A multi$-$tray settling chamber having $10$ trays, including the bottom surface handles $9$m$3/$s of air at $20\backslash$deg C$.$ The trays are $0\mathrm{.}32$m apart and the chamber is to be $1$m wide and $4$m long. What is the particle size for a particle with density $3000$kg$/$m$^3$ that can be collected with $75\%$ efficiency? What is the ratio of particle sizes which can be collected efficiency to that which can be collected at $75\%$ efficiency? Laminar flow condition within the chamber and presence of no dust initially on trays to be assumed. The viscosity of air$($q$)$ at $20\backslash$deg C is $1\mathrm{.}81$x$10-5$kg$/$m$-$s$.$