It has been said many times in one form or another that there is nothing more understandable and practical than
a simple theory. As engineers and scientists, we are always looking for a simple theory, law or equation in every
engineering science to explain behaviours and to use as design tools. Examples of such simple theories are Bernoulli’s
law in fluid mechanics , the first and second laws in thermodynamics , Fourier’s law in conduction heat transfer
 and Newton’s law for convective heat transfer .
Design, on the other hand, has been viewed by many as the subject (I am specifically not using the word “science”)
which is an art in which the engineering sciences are creatively synthesised and where industry experience is preferable
and in many cases essential. It may involve considerable research, thought, modelling, interactive adjustment and
redesign. What it surely is not – is the application of a simple theory.
Because of the lack of industry experience, many university professors find it challenging to teach design to engineering
students. Optimisation methods  have, however, been developed recently with many objective functions,
which now make it possible to conduct designs [6–8] that rely on optimisation procedures. The objective functions
now include not only “engineering science parameters” such as dimensions, temperatures and heat transfer rates, but
also parameters that quantify parameters such as economics, safety, aesthetic, manufacturability, maintainability and
impact on the environment. It shows that design is in many cases not an art anymore and that very good designs can be
produced by people with very little industry experience and that optimum designs should be driven by a simple law.
However, all these designs are not about the time direction of the “movie” of design generation and evolution and it
is not about optimally end design, destiny or entropy. The concept that constructal law defines in physics is “design”
(configuration) as a phenomenon in time.