Figure 1: follow to the second Law, every refrigerators must have actually work excellent on castle in stimulate for warm to flow from a cold human body to a hot body.

You are watching: How does a refrigerator reflect the second law of thermodynamics


The second Law the Thermodynamics describes the restrictions of warm transfer. Many importantly, the sets the end the details idea that heat cannot it is in converted completely to mechanically energy. This crucial idea have the right to be declared in plenty of ways, but there room 3 that will certainly be debated in detail. These are:

Waste warm Statement

The Waste warmth statement, formally known as the "Kelvin-Planck statement" is together follows:<2>

"It is impossible to extract an quantity of heat, represented as QH, from a hot reservoir and use it every to perform work."

This is a explain of the thermal effectiveness in warm transfer, offered by the equation in figure 2.


Figure 2: the is impossible for the thermal effectiveness of one engine to it is in 100%, where every one of the warm from the hot body would certainly be transferred to advantageous work.<2>

This declare is important to understand in regards to practicality of warmth engines. Waste heat is necessary for all engines, and the quantity of job-related that is excellent by the intake of heat provides the thermal performance of a system. Making use of an evaluation of heat and also work on suitable engine, the maximum lot of work that have the right to be completed by a thermodynamic exchange in between two particular temperatures is offered by the Carnot efficiency. Although the Carnot efficiency can never ever be reached in reality, the is useful to to compare to once looking at thermal efficiency of an engine.

For a much more detailed study of this version of the 2nd law please see the hyperphysics web page on the 2nd law: warmth engines.

Refrigeration Statement

Also well-known as the "Clausius statement", this is fundamental to exactly how a refrigeration system works:

"Heat will always flow spontaneously indigenous hotter building material to cooler ones".

This is known as the Clausius statement, and also explains why an ice cube will melt when inserted in a bowl of hot water however ice will not kind from water exterior on a hot day. Daily experience definitely supports this statement, yet it is a deep physical principle limiting what"s possible with energy.

The 2nd law that thermodynamics insurance claims that the is impossible for heat to spontaneously flow from a cold body to a warm body, but it deserve to move in that means if some form of occupational is done.<3> This is exactly how the refrigeration process works, and an example can be viewed in figure 1. Refrigerators job-related by transferring heat from the cold regions inside the the machine to warm regions outside of it, in order to making the cold regions also cooler. This is exactly how refrigerators job-related to save food inside of castle cool, and why they have the right to be feeling blowing warm air out of your vents.<3>


The right part of the picture in figure 2 and 3 describe the impossible scenarios the the second law forbids, therefore a perfect frozen fridge is analogous come a system"s heat transfer operating at 100% efficiency.

In figure 3, the refrigerator takes some warmth from the cold reservoir, Q_c, does some job-related on it, W, and rejects some heat Q_H to the hot reservoir. Therefore the net result of the frozen fridge is to make the cold reservoir chillier by removing warmth from it and also moving that warmth to the hot reservoir. As result of this, a refrigerator is basically a heat engine the runs in reverse. By analyzing how fine a refrigerator have the right to cool the cold reservoir, refrigerators bring with lock a coefficient of performance.

This statement is nicely caught in the humorous tune "The an initial and 2nd Laws the Thermodynamics" by Flanders and Swann. Because that a much more rigorous (but no as funny) compose up of the refrigeration statement of the 2nd law please see the hyperphysics second Law:refrigerator page.

Disorder Statement


Another statement, probably the most crucial in terms of expertise why the Clausius and also Kelvin-Planck statements space true is around entropy (which have the right to be believed of as disorder):<4>

"The entropy the a close up door system have the right to never decrease."

It is necessary to emphasize that this statement describes a "closed system", definition that there room no exterior influences ~ above the system. This is due to the reality that an open up system have the right to have that entropy decreased, as this ability to diminish the entropy is just how refrigerators work! through that said, the earth is an open up system due to the fact that of the solar energy to the planet contributes come the Earth"s energy flows.

Entropy is essentially a measure up of "disorder", for this reason the greater the entropy, the much more disorder the system has. This can be seen when shaking bricks in a can: the bricks are much more likely to type a loosened pile than to turn right into a house. Watch the hyperphysics web page on entropy because that a an ext detailed discussion.

Associated through entropy is the idea the "energy quality". Heat is a low-quality energy, conversely, mechanical power is a high-quality energy. Watched in number 4, the energy quality decreases as entropy increases. Thus in general, because entropy normally increases, power quality will deteriorate. The combination between rise in entropy and also a to decrease in power quality explains why every one of the energy in fuels cannot it is in converted right into mechanical energy. It is feasible to burn fuel, as such directly converting all its power to low-quality heat, yet this low-quality heat cannot climate be turned completely into high-quality mechanical energy or electricity.

See more: What Is The Density Of Cooking Oil (Palm Oil) ? Density Of Cooking Oil


For a more detailed summary of the entropy declare of the 2nd law of thermodynamics please watch the hyperphysics page on the 2nd law: entropy.