How to Beat the Second Law
I like this statement for the Second Law of Thermodynamicsâ€"
"You can't fool Mother Nature."
That seems rather obvious, don't you think? And this very certainty is why the Second Law is called a "law." Now, here is what I mean by saying that Mother Nature can't be fooled. Nature dictates that rocks roll down hill. This is a one-way process. No matter how much you talk to it, a rock will NOT roll up hill. Of course, you can carry it up-hill if you want, but you should eat a good breakfast because some work will be required. There are many other examples of things going only one way in nature. Water flows down-stream. Heat flows "down" from a higher temperature to a lower temperature. The reverse processes NEVER happen, although you might create the appearance of it by putting in work of some kind.
Of course our interest here is in getting as much "free energy" as we can, or at least not paying any more than we have to. As I see it, energy only comes in two kindsâ€"
(1) Stuff we call "work." This can do things for us.
(2) Heat, what we often end up with if we do some work.
As far as I can tell, any form of energy that isn't heat is a kind of work. So, sunlight for example is work. A magnetic field is work. As a general principle, one kind of work can be exchanged for another kind at little or no cost if we are careful. But if you aren't careful, some of the work goes to heat, and eventually it all ends up that way. Nature will let us change our more useful, orderly "work" into heat any time we want. Or, it is only too happy to do it for us. BUT we are not allowed to simply exchange heat for work. Again, this is a one-way process, and really no different than others mentioned before. When a rock rolls down hill, it loses gravitational potential (work) and converts that energy into heat. But once the rock has expended its work, it can't get it back again.
All of these processes that nature urges in one direction we call "spontaneous." Heat will move spontaneously from a place of high temperature to another place at a lower temperature, if there is a path. So we see that heat at a high temperature has more possibilities for use. And, heat at a low temperature is more "useless." A good measure for that is Q /T where Q is the amount of heat added and T is the absolute temperature at which you add the heat. This is called the entropy change. Besides a name, it is also given a symbol, Î"Sâ€"
Î"S = Q /T
As T gets smaller, the entropy change gets bigger, so moving heat from a high temperature to a low temperature increases entropy. Or, changing work to heat will also increase entropy by creating new heat. So, without going into all the details about why Q/T is the right measure, we can see that whenever a process happens, there is a positive entropy change, or at least it isn't negative.
Now, let's write a general equation for processes involving energy changes. Let's say that the state before the change is "1" and the condition after is "2". Some of the heat has been exchanged for work or vice-versaâ€"
W1 + Q1 = W2 + Q2
What we have here is a statement of the First Law of Thermodynamics, that the total amount of energy never changes in a process, if you are careful to account for all of the energy. In order for this process to occur, we will say that the entropy increases, so the entropy after is greater than the entropy before. (This is a form of the Second Law)â€"
Q2 /T2 > Q1 /T1
Notice that so far, T1 can be either bigger or smaller than T2. Here are some conclusions to be drawnâ€"
If T1 > T2, then Q1 may be greater than Q2, and then W2 > W1
If T1 < T2, then Q2 must be greater than Q1, and W1 > W2
I will leave it to you to think through these situations and see that the conclusions follow logically. If W1 = 0 and T1 > T2, then you have the case of an engine. If W2 = 0 and
T1 < T2, then you have the case of a refrigerator or a heat pump. Let's go ahead and look at the case of an engine, where you start with just heat, so W1 = 0 â€"
Q1 = W2 + Q2 where T1 > T2 and Q1 is greater than Q2
And in order for this engine to work, I know that the entropy must increase, in other words, Q2 /T2 > Q1 /T1. I will rearrange these two expressions, remembering that the efficiency of the engine is defined as the work W2 divided by the heat put in from the fuelâ€"
W2 /Q1 = 1 â€" Q2 /Q1
1 > Q2 /Q1 > T2 /T1
Let's call W2 /Q1 = Eff, because that's the efficiency of the engine. It is something positive, but less than one. Combining these expressions, we get the Carnot formulaâ€"
Eff < 1 â€" T2 /T1
All engines that work have to satisfy this formula. In some cases, we could have some complication about defining what the temperatures are, and then you might need to modify the formula some. Whatever the situation is, you can be assured that entropy increases when you run the engine or it flat won't work. If you have a "perfect, reversible" engine, then theoretically, you could use an equal sign in this formula. And, that is the Carnot limit for an engine's maximum efficiency.
What's that?â€"you say I promised to tell you how to "beat the Second Law"? Oh, yes, I did, didn't I. Okay.
Let's look at how a typical engine works. A fuel is burned, and then the heat is used to power the engine. There's the mistake, right there. The fuel contained chemical energy. Chemical energy is WORK. Naturally, if you allow the chemical energy to be converted to heat, nature doesn't mind at all. The entropy went way up right there. And then the engine turns around and tries to convert some of the energy back to work, with a substantial loss and a further increase in entropy, according to the Second Law. If you don't want to be subject to the Second Law, then don't convert work into heat if you don't have to. And, in principle, we know how to do that. Chemical energy can be converted to another kind of work with much less inefficiency. One way to do that is with an electrochemical cell. The chemical energy goes directly to electrical energy, and if you do it right, you can keep as much as 90% of the work you started with. No heat engine can match that.
There are some other ways to beat the Second Law of Thermodynamics, but let's save that story for another day.
Ernie Rogers
As one using thermographic tools I think I understand the 2nd law pretty well. So why is it Momma taught us to to hold the cast iron skillet with a rag while cooling it with cold water?
Naturally I didn't follow her advice the first few times. Even if the handle is just warm to the touch you may wind up with burns.
Quote from: BEP on February 19, 2009, 01:18:40 PM
As one using thermographic tools I think I understand the 2nd law pretty well. So why is it Momma taught us to to hold the cast iron skillet with a rag while cooling it with cold water?
