Electric heating uses electrical energy to generate heat through various resistance heating methods. It has advantages like being clean, pollution-free, easily controlled, and providing uniform heating. The main types of electric heating are resistance, induction, dielectric, and electron bombardment heating. Resistance heating directly passes current through material or uses heating elements, with applications in furnaces, ovens, and devices like irons. Heat is controlled through varying voltage, resistance of elements, or using electronic converters.

1. Electric Heating

2. What is Electric Heating?
• Electric heating is a process in which ELECTRICAL
ENERGY is converted to “HEAT ENERGY”.
• It covers those engineering processes by which this
conversion is used effectively to fulfill our need.

3. Why Electric Heating?
• Clean and atmosphere / Free from dirt.
• No pollution / No flue gas is produced
• Ease of control
• Cost effective
• Comparatively better working condition
• Localized application
• Overall efficiency is much higher
• Uniform heating
• Heating of non-conductive material

4. What are the types?
• Resistance Heating
• Arc Heating
• Induction Heating
• Dielectric Heating
• Electron Bombardment Heating

5. 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
Direct Resistance Heating & Indirect Resistance Heating

6. Direct Resistance 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
A.C.or D.C
High resistance powder
charge
furnace

7. Salt Bath Furnace

8. Salt Bath Furnace (contd…)
• The furnace has a ceramic or metal container filled with
molten salt.
• Bath’s composition consists of one or more salts, nitrates,
chlorides, carbonates, cyanides, caustics, or additives (
sulphates, fluorides, etc.) in small amounts.
• Heat is transferred between work and molten salt by
conduction.
• The salt lends itself to either heating or cooling within a 300o
to 2400o range, as required.

9. Salt Bath Furnace (contd…)
• Used for
i. Carbonizing
ii. Tempering
iii. Quenching
iv. Hardening
• Eliminates Oxidation
• Rapid and Uniform Heating

10. Salt Bath Furnace (contd…)
• Voltage required : 2 – 20V, Current : upto 3kA
• Supply: Step-down transformer having tap changing Gear
• Temperature increases, resistance goes down
• Starts with highest tap, gradually brought down to lowest tap
• Current is controlled by
 Voltage
 Depth of immersion
 distance between electrodes

11. Salt Bath Furnace (contd…)
• To start with
• Current conducting bath is required between electrode
because the dry lumpy salt does have conductivity
• Bridge by a piece of carbon
• Transferring molten salt from an already running furnace
• For high conductive material, highly resistive powder is
sprinkled

12. Indirect Resistance Heating
• In this method of heating,
current is passed through
a high resistance wire
known as heating element
• The heat produced in the
element is transferred to
the charge by radiation or
convection methods
A.C or D.C
Chamber
Heating element
Charge
Furnace

13. Applications
• Room heaters
• Bimetallic strip used in starters
• Water heater i.e. immersion heater
• Ovens like domestic cooking
• Soldering iron
• Flat iron
• Electric kettle

14. Properties of good heating
elements
• High resistivity
• High melting point
• Should not oxidize in operating temperature
• Low temperature coefficient of resistance

15. Heating Elements
• Metal
• CuproNickel : 75% Cu + 25% Ni , upto 400
o
C
Constantan ( 55% Cu + 45% Ni)
• NiCrFe Alloy : 60% Ni, 24% Fe, 16% Cr, upto 950
o
C
• Nichrome : 80% Ni + 20% Cr, upto 1150
o
C
• Kanthal (FeCrAl) : 65-75% Fe + 20-30% Cr + 5% Al, upto 1425
o
C

16. Heating Elements
• Non Metalic
Molybdenum Disilicide (MoSi2), upto 1800
o
C
• PTC Heating elements
PTC rubber, upto 80
o
C - Due to the exponentially
increasing resistivity the heater can never be warmer than this
temperature.
It is a point wise self-regulating heater and self-limiting
heater.

17. Control of Heat
• By Varying Voltage
 By autotransformer or induction regulator
 By series impedance
 By dedicated variable voltage supply
 By using power electronic converter
 By periodically switching off the supply (Integral Cycle
Control)
• By varying resistance of elements
 By varying number of heating elements
 By series-parallel of star-delta arrangement of the
elements

18. By Autotransformer

19. By Series Impedance

20. Power-electronic converters
• Controlled Rectifier (AC/DC)

21. Controlled AC Output

22. Controlled DC output

23. Integral Cycle Control

24. Varying number of elements

25. Closed Loop Control of
Temperature

26. On-Off Control

27. Proportional Control

28. PID Control

29. Design of Heating Elements
•