Chapter 1 Slides

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M E H B 2 1 3 T H E R M O D Y N A M I C S I : C H A P T E R 1

CHAPTER 1

INTRODUCTION AND BASIC CONCEPTS

Prepared by:Saiful Hasmady Abu Hassan, Dr.

Adapted from:Yunus A. Cengel and Michael A. Boles, Thermodynamics: An

Engineering Approach, 8th Edition in SI Units, McGraw-Hill, 2015



Chapter 1 Outcomes

At the end of the chapter, you should be able to:

• Identify the unique vocabulary of thermodynamics and their precise meanings– Important to build foundation for the upcoming thermodynamics

concepts and principles

• Recognize the difference between metric SI and English unit

• Explain the basic concepts of thermodynamics such as system, state (and its postulate), equilibrium, process, and cycle

• Explain concepts of temperature (and its scales) and pressure(absolute and gage)

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Thermodynamics and Energy

The science of energy The ability to cause changes

In principle:• Energy cannot be created nor destroyed• It can only change from one form to another• The total amount of energy remains constant

The Conservation of Energy Principle

these statements made

which EVENTUALLY is

THE FIRST LAW OF THERMODYNAMICS

The First Law is a quantitativeaspect of energy. What about qualitative aspect of energy? Do we have it?



Thermodynamics and Energy

• The First Law of Thermodynamics– Conservation of energy

– Quantitative (main subject of Ch. 4 and 5)

• The Second Law of Thermodynamics– Qualitative (main subject of Ch. 6 and 7)

– Asserts that “energy has quality as well as quantity, and actual (real-life) processes occur in the direction ofdecreasing quality of energy”

• (The Zeroth Law of Thermodynamics)– (we’ll save this for later)

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Approaches in Thermodynamics

• Classical thermodynamics– A macroscopic (or bulk)

approach

– Does not require knowledge of the behavior of individual particle

– Used in this course

• Statistical thermodynamics– A microscopic approach

– Averaged behavior of large groups of individual particles (or aggregates)

– Usually at a graduate level

Water to ice transition simulation using molecular

dynamics (MD)*

“Particles”

*http://biomodel.uah.es/en/water/index.htm



Application Areas of Thermodynamics

*http://chimneysofmalaysia.blogspot.com/2010/05/chimneys-of-putrajaya-power-station.html

Power Plants/Station

**http://mjg-4.blogspot.com/2013/01/20122012-aerial-photography.html

Putrajaya Power Station*

Manjung Power Station**

(among others … )

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Dimensions and Units

• Dimension: characterization of a physical quantity• Unit: the magnitude assigned to a dimension

Categories of Dimensions

The Seven Primary Dimensions (or Fundamental Dimensions)

Mass, m [kg]

Length, L [m]

Time, t [s]

Temperature, T [K]

Electric current, I [A]

Amount of light, Iv [cd]

Amount of matter, N [mol]

Secondary Dimensions (or Derived Dimension)

Velocity, v [m/s2]

Energy, E [J] or [kgm2/s2]

Volume, [m3]

Force, F [N] or [kgm/s2]

.

.

(among others … )

(units in SI)(units in SI)



Dimensions and Units

• Two kinds of unit systems:

– Metric SI system

• Based on decimal relationships

• Simple and logical

• Widely used

– English system

• Arbitrary relationships (e.g. 1 ft = 12 in = 0.305 m)

• Still used in the US

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Systems and Control Volumes

• System: A quantity of matter or a region in space chosen for study– Closed system– Open system

• Surroundings: The mass or region outside the system

• Boundary: The real or imaginary surface that separates a system from its surroundings– Fixed boundary– Movable boundary

Next up: What are the characteristics of closed systems?




• Closed System: A system with fixed amount of mass, and no mass can cross its boundary– But energy (through heat and work transfer) can cross!– Another name: Control mass (we control the mass)

*http://www.chegg.com/homework-help/scenes-represent-physical-change-taking-place-piston-cylinde-chapter-6-problem-29p-solution-9780073402659-exc

A piston-cylinder device/assembly (without

any openings) is an example of a closed system*

Next up: How about the characteristics of open systems?

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• Open system: A properly selected region is space– Both mass and energy can cross its boundary– Devices with mass flow (e.g. nozzle, compressor, turbine)– Another name: Control volume, CV (we control the volume)– The boundaries of a CV is called a control surface

• Can be either real or imaginary

A CV can involve fixed, moving, real, and imaginary boundaries.*http://www.leevalley.com/EN/images/item/Gardening/al902s04.jpg

A nozzle on a garden hose*



Properties of a System

• Property: Any characteristic of a system– E.g. a system is characterized by

pressure P, temperature T, volume ∀, mass m, among others

The Two Kinds of Properties

Intensive Properties

Independent of mass of a

system

E.g. Temperature.

Pressure, Density

Extensive Properties

Depend on the size (or

extent of the system)

If divide with mass,

becomes specific

properties

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Density and Specific Gravity

Density,

Specific volume,

Specific weight,

[kg/m3]

[m3/kg]

[N/m3]

Specific gravity,

note on the inverse to density

“The ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4°C)”



State and Equilibrium

• It is about how manyproperties are sufficient for us to be able to define a ‘state’

• Definition: “The state of a simple compressible system is completely

specified by twoindependent, intensive properties”

The State Postulate

Property #1: T

Property #2: v

State <label>

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Can you point out:-1. What type of system is

this?2. Why?3. Where is the fixed

boundary?4. Where is the moving

boundary?5. Where is the real

boundary?6. Where is the imaginary

boundary?7. What changes?8. What remains the same?