Naturally I didn't follow her advice the first few times. Even if the handle is just warm to the touch you may wind up with burns.
Oh, yes, we can't fool your Momma either.
Ernie Rogers
Quote from: CARN0T on February 17, 2009, 02:01:00 AM
How to Beat the Second Law
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Let's look at how a typical engine works. A fuel is burned, and then the heat is used to power the engine. There's the mistake, right there. The fuel contained chemical energy. Chemical energy is WORK. Naturally, if you allow the chemical energy to be converted to heat, nature doesn't mind at all. The entropy went way up right there. And then the engine turns around and tries to convert some of the energy back to work, with a substantial loss and a further increase in entropy, according to the Second Law. If you don't want to be subject to the Second Law, then don't convert work into heat if you don't have to. And, in principle, we know how to do that. Chemical energy can be converted to another kind of work with much less inefficiency. One way to do that is with an electrochemical cell. The chemical energy goes directly to electrical energy, and if you do it right, you can keep as much as 90% of the work you started with. No heat engine can match that.
There are some other ways to beat the Second Law of Thermodynamics, but let's save that story for another day.
Ernie Rogers
The combustion engine works by burning fuel. Burning is a one way process, so the energy can't be reused to burn again - at least not in an instant.
To do work you actually does nothing at all. Moving an object from A to B does not cost anything. What is payed for is the friction between A and B.
When you start moving an object angular to gravity, you spent energy in accelerating, but you can get this energy back at retardation at point B.
The best way to do this, is to to use electricity and magnetism - an electric driven car. You decharge the battery when accelerating, and charge the battery when breaking. Along the way you loose some
useful energy due to friction, but nevertheless, no net work is done by moving an object from A to B. The traditional thinking is that when you have accelerated an object, this spent potentional energy isn't stored anywhere - just lost as heat.
Maybe I didn't read yout post well enough :)
Br.
Vidar
Dear Carnot,
Please read my post subject Curled Ballistic Thermionics.
I have a number of professors and experts already in agreement.
As you know there is no proof of the 2nd Law.
I now claim there is a proof that the Lord Kelvin statement was a viewpoint and a half baked theory, not a law and it is now relegated to myth.
Phil H
Quote from: BEP on February 19, 2009, 01:18:40 PM
As one using thermographic tools I think I understand the 2nd law pretty well. So why is it Momma taught us to to hold the cast iron skillet with a rag while cooling it with cold water?
Naturally I didn't follow her advice the first few times. Even if the handle is just warm to the touch you may wind up with burns.
Your mom should have taught you NOT to put a hot cast iron skillet under cold water, rag or not. ;D
Hi, Phil,
A statement of the second law: "There is no natural process for which the change in entropy is negative." This can be shown to being equivalent to "heat does not spontaneously flow from a cold place to a hot place." Another equivalent statement is "You can not convert 100% of heat to work."
I guess you have found one or all of these statements to be untrue?
Ernie Rogers
Quote from: Philip Hardcastle on February 24, 2009, 05:53:50 AM
Dear Carnot,
Please read my post subject Curled Ballistic Thermionics.
I have a number of professors and experts already in agreement.
As you know there is no proof of the 2nd Law.
I now claim there is a proof that the Lord Kelvin statement was a viewpoint and a half baked theory, not a law and it is now relegated to myth.
Phil H
(I'm testing out Google Translate from Norwegian to English ...)
Work assumes that there are at least two energy levels that interact on each other. You can have lots of energy, but taken that energy in an environment where the energy density is the same, will not work be carried out.
You can transfer the heat to work, but to exploit the heat 100% of work assumes that the environment has a temperature on the absolute zero.
However, the work, which is created by heating, in areas where the temperature is not at the absolute zero, provides a relatively work that is the difference between the temperature of the machine and the temperature of the surroundings. So anyway, it is quite possible to convert heat to 100% work.
Just a feeling I have about the topic ...
Vidars laws :)
Quote from: Hugo Chavez on February 24, 2009, 01:24:31 PM
Your mom should have taught you NOT to put a hot cast iron skillet under cold water, rag or not. ;D
I was talking about a couple hundred degrees F. Hardly enough to cause damage to the pan when cold water was applied.
The point is - the stored heat should have flowed to the area being instantly cooled. It did not. The heat moved to the handle in less than a second. The handle would cool very quickly afterwards.
I would suggest that there are ways to have an absolute mechanical advantage over matter. If a person has an absolute mechanical advantage over matter then it becomes possible to transform incredible amounts of mass into energy. Then if that energy is put to work through a load that has a higher resistance, more energy can be harvested. This is where the work function becomes perpetual. An analogy would be a hydraulic pump, if you lift 10,000 pounds under one set of conditions and then drop that weight under another set of conditions it could create an accelerated force. The key to becoming perpetual is through the use of an electromagnetic system because the speed of electricity is essentially the speed of light unless you are some fraction of a light year away from the device generating the electromagnetic field. Lightening is a perfect example or proof. An ampere is nothing more than charge accumulated and dispersed in a "reasonable" amount of time.
Quote from: CARN0T on February 17, 2009, 02:01:00 AM
How to Beat the Second Law
I like this statement for the Second Law of Thermodynamics—
"You can't fool Mother Nature."
That seems rather obvious, don't you think? And this very certainty is why the Second Law is called a "law."
<SNIP>
This is a very good conclusion and thread i.g.,
...leaving some room for creative minds.
Like the extentional reply of Philip Hardcastle.
If it don't go tooooo deeply into esotherics,
this could be made sticky as a spoiler for newbies
and as an reminder for oldies.
Best regards,
sushi