The demon of Maxwell is a thought experiment proposed by James Maxwell in 1867 for violating the second law of thermodynamics.

Maxwell was interested in the kinetic theory of gases, where the properties were reduced thermodynamic thereof to the mechanics of a large number of molecules. The heat was then reduced to a particular form of energy in the form of disorderly agitation of the molecules. More unrest is more important the temperature of the gas being high.

But then, the science of energy conversion, including the rules of conversion of heat into usable work, thermodynamics, implies a direction to the passage of time and limits the possible transformations of energy and matter . The heat does not pass spontaneously from a cold body to a warm body, can not transform work if the temperature is the same everywhere in a system and a broken vase does not spontaneously glue or a drop of ink in a glass of water does not gather itself after running.

But if we take very seriously the reduction of thermodynamics to mechanics, this is more than ironic. The equations of motion of particles in a gas or is any other material body, do not differentiate between a movement in a sense of time and movement in the opposite direction. This means that there could be as much chance of breaking a vase than to see recoller spontaneously, or that the drop of ink diffusing in a glass returns to its initial state of concentration. The second principle is therefore true that, on average, approximately, and should therefore be violated even if it would, in practice, very difficult. Except of course for a similar Démon Laplace, ie the famous Maxwell demon!

If we imagine a box with the original molecules of a real gas gathered in a corner, the thermal agitation and thus the second law of thermodynamics, will this gas that will evenly distribute up to occupy the whole volume of the box. You will reach a situation known as equilibrium thermodynamics, where the gas n'exhibe no tendency to come together again in a small volume of the box. This allows to define a meaning for the passage of time.

Now imagine a wall separating the box into two parts, one B is larger than the other A. Part A corresponds to the initial area where the gas prior to broadcast. A small hole is drilled in the wall with a door a small daemon can close or open at will.

The gas is initially distributed uniformly in all parts of the box, when a molecule moves towards the hole, Part B to A, the demon leaves the door open. Conversely, if the molecule comes from A towards B, the daemon closes the door.

It is understandable that after a certain time, the gas will be back in a corner of the box and you will be returned to a situation of non-equilibrium. It therefore violated the second law of thermodynamics!

Thermo. You can not create work in a closed cycle with a single heat source. It takes at least two sources at temperatures T1 and T2 to produce power. The theoretical maximum efficiency is independent while temperatures at which heat is exchanged, the principle of Carnot implies the relationship: Q1 / Q1 + Q2 / Q2 <= 0 with equality for the reversible transformation, Q1 (resp. Q2) designating the amount of heat (measured in algebraic) is provided by the source 1 (resp. to the source 2). 

This is the first statement of the second law of thermodynamics.
Reversible transformation Means a process ideal for two families of real transformation, which can be regarded as a sequence of states of equilibrium far neighbors. Ant. irreversible. 

Chim. Is said, by abuse of language, a reaction likely to evolve in both directions. It should normally speak overwhelming response (Duhem, 1912).

Chemist Henry Louis Le Chatelier (1850-1936) was the first to notice that different phenomena thermochemistry obeying a principle can be stated as: "If you tend to change the terms thermodynamic (pressure, temperature, concentration) from one system to the balance, it reacts to oppose, in part, to changes that it requires, so as to obtain a new balance. " 

The German and the Nobel Prize for Physics Karl Ferdinand Braun (1850-1918) had also discovered and formulated this principle.
Balance is a state where the speed of transformation of substrate into a product, in a reversible reaction, is equal to the speed of processing to the substrate. Thus, the apparent speed of a reaction is reversible at equilibrium is zero.

Can we violate the second law of thermodynamics? This question nagging for the Multivac computer in the news of Isaac Asimov The last question may have a positive response according researchers at the Weizmann Institute in Israel. It would suffice to bring the magic formulas of quantum mechanics. 

The second law of thermodynamics is one of the most solid pillars of physics. It is on it that Albert Einstein relied to prove the existence of quanta of light let through to him that Stephen Hawking discovered the radiation of black holes. This principle has an unpleasant, as was well understood one of its discoverers, Rudolf Clausius. Applied to an isolated system, as is perhaps the universe, it leads him to the dead heat, a total and irreversible decay. 

This great principle may be stated in a surprisingly simple: "The heat does not pass spontaneously from a cold body to a warm body." It is therefore a principle of evolution which establishes the meaning of the transformations of nature. It only translate a set of simple observations. Thus, an ice cube thrown into a glass of warm water not only cools and a broken cup does not glue itself. 

We know that in the quantum world nothing is happening as we suggested in our intuition. Particles sometimes behave like waves and vice versa the walls high and thick are crossed by tunneling. Nothing is completely determined, the evolution of laws concerning the probability of observing a given value of a physical quantity. 

However, the laws of quantum mechanics, which are ultimately the basis of the classical world which operates the second law of thermodynamics. It can therefore legitimately wonder if it is not an approximation, albeit prodigiously effective, but that laws of quantum mechanics can violate when they appear on the atomic level. 

So far, this crime against second principle has never been observed. But the situation could change after the publication of a theory in Nature Kurizki by Gershon, and Noam Erez Goren Gordon of the Weizmann Institute, in collaboration with Mathias Nest at the University of Potsdam, Germany. 

These researchers make a surprising contribution to quantum mechanics known as the Zeno effect. What is it? 

In quantum mechanics, the observer, whether a human being or a measuring instrument, plays a fundamental role. According to the standard interpretation of quantum theory, one can not speak of the actual existence of certain attributes of a quantum system without involving the act of measurement for the observer. In itself, a quantum particle of matter does not exist as an object located on a constant in space and in time. It is the interaction with a classical physical system in a place and time given, which may lead it to manifest itself as a classical object like a billiard ball. 

A quantum system affected by observation 

A quantum system, like a atom coupled to an electromagnetic field or an elementary particle coupled with weak interactions, can in the first case is energized to emit photons, or in the second, other particles such as muons and neutrinos she is a pawn. The coupling is a field in some way as a measure and force the system to evolve. 

The Zeno effect is a reverse effect where the repeated observation of a quantum system by a measuring block its development! In both previous examples, after watching an atom or a pawn to detect the emissions of particulates, it prevents them from doing so! 

In the case examined by four researchers, we consider a quantum system exchanging heat with a reservoir of energy. It turns out that according to their equations obeying the laws of quantum mechanics, according to the frequency of observations to determine whether there is heat, it can actually occur, but in a way violating the second principle ! More specifically, this is one possible interpretation of the consequences of these equations. 

The researchers are cautious, however. After all, at the time, Maxwell believed also to have found a way around the second principle with his demon. Deeper analysis of Leo Zsilard showed thereafter that he was not. 

It seems much safer than the process theorized by researchers should be able to control at will the very rapid exchange of heat between the atomic and molecular systems, a possibility which certainly will have applications in nanotechnology.

When you use energy, the rules are well defined. The first and second laws of thermodynamics have been well understood for more than a century, and the third a little more than a century, but the topic is still considered by most to be rather obscure. That is unfortunate, because these two laws are so important, and because almost everyone has a good understanding of the first and second laws, even if they think they do not. Understanding the implications of the legislation is another matter.

The third principle of thermodynamics, also known as the Nernst theorem, named after the Nobel Prize which was discovered in 1906, reads as: "The entropy of a system can always be taken as zero at the temperature of absolute zero. " 

Strictly speaking, this statement applies only to macroscopic bodies and there are some subtleties regarding quantum degenerate systems. In practice, there are no known physical systems, even degenerate, that violate this principle even if it can be conceived in the context of quantum statistical mechanics. 

Initially, this theorem only applied to condensed systems, such as liquids and solids, but has been generalized to apply also to gaseous systems. 

To understand its origin, it must consider the following relations verified by the free energy F and its variations: 


It follows that  

Nernst was asked the following stronger condition: 

What for changes in the free energy F and Gibbs function G is of course: 

In both cases, we obtain for the variations of the entropy of a system when the temperature tends to absolute zero: 
The result was originally established by Planck Nersnt but went further. It has shown that this condition implies that the entropy of all bodies towards a universal constant when approaching absolute zero. 

