Chapter3 Properties

7/30/2019 Chapter3 Properties

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Chapter 3

Properties of Pure

Substances(Sifat Bahan Tulin)

olehLt Kol Prof Madya Ir Khalid bin Abd Jalil TUDM

Jabatan Kejuruteraan Mekanikal

Universiti Pertahanan Nasional Malsysia.012-2094234

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Integrity

Thermodynamics I (EMM2503)

Chapter 3 – Properties of Pure Substances



Objectives

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Introduce the concept of pure substance.

Discuss the physics of phase-change of processes.

Illustrate the P-V-T property diagram.

Determine the thermodynamics properties.Describe ideal gas and its behavior.



The Pure Substance

Definit ion

Pure Substance – has a homogeneous and invariable chemicalcomposition and may be exist in more than one phase with the samechemical composition.

• Water (solid, liquid and vapor phases)

• Mixture of liquid water and water vapor • Carbon dioxide, CO2

• Nitrogen, N2

• Mixture of gases, such as air, as long as there is no change of phase.

Homogeneous Substance – a substance that has uniformthermodynamic properties throughout is said to homogeneous.

Simple Substance – a substance whose changes in properties isdominated by the effect of a volume change as opposed to surface,

magnetic, electrical changes.

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Phases of Pure Substance

• Substance exit in different phases and its depend on temperatureand pressure.

• In principles, substance have 3 phases:-

- solid (pepejal)~ molecules are relatively fixed positions in solid.

- liquid (cecair)

~not much different from that of the solid phase, except themolecules are no longer at fixed positions relative to each

other and they can rotate and translate freely.

- vapor (wap)

~ molecules are far apart from each other and move about arandom

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Relationships between Pressure (P),

Temperature (T) and Specific Volume (v)

• P, T and v – 3 important properties in thethermodynamic and also a pure substances due to:-

– v and T is a independent variable

–While P, is the function of both P = P(T,v )

•Relationships between P, T and v can be demonstratedin P – v – T Surface for a real substance diagram asshown next slide.

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The P – v – T Surface for a Real Substance that expand upon freezing

example; water

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The P – v – T Surface for a Real Substance that

contracts upon freezing. Example: Nitrogen, CO2

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The P – v – T Surface for a Real Substance

From the Surface diagram, the 3 phases region where

substance like water may exist as a solid, liquid or gas (vapor)

can be easily defined.

a. Single phase region (Satu fasa) – area where P, T and v areindependent properties, although one of the property can

changed without changing of the other property.

b. 2 phase region (Dua fasa) – two properties are in

equilibrium, where pressure and temperature are depends to

one another without changing the other. Example : boilingwater.

c. 3 phase region (3 fasa) – all properties, solid, liquid and

vapor, were in equilibrium.

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The P – v – T Surface for a Real Substance…cont

d. Saturated condition (keadaan tepu) – line for liquid and

vapor meet at critical point and forming a dome. All

compressed liquid are located in the region to the left of

saturated liquid line, called the compressed liquid region. Allsuperheated vapor states are located to the right of saturated

vapor line, called superheated vapor region.

e. Critical Point (titik genting) – defined as the point at which

the saturated liquid and saturated vapor states are identical

and in equilibrium state. At this point, P =22.06 MPa and T= 373.95˚C .

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Phase-Change Processes of Pure Substances

Consider piston-cylinder device containing water at 20ºC and1 atm pressure. At this state, water exits in liquid phase and it

is called a compressed liquid or a subcooled liquid.

Process 1-2:

T and v will increase from the compressed liquid or sub

cooled liquid (cecair sub dingin) , state 1, to saturated liquid(cecair tepu) state 2. In the compressed liquid region (cecair

termampat) , the properties of the liquid are approximately

equal to the properties of saturated liquid state at the

temperature.

Process 2-3:

At state 2, the liquid reached the boiling temperature, called

the saturation temperature (suhu tepu) and is said to exist as

a saturated liquid (cecair tepu). During the phase change,

both temperature and pressure remain constant ( water boil

at 100 ˚C and P=1atm or 101.325 kPa)

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Process 3:

Once the boiling starts, the temperature will stop raising until

the liquid is completely vaporized. At this state, liquid and

vapor are in equilibrium. This phase called saturated liquid

(cecair tepu) and saturated vapor (wap tepu) and also calledsaturated liquid –vapor mixture (campuran cecair-wap tepu).

Process 4:

At state 4, a saturated vapor exists and vaporization is

completed. Any heat loss from this vapor will cause some

vapor to condense (phase change from vapor to liquid). The

vapor that about to condense is called a saturated vapor (wap

tepu). A substance at state between 2 and 4 is often referred to

as a saturated liquid – vapor mixture (campuran cecair-wap

tepu).

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Phase-Change Processes of Pure Substances…conts.



