Electric Heating & Welding | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE) PDF Download

Download, print and study this document offline
Please wait while the PDF view is loading
 Page 1


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UNIT 2 
 
Electric Heating 
 
INTRODUCTION 
 
Heat plays a major role in everyday life. All heating requirements in domestic purposes 
such as cooking, room heater, immersion water heaters, and electric toasters and also 
in industrial purposes such as welding, melting of metals, tempering, hardening, and 
drying can be met easily by electric heating, over the other forms of conventional 
heating. Heat and electricity are interchangeable. Heat also can be produced by 
passing the current through material to be heated. This is called electric heating; there 
are various methods of heating a material but electric heating 
is considered far superior compared to the heat produced by coal, oil, and natural gas. 
 
ADVANTAGES OF ELECTRIC HEATING 
 
The various advantages of electric heating over other the types of heating are: 
 
(i) Economical 
 
Electric heating equipment is cheaper; they do not require much skilled persons; 
therefore, maintenance cost is less. 
(ii) Cleanliness 
 
Since dust and ash are completely eliminated in the electric heating, it keeps 
surroundings cleanly. 
(iii) Pollution free 
 
As there are no flue gases in the electric heating, atmosphere around is pollution free; 
no need of providing space for their exit. 
(iv) Ease of control 
Page 2


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UNIT 2 
 
Electric Heating 
 
INTRODUCTION 
 
Heat plays a major role in everyday life. All heating requirements in domestic purposes 
such as cooking, room heater, immersion water heaters, and electric toasters and also 
in industrial purposes such as welding, melting of metals, tempering, hardening, and 
drying can be met easily by electric heating, over the other forms of conventional 
heating. Heat and electricity are interchangeable. Heat also can be produced by 
passing the current through material to be heated. This is called electric heating; there 
are various methods of heating a material but electric heating 
is considered far superior compared to the heat produced by coal, oil, and natural gas. 
 
ADVANTAGES OF ELECTRIC HEATING 
 
The various advantages of electric heating over other the types of heating are: 
 
(i) Economical 
 
Electric heating equipment is cheaper; they do not require much skilled persons; 
therefore, maintenance cost is less. 
(ii) Cleanliness 
 
Since dust and ash are completely eliminated in the electric heating, it keeps 
surroundings cleanly. 
(iii) Pollution free 
 
As there are no flue gases in the electric heating, atmosphere around is pollution free; 
no need of providing space for their exit. 
(iv) Ease of control 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
In this heating, temperature can be controlled and regulated accurately either manually 
or automatically. 
(v) Uniform heating 
 
With electric heating, the substance can be heated uniformly, throughout whether it 
may be conducting or non-conducting material. 
(vi) High efficiency 
 
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of 
heat can be successfully utilized. So, overall efficiency of electric heating is very high. 
 
(vii) Automatic protection 
 
Protection against over current and over heating can be provided by using fast 
control devices. (viii) Heating of non-conducting materials 
The heat developed in the non-conducting materials such as wood and porcelain is 
possible only through the electric heating. 
(ix) Better working conditions 
 
No irritating noise is produced with electric heating and also radiating losses are low. 
 
(x) Less floor area 
 
Due to the compactness of electric furnace, floor area required is less. 
 
(xi) High temperature 
 
High temperature can be obtained by the electric heating except the ability of the 
material to withstand the heat. 
(xii) Safety 
 
The electric heating is quite safe. 
 
MODES OF TRANSFER OF HEAT 
 
The transmission of the heat energy from one body to another because of the 
temperature gradient takes place by any of the following methods: 
1. conduction, 
 
2. convection, or 
 
3. radiation. 
Conduction 
 
In this mode, the heat transfers from one part of substance to another part without the movement in 
the molecules of substance. The rate of the conduction of heat along the substance 
Page 3


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UNIT 2 
 
Electric Heating 
 
INTRODUCTION 
 
Heat plays a major role in everyday life. All heating requirements in domestic purposes 
such as cooking, room heater, immersion water heaters, and electric toasters and also 
in industrial purposes such as welding, melting of metals, tempering, hardening, and 
drying can be met easily by electric heating, over the other forms of conventional 
heating. Heat and electricity are interchangeable. Heat also can be produced by 
passing the current through material to be heated. This is called electric heating; there 
are various methods of heating a material but electric heating 
is considered far superior compared to the heat produced by coal, oil, and natural gas. 
 
ADVANTAGES OF ELECTRIC HEATING 
 
The various advantages of electric heating over other the types of heating are: 
 
(i) Economical 
 
Electric heating equipment is cheaper; they do not require much skilled persons; 
therefore, maintenance cost is less. 
(ii) Cleanliness 
 
Since dust and ash are completely eliminated in the electric heating, it keeps 
surroundings cleanly. 
(iii) Pollution free 
 
As there are no flue gases in the electric heating, atmosphere around is pollution free; 
no need of providing space for their exit. 
(iv) Ease of control 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
In this heating, temperature can be controlled and regulated accurately either manually 
or automatically. 
(v) Uniform heating 
 
With electric heating, the substance can be heated uniformly, throughout whether it 
may be conducting or non-conducting material. 
(vi) High efficiency 
 
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of 
heat can be successfully utilized. So, overall efficiency of electric heating is very high. 
 