Taking this as a universal constant value 0, it thus followed in the third law of thermodynamics stated above. 
This had important consequences because if we took the molar heat capacity at pressure (volume) constant C p for a mole of a body, it should verify the following relationship which can become problematic when T tends to absolute zero. 

The only way to avoid endless differences being put 

it leads to a contradiction with the law of Dulong and Petit for which in the case of a lens system, obtained by condensation of a gas for example, the heat capacity must be a constant value 3R where R is the gas constant . 

The law of Dulong and Petit is actually not true at low temperature and in the context of classical statistical thermodynamics, it should be. 

The resolution of this contradiction was given by Einstein involving quantum theory. This was the first convincing result for the quantum theory of Planck, within the scientific community at the time.

If any of the entropy is zero, then no change of entropy are possible and there is no way to do it for cooling. In fact, the law is observed that the change of entropy is always zero. It is easy to declare all entropies zero at absolute zero, which corresponds to the statistical interpretation of entropy. It can get very close (in degrees) of absolute zero - the current record is around 10-10K, but it gets closer, it becomes more difficult to cool. 

It is not cold.

NB.

Entropy 
The idea of entropy is associated in most minds with the ideas of order and disorder (entropy higher = more disorder). That is correct, but the origin of the idea comes from the flow of heat. If a quantity q of heat enters a system (absolute) temperature T, then the system increases the entropy of q / T. That is the definition of entropy. If we look at the first heat engine above, the entropy of the hot reservoir decreases q1/T1 and the increase of the cooler by q2/T2. If the engine is reversible, q2/q1 = T2/T1, so the overall change in entropy is zero. It is a characteristic of the process is reversible. In real process, the total change of entropy is always positive. One example is the flow of heat from a warm body to a cooler - the hot body loses entropy, the cooler, but we win more than one has lost the hottest since the T in the q / T is the most small and q is the same.

The total change of entropy of a system and its environment is always positive, and tends to zero for the transformation towards reversibility.

The thermodynamics is based on two essential principles:

the first-principle, which establishes the equivalence of different forms of energy, including heat and work. It is a principle of conservation, it implies that the sum of the energies associated with a system even if this energy can be transformed into each other according to their equivalence.

-the second principle, which introduces in addition to the energy of a physical system a magnitude characterizing the system and is called entropy. This is a principle of evolution, because it determines how far and in what sense the various transformations of energy in the world are possible. For example, some chemical transformations are possible and others not. Likewise all the warmth of a body, eg the ocean, can not be transformed completely into work.

The second principle has a long history where there are names as famous as Carnot, Clausius, Kelvin, Helmholtz, Gibbs and Boltzmann especially.

Applied to an isolated system, trade or work or heat with the outside world, the second principle states that the system state called entropy can only increase to a maximum value where the system remains in balance. This is a translation of the complicated simple observation that any physical system left to itself, as a living being, tends to disrupt. This implies that in any transformation of energy in these systems, the ability to use energy to produce work and organization is lost, is often a deterioration in the quality of energy. That's why it introduces a non-equivalence between the past and the future and irreversibility of the transformations, an arrow and a sense of time then.

This raises many questions.

Applied to the universe conceived as an isolated system, it would mean that it is moving slowly but inexorably towards the "dead heat" where disorder is maximal.

Thermodynamics can be deduced from the mechanical basis of certain assumptions of order statistics, or the laws of mechanics, they are reversible! The arrow of time and the second principle would be illusions and simple approximations practices but fundamentally false.

These issues are still not resolved today and are the subject of incessant debate.

Branch of physics and chemistry related to the study of thermal behavior of the body, the study of energy and its transformations (in particular the internal energy). 

Thermo. Thermodynamics studies the transformations of the systems (sets of body separated by a physical boundary or not) open or closed (depending on whether or not exchange matter with the outside) insulated or not (depending on whether or not exchange energy with the outside world) represented by state variables (intensive or extensive). 

The basic theoretical concepts of thermodynamics are the heat, the thermodynamic temperature, internal energy, the enthalpy, the entropy, reversibility. 

The experimental quantities are the heat capacity, pressure, volume, ... 

The principal laws of thermodynamics is the first principle, the second principle (V. Carnot and Clausius), (the third law of thermodynamics V. Nernst). 

The thermodynamic study of the body includes the design and validation of models of the thermal behavior of bodies, the equations of state, derived from experimental values. In practice, the equilibrium predicted by thermodynamics can be thwarted by the influence of time (to obtain the thermodynamic equilibrium might sometimes require a long time) and are governed by kinetics (cf. Arrhenius). In chemistry, equilibrium thermodynamics is the law of mass action (Guldberg V.).

One might think that our sense of passing time actually comes from increasing entropy is by measuring how unconscious entropy increases around us that we "feel" the passage of time, as events occur over time ... etc. 

we can see the thermodynamic equilibrium as a state where entropy increases more (assuming our isolated system), ie not undergoing the most over time. Yet we know that this event, a system that has reached thermodynamic equilibrium, takes place in time, time continues to pass. 

To based on these findings, it seems that our idea of a state of balance (which is not really as valid for systems perfectly isolated approach but very many of the physical phenomena), the image that it will be done, what our intuition tells us ... etc.. Maybe this night finally our understanding of time and we can not capture its ineffable.

This confusion has developed since the late nineteenth century and we still observe the effects, because our way of saying the customary time, the semantically linked to the temporality of the phenomena, tend to forget that when the arrow time disappears from the evolution of a system, ie when the evolution of the system becomes stationary, when it happens for him nothing new, over time, it continues to manufacturing time, a period which certainly does not change anything, but simply that guarantees the permanence of the system that we claim to describe.

Now imagine that the truck that we have considered so far starts to brake. So he finally stopped (so it has more kinetic energy) at the bottom of the slope (so it has more potential energy rather than at this time). And therefore was able to spend the energy it possessed? 

In fact, it has not disappeared. Simply, it was dissipated by the brakes of the trolley, and it increases their temperature. You have already tried to vigorously rub your hand on your sweater, for example. It is a sensation of heat at the surface of your palm, where it rubs precisely. This is exactly the same thing. 

Indeed, when an object is hot, is that molecules, atoms that compose it are agitated. Is the thermal agitation. More an object is hot, its molecules have more kinetic energy, they are agitated. This explains two things: 

Need to spend energy to heat something (consumption of electricity to boil water, for example), since heat is to move molecules (even if it is not because it is not a movement of all). 

That the potential energy that the truck was at the top of the slope had not disappeared. She had just turned into thermal agitation. 

Temperature, thermal agitation is also a type of energy. It does not differ so much, finally, the kinetic energy. But here is the disorderly agitation of small particles (atoms, etc. ...). So we talk more kinetic energy for large objects. It is said that the thermal agitation is the internal energy.

It is said that the trolley gobal energy, potential and kinetic was dissipated. And as we shall see, the problem it is not that energy is gone, it still drives the atoms, but we can not so recover. The trolley will not recover spontaneously moving. In our view, energy is lost, wasted. This is the second law of thermodynamics.

It does not create energy from nothing, ok. But see when you shine a light bulb, it heats, heating and light it encounters. That is, in terms of particles that make us, that light the bulb more thrilled our particles. More an object has particles that vibrate, which are agitated, the more it is hot. A hot object, in fact, because its particles are agitated, a lot of energy. 

And if once the light turned in temperature, there was a machine capable of recovering this energy vibration, agitation of the particles back into electricity? This does not contradict the first law of thermodynamics, since it does not produce energy from nothing. And it would still be super power and "recycle" that energy. 

Unfortunately, it is not possible, but this time because the second law of thermodynamics, which says that the energy is the energy lost - if it has not been stored. For example, if you run, you have spent energy, nothing receuillis. It is therefore lost. For against, when you eat a plant, the energy it contains is transferred - and it is stored, so no wasted (even if a small part is the force). 

