International Journal of Heat and Mass Transfer 55 (2012) 4929–4935

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International Journal of Heat and Mass Transfer

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Why we want power: Economics is physics

In view of the interest in ‘‘sustainability’’ and resuscitating theglobal economy. I propose a physics [1,2] perspective on howpower is generated and flows on the earth’s surface. Power flowswith predictable ‘‘design’’, which means configuration, pattern,rhythm and geometry. The design of the flow of power grows inan evolutionary manner, in time, as thicker and more efficientstreams that serve, empower and liberate humanity over greaterterritories.

A physics basis for why we need power is necessary, because to-day’s focus on efficiency and conservation gives the false impres-sion that the future belongs to burning less fuel, uniformity andbelt tightening, particularly in the advanced countries where mostof the power is being generated and consumed. It is a timely topicfor science because until recently our energy doctrine said abso-lutely nothing about how the design of power generation shouldevolve on earth and in time.

1. The flow of power: nonuniform, vascular, and growing

Two facts stand out. The first is that fuel is being burned non-uniformly on earth, and consequently the generated power is con-sumed (dissipated) nonuniformly. One example is Fig. 1: thepattern of air mass transit on earth in 2002 [3]. Humanity sweepsthe globe nonuniformly, as a vascular design like a river basin, withfew large and many small streams. This is reality, because Fig. 1 isbased on measurements of the persistent condensation trails be-hind aircraft.

Our movement is a living shell—the human sphere—that thriveson the whole globe as part of the biosphere. It is like the vascula-ture that grows on the inside surface of the egg shell during thedevelopment of the chicken embryo. This organism has a heartwith two chambers, Europe and North America, several importantorgans in the Far East, and a vascular tissue that covers the globe.In 2050 the organism will have the same structure but all thestreams will be thicker.

The arrow of time points toward more fuel and food consumed,and more power produced and spent. Throughout human history,power was produced by people and animals, with medieval contri-butions from windmills and water wheels. The big change was thedevelopment of heat engines, which use fuel not food (Fig. 2). Theheat engines spurred two revolutions, the industrialization andelectrification of the globe, and the empowering of science withan entirely new discipline: thermodynamics.

The second fact is that the technology of power generation con-tinues to evolve toward greater efficiencies (Fig. 2, middle) [4].Every stream in every machine is being configured and reconfigured

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to flow with progressively fewer losses, just like every rivulet in theconstantly evolving river basin. From this never ending struggleemerges the design—the flow configuration that keeps on changing.Steam engines were joined by many designs of power plants in thelate 1800s and the 1900s: steam-turbine, gas-turbine, internal com-bustion, hydroelectric, nuclear, solar, aeolian, ocean thermal, oceanwaves, etc. Country roads were joined by railroads, highways and airroutes. Fuels too have become more diverse, from coal and waterfalls, to petroleum, nuclear fuel, solar heating and the wind. Thenew did not eliminate the old: the new came in addition to theold, and together they enhanced the global flow.

2. Beliefs

There is the belief that conservation (the use of less fuel) comesfrom increasing efficiency. True is that from every kilogram of fuelthe power plant produces two energy streams, a stream of work forour use, and a stream of heat that must be rejected to the ambient.Higher efficiency means more work (and less heat rejected) fromthe consumed unit of fuel. When the work requirement is speci-fied, higher efficiency also means less fuel consumption, and lessheat dumped into the environment during the generation of workfrom fuel.

It all makes sense, and our need to extract more work from fuelmakes the pursuit of higher efficiency a social virtue, because wethink that we help the environment not just our standard of living.But, does the pursuit of higher efficiency lead to less fuel consump-tion and less heat dumped into the environment?

No, and the evidence is massive and in complete accord withphysics. The direction has been one way, more power for moreindividuals over larger territories, and more power for every indi-vidual. This means greater fuel use globally, not less. When onesource of power proved insufficient, a new one was added, in avery clear direction over time: from work animals to water wheelsand heat engines, all in a growing river basin of power flow and use(dissipation) on earth.

Why does the evidence contradict the popular belief? The reasonis that so far the focus of energy science has been on the generationof power, not on what happens after. Never questioned was why weneed power, and where all this power goes. Clearly, not even themost efficient among us are saving anything in a ‘‘power bank’’.

