“…,0 00 11 11 11 The variables to obtain from Equation ( 5) are the radiation flux losses ( 0 q ), the heat flux absorbed by the tubes without convection losses ( j q , 1,..., jn ) and the refractory wall temperature ( 1 n T ). Then, it is necessary to know the environmental temperature ( 0 T ), which is calculated according to Equation (6) [29], the heat flux that arrives to the receiver ( h q ), which is obtained from the radiation map, the conductive losses through the refractory wall ( 1 n q ), that in this case are neglected, and the effective outer wall temperature of the tubes for radiation ( j T , 1,..., jn ) which are estimated. In order to minimize the error in the discretization of the tubes, the relative importance of each tube section has been considered using the crossed-strings method to calculate the view factors ( F ) [26].This method discretizes the tubes in circumferential and axial directions.…”