The Second Law and Swamp Coolers

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Heat Can Be Transferred From a Cold Body to a Hot Body: The Air Conditioner.

When I was an undergraduate, I had a physical chemistry professor who claimed that air conditioners that were completely inside a room could not possibly work.  Opening the refrigerator door on a hot day will not make your house cooler.

The refrigerator gives off more heat than it transfers from inside itself; a refrigerator is actually heating the house.  If the door is left open, the refrigerator works harder to try to maintain a cool temperature in accordance with its thermostat setting.  As the refrigerator works harder, it releases more heat into the house.

My professor, however, was not correct.  It is possible to have a cooling unit that does more cooling than it releases heat to the environment.  The trick with indoor coolers is that the process by which they operate is not cyclic.

Heat Can Be Transferred From a Cold Body to a Hot Body: The Air Conditioner

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Hydrogen Economy.

As of 10/26/2010, a survey on this site shows that 25% (Final result 21%) of the respondents thus far think that the second law of thermodynamics says that heat cannot be transferred from a cold body to a hot body.

Not only are these people mistaken, but they are also ignoring their own common experience of the world.

It is possible to transfer heat from a cold reservoir to a hot reservoir! 

The Hydrogen Economy

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled Perpetual Motion.

The media often perpetuate the idea that the so-called hydrogen economy is the solution to all of our energy needs.  Hydrogen is abundant everywhere; in fact there are oceans full of hydrogen in the form of water, just waiting to be extracted, oxidized and used as an endless source of energy, right?

Perpetual Motion

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled The Definition of Entropy.

It is a consequence of conservation of energy and the second law of thermodynamics that it is impossible to build a perpetual motion machine. There are many types of proposed perpetual motion machines.

There is a post that goes into a lot of detail of the various sorts of perpetual motion machines by Kevin T. Kilty, entitled Perpetual Motion.   Rather than go into arcane detail about different types of perpetual motion machines, I think it suffices to refer the interested reader to Kilty's post.

No machine can generate more more energy than put in (first law of thermodyanics, conservation of energy, Noether's theorem).  The first law of thermodynamics states that work can be converted into heat, and heat can be converted into work, but that the sum, the so-called internal energy (E or U) is a conserved quantity.

The Definition of Entropy

This post is part of a series, Nonsense and the Second Law of Thermodynamics. The previous post is entitled: The Carnot Cycle.  This post is heavily dependent on the previous post; so I recommend reading it first. 

Let q represent the heat transferred in a process, and qrev represent the heat transferred in a reversible process. Let T be the absolute temperature (in Kelvin).

The sum of  qrev/T for all steps of the process over a full Carnot cycle is equal to zero.  In fact, it is true for any reversible cyclic process.

The Carnot Cycle

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  Reversible Processes.

In 1824, Nicolas Léonard Sadi Carnot tried to explain how heat could be converted into useful work. He came up with a four-step cycle that is known as the Carnot cycle.

Reversible Processes

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  Entropy is Not a Measure of Disorder.

To understand the macroscopic thermodynamic definition of entropy,  it is important to understand something called a reversible process.  A reversible process is just what it sounds like: a process that is reversible.

A reversible process should be thought of as an ideal case. In a reversible process, the system is in equilibrium for every infinitesimal step of the process.  Imagine a balloon filled with gas, and imagine that the balloon is perfect, i.e., we need not concern ourselves with the properties of the balloon itself: we care only about the gas inside the balloon and the gas outside the balloon.

At equilibrium, the pressure on each side of the balloon is equal.  If the pressure outside of the balloon is reduced, the balloon expands until the pressures are equal again.  In a reversible process, the balloon is allowed to expand continuously by infinitesimal steps.  The reversible process acts as a  limit to any real process.

Entropy Is Not a Measure of Disorder

This post is part of a series, Nonsense and the Second Law of Thermodynamics.  The previous post is entitled:  What the Second Law Does Say.

Entropy is not a measure of disorder.  Entropy is not a measure of disorder.

To paraphrase Stanford  Professor H.C. Anderson, there are a lot of sentences in the English language that contain the words "entropy" and "disorder," and most of them are wrong.  There are many reputable text books and sources that say that entropy is disorder; nevertheless, entropy is not a measure of disorder.