390 Energy Project Financing: Resources and Strategies for Success
allows the axial turbine to be inserted into the fluid stream and uses
existing pipe as the meter body. Because the insertion turbine meter only
measures fluid velocity at a single point on the cross-sectional area of
the pipe, total volumetric flow rate for the pipe can only be accurately
inferred if the meter is installed according to manufacturer’s specifica-
tions. Most important with insertion turbine meters is installation in
straight sections of pipe removed from internal flow turbulence. This
type of meter can inserted without having to shut down the system.
Insertion meters can be used on pipelines in excess of four inches with
very low pressure loss. Turbine meters provide an output that is linear
with flow rate. Care must be taken when using turbines as they can be
damaged by debris and are subject to corrosion. Insertion meters can
be damaged during insertion and withdrawal.
Vortex meters
They utilize the same basic principle that makes telephone wires
oscillate in the wind between telephone poles. This effect is due to
oscillating instabilities in a low pressure field after it splits into two
flow streams around a blunt object. Vortex meters require minimal
maintenance and have high accuracy and long-term repeatability. Vortex
meters provide a linear output signal that can be captured by meter/
monitoring equipment.
Non-Interfering Flow Meters
They are well suited to applications where the pressure drop of an
intrusive flow meter is of critical concern, or the fluid is dirty, such as
sewage, slurries, crude oils, chemicals, some acids, process water, etc.
Ultrasonic flow meters
They measure clean fluid velocities by detecting small differences
in the transit time of sound waves that are shot at an angle across a
fluid stream. Accurate clamp-on ultrasonic flow meters facilitate rapid
measurement of fluid velocities in pipes of varying sizes. An accuracy
rate from 1 % of actual flow to 2% of full scale are now possible, al-
though this technology is still quite expensive. Recently, an ultrasound
meter that uses the Doppler principle in place of transit time has been
developed. In such a meter a certain amount of particles and air are
necessary in order for the signal to bounce-off and be detected by the
receiver. Doppler-effect meters are available with an accuracy between