Mechanical Engineering Dept. Shahid Bahonar University of Kerman Thermodynamics-1 S. M. Hosseini Sarvari Chapter 1 Introduction & Basic Concepts
Mechanical Engineering Dept. Shahid Bahonar University of Kerman The objectives: Identify the unique vocabulary associated with thermodynamics through the precise definition of basic concepts to form a sound foundation for the development of the principles of thermodynamics. Review the metric SI and the English unit systems that will be used throughout the text. Explain the basic concepts of thermodynamics such as system, state, state postulate, equilibrium, process, and cycle. Review concepts of temperature, temperature scales, pressure, and absolute and gage pressure. Introduce an intuitive systematic problem-solving technique. 2
Thermodynamics : Science of Energy Energy : Ability to cause change thermodynamics = therme (heat) +dynamis (power) Today the same name is broadly interpreted to include: all aspects of energy energy transformations, including power generation, and refrigeration relationships among the properties of matter. 3
Conservation of Energy 4
Conservation of Energy E in E out E 5
First and Second Laws of Thermodynamics 6
Two Forms of Thermodynamics Classical thermodynamics: macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of individual particles Statistical thermodynamics: A more elaborate approach, based on the average behavior of large groups of individual particles 7
Application Areas of Thermodynamics 8
Application Areas of Thermodynamics 9
DIMENSIONS AND UNITS The seven fundamental (or primary) dimensions and their units in SI are listed in table 1-1. 10
DIMENSIONS AND UNITS SI system: unit of mass = meter (m) unit of length = kilogram (kg) unit of temperature = Celsius ( o C) unit of time = second (s) English system: unit of mass = pound-mass (lbm) unit of length = foot (ft) unit of temperature = Farenheight ( o F) unit of time = second (s) 11
DIMENSIONS AND UNITS 1N 1kg. m/ s 2 1lbf 32.174 lbm. ft / s 2 12
Some SI and English Units Unit of Weight: W m g (N) Unit of Specific weight ( ): g Unit of Work: 1J 1N. m 13
SYSTEMS AND CONTROL VOLUMES 14
SYSTEMS AND CONTROL VOLUMES Closed system (control mass) 15
SYSTEMS AND CONTROL VOLUMES 16
SYSTEMS AND CONTROL VOLUMES Open System (Control Volume) 17
PROPERTIES OF A SYSTEM 18
Continuum Continuum: a continuous, homogeneous matter with no holes. There are about 3 10 16 molecules of oxygen in the tiny volume of 1 mm 3 at 1 atm pressure and 20 o C 19
Continuum Example: consider a small volume of a system, and let mass be designated. The specific volume is defined by m V v lim V V V m 20
DENSITY AND SPECIFIC GRAVITY Density: m / V, ( kg / 3 m ) Incompressible substances: Constant Specific volume: v V / m 1/, ( m 3 / kg) Specific gravity (relative density): SG / H2 O 21
DENSITY AND SPECIFIC GRAVITY 22
STATE AND EQUILIBRIUM State: set of properties that completely describes the condition. 23
STATE AND EQUILIBRIUM Equilibrium state: In an equilibrium state there are no unbalanced potentials (or driving forces) within the system. A system in equilibrium experiences no changes when it is isolated from its surroundings. Equilibrium Non-Equilibrium 24
STATE AND EQUILIBRIUM Thermal equilibrium: a system is in thermal equilibrium if the temperature is the same throughout the entire system. Mechanical equilibrium: a system is in mechanical equilibrium if there is no change in pressure at any point of the system with time. Phase equilibrium: If a system involves two phases, it is in phase equilibrium when the mass of each phase reaches an equilibrium level and stays there. Chemical equilibrium: system is in chemical equilibrium if its chemical composition does not change with time, that is, no chemical reactions occur. 25
The State Postulate State postulate: The state of a simple compressible system is completely specified by two independent, intensive properties. Simple compressible system: A system in the absence of electrical, magnetic, gravitational, motion, and surface tension effects. Independent Properties: Two properties are independent if one property can be varied while the other one is held constant. 26
PROCESSES AND CYCLES 27
PROCESSES AND CYCLES 28
PROCESSES AND CYCLES Quasi-equilibrium process 29
PROCESSES AND CYCLES Non-Equilibrium Process 30
PROCESSES AND CYCLES Cycle: A system is said to have undergone a cycle if it returns to its initial state at the end of the process. for a cycle the initial and final states are identical 31
The Steady-Flow Process Steady flow process 32
The Transient Process Transient Processes 33
ZEROTH LAW OF THERMODYNAMICS Thermal Equilibrium 34
Celsius scale ( o C) Temperature Scales Fahrenheit scale ( o F) o o T( F) 1.8T ( C) 32 Kelvin scale (K) o T ( K) T ( C) 273.15 Rankine scale (R) o T ( R) T ( F) 459.67 T ( R) 1.8T ( K) 35
Temperature Scales Ideal-gas temperature scale: T a b P 36
PRESSURE P vac P atm P abs P gage P abs P atm 37
PRESSURE Variation of Pressure with Depth 38
PRESSURE F z m a z 0 P2 x P1 x g x z 0 P P 2 P 1 g z s z 39
PRESSURE z 40
PRESSURE P P atm gh or P gage gh 41
PRESSURE Pascal s law ideal mechanical advantage 42
THE MANOMETER Manometer: P P Patm gh 2 1 43
THE MANOMETER P atm 1 P 1gh1 2gh2 3gh3 44
THE MANOMETER P 1 1g a h) ( gh ga P 2 1 2 1 2 ( 2 1 if 1 2 P P ) gh P1 P2 2gh 45
THE BAROMETER P C 0, P P P P g h B atm B C P atm g h 46
ATMOSPHERIC PRESSURE Altitude (m) Sea level 1000 2000 5000 10000 20000 P atm (kpa) 101.325 89.88 79.50 54.05 26.50 5.53 47
PROBLEM-SOLVING TECHNIQUE Step 1: Problem Statement Step 2: Schematic Step 3: Assumptions and Approximations Step 4: Physical Laws Step 5: Properties Step 6: Calculations Step 7: Reasoning, Verification, and Discussion 48