A simple gravity collector, having a height of 4 m, can remove 95% of 40 pm sized particles dust. Density of the particle and viscosity of air is 1500 kg/m2 and 16'10 m/s, respectively. The gas enters the gravity collector at a bulk velocity of 1 m/s. Considering three trays being used for the same efficiency, estimate the length of the gravity collector. Assume bottom floor as an additional tray Neglect the density of air.