This sixth edition of Rules of Thumb for Chemical Engineers continues the transition that started when I took over the authorship from Carl Branan for the fifth edition, published in 2012. Now much more than a concise “manual of quick, accurate solutions to everyday process engineering problems”, I strive to provide process and project engineers the information you need to address each of the various topics. This includes lists of proven results (the “rules of thumb”) and equations (sometimes replacing nomograms from the early editions) as always. But it also means giving context for the subject in the introduction to each chapter, and comparing alternatives in the body of the text.
I’ve reorganized the chapter sequence for the sixth edition, and added two new ones: Filtration and Bioprocessing. Safety takes a more prominent position, being the both the first chapter and leading off in many of the equipment chapters. I’ve corrected a few errors, and added new and refreshed material throughout.
In The ABCs of How We Learn: 26 Scientifically Proven Approaches, How They Work, and When to Use Them, Schwartz et. al. say, "For judgment under uncertainty, people should use probabilistic reasoning. Instead, people typically draw upon comfortable heuristics. A heuristic is a rule of thumb or judgmental shortcut that works most of the time. In contrast, an algorithm yields a correct answer every time."
We should apply critical thinking to our work to challenge our assumptions and reality check the results. We should explore the effect of changing our input values (sensitivity testing), and perform “what if” analyses to our designs (e.g., “what happens if the cooling water temperature is warmer in the summer and colder in the winter?”). And we should run calculations instead of relying on tabular data we know enough about our equipment and the operating conditions to satisfy the calculation’s input requirements.
Whether the answers come from dynamic process simulations or detailed calculations, or tabulated rules of thumb, I urge you to document the methods and assumptions that lead to the results. You could be reassigned in the middle of the project, leave for a new job, become disabled and unable to contribute, or worse. My first rule of thumb in this book is this: Document your work so that others could pick it up and continue, if needed. I call it the “Hit by a Bus” rule of thumb.
Hall, Stephen M., Rules of Thumb for Chemical Engineers, Sixth Edition, Elsevier, London, 2017