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Volume
X: The World Market for Flowmeters, 4th Edition
Publication Date Q2
2012
Module
A: Strategies, Industries, & Applications
Publication Date Q3
2012
All
Flowmeter Studies
Articles
about Open Channel
About
Open Channel Flow
Growing
environmental regulations and the increasing importance of water as a
natural resource are generating growing interest in measuring flow in open
channels. Flow in open
channels, or conduits, is contrasted with flow in closed pipes.
Measurement of flow in closed pipes is very common in industrial
and process control environments, and many different types of meters are
used for this purpose. Open
channel flow measurement occurs in industrial applications, but it also is
very common in towns and municipalities that monitor drinking water and
wastewater treatment flows.
Open
channel flow occurs when liquid flows in a conduit or channel with a free
surface. Rivers, streams,
canals, and irrigation ditches provide examples of open channel flow.
What is slightly confusing about this terminology is that that the
flow of liquids in partially filled pipes, when not under pressure, is
also considered open channel flow. For
example, water flowing through a culvert running underneath a street is
considered open channel f low. Likewise,
flow in sewers and tunnels are classified as open channel flows, along
with other closed channels that flow partly filled.
Other examples of open channel flow include flow in water treatment
plants, storm and sanitary sewer systems, industrial waste applications,
sewage treatment plants, and irrigation systems.
One
way to understand the difference between open channel and closed pipe flow
is to think of it as the difference between gravity-induced and
pressurized flow. Flow in
uncovered channels such as irrigation ditches depends on gravity.
Likewise, flow in partially filled closed conduits, such as
culverts and drain pipes, also is gravity-dependent.
Flow in closed pipes for industrial applications occurs under
pressure. So open channel
flow might be called gravitational flow, while closed pipe flow could be
called pressurized flow. This
explains why flows in both uncovered conduits and partially filled pipes
are considered to be open channel flow: they are both examples of
gravitational flow.
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