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THERMODYNAMICS OF TIME AND SPACE
In our introduction to the physics of green design, we introduced a number
of thermodynamic concepts. All engineering disciplines must be grounded in
thermodynamics, but chemical engineers are arguably those who deal with it
incessantly. It should not come as a surprise that chemical engineering has been
a leader in green approaches. After all, “chemical engineering is a broad disci-
pline dealing with processes (industrial and natural) involving the transformation
(chemical, biological, or physical) of matter or energy into forms useful for
mankind, economically and without compromising environment, safety, or fi-
nite resources.”
4
In fact, chemical engineering's central integrating theme is the
reactor. In the reactor we can visualize mass and energy balances. Thus, it is
impossible to think about a design without making use of chemical engineering
concepts.
The reactors that most chemical engineers work with are at the industrial
scale. This, of course, includes tanks and vats that have certain materials and
energy that enters and certain, but different, forms and amounts of materials and
energy that leave. In environmental engineering, these thermodynamic behaviors
also occur but over a widely diverse domain, at scales ranging from subcellular
to global (see Fig. 4.1). For example, the processes that lead to a contaminant
month
corporation
week
site
day
plant
h
apparatus
min
Figure 4.1
Scales and
complexities of reactors.
Note
: ms, millisecond; ns, nanosecond;
ps, picosecond.
Adapted from W. Marquardt, L. von
Wedel, and B. Bayer, “Perspectives on
lifecycle process modeling,” in
Foundations of Computer-Aided
Process Design
,M.F.Malone,J.A.
Trainham, and B. Carnahan, Eds.,
AIChE Symposium Series 323
, Vol. 96,
2000, pp. 192-214.
single and
multiphase systems
s
particles,
thin films
ms
small
intermediate
large
molecule
clusters
Chemical scale
ns
molecules
ps
1 pm
1nm
1 mm
1 cm
1 m
1km
Length scale
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