Science about Heat Before starting this story You have to know Force → Energy

Every one experiences “hotness” and “coldness”, but how to describe it ?

Temperature and Its Measurement and How do we measure it ? Galileo’s thermoscope, 1595 A digital fever thermometer use the temperature dependence of the electric resistance of a semiconductor crystal to measure temperature Thermal expansion

Development of the temperature scales Celsius scale 0 C (1743) Fahrenheit scale 0 F (1700)

— Kelvin scale k, 1848 A constant-volume gas thermometer Experimental results: The pressure plotted as a function of temperature for different gases. When extended backward, the lines all intersect temperature axis at the same point. † absolute zero: 0 0 k = C † Can we reach the absolute zero ?

What is temperature ? x z y x’ z’ y’ — the physical properties (such as volume) of each object may change right after it was placed in contact with other ones. — as the time goes long enough, the physical properties of the objects are no longer changing. These objects are said to be in thermal equilibrium. We said “They have the same temperature”. The Zeroth Law of Thermodynamics We still haven’t answer the question: what is temperature ?

How do objects with different temperature reach thermal equilibrium when they contact ? — Heat flows from one object to another when there is a different in temperature between the objects. — Temperature is the quantity that indicates whether or not, and in which direction, heat will flow. What is Heat ?what is temperature ?

— 18 century, most people accepted a material model of heat caloric theory of heat: heat was supposedly an invisible fluid called “caloric” Antoine Lavoisier ( )Joseph Black ( ) The science of thermodynamics progressed quite nicely during this period, even though the basic concept of heat was wrong ! Material or Motion ？

— Benjamin Thompson ( ) Count Rumford of Bavaria 1798, What is the source of heat that raises the temperature of drill and the cannon barrel ? — 1799, Humphry Davy. melting of two ice cubes by rubbing Where is the Caloric coming from ?

— James Joule ( ) Joule’s experiment (1840), a falling mass turns a paddle in an insulated beaker water in this schematic representation of Joule’s apparatus for measuring the temperature increase produced by doing mechanical work on a system. Joule’s found that 4.19 Joul of work was required to raise the temperature of water by 1 0 C 1 cal =4.2 Joul

The most important consequence in Joule’s experiment: Heat flow is a transfer of energy If energy is added to a system either as work or as heat, the “internal energy” of the system increased accordingly. The change in internal energy is equal to the net amount of heat and work transferred into the system. Total Energy is Conserved !

Energy Can Be Neither Created Nor Destroyed

The First Law of Thermodynamics Total energy is conserved ! the change in internal energy of the system Note: In the macroscopic approach of thermodynamics, there is on need to specify the physical nature of the internal energy. However, it is worth noting that the internal energy is the sum of all possible kinds of energy “stored” in the system. state variables, thermodynamic variables

卡諾機 vs. 永動機

A model of Rumford’s cannon-boring experiments carried out at the arsenal at Munich in 1797~8

Newcomen’s atmospheric steam engine in 1712

James Watt’s single-acting steam engine of The boiler C is placed in an outhouse. The cylinder E is kept at a high temperature all the time. F is the separate condenser and H an air pump.

James Watt’s single-acting steam engine of 1788.

Industrial Revolution

— Newcomen used a steam engine to pump water from a mine in 1712 — After significant improvements made by James Watt between 1763 and 1782, the steam engine supplied the motive force for the industrial revolution. What is the best efficiency that we could achieve ? What factors determine efficiency ? Sadi Carnot (1796 ~ 1832)

In order to consider in the most general way the principle of production of motion by heat, it must be consider independent of any mechanism or any particular agent. It is necessary to establish principles applicable not only to steam engine but to all imaginable heat-engine, whatever the working substance and whatever the method by which it is operated. Sadi Carnot (1796 ~ 1832) “Reflections on the Motive Power of Fire”, 1824

Heat Engine Efficiency of a heat engine ( automobile engine, diesel engine, jet engine, steam turbine,……) engine Sadi Carnot & caloric theory

Carnot engine An ideal engine in which all of the processes had to occur without undue friction or departure from equilibrium. This condition means that the engine is completely reversible. Efficiency of the Carnot engine

The internal energy is unchanged for one complete cycle, so the first law gives W=Q net. and we also know PV  =constant for an adiabatic process TV  - 1 =constant ( ideal gas) so Finally we obtain the efficiency of the Carnot engine

Carnot’s theorem the efficiency of the Carnot engine 1. All reversible engines operating between two given reservoirs have the same efficiency. 2. No cyclical heat engine has a greater efficiency than a reversible engine operating the same two temperatures.

Clausius’ statement (1850): It is impossible for a cyclical device to transfer heat continuously from a cold body to a hot body without the input of work or other effect on the environment. Second Law of Thermodynamics Kelvin’s statement (1851): It is impossible for a heat engine that operates in a cycle to convert its heat input completely into work. impossible heat engine ( 1824 ~ 1907 ) ( 1822 ~ 1888 ) impossible heat engine

Equivalence of the Kelvin and Clausius statement A. if Clausius is false  Kelvin is false B. if Kelvin is false  Clausius is false

Proof of Carnot’s theorem If some engine did have an efficiency greater than the Carnot efficiency, the second law of thermodynamics would be violated. Ex: violate Kelvin statement !

Rudolf Clausius, 1822 ~ Energy is conserved 2. Heat flows naturally from hot to cold. – 1850

Carnot Engine ( Reversible Engine) Efficiency of a heat engine engine The ratio of heat to temperature is a constant for a reversible process. Kelvin scale

What about the ratio is for an irreversible process ?

…since I think it is better to take the name of such quantities as these, which are important for science, from the ancient language, so that they can be introduced without change into all the modern languages, I propose to name the magnitude S to “entropy” of the body, from Greek word [for] a transformation. I have intentionally formed the word entropy so as to be as similar as possible to the word energy, since both these quantities are so nearly related to each other in their physical significance The Ratio Is called “Entropy”

Rudolf Clausius, 1822 ~ Energy of the universe is conserved 2. The entropy of the universe tends toward a maximum – 1865 Time Arrow

What is Entropy ？ after all that…..

from Kinetic Theory of Gas to Statistical Thermodynamics

Ludwig Boltzmann 1844 ~ 1906 The Man Who Trusted Atoms