Page 110 - Fluid mechanics, heat transfer, and mass transfer

FLOW MEASUREMENT 87

Double U-tube Coriolis mass flow meter designs.
FIGURE 4.30

& Bent tube Coriolis flow meters are preferred wher- the readings. They must be properly sized for the flow
ever highly accurate, reliable, rangeable mass flow is rates involved.
required. & Temperature is constantly measured because the
& Straight tube meters are preferred when raw material oscillatory properties of the tube vary with
contamination is to be avoided. Between runs of the temperature.
same material or between runs of different materials & Use of these meters is limited for smaller pipe sizes
it may be necessary to avoid cross-contamination (usually 7–10 cm) as they become expensive for
. What are the applications of Coriolis flow meters? larger pipe sizes.
& Used for clean liquids and gases flowing fast enough & Some low-pressure gases do not have sufficient
to operate the meter. density to operate the meter.
& Coriolis meters can be used to measure flow of both & The main limitation of the Coriolis meter is that
liquids and gases. pressure drop can become large as fluid viscosity
& These meters can be used to measure the flow of some increases.
fluids with varying densities that cannot be measured & Coriolis flow meters have a relatively high initial
by other flow meters. cost, which is offset by normally low maintenance
. What are the limitations of Coriolis flow meters? costs.
& These meters are sensitive to pipe and building . What type of application Coriolis flow meters is par-
vibrations. ticularly advantageous over conventional ones?
& Not suitable for flow measurement involving slug & General-purpose gas or liquid flow.
flow of two-phase gas–liquid systems. Entrained air & Blending ingredients and additives.
or gases in liquid flow measurement could cause & Conducting a primary check on secondary flow
significant errors in measurements. They under pre- meters.
dict the actual flow rates at low void fractions & Metering natural gas consumption.
and over predict flows at high void fractions of
& Monitoring such fluids as syrups, oils, suspensions,
entrained gases. Such errors could be as high as
and pharmaceuticals.
20% or more when entrained gases or low flow rates
& True mass flow capability of Coriolis meters provide
are involved.
accurate flow requirement of expensiveraw materials
& Over sized meters could result in low flow rates
without wastage, for example, detergents, shampoos,
which reduce Coriolis effect and hence accuracy of
and toothpastes.