me6101 basics
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Basic Thermodynamic Terminology
Dr. Md. Zahurul Haq
ProfessorDepartment of Mechanical Engineering
Bangladesh University of Engineering & Technology (BUET)Dhaka-1000, Bangladesh
zahurul@me.buet.ac.bdhttp://teacher.buet.ac.bd/zahurul/
ME 6101: Classical Thermodynamics
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology M E 6101 (2015) 1 / 17
Thermodynamic System
T006
A thermodynamic system is simply any object, quantity of matter,
or region of space that has been selected for thermodynamic
study. Everything that is not part of the system is referred to as
the surroundings.
Boundary or control surface (CS) separates the system from itssurroundings whichmay be real or imaginary, at rest or in motion
may change its shape and size
neither contains matter nor occupies volume
has zero thickness and a property value at a point on the boundary
is shared by both the system and its surroundings.
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T009
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T061
A system defined to contain all of the air in a piston-cylinder device.
T062
A system defined to contain all of the air that is initially in a tank that
is being filled.c
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Control Mass (CM) or Closed System
T007 T078
In Control Mass (CM) or Closed system, the CS is closed to mass flow,
so that no mass can escape from or enter into the system. Heat & work
may cross the CS, but the system contains the same amount of matter
at all times.
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology M E 6101 (2015) 5 / 17
Control Volume (CV) or Open System
T008
T082
When there is flow of mass through CS,
the system is called a Control Volume
(CV) or Open system.
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology M E 6101 (2015) 6 / 17
Adiabatic System
T079 T083
An Adiabatic system is one in which the boundary is impermeable to
heat.
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology M E 6101 (2015) 7 / 17
Classification of Thermodynamic Systems
T001
An Isolated system is a special case of CM system that does notinteract in any way with its surroundings.
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Thermodynamic Equilibrium
A system in thermodynamic equilibrium satisfies the followingstringent requirements:
1 Mechanical Equilibrium: no unbalance forces acting on any part of
the system or the system as a whole.2 Thermal Equilibrium: no temperature differences between parts of
the system or between the system and the surrounding.3 Chemical Equilibrium: no chemical reactions within the system and
no motion of any chemical species from one part to another part of
the system.
Any property has a fixed value in a give state in a given
equilibrium state, regardless of how the system arrives at the state.
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology M E 6101 (2015) 13 / 17
T077
T076
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A system is said to be in Stable/Equilibrium State when no finite
change of state can occur unless there is an interaction between
the system and its environment which leaves a finite alteration in
the state of the environment.
During a quasi-static process, the system is at all timesinfinitesimally near a state thermodynamic equilibrium; this
implies that the process should be carried out infinitely slowly to
allow the system to settle to a stable state at the end of each
infinitesimal step in the process.
Theoretical calculations must relate to Stable states, since it is
only for these we have thermodynamic data.
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology M E 6101 (2015) 15 / 17
Categories of Thermodynamics Quantities
1 State functions: all properties are state functions.
2 Process or Path functions: quantities whose values depend on the
path of the process.
T038
2
1 dy =
y 2−
y 1 =
∆y ⇒ dy = 0State function
2
1δZ ≡ Z 12 = ∆Z
T013
Path function
c Dr. Md. Zahurul Haq (BUET) Basic Thermodynamic Terminology ME 6101 (2015) 16 / 17
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Zero’th Law of Thermodynamics
Zero’th Law of Thermodynamics
Two systems with thermal equilibrium with a third are in thermal
equilibrium with each other.
T045 T002
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