Additional simulations of one part of the high temperature
zone were conducted to determine the best setting of the
guide plates to obtain the most even air temperature distribution
over the belt width. They were tested with different
lengths and number of guides. The best result was achieved
with a roof length l ¼ 0.8 m at every slot on both sides. The
mean temperatures along the belt length, the standard deviation
and the coefficient of variation were calculated to evaluate the homogeneity of the temperature for different
roof lengths (Table 5). The standard deviation and coefficient
of variation decrease substantially between 0 m and 0.6 m roof
length and were lowest for 1.0 m. The material costs and the
free flow area for the upstreaming air were taken into account
when deciding the optimum length for the roof.