3. Why power?

The need to have power was written on the wall from the begin-ning, but not in the laws of thermodynamics. Matthew Boulton, the

Fig. 1. Where aircraft flew in 2002 (top) and where aircraft will fly in 2050 (bottom): the persistent condensation trail coverage for the entire aviation fleet [3].

4930 A. Bejan/ International Journal of Heat and Mass Transfer 55 (2012) 4929–4935

business manager and partner of James Watt, declared to a visitorto the Boulton-Watt Works in 1776: ‘‘I sell here, Sir, what all theworld desires to have—POWER’’.

Sadi Carnot spelled out the prescription for how to change theconfigurations of future engines so that they produce more powerper unit of fuel burnt. His view is the doctrine of energy engineer-ing today: avoid friction of all types, heat transfer across finite tem-perature differences, heat leaks, shocks, and mixing [5].

In spite of this teaching, there was no law in classical thermody-namics that called for ‘‘design’’ and ‘‘design change’’ and ‘‘designevolution’’ in any thermodynamic system—not in animal designevolution, and not in all the other evolutionary designs (geophys-ics, technology, social dynamics). Yet, design and design evolutionhappen, and that is nature (physics).

4. The engine + brake design of nature

Fuels and power plants are only half of the picture. The otherhalf is what happens to the generated power. Every bit of thepower is destroyed (dissipated) instantly and forever. The powerthat moves the body of the animal, the vehicle, the constructionmaterial and the wheels of manufacturing is dissipated entirelyas heat into the ambient.

The movement dissipates the useful energy derived from thefuel (Fig. 3, top). Muscles and engines are just intermediaries,and they represent the biosphere, as a natural design inserted in

the path of the heat currents that before the biosphere were flow-ing from fires straight into the ambient.

The visible result of the consumption of fuel is the movement—the rearranging of mass on the horizontal landscape. This is thephysics phenomenon summarized by the Constructal law: the nat-ural tendency of all flow systems to change their configurations intime (to generate ‘‘design’’) so that they flow more and more easily[1,2]. Without fuel consumption, nothing moves, not our stuff, andnot the stuff of the environment. Without movement there is nodesign in nature.

Everything that moves is an engine connected to a brake. Theearth too is an engine + brake system (Fig. 3, bottom). The fuel issolar heating, and the heat rejection is the thermal radiation tothe cold sky. The heat inflow equals the heat outflow. Betweenthe inflow and the outflow hangs the globe, which is a tapestryof many moving designs, all rubbing in ways that resist movement:atmospheric and oceanic currents, river basins, forests, heat leaksfrom burning fires and animal and human movement. Life is all thisevolving movement, animate and inanimate [1]. The constantlymorphing global vasculature is climate: temperature zones, windspeed, diurnal temperature change, and more [6,7].

Economic activity represents the movement of all the streamsof a live society: people, goods, information, communications,and everything that flows inside the live human bodies and therunning engines that drive this movement. This is the physics do-main in which economics belongs, and it is made evident by Fig. 4.

Fig. 2. Animal and engineered power in the evolution of civilization. The efficien-cies of heat engines have been increasing in time, and the more efficient are bigger.The efficiency g is _W= _QH , cf. Fig. 3, middle. The second law efficiency gII is the ratio_W= _Wrev , where _Wrev is the power generated with the same heat input _QH in the

theoretical limit of reversible operation.

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The annual domestic economic activity of a country (the GrossDomestic Product, or DGP) is proportional to the amount of fuelconsumed annually in the country [1]. The amount of fuel con-sumed is proportional to the total movement that occurs on thelandscape, which is the product ML—the mass M moved to the dis-tance L (cf. Fig. 3 caption). Fuel consumption sustains our civiliza-tion and standard of living, and increases our persistence (i.e. life)in time on earth (Fig. 5).

Wealth is physics. More economic activity means more fuelconsumption, not less, and more fuel consumption means moremovement on the landscape. Improvements in efficiency lead tomore fuel consumption, not to ‘‘fuel conservation’’. The improve-ments are akin to the removal of obstacles to flow, after whichthe flow increases. This answers an old puzzle known in economicsas Jevon’s paradox [9], which was the observation that the moreefficient use of coal in the industrialized world in the 1800s actu-ally increased the consumption of coal and other resources, insteadof ‘‘saving’’ them.

