IE 211

INTRODUCTION TO ENGINEERING THERMODYNAMICS

Chapter1Introduction and Basic Concepts

INDUSTRIAL REVOLUTION

A period in 18th and early 19th

centuries

Major changes in agriculture, mining,

manufacturing, and transportation

The First Industrial Revolution, which

began in the 18th century, merged into the

Second Industrial Revolution around 1850,

when technological and economic

progress

Emerged in United Kingdom, then

spread throughout Europe, North

America and eventually the world

It started with the mechanisation of the textile industries, the development of iron-

making techniques

Trade expansion was enabled by the introduction of canals, improved roads and railways.

The introduction of steam power resulted in enourmous increase in production capacity.

THERMODYNAMICS deals with energy and can be defined as the science of energy. It gives the relation between energy, heat and work.

Therme (heat) dynamis (power)

Stems from the Greek words

Thermodynamics emerged as a science during the construction of the first successful atmospheric steam engines in England (1697-1712)

Thermodynamics term was firstly used in a publication of Lord Kelvin in 1849. The first thermodynamic

textbook was written in 1859 by William Rankine

German physicist, created the science of thermodynamics. The first law of thermodynamics:

(conservation of energy)

He developed the idea of absolute zero and independently recognized its first and second laws of thermodynamics. With James Prescott Joule, Kelvin discovered that gases cool when allowed to expand, the Joule-Thomson effect.

Rudolph Clausius

(William Thomson )Lord Kelvin

The first and second law of thermodynamics emerged simultaneously in 1850s, primarily out of the work of William Rankine, Rudolph Clausius and Lord Kelvin

Proposed another thermodynamic temperature scale which also assigned 0 to thermodynamic absolute zero, but used the degree Fahrenheit as its base unit.

William Rankine

The first law of thermodynamics: (conservation of energy)

‘’Energy can be changed from one form to another, but it cannot be created or destroyed. ‘’

The total amount of energy and matter in the Universe remains constant, merely changing from one form to another.

i.e. Falling of a rockConversion of potential energy to kinetic energy

i.e. Human body

The second law of thermodynamics: (energy has quality as well as quantity)

‘’Heat always flows from a warm body to a cooler one, never the other way.‘’

i.e. Cooling of a cup of coffee

- Actual processes occur in the direction of decreasing quality of energy

THERMODYNAMICS

Classical Thermodynamics Statistical ThermodynamicsAnalyses the macroscopic properties of the system using classical laws of thermodynamics

Analyzes thermodynamic properties by relating them to molecular-level models of microscopic behaviour

Application Areas

Household Appliances-Heating and air conditioning system-Refrigerator-Water heater-The shower

In the design of -Automotive engines-Rockets-Jet engines-Power Plants -Solar collectors

DIMENSIONS AND UNITSPhysical quantity is characterized by dimensions. The magnitudes of the dimensions are specified by units.

1) Fundamentals dimensions; mass(m), length(L), time(t), temperature(T)2) Secondary (drived) dimensions; velocity(v), energy(E), volume ( )

Two sets of units

English SystemUnited States Customary System (USCS)

Metric, SI, International system

Based on decimal relationship between units

.......10-3(milli,m), 10-2(centi, c), 10-1 (deci,d), 101 (deka, da).....

Example:

Dimension:Length; Unit: METER(m) ....mm, cm, m, ..,km....

Dimension:Mass; Unit: GRAM(g) ....mg, cg, g,..., kg

SOME SI and ENGLISH UNITS

SI unit English unit

Kilogram (kg)Meter (m)Second(s)Newton(N)= 1 kg.m/s2

Joules(J) = N.m...

Dimension

MassLengthTimeForceEnergy...

Pound-mass (lbm)Foot(ft)Second(s)1 lbf=32.174 lbm.ft/s2

British thermal unit(Btu)...

1) MASS and WEIGHTMass is an intrinsic property of matterWeight is a force that results from the action of gravity on matter (It’s magnitude is determined from Newton’s second law)

W = m.g (N)

g decreases with altitude, so that a body weighs less on top of a mountain On the surface of moon, an astronaut weighs about one-sixth of what he or she normally weighs on earth

2) DENSITY

= m/V ; (kg/m3 or lbm/ft3)

= f(P,T)

For most gases P 1/T For liquids and solids variation of density with pressure is negligableEffect of temperature;

water= 998 kg/m3 20oC at 1 atm

water = 975 kg/m3 75oC at 1 atm

Specific gravity: density of a substance relative to density of a well-known substance, e.g. water

S.G. = / water(at 4 oC)

Specific weight: The weight of a unit volume of a substance

s = .g

3) TEMPERATURE

We can measure temperature;

by our sensations; freezing cold, warm, hot, red-hot

Mercury in glass thermometer (based on the expansion of

mercury with temperature)

Many physical properties of materials including the phase (solid, liquid, gaseous or

plasma), density, solubility, vapor pressure, and electrical conductivity depend on the

temperature.

