To find the coefficient of velocity for a small orifice.

Object: To find the coefficient of velocity for a small orifice.

Orifice

Apparatus Required:

• Hydraulic Bench with orifice (and notch) apparatus, and Vernier calipers.
  

Theory:

• Let Cv = coefficient of velocity.
  

ThenCv = actual velocity at vena contracta (cc) / Theoretical velocity LetH = head causing flow(Fig. 3.1)

v = actual velocity

ThenCv = v /(3.1)

2g H

orv = Cv

2g H

• The difference between the theoretical and actual velocities is due to friction at the orifice and is very small for sharp-edged orifices. The coefficient of velocity will vary slightly for different orifices, depending on the shape and size of the orifice and on the head. An average value for Cv is about 0.97.
  

Consider Fig 3.2

Let H = height of liquid above centre of orifice

Fig. 3.2. Trajectory of the orifice jet

Consider a particle of liquid in the jet at P (x y) and let the time taken for this practical to move from cc to P be t sec.

Thenx = vt

andy = ½ gt²

Equating the values of t² from these two equations, x²/ v² = 2y / g

orv =

gx ² / 2y

Cv = v/

2g H

=(3.2)

x2 / 4yH

Procedure:

Observations:

Orifice dia, d =cm

Results & Comments: