We are delighted to unveil the official program of the 16th Constructal Law Conference (CLC2026), to be held on 12–15 October 2026 in Paris, France, hosted by École nationale supérieure d’architecture Paris-Malaquais – PSL, across the historic spaces of the Beaux-Arts de Paris and Université Paris Sciences et Lettres.

CLC2026 OFFICIAL PROGRAM

Under the theme Design in Nature — The Evolution of Designs, the program brings together four days of lectures, scientific sessions, awards, posters, workshops, and research encounters, gathering scientists, engineers, architects, and scholars from across the natural and social sciences.

CLC2026 will explore how living and non-living flow systems acquire and evolve their configurations through time—from organisms, rivers, and energy systems to buildings, cities, technologies, information, and societies. At the heart of the program lies a fundamental question: how does the world acquire form through flow?

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Ultimately, batteries are thermodynamic devices. Materials science determines what reactions are possible, and electrochemistry describes how charge is transported and stored, but neither explains how much useful work is destroyed in the process, nor how much additional work should be spent to preserve it. Every watt dissipated, every temperature gradient, every pressure drop and every side reaction contributes to the degradation of exergy—the capacity of the battery to perform useful work. For this reason, battery management is fundamentally a thermodynamic problem: one of distributing limited cooling resources in a way that minimizes irreversibility over the lifetime of the system.

The first paper (Ignuta-Ciuncanu, Marinescu & Martinez-Botas), published in the International Journal of Heat and Mass Transfer, introduces a hierarchical generative design framework for battery packs using phase change materials. Cooling architectures are allowed to morph freely across scales: from high-conductivity inserts surrounding individual cells, to functionally graded module assemblies, and finally to battery pack layouts treated as evolving porous media. The resulting designs reduce hotspot temperatures by up to 60% while requiring only a fraction of the pumping power demanded by uniform configurations.

In my second paper (Ignuta-Ciuncanu), recently published in International Communications in Heat and Mass Transfer, I answer a different question: how much cooling should a battery receive? Using entropy generation minimization, I show that neither fixed cooling rates nor fixed battery temperatures are thermodynamically optimal. Instead, the cooling effort should evolve together with the battery itself. As cells age, they require progressively greater access to the cooling stream, in agreement with the Constructal Law.

Together, these studies suggest a new direction for battery thermal management. The first addresses the evolution of form—how cooling structures should be configured in space. The second addresses the evolution of rhythm—how cooling intensity should evolve in time.

One changes geometry. The other changes control.

Both point toward the same conclusion: that freedom to morph is freedom to cool (wisely) and persist in time.

Perhaps this is how the next generation of battery thermal management systems will be designed: not as fixed objects, but as architectures free to change, guided by physics and informed by computation. In one word: construcally.

The first channel is the hardest. The current that crosses over a new threshold into untouched ground bears the full weight of the resistance—no one has loosened the earth ahead of it.

Adrian Bejan began carving that first channel nearly thirty years ago, and has been deepening it since: bolstering the law across disciplines, across skepticism great and small, across the quiet weight of being the one who saw it first. He tells his students, “Your mother only made one of you.”

Adrian expounds on this in his latest book Diversity Through Freedom: “You are an individual, irrepressible, and irreplaceable. Nobody is like you. You are an important person, the one-of-a-kind. Seek freedom, it’s all right.”

What happens when one lone creative does seek freedom and trusts that his ideas are important? When one pioneer chooses to cut the channel and forge the pathway?

The Constructal Law tells us that the pathway will branch — a river reaches the sea not as one line, but as a diverse configuration of flows working as one.

The diverse research and strengths of the Constructal Community bring the movement to life. From Mary Bejan and Terry Bristol for their presence and grounding, to Umit Güneş and Elsie Gothman for their dedication to organizing and circulating the research — together, this community has been a true expression of an evolving living system, working with its natural diversity to spread new ideas across the globe. (And we can thank Dan Baciu for the maps and research to visualize it!)

I am one who now enjoys the fruit of that path-paving.

I’m Christine Bizzell, a strengths practitioner, independent researcher, and founder of Canon Collaborative in Tulsa, Oklahoma. For six years I’ve been researching how the Constructal Law maps onto human experience. It was 2020 when I sent a cold email to Bejan, whose work with Marcelo Errera on wealth inequality had sparked a serious pull toward research for the first time in my life. (I’m telling more of that story over at my blog, Patterns in the Wild.)

With Adrian’s encouragement, I presented at my first Constructal Law Conference in Torino in 2023. With a real hypothesis and a real fear of public speaking, I presented early before the courage could sink into the comfy red cushions.

12th Constructal Conference 2023, Energy Center of Torino

Hosted by Umberto Lucia and Giulia Grisolia of Politecnico di Torino, Italy

What I remember most are the smiles, the warm applause, and thoughtful questions from Mircea Scurtu, Adrian Pet’rescu’, and Miguel Panão. And Adrian, who warmly congratulated me on my debut presentation while assuring me this was only the beginning (this guy really can predict the future, it seems). My idea felt seen by a room of world-class scientists.

In Bucharest the next year, I understood that this was no longer a group I was visiting but a community I belonged to—a room full of colleagues laying new pathways themselves. I am in the greatest company.

14th Constructal Conference Dinner 2024, Bucharest, Romania

Standing from left to right: George Stanescu, Adrian Bejan, Marcelo Errera, and Dan Baciu.

As Bejan shares, we have an opportunity to speed the process of creating design to better serve society—as individuals, and as a whole. As this community comes together for the 30th anniversary of the Constructal Law and 16th conference in Paris, we celebrate the countless pioneers among us—made possible by our first pathway paver, Adrian Bejan, whose own words hold the invitation: “The holistic view is the key to understanding design in nature and predicting the future.”

At the 15th Conference in Miami, I initiated the Constructal Strength Ecosystem—an invitation for this community to map its diverse strengths together, and to explore what becomes possible when an empowered community unites its strength toward this shared purpose.

The Constructal Strength Ecosystem is now live: canoncollaborative.com/constructal-strength

15th Constructal Law Conference, Florida International University, Miami — with Adrian Bejan: Constructal Pioneer and Chief Jokester

In this lecture, Adrian Bejan returns to the model he built earlier for movers, where a vehicle is treated as the same thing as an animal, the motor stands for muscle mass and the fuel stands for the food carried in the body. He first recalls the two organ model, in which the mass of the mover is dominated by the fuel load and the motor, and shows how the balance between them is settled by the constructal law. He then makes the model heavier by adding the dead weight of the chassis, the seats, the roof and the occupants, and finds that the conclusion survives unchanged. Finally he divides life travel by speed to arrive at lifetime, and explains why the bigger animals and vehicles live longer.

• A vehicle is an animal: Bejan asks the audience to treat vehicles and animals as the same kind of mover, where the motor means muscle mass and the fuel means the food in the stomach, or the grains a bird gathers in the sack under its beak. This is why the same reasoning covers runners, birds and fish as well as land vehicles, air vehicles and ships.

• Two organs and one degree of freedom: In the earlier model the mass of the mover was assumed to be dominated by two organs, the fuel load and the motor, with the total mass held fixed, so the only freedom left is the relative size of these two parts. The burned fuel delivers its heating value as a heat input, the motor turns part of it into work, and that efficiency is greater when the motor is bigger, which is the predicted phenomenon of economies of scale.

• Movement is what the design maximizes: Bejan calls the product of the body mass and the travel movement, and according to the constructal law an object that has the freedom to change will change in the direction that makes this quantity greater. Working out that balance gives the motor and the fuel as fixed fractions of the total mass, so the more muscular birds are the ones flying from Alaska to New Zealand on larger stores of fat, and the bigger movers travel farther.

• Adding the dead weight does not change the answer: The new step in this lecture is a three part model, where the chassis, the seats, the roof, the occupants and the suitcases are counted as dead weight and taken as a fixed fraction of the total size, the way a shipyard states the size of a cargo ship in tons of dead weight, the shell alone. The longer algebra ends at exactly the same conclusion, which is what Bejan means when he calls a result robust.

• Lifetime is life travel divided by speed: Since the bigger movers travel farther and also move faster, whether they are runners, birds, fish or land, air and maritime vehicles, the two effects combine into a lifetime that grows with body size. The exponent that falls out of this back of the envelope sketch is comparable with one half or two thirds.