Ice (freezing) point: A mixture of ice and liquid water that is in equilibrium

with air saturated with vapor at 1 atm. pressure is said to be at the ice point.

Steam (boiling) point: Mixture of liquid water and water vapor (with no air) in

equilibrium at 1 atm. pressure is said to be at the steam point.

Phase Changes;

Celcius(oC), Fahrenheit(oF), Kelvin(K), Rankine(R)

In most of the world the Celsius scale is used for most temperature measuring

purposes.

TEMPERATURE SCALES:

SI Units English System

oC (Celcius scale)

0 oC

100 oC

oF (Fahrenheit scale)

32 oF

212 oF

Ice point.............

Steam point.....

These are often referred to as two-point scales since temperature values are

assigned at two different points

Conversion: 9/5T(oC) + 32 = T(oF)

Temperature scale that is independent of the properties of any substance is

called thermodynamic temperature scale.

Kelvin(K) scale (lowest temperature on this scale is 0 K)

SI Units English System

K (Kelvin scale) R (Rankine scale)

Conversion:

T(R) = 1.8T(K)

T(K) = T(oC) + 273.15

T(R) = T(oF) + 459.67

T(oF) = 9/5T(oC) + 32

SI system English system

Temp. Difference:

T(oC) = T(K)

T(oF) = T(R)

IDEAL GAS TEMPERATURE SCALE:

The temperatures on this scale are measured using a constant-volume gas

thermometer, which is basically a rigid vessel filled with a gas, usually hydrogen or

helium, at low pressure.

This thermometer is based on the principle that at low pressures, the temperature

of a gas is proportional to its pressure at constant volume.

T = a + bP

Ideal gas temperature scale can be

developed by measuring the pressure of gas

at ice and steam points

ABSOLUTE GAS TEMPERATURE SCALE:

Constant ‘’a’’ is assumed to be zero.

T = bP

4) PRESSURE

A normal force exerted by a fluid per unit area (related to gas or liquid). In solids

it is normal stress.

It has the unit of newtons per square meter (N/m2), which is called

a pascal (Pa)

Other pressure units: bar, standard atmosphere, kilogram-force per square

centimeter

How a person can walk on fresh snow without sinking by wearing large

snowshoes? And how a person cuts with little effort when using a sharp

knife?

SI Units English System

Pa (N/m2), atm, bar, kgf/cm2 , mmHg psi(lbf/in2), Psia, lbf/ft2, in Hg

Conversion between SI units:

1 bar = 105 Pa = 0.1 MPa1 atm = 760 mmHg = 101.325 kPa = 1.01325 bars1 kgf/cm2 = 9.807 N/cm2 = 9.807x104 Pa = 0.9807 bar = 0.9679 atm

ABSOLUTE PRESSURE: The actual pressure at a given position. It is measured

relative to absolute vacuum(absolute zero pressure)

GAGE PRESSURE: The difference between the absolute pressure and the

local atmospheric pressure.Example:The gage used to measure the air pressure in an automobile tire relative to atmospheric pressure

VACUUM PRESSURE: Pressure below atmospheric pressure

Pgage = Pabs - PatmPvac = Patm - Pabs

In thermodynamic calculations absolute pressure is used.

VARIATION of PRESSURE WITH DEPTH

Pressure in a fluid increases with depth because more fluid rests on deeper

layers.

P2 = Patm + gh

A consequence of the pressure in a fluid remaining constant in horizontal

directions is that ‘’ the pressure applied to a confined fluid increases the pressure

throughout the same amount’’ This is called PASCAL’S LAW

Force applied by a fluid is proportional to the surface area

This enables us to lift a car easily by one arm, e.g. Hydraulic lifts

Two hydraulic cylinders of different areas

could be connected, and the larger could

be used to exert a proportionally greater

force than that applied to the smaller.

P1 = P2 at the same levels, then;

F1/A1 =F2/A2 F2/F1 = A2/A1

THE MANOMETER

A manometer consists of a glass or plastic U-tube containing mercury,

water, alcohol or oil and it is used measure the gas pressures

P2 = Patm + gh

P2 = Patm + 1gh1 + 2gh2 + 2gh2

A manometer containing multiple immiscible fluids:

THE BAROMETER

Atmospheric pressure is measured by barometer (Italian Evangeliste Torricelli,

1608-1647)

Atmospheric pressure can be measured by inverting a mercury filled tube into

a mercury container that is open to the atmosphere.

PB = Patm, Pc 0

Pc + gh = PB = Patm

Patm = gh

Pressure units

760 mmHg = 1 atm

1 mmHg = 1 Torr

1 atm = 101.325 kPa

At sea level !!!