Exit also the motion of a second species!

The motion was for a very long (and sometimes still is) a sort of Holy Grail of the inventor, as the transmutation of metals was among alchemists. 

The idea is simple: what if someone invented one day a kind of universal motor, which would alone any moving mechanism, in short, which could supply energy at will? This would certainly be the inventor for eternal glory ... 

But it seems that the existence of such a machine would contradict the laws of classical physics, especially one of the most basic laws of physics: the conservation of energy, which is found naturally in thermodynamics (the science that was originally invented precisely to study the machinery - steam, in fact), but also mechanics, relativity and quantum mechanics! 

Indeed, it is said that energy is what is called a quantity, we will say "something" that is preserved: this means that it carries, it turns, but never that, but then she never comes out of nowhere. 

The energy contained in our muscles is that we eat. What we eat has to be other animals that eat plants or plant directly, which are a form of energy. This energy comes in fact from sunlight, which in turn derives its energy from nuclear reactions taking place within it. In short: it never fails to draw energy from nowhere. If you take an object, whatever it is, even if the uranium that runs nuclear power plants, it contains a finite amount of energy. 

Imagine that there may be a machine, a classical mechanics capable of providing energy at will is pure utopia. This is called a perpetual motion of the first kind, because there is another type of perpetual motion, and because it would undermine one of the principles of physics the more established, the first principle of thermodynamics. 

I recently saw a television broadcast on a large public network, an evening of listening, which praised the invention of an enlightened: he built a machine that never stops! The perpetual motion! And we explained that he had seriously lucky that it fell on him, and he built a museum (!) Of motion (which incidentally, did not look having been able to operate more than two hours). It would seem that no one had thought to warn that such fads (relatively common since found a lot of machines on the internet that produce energy but-n-that-never-have-been-built - lack-of-sub) was increased from fashion since the discovery of the laws of thermodynamics! And without necessarily being insane, the paper in question was hardly aware of physical theories - in any case hardly believe ...

The question comes up again and again from various people: "Is GreenFuel a scam?" "Are all these photobioreactor companies scams?"

This question is inevitable when someone takes advantage of human nature and wickedness to sell something.

Was Skype a scam? Was A.O.L. a scam? Both companies sold at the peak of a hype-wave, and did not live up to the expectations of the acquirer. At the same time nobody would equate these companies with selling penis-enhancement formula over the Internet, even if the basic premise is the same: exploiting human emotion to sell something that would not quite live-up to the buyer expectation.

GreenFuel Technologies and other algae companies have a business proposition that is certain to get everyone juiced up. You take water, mix it with the dangerous CO2 pollutant, add sunlight, which is free and abundant, and you get precious fuel, just when we are running out of oil. On the surface, there can't be a better proposition. Only thing missing is ponies and flowers.

Moreover, at the very basic level, these technologies do work: yes, you can grow algae in photobioreactors; yes, you can make fuel from them, and yes, they are likely to grow faster than terrestrial plants like corn.

The only issue is that it makes no economic sense and never will, as long as the laws of thermodynamics are valid. It's too costly.

Yet, with the help of good lawyering and "caveat emptor", these companies can ride the wave of human wickedness and make money off of it, without suffering any consequences.

Therefore, from now on, we will refrain from answering the question "Is GreenFuel Technologies a Scam?". It all depends on the definition...

How can one not like GreenFuel Technologies? These people say they can convert emissions from power plants into biofuels using algae in proprietary photobioreactors, which has so far resulted in tons of positive press, awards and accolades. And why wouldn’t it? You take CO2-containing pollutants and turn them into valuable, clean-burning fuels, just when we are running out of oil? Could there BE a better idea than that?

Actually, I for one do have a better business idea. Why not just skip the algae altogether, take water and CO2, put them in some Magic-o-Matic reactor and Voila! get oil out of it?

There is just one slight problem with mine and GreenFuel’s ideas: they break the Law. Now, events from the past few years suggest that anytime the end result is something that looks like oil… well… breaking laws is sort of OK. The problem with this Law is that nobody has succeeded in breaking it, and boy, have people tried?! It has the pretentious name of First Law of Thermodynamics, and basically says that when you convert energy from one kind into another you cannot gain energy, you can only lose it.

In other words, if we picture different types of energy as rectangles, where the height is the amount of energy, then an energy conversion chain can only look like a telescope, where every rectangle is narrower than the previous one.

Now let’s look at what GreenFuel is trying to accomplish in each square meter of their reactors. First, they take solar energy and convert it into algal biomass via photosynthesis. Not all of the solar energy is suitable for photosynthesis, the part that can be used is called photosynthetically active radiation (PAR). You want to know how much PAR you get in your neck of the woods? Check this website, they have the best PAR maps out there.

The energy - in the form of biomass - that can be obtained via photosynthesis thus depends on the level of PAR and the efficiency of the conversion process Q. 

Ebiomass = PAR x Q

Photosynthetic organisms use eight photons to capture one molecule of CO2 into carbohydrate (CH2O)n Given that one mole of CH2O has a heating value of 468kJ and that the mean energy of a mole of PAR photons is 217.4kJ, then the maximum theoretical conversion efficiency of PAR energy into carbohydrates is:

468kJ/(8 x 217.4kJ) = 27% 

This is the ideal yield on PAR energy that is: (i) actually absorbed by the photosynthetic organism, (ii) in conditions where this organism operates with 100% photosynthetic efficiency (every photon that is absorbed is effectively used in photosynthetic reactions), and (iii) the organism does not waste any energy on any life-support functions, other than building biomass.

Ideally, you want your algae photobioreactor plant to be someplace sunny, and according to the maps, the sunniest place in America is in the Southwest. One little problem: algae require tons of water but in the southwest water is not that abundant and is already being used for more vital purposes, like the Bellagio fountains in Vegas, for example.

Let’s sidestep the water issue and look into a square meter of photoreactors installed in the Southwest that convert PAR into biomass. From the maps, the mean annual PAR is about 105J/s, which translates into 3.3GJ/yr (there are about 31.5 million seconds in a year). If this gets converted using the absolutely highest, super-duper, theoretical photosynthetic efficiency of 27% it will equal to 0.89GJ/yr of energy locked into biomass. 

So far so good! Now this biomass has to be converted into biodiesel, which has an energy content of 126,200BTU/gal or roughly 0.133GJ/gal. A look at the last page (Examples 2 through 5) of the patent application filed by GreenFuel shows you that they plan on getting something like 342,000 bbl of biodiesel per year from a 1.3sq.km. plant built in the Southwest. By doing some simple math conversions (342,000bbl x 42gal/bbl x 0.133GJ/gal : 1.3M sq.m.) one gets to … tah-dah… 1.47GJ/yr from a square meter!

Now we’ve done it! The process gained energy out of nowhere, which is against the First Law. We can add this patent to the list of other similar claims, that have invariably failed to materialize.

So what is a more realistic outcome for the conversion of PAR into biodiesel? First of all, the maximum achievable efficiency is of course not 27%, but more like 10%. Why? Not all of the PAR gets into the reactor in the first place, there are all kinds of transmission, reflection, and shading losses. Then, not all of the light that gets in gets actually absorbed by algae. Photosynthetic organisms have no good use for the green light and don’t bother to absorb it but rather reflect it back (you wouldn’t guess that by their color, would you?). Finally, algae don’t pile up all of the converted energy in a pile of biomass; they use some for their own life’s needs (this comes especially handy at night-time).

