## 2 Materials and Methods
### Description and Working Mechanism of CSR  
Scheffler concentrator (10 m2) focuses the incoming direct normal irradiance (DNI) at a 360 mm diameter and 10 mm thick casted aluminum surface of a heat receiver. With the design configuration of the lateral part of a paraboloid, the frame of Scheffler concentrator is inclined at an angle of (43.23 \(\pm\)\(\alpha\)/2) degrees, therefore, the effective aperture area (A\({}_{\text{C}}\)) of the concentrator is taken as A\({}_{\text{C}}\times\cos\) (43.23 \(\pm\)\(\alpha\)/2). The total input energy available (Q\({}_{\text{a}}\)) at the face of the concentrator is the DNI measured by pyranometer (E\({}_{\text{DNI}}\)) times this fraction of the effective aperture area and is calculated from Equation (2) [21]:  
\[Q_{a}=E_{DNI}A_{c}cos\left(43.23\ \pm\ \frac{\alpha}{2}\right), \tag{2}\]  
\(\alpha\) is the solar declination angle and equated according to [22] for any day of the year. The energy is distributed as absorbed radiation (\(Qup\)) and reflected radiation (\(Qpr\)). The absorbed radiation component of energy (\(Qup\)) depends upon the reflectivity of the material used (Highly reflected mirrors \(>\)90%). Therefore, the energy available after primary concentrator (\(Qpr\)) is given as [21]:  
\[Q_{pr}=R_{p}Q_{a}, \tag{3}\]  
where \(R_{p}\) is the reflectivity of the material used for the Scheffler concentrator. Some of the radiations are reflected from the primary concentrator out of the focus. This deviation is due to the improper concentrator profiles and inadequacy in daily and seasonal tracking. The fraction \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Parameters** & **Goal** \\ \hline \multirow{3}{*}{Factors} & Feeding capacity (kg) & Maximize \\  & Conveyor speed (rpm) & In range \\  & Thermal oil flow rate (Ls\({}^{-1}\)) & Minimize \\  & MC (\%) & Minimize \\  & L* (light) & Target \(\rightarrow\) 43 \\  & L* (medium) & Target \(\rightarrow\) 48.5 \\  & L* (dark) & Target \(\rightarrow\) 53 \\ \hline \hline \end{tabular}  
* L*: Hunter Labs colorimeter color value.  
\end{table} 
Table 1: Optimization criteria for Continuous Solar Roaster (CSR). available at the targeted focus (\(F_{f}\)) in general calculation is taken as 0.90. The energy available at the solar receiver (\(Q_{rcv}\)) is given as [15]:  
\[Q_{rcv}=Q_{pr}F_{f}, \tag{4}\]  
The energy available on the surface of the heat receiver (\(Q_{rcv}\)) is transferred to the roasting cylinder by the circulation of Shell S2 heat transfer oil [23]. Inside the heat receiver, 16 mm thick ribs are casted on the back side of the receiver's surface to shape oil galleries in such a way that thermal oil flows in a zigzag pattern which increases the retention time for effective heat transfer. An iron cover attached with a gasket is installed on the backside of the receiver and sealed with high temperature silicon paste to prevent any leakage. The heat receiver is packed with 50 mm rockwood insulation from back and sides and entire unit is fixed in a stainless-steel (S.S) case which is mounted on an iron stand. Thermal oil absorbs heat energy in the heat receiver and desorbs it to the bottom of a 2 m long and 0.45 m in diameter food grade S.S roasting cylinder while flowing inside a semi-circular cavity which is fixed with the lower semi-circumference of the roasting cylinder having a 0.7 m perimeter. The flow rate of thermal oil is varied from 0.01 to 0.05 Ls\({}^{-1}\) with a gear pump to regulate the temperature conditions inside the roasting cylinder while the excessive heat energy is stored in an insulated heat storage reservoir using sensible heat storage mechanism. Roasting temperature is adjusted according to the product from electric control panel. Two solenoid valves with thermocouple sensors are provided, one at the inlet of roasting cylinder and other at the inlet of heat storage reservoir, to control the flow path of thermal oil. During the heating phase up to set temperature, they allow the thermal oil to flow in the flowing path (Path-I).