Black box approach

black box
A generic black box: the type of view used to model systems in thermodynamics.
In thermodynamics, the black box approach or "black box thermodynamics" is black box systems model that refers to the premise or conceptualization that according to the classical thermodynamic viewpoint systems, whatever the form or composition, can be studied or conceptualized as “black boxes”, about which the container contents are irrelevant, but ones whose nature can be quantified by boundary measurements.

The etymology of the term "black box" used in thermodynamics seems to be a late 19th century term use, although the exact source remains to be tracked down. The term “black box” may be a linguist cross over (similar to the way the 17th century term “perfect vacuum” was transformed linguistically into perfect gas, then perfect ideal gas, then ideal gas, as it is known in modern terms) derived from Gustav Kirchhoff and his 19th century radiation studies in his so-called “black box” or hollow body, covered in black soot, whose heated walls emitted or absorbed radiation. [5] This gave way to the idea of the black body, the radiation thermodynamics, and then quantum mechanics (or quantum thermodynamics), all generally introduced by Max Planck.

In 1925, Gilbert Lewis was discussing the thermodynamics of a "box of unknown contents" with two wires protruding, having a known voltage difference, known current drawn from the wires, and known amount of heat given off. [8]

In 1951, the phrase “thermodynamic analysis is essentially ‘black-body’ analysis”, had entered the engineering vernacular, and soon thereafter become a stable fixture of thermodynamics jargon. [6]

In 1982, plastics engineer Harry Hull published his An Approach to Rheology through Multivariable Thermodynamics, with the subtitle Inside the Thermodynamic Black Box, which he explains in namesake. [4]

In 1985, American physical chemist George Scott comments in his Atoms of the Living Flame: an Odyssey into Ethics and the Physical Chemistry of Free Will, that: [7]

“The laws of thermodynamics, we assume, apply to the whole biosphere of life in exactly the same way they apply to machinery and black boxes.”
Thermodynamics and Control of Biological Free Energy Transduction (1987)
A depiction of the “black box” approach on Hans Westerhoff and Karel Dam’s 1987 Thermodynamics and Control of Biological Free Energy Transduction, wherein the view different “biological” volumes, from a thermodynamic point of view, as a black box. [9]

A variation of this was expressed by Venezuelan-born English thermodynamicist Erich Muller who stated in his 1998 article “Human Societies: a Curious Application of Thermodynamics: [3]

“Curiously, none of the founding fathers of thermodynamics, Watt, Carnot, Joule, Clausius, Gibbs, among others, had an appreciable comprehension of the exact constitution of matter. The relations and results obtained in early classical thermodynamics are independent of the actual nature of the systems studied and are indeed very general. This happy occurrence is the reason we can extrapolate the fundamental concepts of thermodynamics to other modern disciplines.”

To quote from a recent 2006 article on the mathematics of thermodynamics: [2]

“Thermodynamics is unique among physical and chemical descriptions of our surroundings in that it does not rely on a detailed knowledge of any interior structure of the systems to which it pertains but rather treats such systems as ‘black boxes’ whose equilibrium states are determined by the surroundings with which they can coexist and which can be described by a few parameters. This feature assures that the theory holds true when the system is a collection of molecules, or a beaker of water, or a black hole.”

In 2010, mechanical engineer Robert Balmer states in his 2010 Modern Engineering Thermodynamics textbook: [1]

“One of the most powerful aspects of thermodynamics is its ‘black box’ approach to system analysis. It is not necessary to know what takes place inside the box, it is necessary only to watch the box’s boundaries and see what, and how much, crosses them.”

(add discussion)

To note, although the black box conceptualization is a good introductory way to initially dig into a thermodynamic problem, there are a number of areas where this model begins to become non-applicable.

Firstly, on one hand, yes the "black box" model is universal in that it is founded on French physicist Sadi Carnot's 1824 statement that thermodynamics is the science of the study of "any" working substance, whatever it may be and by whatever means it may be operated; a statement which was based on Boerhaave's law (1720) of the premise that any body of the universe can be made to expand or contract in volume, by the addition or removal of heat.

Secondly, however, on the other had, an actually reading of German physicist Rudolf Clausius' 1865 The Mechanical Theory of Heat, which is the founding book of thermodynamics, will show that a number of formulations in thermodynamics are based on speculations about the work the molecules of the system do on each other, i.e. internal work, as well as other derivations, such as in the forces that brought the system to its present internal energy configuration.

Moreover, in chemical thermodynamics, and in animate thermodynamics, all the way down to single particle thermodynamics, internal system descriptions become the key focus, where factors such as bond energy, energy coupling, transformation content energy, etc., become focused topics of discussion and theory development.

In sum, there are two sides to the so-called black box idiom of system modeling, albeit the black box model is a good starting point, but not the say all.

1. Balmer, Robert T. (2010). Modern Engineering Thermodynamics (black box, pg. 33). Academic Press.
2. Salamon, Peter, Andresen, Bjarne, Nulton, James, and Konopka, Andrzej J. (2006). “The Mathematical Structure of Thermodynamics”,
3. Müller, Erich. A. (1998). “Human Societies: a Curious Application of Thermodynamics" (scan) (abstract) Chemical Engineering Education, Vol. 1, No. 3, Summer.
4. Hull, Harry H. (1982). An Approach to Rheology through Multivariable Thermodynamics or Inside the Thermodynamic Black Box (black box, 4+ pgs). Publisher.
5. Untermeyer, Louis. (1955). Makers of the Modern World (pg. 271). Simon and Schuster.
6. Anon. (1951). “Article”, Engineer Bulletin (pg. 10). Purdue University.
7. Scott, George P. (1985). Atoms of the Living Flame: an Odyssey into Ethics and the Physical Chemistry of Free Will (thermodynamics, pgs. 181-84; ubiquitous quote: pg. 265). University Press of America.
8. Lewis, Gilbert N. (1925). The Anatomy of Science (pg. 141). Silliman Lectures; Yale University Press, 1926.
9. Westerhoff, Hans V. and Dam van, Karel. (1987). Thermodynamics and Control of Biological Free Energy Transduction. Elsevier.

External links
‚óŹ Black box – Wikipedia.

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