• In thermodynamics, a state of a system is always in equilibrium

• Equilibrium: A condition of balances (no unbalanced driving forces)

• Types of equilibrium in a system:– Thermal equilibrium

• Temperature same everywhere

– Mechanical equilibrium• Pressure same everywhere

– Phase equilibrium• Mass of each phases remains the

same with time

– Chemical equilibrium• Chemical composition remains the

same, i.e. no chemical reaction

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Processes and Cycles

• Process: Any change that a system undergoes from one equilibrium state to another

• Path: The series of states through which a system passes during a process

• A process is properly described when:1. The initial and final states

are specified

2. The process path is known

3. Its interaction with surroundings is known

A process diagram or a ‘property diagram’




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• Common processes that you will encounter in this course:

Isothermal process: Temperature remains constant

Isobaric process: Pressureremains constant

Isochoric process: Volumeremains constant




• Cycle: A process duringwhich the initial andfinal states areidentical

• E.g. Compression –expansion process

– P- diagram

compression

expansion

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• Steady-flow process: A process during which fluid flows through a CVsteadily

• ‘Steady’ means does not change with time– Opposite: Unsteady flow

or transient flow

• Steady-flow devices will be one of the main topics in Chapter 5




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The Zeroth Law of Thermodynamics

• “If two bodies are inthermal equilibriumwith a third body, they are also in thermal equilibrium with each other”

• Two bodies are in thermal equilibrium if both have the same temperature reading– Even though they are

not in contact

BodyA

BodyB

BodyT

BodyT

• Both Body A and Body B are in thermal equilibrium with Body T

• Body T is replaced with a thermometer• Body A and B have same temperature• Hence Body A and B are in thermal

equilibrium with each other



divide equally

Temperature Scales

• Temperature scales are commonly made by reference to easily reproducible states

– Ice point (or freezing point of water)

• A mixture of ice and water that is in equilibrium with air saturated with vapor at 1 atm pressure (0°C)

– Steam point (or boiling point of water)

• A mixture of liquid water and water vapor (with no air) in equilibrium at 1 atm pressure (100°C)

measuring devices

0°Cfix

100°Cfix

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Temperature Scales

• Some types of temperature scales:– Celsius and Kelvin scales

(SI units)• T [K] = T [°C] + 273.15

• ΔT [K] = ΔT [°C]

– Fahrenheit and Rankinescales (English units)• T [R] = T [°F] + 459.67

• ΔT [R] = ΔT [°F]

– T [°F] = 1.8T [°C] + 32

Comparison of magnitudes of various temperature units.



Temperature Scales

• Other temperaturescales:– Thermodynamic

temperature scale• A temperature scale

that is independent of the properties of any substance.

– Ideal-gas temperature scale• Measured using a

constant-volume gas thermometer

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Temperature Scales

“the state at which all three phases of water coexist in equilibrium), which is assigned the value 273.16 K”

Triple point of water



Pressure

• Pressure: A normal force exerted by a fluid perunit area

• 1 Pa = 1 N/m2

• 1 bar = 100 kPa =

• 1 atm = 101.325 kPa = • 1 atm =

What is a normal force?What is the difference between ‘pressure’ and ‘stress’?

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Pressure

• Absolute pressure: The actual pressure at a given position, measured relative to absolute vacuum– Pabs (or just P)

• Gage pressure: The difference between the absolute pressure and the local atmospheric pressure – Pgage = Pabs – Patm (will be specified)– Most pressure-measuring devices are calibrated to

read zero in the atmosphere, and so they indicate gage pressure

• Vacuum pressure: Pressures below atmospheric pressure– Pvac = Patm – Pabs



Pressure

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Pressure Variation with DepthConstant density fluid

Variable density fluid

Patm

h

P



Pressure

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Pressure

• Pascal’s Law: “The pressure applied to a confined fluid increases the pressure throughout by the same amount”

ideal mechanical advantage of the hydraulic device (e.g. jack)



Pressure

However!

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Pressure Measurement Devices

• Barometer– To measure atmospheric

pressure

– Standard atmosphere: the pressure produced by a column of mercury(Hg) of• 760 mm in height,

• at 0°C,

• under standard gravitational acceleration of g = 9.81 m/s2

– 1 atm = 760 mmHg




Old barometers. They have been around since 1600’s!

- Wikipedia

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• Manometer– To measure small and moderate

pressure differences

– Can contain fluids such as mercury, water, alcohol or oil



What we covered• Thermodynamics and energy

– Application areas of thermodynamics

• Importance of dimensions and units– Some SI and English units, Dimensional homogeneity, Unity conversion ratios

• Systems and control volumes• Properties of a system• Density and specific gravity• State and equilibrium

– The state postulate

• Processes and cycles– The steady-flow process

• Temperature and the zeroth law of thermodynamics– Temperature scales

• Pressure– Variation of pressure with depth– The barometer and manometer

Documents

Chapter 1 Slides