• The data were waiting in the zoology books: Only after the sketch is finished does Bejan open the books of zoology, which are full of plots of lifetime versus body size, and the dots line up along a power law with this kind of exponent. Those books report the exponent without explaining it, and his point is that the exponent is the real question, because everybody knows that the bigger live longer but very few question what everybody knows.

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In this video, Adrian Bejan takes on turbulence, a phenomenon he says people treat as a statement of admitting defeat, and explains it through the life of a single eddy, a rolling blob of water rolling in water, the fluid equivalent of the rolling stone. Starting from a jet discharged into a swimming pool, he shows how eddies are born where moving water meets still water, how friction with the surroundings slows each eddy until it fades away, and why the bigger eddies live longer, travel farther, and complete more turns before disappearing. He closes by arguing that turbulence is no longer an enigma, and that it is time to close the book and move on.

• Where eddies come from. A jet discharged into a pool spreads predictably as a cone, but a closer look reveals a meandering flow that thickens and travels forward like a wave. Eddies have to form because the moving water interacts with the surrounding water that is not moving.

• Every eddy lives and dies. Friction between the rolling blob and its slower surroundings retards its turning, making it slower and slower as it travels downstream. Eventually the eddy becomes indistinguishable from its surroundings, which means it dies.

• A story about rolling stones. As a junior at MIT, Bejan took a psychology course whose professor, opposed to students experimenting with LSD, ran a controlled experiment asking a sober student and a student who was high the same question: what happens to a rolling stone? The high student answered, do not throw rolling stones into a glass house because they gather no moss, two sayings interbred into nonsense, and the lesson is simple, do not play with your brain.

• Bigger live longer and travel farther. By comparing an eddy’s inventory of kinetic energy with the rate at which friction dissipates it, Bejan predicts that bigger eddies should live longer and travel farther. In a population of many sizes, this predicts a diversity of lifetimes, a few long-lived movers among many short-lived ones, and those words apply to every diverse group of movers.

• The number of rolls is set at birth. Every roll of an eddy is like the tick of a clock, and the number of rolls until death is dictated from the eddy’s birth. Bigger and faster-rolling eddies make more turns before they disappear.

• The birth of turbulence has a threshold. Each eddy’s size and rotational speed define its own identity, what Bejan calls the local Reynolds number, like the brand name of a particular eddy. When this number reaches roughly one hundred, eddies are born and the flow shifts from laminar to turbulent, and below that threshold no eddy appears.

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We are delighted to announce the 17th Constructal Law Conference (CLC2027), to be held on 22-24 September 2027 at Imperial College London, UK. Under the theme Power, Structure and Mobility, CLC2027 will bring together scientists, engineers, architects, and scholars from across the natural and social sciences to explore how flow systems, living and non-living, evolve their configurations to gain access, generate power, and move more easily, with Freedom. Building on the momentum of recent conferences in Turin (CLC2023), Bucharest (CLC2024), Miami (CLC2025), and Paris (CLC2026), we look forward to welcoming you to London.

In this video, Adrian Bejan asks why bigger things live longer, a pattern long noticed in animals but never predicted from physics. He argues that life and travel are really the same idea, so a rule that works for animals should work for anything that moves, from vehicles and rivers to winds and rolling stones. Using a single rolling stone that slowly comes to a stop, he shows how its kinetic energy, worn away by friction, sets both how far it travels and how long it lasts. He then asks how many rolls a stone makes before stopping, and uses the constructal law to explain why moving bodies, from eroding rocks to the human-made wheel, evolve toward easier rolling.

• Why the bigger live longer. Bejan starts from a trend in zoology, sometimes called animal design, that bigger animals live longer, the same way big dogs outlive tiny ones. His aim is not just to describe this pattern but to predict it, since describing something is not the same as explaining why it must happen.

• Life and travel are the same thing. A large river carries water far and lasts a long time, while milk spilled on the kitchen floor goes nowhere and is gone in moments. Because moving and living are tied together, the same rule should hold for animals, vehicles, rivers, winds, and rolling stones alike.

• A rolling stone tells the story. A stone hurtling downhill carries kinetic energy that friction slowly wears away until it stops, having covered a certain distance over a certain lifetime. From this single balance, Bejan predicts that more initial speed buys both a longer journey and a longer life.

