Air with temperature $50C$ is pumped by fan to the equipment where overpressure is equal to $p_m=460\frac{N}{m^2}.$ Air flow rate is equal to $V_g=0\mathrm{.}16\frac{m^3}{s}$; air density $=1\mathrm{.}09k\frac{g}{m^3}$; air dynamic viscosity $=0\mathrm{.}0196{10}^{-3}$ Pas. Pipe line has outer diameter $d_z=102mm$ and inner diameter $d_w=90mm.$ Length of the pipeline is equal to $20m.$ Pipe line is equipped with $4$ reducing pipes $($coefficient of local resistance ${}_1=18\mathrm{.}2),3$ gate valves $(($:${}_2=0\mathrm{.}5\}$ elbows $({}_3=0\mathrm{.}23),1$ inlet stub pipe $)=(0\mathrm{.}2$ outlet stub pipe $)=(1.$ Electric motor has electric power $N_{el}=1\mathrm{.}35KW$; efficiency of electric motor is ${}_{el}=0\mathrm{.}95.$ Calculate efficiency of the fan ${}_f.$