Any design change is evaluated on the same basis, in economics,engineering, and animate and inanimate systems. If it facilitates glo-bal flow, the design change (the invention) is adopted and survives.This is particularly evident in economics. The invention of moneywas a huge improvement in facilitating the flow of traded goods—it was huge relative to trading in nature. Regional free trade agree-ments between countries lead to increased economic activity. Thereplacement of bank tellers with ATMs tells the same story of great-er economic activity through flow designs with fewer obstacles.

5. Why ‘‘more power’’?

Why should our use of power increase in time? This is a hugelyimportant question, because our planet is finite and receives stea-dy (constant) heating from the sun. This heat current drives every-thing that moves on the landscape, river basins and the movementof humanity and animal migrations. It drives it all the same way,with design evolution in the constructal-law direction.

Under this steady forcing scenario, the river basin forms thisway: the rain falls steadily (i.e. the total water flow rate is constant,as it falls on the ground), but the flow architecture improves overtime. It evolves from a wet marsh all over the plain to a crisp de-sign of river channels that become more and more polished. Theevolution of this design never ends, and consequently the flowrates increase. We can call this one-way tendency ‘‘channeling’’,and its effect is visible as more and more flow in every channel,even if the rain were to remain steady. In the movement of human-ity, the fuel ‘‘rain’’ is not steady, in fact, it intensifies as technolo-gies evolve, and as the collecting flows increase (fuel science,geophysics, exploration, extraction, mining, processing).

The flow rates of the channels increase forever, but everyspreading flow has its own S curve [10,11], Fig. 6. The increase isinitially slow, then it becomes fast, and finally it slows down. Theincrease does not end, unless the rain stops, as in the seasonalspreading of the Okavango river delta in the Kalahari Desert. Thereis no end to this design evolution, no cataclysm, no disaster. Thereis just hitting the wall, slowly, where there is no wall.

Getting smarter is the Constructal law in action. We invent newscience and technology and business practices to move us and ourstuff more easily. Science is a design to guide motion, to make itflow easier. Our movement as a civilization is no different than riv-er basin evolution. We are the evolving human-and-machine spe-cies, which is a flow system immensely bigger and morepowerful than the naked human body. More and more of the flow-ing landscape (namely fuels, food, driven by the steady sun) is col-lected by us to flow through us, to drive our flow. We are the‘‘channels’’ and we are moving more and more stuff. More move-ment means more fuel used over time.

The direction is one way, toward more. But the rate of increaseis destined to diminish steadily because every spreading move-ment has a S-shaped history [10,11]. Every technology is an evolv-ing river basin on the landscape. Think of the railroads: they spreadtheir freight in S curve fashion on the globe, and so did the fuelconsumed for driving all the trains. Today this technology isold—it has hit the wall, softly, but railroads are still being builtwhere their flow architecture has not spread yet.

Fig. 3. The ‘‘engine + brake’’ systems of civilization dissipate the work produced with food and fuel, and reject it as heat to the ambient. The produced work is destroyed inproportion with the force that resists the movement times the distance traveled (L). The force is proportional to the weight of the mass (M) moved. In sum, fuel consumptionis movement (ML). An absent heat engine can be modeled as a heat engine connected to a brake (the middle drawing). All the heating received from the fire is rejected as heatto the ambient. The earth is a heat engine that dissipates all its power in the movement of its atmospheric and oceanic circuits, turbulent whirls, animal migration cycles, andhumanity (transportation, construction, manufacturing, agriculture, science, education, information, etc.).

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The S-curve invasion of the railroads has been joined (not re-placed) by highways invasion, and more recently by the globalair traffic system. Every new technology attracts more flow andadds it to the existing flow. It moves the increased flow all overthe globe, and necessarily it consumes more fuel. Using more fueldoes not mean that climate change is inevitable. Humanity willadapt, to keep on flowing. Every animal does this, and every river

channel does the same. If a new technology kills us, like trains atrailroad crossings, then we invent flashing signs and build under-passes, to keep on moving.

Carbon emissions and climate change are consequences of theS-curve phenomenon. The S-curve histories however belong towhat is flowing and spreading on the landscape, for example, pop-ulations, autos, air traffic, etc. Because each spreading flow has an S

Fig. 4. Wealth is movement. Economic activity means fuel that is being burned for human use: the GDP (Gross Domestic Product) of regions and countries all over the globeversus their annual consumption of fuel [1]. The data are from Ref. [8].

