Page 64 - Applied Process Design for Chemical and Petrochemical Plants Volume I

Fluid Flow

The flow of compressible and non-compressible liq- method. Then, when such programs are purchased by
uids, gases, vapors, suspensions, slurries and many other others, or used in-house by others, some serious and
fluid systems has received sufficient study to allow definite erroneous design results can be generated. On the other
evaluation of conditions for a variety of process situations hand, many design procedures that are complicated and
for Newtonian fluids. For the non-Newtonian fluids, con- require successive approximation (such as distillation)
siderable data is available. However, its correlation is not but are properly programmed, can be extremely valuable
as broad in application, due to the significant influence of to the design engineers.
physical and rheological properties. This presentation is Except as a limited reference, computer programs are
limited to Newtonian systems, except where noted. not emphasized anywhere in these volumes. Instead,
Primary emphasis is given to flow through circular important mechanical details are given to emphasize the
pipes or tubes since this is the usual means of movement mechanical application of the process requirements (see
of gases and liquids in process plants. Flow through duct Figure 2-2). Many of these details are essential to the prop-
systems is treated with the fan section of Compression in er functioning of the process in the hardware. For two funda-
Volume 3. mental aspects of fluid flow, see Figures 2-1 and 2-3.

Scope
The basis for single-phase and some two-phase friction
The scope of this chapter emphasizes applied design
techniques for 85%2 of the usual situations occurring in loss (pressure drop) for fluid flow follows the Darcy and
the design and evaluation of chemical and petrochemical Fanning concepts. The exact transition from laminar or
plants for pressure and vacuum systems (see Figure 2-1). viscous flow to the turbulent condition is variously identi-
Whereas computer methods have been developed to fied as between a Reynolds number of 2000 and 4000.
handle many of the methods described here, it is the For an illustration of a portion of a plant piping system
intent of this chapter to present only design methods per (see Figure 2-2).
se that may be applied to computer programming. First,
however, a thorough understanding of design methods, Incompressible Flow
their fundamental variations and limitations is critical.
There is a real danger in losing sight of the required For liquids, laminar or turbulent flow in a pipe [31
results of a calculation when the computer program is
“hidden” from the user and the user becomes too enam- pfv 2L
ored with the fact that the calculations were made on a AP = 144D (2g)’ lbs / square in. (2-1)
computer. A good designer must know the design details
built into the computer program before “blindly” using it
and its “cold” results. There are many programs for or,
process design that actually give incorrect results because
the programmer was not sufficiently familiar with the h, = - fluid flowing
e
,
ft
of
design procedures and end limits/limitations of the D (2g)
52