Fluid Mechanics and Hydraulic Machines
Experiment No :1 Calibration of Venturimeter
To determine the coefficient of discharge of the given flow meter.
:Venturimeter experimental setup, stop watch.
: A flow meter is used to measure the flow rate of a fluid in a pipe. A venturimeter consist of short
length of a pipe narrowing to a throat in the middle and then diverging gradually to the original diameter
of the pipe. As the water flow through these meters, velocity is increased due to the reduced area and
hence there is a pressure drop.
A venturi meter is a device which is used for measuring the rate of flow of fluid through the pipe.
:The basic principle on which a venturimeter works is that by reducing the cross sectional
area of the flow passage, a pressure difference created and the measurement of the pressure difference
enables the determination of the discharge through the pipe.
Venturi meters consist of 1. An inlet section which is in the form of convergent cone 2. Throat 3.outlet
section which is in the form of divergent cone. The inlet section of the venturi meter is of the same
diameter as that of the pipe diameter. The convergent cone is a short pipe which tapers from the original
size of the pipe so that the throat of the venturimeter. The throat is a short pipe having its cross sectional
area smaller than that of the pipe .The divergent cone of the venturimeter is a gradually diverging pipe
with its cross section area increasing from that of throat i.e 1 and 2 of the venturimeter
Pressure taps are provided through the pressure ring as shown in the figure.
The length of convergent cone is equal to the (Dd).where ‘D’ is the diameter of the inlet section and ‘d’
diameter of throat .The length of the pipe is equal to the diameter of the pipe. The diameter of the throat
may vary from 1/3 to ¾ of the pipe diameter.
The divergent cone has more length as that of the convergent cone due to avoid the possibility of flow
separation (eddies) and energy loss.
The cross section area of the throat is smaller than the cross section area of the inlet section .According to
the the flow at the throat result in the decrease in the pressure .so the
pressure difference will be developed between the inlet and the throat .This pressure difference can be
determined by using suitable manometer.