Prof Sporlan

27-09-2002, 04:27 AM

There are 4 laws of thermodynamics. They are as follows:

Zeroth Law: When two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other.

This may seem to make obvious sense, but this simple observation allows us to create thermometers, and use temperature measurements for analytical work.

First Law: Heat entering a system can either increase temperature (internal energy) or be used to perform useful work.

This is law of energy conservation. An interesting concept, BTW. It states energy cannot be created or destroyed. Einstein further expanded on this concept by proving that both mass and energy are conserved, since mass can be converted to energy and vice versa, via the equation: e = mc<sup>2</sup>. This implies mass and energy were never created; they have always existed, and always will exist.

Second Law: The entropy change of any isolated system is positive, and approaches zero for any process that approaches reversibility.

This law is considered the fundamental law of natural science.

When we convert one form of energy to another, say electricity to running a refrigeration system to produce cooling, some of the energy is lost in the conversion. This "lost" energy can be measured in terms of entropy. One cannot have a perfectly efficient (zero entropy change) process. Even an ideal vapor compression refrigeration system will have two sources of positive entropy change: desuperheating in the condenser and flow thru the expansion device.

The second law has been used to predict the end of the universe (all mass and energy will eventually disintegrate into useless heat), it has been shown that it gives us our direction of time (the second law tells us we cannot go backwards in time), and it has been used to prove the existence of God. It is definitely the thermodynamic law worth discussing at refrigeration wholesaler open house events… :)

Third Law: It is impossible to cool a body down to absolute zero.

Thermodynamic laws can be simplified as follows:

First Law: You can’t win, you can only break even

Second Law: You can only break even at absolute zero

Third Law: You can never reach absolute zero.

Zeroth Law: When two systems are in thermal equilibrium with a third system, they must be in thermal equilibrium with each other.

This may seem to make obvious sense, but this simple observation allows us to create thermometers, and use temperature measurements for analytical work.

First Law: Heat entering a system can either increase temperature (internal energy) or be used to perform useful work.

This is law of energy conservation. An interesting concept, BTW. It states energy cannot be created or destroyed. Einstein further expanded on this concept by proving that both mass and energy are conserved, since mass can be converted to energy and vice versa, via the equation: e = mc<sup>2</sup>. This implies mass and energy were never created; they have always existed, and always will exist.

Second Law: The entropy change of any isolated system is positive, and approaches zero for any process that approaches reversibility.

This law is considered the fundamental law of natural science.

When we convert one form of energy to another, say electricity to running a refrigeration system to produce cooling, some of the energy is lost in the conversion. This "lost" energy can be measured in terms of entropy. One cannot have a perfectly efficient (zero entropy change) process. Even an ideal vapor compression refrigeration system will have two sources of positive entropy change: desuperheating in the condenser and flow thru the expansion device.

The second law has been used to predict the end of the universe (all mass and energy will eventually disintegrate into useless heat), it has been shown that it gives us our direction of time (the second law tells us we cannot go backwards in time), and it has been used to prove the existence of God. It is definitely the thermodynamic law worth discussing at refrigeration wholesaler open house events… :)

Third Law: It is impossible to cool a body down to absolute zero.

Thermodynamic laws can be simplified as follows:

First Law: You can’t win, you can only break even

Second Law: You can only break even at absolute zero

Third Law: You can never reach absolute zero.