# Thermodynamics

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28 Οκτ 2013 (πριν από 4 χρόνια και 6 μήνες)

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Definitions

(Sorted Alphabetically)

1

1
st

Law
(Conservation of
energy)

Cyclic integral of work is directly proportional to the cyclic
integral of heat transfer.

Energy cannot be created or destroyed but can be transferred
from one
form to another

2

2
nd

Law

Planck’s:

It is impossible to construct a device that operates in a cycle
and

produce no effect except the raising of a weight and
exchange heat with the same

reservoir.

Clausius
:

It is impossible to construct a device that opera
tes in a cycle
and produces no

effect other transferring heat form a cooler
body to a hotter one without work input.

3

A process is

one in which there is no heat transfer into or out
of the system

(insulated)

4

Boundary

The barrier between the

system being studied and the
surrounding.

-
Real (physical)
: can be seen or touched. eg. Walls of a
room.

-
Imaginary
: cannot be touched or seen eg. Part of the room

-
Fixed
: Doesn’t move or change dimensions eg. Closed
container.

-
Movable
: Changes dim
ension with changing system eg.
Gas in a piston/ cylinder system.

5

Caloric Value

The amount of energy produced per Kg of fuel.

6

Closed system
(control mass)

A quantity of matter of fixed mass that doesn’t allow mass
to cross the boundary. En
ergy can cross.

7

Cycle

A closed path of successive states in which system finally
reaches the initial state.

8

District heating and
cooling

Taking advantage of varying conditions of different systems
working at the same time.

9

Dryness factor
(Steam

quality)

Ratio of vapor mass to total mass.

10

Efficiency

Ratio between energy sought (output required) to energy of
cost (input needed).

Heat engine
: work produced to energy supplied.

Refrigerator (COP)
: cooling effect required to compressor
input work
needed.

Heat pump (COP)
: Heating effect required to compressor
input work needed.

11

Energy

The ability to produce an effect

12

Enthalpy

A thermal function defining the thermal and mechanical
properties of a system.

13

External T. Properties

Observable
properties of a system which characterize its
location and motion.

14

Heat transfer

Energy transferred due to temperature difference.

15

Internal Energy

Stored energy in the system which doesn’t include the effect
of: electricity, magnetism, motion and g
ravity.

16

Internal T. Properties

Observable properties of a system which characterize it in
equilibrium.

Intensive: Mass Independent properties. Eg. Pressure,temp.

Extensive: Mass dependent properties. Eg. Length, weight,
volume.

17

Irreversible process

A

process that cannot

return both the system and the
surroundings to

their original conditions.

18

Isentropic

A reversible adiabatic process ( change in S=0,Q=0)

19

Isobaric

A process of in which pressure stays constant

20

Isocharic

A process of in wh
ich volume stays constant

21

Isolated system

System that doesn’t allow neither mass nor energy to cross
the boundary.

22

Isothermal

A process of in which temperature stays constant

23

Kinetic Energy

Energy possessed by a system due to its motion.

24

Open system
(control volume)

A control volume that allows mass to cross the boundary
into or out of the system. Energy can cross.

25

Potential Energy

Energy possessed by a system due to its relative position
from earth.

26

Power

Rate of

doing work

27

Process

A path of successive states in which system passes

28

Process diagram

A diagram which describes the system using 2 independent
properties. Eg. P
-
V, P
-
T, T
-
S, P
-
H……

29

Pure substance

A substance which has same chemical composition
in all
state.

30

Quasi
-

Equilibrium
process

A process in which deviation from the state of equilibrium

is
infi
nite
simal

(very
very
small).

31

SSSF

Flow)

Open system (control volume) which:

doesn’t move

s
tate of mass inside system doesn’t change

state of mass crossing boundary doesn’t change

Constant rate of work and heat transfer crossing boundary.

32

State

Status of the system defined by it’s properties

33

A state when the system is in equ
ilibrium. In = out

34

Sub cooled

steam

It is steam in liquid form only maintained
at low temperature
and high pressure.

35

Super heated

steam

It is steam in vapor form only maintained at

high temp and
low pressure.

36

Surroundings

Anything that is outsi
de the system boundary.

37

System

A device or a combination of devices containing a quantity
of matter being studied

38

Thermal Reservoir

A body of high thermal capacity and which transfers heat
with surrounding without change in temperature.

39

Thermal

Sink

A heat reservoir which receives energy in the form of heat.

40

Thermal Source

A heat reservoir which Supplies energy in the form of heat.

41

Thermodynamics

Science concerned with heat and work and properties of
systems related to heat and work

4
2

Throttling

A process in which there is no change in enthalpy from one
state to another, no work is done and the process is

43

Wet steam

A mixture of liquid and vapor water

44

Work

Force acting though distance.

Energy that can be transferred
mechanically.

45

Working fluid

The fluid which transfers energy through the system and can
apply all thermodynamics laws on.