Introduction & Basic Concepts of Thermodynamics Introduction to ...
Thermodynamics - Introduction
-
Upload
uzair-khaleeq -
Category
Documents
-
view
42 -
download
0
description
Transcript of Thermodynamics - Introduction
-
ME 302 - THERMODYNAMICS
Course Instructor
Engr. Uzair Khaleeq uz Zaman
-
Course Plan
Credit Hours = 2 1
Text Book
Fundamentals of Engineering Thermodynamics by Michael J. Moran and Howard N. Shapiro (5th or 7th Edition)
Reference Books
Thermodynamics: An Engineering Approach by Y. A. Cengel and M. A. Boles, Latest Edition
Applied Thermodynamics by T.D. Eastop and A. McConkey
-
Course Plan (contd)
Course Objectives & Learning Outcomes
Gain basic knowledge and skills in the area of thermodynamics
Understand the concept of heat energy, fluid properties, inter-conversion of heat and work, reversible and irreversible processes
Attain better understanding of operational procedure of machines such as IC Engines, Turbo machinery, Steam and Gas Turbines,
Compressors, etc.
Learn about inter-conversion of heat and work energies
Gain sufficient knowledge to understand power plant basics and operational / maintenance procedures for static and /or rotary
equipment
Understand the concepts which will help design thermal systems.
-
Course Plan (contd)
Lectures Schedule
Sr. No. Topic Week / Lecture
1
Introductory concepts and definitions, types of systems,
temperature and pressure scales, evaluating energy transfer by
work and heat, first law of thermodynamics, types of cycles and
respective calculations
1-3
2
Properties of a system; pressure-volume, pressure-volume
temperature and temperature-volume curves, phase change,
concepts of internal energy and enthalpy, gas laws and respective
calculations
4-5
3 Control Volume Analysis: Turbines, nozzles and diffusers,
compressors and pumps, heat exchangers, and throttling devices 6-8
4
The Second Law of Thermodynamics: Statements of the 2nd Law,
heat engines, refrigeration devices, reversible versus irreversible
processes, the Carnot cycle and respective calculations
9-11
5
Entropy and Enthalpy-Clausius inequality, the increase in entropy
principle, entropy change of pure substances, enthalpy and
specific heats;
12-13
6 Vapor Power Systems and Gas Power Systems 14-16
-
Course Plan (contd)
Grading System
Sessional = 25 %
Quizzes/Assignments = 10 %
Lab = 25%
Final Exam = 40 %
-
Introductory Concepts and Definitions
What is Thermodynamics? Storage
Transformation
Transfer
Storage in terms of
Internal energy (associated with temperature)
Kinetic energy (due to motion)
Potential energy (due to elevation)
Chemical energy (due to chemical composition)
Transformation from one form to another
Transfer across a system boundary as heat or work
ENERGY
-
Introductory Concepts and Definitions
(contd)
The word; Thermo-dynamic
First used by Thomson (later Lord Kelvin)
Has Greek origin
Translated as the combination of
-
Introductory
Concepts and Definitions
(contd)
Applications
Automobile Engines
Compressors, Pumps
Turbines
HVAC&R systems
Solar activated heating and
Power generation
Biomedical Applications
Life support systems
Cooling of Electronic
Equipment
-
Introductory Concepts and Definitions
(contd)
Plot KE(t) and PE(t) with and without drag forces, g = 9.81m/s2
-
Introductory Concepts and Definitions
(contd)
Functions of KE(t) and PE(t)
Without Drag force With Drag force
Same amount of PE but less KE Less Total Mechanical Energy = >
THERMAL ENERGY
-
Introductory Concepts and Definitions
(contd)
System
Whatever we want to study (quantity of fixed mass under investigation)
As simple as a free body
As complex as a refinery
Content inside the system may change or remain fixed by chemical reactions
Surroundings
Everything external to the system
System Boundary
Interface separating system and surroundings
May be at rest or in motion
-
Introductory Concepts and Definitions
(contd)
Heat can get into the system
(Potato can get hot)
Work can cross out of the system
(Potato can expand)
-
Introductory Concepts and Definitions
(contd)
Types of Systems
1. Closed System (Control Mass)
Contains fixed quantity of matter
Always contains the same matter
NO MASS TRANSFER ACROSS THE BOUNDARY
2. Open System (Control Volume)
Region of space through which mass can flow
MASS TRANSFER ACROSS BOUNDARY
3. Isolated System
NO INTERACTION WITH THE SURROUNDINGS
Potato with THICK and INELASTIC skin
-
Introductory Concepts and Definitions
(contd)
Control Surface
When the terms control mass and control volume are used, the boundary of a system is referred to as the control surface
-
Introductory Concepts and Definitions
(contd)
How to Select System Boundary
What is known about the system
Objective of the analysis
Example: Air Compressor and storage tank
System boundary encloses what?
If electrical power input is known,
this boundary might be selected.
Objective:
How long compressor must operate for
the pressure in the tank to rise to a
specified value?