(vii) Automatic protection 
 
Protection against over current and over heating can be provided by using fast 
control devices. (viii) Heating of non-conducting materials 
The heat developed in the non-conducting materials such as wood and porcelain is 
possible only through the electric heating. 
(ix) Better working conditions 
 
No irritating noise is produced with electric heating and also radiating losses are low. 
 
(x) Less floor area 
 
Due to the compactness of electric furnace, floor area required is less. 
 
(xi) High temperature 
 
High temperature can be obtained by the electric heating except the ability of the 
material to withstand the heat. 
(xii) Safety 
 
The electric heating is quite safe. 
 
MODES OF TRANSFER OF HEAT 
 
The transmission of the heat energy from one body to another because of the 
temperature gradient takes place by any of the following methods: 
1. conduction, 
 
2. convection, or 
 
3. radiation. 
Conduction 
 
In this mode, the heat transfers from one part of substance to another part without the movement in 
the molecules of substance. The rate of the conduction of heat along the substance 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
depends upon the temperature gradient. The amount of heat passed through a cubic body with 
two parallel faces with thickness ‘t’ meters, having the cross-sectional area of ‘A’ square 
meters and the temperature of its two faces T1°C and T2°C, during ‘T’ hours is given by: 
 
 
 
where k is the coefficient of the thermal conductivity for the material and it is measured 
in MJ/m3/°C/hr. 
 
Ex: Refractory heating, the heating of insulating materials, etc. 
 
Convection 
 
In this mode, the heat transfer takes place from one part to another part of substance 
or fluid due to the actual motion of the molecules. The rate of conduction of heat 
depends mainly on the difference in the fluid density at different temperatures. Ex: 
Immersion water heater. 
The mount of heat absorbed by the water from heater through convection depends 
mainly upon the temperature of heating element and also depends partly on the 
position of the heater. Heat dissipation is given by the following expression. 
H = a (T1 – T2)b W/m2, 
 
where ‘a’ and ‘b’ are the constants whose values are depend upon the heating surface and 
 
T1and T2 are the temperatures of heating element and fluid in °C, respectively. Radiation In 
 
this mode, the heat transfers from source to the substance to be heated without heating the 
 
medium in between. It is dependent on surface. 
 
Ex: Solar heaters. 
 
The rate of heat dissipation through radiation is given by Stefan's Law. 
 
 
 
 
 
where T1 is the temperature of the source in kelvin, T2 is the temperature of the 
substance to be heated in kelvin, and k is the radiant efficiency: 
= 1, for single element 
 
= 0.5–0.8, for several elements 
 
e = emissivity = 1, for black body 
Page 4


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UNIT 2 
 
Electric Heating 
 
INTRODUCTION 
 
Heat plays a major role in everyday life. All heating requirements in domestic purposes 
such as cooking, room heater, immersion water heaters, and electric toasters and also 
in industrial purposes such as welding, melting of metals, tempering, hardening, and 
drying can be met easily by electric heating, over the other forms of conventional 
heating. Heat and electricity are interchangeable. Heat also can be produced by 
passing the current through material to be heated. This is called electric heating; there 
are various methods of heating a material but electric heating 
is considered far superior compared to the heat produced by coal, oil, and natural gas. 
 
ADVANTAGES OF ELECTRIC HEATING 
 
The various advantages of electric heating over other the types of heating are: 
 
(i) Economical 
 
Electric heating equipment is cheaper; they do not require much skilled persons; 
therefore, maintenance cost is less. 
(ii) Cleanliness 
 
Since dust and ash are completely eliminated in the electric heating, it keeps 
surroundings cleanly. 
(iii) Pollution free 
 
As there are no flue gases in the electric heating, atmosphere around is pollution free; 
no need of providing space for their exit. 
(iv) Ease of control 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
In this heating, temperature can be controlled and regulated accurately either manually 
or automatically. 
(v) Uniform heating 
 
With electric heating, the substance can be heated uniformly, throughout whether it 
may be conducting or non-conducting material. 
(vi) High efficiency 
 
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of 
heat can be successfully utilized. So, overall efficiency of electric heating is very high. 
 
(vii) Automatic protection 
 
Protection against over current and over heating can be provided by using fast 
control devices. (viii) Heating of non-conducting materials 
The heat developed in the non-conducting materials such as wood and porcelain is 
possible only through the electric heating. 
(ix) Better working conditions 
 
No irritating noise is produced with electric heating and also radiating losses are low. 
 
(x) Less floor area 
 
Due to the compactness of electric furnace, floor area required is less. 
 
