Name: JanVince Joshua B. Vicente
BSCEN IV
Subject: CVE 112 – Hydraulics
Assignment No. 2
Research on the following questions below:
1.) What is an orifice, its uses/applications?
A small aperture on the side or bottom of a tank through which any form of fluid
is flowing is known as an orifice. The cross section of the hole might be circular,
triangular, or rectangular, and they are termed according to their shape. The main purpose
of orifices is to measure the rate of fluid flow.
Uses and Applications:

It is used to measure the flow rate of fluids in their single state (i.e. gaseous state
or liquid state).

It can also be used to measure the flow rate of fluids in a mixed state (both gaseous
and liquid states) such as, wet steam, or natural gas with water.

In water treatment plants orifice meters are used to measure the runoff flux from
the water treatment plant. Flow is measured as the amount of water passing
through an orifice meter and converted to a value of discharge by comparison
with known flow.

Hydropower plants use orifice meter for measuring water flow rate and discharge
for efficient operation.

Refineries use orifice meters for measuring the oil and the gas flow rate and
discharge from the pipeline. The orifice meters allow refineries to efficiently
control the operation of their facilities, optimize production and maintain a
healthy balance between stock and demand.

Chemical industries use orifice meter for measuring flow of fluids, gases, steam,
etc., through pipelines used in chemical plants for efficient operation and high
production chemicals.
2.) Classification of orifice
Orifices are classified based on the shape or the cross-sectional area as:

Rectangular orifice

Circular orifice

Triangular orifice and

Square orifice
Orifices are classified based on the size of the orifice and the head of fluid above the
orifice as:

Small orifice
If the head of fluid is greater than 5 times the depth of the orifice, then it
is categorized as small orifice. In the case of small orifice, the jet of fluid possesses
a constant velocity throughout the cross-section. Hence, the discharge is
calculated as:

Large orificeIf the head of fluid is less than 5 times the depth of the orifice, then it is
categorized as a large orifice. Here, the velocity over the entire cross-section of
the jet of fluid is not constant, hence discharge cannot be determined by Equation1. Hence, the total discharge of fluid for a large orifice is given by:
Depending on the shape of the upstream edge of the orifices, they are classified as:

Sharp-edged orifice and

Bell-mouthed orifice
They are also classified based on the nature of the discharge as:

Partially submerged or drowned orifice

Fully submerged or drowned orifice

Free discharging orifices
3.) Values of H (total head) for various conditions

Submerged Orifice
The greater depth on the center of the orifice is H1 and the lesser the depth
is H2. The assumptions are usually made that every filament passing through the
orifice is being acted upon by the head, H1-H2=H, the difference in elevation of the
liquid surfaces. On this assumption, writing the energy theorem from point 1 to point
2 in the jet, neglecting lost head,
Applying the usual orifice coefficients Q=Cd.a.√2gH. The assumption that H2 is the
pressure head on the center of the orifice at its lower side is not strictly true unless all
the velocity of the liquid leaving the orifice is lost in friction and turbulence as
velocity is reduced to zero.

Orifices under low ends
The discharge of orifices under low ends can be determined by the formula:

Discharge under falling head
Discharging a liquid through an orifice under a head H1. If there is no
compensating inflow, the depth or head will gradually decrease. The time that will
elapse while the head is being reduced from H1 to H2 is required. At this instant
when the head H the discharge is:
4.) 3 orifice coefficients and values

Co-efficient of velocity, 𝑪v
It is the ratio between the actual velocity of the jet of fluid at the venacontracta to the theoretical velocity of fluid.
Generally, the value of 𝐶𝑉 varies from 0.95 to .99 for different orifices depending
upon their size, shape, head etc. for calculation purposes we assume the value of
𝐶𝑉 as 0.98 generally

Co efficient of contraction, 𝑪c
It is the ratio of area of the jet at vena-contracta to the area of orifice.
Where 𝑎c is the area at the vena-contracta and a is the area of orifice. The value
of 𝐶c varies from 0.61 to 0.69 depending upon the size, shape and head of orifice
in which flow takes place. In general, the value is taken as 0.64.

Coefficient of discharge, 𝑪d
It is defined as the ratio of the actual discharge from an orifice to the
theoretical discharge from the orifice.
The value of 𝐶𝑑 varies from 0.61 to 0.65. In general, the value of 𝐶d is taken as
0.62 for all calculation purpose.
5.) What is vena contracta?
Vena Contracta is the point in a fluid stream where kinetic energy is maximum
and pressure energy is minimum. At Vena Contracta fluid stream where velocity is
maximum and the diameter of stream is minimum. In orifice meter maximum contraction
or Vena Contracta takes place at a section slightly down the stream of the flow, at that
section where the jet is more or less horizontal.
6.) What is steady flow and unsteady flow through orifice?
The flow through orifice, weirs, or tubes is said to be steady only if the total
head producing flow, H, is constant. This means that the height of the liquid is constant
or does not change with respect to time. Consider the vessel shown in figure 1 to be
supplied with a fluid (inflow) and simultaneously discharging through an outlet (either an
orifice, tube, weir or pipe). Obviously, if Qin = Qout, the head will remain constant. In
some conditions, however, the flow through orifice, weirs, or tubes is said to be unsteady
only if the total head producing flow, H, is not constant. This means that the height of the
liquid might fall or rise with respect to time. Also, consider the vessels shown in figure 2
to be supplied with a fluid (inflow) and simultaneously discharging through an outlet
(either an orifice, tube, weir or pipe). Obviously, if Qin > Qout, the head will rise and if
Qin < Qout, the head will fall. The most common example for the height of the liquid to
be fell is when Qin = 0