Chemical Engineering October 2021 - 37

analysis, slurry modeling,
pulsation analysis,
and more.
What type of information
is needed to build a
flow analysis model of a
pump and piping system?
The easy answer is
that if it's in the system,
include it in the model.
Let's start with the fluid
FIGURE 3. Shown here is a piping system flow-analysis model of a
raw brine injection system with five vertical pumps in parallel and
five horizontal pumps located elsewhere throughout the system
accomplish involve system scale-up
evaluation,
pressure/flow/temperature
distribution, design feasibility
analysis, heat transfer, system operation
troubleshooting and more.
It is also important to quantify pipe
system scaling/fouling, pump degradation,
code compliance, cost
properties. To capture
the system hydraulics,
the fluid density and viscosity
are needed as a
minimum. Vapor pressure
is important to identify
if cavitation is happening
anywhere in the
system when compared
to the static pressure that
changes throughout the
system. To evaluate heat
transfer in the system,
thermodynamic properties
such as heat capacity,
thermal conductivity
and enthalpy are needed.
If you are modeling compressible-flow
situations,
other parameters are needed like the
universal gas constant, compressibility
factor, specific heat ratio, entropy
and sonic speed. For a waterhammer
simulation, you also need the bulk
modulus of elasticity of the fluid, which
is an important parameter in the calculation
of the wave speed. The wave
speed dictates how fast a transient
pressure wave in a surge event will
propagate through the system. Overall,
fluid properties are important, and
they need to be accurate.
Information
needed
to
model
piping includes the inner diameter,
length, frictional information such as
roughness, Hazen-Williams factor
and elevation changes. This is minimal
detail needed for hydraulic calculations.
More sophistication can
be included where the inner diameter
can be determined from a type
of material (like steel, HDE, ductile,
iron and so on), nominal size, and
the schedule or type that is coupled
with the wall thickness. This helps
match a model to reality a bit more
and may be easier than entering an
inner diameter directly.
Boundary condition information is
required so that the system of fluid
dynamic equations can be solved
for the piping network. In simplest
terms, either a known flow rate
boundary OR a known pressure
boundary is required. Temperature
would be needed for heat transfer
calculations. In a flow simulation, it
is not possible to specify both flow
and pressure at a boundary, because
this would over-constrain the
system and the fluid dynamic equations
would have nothing to solve for.
Therefore, if you specify a pressure
boundary, the flowrate from it will be
calculated. If you specify a flowrate
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OCTOBER 2021
37
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Chemical Engineering October 2021

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