• Lifespan grows with the square root of travel. A surprising result is that lifetime rises only with the square root of the distance covered. As Bejan puts it, moving farther when you are old does not make you live longer.

• Why stones become round. Counting how many times a stone rolls before stopping gives a simple answer, few rolls for rough shapes and many more for smooth ones, just as a ball bearing rolls far more freely than a jagged rock. The constructal law predicts that a moving stone keeps changing toward less friction, becoming rounder rather than breaking apart.

• The same pull toward easier rolling. This drive toward smoother movement runs from eroding rocks to rivers cutting their channels, and even to the human biped, which Bejan pictures as a wheel with only two spokes. About 10,000 years ago the human-made wheel appeared and evolved from solid disks toward spoked forms, following the very same direction.

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In this video, Adrian Bejan turns the S-curve into a lesson about innovation. He explains that anything useful spreads in the same S shape, growing slowly, then quickly, then slowly again, until it reaches a plateau where the maker runs into trouble. The way out, he argues, is to replace the old with something new before the curve flattens, thereby launching a fresh S-curve and keeping the company alive. He illustrates this with Apple’s run of iPhone models, the rise of maritime technology in Western Europe, and the link between wealth, movement, and freedom.

• Why things spread. Anything that spreads, from a news item to the latest iPhone model, does so because it is useful and becomes attached to or adopted by a person. Bejan notes that none of us is a “naked animal” anymore, since that picture disappeared when we adopted fire.

• The maker’s problem. The same S-curve that rewards everyone who adopts a new technology leaves the manufacturer in trouble once growth reaches the plateau. The question then becomes how to make the curve steeper and keep the product spreading.

• Innovation is replacement. Bejan’s answer is to replace something old with something new, which is what innovation means. Drawing on the constructal law, he says you need the freedom to redraw the picture, sending the invasion in new directions rather than waiting for slow consolidation.

• The rhythm of new models. With the iPhone, marketing teams learn to detect the inflection point of each curve and launch a new model before the old one flattens. Each launch starts a fresh S-curve of income, and that rhythm has carried Apple through some sixteen models.

• Innovation is not spread evenly. Maritime technology, including the compass, the telescope, and maps, developed in Western Europe and spread across the oceans from there. Even the name “Americas” comes from a Florentine map maker, Amerigo, a reminder that it pays to be on the map.

• Wealth, movement, and freedom. Two graphs in the lecture show that wealth measured as GDP rises with movement, and that movement rises with economic freedom. Quoting Cicero, Bejan defines freedom as the power to live as one wishes, which to him means the power to make the changes that are good for you.

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In this video, Adrian Bejan explains the logistics S-curve, the universal shape that describes how almost anything spreads or is collected over time. He traces the word “logistics” back to military engineering rather than philosophy, argues that the “exponential growth” people invoke for viral phenomena is actually the wrong word, and then shows how a simple two-dimensional conduction model reproduces the S-curve through two stages he calls invasion and consolidation. He ties the whole idea to the German blitzkrieg through France and even to rainwater spreading across the ground.

• Where “logistics” comes from. Bejan opens with Napoleon, who understood that an army “marches on its belly” and needs food and lodging to keep moving. That need for lodging from stop to stop is the origin of the word logistics, meaning military engineering, not logic or philosophy.

• The S-curve is universal. Anything that spreads or is collected grows slowly, then fast, then slowly again, tracing the same S shape that you cannot defeat. Bejan’s recent contribution was not just to observe this curve but to predict it.

• “Exponential” is a misnomer. People call the steep early part of viral growth exponential, but a true exponential curve starts at minus infinity and keeps climbing forever. Since nothing in nature starts before the Big Bang, Bejan says that calling real growth exponential forgets your high school mathematics.

• Invasion then consolidation. In his model, a hot blade first cuts long and fast into a cooler square, then grows across it like a finger, producing the convex early rise. Once it reaches the far wall, the heat spreads sideways more slowly to fill the rest, the concave tail, which are the two phases he calls invasion and consolidation.

• A wartime newsreel made it click. The idea came from a Hollywood newsreel of Germany’s blitzkrieg into France, which bypassed France’s fortified eastern frontier by marching through Belgium. Tanks raced down the highway to Paris while trucks behind them spread sideways to protect the channel, an invasion followed by consolidation, exactly as in his model.

