## 3 Results and Discussion
### Thermal Analysis of CSR  
During the roasting experiments, an infrared camera was used for capturing the thermal images of the surface of the heat receiver to observe the temperature distribution. As one of the images taken on 24 March 2018 is shown in Figure 7. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Nutritional Composition**} & \multirow{2}{*}{**Raw Groundnut**} & \multicolumn{3}{c}{**Roasting Condition**} \\ \cline{3-5}  & & **Light** & **Medium** & **Dark** \\ \hline Crude carbohydrates [1] & 25.30 & 26.60 & 26.90 & 27.50 \\ Crude fat [1] & 39.10 & 40.10 & 40.40 & 40.80 \\ Crude fibers [1] & 2.91 & 3.11 & 3.19 & 3.31 \\ Energy [2] & 551.9 & 573.20 & 579.80 & 588.20 \\ Potassium [3] & 988.30 & 1041.20 & 1059.10 & 1082.30 \\ Calcium [3] & 89.30 & 77.80 & 75.30 & 73.70 \\ Magnesium [3] & 210.30 & 208.90 & 207.80 & 207.20 \\ Phosphorus [3] & 340.20 & 364.20 & 369.80 & 380.10 \\ Zinc [3] & 3.89 & 3.01 & 2.80 & 2.50 \\ \hline \hline \end{tabular} \({}^{1}\) OBS, %, \({}^{2}\) cal/100g, \({}^{3}\) mg/100g.  
\end{table} 
Table 7: _Cont._  
Figure 7: Temperature distribution on the heat receiver surface of CSR. The surface temperature of the heat receiver was found to be 358.8 \({}^{\circ}\)C at the center point of the targeted focus by Scheffler concentrator during peak hours as shown in Figure 7 (point 1). It can be observed that the temperature decreases gradually towards the outer ends of heat receiver. It is due to the fact that the Scheffler concentrator focuses maximum intensity of converged DNI at the centre of targeted focus due to overlapping of reflection of more mirror strips and the intensity of focused radiations reduces with moving away from the centre point. Overall, a good medium to high range temperature distribution can be seen at the surface of heat receiver which provides sufficient heat energy for heating HTF to produce reasonable roasting temperature in the roasting cylinder. These observations also justify the design configuration of circular thermal heat receiver (having diameter of 350 mm) with respect to solar concentrator (having surface area of 10 m\({}^{2}\)) in accordance with the geometric concentration ratio which is 100 in this case. The surface temperature of the heat receiver and inlet temperature variations of the roasting cylinder corresponding to available DNI at each time interval (10 min) were also logged with thermocouples (K-type) and pyranometer, respectively. The recorded results for 24 March 2018 between 09:00 am to 03:00 pm are represented in Figure 8.  
It is evident from the inlet temperature line in Figure 8 that the preheating of thermal oil was completed before 10:30 am and a temperature about 183 \({}^{\circ}\)C was available for roasting at the inlet of roasting cylinder. After 10:30 am, the inlet temperature of roasting cylinder was increased and remained almost constant at 211 \({}^{\circ}\)C \(\pm\) 1 till 02:30 pm, when the DNI were available at their peak with slight fluctuations due to minor clouds. The excessive temperature (\(>\) 180 \({}^{\circ}\)C) at roasting cylinder inlet was automatically maintained by the solenoid valves during the experiment by directing the thermal oil flow path through thermal oil reservoir to the heat receiver. After 2:30 pm, temperature of thermal oil gradually decreased because lesser intensity of radiations reduced the input energy to the system. During the whole period, temperature at the surface of the heat receiver remained almost constant around 350 \({}^{\circ}\)C and there was only a minor decrease due to the variations in DNI. These observations revealed that the desired roasting temperature was available around 4.5 h on a sunny day with DNI ranging between 650 to 800 Wm\({}^{-2}\), hence, establishing the fact that CSR was able to roast 288 kg, 202 kg and 140 kg groundnuts subjected to light, medium and dark roasting conditions. Figure 8: Variation in inlet temperature of roasting cylinder vs DNI.