**Determination
of fan characteristics**.

Objective:

From
the fan testing facility provided in the mine ventilation laboratory,
development of total, static, and fan efficiency curve, for the axial flow fan
for the given operating speed.

Introduction:

Fan
rating tests are conducted for the determination of fan characteristics. The
rating test aims at finding out the fan static and total pressures, power input
to the fan and total efficiency of the fan for various flow rates at the rated
speed so that the fan characteristics can be drawn.

The standard test setup existing in
the laboratory confirms to the AMCA, USA recommendations. The necessary
measurements are the

Ø
Static
and velocity pressures at the duct at the traverse section

Ø
The
RPM and the power input to the fan

Ø
Barometric
pressure and the dry wet bulb temperatures on the path of inflowing air, and
dry bulb temperature at the traverse section.

The characteristic curves are drawn for

ü
Fan
total pressure

ü
Fan
static pressure, and

ü
Fan
and motor efficiency as a function of fan inlet quantity.

The fan total pressure, which is the total pressure
at the fan outlet, is an algebraic summation of the fan static pressure and the
velocity pressure. The fan total pressure is obtained by adding the (friction)
pressure loss in the intervening duct, and in the straightener, to the static
and average velocity pressures measured in the duct. If P_{vo} is the
average velocity pressure in the duct, then the friction pressure loss in the
duct (P_{1}) is given by:

**P _{1}= 0.02 * (L/D) P_{vo}**

Where L is the length of the duct from the fan
outlet to the traverse section and D is the duct diameter. The pressure loss in
the straightener (P_{2}) is given by:

**P _{2} = 0.08 P_{vo} **

The fan velocity pressure is given by:

**P _{v} = P_{vo} (A_{0}/A)^{2}**

where A_{0 }and A refer to the cross section
areas at the duct and fan outlet respectively.

The fan inlet quantity Q is found by:

**Q = (****r**_{0}**/****r****) * A _{0}
* (2 * P_{vo}/**

The density of the air in the duct (r_{0}) is related to the inlet
air density (r) as follows:

**r**_{0}** = ****r**** * (T/T _{0}) * ((B+ P_{s})/B)**

where T and T_{0} are the dry bulb
temperatures at the fan inlet and in the duct respectively, B is the barometric
pressure and P_{s} is the static pressure measured in the duct Pa. For
fan pressures below 1 kPa, the may be assumed to be constant.

The input power to fan is equal to the input
power to the motor multiplied by the motor efficiency. Air power is the product
PQ, where P is the fan total pressure.

The fan efficiency = Air power/ Fan input power

The fan RPM is measured with a Stroboscope to within
a limit of 1 % and all measurements of quantity, pressure and power are
converted to rated RPM using the following relations:

Quantity a speed

Pressure a speed^{2}

Power a speed^{3}

Instruments:

AMCA
standard fan testing setup, Askania minimeter, inclined tube manometer, pitot
static tube, wattmeter, Stroboscope, Assmann Psychrometer, Aneroid barometer,
Scale and calipers.

Procedure:

(1)
at
the traversing section in the duct plane the pitot static tube with the nose at
center, facing the air in the air
stream

(2)
To
the Pitot tube connect the Askania to measure velocity pressure, and inclined
tube manometer to measure the static pressure. Level these two instruments and
take their initial reading.

(3)
Make
wattmeter connections and start the fan. Use the symmetrical conical throttle
provided at the duct outlet to vary the quantity in the duct.

(4)
For
each throttle bottle measure the

ü
Motor
input power

ü
Fan
RPM

ü
Static
and velocity pressures at the traverse section

(5) Measure the L and D values, obtain wet and dry bulb temperatures and barometric pressures at the fan inlet. Obtain a representative of dry bulb temperature inside the duct.

Remarks:

The
average velocity pressure in the duct (P_{vo}) is obtained by
multiplying the central velocity pressure measurement with the method factor
computed in the other experiments. Fom the relationships explained in the
“introduction” section compute fan total, and static pressures, fan quantity,
and fan efficiency values for each throttle condition. Plot the pressure and
efficiency values as functions of quantity.

************************************************************************