• The same pattern is everywhere. Rainwater falling on the ground first runs as a rivulet, then diffuses laterally and turns the patch into mud or swamp. The S-curve, Bejan argues, governs everything that fills a territory in time.

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At the heart of the book’s scientific framework is the counterintuitive revelation that “perfection is the enemy of evolution” (p. 23). Bejan explains how nature does not strive for a singular, frozen state of flawless design but instead keeps what works, allowing life and movement to flourish in a “broadband of slightly imperfect designs” (p. 3). Through clear, mathematics-free illustrations of convex performance curves, Bejan shows that a vast multitude of diverse shapes and rhythms can achieve nearly the same performance as a theoretically perfect design. This fundamental principle dictates how an immense diversity of solutions emerges from the freedom to be slightly imperfect, ensuring resilience and progress in everything from the layout of airport concourses to the architecture of city streets.

Bejan masterfully applies this physics lens to human and animal movement, illustrating how elite performance naturally gives rise to diverse physical forms. He explores the divergent evolution of athletic body types, demonstrating through physics why the fastest sprinters tend to have a higher center of mass, while the fastest swimmers have a lower one. These insights not only unify the study of animal locomotion and human sports but also highlight that natural hierarchies of merit are born from freedom and competition. Furthermore, Bejan challenges the narrow focus on convergent evolution by showing how divergent evolution operates simultaneously, as in the distinct cross-sectional shapes of fish compared to those of aquatic mammals, thereby proving that nature actively generates endless variety to optimize flow and heat retention.

The book moves seamlessly from the natural world to human institutions, offering a rigorous defense of the merit system and the solitary thinker. Examining the world university system, Bejan reveals that institutional prestige and rankings are not the result of artificially imposed diversity or sheer size, but rather the natural byproduct of groundbreaking ideas generated by brilliant individuals. He vigorously dismantles the contemporary push for the “collectivization of research” (p. 136), warning that monumental ideas originate in the mind of the solitary investigator, not within the confines of groupthink tanks or bureaucratic task forces. By defending the “majority of one” (p. 15), Bejan inspires readers to value the creator who, like a beautiful flower, attracts a diverse crowd of followers.

Perhaps the most gripping and deeply personal aspect of Diversity Through Freedom is Bejan’s critique of what he terms “unnatural diversity.” (p. 137) Drawing on his harrowing childhood experiences under communism in Romania, he draws striking parallels between modern diversity, equity, and inclusion (DEI) policies and the oppressive class-struggle tactics of the Soviet-era Red Terror. Bejan uses the poignant metaphor of a man walking a dog on a leash to illustrate the built-in inefficiency and suffering caused by collectivism: When forced to move at a dictated, uniform speed, both the man and dog are deprived of their natural, most economical rhythms. He argues that policies aimed at artificially engineering equality of outcome restrict human potential and are inherently destined to fade away because they run counter to the natural laws of evolution.

Diversity through Freedom is an empowering, holistic manifesto for liberty, common sense, and the unconquerable human spirit. Bejan successfully connects disparate phenomena, from the meandering of rivers and the rhythm of breathing to the cyclical nature of economic growth and the hierarchy of universities, under one elegant unifying principle. He challenges readers to reject ideological jargon, to ask difficult questions, and to recognize that society is at its healthiest when individuals are free to associate, compete, and evolve on their own terms. For anyone seeking a scientifically grounded and profoundly liberating understanding of how the world truly works, Bejan’s ultimate advice resonates clearly: “If you want diversity, give the population freedom, not the leash.” (p. 155).

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16th Constructal Law Conference (CLC2026)

🗓️ 12-15 October 2026, Paris-Malaquais School of Architecture-PSL (Paris Sciences et Lettres) University, Paris, France

Deadlines

• Extended Abstract Submission: June 3, 2026

• Extended Abstract Acceptance: June 20, 2026

• Registration Deadline: June 30, 2026

Accepted extended abstracts will be presented as oral presentations or posters.

Submit Your Extended Abstract

Registration Fee

• Full: €400

• Student: €150

The registration fee covers admission to all conference sessions and coffee breaks. However, lunches and dinners are not included in this fee.

