Introduction
Whilst this may not be as obvious to today’s students of the subject as it should be, chemical engineering is a kind of engineering, rather than a branch of chemistry.
Similarly, professional engineering design practice has next to nothing to do with the thing called process design in many university chemical engineering departments.
I will cover the reasons for this elsewhere, but first let’s start by dispelling some confusion, by clearing up what engineering is (and is not), and what design is all about.
What is engineering?
I still feel glad to emphasize the duty, the defining characteristic of the pure scientist—probably to be found working in universities—who commit themselves absolutely to specialized goals, to seek the purest manifestation of any possible phenomenon that they are investigating, to create laboratories that are far more controlled than you would ever find in industry, and to ignore any constraints imposed by, as it were, realism.
Further down the scale, people who understand and want to exploit results of basic science have to do a great deal more work to adapt and select the results, and combine the results from different sources, to produce something that is applicable, useful, and profitable on an acceptable time scale.
C.A.R. Hoare
Engineers are those people “further down the scale” as Hoare the classicist and philosopher puts it, although I disagree that we “exploit the results of basic science.” Our profession stands on other foundations, though you may have been taught something different in university.
In academia there is almost universal confusion between mathematics, applied mathematics, science, applied science, engineering science, and engineering. Allow me to unconfuse anyone so confused before we get started:
Mathematics is a branch of philosophy. It is a human construction, with no empirical foundation. It is made of ideas, and has nothing to do with reality. It is only “true” within its own conventions. There is no such thing in nature as a true circle, and even arithmetic (despite its great utility) is not factually based.
Applied mathematics uses mathematical tools to address some real problem. This is the way engineers use mathematics, but many engineers use English too. Engineering is no more applied mathematics than it is applied English.
Science is the activity of trying to understand natural phenomena. The activity is rather less doctrinaire and rigid than philosophers of science would have us believe, and may well not follow what they call the scientific method, but it is about explaining and perhaps predicting natural phenomena.
Applied science is the application of scientific principles to natural phenomena to solve some real-world problem. Engineers might do this (though mostly they do not) but that doesn’t make it engineering.
Engineering science is the application of scientific principles to the study of engineering artifacts. The classic example of this is thermodynamics, invented to explain the steam engine, which was developed without supporting science.
Science owes more to the steam engine than the steam engine owes to Science.
L.J. Henderson
This is the kind of science which engineers tend to apply. It is the product of the application of science to the things engineers work with, artificial constructions rather than nature.
Engineering is a completely different kind of thing from all preceding categories. It is the profession of imagining and bringing into being a completely new artifact which achieves a specified aim safely, cost-effectively, and robustly.
It may make use of mathematics and science, but so does medicine if we substitute the congruent “medical science” for “engineering science.” If engineering was simply the application of these subjects, we could have a more-or-less common first and second year to medical and engineering courses, never mind the various engineering disciplines.
Now that we are clear about what engineering is, let us consider what design is.
What is design?
Rather than being some exotic province of polo-necked professionals, the ability to design is a natural human ability. Designers imagine an improvement on reality as it is, we think of a number of ways we might achieve the improvement, we select one of them, and we transmit our intention to those who are to realize our plan. The documents with which we transmit our intentions are, however, just a means to the ultimate end of design—the improvement on reality itself.
I will discuss in this book a rather specialized version of this ability, but we should not lose sight of the fact that design is in essence the same process, whether we are designing a process plant, a vacuum cleaner, or a wedding cake.
Designers take a real-world problem on which someone is willing to expend resources to resolve. They imagine solutions to that problem, choose one of those solutions based on some set of criteria, and provide a description of the solution to the craftsmen who will realize it. If they miss this last stage and if the design is not realized, they will never know whether it would have worked as they had hoped.
All designers need to consider the resource implications of their choices, the likelihood that their solution will be fit for the purpose for which it is intended, and whether it will be safe even if it not used exactly as intended.
If engineers bring a little more rigor to their decision making than cake designers, it is because an engineer’s design choices can have life and death implications, and almost always involve very large financial commitments.
So how does engineering design differ from other kinds of design?