Objective

To draw the characteristics curve of backward bladed centrifugal fan.

Apparatus used:

Pitot Tube, Inclined U-Tube Manometer, Flexible Rubber Tubes, Ventilation Duct, Cardboards of different diameters, Centrifugal fan etc.

Description Backward Curved Fans: Backward Curved Fans also known as Radial Fans are Centrifugal Fans with Backward Curved Blades. These Centrifugal Fans provide very good cooling at high-pressure conditions. The impellers of these industrial fans are highly resistant to dirt and dust.

STEP  1 

Start the motor to allow the fan to attain the constant 300 rpm.

The knob is being rotated

The Motor reading = 300 rpm

STEP  2 

Calculating the angle of inclination of inclined U-Tube Manometer.

↑

tan θ = h/l

θ = tan^-1( h/l)

θ = (θ₁+θ₂+θ₃)/3 = 7.74°

Point No

Length(l)(cm)

Height(h)(cm)

Angle(θ°)

STEP  3 

Connect flexible rubber tube of manometer to Pitot Tube fixed at point 1 of ventilation duct.

Note:

1.The Pitot Tube should be fixed at point 1 in the ventilation duct tightly.
2.Connect one flexible rubber tube of manometer with Total Head of Pitot Tube to take the reading of static pressure.
3.Remove rubber tube from Total Head and connect that with Static Head of Pitot Tube to take the reading of total pressure.
4.Now, connect one flexible rubber tube of manometer with Total Head and another with Static Head of Pitot Tube to take the reading of velocity pressure.

    Now, repeat the same procedure for 8 different cardboards and note down the readings of Static, Total and Velocity Head at point 1.

   

Point 1

Total Head

Pitot Tube

Static Head

First flexible rubber tube is connected to the Static Head

Second flexible rubber tube is connected to the Total Head

Both flexible rubber tubes are connected to the Static Head and Total Head

Place the cardboard in front of the ventilation duct

Isometric View of the Ventilation Duct

Observations:

Dia(m)

Area (m2)

Static Head Pressure(Ps1)

Total Head Pressure(Pt1)

Velocity Head Pressure(Pv1)

Density of air (q) = 1.2 kg/m³

STEP  4 

 Plot graph of Axial Load Vs Penetration.

Download Graph

STEP  5 

Start the motor to allow the fan to attain the constant 400 rpm.

The knob is being rotated

The Motor reading = 400 rpm

STEP  6 

Connect flexible rubber tube of manometer to Pitot Tube fixed at point 1 of ventilation duct.

Trial 2

Total Head

Pitot Tube

Static Head

Keep the cardboard in front of the ventilation duct

Now, repeat the same procedure for 8 different cardboards and note down the readings of Static, Total and Velocity Head at point 1.

   

Observations:

Dia(m)

Area (A) (m2)

Static Head Pressure(Ps1)

Total Head Pressure(Pt1)

Velocity Head Pressure(Pv1)

Density of air (q) = 1.2 kg/m³

STEP  7 

Draw the graph of Total Pressure Vs Volume Flow.

Total Pressure v/s Volume Flow graph for 400 rpm