Department of Technical Education
Andhra Pradesh
Name of the faculty
Designation
Branch
Institute
Year / Semester
Subject
Sub. Code
Topic
Duration
Sub. Topic
Teaching Aids
Revised By
: V. Narsimha Reddy
: Lecturer in EEE
: E.C.E.
: GMR. Polytechnic Gajwel
: VI Semester
: Electrical Utilization & Automation
: EE605A
: Electric Heating
: 50 Mins
: Advantages and Requirements of
Electric Heating
: PPT, Animation
: K. Chandra Sekhar, L/EEE, GPT, HYD
9EE605A.11
1
Known to Unknown
• What is the necessity of heat in our lives?
• What is meant by electric heating?
9EE605A.11
2
Objectives
On completion of this topic you would be able to know
• Electric Heating
• Advantages of Electrical Heating
• Requirements of Good Heating Element
• Materials for Heating Element
9EE605A.11
3
Introduction of Heating
• Heat plays an important role in everyday life
• Heat or fire and wheel are the basis for human
civilization
• Without fire and wheel, man wheel go back to stone age
• Man used fire to cook food
• In present days heat is used to extract the metals from
the ores
9EE605A.11
4
Electric Heating
• Heat and electricity are interchangeable
• Heat can be produced by passing the current through a
conductor
• This method is superior compared to other methods
9EE605A.11
5
Advantages of Electrical Heating
• Cleanliness
• High Efficiency
• No Pollution
• Localized Heating.
• Ease of Control
• Uniform Heating
9EE605A.11
6
Advantages of Electrical Heating
Contd…
• Better working conditions
• Less floor area is required
• No carrying expenses
• Low attention and maintenance cost
• Economical
• Safety
9EE605A.11
7
Modes of Heat Transfer
The heat is transferred from a hot body are
• Conduction
• Convection
• Radiation
9EE605A.11
8
Modes of Heat Transfer
Conduction
• The heat transferred depends on the difference
•
•
•
between the temperature of the two points
The heat transfer by conduction takes place in solids,
liquids and gases
In solids, heat is transferred from one molecule to
adjacent molecule and so on
There is no actual motion of molecules
9EE605A.11
9
Modes of Heat Transfer
Convection
• Heat is transferred from One point to the other point due to
motion of molecules .
•
Heat dissipation: H = 3.875 (T1-T2)1.25 w/m2
•
T1 = Temperature of the heating surface (0K)
•
T2 = Temperature of the Air (0K)
9EE605A.11
10
Modes of Heat Transfer
Radiation
•
The heat transfer is confined to surfaces
•
The radiant energy is emitted and absorbed by different
surfaces.
•
Heat dissipation: H=5.72Ke [(T1/100)4 – (T2/100)4] w/m2
T1 = Temperature of source (0K).
T2 = Temperature of absorbing surface (0K)
.
9EE605A.11
11
Modes of Heat Transfer
where e = emissivity
= 1 for black body
= 0.9 for resistance heating element
k= radiating efficiency or a constant
=1 for single element
= 0.5 to 0.8 for several elements placed side by
side
9EE605A.11
12
Requirements of Good Heating Material
The material used for heating element should posses the
following properties
• High specific resistance
• Low temperature coefficient of resistance
• Free from Oxidation
• High melting point
• Non corrosive
9EE605A.11
13
Requirements of Good Heating Material
The material used for heating element should
posses the following properties
• Ductile
• Positive temperature Coefficient of Resistance
• High mechanical strength
• Economical
9EE605A.11
14
Materials for Heating Elements
The materials normally used as heating elements are
• Nickel-chromium
• Nickel-chromium iron
• Nickel-chromium aluminum and
• Nickel-copper
9EE605A.11
15
Properties of Heating Elements
SI.
NO
TYPE OF
ALLOY
COMPOSITION
1
Nickelchromium
2
Nickelchromium Iron
3
Iron chromium 65-75% Fe
Aluminum
20-30% Cr.
5% Al.
4
Nickel- Copper
80% Ni
20% Cr.
60% Ni
16% Cr.
24% Fe
45% Ni
55% Cr.
COMMERCIAL
SPECIFIC
SPECIFIC MAXIMUM
0
NAME
RESISTANCE AT 20 C GRAVITY TEMPERAT
URE
Nichrome
-
1.03 μΩ-m
1.06 μΩ-m
8.35
11500C
8.27
9500C
Kanthal
1.4 μΩ-m
7.2
1150 to
13500C
Eureka
0.49 μΩ-m
8.88
4000C
9EE605A.11
16
Reasons for failure of Heating Elements
The reasons are
• Formation of hot spots
• Oxidation of elements and intermittency of
operation
• Embrittlement caused by grain growth
• Corrosion
9EE605A.11
17
Summary
In this class we have discussed about
• Advantages of Electrical Heating
• Modes of Heat Transfer
• Requirements of Good Heating Element
• Materials employed for Heating Element
9EE605A.11
18
Quiz
1.
Electrical Heating is
a)
Uniform
b)
Non-uniform
c)
Both a & b
d)
None
9EE605A.11
19
Quiz
2. The heating element should posses
a)
High melting point
b)
Low melting point
c)
Both a & b
d)
None
9EE605A.11
20
Frequently Asked Questions
1. State the advantages of electric heating
2. What are the requirements of good heating element ?
3. What are the materials employed for heating element ?
9EE605A.11
21
THANK YOU
9EE605A.11
22