Next we have the question of how to turn the biomass into biofuels. There are three ways to do it: 
  -pyrolysis: this is a process where you heat the biomass to anywhere from 300 to 800 oC to get liquid fuels, gas and char. If you ever run into somebody who’s into pyrolysis, chances are that you’ll be made to believe pyrolysis is a divine answer to everything that we’ll ever need. These people are true pyro(lys)maniacs. In reality, though there are no substantial commercial installations for pyrolysis and it is not clear how much net energy you gain after taking into account the heat that one needs to input in the process.
  -fermentation: this is how the most ubiquitous biofuel – ethanol - is being made from the sugars in corn or sugarcane. In a theoretical 100% conversion from glucose, two of the six CO2 molecules that were captured by photosynthesis are released, and 118kJ per mole are lost to support the lifestyle of the fermenting microbes. That’s not so bad, but there is a better option (next).
  -transesterification of lipids into biodiesel. Biodiesel is the highest-priced liquid fuel, it sells at wholesale for $2.50/gal, which translates into $18.80/GJ. The allure of biodiesel comes not only from these high selling prices, but also from its easy and efficient manufacturing by transesterification, which is becoming a well established method, with low capital costs and high efficiency.

What you need for transestrification is lipids (fats). Algae are thought capable of providing high lipid content, some species can accumulate 30-60% (mass) and in some cases higher lipid contents.

There’s a catch, though! These “fat” algae develop only in conditions of cellular stress, most notably lack of a nitrogen source needed for making proteins. Feeding algae with mostly sunshine and no nitrogen is the same as raising your kids only on sweets - they may grow fat but they are not healthy and don’t develop properly. Similarly, growing “fat” algae is not worth it as they don’t grow properly and their overall photosynthetic efficiency is poor.

A reasonable best-case estimate then, for a healthy and efficient algal culture is to put aside 50% of all captured energy into fats and the rest into other things needed for their well-being: proteins, carbohydrates, chlorophyll, etc. These can be used and sold, too, as by-products in a variety of schemes, however, they won’t be fetching the same juicy dollars per gigajoule as biodiesel does.

What we get as maximum achievable yield for our square meter in the Southwest is the following:

“OK,” one may say, “last time I checked sunshine was still free and the algae grow by themselves. You get what you can: 5%, 1%, half percent, whatever... who cares… you still make valuable biodiesel out of free stuff! You can’t beat that!”

To which someone - a little more perceptive - might reply, “The land is not free, you silly, how do you get enough land to grow enough algae to get enough lipids to turn it into enough biodiesel if one only gets so much from a square meter?”

In fact, both of these imaginary friends would be wrong. The biodiesel will be far from free, and the reason is not the cost of the land, as shocking as this may sound for anyone from the San Frascisco Bay Area. How so? We’ll let our favourite author on energy issues, Kenneth S. Deffeyes explain it:

“At typical efficiencies of 10%, a solar collector has to occupy five square miles to deliver 1,000 megawats. I can direct you to any of several Nevada basins where you can get the five square miles; your problem is the capital cost of paving five square miles with solar collectors” (from “Hubbert’s Peak”, 2001)

Building and operating the photobioreactors on significant acreage is quite expensive. How expensive? We don’t know, it is not on GreenFuel’s website and something tells us that it’s not going to be there anytime soon. Nevertheless, we can look at comparable examples of solar capture systems to get an idea.

Something that many would simply call a big field of mirrors, and in fact, it is exactly that:

These are all installations that convert sunlight into something useful. The algal photoreactors are intended to convert it into biodiesel, while the greenhouse turns it into flowers and vegetables: both systems use photosynthesis for the purpose. As for the mirrors, they are used to reflect the sunlight into a central receiver which gets heated and the heat is then turned into electricity – technology known as concentrated solar power (CSP).

Now let’s look with higher resolution at the individual elements.

A report on the greenhouse industry for the state of New York in the year 2000, puts the average revenue per square meter at $161.77/sq.m./yr, with a gross margin of 24%, for gross profits of $38.82/sq.m./yr. That’s pretty typical for the industry. $161 looks like a very decent number, are greenhouses really so proficient at capturing Sun’s energy? No! The solar yield in a greenhouse is probably on the order of 0.5W/sq.m., (0.015GJ/sq.m./yr), or up to twenty times less than what we estimated for the best-case GreenFuel reactors. The key here is what this energy is being converted into. Turns out that a gigajoule of sunlight - captured into winter tomatoes or poinsettias around Christmas-time - has a very high value, which covers up the expenses for building and operating a greenhouse. 

What about the CSP example? It produces electric energy, not vegetables, therefore should be a more relevant example, right? CSP power plants are not competitive at today’s prices of electricity, so there is not much hard data for analysis. However, if we look at this report, done by a respected consultancy, we will find some projections.

For the near term, a CSP power plant will break even if it could sell electricity at $0.14/kWhr ($38.89/GJ). These near-term plants are expected to convert sunlight into 46W/sq.m., or 1.46GJ/sq.m./yr of electricity. At $38.89/GJ, the dollar yield will be $56.77/sq.m./yr, which should be enough to cover the expenses to build and operate the plant.

For the medium term, CSP plants are expected to become both slightly cheaper to build and slightly more efficient in capturing sunlight. The corresponding projections are:
breakeven electricity costs of $0.08/kWh ($22.22/GJ);
solar-to-electric capture of 55W/sq.m. (1.73GJ/sq.m./yr),
resulting in breakeven cash yield of $38.15/sq.m./yr.
Remarkably similar to the greenhouse profits of $38.82/sq.m./yr!

Now let’s look at GreenFuel’s biodiesel. We saw above that the maximum achievable yield of biolipids is ~0.16GJ/sq.m./yr. If we assume that these get converted with 100% efficiency (a truly heroic assumption) into biodiesel , which currently sells at $18.80/GJ wholesale, then we get a paltry three dollars per square meter per year ($3/sq.m./yr)
What biodiesel price would be required to achieve the same $38 /sq.m./yr cash yield as from a greenhouse, or from a projected medium-term CSP plant?

Here’s the calculation: $38/0.16GJ = $237.5/GJ,

which incidentally also equals to $31.60 per gallon of biodiesel or $1,327 per barrel. (The study uses more optimistic assumptions and arrives at ~$20/gal and ~$850/bbl).

Stunned?!

Twenty to thirty bucks per gallon?

Thousand bucks per barrel?

Well, as shocking as these prices are, they would still be lower than what you pay for soft drinks at major league ballparks, or for that most expensive fluid on the planet – ink for inkjet printers. If we are running out of oil and if the global warming is gonna get us, maybe it is worth paying up for a renewable fuel like biodiesel from algae… sigh?

Relax, folks! There are better options for both post-oil fuels and for CO2 mitigation. The study mentions some of them, and there are others that would certainly be economic at prices much lower than that.

How did we get there? How can a process and a company based on such feeble premises get funding, awards, and so much prominence in the media? Let’s again turn for explanation to Dr. Deffeyes:

“There will be numerous voices claiming to have the new, new thing to solve the energy problem. They are not necessarily con artists. Some of them convince themselves first, then they try to con the rest of us. They are their own first victims.”

In a free market world there is no Central Committee that says what makes sense and should be tried and what doesn’t and should be banned. If somebody promises to break the laws of physics and if somebody else is a GreenFool enough to invest their money there, so be it! No harm to the public, right?

Except that today many people don’t invest their own money. The contemporary world functions through a sophisticated web of financial intermediaries. When you put part of your salary into your company’s 410(k) or you make a donation to the endowment fund of your alumni college, the money flows through a chain of financial managers into mutual funds, hedge funds, venture capital funds, each with their own money managers.

These financial agents are, or course, motivated to make profits, however they are also getting paid a fixed percentage of the assets they manage. So, in other words, the upside is there for them, but there is no real downside: whether the investment fails or not, these people still get paid.

I happen to know the person responsible for the largest piece of money invested in GreenFuel - Jennifer Fonstad, who oversees the $6mln invested by Draper Fischer Jurvetson. Jennifer is a businesswoman with impeccable credentials, yet with a marked tendency to disregard the scientific reality.

Any ordinary person would be extra careful not to put their life’s savings into ventures that promise to break the laws of physics. If financial managers with Jennifer Fonstad’s high intelligence and Harvard degrees were as vigilant and careful when investing other people’s money, the world would be a much better place and no energy or environmental catastrophes would be a match to humankind. 

