QUESTION $3($FANS$)$

$[24]$

$3\mathrm{.}1$ Explain what is meant by a fan stall$-$zone.

$3\mathrm{.}2$ Suggest FOUR factors that would indicate that a fan is operating in the stall$-$zone.

$3\mathrm{.}3$ Illustrate with an aid of diagram, the fan characteristic curves for a centrifugal fan with radial blades.

$3\mathrm{.}4$ A fan handles $5\mathrm{.}0m\frac{3}{s}$ at $900$ Pa $.$ the electrical input power to the fan motor is $6\mathrm{.}0$ kW and the motor output power is $5\mathrm{.}5$ kW $.$ The fan input power is $4\mathrm{.}0$ kW $.$

Calculate the following:

$3\mathrm{.}4\mathrm{.}1.$ The motor efficiency

$3\mathrm{.}4\mathrm{.}2.$ The drive efficiency

$3\mathrm{.}4\mathrm{.}3.$ The fan efficiency

$3\mathrm{.}4\mathrm{.}4.$ The overall efficiency

$3\mathrm{.}5$ Which methods can be used to control the fan performance of an axial flow fan?

$(5)$