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CHAPTER

1MEC 451Thermodynamics

FundamentalConcepts

Lecture Notes:

Dr Alhassan Salami Tijani

Faculty of Mechanical Engineering

Universiti Teknologi MARA, 40450

Shah Alam, Selangor

For students EM 220 and EM 221 only

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Energy:The ability to do work

Heat:The form of energy that is

transferred between two systems

(or a system and its surroundings)

by virtue of a temperature difference.

Different forms of energy are: thermal,

mechanical, kinetic, potential, electric,

magnetic, chemical, and nuclear

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MECHANICAL FORMS OF WORK

Non-mechanical Forms of Work

Electrical work:The force is the voltage(the electrical

potential), displacement is the electrical charge.

rotating shaft workcompressing workPaddle wheel work

Work:The force acting on an object through a distance

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The only two forms of energy interactions associated

with a closed system are heat transferand work.

Heat vs. Work Systems possess energy, but not heat or work.

Both are associated with aprocess, not a state.

Unlike properties, heat or work has no meaning ata state.

Both heat and work are recognized at the boundaries of a system as they cross the

boundaries.

Conversion of mechanical Shaftwork to thermal energy

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What is Thermodynamics?

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The science of energy, concerned

with the ways energy is stored

within a body.

Energy transformations mostly

involve heat and work movements.

The Fundamental law is the

conservation of energy principle:

energy cannot be created or

destroyed, but can only be

transformed from one form to

another.

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Faculty of Mechanical Engineering, UiTM

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System, surroundings and boundary

System:A quantity of matter or a

region in space chosen for study.

Surroundings:The mass or region

outside the system

Boundary:The real or imaginary

surface that separates the systemfrom its surroundings.

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Type of system(isolated system)

Isolated systemneither

mass nor energy can crossthe selected boundary

Example (approximate): coffee in

a closed, well-insulated thermos

bottle

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Type of system(Closed system)

Closed systemonly energy

can cross the selected

boundary

Examples: a tightly capped cup of

coffee

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Type of system(Open system)

Open system

both mass andenergy can cross the selected

boundary

Example: an open cup of coffee

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Properties of a system

A characteristic of a system that is in equilibrium.

Properties may be intensive or extensive.

Intensiveindependent of the amount of mass

e.g: specific volume, pressure, temp.

Extensivevaries directly with the mass

e.g:mass, volume, energy, enthalpy

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State, Equilibrium and Process

Statea set of properties that

describes the conditions of a

system.

Thermodynamic equilibrium -

system that maintains thermal,

mechanical, phase and chemical

equilibriums.

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State, Equilibrium and Process

Processchange from oneequilibrium state to another.

Process

Property held

constantisobaric pressure

isothermal temperature

isochoric volume

isentropic entropy

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Types of Thermodynamics Processes

Cyclic process- when a system in a given initial

state goes through various processes and finally

return to its initial state, the system has undergone

a cyclic process or cycle.

Reversible process - it is defined as a process

that, once having take place it can be reversed. In

doing so, it leaves no change in the system or

boundary.

Irreversible process - a process that cannot

return both the system and surrounding to their

original conditions

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Types of Thermodynamics Processes

Adiabatic process- a process that has no heat transfer

into or out of the system. It can be considered to be

perfectly insulated.

Isentropic process- a process where the entropy of the

fluid remains constant.

Polytropic process- when a gas undergoes a reversible

process in which there is heat transfer, it is represented

with a straight line,PVn= constant.

Throttling process - a process in which there is no

change in enthalpy, no work is done and the process is

adiabatic.

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Zeroth Law of Thermodynamics

If two bodies are in thermal equilibrium with a thirdbody, there are also in thermal equilibrium with each

other.

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Application Areas of Thermodynamics

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