-
Introductory Concepts and Definitions
(contd)
Macroscopic vs Microscopic
Macroscopic (Classical Thermodynamics)
Overall system is studied
No models of the structure of matter at molecular, atomic and sub atomic levels are used
Microscopic (Statistical Thermodynamics)
Concerned directly with the structure of the matter
Average behavior of particles making up a system is studied
-
Introductory Concepts and Definitions
(contd)
Continuum (Assumption of matter in this course) Discrete changes from molecule to molecule can be ignored
Distances and times are much larger than those of the molecular scale (continuously distributed through out region of interest)
Applications of continuum assumption
Rarefied gas dynamics of outer atmosphere (for low orbit space vehicles)
Nano-scale heat transfer (in cooling of computer chips)
ENABLE THE USE OF CALCULUS IN CONTINUUM
THERMODYNAMICS
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance Phase
Quantity of matter that is homogenous throughout In chemical composition In physical structure
Phase Boundaries Interfaces between different phases
Pure Substance Uniform and invariable in chemical composition Can exist in more than one phase BUT chemical composition must be
the same in each phase
If one phase is not identical to other phase = NOT a pure substance
Example of single phase ICE, LIQUID WATER
Example of two or multi phase mixture GLASS OF ICE WATER Phase boundaries = at the edge of each ice cube
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
State
Condition described by observable macroscopic properties
Property
Macroscopic characteristic, has a unique value
Quantity that only depends on the state of the system and is independent of the history of the system
Ex: Mass, Volume, Temperature, Pressure, Energy
TWO STATES ARE EQUIVALENT IF THEY HAVE THE SAME PROPERTIES = NOTE
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd) Process
Transformation from one state to another
When property changes, state changes, and process occurs
Steady State
When properties remain same, state remains same
None of the properties change with time
Thermodynamics Cycle
Sequence of processes that begins and ends at the same state
Change in value of a property from one state to another is solely dependent on the two end states and is INDEPENDENT of the path of the process
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
Extensive Property
Depends on the mass (or extent) of the system
Its value for an overall system is the sum of its values for parts into which it is divided
Can change with time
Ex: mass, total volume, total energy
Intensive Property
Independent of the mass of the system
Ex: Temperature, Pressure, Specific Volume
What would happen
to the extensive and
intensive properties
when you cut a
system in half?
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
Equilibrium
Condition of balance / No spontaneous changes observed with respect to time
Procedure to attain equilibrium
ACTUALLY WE NEVER REACH EQUILIBRIUM, WE ONLY APPROXIMATE IT (It takes infinite time to
reach final equilibrium)
ISOLATE SYSTEM FROM
SURROUNDINGS
WATCH ANY CHANGE IN PROPERTIES
IF NO CHANGE, AT EQUILIBRIUM
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
Equilibrium (contd)
Mechanical Equilibrium = Characterized by Equal Pressure
Thermal Equilibrium = Characterized by Equal Temperature
Metastable Equilibrium = If a system would undergo large change in its properties when subjected to small disturbance
(Ex: mixture of gasoline and air or large bowl on a small table)
PROCESS vs QUASIEQUILIBRIUM PROCESS ??
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
Quasiequilibrium Process
Process in which the departure from thermodynamic equilibrium is almost not possible (infinitesimal)
Each state can be considered as equilibrium states
Why do we want to model a process as quasiequilibrium?
To develop systems which can give qualitative information
To deduce relationships that exist among propoerties at equilibrium
Helps to generate constant line on P-V diagram
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
Quasiequilibrium Process (contd)
Thermodynamically slow
compression of air in a
cylinder = Quasiequilibrium
process
Combustion in a cylinder = series
of non-equilibrium states
Dashed because properties are not
uniform = State cant be defined
Solid because properties are
uniform = State can be defined
-
Introductory Concepts and Definitions
(contd)
Properties and State of a Substance (contd)
Quasiequilibrium Process (contd)
If I need to add weight, W, on a piston, how should I add it in:
Quasiequilibrium manner?
Non-equilibrium manner?
Cycle
When a system in its initial state experiences a series of quasiequilibrium processes and returns to the initial state,
the system undergoes a cycle.
-
Introductory Concepts and Definitions
(contd)
Fundamental Variables and Units
Mass
Kilogram (kg) = a mass equal to the mass of the international prototype of the kilogram (a platinum
iridium bar stored in Paris), roughly equal to the mass of
one litre of water at S.T.P
Pound mass (lbm)
Length
Meter (m) = length of the path travelled by light in vacuum during a time interval of 1/299792458 of a
second
Foot (ft)
-
Introductory Concepts and Definitions
(contd)
Fundamental Variables and Units (contd)
Time
Second (s) = the duration of 9192631770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom
Second (s) = English time unit identical to SI unit
Temperature
Kelvin (K)
Celsius (oC)
Rankine (oR)
Fahrenheit (oF)
-
Introductory Concepts and
Definitions (contd)
Secondary
Variables and
Units
Force
Energy
Specific
Volume
Density
Pressure
-
Introductory Concepts and Definitions
(contd)
Measurable Properties
Density
Depends on relativity of continuum
Intensive property
May vary from point to point in the system
Specific Volume
Inverse of density (volume per unit mass)
Intensive property (may vary from point to point)
-
Introductory Concepts and Definitions
(contd)
Measurable Properties (contd)
Molar Basis
To express sp. Volume on molar basis in terms of kmol or lbmol (used in certain applications)
Ratio of mass (kg) and molecular weight (kg/mol)