Heat Pump pump heat from one location and return it to another. That's why, that logically, it is called a "heat pump". All heat pumps operate basically on the same principle. This is a circuit of a liquid that "brings the heat: condensation. When forced to evaporate, it takes the heat that surrounds it. You know this principle is that of sweat. You sue because evaporates, the water is cool. Then forces the liquid condensate in the tablet (that is why heat pumps have a compressor) to liquefy. In doing so, it restores the heat he has taken to another place to evaporate. For a house, it is clear that it is interesting to cool the outside if it is to heat the interior. For a fridge in the kitchen, the refrigerator cools its interior by heating the kitchen! 

If it takes heat to evaporate a fluid is that its molecules are very attracted by each other. To take off a few, must be shaken very hard, so warm. Or in any case, when a molecule leaves the liquid, it is banged by neighbors who eject. Once the molecule part, his former neighbors least segment they used their energy to eject the molecule. So they are less hot. Evaporation cools it. 

Conversely, when a gas molecule occurs in a fluid, it is attracted by its neighbors. Suddenly, just when it happens, it becomes even more speed (because it is drawn) and it will knock her new neighbors. That the coup sagment more condensation (from gas to liquid) provides the heat. 

That's how it works! 

For the moment, most heaters operate using energy (electrical in the case of electric heating, or chemical in the case of heating oil or gas) and the dissipating completely. That is to have heat, we burn oil or gas and electricity increases in resistance to it is transformed into heat. And to be honest, it's a beautiful mess. Because this energy could be used to power a heat pump! 

The gas contains energy "chemical". When you burn 1 Joule gas or fuel oil (that is, a unit of energy per kilowatt hour or calories) it provides 1 Joule heat your home. But if you use a heat pump for each Joule provided the pump, pump it between 3 and 7 to the outside! In short, it can provide you with up to 7 Joules of energy. Conclusion: for now, our way of heating reflects the fact that we have energy in abundance enough to waste it! But as it rique not last (it will take some years to consume 4 to 5 times less energy than today) many people might make the heat pump. It will become very profitable. 

It may seem paradoxical that a heat pump is still able to take the heat when it's cold outside (like 4 ° C). Yes, but in fact, everything depends on the scale that we take. When a body is hot, is that its molecules are agitated. If they are agitated because they have energy (ie kinetic). If the molecules of an object does not move at all, it is at absolute zero, 0 Kelvin. The Kelvin unit is the true temperature. In fact, 4 ° C corresponds to 273 4 = 277 Kelvin. While you, at 37 ° C, you are 273 +37 = 310 Kelvin. In fact, 4 ° C is really hot from that point of view. It contains a lot of heat, we can take. 

Heat pumps, you know: there are fridges, air conditioners (which take the heat inside to reject it out), also known as geothermal energy (in fact it is a pump heat that takes the heat in the soil). There are many kinds of heat pumps. One of the easiest to implement is a cooling in reverse, taking heat to outside air and return it to the inside. And it works not bad!

Heating and Cooling with a Heat Pump

Ground-Source Heat Pumps
(Earth-Energy Systems)

A ground-source heat pump uses the earth or ground water or both as the sources of heat in the winter, and as the "sink" for heat removed from the home in the summer. For this reason, ground-source heat pump systems have come to be known as earth-energy systems (EESs). Heat is removed from the earth through a liquid, such as ground water or an antifreeze solution, upgraded by the heat pump, and transferred to indoor air. During summer months, the process is reversed: heat is extracted from indoor air and transferred to the earth through the ground water or antifreeze solution. A direct-expansion (DX) earth-energy system uses refrigerant in the ground-heat exchanger, instead of an antifreeze solution.

Earth-energy systems are available for use with both forced-air and hydronic heating systems. They can also be designed and installed to provide heating only, heating with "passive" cooling, or heating with "active" cooling. Heating-only systems do not provide cooling. Passive-cooling systems provide cooling by pumping cool water or antifreeze through the system without using the heat pump to assist the process. Active cooling is provided as described below.
How Does an Earth-Energy System Work?

All EESs have two parts: a circuit of underground piping outside the house, and a heat pump unit inside the house. Unlike the air-source heat pump, where one heat exchanger (and frequently the compressor) is located outside, the entire ground-source heat pump unit is located inside the house.

The outdoor piping system can be either an open system or closed loop. An open system takes advantage of the heat retained in an underground body of water. The water is drawn up through a well directly to the heat exchanger, where its heat is extracted. The water is discharged either to an above-ground body of water, such as a stream or pond, or back to the underground water body through a separate well.

Closed-loop systems collect heat from the ground by means of a continuous loop of piping buried underground. An antifreeze solution (or refrigerant in the case of a DX earth-energy system), which has been chilled by the heat pump's refrigeration system to several degrees colder than the outside soil, circulates through the piping, absorbing heat from the surrounding soil.

The Heating Cycle

In the heating cycle, the ground water, the antifreeze mixture, or refrigerant (which has circulated through the underground piping system and picked up heat from the soil), is brought back to the heat pump unit inside the house. It then passes through the refrigerant-filled primary heat exchanger for ground water or antifreeze mixture systems. In DX systems the refrigerant enters the compressor directly, with no intermediate heat exchanger.

The heat is transferred to the refrigerant, which boils to become a low-temperature vapour. In an open system, the ground water is then pumped back out and discharged into a pond or down a well. In a closed-loop system, the anti-freeze mixture or refrigerant is pumped back out to the underground piping system to be heated again.

The reversing valve sends the refrigerant vapour to the compressor. The vapour is then compressed which reduces its volume, causing it to heat up.

Finally, the reversing valve sends the now-hot gas to the condenser coil, where it gives up its heat. Air is blown across the coil, heated, and then forced through the ducting system to heat the home. Having given up its heat, the refrigerant passes through the expansion device, where its temperature and pressure are dropped further before it returns to the first heat exchanger, or to the ground in a DX system, to begin the cycle again.

Domestic Hot Water

In some EESs, a heat exchanger, sometimes called a "desuperheater", takes heat from the hot refrigerant after it leaves the compressor. Water from the home's water heater is pumped through a coil ahead of the condenser coil, in order that some of the heat that would have been dissipated at the condenser is used to heat water. Excess heat is always available in the cooling mode, and is also available in the heating mode during mild weather when the heat pump is above the balance point and not working to full capacity. Other EESs heat domestic hot water (DHW) on demand: the whole machine switches to heating DHW when it is required.

Hot water heating is easy with EESs because the compressor is located inside. Because EESs have relatively constant heating capacity, they generally have many more hours of surplus heating capacity than required for space heating.

Cooling Cycle

The cooling cycle is basically the reverse of the heating cycle. The direction of the refrigerant flow is changed by the reversing valve. The refrigerant picks up heat from the house air and transfers it directly in DX systems or to the ground water or antifreeze mixture. The heat is then pumped outside, into a water body or return well (in the case of an open system), or into the underground piping (in the case of a closed-loop system). Once again, some of this excess heat can be used to preheat domestic hot water.

Unlike air-source heat pumps, EESs do not require a defrost cycle. Temperatures underground are much more stable than air temperatures, and the heat pump unit itself is located inside; therefore, the same problems with frost do not arise. 
Parts of the System

As shown in Figure 7, earth-energy systems have three main components: the heat pump unit itself, the liquid heat exchange medium (open system or closed loop), and the air delivery system (ductwork).

Ground-source heat pumps are designed in different ways. Self-contained units combine the blower, compressor, heat exchanger, and condenser coil in a single cabinet. Split systems allow the coil to be added to a forced-air furnace, and use the existing blower and furnace.

Figure 7: Components of a Typical Ground-source Heat Pump

Energy Efficiency Considerations

As with air-source heat pumps, earth-energy systems are available with widely varying efficiency ratings. Earth-energy systems intended for ground-water or open-system applications have heating COP ratings ranging from 3.0 to 4.0, and cooling EER ratings between 11.0 and 17.0. Those intended for closed-loop applications have heating COP ratings between 2.5 and 4.0, while EER ratings range from 10.5 to 20.0.

