Logic, Science and Beyond

May 27, 2003

We're all under pressure to get results. But how?

Developing a clear understanding of processes and systems is an important step. To maximize yields and minimize problems ," and get the desired results ," plant operators must seek to understand every idiosyncrasy of their unique processes.

Of course, modeling tools are available to help. Modeling can take several forms, including computer simulation and flow visualization. Computer simulations continue to de-velop. Some companies have 3D projection rooms for viewing solutions.

Modeling laminar- flow is not difficult because now comp-uters and computational techniques have advanced significantly. Turbulent-flow modeling also has come a long way through large eddy simulation (LES) and direct numerical simulations (DNS). Used in weather forecasting, LES calculates the behavior of large flow structures from spaced-averaged equations of motion. The small turbulence is modeled. DNS uses the instantaneous equations of motion directly.

LES and DNS provide information that was unavailable with other earlier modeling techniques. Turbulence was perhaps the most challenging scientific problem of the 20th century. Now light can be seen at the end of the tunnel. Computational techniques now are solving ," and will continue to solve ," turbulence-related problems in the 21st century.

Computer simulation remains difficult in four areas: geometric characterization, boundary conditions, multiphase systems and solids flow. For example, the great number of different geometries used in processing equipment makes translation into computer simulations extremely challenging. Moreover, modest changes in geometry often can upset a simulation. In addition, boundary conditions, which fix a solution, simply are not known.

However, academic researchers, computational companies such as Fluent and large corporations such as DuPont continue to work on solutions. Perhaps one day their efforts will lead to complete simulations of all processes, not just a few.

Modeling can go well beyond computer simulation through flow visualization and cold flow studies. Flow visualization involves a simple method for photographing the flow of a process. Cold flow studies simulate an active process; the recreated process is not active.

Side-by-side flow visualization is very useful in rapid equipment comparisons. The technique is like test-driving two automobiles at the same time. If you have not tried this technique, you are in for a wonderful surprise.

You probably should not limit yourself to one type of modeling technique. Your process is likely to follow many paths. You might benefit from multiple models, too.

Beyond modeling

Beware of falling into a trap where you rely solely on mathematical or technical models, however. The attainment of results often requires more than logic and science. Not everything is black and white.

For example, the "design of experiments" technique, which groups various statistical tools and methods, establishes cause and effect between seemingly unconnected process variables. Analogies, intuition and other factors also come into play. Use your whole "mental toolkit" to solve problems and get the results you need.

My students regularly must identify solutions to process problems. They too often give me "extraordinary" answers ," pipe diameters approaching 1 mile, flows moving at 1 micron per year. I never cease to be astonished by the most commonly uttered answer when I question their results: "That is what the equations gave me."

Reflection is required for learning. Yes, you can plug numbers into an equation and play pretend engineering. However, almost anyone can do that. Engineering comes from interpretation of the results, which is the result of reflection on reality.

Use your whole brain. Holistic thinking is critical. Include everything ," instinct, intuition, gut feelings, computer simulations, experience ," to think beyond the answers provided by each individual result. Then look to the synergy that arises from the combination of the results. That's where understanding lies.

My father loved to tell a story about a college lecturer whose specialty was process design. After a presentation at a major university, the students had an opportunity to ask questions. One question was: "What level of mathematics should an engineer have?"

His response was that he had built chemical plants all over the world using simple arithmetic. He never learned calculus, nor did he need it.

He was, however, a master at process reflection ," using scientific tools, experience, instinct and more to reach an understanding and design the best plant possible.

Makes sense to me.

Tatterson is a technical editor for

Chemical Processing. He is a professor at North Carolina A&T State University in Greensboro. Contact him at [email protected]. He also teaches short courses for the Center for Professional Advancement, www.cfpa.com.

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