Contact: info@constructallaw.com

More Information about CLC2026

In this video, Adrian Bejan describes design and evolution in time as rhythm or frequency, and adds two examples, defrosting a refrigerator and the logistics S-curve of spreading and collecting. He explains that defrosting is a rhythmic life of the appliance, with on operation and off operation, and that heat transfer and timing matter in the kitchen. He sketches the refrigerator as a flow system with room temperature, insulation, the beer place, and the evaporator at T minimum, where a layer of frost grows in time with thickness delta. He connects the heat leak Q, power W, and the refrigeration load to the cycle with durations T1 and T2, and asks how long the machine should run before the buildup becomes a thermal resistance. He also links this to Carnot efficiency, second-law efficiency, a short history of refrigeration, George Claude, and John Gori.

• Bejan frames the examples as designs that manifest as rhythm, with diversity in the optimized rhythm and frequency. He treats defrosting as a repeating cycle that you can recognize from spending time in the kitchen.

• He draws temperature levels from room temperature through the insulation to the beer place, then down to the evaporator at Tmin. He says the frost layer forms on the coldest surface because air containing water vapor is mixed with it.

• Bejan describes a heat leak, Q, that steadily penetrates when the motor is working and stops during defrosting. He defines the rhythm with T1 for the operation and T2 for defrosting, and focuses on the degree of freedom called T1.

• He explains that the delta increases over time and acts as a thermal resistance, so Q decreases as the ice layer accumulates. He notes diffusion processes are effective early, not late, and that a resistance generates heat to melt the water on the evaporator surface during T2.

• Bejan connects the analysis to Carnot efficiency and second-law efficiency, and says that refrigeration means repeated cooling because heat leaks keep leaking. He adds history about George Claude and an Otch power plant, and says the first refrigeration machine was built by an American dentist, John Gorrie, in Apalachicola, Florida.

16th Constructal Law Conference (CLC2026)

🗓️ 12-15 October 2026, Paris-Malaquais School of Architecture-PSL (Paris Sciences et Lettres) University, Paris, France

Deadlines

• Extended Abstract Submission: May 15, 2026

• Extended Abstract Acceptance: May 31, 2026

• Registration Deadline: June 30, 2026

Accepted abstracts will be presented as oral presentations or posters.

Submit Your Extended Abstract

Registration Fee

• Full: €400

• Student: €150

The registration fee covers admission to all conference sessions and coffee breaks. However, lunches and dinners are not included in this fee.

Contact: info@constructallaw.com

More Information about CLC2026

In this video, Adrian Bejan discusses a celebration at Duke and uses 7 slides to give a brief overview of his work. He begins with acknowledgments to Mary and their children, and he explains how two photographs make one point about footprints, the leopard, the giraffe, and the stability of quadripeds on the ground. He describes a career spanning more than four decades and says he enjoyed the freedom of a university professor, surrounded by inquisitive, bright students who appreciated learning. He recalls his start at MIT in thermodynamics and cryogenics, the difficult time getting a position, rejections, and how a book was published, which led to entropy generation minimization and textbooks in thermodynamics and heat transfer. He says what really matters is configuration, and he connects this to convection, freedom of the flow architecture, and a line of design science books. He ends with a punchline about a school of thought associated with Duke, the primordial presence of the idea before observation, and conferences from Duke to Paris and London.

• Bejan shows footprints of a leopard and says the rear foot touches the spot left by the front paw on the same side of the body. He says the giraffe photograph shows the same thing, and he connects it to extreme stability per unit weight of design.

• He says the recipe for an individual's happy and creative life is freedom and humility, surrounded by inquisitive, bright students appreciative of learning. He points to the Duke student who comes voluntarily to be shaped in life.

• Bejan describes the book cover as an accident from Africa, with an Egyptian goose on a branch, which he recognized as Adrian. He calls this an individual investigator standing on dead wood with infinite freedom to the blue sky of ideas.

• He recalls training at MIT and work in cryogenics, then a postdoc in Berkeley, and being hired at the University of Colorado. He says a book led to entropy generation minimization, and he connects thermodynamics and heat transfer to configuration and convection.

• Bejan says this kind of thinking represents a school of thought associated with Duke and calls it thermodynamics of 2026, tied to design in nature or constructal law. He says the idea is the fastest and cheapest investigation method, and he mentions the 16th Constructal Law Conference in Paris and the next year at Imperial College in London.