Process 4-5:

If the constant pressure heating is continued, the

temperature will begin increase above the saturated

temperature (suhu tepu) and the volume also

increases. State 5, is called a superheated (wap panas

lampau) state because T 5 is greater that saturation

temperature (above 100˚C) for the pressure and the

vapor is not about to condenser.

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Phase-Change Processes of Pure Substances…conts.



Phase-Change Processes

of Pure Substances… cont

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T-v diagram for heating process of water at constant

pressure.

Water boils at 100C

at 1 atm pressure



T – v diagram of

constant pressure

phase-change

processes of a pure

substance at various

pressure

Pc=22.09MPa

Tc=374.14C

v c = 0.003155m³/kg

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The T- v Diagram

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The 2 lines (saturated liquid lines and saturated vapor lines) intersect at critical point and form is

called the “steam dome”.

The region between saturated liquid line and saturated vapor lines is called saturated liquid-vapor

mixture region .

At given pressure, temperature at which a pure change phase is called Saturation Temp., Tsat

At given temperature, pressure at which a pure substance change phase is called saturation

pressure Psat.Table A-1 page 910, Critical point properties.



The region to the left of the saturated liquid line and below the critical temp is

called the compressed liquid region.

The region to the right of the saturated vapor line and above critical temp is

called superheated region.

At temp & pressure above the critical point, the phase transition from liquid tovapor is no longer discrete.

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Superheated

vapor region

Compressed

liquid region



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Figure shows the P-T diagram, often called the phase diagram, for pure substances that contract and expand during freezing.

P=0.6113kPa

T=0.01 ºC

Relationship between solid, liquid and vapor

P=22.06 MPa

T=373.95 ºC



Property Table

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For most substances, the relationships among thermodynamic properties are too complex to be

expressed by simple equations. Therefore, properties are frequently presented in the form of tables.

Table A-2 & A-3 (page 914/915) Properties of common liquids, solids & foods.

Table A-4 (page 916) Saturated water – Temperature table

Table A-5 (page 918) saturated water – Pressure table

Table A-6 (page 920-923) superheated water

Table A-7 (page 924) Compressed liquid water

Table A-8 (page 925) saturated ice-vapor



FIGURE 2-40

A partial listing

of Table A –6.

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Enthalpy – is the thermodynamic property of fluid (combination property) and It can be

used to calculate the heat transfer during a quasistatic process taking place in a closed

thermodynamic system under constant pressure.

The enthalpy is a convenient grouping of the internal energy, pressure, and volume:-

h is useful to calculating the energy of mass streams flowing into and out of

control volumes. (kJ/kg)

Note:Is called the enthaply of vaporization (or

latent heat of vaporization). It decreases

as temp. or px increase and becomes

zero at the critical point.

hf – specific enthaply of saturated liquid

hg – specific enthaply of saturated gas

http://en.wikipedia.org/wiki/Quasistatic_process

http://en.wikipedia.org/wiki/Closed_system

http://en.wikipedia.org/wiki/Thermodynamic_system

http://en.wikipedia.org/wiki/Thermodynamic_system

http://en.wikipedia.org/wiki/Closed_system

http://en.wikipedia.org/wiki/Quasistatic_process



Using saturated water Table A –4 and A-5, find

temperature/pressure, specific volume of saturated liquid, Vf ,internal energy of saturated vapor, Ug and enthalpy of evaporation

hfg , if the:-

a. pressure is 50kPa.

b. Temperature 120ºC

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Saturated Liquid-Vapor Mixture (campuran Cecair-wap Tepu)

-During a vaporization process, a substance

exists as part liquid and part vapor, also called

a mixture of saturated liquid and saturated

vapor.

- at this point liquid and vapor are in

equilibrium.

- To analyze this mixture properly, we need to

know the proportions of the liquid and vapor

phase in the mixture.

- The ratio of the mass of vapor to the total

mass of the mixture is called the quality, x

X = m vapor = mg (1)

m vapor + m liquid mg + mf

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Th d i I (EMM2503)



Saturated Liquid-Vapor Mixture…cont (campuran Cecair-wap Tepu)

-The quality is zero (0) for the

saturated liquid and one (1) for the

saturated vapor, (0 < x < 1).

- the bigger x values, showed the

total of saturated vapor areincreased, and we can write as

follow:-

( 1- x) = m f m g + m f (2)

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Th d i I (EMM2503)




- Consider a tank that contains a saturated liquid-vapor mixture. The

volume occupied by saturated liquid is Vf and the volume occupied by

saturated vapor Vg,. The total volume V is sum of the two:

V = Vf + Vg m³ (3)

(mg+ m f ) v = m g v g + m f v f

If, V = mv mv av = m f v f + m g v g

v = m f . v f + m g . v g

m g+ m f m g+ m f

Specific Volume

v = (1 - x ) v f + x v g = v f + x (v g - v f )Replace (1) and (2)

v = v f + x v g f m³ /kg (4)

v fg = v g - v f By replacing

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Th d i I (EMM2503)




