The mass flow rate of the filter granules was controlled to be 460 g/min, and the rotational speed of trommel body was set at 33 rpm. Both undersized (less than 2mm) and oversized (ranging from 2 to 4mm) filter granules were utilized. 5 kg of undersized filter granules and 50 kg of oversized filter granules were used. Variation of the screening efficiency with the inclination angle of the trommel body. When the inclination angle of trommel body was between 2◦ and 5◦, a higher angle caused a higher screening efficiency. With the increase of the inclination angle, the motion velocity V of the filter granules increased. Hence, the screening efficiency was relatively higher when the inclination angle of the trommel body was higher, because in this case, the influence of the vertical velocity Vn was much higher than that of the horizontal velocity Vr. However, the screening efficiency was of trommel body was between 23 and 43 cm/s, it can be seen that the increase of the rotational speed of trommel body caused an increase in the screening efficiency under various mass flow rates of filter granules. When the rotational speed of the trommel body was lower, slumping motion of the filter granules occurred. In this motion mode, only the lower layer of smaller-sized filter granules near the wall of the trommel body was screened. Because the upper layers of smaller-sized filter granules did not pass through the packed filter granules near the wall of trommel body, the screening efficiency was lower. When the trommel body’s rotational speed increased, the motion mode switched from slumping to cataracting. Granules became detached from the trommel body and were thrown off into free space within the trommel body. In other words, this motion mode caused size segregation of the filter granules, with the smaller-sized filter granules passing relatively easily through the packed thickness of filter granules near the wall of the trommel body. It implies that the cataracting motion seems to have great influence on the generation of Brazil nut effect, i.e., the smaller-sized particles fall into the spaces underneath the largersized particles. This also resulted in higher screening efficiency. At the optimum speed of 43 rpm, it was observed that better screening efficiency was obtained during the cataracting motion. When the rotational speed of the trommel body exceeded 43 rpm, the screening efficiency decreased. This can be explained from observations during the experiment process. A higher rotational speed of the trommel body would lead to more particles adhering to the wall of trommel body and these would leave the trommel screen system later. We also found the screening efficiency to be lower if the rotational speed of the trommel body was too high. Consequently, better collection efficiency promoted by the suitability rotational speed of trommel body could be attributed to the effect of the motion mode of filter granules in the trommel body. It's critial to separate the waste stream in MRF. Waste segregation machines needs the lots of testing results like this to make more efficiency.
