Lecture 1 - Fundamental Concepts of Thermodynamics and IS system of Units
-
date post
27-Apr-2015 -
Category
Documents
-
view
66 -
download
0
Transcript of Lecture 1 - Fundamental Concepts of Thermodynamics and IS system of Units
1
Mechanical Theory I
MET3405
1. Thermodynamics
1
2
Lecture 1
1.1 Fundamental Concepts of Thermodynamics
3
1.1.1 Introduction
Heat
Dynamis
Force
Therme
Thermodynamics
4
Thermodynamics
capacity of hot bodies to produce work
5
Thermodynamics
It is a branch of engineering science that deals with the relationship between
�energy associated to heat
�and other forms of energy
•••• mechanical
•••• electrical
•••• chemical
•••• ….
6
Resources in nature
Fossil Fuels
Radioactive Substances
7
People’s needs for energy
8
People’s needs for energy
Air conditioning
Heating
9
Provision of energy is one
of the main tasks of ME
The branch of science that
�explains how much energy people may extract from various sources
�and predicts how efficiently people may use the extracted energy in a particular situation is called:
10
1.1.2 Basic Concepts
11
Fluids
Fluids are substances that:
• flow, even under the action of small forces;
• and take the shape of their container.
12
GasesLiquids
Incompressible
FluidsVolume = const
Compressible
FluidsVolume ≠≠≠≠ const
13
Thermodynamic System
System is the subject of analysis.
It may include:
•••• single simple body,
•••• or very complex assembly of many component and parts.
14
Schematic presentation
of a System
System
Surroundings
System Boundary
15
Closed System
Closed Reservoir
m = constThe substance in the reservoir cannot leave.New substance cannot enter in the reservoir.
m : mass of the substance
16
Cylinder - Piston Assembly
Cylinder
Piston
Boundary
System: Working
Fluid
m = const
V ≠≠≠≠ const
17
V2 > V1 Expansion
V1
State 1
V2
State 2
18
V1 > V2 Compression
V2
State 2
V1
State 1
19
Cylinder - Piston Assembly
This device has very important role in engineering practice and is commonly used in many gas power cycles such as internal combustion engines.
20
Closed System ≡ Control Mass
In some textbooks, the closed system is also called Control Massbecause in a closed system the mass of the working substance is under consideration.
21
Open System
Pipe
Control Volume
22
Open System
Examples of open system include pipes, nozzles and diffusers, boilers, heat exchangers, valves, turbines, pumps and compressors.
23
Thermodynamic Property
Properties are quantities that can be measured,
so their values can describe the condition of the system
without knowing how the system came to that condition.
24
Examples of Properties
• Mass of the working fluid employed in the process
• Volume occupied by the working fluid
• Temperature of the working fluid
• Pressure of the working fluid
25
State
State is a term for a condition of the system
as it is described by its properties.
26
Example for a State
• Closed System
Our lecture theatre
• Working Fluid in the lecture theatre:
Air
• Temperature of Air: 20oC
• Pressure of Air: 1 bar
• The state of the system is given with: 20oC and 1 bar.
27
Process
Process is a transformation of the system
from one state
to another state.
28
Example for a Process
• Closed System: Our Lecture Theatre
• Initial State: 20oC, 1 bar
• Air-conditioning system switched off
• Process: Heating of the air (due to transfer of heat from outside and from students)
• Final State: 30oC, 1 bar
29
1.1.3 The SI System of Units in Thermodynamics
30
International System of Units: Basic Units
Mass Length Time
Symbol m (Note)
L t
Unit kilogramme metre second
Symbol for unit
kg m s
31
Note (Very Important!)
�Quantity mass with unit kg is characteristic for Closed Systems.
�For Open System, corresponding quantity is
called Mass Flow Rate
m&the symbol is
and the unit is kg/s
32
Additional Basic Unit
for Heat Interactions:
Temperature
No negative values for temperature
Kelvin Scale
Only positive values for temperature
Absolute Zero Temperature
Temperature (T) expressed in Kelvin degrees: K
33
Additional Basic Unit
for Heat Interactions:
TemperatureCelsius Scale
Negative values for temperature
Positive values for temperature
Zero Temperature
Temperature (t) expressed in Celsius degrees: oC
34
Relation between Kelvin and Celsius Scales
0 K = - 273.15 oC
0 oC = 273.15 K
T (K) = t (oC) + 273.15
t (oC) = T (K) - 273.15
∆∆∆∆T (K) = ∆∆∆∆t (oC)∆∆∆∆T = T2 - T1; ∆∆∆∆t = t2 - t1
35
SI System of Units:
Derived Units
36
Examples
• Area
aA=a2
a
b
A=ab d
A=d2ππππ/4
Unit: m 2
37
Examples
Volume
ab
c V = abc
Unit: m 3
38
Examples: Volume
Liter (l)
• 1 liter = 1 dm3
• 1 dm = 10 cm
• 1 m = 10 dm
• 1 m3 = 1000 dm3 = 1000 l
39
Force
F = maF: force acting on the body;
m: mass of the body, kg;
a: acceleration, m/s2;
Unit for force: Newton (N)
2s
m X kg F forcefor Unit =
40
Weight
w = mgw: weight of the body, N;
m: mass of the body, kg;
g: acceleration due to gravity, m/s2;
g = 9.81 m/s2
41
Density
ρρρρ = m/V
ρρρρ: density, kg/m3;
m: mass of the body, kg;
V: volume occupied by the mass, m3;
m = ρρρρV
42
Specific Volume
v = 1/ρρρρ = V/m
v: specific volume, m3/kg;
V: volume, m3;
m: mass of the body, kg;
m = V/v
43
Relative Density
s = ρρρρsubstance/ρρρρwaters: relative density, no unit;
Example:
ρρρρmercury = 13595 kg/m3;
ρρρρwater = 1000 kg/m3;
⇒⇒⇒⇒ s = 13595/1000 = 13.595
44
Pressure
p = F/A
p: pressure
F: normal component of the force acting over the body, N;
A: area over which the force acts, m2;
Unit for pressure = N/m2 = Pascal = Pa
1 bar = 105 Pa
1 atmosphere pressure = 101325 Pa
= 1.01325 bar
45
Reference: Basic Thermodynamics
by K. Iynkaran and D. J. Tandy
�Suggested Additional ReadingChapter 1: Introduction to Thermodynamics
�Suggested Examples1.1 - 1.5
�Suggested Tutorial Problems1.1 - 1.8