venturi meter
CHARLES DARWIN UNIVERSITY
ENG243 – THE VENTURI METER AND THE ENERGY LINE
1.
Introduction
A Venturi meter is a device for determining the flow-rate of a fluid down a pipe. One measures the pressure difference between the venturi inlet and neck, and from this the flow-rate can be determined. The apparatus used on this experiment also has a number of straight tube manometers at equally spaced intervals. These will be used to determine the hydraulic grade line of the fluid as it passes through the manometer.
2.
Apparatus and theory of the venturi
A diagram of the Venturi apparatus used for this experiment is show below.
The ideal theoretical (volumetric) flow-rate Q from a venturi meter is given by:
Q = A1
2 g∆H
X 2 −1
(
(1)
)
where A1 is the area of the venturi inlet, g = 9.783 m/s2 local gravitational acceleration, X is the ration of the area of the venturi inlet to neck, i.e. X = A1/A2. The diameter at the venturi inlet is26 mm and the diameter at the venturi neck is 16 mm. The pressure difference, ∆H expressed as an elevation change is
∆H = h1 − h2 =
p1 − p 2
γ
(2)
where γ is the specific weight of the fluid in the manometer.
When real world effects such as fluid friction and turbulence are included its is found that equation
(1) is not obeyed exactly. A correction factor, call the coefficient of discharge, Cd is introduced into the Venturi equation giving
Q = C d A1
2 g∆H
X 2 −1
(
)
(3)
The discharge coefficient, Cd does depend on the flow-rate.
3.
Procedure and Analysis for the venturi meter
The flow through the Venturi can be regulated using the valves on the hydraulic bench and the apparatus itself. Try and set up the apparatus initially so that the variation in pressure between the entrance and neck is as large as possible; this will occur when the flow-rate is largest. It may be necessary to adjust the overall water level in the tubes by using the bike pump to
ENG243 – THE VENTURI METER AND THE ENERGY LINE
1.
Introduction
A Venturi meter is a device for determining the flow-rate of a fluid down a pipe. One measures the pressure difference between the venturi inlet and neck, and from this the flow-rate can be determined. The apparatus used on this experiment also has a number of straight tube manometers at equally spaced intervals. These will be used to determine the hydraulic grade line of the fluid as it passes through the manometer.
2.
Apparatus and theory of the venturi
A diagram of the Venturi apparatus used for this experiment is show below.
The ideal theoretical (volumetric) flow-rate Q from a venturi meter is given by:
Q = A1
2 g∆H
X 2 −1
(
(1)
)
where A1 is the area of the venturi inlet, g = 9.783 m/s2 local gravitational acceleration, X is the ration of the area of the venturi inlet to neck, i.e. X = A1/A2. The diameter at the venturi inlet is26 mm and the diameter at the venturi neck is 16 mm. The pressure difference, ∆H expressed as an elevation change is
∆H = h1 − h2 =
p1 − p 2
γ
(2)
where γ is the specific weight of the fluid in the manometer.
When real world effects such as fluid friction and turbulence are included its is found that equation
(1) is not obeyed exactly. A correction factor, call the coefficient of discharge, Cd is introduced into the Venturi equation giving
Q = C d A1
2 g∆H
X 2 −1
(
)
(3)
The discharge coefficient, Cd does depend on the flow-rate.
3.
Procedure and Analysis for the venturi meter
The flow through the Venturi can be regulated using the valves on the hydraulic bench and the apparatus itself. Try and set up the apparatus initially so that the variation in pressure between the entrance and neck is as large as possible; this will occur when the flow-rate is largest. It may be necessary to adjust the overall water level in the tubes by using the bike pump to