Orifice:

•    Orifice is a small opening of any cross sections such as circular, triangular or rectangular on the side or at the bottom of a tank, through which a fluid is flowing.

•    It is used to measure the discharge of liquid from a tank or reservoir.

Classification of Orifice:

(1)    Depending upon size

   (i) Small orifice   (ii) Large orifice

(2)    Depending upon shape

(i)    Circular
(ii)    Rectangular
(iii)    Triangular
(iv)    Square

(3)    Depending upon the shape of upstream edge of orifice
 
(i) Sharp edge orifice      (ii) Bell-mouthed orifice

(4)    Depending upon nature of discharge

(i)    Free discharge orifice
(ii)    Drowned or sub-merged orifice

(a)    Fully submerged orifice
(b)    Partially submerged orifice

Consider a tank fitted with a circular orifice is one of its sides.


Let H be the head of liquid above the center of the orifice.

Consider two points at inside the tank and at vena-contract respectively.

Let flow is steady and at a constant head H

Apply Bernoulli’s Equation

+ V₁² / 2g + Z₁ = P₂ / γ + V₂² / 2g + Z₂

Pressure at (1) - (1)   (P / γ = H)

Pressure   (2) - (2)      (P / γ) = 0 atmospheric pressure

Z₁  =  Z₂

V1 is very small as compare to  V₂ as A₁ > A₂

V₁  = 0              H -0 = 0- V₂ / 2g

V₂²  = 2gh          V₂  = √2gh

This is theoretical velocity. Actual velocity is less than this value.

For more help in Flow through Orifice click the button below to submit your homework assignment