The minimum efficiency in each range is regulated in the same jurisdictions as the air-source equipment. There has been a dramatic improvement in the efficiency of earth-energy systems efficiency over the past five years. Today, the same new developments in compressors, motors, and controls that are available to air-source heat pump manufacturers are resulting in higher levels of efficiency for earth-energy systems.

In the lower to middle efficiency range, earth-energy systems use single-speed rotary or reciprocating compressors, relatively standard refrigerant-to-air ratios, but oversized enhanced-surface refrigerant-to-water heat exchangers. Mid-range efficiency units employ scroll compressors or advanced reciprocating compressors. Units in the highefficiency range tend to use two-speed compressors or variable speed indoor fan motors or both, with more or less the same heat exchangers.

Figure 8: Open System Earth-energy System Efficiency (at an entering water temperature of 10oC)


Figure 9: Closed-Loop Earth-energy System Efficiency (at an entering anitfreeze water temperature of 0oC)

Sizing Considerations

Unlike the outside air, the temperature of the ground remains fairly constant. As a result, the potential output of an EES varies little throughout the winter. Since the EESs output is relatively constant, it can provide almost all the space heating requirement — with enough capacity left to provide hot water heating as an "extra."

As with air-source heat pump systems, it is not generally a good idea to size an EES to provide all of the heat required by a house. For maximum cost-effectiveness, an EES should be sized to meet 60 to 70 percent of the total maximum "demand load" (the total space heating and water heating requirement). The occasional peak heating load during severe weather conditions can be met by a supplementary heating system. A system sized in this way will in fact supply about 95 percent of the total energy used for space heating and hot water heating.

EESs with variable speed or capacity are available in two speed compressor configurations. This system can meet all cooling loads and most heating loads on low speed, with high speed required only during high heating loads.

A variety of sizes of EESs are available to suit the Canadian climate. Units range in size from 0.7 kW to 35 kW (2 400 to 120 000 Btu/h), and include domestic hot water (DHW) options.
Design Considerations

Unlike air-source heat pumps, EESs require that a well or loop system be designed to collect and dissipate heat underground.

OPEN SYSTEMS

As noted, an open system (see Figure 10) uses ground water from a conventional well as a heat source. The ground water is pumped into the heat pump unit, where heat is extracted. Then, the "used" water is released in a stream, pond, ditch, drainage tile, river, or lake. This process is often referred to as the "open discharge" method. 

Another way to release the used water is through a rejection well, which is a second well that returns the water to the ground. A rejection well must have enough capacity to dispose of all the water passed through the heat pump, and should be installed by a qualified well driller. If you have an extra existing well, your heat pump contractor should have a well driller ensure that it is suitable for use as a rejection well. Regardless of the approach used, the system should be designed to prevent any environmental damage. The heat pump simply removes or adds heat to the water; no pollutants are added. The only change in the water returned to the environment is a slight increase or decrease in temperature.

Figure 10: Open System Using Ground Water from a Well as a Heat Source


The size of the heat pump unit and the manufacturer's specifications will determine the amount of water that is needed for an open system. The water requirement for a specific model of heat pump is usually expressed in litres per second (L/s) and is listed in the specifications for that unit. The average heat pump unit of 10 kW (34 000 Btu/h) capacity tends to use 0.45 to 0.75 L/s while operating.

Your well and pump combination should be large enough to supply the water needed by the heat pump in addition to your domestic water requirements. You may need to enlarge your pressure tank or modify your plumbing to supply adequate water to the heat pump.

Poor water quality can cause serious problems in open systems. You should not use water from a spring, pond, river, or lake as a source for your heat pump system unless it has been proven to be free of excessive particles and organic matter, and warm enough throughout the year (typically over 5C) to avoid freeze-up of the heat exchanger. Particles and other matter can clog a heat pump system and make it inoperable in a short period of time. You should also have your water tested for acidity, hardness, and iron content before installing a heat pump. Your contractor or equipment manufacturer can tell you what level of water quality is acceptable and under what circumstances special heat-exchanger materials may be required.

Closed-loop Systems

A closed-loop system draws heat from the ground itself, using a continuous loop of special buried plastic pipe. Copper tubing is used in the case of DX systems. The pipe is connected to the indoor heat pump to form a sealed underground loop through which an antifreeze solution or refrigerant is circulated. While an open system drains water from a well, a closed-loop system recirculates its heat transfer solution in pressurized pipe.

The pipe is placed in one of two types of arrangements: vertical or horizontal. A vertical closed-loop arrangement (see Figure 11) is an appropriate choice for most suburban homes, where lot space is restricted. Piping is inserted into bored holes that are 150 mm (6 in.) in diameter, to a depth of 18 to 60 m (60 to 200 ft.), depending on soil conditions and the size of the system. Usually, about 80 to 110 m (270 to 350 ft.) of piping is needed for every ton (3.5 kW or 12 000 Btu/h) of heat pump capacity. U-shaped loops of pipe are inserted in the holes. DX systems can have smaller diameter holes which can lower drilling costs. 

Figure 11: Closed-Loop, Single U-bend Vertical Configuration


The horizontal arrangement (see Figure 12) is more common in rural areas, where properties are larger. The pipe is placed in trenches normally 1.0 to 1.8 m (3 to 6 ft.) deep, depending on the number of pipes in a trench. Generally, 120 to 180 m (400 to 600 ft.) of pipe are required per ton of heat pump capacity. For example, a well-insulated, 185 m2 (2 000 ft.2) home would probably need a three-ton system with 360 to 540 m (1 200 to 1 800 ft.) of pipe.

Figure 12: Closed-Loop, Single Layer Horizontal Configuration


The most common horizontal heat exchanger is two pipes placed side-by-side in the same trench. Another heat exchanger sometimes used where area is limited is a "spiral" - which describes its shape. Other horizontal loop designs use four or six pipes in each trench, if land area is limited.

Regardless of the arrangement you choose, all piping for antifreeze solution systems must be at least series 100 polyethylene or polybutylene with thermally fused joints (as opposed to barbed fittings, clamps, or glued joints), to ensure leak-free connections for the life of the piping. Properly installed, these pipes will last anywhere from 25 to 75 years. They are unaffected by chemicals found in soil and have good heat-conducting properties. The antifreeze solution must be acceptable to local environmental officials. DX systems use a refrigeration-grade copper tubing.

Neither the vertical nor the horizontal loops have an adverse impact on the landscape as long as the vertical boreholes and trenches are properly backfilled and tamped (packed down firmly).

Horizontal loop installations use trenches anywhere from 150 to 600 mm (6 to 24 in.) wide. This leaves bare areas that can be restored with grass seed or sod. Vertical loops require little space and result in minimal lawn damage.

It is important that the horizontal and vertical loops be installed by a qualified contractor. Plastic piping must be thermally fused, and there must be good earth-to-pipe contact to ensure good heat transfer, such as that achieved by Tremie-grouting of boreholes. The latter is particularly important for vertical heat-exchanger systems. Improper installations may result in less than optimum heat pump performance.

The entropy can be interpreted as a measure of disorder, but we will especially see an increase in entropy means a waste of energy. 

Imagine a trolley at the top of a slope. Imagine that on wheels, we will install a dynamo bicycle, which charge a battery. The dynamo will take the kinetic energy to the trolley when it will set in motion, and therefore the brake. To those, I hope many who have already used a dynamo on a bicycle, you know that is more difficult to move when it works is simply that energy you spend does not just put you in motion, but also to turn the dynamo, which produces electricity. If we charge a battery to the dynamo, at the end of the experiment, the trolley will also be moving down the slope, but all its potential energy has been dissipated. A portion was converted into electricity by dynamo, and stored in the battery. 

In fact, if the battery has managed to recover all of the potential energy, the entropy of the system did not increase, because energy is always tidy. It is simply stored in the battery now. So if no energy was lost in the form of thermal agitation, disorder has not increased. 

