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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?

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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

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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