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curve, the Constructal-law prediction is that none of these flowswill spread forever, and none will end with cataclysm. They willhit the invisible wall in the desert, unnoticeably.

Likewise, the Constructal law predicts that phenomena such aspopulation growth and the expansion of developing economieswill hit the wall too. As a consequence, climate change will stop,slowly. Forty years ago, the big cry was population explosion, notclimate change. Some became famous by predicting the end ofthe world because of ‘‘population explosion’’ and ‘‘limits togrowth’’. Neither happened. Look at the S-curves of populationgrowth today. The advanced regions have old looking S curves thathave reached the ceiling. The developing regions have younger Scurves, which will become mature S curves, predictably.

6. Science, economics, technology and politics

The dams that we and the beavers make are flow configurationswith purpose. They belong to us and the beavers. They are unlikethe randomly falling tree trunk, which is a temporary impedimentthat the entire river basin removes. Dams represent our design ofhow the ‘‘fuel’’ collected from the rainy landscape is channeledto us. The fuel contained in high water is gravitational potential en-ergy. With dams and other human designs, the rain water is chan-neled to flow through our turbine in the valley. The powerproduced by the turbine moves us and our stuff. The beavers’dam emerges for a similar reason, to channel toward the beaverswhat the beavers need.

Without dams, the rainwater slides down the hill anyway, and,at best, it sets some debris in motion. It does not move us. In con-trast, human ingenuity (technology, power plants) intercepts thewater as it falls, and, thanks to the dam & turbine flow configura-tion, it extracts power from the falling water.

The dam is an impediment only to flowing the wrong way, awayfrom the turbine below. The dam is a design for channeling thewater in the purposeful direction, toward delivering its fallingpower to us. Impediment to sideways spillage is synonymous withfacilitator to longitudinal flow. This is what ‘‘channel’’ means: easyflow longitudinally is synonymous with difficult flow laterally(leakage).

Businesses and the rule of law in general are no different thanthe channels built for electric power and beaver life. Businesses,laws, and regulations are the rules of the road that maintain thechannels that move all of us. They are good for the entire livingand moving population, and in a free society they keep morphingto flow better.

Businesses are not check points that milk something from theflow of commerce. They are the opposite—they are valve open-ers—which is why businesses (like laws, regulations, government)emerge naturally. They all happen because they facilitate our flowon earth (our bodies, vehicles, and belongings).

Research and development (R & D) means better and betterchannels. What flows in R&D? We flow, inside (in our thinking)and outside (in our working with colleagues to make the newthings that facilitate our movement on earth). Our movementwhile making contrivances is an integral part (the screw, nut,and engine) of the global movement.

What flows in R&D is illustrated by the history of the sciencethat preceded R&D. Geometry and mechanics were the first designthat facilitated flow. They were made faster and more efficient byalgebra. Next, all three were made even faster by mathematicalanalysis (calculus) as an add-on. Now we have software. All this,for the inside flow, which is our thinking. On the outside, anothersequence emerged: from the one-room school (Plato, early church),to universities (Alma Mater Studiorum in Bologna), libraries,

Fig. 5. Economics is physics: the consumption of fuel sustains not only our movement on the landscape (as in Fig. 3) but also the other design features of civilization andstandard of living. Warm living spaces in cold climates, air-conditioned spaces in hot climates, and running fresh water in arid regions facilitate the movement of humanity togreater distances and time scales. Together, Figs. 3–5 illustrate the Constructal-law design of the evolution of the human-and-machine species.

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journals, and now the internet—all are lined up, designed and con-structed to make our flow easier toward new contrivances thatmake our global movement easier.

The inside-outside evolution of science and technology can alsobe written in terms of economics, business and why more efficientbusinesses survive. Software also flows with design, which is morp-hing freely—lines of code, which are diverse, and accessed withhierarchy, like the words in a text. Some words are used a lot morefrequently than others, some are new because they are better(shorter) than the old, and some are entirely new (invented). Touse the Constructal law in software development is to acceleratethis natural evolution by focusing on its secret, which is the freelymorphing design: to question it, change it, discard it, create it.

