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5.7 Laboratory Test of a Centrifugal Fan
5.7.2 Measurements
The input power of the fan follows from
• The torque and the rotational speed on the fan shaft determined with the characteristics of the driving motor with its controller by reading the electric input
power.
The output power of the fan follows from
• The mass flow rate determined with the measuring nozzle.
• The energy rise determined from the pressure and temperature at the fan inlet and
outlet. The mechanical energy rise is determined with the Bernoulli formula for
density equal to the average value between inlet and outlet. The kinetic energy at
the inlet is zero (atmospheric plenum). The kinetic energy at the outlet follows
from the velocity at the outlet. Velocity is calculated from the mass flow rate and
the density at the fan outlet, determined from p and T.
5.7.3 Measurement Procedure
• Select a rotational speed of 2000, 2400, 2750, 3000 or 3200 (idling rotational
speed) on the frequency controller of the driving motor. Read atmospheric pressure and atmospheric temperature.
• Turn the flow control cone at the end of the measuring tube completely open.
The flow rate through the fan and the electric input power are then maximal. The
frequency controller has a power limiter. At an idling rotational speed of 3000
and 3200 rpm, the power limiter switches the frequency controller off with a
completely open cone. Open the cone at these rotational speeds that much, that
the power limiter just does not intervene. The power limiter does not intervene
at other rotational speeds. Read the maximum power input. Close then the flow
control cone completely, however without forcing it, and read the corresponding
input power. The fan has straight blades with only moderate backward leaning.
So, the energy rise is almost constant for varying flow rate and thus is the input
power approximately proportional to the flow rate.
• Vary the mass flow rate by opening or closing the cone. Select eight operating points approximately evenly distributed over the power input range from
minimum to maximum. When performing pressure measurements of the nozzle,
it is advisable to measure the pressure upstream of the measuring nozzle and
the pressure difference over the nozzle (and not the pressure downstream of the
nozzle).
• Measure at each operating point: T , p, p 1 ,
1
2
p p p
D = − , P input .
5.7 Laboratory Test of a Centrifugal Fan
5.7.2 Measurements
The input power of the fan follows from
• The torque and the rotational speed on the fan shaft determined with the characteristics of the driving motor with its controller by reading the electric input
power.
The output power of the fan follows from
• The mass flow rate determined with the measuring nozzle.
• The energy rise determined from the pressure and temperature at the fan inlet and
outlet. The mechanical energy rise is determined with the Bernoulli formula for
density equal to the average value between inlet and outlet. The kinetic energy at
the inlet is zero (atmospheric plenum). The kinetic energy at the outlet follows
from the velocity at the outlet. Velocity is calculated from the mass flow rate and
the density at the fan outlet, determined from p and T.
5.7.3 Measurement Procedure
• Select a rotational speed of 2000, 2400, 2750, 3000 or 3200 (idling rotational
speed) on the frequency controller of the driving motor. Read atmospheric pressure and atmospheric temperature.
• Turn the flow control cone at the end of the measuring tube completely open.
The flow rate through the fan and the electric input power are then maximal. The
frequency controller has a power limiter. At an idling rotational speed of 3000
and 3200 rpm, the power limiter switches the frequency controller off with a
completely open cone. Open the cone at these rotational speeds that much, that
the power limiter just does not intervene. The power limiter does not intervene
at other rotational speeds. Read the maximum power input. Close then the flow
control cone completely, however without forcing it, and read the corresponding
input power. The fan has straight blades with only moderate backward leaning.
So, the energy rise is almost constant for varying flow rate and thus is the input
power approximately proportional to the flow rate.
• Vary the mass flow rate by opening or closing the cone. Select eight operating points approximately evenly distributed over the power input range from
minimum to maximum. When performing pressure measurements of the nozzle,
it is advisable to measure the pressure upstream of the measuring nozzle and
the pressure difference over the nozzle (and not the pressure downstream of the
nozzle).
• Measure at each operating point: T , p, p 1 ,
1
2
p p p
D = − , P input .