## 3 Results and Discussion
### Effect of Operating Parameters on Responses
#### 3.1.2 Interactive Effect of Parameters on Moisture Contents (MC)  
Figure 3a shows the interactive effect of feeding capacity and conveyor speed on MC at the center level of the thermal oil flow rate, 0.03 Ls\({}^{-1}\). A positive effect on MC is observed both by the feeding capacity and conveyor speed, in which conveyor speed has a more significant effect than feeding capacity because it regulates the time of roasting. It is clear from the 3D surface plot that increasing the feeding capacity and conveyor speed to maximum levels, resulted in higher percentage of MC (2.41%). On the other hand, MC decreased to 1.59% after decreasing the feeding capacity and conveyor speed to minimum levels. It is because a lower conveyor speed gives longer roasting time, which offers adequate heat transfer to groundnuts even at maximum feeding capacity. This result infers that at prolonged roasting time, more moisture can be removed from groundnut kernels. The experimentation of many authors also revealed that the roasting time is an essential parameter for moisture variations during roasting and MC can be lowered with longer roasting time keeping the temperature constant [32; 33].  
Figure 3: \(Cont.\)  
The interactive effect of feeding capacity and thermal oil flow rate on the MC of groundnuts is shown in the 3D surface plot (Figure 3b), while the conveyor speed was maintained at 1.0 rpm. The percentage of MC decreased almost linearly with decreasing the feeding capacity and thermal oil flow rate. The obtained MC of roasted groundnuts was 2.62% at the maximum level of feeding capacity and thermal oil flow rate. A much lower value of MC (1.17%) resulted in minimum feeding capacity and thermal oil flow rate. According to [30], the roaster efficiency is defined on the basis of thermal heat utilization during the  
Figure 3: (**a**) Interactive effect of conveyor speed and feeding capacity on MC. (**b**) Interactive effect of thermal oil flow rate and feeding capacity on MC. (**c**). Interactive effect of thermal oil flow rate and conveyor speed on MC.  
roasting, therefore, it can be concluded that heat energy is sufficiently available for roasting up to the designed product capacity of the machine. It is also evident that the thermal oil flow rate more significantly affected the groundnut MC than feeding capacity and even at maximum feeding capacity (15 kg), MC was lowered to 1.54% by changing the thermal oil flow rate minimum level (0.01 Ls\({}^{-1}\)). These results are within the range for MC of roasted groundnuts as stated by many authors [8; 19; 32].  
Like Figure 3b, the positive and almost linear interactive effect of conveyor speed and thermal oil flow rate is observed on MC (Figure 3c) when the feeding capacity was kept constant at 10 kg. It is evident that at the lowest thermal oil flow rate and conveyor speed MC decreased to 0.93% during roasting whereas it was found to be 2.71% on maximum levels. It is due to the reason that the low thermal oil flow rate yields in high roasting temperature due to higher heat transfer rate to the groundnuts whereas low conveyor speed gives longer roasting time and MC dropping is mainly dependent on both the roasting temperature and time. [31; 34] investigated the similar effect of time and temperature on groundnut roasting and their findings also support the obtained results. However, MC is influenced more significantly by thermal oil flow rate than conveyor speed because the moisture is released more quickly from groundnut kernels at high roasting temperatures [20]. It can be concluded that at any specific conveyor speed, lowering the thermal oil flow rate decreases MC more rapidly.