A multi$-$tray settling chamber handles $6$ m$3/$sec of air at $20$C$.$ There are $8$ trays including the bottom surface spaced $0\mathrm{.}25$m apart. The chamber is $4$m long and $1$m wide. For particles of density $2000$ and Kg$/$m$3$ and sizes $40\backslash$mu m$,$ calculate the efficiency of collection $(\backslash$eta $).$ Assume Laminar flow and terminal velocity $0\mathrm{.}04$ m$/$s