1 Basic Concepts of Thermodynamics

1-1 Thermodynamics and Energy

Thermodynamics is defined as the science of energy. Engineering thermodynamic deals with the principles of energy and energy conversion in engineering and the thermal properties of substances as well.

1-1-1 Definition of Thermodynamics

The Basic Laws of Thermodynamics :

(1) The First Law of Thermodynamics:

an expression of the quantity relationship during energy change

(2) The Second Law of Thermodynamics:

an expression of the quality relationship during energy change

1-1-2 Contents of Thermodynamics

It can be divided into: Classical Thermodynamics--------macroscopic approach

Statistical Thermodynamics--------microscopic approach

The Properties of Material

(1) Ideal Gas

(2) Vapor: Water Steam, Freon , Ammonia

(3) Mixtures: Gas mixture, Gas-vapor mixture

Practical Application

Gas Power Cycle

Vapor and Combine Power Cycle

Refrigeration

Any physical quantity can be characterized by dimension

The arbitrary magnitudes assigned to the dimensions are called Units

Primary( foundamental ) dimensions and units:

Mass m, Length L, time t, temperature, T, mol Secondary dimensions:

velocity V, energy E , volume V

English system:

Also known as the United States Customary System(USCS)

SI: International System

1-1-3 Dimensions and Units

From Le Systeme International d’Unites

History :

1.1790 French National Assembly charged the French Academy of Science

2. 1875 The Metric Convection Treaty was signed by 17 nations.General Conference of Weights and Measures ( CGPM ) was established

3. 1960 the CGPM produced the SI

Some SI and English units

Refer to our Text book

Dimensional Homogeneity

Every term in an equation must have the the same units.

* the student must keep in mind that a formula which is not dimensionally homogeneous is definitely wrong, but a dimensionally homogeneous formula is not necessarily right

1-2-1 The definition of Thermodynamics SystemSystem : A quantity of matter or a region in space for study

The real or imaginary surface that separates the system from its surroundings is called boundary

Anything outside the boundary is called surrounding

The boundary can be real or imaginary; fixed or changeable, has no thickness and volume , and does not contain any substance.

1-2 Thermodynamics System

Closed system : 1-1-3-2 The Classification of Thermodynamics system

A system that only energy can cross the boundary but no mass can enter or leave ( also known as control mass )

Opened system :

A system that not only energy but also mass can cross the boundary (also known as control volume )

isolated system :

A system that neither energy nor mass can cross the boundary (a special closed system)

The Universe

1-3 State and Equilibrium1-3-1 Definition: All macroscopic characteristics of a system at one time point

1-3-2 Classification:

1-3-3.Conditions of Equilibrium

Equilibrium state:

any part of the system have the same characteristics

any characteristics don’t change with time

Nonequilibrium state:

•Thermal equilibrium

•Mechanical equilibrium

•Chemical equilibrium

•Phase equilibrium

1-4 Properties of System1-4-1 Definition

Any characteristic of a system is called a property1-4-2 Characteristic of propertyRelated with States but have nothing to do with the path from one state to another

According to mathematics ：

∮dx = 01-4-3 Classification of property

Intensive property ： Properties independent of the size of system, such as ：

temperature, pressure, specific volume

Extensive property ：

Properties whose values depend on the size or extent of system, such as ：

volume, entropy, enthalpy

1-5 The state postulate

The state of system is described by its properties,But obviously we don’t need to specify all the properties to fix a state,Then how many properties are enough to fix a state?State postulate

The state of a simple compressible system is completely specified by two independent, intensive properties

A system is called simple compressible system in the absence of electrical, gravitational, motion, and surface tension effects.

1-6 Thermodynamics Property Coordinates

Since two properties can fix a state, it’s very convenient to draw a state point on a two-dimension coordinates.

p

v

equilibrium state

nonequilibrium state

The usually used coordinates are: p-v coordinates, T-s coordinates, h-s coordinates

1-7 Process and Cycle

Process:

any change that a system undergoes from one equilibrium state to another

a process proceeds in such manner that the system remains infinitesimally close to an equilibrium state at all time

How to change under

equilibrium state?

Quasi-static process:

p

v

Quasi-static process

nonequilibrium process

Initial state

final state

Cycle:A path-closed process

p

v

1-8 Forms of energy1-8-1 Total energy

The total energy E of a system is the sum of thermal, mechanical, kinetic, potential, electric,chemical and nuclear energy.

On a unit mass basis,

1-8-2 Classification of energy

1.Macroscopic form : kinetic energy KE and potential energy PE

mEe /

2KE

2mV mgzPE

On a unit mass basis

2ke

2V gzpe

and

and

2.Microscopic form:

relate to the molecular structure of a system and the degree of the molecular activity. The sum of all the microscopic forms of energy is called the internal energy, denoted by U or u on a unit mass basis.

1-8-3 Expression of total energy

mgzmV

UPEKEUE 2

2

gzV

upekeue 2

2

On a unit mass basis

1-9 Pressure1-9-1 definition

The force exerted by a fluid per unit area

Calculation:

A

FP

Unit:

SI: Pa--------N/m2

English: psi------lbf/in2

1bar=105 Pa

= 0.1 Mpa

=100 kPa

1atm=101,325 Pa

= 101.325 kPa

=1.01325 bar

=14.696 psi

1-9-2 Gage pressure and vacuum Pressure

Absolute pressure: the actual pressure at a given position is called the absolute pressure

The pressure calculated by formula P=F/A

manometer

Gage pressure:The pressure over atmospheric pressure while gas pressure is larger than that of atmosphere ， expressed by Pg

atmabsg PPP

Vacuum pressure:The pressure below atmospheric pressure while gas pressure is smaller than that of atmosphere ， expressed by Pv

absatmv PPP

In SI the unit also is Pa, but in English psig usually employed

Absolute pressure? gage pressure? vacuum pressure? woooooooo!

Which one is the state property?

1-10-1 The zeroth law of thermodynamics

If two bodies are in thermal equilibrium with a third body , they are also in thermal equilibrium each other .

1-10 TemperatureI think it is the measure of hotness or coldness

Am I right?

What is temperatur

e?

1-10-2 thermodynamics definition of temperature

It’s the property to describe if systems are in thermal equilibrium

1-10-3 Temperature scaleThree factors of Temperature scale ：• zero point • two states point ( easily reproducible states ) • Scale

Temperature scale in history

SI: Celsius scale

English: Fahrenheit scale

Formerly called the centigrade scale, in 1948 it was renamed after the Swedish astronomer A.Celsuis (1701-1744)

named after the German instrument maker G.Fahrenheit (1686-1736)

SI: Kelvin scale

English: Rankine scale

Thermodynamics temperature scale:

Relations of scales:

15.273)C()K( 。 TT

67.459)F()R( 。 TT

)K(8.1)R( TT

32)C(8.1)F( 。。 TT