Centrifugal Fan
Consider you are conducting an experiment, and need to run a test specimen on a centrifugal fan. After turning on the 10 kW machine with the 0.25 m diameter fan running at 2,000 rpm for 5 minutes, what is the fan's efficiency if the measured pressure rise was 1 kPa and the fluid (air at 300 K, 101 kPa) flow rate was 6 m^3/s?
Expand Hint
Pump Power Equation:
$$$\dot{W}=\frac{Q\gamma h}{\eta }=\frac{Q\rho gh}{\eta}$$$
where
$$Q$$
is the volumetric flow,
$$h$$
is the head for the fluid to be lifted,
$$\eta$$
is the total efficiency, and
$$\dot W$$
is the power.
Hint 2
Since
$$\Delta P=\gamma h$$
, our equation for a typical backward curved fan is:
$$$\dot{W}=\frac{\Delta PQ}{\eta }$$$
where
$$\Delta P$$
is the pressure rise.
Pump Power Equation:
$$$\dot{W}=\frac{Q\gamma h}{\eta }=\frac{Q\rho gh}{\eta}$$$
where
$$Q$$
is the volumetric flow,
$$h$$
is the head for the fluid to be lifted,
$$\eta$$
is the total efficiency, and
$$\dot W$$
is the power.
Since
$$\Delta P=\gamma h$$
, our equation for a typical backward curved fan is:
$$$\dot{W}=\frac{\Delta PQ}{\eta }$$$
where
$$\Delta P$$
is the pressure rise. Solving for
$$\eta$$
:
$$$\eta =\frac{\Delta PQ}{\dot{W}}=\frac{(1kPa)(6m^3/s)}{10kW}$$$
Since efficiency is unitless, remember to convert the pressure and power units to base units:
$$$1kPa=\frac{kN}{m^2}$$$
$$$1kW=\frac{kN\cdot m}{s}$$$
Thus,
$$$\eta =\frac{(1kN)(6m^3)\cdot s}{10kN\cdot m\cdot m^2\cdot s}=0.6$$$
0.6
Time Analysis
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