- The analysis given can be repeated for internal energy, u and

enthalpy, h with the following results:

Specific enthalpy

h = (1 - x ) h f + x h g

= hf + x (h g - h f ) = h fg + x h g f (kJ/kg) (5)

Specific internal energy

u = (1 - x ) u f + x u g

= uf + x (u g - u f ) = u fg + x u g f (kJ/kg) (6)

Note: Persamaan (4), (5) dan (6) digunakan untuk mendapatkan sifat-sifat termodinamik

bahan pada fasa cecair dan wap tepu sahaja

In thermodynamics and molecular chemistry, the enthalpy or heat content (denoted as H , h, or rarely as χ ) is a quotient or description of

thermodynamic potential of a system, which can be used to calculate the "useful" work obtainable from a closed thermodynamic system under

constant pressure and entropy.

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Th d i I (EMM2503)



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Compressed Liquid (Cecair termampat)

It happen when the temperature is

below from saturated temperature

under certain pressure.

Different between saturated

temperature and compressed liquid

temperature under same pressure

is called sub cooled degree (darjah

sub dingin)

∆Tsub=Ts –T

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Compressed Liquid (Cecair Termampat)

A substance is said to be compressed liquid when the pressure is greater than the

saturation pressure for the given temperature.

Compressed Liquid properties depends on temperature much more than pressure.

For analysis, the value for saturated liquid properties is used as a reference at the given

temperature, such as:

V = Vf at given temperature or V= Vf (T)

U= Uf at given temperature or U = Uf (T)

h = h f at given temperature or h = h f (T)

In general, the compressed liquid is characterized by:

Higher Pressure (P>Ps at given T)

lower Temperature (T<Ts at given P)

Lower specific Volume (V < V f at given P or T)

Lower specific internal energy (U < U f at given P or T)

Lower enthalpies (h< h f at given P or T)

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Superheat Vapor (Wap panas lampau)

In the region to the right of the

saturated vapor line and temperature

above the critical point, a substance

exists as superheated vapor.

Since the superheated region is a

single-phase region, temperature and

pressure are no longer dependent

properties and there can conveniently

be used in as the two properties in the

tables.

∆Tpl = T – Ts

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Superheat Vapor (Wap panas lampau)

A substance is said to be superheated if the given temperature is greater thanthe saturation temperature for the given pressure.

In the region to the right of the saturated vapor line and temperature above the

critical point, a substance exists as superheated vapor.

Since the superheated region is a single-phase region, temperature and pressure

are no longer dependent properties and there can conveniently be used in as thetwo properties in the tables.

Superheated vapor can be characterized by :

Low Pressure (P<Ps at given T)

Higher Temperature (T>Ts at given P)Higher specific Volume (V > V g at given P and T)

Higher specific internal energies (U > Ug at given P or T)

Lower Specific enthalpies (h > h g at given P or T)

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Interpolation Method

(kaedah tentu dalaman)

• if required data is in between 2 given data.

• Using linear function y=f(x)

• Example:Properties 1 Properties 2

x1 y1xt yt

x2 y2(yt – y1) (xt – x1)

(y2 – y1) (x2 – x1)=

yt

(xt – x1)

(x2 – x1)(y2 – y1)= + y1

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Link to excel file to calculate


http://d/nota/termo%20sem1%200809/interpolation%20method_calculation.xlsx



Property Table (Jadual Sifat)For most substance, the relationships among the

thermodynamic properties are too complex to be expressby simple equation, therefore, properties value are

frequently presented in the form of table.

(Compress liquid table A-7 )

3 types of Table

(Saturated liquid table

A-4 and A-5)

(Superheated table A-6)

(Saturated water table)

(Saturated liquid table A-4)

(Saturated liquid table

A-5)

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If U < U f - compressed liquid

U f < U < Ufg - saturated mixture

U > Ug – superherated

If

P>Ps - compressed liquidP = Ps – saturated mixture

P<Ps – superheated

If

T<Ts – compressed liquid

T=Ts - saturated mixture

T>Ts – super heated

If

V < V f - compressed liquid

Vf <V < Vfg - saturated mixture

V> Vg – superheated.

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Table selection




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(kJ)

entropy is a measure of the unavailability of

a system’s energy to do work.

that energy which cannot be used for external

work

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Example :

1. Determine saturated temperature Ts of water if the pressure is 5.3 bar.

2. Determine specific volume and specific enthalpy of water at pressure 14bar

and temperature 420ºC.

3. Determine the enthalpy of 1.5 kg of water contained in volume of 1.2 m³ at

pressure 200kPa.

4. 1kg of water vapor at 200kPa fills the 1.1989m³ left chamber of a partitioned

system shown in figure below. The right chamber has twice the volume of

the left and is initially evacuated. Determine the final state of volume and

pressure of the water after the partition has been removed and enough heat

has been transferred so that the temp. of the water is 3 ºC.

Chapter3 Properties

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