operating costs, however, for dryers with specific hydrodynamic requirements, costs with electricity can also become an important component. For both dryers, electric power consumption was higher \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Dryer Type** & **Whiteness Index** & **Lightness** & **Chroma** & **Appearance Score** \\ \hline Fixed-bed & \(41.2\,^{\text{a}}\pm 1.6\) & \(89.3\,^{\text{a}}\pm 0.9\) & \(7.0\,^{\text{a}}\pm 0.6\) & \(6.1\,^{\text{a}}\pm 0.6\) \\ Pneumatic & \(37.0\,^{\text{b}}\pm 3.2\) & \(88.9\,^{\text{a}}\pm 1.4\) & \(7.7\,^{\text{a}}\pm 0.4\) & \(6.1\,^{\text{a}}\pm 1.0\) \\ \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 4: Whiteness Index, lightness, chroma and appearance score of cassava flour produced using a fixed-bed dryer and a pneumatic dryer in Ghana. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Operating Costs** & \
\begin{tabular}{c} **Relative Difference from the** \\ **Fixed-bed Dryer (USD kg\({}^{-1}\))** \\ \end{tabular} &
\begin{tabular}{c} **Percentage Difference from the** \\ **Fixed-bed Dryer (\%)** \\ \end{tabular} \\ \hline Fuel & \(-0.060\) & \(-42.9\) \\ Electric power & \(+0.005\) & \(+25.0\) \\ Labour & \(0.000\) & \(0.0\) \\ Maintenance & \(0.000\) & \(0.0\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Fixed-bed dryer and pneumatic dryer differences in operating costs. than the values reported by [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [54] on pneumatic drying of cassava, suggesting less efficient fan design. To produce 1 kg of dried cassava grids, the fixed-bed dryer consumed 25.1 \(\pm\) 0.2 W of electric power and the pneumatic dryer consumed 57.4 \(\pm\) 14.8 W, the difference being significant by the LSD test at 5% level of significance. Considering the cost of electricity, to produce 1 kg of dried cassava grids, USD 0.004 was spent when the fixed-bed dryer was used and USD 0.009 was spent when the pneumatic dryer was used. Regarding labour, the fixed-bed dryer and the pneumatic dryer had very distinct working regimes.