Objective

To determine the shock loss factor for a right–angled bend in a ventilation ducts with the centrifugal fan running at a given rpm.

Apparatus used:

Ventilation duct set-up, Pitot tube, Inclined U–tube manometer, Rubber hoses etc.

Description Shock Loss Factor: The pressure loss due to obstructions, area changes, bends, loss in pressure of air flowing through mine airways besides shape and size of mine airways and their corresponding roughness are termed as Shock Loss. While deriving equation for Shock Pressure Loss the term called Shock Loss Factor. Its value is not constant and depends on type of area changes, obstructions, type of bends etc. The values of shock loss factors for most of these are determined empirically.

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 

Measure the length between the two chosen points and the diameter of the ventilation duct.

The length between the two chosen points is = _______ m.

The diameter of the ventilation duct is = _______ m.

STEP  4 

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.

   

Top View of the inclined U-Tube Manometer

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

Observations:

Variables in calculation θ :Angle of inclination of the manometer tube = 7.74°

ρ :Specific gravity of the manometer liquid = 0.789

g :Acceleration due to gravity = 9.8 ms^-2

q :Density of air = 1.2 kg/m³

L_s1 :Length of static head at point 1

L_t1 :Length of total head at point 1

L_v1 :Length of velocity head at point 1

π = 3.14

	Static Head(cm)			Total Head(cm)			Velocity Head(cm)
No	Left Limb Reading	Right Limb Reading	Diffe rence (Ls1)	Left Limb Reading	Right Limb Reading	Diffe rence (Lt1)	Left Limb Reading	Right Limb Reading	Diffe rence (Lv1)
1

STEP  5 

Connect flexible rubber tube of manometer to Pitot Tube fixed at point 2 of ventilation duct.

Top View of the inclined U-Tube Manometer

Point 2

Observations:

Variables in calculation θ :Angle of inclination of the manometer tube = 7.74°

ρ :Specific gravity of the manometer liquid = 0.789

g :Acceleration due to gravity = 9.8 ms^-2

q :Density of air = 1.2 kg/m³

V₁ :Velocity of air at point 1 = m/s

L_s2 :Length of Static Head at point 2

L_t2 :Length of Total Head at point 2

L_v2 :Length of Velocity Head at point 2

	Static Head(cm)			Total Head(cm)			Velocity Head(cm)
No	Left Limb Reading	Right Limb Reading	Diffe rence (Ls2)	Left Limb Reading	Right Limb Reading	Diffe rence (Lt2)	Left Limb Reading	Right Limb Reading	Diffe rence (Lv2)
2

Observations:

Variables in calculation P_t1 :Total Head pressure at point 1 = Pa

P_t2 :Total Head pressure at point 2 = Pa

A :Area of cross section = 0.159

V₂ :Velocity of air at point 2 = m/s

Q₁ :Quantity of air passing through the ventilation duct at point 1 (Q₁) = m/s

L :Distance between the two chosen points in the ventilation duct = 1.5 m

π = 3.14

R :Frictional resistance of airway = 5.277 Ns²/m⁸

K :Atkinson’s friction factor = 0.010 Ns²/m⁴

Result:

1.The shock loss factor is, X = ______.

2.The Equivalent length is, L_eq = _____ m.