7. Why is this useful to know?

Human life is an assembly of converters of fuel and food intomass (M) moved to distance (L). Movement is proportional to the

product ML, and so is the amount of fuel used (Fig. 3, caption).The net effect is the more intense rearranging of the global land-scape—more intense than in the absence of humans.

Diversity and hierarchy are necessary features of this naturalflow design. Not every moving thing shapes the earth’s surface asdeeply as its neighbor. All the river channels scour the earth, butthe big river does more scouring than the small river. The truckon the highway moves more mass than the family car on the street.The cat moves more mass than the mouse.

The large are few, and the small are many. Hierarchy is part ofthe natural design, and it is predictable [12]. The same holds for thehierarchy of power producers and users, allocated to areas in a vas-cular design that covers the globe. The inhabitants of an advancedcountry move more mass over longer distances, through biggerchannels (e.g. Fig. 1). The entire economic activity of a countryis this movement, and now we see why the annual GNP of a coun-try should be proportional to the fuel consumed on its territory(Fig. 4).

Fig. 6. S-curve phenomena are everywhere: the growth of brewer’s yeast, thespreading of radios and TVs, the growth of the readership of one scientificpublication. Spreading and collecting flows connect points (sources, sinks) withareas and volumes. All such flows develop configurations in the Constructal-lawdirection (toward greater access). The S curve history is predicted analytically[10,11] as a two-mechanism flow of fast ‘‘invasion’’ along preestablished lines (e.g.trees) and slow ‘‘consolidation’’ by diffusion.

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8. What we should do

How should we proceed toward energy sustainability? By rec-ognizing the complete picture (Fig. 4) and the physics certainty

that the use of power will continue to increase, and that its hierar-chical (vascular, nonuniform) distribution on earth will persist.

The best way to bring the less advanced areas into the flow ofthings is to allow the rivers of power, goods, people and informa-tion to bathe the whole globe. This is already happening, throughthe spreading of all kinds of power, education in English, air travel,and the Internet. The trend is to cover the areas that until recentlywere untouched.

For this to happen even faster, the flow design must have free-dom to morph. Freedom is good for design. The freely changingflow configurations have the ability to attach the overlooked areasto the big branches. The physics phenomenon of design evolution(the Constructal law) should be recognized, so that policy makersmay make the right decisions, and make them faster.

References

[1] A. Bejan, S. Lorente, The constructal law and the evolution of design in nature,Phys. Life Rev. 8 (2011) 209–240.

[2] A. Bejan, J.P. Zane, Design in Nature: How the Constructal Law GovernsEvolution in Biology, Physics, Technology and Social Organization, Doubleday,New York, 2012.

[3] K. Gierens, R. Sausen, U. Schumann, A diagnostic study of the globaldistribution of contrails, Part 2: Future air traffic scenarios, Theor. Appl.Climatol. 63 (1999) 1–9.

[4] A. Bejan, S. Lorente, B.S. Yilbas, A.Z. Sahin, The effect of size on efficiency:power plants and vascular designs, Int. J. Heat Mass Transfer 54 (2011) 1475–1481.

[5] A. Bejan, Entropy Generation Minimization, CRC Press, Boca Raton, FL, 1996.[6] A.H. Reis, A. Bejan, Constructal theory of global circulation and climate, Int. J.

Heat Mass Transfer 49 (2006) 1857–1875.[7] A. B ejan, Advanced Engineering Thermodynamics, third ed., Hoboken, 2006.[8] International Energy Agency, Key World Energy Statistics, 2006.[9] J.B. Alcott, Jevon’s paradox, Ecol. Econ. 54 (2005) 9–21.

[10] A. Bejan, S. Lorente, The constructal law origin of the logistics S curve, J. Appl.Phys. 110 (2011) 1–4. 024901.

[11] A. Bejan, S. Lorente, The physics of spreading ideas, Int. J. Heat Mass Transfer55 (2012) 802–807.

[12] S. Lorente, A. Bejan, Few large and many small: hierarchy in movement onearth, Int. J. Design Nat. Ecodyn. 5 (3) (2010) 254–267.

Adrian BejanDuke University,

Department of Mechanical Engineering and Materials Science,Durham,

NC 27708-0300, USAE-mail address: abejan@duke.edu

Received 11 March 2012Received in revised form 11 May 2012

Accepted 11 May 2012

Available online 13 June 2012