If we had not put battery, disorder would have been much greater. We have squandered all the potential energy in the form of thermal agitation. The increase in the disorder would have been possible. 

What is happening in practice, an intermediate situation. Some of the initial potential energy of the truck is recovered in the battery, the other is wasted. The increase in the disorder is not zero, but it is not possible. 

For against, one thing is not possible: that the thermal agitation, which is a lot of energy still got to put the cart in motion, voluntarily, even small movements. This charge the battery, and would mean we have managed to recover thermal energy from the rails. Decreased disorder. Maybe we can slow the increase in the disorder by recovering energy, but not to reduce the disorder. It is forbidden by the second principle! 

We therefore concluded that 

Anywhere a spontaneous evolution of a system is possible (where an increase of entropy is possible) this means that energy can be recovered. 

An increase of entropy is a waste of energy. 

Wasted energy is irreversible. The wasted energy can be recovered, this would contradict the second principle.

This is the natural continuation of my previous article entitled Thermodynamics: The Fundamentals. I will present the 4 major principles that are posed by the thermodynamics, which led to the understanding, construction and improvement of thermodynamic machines like the steam engine, the gasoline engine, the heat pump or air conditioner .
Zero Principle
It's called principle zero because it is this principle that allows the study of thermodynamics using the variable temperature. It can be expressed as follows:

The foundations and implications of this principle, related to quantum physics are complex but did not affect the classical thermodynamics and the construction of thermal machines. I can therefore not go into details here.

The thermal machines
A thermal machine can respond to 2 main functions:
- Transforming the Work in the heat (to move an object from heat): steam engine, heat engine (internal combustion engine, gasoline, diesel, alcohol or gas in cars, jet engines on airplanes) and so on.
- Transforming work into heat (from hot to cold or from a moving object): heat pump, refrigerator, air conditioner, etc..
The thermal machines are based on a set of thermodynamic transformations that one comes to subject a fluid and cyclical. In our study thermodynamics, fluid is then our system will come from the heat exchange and work with the external environment.

- In a steam engine, the fluid in question is the water that we usually just heat with a coal boiler to evaporate water (a pport heat). The steam then activates a piston that will lead to a wheel through a crankshaft and cause a rotational movement (job creation). Illustration of a steam engine (source: Wikipedia):
- For a motor car explosion, the fluid used is of the essence, diesel, alcohol or gas (LPG) by the motors. In a petrol engine 4 stroke classic, it comes to blow up a air / fuel mixture in a combustion chamber with a small spark foune by candles (heat). This explosion allows the movement of a Pison which will generate a rotary motion via a crankshaft to rotate the wheels (the creation of work). Illustration of a 4 stroke engine (source: Wikipedia):
- In refrigerators use a fluid called "refrigerent" as a heat transfer fluid (which carries the heat). Freon was used at the beginning but now they are complex fluids such as dichlorodifluoromethane, the tetrafluoroethane or methylpropan that are less harmful to the environment. The general principle of the refrigerator is to compress a fluid through a compressor (labor input) and then perform a relaxation (decrease fluid pressure suddenly) to the cold. Air conditioners are based on the same principle and heat pumps are just air conditioners that work 'in reverse'. A future note will be dedicated to refrigeration machines.

For convenience, we represent these transformations in diagrams that can be of various natures. One of the best known is the Clapeyron diagram that illustrates the evolution of pressure and volume of fluid during the transformation. Thus, each line between 2 points in the diagram corresponds to a processing performed by special equipment (heat exchanger, valve, turbine, piston ...) between 2 states of the fluid.

Carnot Cycle
the early 19 th century, Sadi Carnot, the famous physicist and french engineer, sets the ideal thermodynamic cycle to produce mechanical work from a heat source and a cold: The Carnot cycle. Carnot's research was vital in his time machine to produce steam optimal improving yields and it is also the first to express the scientific principle of heat engine in which all the engines are now built in cars and aircraft (engine explosion and jet engines).

This cycle is reversible, if taken in the opposite direction, there is also the ideal cycle to share the warmth of a hot spring in a cold source from a source of employment data. In other words: the ideal refrigeration cycle!

The Carnot cycle consists of a set of reversible adiabatic transformations 2 (no heat exchange with the outside entropy constant) and 2 transformations isotherms (constant temperature). In the direction of clockwise, it is a motor cycle and the transformations are:
- From 3 to 4: Isotherme compression Q1 where heat is extracted from the system to the cold source is at a temperature T1 (ie Q1 <0)>Reversible adiabatic (isentropic) Compression
- From 1 to 2: Isothermal heat addition where Q2 is given to the system via a source that is hot at the temperature T2 (ie Q2> 0)
- From 2 to 3: Reversible adiabatic (isentropic) expansion The Carnot engine cycle in the Clapeyron diagram (according to the Pressure Volume)

In total, this cycle produces a mechanical work W = Q1 + Q2 and a quantity of heat Q1 for a given quantity of heat equal to Q2, and this is the best cycle between a hot and a cold source.

If we apply the 2nd law of thermodynamics in this cycle by saying that it is ideal (adiabatic reversible transformation, thus constant entropy), we can make a balance of entropic cycle.

- During the transformation from A to B, the entropy extracted from the system is equal to the amount of heat Q1 negative divided by T1, see equation (1)

- During the conversion of C to D, the entropy provided to the system is equal to the amount of heat Q2 positive divided by the temperature of processing, or T2, see equation (2)

- The other 2 changes are therefore reversible adiabatic transformations entropy remains constant. We can therefore say that the entropy lost between A and B is equal to the entropy gained between C and D, see equation (3) represents the equation of Clausius-Carnot and defines the necessary heat exchange between a hot source (at temperature T2) and source cold (at temperature T1).
Example of Carnot cycle
It is considered a kind of ideal steam engine that uses water as a fluid and which is based on a Carnot cycle (impossible to achieve). In our hypothetical machine, the cold source is at room temperature, ie T1 = 20 ° C = 293 kelvin. The heat is the temperature of the water vapor that is T2 = 100 ° C = 373 kelvin. If we make a quantity of heat Q2 = 500 watt, then the amount of heat is extracted from the system according to the equation of Clausius-Carnot equal to Q1 = - T1 * (Q2/T2) = - 293 * (500/373) = -393 Watt. The work provides is equal to W = Q1 + Q2 = 500 - 393 = 107 Watt.

This means that between 20 ° C and 100 ° C, if we make a quantity of heat of 500 watts, we can extract the best of cases a mechanical power of 107 watts, peak performance is W/Q2 n = = 107/500 = 21%. Physics teaches us that it is impossible to manufacture a machine with a thermal efficiency greater than 21% between 20 ° C and 100 ° C. More generally it can be shown that the performance for a Carnot engine depends only on warm and cold temperatures and that this return is equal to:
All thermodynamic machines trying to get closer to the Carnot cycle but it is unattainable in part because the second law of thermodynamics which states that any transformation generates entropy. Transformations isentropic (reversible adiabatic) are impossible, as well as isothermal compressions because when a gas compresses, it just generates heat due to friction, which has the effect of increasing the temperature of the system.

For example, a gasoline combustion engine operates between 20 ° C (293 K) and 500 ° C (773 K) around its Carnot efficiency is therefore 1-273/773 = 62%. In fact, a gasoline engine has an efficiency of about 36% in operation and 15% in degraded operation (eg in town) because of the generation of entropy in the various transformations and the generation of heat of compression.

The second law of thermodynamics states that disorder a set of objects left to themselves (ie single) or entropy can only increase with time.

We will see that it is not contrary to the second principle that sometimes the order increases. We will take a simple example, and yet very relevant. That is what I found best answer to my dad, who once forced me to keep my room ...

