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Transcript of 1 Name of the faculty: V. Narsimha Reddy Designation: Lecturer in EEE Branch : E.C.E. Institute :...
1
Name of the faculty : V. Narsimha Reddy
Designation : Lecturer in EEE
Branch : E.C.E.
Institute : GMR. Polytechnic Gajwel
Year / Semester : VI Semester
Subject : Electrical Utilization & Automation
Sub. Code : EE605A
Topic : Electric Heating
Duration : 50 Mins
Sub. Topic : Advantages and Requirements of
Electric Heating
Teaching Aids : PPT, AnimationRevised By : K. Chandra Sekhar, L/EEE, GPT, HYD
9EE605A.11
Department of Technical Education Andhra Pradesh
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Known to Unknown
• What is the necessity of heat in our lives?
• What is meant by electric heating?
9EE605A.11
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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
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
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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
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Advantages of Electrical Heating
• Cleanliness
• High Efficiency
• No Pollution
• Localized Heating.
• Ease of Control
• Uniform Heating
Advantages of Electrical Heating
• Better working conditions
• Less floor area is required
• No carrying expenses
• Low attention and maintenance cost
• Economical
• Safety
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Contd…
Modes of Heat Transfer
The heat is transferred from a hot body are
• Conduction
• Convection
• Radiation
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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
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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)
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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)
.
Modes of Heat Transfer
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
side9EE605A.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
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The material used for heating element should
posses the following properties
• Ductile
• Positive temperature Coefficient of Resistance
• High mechanical strength
• Economical
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Requirements of Good Heating Material
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Materials for Heating Elements
The materials normally used as heating elements are The materials normally used as heating elements are
• Nickel-chromium Nickel-chromium
• Nickel-chromium iron Nickel-chromium iron
• Nickel-chromium aluminum and Nickel-chromium aluminum and
• Nickel-copper Nickel-copper
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SI.NO
TYPE OF ALLOY
COMPOSITION COMMERCIAL NAME
SPECIFIC RESISTANCE AT 200C
SPECIFIC GRAVITY
MAXIMUM TEMPERATURE
Nickel-chromium
Nickel-chromium Iron
Iron chromium Aluminum
Nickel- Copper
80% Ni20% Cr.
60% Ni16% Cr.24% Fe
65-75% Fe20-30% Cr.5% Al.
45% Ni55% Cr.
Nichrome
Kanthal
Eureka
1.03 μΩ-m
1.06 μΩ-m
1.4 μΩ-m
0.49 μΩ-m
8.35
8.27
7.2
8.88
11500C
9500C
1150 to 13500C
4000C
1
2
3
4
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Properties of Heating Elements
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
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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
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Quiz
1. Electrical Heating is
a) Uniform
b) Non-uniform
c) Both a & b
d) None
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Quiz
2. The heating element should posses
a) High melting point
b) Low melting point
c) Both a & b
d) None
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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 ?
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THANK YOU