Page 64 - FoodFocusThailand No.211 OCTOBER 2023

SOURCE OF ENGINEER

fluid to one single meter, but this is only applicable if all pipes
are of the same type.
The pressure rate to be measured also plays a major
role in the selection of flow meters. For example, since the
measurement of supercritical carbon dioxide flow rate
requires pressure-resistant materials, the strength, price,
weight, and size of the chosen flow meter must be taken into
account.
Most meters require pipework to be set up both upstream
and downstream. The selection of meters should take into
consideration factors related to installation areas, such as
room for maintenance. If the meter needs to be occasionally
removed for calibration, careful selection is required. For
instance, an ultrasonic meter requires annual calibration, but
orifice plate only requires on-site inspection for calibration
of differential pressure transmitter. In these cases, varying
factors, such as convenience and operational adequacy,
need to be considered.
accuracy than that of other fluid types with lower value or less For meter installation, additional accessories that work
strict safety requirements: for instance, wastewater being compatibly with each specific meter may be necessary. These
discharged to a treatment pond may not require highly accurate may include, for example, temperature and pressure meters,
measurement. densitometers, valves, and compatible actuators for valve
Next variable is the state of fluids in the system, such as opening and closing. Furthermore, the mixing system for
two-phase wet gas or multiphase mixture. Pressure range, fluid or liquid in pipework also need to be taken into account.
flow rate range, measurement temperature range, density For instance, if the fluid has multiple components, a static
range, and viscosity range will affect Reynolds number values mixer, an inline mixer, or a ribbon mixer may be a viable
as well as subsequent selection of an adequate flow meter. choice as it can facilitate the mixing process and ensure that
Hence, density, viscosity, and Reynolds number, which the measurement of flow rate is carried out more accurately.
are closely related to the environmental conditions in In addition to said guidelines, the conditions of relevant
which the measurement is conducted, are three pivotal procedure, physical conditions, environmental conditions,
factors that will lead to proper selection of flow meters. practical application, and budget need to be considered to
Moreover, any measurement in a two-phase flow constitutes ensure the best selection of functionally ideal meters.
more challenges than that in a single-phase flow. This is seen, Furthermore, operation teams and users should also be
for instance, when wet saturated steam is measured in an consulted to ensure that all factors are deliberately and
environment with the combined presence of vapor, liquid, and thoroughly considered.
reduced pressure. Another example is when the vaporization
of saturated liquid partially produces gas, which may affect Types of Industrial Valves
flow measuring process. Therefore, pressure and dew point Industrial valves can be classified into 3 groups according
are essential points of consideration in the selection of flow to their opening and closing mechanisms.
meters. Furthermore, if the fluid has corrosive properties, the 1) Shutoff valves or on-off valves include, for instance,
chosen flow meter should be made of resistant material. gate or water gate valves and ball valves.
The conditions of the metering process also determine the 2) Control valves feature an opening mechanism, which
final specs of a flow meter. One of these conditions is, for can be adjusted from 0 to 100 percent, to control and achieve
instance, the sensitivity of flow meter toward physical properties desired flow rate. These include, for example, globe valve,
and Reynolds number of the measured range. To be taken ball valve, butterfly valve, and plug valve.
into consideration as well is the turndown ratio, which yields 3) Check valves for control of flow direction include,
linear output and is known as range ability, flow range, or ratio for instance, wafer check valve, piston check valve, pressure
of the maximum capacity of measurement to the minimum check valve, and swing check valve.
requirement for measurement. For example, if the range of
flow rate is 0 – 100 m /min and the measured value at accuracy Factors for Selection of Functionally Viable
3
is 5 m /min, the turndown ratio is, therefore, 20:1. Valves
3
Additionally, in case of multiple streams, such as when a Valve selection can be based on real operations. If opening
fluid travels through multiple pipelines toward the main one, and closing are required, a valve with vertical opening and
a separate flow meter may need to be installed in each closing mechanism, such as gate valve, may be a better
individual pipeline. Alternatively, a bypass pipeline may be choice as it may be more functionally suitable for such
added to each pipeline to create a pathway that guides the operation than a delay valve with partial opening mechanism,

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