In this video, Adrian Bejan describes the design of the ice maker in a domestic refrigerator, where water freezes on a refrigerated surface called an evaporator, forming a layer of ice whose thickness increases over time, eventually reaching a point where it stops growing rapidly. He explains that the ice maker must then remove the manufactured ice to clean the surface, so the process repeats as a cycle with two time scales: a freezing time and a surface renewal time. He treats the surface renewal time as a known constant given by engineers and focuses on selecting the freezing time as the degree of freedom. The purpose is to maximize the time-averaged rate of ice production, which depends on how much ice is produced before removal and on the full cycle time. He connects this trade-off to familiar designs from domestic life to animal design and industry, where surfaces must be cleaned rhythmically to maintain high performance.

• The heart of ice making is a cold, refrigerated surface where water at the freezing point accumulates a layer of ice. Over time, the process runs out of zip because the layer no longer grows quickly, so the surface must be cleaned.

• Ice removal is a second time interval that renews the surface, and designs like ice trays with little cubicle alvoli help remove a whole bunch at once. This surface renewal time is treated as a constant, assumed to be known.

• The object of the game is to determine the freezing time as the degree of freedom selected rationally. The purpose is to maximize the time-averaged rate of ice production over the cycle, including freezing and surface renewal.

• The trade-off has two extremes: short freezing time on one side and long freezing time on the other. High values occur when the freezing time is determined by the time required to remove or clean the surface, which is good news for mechanical methods of scraping ice off.

• The same idea appears in the windshield wiper that cleans the window and in the eyelids that lubricate and clean the eyeball rhythmically. He also points to heat exchangers whose ducts get clogged by debris or gunk called scale, like plaque on teeth, and to the cost of shutting down a power plant to clean the tubes internally.

• Bejan starts from the idea of predicting the evolution of design and shifts from design in space to design in time. He connects this to rhythmic functioning in the body and the daily cycle.

• He frames respiration as a problem of posing the right questions, especially why inhaling time t1 equals exhaling time t2. He also links the same type of solution to heartbeating.

• Bejan models inhaling as atmospheric air entering the trachea and increasing the thorax volume by capital V, driven by a partial vacuum and limited by a global resistance R. He uses a pressure difference proportional to R and a velocity to an exponent n, and writes conservation of mass for the inflow and the accumulated air.

• He models exhaling as the thorax volume shrinking, indicated by a capital V, with an excess pressure delta p2, flowing out through the same resistance and cross-section, with an average velocity u2. He then computes work as the integral of p dv over the two parts and expresses average power in terms of V, af, and the time intervals.

• Bejan introduces alveoli and diffusion, where oxygen transfer scales with the square root of time and becomes inefficient, leading to intermittency and surface renewal through finite inhaling followed by exhaling. With a fixed oxygen requirement per unit time K, he minimizes average power and obtains the result that t1 and t2 are nearly equal, and higher K corresponds to shorter times and frequent breathing during running.

In this video, Adrian Bejan explains how the Atlanta airport story and a question at the 2009 ASHRAE congress led him from the golden ratio, or divine proportion, as a popular observation to a brief explanation of why it happens. He connects what people like in paintings, facades, the laptop screen, and other rectangles to how the two eyes scan an image with saccades, taking snapshots at 5 per second across the flat field of vision. He describes scanning horizontally and up and down, and considers the best shape to be the one that lets the eyes scan the whole area as quickly as possible, because fast scanning helps you grasp the meaning of a message and move on. He then uses the binoculars drawing, with two discs and their intersection, to argue that vertical and horizontal scanning differ because the eyes move upward in parallel but horizontally in series. He ends by tying well-proportioned and complex rectangles stacked on rectangles, and by saying eyes and ears sit on the horizontal because the world is flat, and because fast scanning and fast understanding are useful.

• Adrian Bejan says the Atlanta airport story first appeared in his 2000 book and was presented at the 2009 ASHRAE Congress. A participant said the drawing looked like the golden ratio, and Adrian Bejan said he figured out how to predict it and why it happens.

• Bejan describes two eyes that jiggle with saccades, taking snapshots at 5 per second as they scan the field of vision. He says the shape matters because scanning fast helps you understand fast, and that is useful.