5) HEAT (Q)

Heat is defined as an energy transfer to a body in any other way than due

to work performed on the body

SI Units :Joules(J)

Energy transfer by heat can occur between objects by radiation, conduction

and convection

A red-hot iron rod from which heat transfer to the

surrounding environment will be primaily through

radiation.

HEAT TRANSFER

6) WORK (W)

Form of energy; force times distance, (N.m) or joules(J)

In metric system: The amount of energy needed to raise the temperature of 1 g of water at 14.5 oC by 1 oC is defined as 1 calorie (cal)

1 cal = 4.1868 J

In English system: Energy unit is the Btu (British thermal unit) : energy required to raise the temperature of 1 lbm of water at 68 oF by 1 oF

1 Btu = 1.0551 kJ

Definition of work

SYSTEMS AND CONTROL VOLUMES

The mass or region outside the system

The real or imaginary surface that seperates system from its surroundings (has zero thickness)

Quantity of matter or region in space chosen for study

SYSTEMS

Closed Systems (Control mass) Open Systems (Control volume)

Consists of fixed amount of mass No mass can cross its boundaryEnergy (heat&work) can cross the boundary Volume does not have to be fixed

Special Case: isolated system

Rigid walls. No mass and energy (heat&work) transfer!

Encloses a device that involves mass flow such as a compressor, turbine or nozzleBoth mass and energy(heat&work) can cross the boundary A control volume may also involve a moving boundary

Control surface

Adiabatic system: A kind of closed system

No mass transfer Energy can cross the boundary only in the form of work

Water heater

Car radiator

Air compressor

Examples of Open Systems (Control Volumes)

Wind Turbine

Gas Turbine

PROPERTIES OF A SYSTEM

Any characteristics of a system is called property

e.g. Pressure, temperature, volume, mass, viscosity, thermal conductivity, thermal expansion coefficient

1) Intensive Properties: Independent of the mass of a systemTemperature (T); (oC, K, oF, oR)Pressure (P); (Pa or Psi)Chemical potential ( i); (kJ/mole, Btu/mole)

2) Extensive Properties: Depend on the size or extent of the systemMass(m); (kg or lbm)volume ( ); (m3 or ft3)Momentum EnergyEnthalpyEntropy

Extensive properties per unit mass are called specific properties

e.g. Specific volume; = /m; (m3/kg or ft3/lbm)Specific total energy, e = E/m; (kJ/kg)

STATE AND EQUILIBRIUM The stationary condition of the system at which properties are defined is called state of system.

Equilibrium implies a state of balance.A system in equilibrium experiences no changes when it is isolated from its surroundings

• Thermal equilibrium (temp. is same)• Mechanical equilibrium (pressure is same)• Phase equilibirum (mass of each phase reaches an equilibrium level)• Chemical equilibrium (chemical composition does not change with time)

Expansion of gas

THE STATE POSTULATE

When sufficient number of properties are specified the rest of the properties assume certain values automatically.

The number of properties required to fix the state of a system is given by the system postulate

The state of a simple compressible system (absence of electrical, magnetic, gravitational, motion and surface tension effects) ;

Specified by two independent, intensive properties (temperature and specific volume)

PROCESSES AND CYCLES Process: changes that occur when a system changes its state from one

equilibrium state to another

(Series of states that system passes during a process)

Cycle: a system is said to have undergone a

cycle if it returns to its initial state at the end of

process

Property A

Property B

State 1

State 2

Quasistatic or quasi-equilibrium process: System is close to equilibrium

Example: Very slow compression of a gas

Gas molecules will have sufficient time to redistribute and there

will not be a molecule pile up in front of the piston

PROCESSES

Isothermal Process Isobaric Process Isochoric (or isometric) Process

Temperature remains

constant

Constant pressureConstant specific volume

STEADY-STATE

A system in a steady state has numerous properties that are unchanging in time

In steady-state processes fluid flows through a control volume steadilyExample: Turbines, pumps, boilers, refrigeration systems

During steady-state flow fluid properties can change from point to point within

the control volume, but at any fixed point they remain the same during the entire

process

Therefore, volume ( ), mass(m) and total energy (E) remain constant

TEMPERATURE AND ZEROTH LAW OF THERMODYNAMICS

When two materials at different temperatures contact each other heat is

transferred from the body at higher temperature to one lower temperature until

both bodies attain the same temperatures (thermal equilibrium)

Zeroth Law of Thermodynamics: If two bodies are in thermal equilibrium with

a third body, they are also in thermal equilibrium with each other

Third body may be replaced by a thermometer (object#1)

Note: they are not in contact

Assignments:

Examples 1-6, 1-7, 1-8, 1-9