## 3 Results and Discussion  
### Operating Conditions and Energy Performance  
Table 2 shows the operating conditions of the fixed-bed dryer and the pneumatic dryer. Regarding the solid mass flow rate, the throughput of wet cassava grits was \(84.1\pm 4.8\) kg h\({}^{-1}\) for the fixed-bed dryer and was \(66.9\pm 13.9\) kg h\({}^{-1}\) for the pneumatic dryer. The throughput of dried cassava grits was \(51.6\pm 2.9\) kg h\({}^{-1}\) for the fixed-bed dryer and was \(41.2\pm 9.4\) kg h\({}^{-1}\) for the pneumatic dryer. While \(\dot{m}_{\text{ws}}\), \(\dot{m}_{\text{ds}}\) and \(\dot{m}_{\text{dm}}\) between the dryers were significantly different, the amount of dried cassava grit obtained in one day of operation was not significantly different by LSD test at 5% level of significance. The fixed-bed dryer was in operation for 6.0 h per day producing, on average, a total of \(307.1\pm 6.4\) kg while the pneumatic dryer was in operation for 7.5 h per day producing, on average, a total of \(309.2\pm 70.2\) kg. Loading and unloading periods is a known drawback of a batch-operated dryer [12] and on average \(0.73\pm 0.05\) h were needed to load the fixed-bed dryer and \(0.77\pm 0.07\) h to unload it. The air at the inlet of the dryers is shown in Table 2. Fixed-bed dryers, in general, operate at a lower temperature [46], particularly when compared with pneumatic dryers [47] that, for certain products, can operate at temperatures as high as 700 \({}^{\circ}\)C [48]. The temperature of the drying air has a direct impact on both, the energy performance of the dryer [49] and on the quality of the dried product [32]. In general, better energy performance is obtained with higher drying air temperature [31] and [PERSON] et al. [50] studying the drying kinetics of cassava starch in pneumatic dryers observed significant improvement in its energy performance by increasing air temperature. However, high drying air temperature can have a detrimental effect on product quality [51], particularly for solids rich in starch [52], and for cassava drying, to avoid starch gelatinization, the temperature of the solid must remain below \(64.3\)\({}^{\circ}\)C [5]. To estimate solid temperature during drying, the wet-bulp temperature of the drying air can be used [53] and at the fixed-bed dryer, the wet-bulp temperature of the drying air was on average \(36.9\pm 0.2\)\({}^{\circ}\)C. In contrast, at the pneumatic dryer, the wet-bulp temperature of the drying air was on average \(51.9\pm 3.8\)\({}^{\circ}\)C. However, at the end of the drying process, temperature of the dried cassava grits at the fixed-bed dryer was on average \(50.0\pm 2.8\)\({}^{\circ}\)C and \(T_{\text{ds}}\) at the pneumatic dryer was on average \(57.2\pm 5.3\)\({}^{\circ}\)C. Therefore, despite the higher temperature used in the pneumatic dryer, on both dryers, the solid temperature remained under the gelatinization threshold. Regarding the moisture content of the wet cassava grits, Table 2 shows no significant differences. In addition, Table 2 shows no significant differences between the two dryers in the moisture content of the dried cassava grits. When comparing the energy performance of two different dryers, it is not necessary to have the same capacity, but it is important to use the same material and assure that initial and final moisture content between the dryers is similar [30]. This is even more important when drying a material that is rich in starch because the energy needed to overcome capillary forces increases exponentially as the solid dries [42]. During the evaluation of the dryers, no significant differences, by LSD test at 5% level of significance, were observed regarding ambient air temperature, relative humidity and pressure. They were on average \(33\)\({}^{\circ}\)C, \(62.8\%\)th and \(101.0\) kPa, respectively.