• He treats the image as H and L, with scanning times along the horizontal and vertical axes, and he seeks the minimum total time. He says the fastest shape depends on the scanning speeds.

• Bejan uses binoculars and the intersection of two discs to compare how the eyes sweep vertically and horizontally. He gets an order-of-magnitude ratio and links it back to the rectangles people like.

• He connects the Renaissance and Uklid to the 618 dot dot dot ratio and the label divine proportion, then says science explains the attractiveness. He extends this to paragraphs, faces, and complexity as smaller rectangles stacked on bigger rectangles.

In this video, Adrian Bejan describes how a city grows from a small village road into a city block and then into a grid, and how the center and the periphery change over time as the population and the diameter increase. He explains that travel across the city becomes slower as the city grows, and he describes a stepwise change in which going around becomes shorter than going through, leading to the appearance of a beltway. He notes that speed on the beltway can increase because there are no traffic lights and because decisions are made by the city government and politicians, leading to an upward trend. He connects this to a threshold moment when people begin “banging on the doors” of decision makers, and he says that later another beltway with a bigger diameter will occur in the same predictable manner. He then links this way of looking at design and movement to earlier developments, moving to boats with sails, the Near East, the Mediterranean, and a Greek ship with oars on three floors that he compares to a gearbox.

• Bejan starts from the city block in the smallest and oldest village, describing a dirt road between a few houses that became the city block. He says cities grew from city blocks arranged in a grid and points to places like Paris, Florence, and Rome.

• He describes two kinds of cities: an old center of very narrow streets and almost square city blocks, built for carriages, horses, or oxen, and built in stone. He says the old city is not destroyed, while the periphery migrates outward as population increases.

• He explains that as the diameter increases, the time it takes to cross the city increases, even at relatively low speeds through the grid. He then describes the beltway as a way to avoid traffic, noting that going around is shorter than going across.

• Bejan says the beltway speed can increase over time because there are no traffic lights and because speed is increased by decisions made by the city government and politicians. He connects faster allowable vehicle speed with the earlier arrival of the beltway and says the tendency is tied to facilitating movement and life.

• He shifts to boats with sails and a story about the Near East and the Mediterranean, naming Lebanon, Israel, Iberia, the Phoenicians, Tunisia, Carthage, and the Greeks. He describes the Triim, with convicts pulling oars on three decks, and says this is the design of the gearbox, adding notes on Greek and Latin words.

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Adrian Bejan talks about denser packages that become lighter things to carry, and he connects this to what you want with your desires. He says that wanting bigger leads necessarily leads to opting for smaller objects, and he calls this the evolution of this technology toward miniaturization. He notes that what you have in your iPhone isn't this because the iPhone doesn’t have a fan inside, and he mentions a next, third variation on this theme. He says we like things that are smaller because we want to carry more of this artificial intelligence with us, beginning with arithmetic. He then links this to metabolism and to obesity, using the donkey, the whale, and the goose from Alaska flying to New Zealand, obese, where extra weight and so-called fat can be good under extreme circumstances for power and insulation in cold air at altitude in darkness.

Adrian Bejan presents three parts that go together, starting with how movement gives us the idea of the physics of wealth, underpinned by the natural birth of hierarchy on the map. He then turns to the birth of the beltway around the city, meaning beltways happened. He ends with the basic physics of attractiveness, also known as beauty, and calls it a pleasant surprise because there’s only one idea. He connects the urge to move stuff in an area with less fuel to a road map with a few larger and many small pathways, and then shows data where gross domestic product GDP and annual consumption of fuel crowd on a diagonal with a slope of one.

• He says the road map is a hierarchical display of movement, with a few larger pathways and many smaller ones. The large ones are traveled by big movers, and the smaller ones by smaller movers.

• He says the money people pay to make movement possible represents wealth, and the annual measure of wealth is called the gross domestic product GDP. He says fuel consumption to move stuff is synonymous with what people report as wealth: money spent annually.

• He describes a companion drawing in which GDP per capita and fuel per capita show the same distribution along the diagonal. He says the wealthier burn more, and the purpose of that so-called fuel consumption is to move stuff.

• He says life is movement because the antonym of no movement is death, and he calls reducing fuel consumption an argument for reducing the movement of life. He says no living group is reducing fuel consumption and never will, because history is a progression toward greater movement.