1 Basic Concepts of Thermodynamics 1-1 Thermodynamics and Energy 1-1-1 Definition of Thermodynamics 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. It can be divided into: Classical Thermodynamics--------macroscopic approach Statistical Thermodynamics--------microscopic approach 1-1-2 Contents 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

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

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 1-1-3 Dimensions and Units 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 From Le Systeme International d’Unites

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 Thermodynamics System 1-2-1 The definition of Thermodynamics System System : 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.

1-1-3-2 The Classification of Thermodynamics system Closed 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 Equilibrium 1-3-1 Definition: All macroscopic characteristics of a system at one time point 1-3-2 Classification: Equilibrium state: any part of the system have the same characteristics any characteristics don’t change with time Nonequilibrium state: 1-3-3.Conditions of Equilibrium Thermal equilibrium Mechanical equilibrium Chemical equilibrium Phase equilibrium

1-4 Properties of System ∮dx = 0 Intensive property： 1-4-1 Definition Any characteristic of a system is called a property 1-4-2 Characteristic of property Related with States but have nothing to do with the path from one state to another According to mathematics： ∮dx = 0 1-4-3 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

How to change under equilibrium state? 1-7 Process and Cycle Process: any change that a system undergoes from one equilibrium state to another Quasi-static process: a process proceeds in such manner that the system remains infinitesimally close to an equilibrium state at all time p v Quasi-static process nonequilibrium process Initial state final state

Cycle: A path-closed process p v

1-8 Forms of energy 1-8-1 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 and On a unit mass basis 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 On a unit mass basis

1-9 Pressure 1-9-1 definition The force exerted by a fluid per unit area Calculation: 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

The pressure calculated by formula P=F/A 1-9-2 Gage pressure and vacuum Pressure Absolute pressure: the actual pressure at a given position is called the absolute pressure manometer

In SI the unit also is Pa, but in English psig usually employed Gage pressure:The pressure over atmospheric pressure while gas pressure is larger than that of atmosphere，expressed by Pg Vacuum pressure:The pressure below atmospheric pressure while gas pressure is smaller than that of atmosphere，expressed by Pv

Absolute pressure? gage pressure? vacuum pressure? woooooooo! Which one is the state property?

1-10 Temperature I think it is the measure of hotness or coldness Am I right? 1-10 Temperature What is temperature? 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 .

1-10-2 thermodynamics definition of temperature It’s the property to describe if systems are in thermal equilibrium 1-10-3 Temperature scale Three factors of Temperature scale ： zero point two states point ( easily reproducible states ) 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) Temperature scale in history SI: Celsius scale English: Fahrenheit scale

Thermodynamics temperature scale: SI: Kelvin scale English: Rankine scale Relations of scales: