## Materials and Methods
### Operating Conditions and Energy Performance
Following ASHRAE standard 111-2008 [40], a 1.5 m long circular duct with a diameter of 0.30 m was added to the air inlet of the heat exchangers of each dryer and a total of 18 readings were taken across the traverse plane and then averaged. To assess the uniformity of the airflow across the perforated screen of the fixed-bed dryer, air velocity was measured with a vane anemometer (AFP1, Rotronic) using a six by six grid pattern. Measurements were performed with the dryer loaded, during the first 0.25 h of the drying operation, using three repetitions. Psychrometric calculations used the formulas provided by the British Standard [41] and energy performance indices were calculated according to Kudra [30]. The solid mass flow rate on a dry basis, \(\dot{m}_{\mathrm{dm}}\) (kg h\({}^{-1}\)), was obtained using Equation (1):  
\[\dot{m}_{\mathrm{dm}}=\dot{m}_{\mathrm{ws}}-\dot{m}_{\mathrm{ws}}\bigg{(} \frac{X_{\mathrm{ws}}}{1+X_{\mathrm{ws}}}\bigg{)}, \tag{1}\]  
where \(\dot{m}_{\mathrm{ws}}\) (kg h\({}^{-1}\)) is the mass flow rate of the wet cassava grits and \(X_{\mathrm{ws}}\) (kg\({}^{-1}\)) is its moisture content on a dry basis. Heat input rate to the dryer (\(\dot{Q}_{\mathrm{in}}\)) was calculated using Equation (2):  
\[\dot{Q}_{\mathrm{in}}=\dot{m}_{\mathrm{air}}(h_{1}-h_{\mathrm{amb}}) \tag{2}\]  
where \(\dot{m}_{\mathrm{air}}\) (kg h\({}^{-1}\)) is air mass flow rate on a dry basis, \(h_{1}\) (kJ kg\({}^{-1}\)) is the enthalpy of the air at the dryer inlet and \(h_{\mathrm{amb}}\) (kJ kg\({}^{-1}\)) is the enthalpy of the ambient air. The value for \(\dot{m}_{\mathrm{air}}\) was calculated multiplying the air volume flow rate, \(\dot{V}_{\mathrm{air}}\) (m\({}^{3}\) h\({}^{-1}\)), to the air density on a dry basis, \(\rho_{\mathrm{air}}\) (kg m\({}^{-3}\)), and the value for \(\dot{V}_{\mathrm{air}}\) was calculated multiplying \(v_{\mathrm{amb}}\) to the cross-sectional area of the pipe added to the heat exchanger air inlet. The values of \(\rho_{\mathrm{air}}\) and \(h_{\mathrm{amb}}\) were calculated using \(\Psi_{\mathrm{amb}}\), \(T_{\mathrm{amb}}\) and \(P_{\mathrm{amb}}\). The value for \(h_{1}\) was calculated using \(T_{1}\) and \(P_{1}\) but because of the elevated temperature at this location, air relative humidity (\(\Psi_{1}\)) was not measured, but calculated from the ambient air conditions. Water evaporation rate, \(\dot{m}_{\mathrm{w}}\) (kg h\({}^{-1}\)), was calculated using Equation (3):  
\[\dot{m}_{\mathrm{w}}=\dot{m}_{\mathrm{dm}}(X_{\mathrm{ws}}-X_{\mathrm{ds}}) \tag{3}\]  
where \(X_{\mathrm{ds}}\) (kg kg\({}^{-1}\)) is the dried cassava grits moisture content on a dry basis. Specific heat consumption, \(q_{\mathrm{s}}\) (kJ kg\({}^{-1}\)), was calculated using Equation (4):  
\[q_{\mathrm{s}}=\frac{\dot{Q}_{\mathrm{in}}}{\dot{m}_{\mathrm{w}}}, \tag{4}\]Energy efficiency (\(\eta\)) was calculated using Equation (5):  
\[\eta=\frac{\dot{Q}_{\rm w}}{\dot{Q}_{\rm in}}, \tag{5}\]  
where \(\dot{Q}_{\rm w}\) (kJ h\({}^{-1}\)) is the heat used for moisture evaporation, calculated by multiplying \(\dot{m}_{\rm w}\) to the cassava starch sorption energy, \(Q_{\rm st}\) (kJ kg\({}^{-1}\)), provided by [PERSON] et al. [42]. Sorption energy was used instead of the latent heat of vaporization (\(\lambda\)), to account for the energy required to overcome capillary forces.