Transcript Resistance Heating , Methods of Resistance Heating , Applications

Department of Technical Education
Andhra Pradesh
Name
Designation
Branch
Institute
Year / Sem.
Subject
Subject Code
Topic
Duration
Sub topic
Teaching Aids
Revised By
: V. Narsimha Reddy
: Lecturer in EEE
: D.E.C.E.
: GMR. Polytechnic Gajwel
: VI Semester
: Electrical Utilization & Automation
: EE605A
: Electric Heating
: 50 Minutes
: Direct & Indirect Resistance Heating
: PPT, Diagrams, Animation
: K. Chandra Sekhar, L/EEE, GPT, HYD
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Recap
In the last class you have learnt about
• Advantages of Electric Heating
• Requirements of Good Heating Material
• Materials employed for Heating Element
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Objectives
On completion of this topic you would be able to know
• Resistance Heating
•
Methods of Resistance Heating
•
Applications of Resistance Heating
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Resistance Heating
• When current passes through a resistance ,Power loss takes
place there in ,which appears in the form of heat
• Electrical energy converted into heat energy
H = I2Rt
Power loss = I2R watts
= VI Watts
= V2/R watt
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Resistance Heating
Where R=Resistance of the element (Ω)
V=Voltage (Volt)
I=Current (ampere)
•
The loss of energy takes place only in transferring
heat from element to charge or load
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Types of Resistance Heating
The resistance heating is further classified into
three types
• Direct resistance heating
• Indirect resistance heating.
• Infra red or Radiant heating.
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Direct Resistance Heating
A.C.or D.C
High resistance powder
furnace
charge
Fig. 1
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Direct Resistance Heating
• Fig.1 shows direct
resistance heating
• In this method of heating,
current is passed through
the material or charge to
be heated
• Charge is considered in a
furnace and two
electrodes or three
electrodes for 3phase are
immersed in the charge
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A.C.or D.C
High resistance powder
furnace
charge
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Direct Resistance Heating
• The resistance offered by
the charge to the flow of
current causes power
loss I2R and it results in
the heating of the charge
• The charge may be in the
form of solid pieces,
powder or liquid
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A.C.or D.C
High resistance powder
furnace
charge
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Direct Resistance Heating
• When solid pieces are to
be heated a powder of
high resistivity material is
sprinkled over surface of
charge
• This is to avoid pinch
effect
• The current passes
through the charge and
heat is produced
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A.C.or D.C
High resistance powder
furnace
charge
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Applications
This method of heating is used in
• Resistance welding
• The electrode boiler for heating water
• Salt bath furnace which is used for hardening steel
tools and prevents oxidation
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Indirect Resistance Heating
A.C or D.C
Chamber
Heating element
Charge
Furnace
Fig. 2
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Indirect Resistance Heating
• Fig.2 shows indirect
resistance heating
• In this method of heating,
current is passed through
a high resistance wire
known as heating
element
• The heating element can
be placed above or below
the furnace/charge
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A.C or D.C
Chamber
Heating element
Charge
Furnace
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Indirect Resistance Heating
• Charge will enclose the
heating element for
efficient heat transfer
A.C or D.C
Chamber
Heating element
• The heat produced in the
element is transferred to
the charge by radiation or
convection methods
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Charge
Furnace
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Application
This method of heating is used in
• Room heaters
• Bimetallic strip used in starters
• Water heater i.e. immersion heater
• Ovens like domestic cooking
• Salt bath furnace
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Summary
In this class we have discussed about
• Resistance Heating
• Direct and Indirect Resistance Heating
• Applications of Resistance Heating
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Quiz
1.
Which type of heating is used in resistance welding
a)
Direct resistance heating
b)
Indirect resistance heating
c)
Infrared heating
d)
None
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Quiz
2.Which type of heating is used in immersion water heaters
a) Direct resistance heating
b) Indirect resistance heating
c) Infrared heating
d) None
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Frequently Asked Questions
1) What is resistance heating ?
2) Classify the different methods of electric heating
3) Explain direct resistance heating with a neat sketch ?
4) Explain Indirect resistance heating with neat diagram ?
5) State the applications of Direct resistance and Indirect
resistance heating ?
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THANK YOU
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