Finally, keep her room, put it a little more order, ultimately, reduce the entropy. It is perfectly true. Only, and you have seen many times, your room does not arrange itself - we have you had to repeat it. Yes. It is you who are going to tidy up your room. But it will take time, especially, energy. You are going to spend the energy to do so. For example, if you fold a sweater to put on your shelf, the pull will have increased its potential energy. You have read, but in doing so, you also warm part of the energy you've spent has been transformed into thermal agitation. And the thermal agitation, it is a much bigger mess than pull the ground, in terms of entropy!

So your room is row, yes, it has a decreased entropy, also yes. But if it does not contradict the second law of thermodynamics, because it has not been left to itself: it did not row alone, you are involved, it is not a system isolated. So the second principle was not violated. On the contrary, you've wasted the energy to do so. So you have increased the disorder of the universe in general, it is indeed an isolated system. So storing her room inevitably leads to increasing disorder in the universe! If after that you can still force you to store anything!

Another example of higher order in the universe, of course, life a living being is a very complex construction, and very orderly. How is it that when life appears as the second principle says that the disorder must increase? Well is that living beings are not isolated. Actually a living being isolated as a mouse in an airtight container, ends quickly die. To maintain the living things need an external energy. In fact, they benefit from the waste environment.

Imagine, in fact, there are no plants. Sunlight merely serve to warm the earth, and that's all. It would be lost. Or plants in the receiving, using his energy to live. They store this energy in their leaves. The animals eat the leaves, with the drawing of energy. Energy that ultimately, they spend moving, etc ... So the sun's energy is finally dissipated. However, in the meantime, it was used to living beings. So living beings enjoy the abundance of ambient energy, which would otherwise be wasted, in order to exist. They are like dams they pass water (energy), but they make a reservation, and they slow down his fall (his loss in the form of temperature). They are slowing down in scale the increasing disorder in the universe. And it only works where otherwise much energy would be wasted. As soon as energy is available, the living land: the mold as soon as there is something to develop, etc ...

During my second year of studies, I attended a summer school on the physics of low temperatures and there was obviously a reminder of basic thermodynamics. From memory, here is the introductory sentence of our teacher (who is more than true):

"The first time we study the thermodynamics, it does nothing. The second time, we think he understood. And the third time, it is sure to have understood nothing, but it is not serious because it happens all the same to use and it works! "


Thermodynamics is a major discipline of physics and experienced many changes over the centuries. Its function is the first study of heat and different thermal machines but also as a mission the study of systems in equilibrium. The thermodynamics was developed mainly in the 19th century by renowned scientists with, among other Carnot, Clapeyron, Lord Kelvin, Clausius, Boltzmann, Van der Waals etc. (see portrait above, you will notice the importance of the beard).

It is a vast and complex subject, my ticket blog that bears the title "thermodynamics" is ambitious, but I will try as much as possible to give you a concise overview and as fair as possible, which is not clear a spot ... If you simply want to know the principles and applications in thermal machines, see Thermodynamics: Principles and Applications.

The concept of system

Studying the thermodynamics of systems. A system is a portion of the universe that is isolated by the thought and all that is out of this system is called the external environment. There are three types of systems:

- The open systems that exchange of matter and energy with the external environment. Ex: a plastic water bottle open: it can fill or empty it exchanges heat with the ambient air and is deformable.

- Closed systems which do not matter with the external environment but which can exchange energy in the form of mechanical work and heat. Ex: a plastic water bottle closed. It can be distorted and heat exchange with the outside but the quantity of matter inside does not change.

- The isolated systems where there is no exchange with the external environment (or matter, or energy). Ex: a thermos bottle closed ideal rigid.

The state variables

Different quantities (or variables) are used in physical thermodynamics. It is important to understand and to classify them into different categories and then use them. First, one must distinguish between extensive and intensive quantities:

- An extensive quantity is a physical quantity that is proportional to the size of the system (you can add). Eg mass, volume, quantity of material, etc..

- An intensive quantity is a physical quantity does not depend on the amount of material in question (you can not add). Ex: temperature, pressure, density, etc..

Thermodynamics seeks to calculate the physical quantities from one system to a state of equilibrium in terms of other quantities. To do this, we define state variables that are measurable physical quantities to determine the state of a system, regardless of the path followed to reach this state.

Explanation: A few weeks ago I made an exit in skiing in the Swiss Alps and we had to reach the Mont Tellier located 2951 m from a parking lot located at 1925 m. Two groups left the car park by two different routes:

- The first group made a direct ascent regular totaling 2951-1925 = 1026 m elevation gain (blue route).

- The second group has taken a path requiring longer fitted and descents. The total route of 1,500 m elevation gain (red route).

In this example, we can define the state of the system by the variable "altitude" because the difference in elevation between the parking and the top 2 of routes is the same: to DA = 2951-1925 = 1026 m altitude is therefore a state variable.

However, the effort provided by the mechanical red group is significantly higher than the mechanical effort provided by the blue: the variable mechanical effort is not a state variable because it depends on the path followed between 2 states in equilibrium.

In thermodynamics, the main state quantities are:

- The temperature (T) which is measured in degrees kelvin, see ticket Temperature for more details.

- The pressure (P), which is a force per unit area. The pressure is measured in pascal (1 Pa = 1 N / m²) but is often used for convenience the bar (1 bar = 100 000 Pa). A car tire inflated to 2 bars means that the air applies a force of 200 000 newtons per square meter on the tire.

- The volume (V) is measured in cubic meter.

- The internal energy (U), which represents all the energy of a microscopic system and is measured in J / kg. The internal energy is the sum of energies due to thermal agitation of the particles and the links between the nucleons, atoms and molecules.

- The enthalpy (H) is a thermal engineering practice because when that transformation takes place at constant pressure, the change in enthalpy reflects the amount of heat exchanged. The enthalpy is measured in J / kg and is defined by H = U + P * V.

- The entropy (S) which represents a kind of "microscopic chaos" of a system and is measured in J / kg-K. We will come back a little later on the concept of entropy.

The thermodynamic quantities that are not state variables (which depend on the path) are:

- The work (W) which is measured in watts and is a mechanical energy per second.

- The heat (Q) which is also measured in watts, which represents a thermal energy per second.

The functions of state

The different state variables are not independent of each other: they are linked in a more or less complex and thermodynamics then to define the "equation of state" or "state functions" which relations in different quantities at steady state.

The function of thermodynamic state the simplest and is known ideal gas equation can be written:

P * V = n * R * T

where the state quantities are the pressure (P), volume (V) and temperature (T) with n the quantity of matter and "R" the famous gas constant. This equation is a reliable model for gases said perfect, ie the gas consisting of particles far enough apart to neglect the interactions: the
nitrogen and oxygen in our atmosphere is one example.

Transformations

Transformation is called the passage of a state of initial equilibrium to a final state of equilibrium. It often identifies the transformations by a state variable that remains constant: a transformation at constant temperature (isothermal), at constant pressure (isobaric), constant volume (isochoric), at constant enthalpy (isenthalpic), constant entropy (isentropic).

It also often speak of adiabatic transformation, it simply means that a transformation during which the system was no heat with the surroundings.

More generally, there are two main classes of transformations:

- The reversible transformation: Once the conversion is made, the initial state can be reached from the state by applying a minor on the system. Ex: A closed bottle of water temperature and ambient pressure (20 ° C, 1 bar) is left under a blazing sun. The temperature rises to 30 ° C and the pressure at 2 bar. If the sun disappears under a cloud, the bottle regains its original state after a certain time.

- Transformations irreversible: once the transformation, it is impossible to return to the initial state since the final fast and simple. Ex: A bottle is filled with liquid 2 of the same density and different colors (blue and yellow) separated by a watertight wall. Removing the wall and the 2 liquids mix. It is impossible to find just the initial state.

A transformation is generally considered reversible if intensive quantities are continuous, if the conversion is slow (they say then it is quasi-static) and if there is no dissipative phenomena (diffusion, friction, etc.). .

We can also accept that transformation adiabatic (which was no heat with the external environment) and is a reversible isentropic transformation.

To see more, which explains the principles of thermodynamics with thermal machinery introductions: Thermodynamics: Principles and Applications