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ENGG1050EngineeringThermodynamics

Basic Concepts in Thermodynamics

Content

Basic concepts

Basic laws

Systems

System properties

See Cengel & Boles: 1-1 to 1-6

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Basic concepts

Energy (“capacity to do work”)

Heat (“energy that flows”)

Temperature (“a measure of internalenergy”)

Entropy (“the quality of energy”)

Basic Laws

0th law: helps define temperature T

1st law: energy is conserved

helps define internalenergy, U

2nd

law: unavailable energy helps define entropy, S

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Systems – where all this takes place

Some physical region we want tostudy–What systems can you name?

–Characteristics?System + boundary/surface + surroundings

Types:

– Isolated (no mass and heat transfer)–Closed (no mass but heat transfer)

–Open (both mass and heat transfer)

Examples of systems

Domestic hot water heater

–Sketch it … what type of system is it?

A refrigerator

–Sketch it … type of system?

Potatoes in a microwave oven

–Sketch … type of system?

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System properties

Types:

–Temperature (T)

–Pressure (P)

–Volume (V)

–Mass (m)

Classes of properties:

–Extensive (changes with extent of 

system)– Intensive (independent of system

extent)Question: How do you classify the system properties above?

Some properties

Density

Specific volume

V 

m= ρ 

m

V v ==

 ρ 

1

Units = kg/m3

Units = m3 /kg

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Units

Commonly SI, sometimes Imperial(British)

Consistent use of units is veryimportant !

Mass: m (kg)

Weight: W = m.g (units?)Total = My mass (m) + your weight

(W) ??

kg m s-2

State and equilibrium

State:

–A set of properties describing a system

Equilibrium:

–A condition of balance in a system

Thermal (temperature)

Mechanical (pressure)

Phase (mass)

Chemical (composition)

Question: What properties could be used to describe this room?

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State Postulate

 “All of the equilibrium states of asimple compressible system arecompletely specified by 2independent, intensive properties” 

e.g. for a gas: T and v (specific volume)

Equations of State

For gases T, V and P are not allindependent

Ideal gas equation of state is:

PV = nRT

n = moles of gas

R = ideal gas constant (J/mol/K)

Is this consistent in terms of units?Check it!

P = N/m2 = ?

J = N m = ?

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Processes

Going from one equilibrium state toanother

P1, V1

P2, V2

V

P

P1, V1

P2, V2

• Types of processes• isothermal (T constant)• isobaric (P constant)• isochoric (v constant)

Thermodynamic

path

(State 1)

(State 2)

(State 1)

(State 2)

Review

Basic thermodynamic units andprefixes

Systems help us to define regions of interest – what are the 3 mainsystems?

We need properties to characterize

systems – intensive and extensiveMaking sure units are consistent !

Understanding thermodynamicprocesses and cycles – how to movearound the P,v and other regions.

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Some other information

These slides available on course webpage:

http://www.cheque.uq.edu.au/ugrad/engg1050/

Textbook Cengel and Boles hastutorial problems

Please make arrangements with

tutors if you are going to misstutorials