(xi) High temperature 
 
High temperature can be obtained by the electric heating except the ability of the 
material to withstand the heat. 
(xii) Safety 
 
The electric heating is quite safe. 
 
MODES OF TRANSFER OF HEAT 
 
The transmission of the heat energy from one body to another because of the 
temperature gradient takes place by any of the following methods: 
1. conduction, 
 
2. convection, or 
 
3. radiation. 
Conduction 
 
In this mode, the heat transfers from one part of substance to another part without the movement in 
the molecules of substance. The rate of the conduction of heat along the substance 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
depends upon the temperature gradient. The amount of heat passed through a cubic body with 
two parallel faces with thickness ‘t’ meters, having the cross-sectional area of ‘A’ square 
meters and the temperature of its two faces T1°C and T2°C, during ‘T’ hours is given by: 
 
 
 
where k is the coefficient of the thermal conductivity for the material and it is measured 
in MJ/m3/°C/hr. 
 
Ex: Refractory heating, the heating of insulating materials, etc. 
 
Convection 
 
In this mode, the heat transfer takes place from one part to another part of substance 
or fluid due to the actual motion of the molecules. The rate of conduction of heat 
depends mainly on the difference in the fluid density at different temperatures. Ex: 
Immersion water heater. 
The mount of heat absorbed by the water from heater through convection depends 
mainly upon the temperature of heating element and also depends partly on the 
position of the heater. Heat dissipation is given by the following expression. 
H = a (T1 – T2)b W/m2, 
 
where ‘a’ and ‘b’ are the constants whose values are depend upon the heating surface and 
 
T1and T2 are the temperatures of heating element and fluid in °C, respectively. Radiation In 
 
this mode, the heat transfers from source to the substance to be heated without heating the 
 
medium in between. It is dependent on surface. 
 
Ex: Solar heaters. 
 
The rate of heat dissipation through radiation is given by Stefan's Law. 
 
 
 
 
 
where T1 is the temperature of the source in kelvin, T2 is the temperature of the 
substance to be heated in kelvin, and k is the radiant efficiency: 
= 1, for single element 
 
= 0.5–0.8, for several elements 
 
e = emissivity = 1, for black body 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
= 0.9, for resistance heating element. 
 
From Equation (4.1), the radiant heat is proportional to the difference of fourth power 
of the temperature, so it is very efficient heating at high temperature. 
 
ESSENTIAL REQUIREMENTS OF GOOD HEATING ELEMENT The 
materials used for heating element should have the following properties: 
 
o High-specific resistance 
 
Material should have high-specific resistance so that small length of wire may be 
required to provide given amount of heat. 
 
o High-melting point 
 
It should have high-melting point so that it can withstand for high temperature, a small increase 
 
in temperature will not destroy the element. 
 
o Low temperature coefficient of resistance 
 
From Equation (4.1), the radiant heat is proportional to fourth powers of the 
temperatures, it is very efficient heating at high temperature. For accurate temperature 
control, the variation of resistance with the operating temperature should be very low. 
This can be obtained only if the material has low temperature coefficient of resistance 
o Free from oxidation 
The element material should not be oxidized when it is subjected to high temperatures; 
otherwise the formation of oxidized layers will shorten its life. 
 
o High-mechanical strength 
 
The material should have high-mechanical strength and should withstand for 
mechanical vibrations. 
 
o Non-corrosive 
 
The element should not corrode when exposed to atmosphere or any other chemical fumes. 
 
o Economical 
 
The cost of material should not be so high. 
 
MATERIAL FOR HEATING ELEMENTS 
 
The selection of a material for heating element is depending upon the service conditions such 
as maximum operating temperature and the amount of charge to be heated, but no single 
element will not satisfy all the requirements of the heating elements. The materials normally 
used as heating elements are either alloys of nickel–chromium, nickel–chromium–iron, nickel– 
Page 5


      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
 
 
 
 
 
 
 
 
 
 
 
 
 
UNIT 2 
 
Electric Heating 
 
INTRODUCTION 
 
Heat plays a major role in everyday life. All heating requirements in domestic purposes 
such as cooking, room heater, immersion water heaters, and electric toasters and also 
in industrial purposes such as welding, melting of metals, tempering, hardening, and 
drying can be met easily by electric heating, over the other forms of conventional 
heating. Heat and electricity are interchangeable. Heat also can be produced by 
passing the current through material to be heated. This is called electric heating; there 
are various methods of heating a material but electric heating 
is considered far superior compared to the heat produced by coal, oil, and natural gas. 
 
ADVANTAGES OF ELECTRIC HEATING 
 
The various advantages of electric heating over other the types of heating are: 
 
(i) Economical 
 
Electric heating equipment is cheaper; they do not require much skilled persons; 
therefore, maintenance cost is less. 
(ii) Cleanliness 
 
Since dust and ash are completely eliminated in the electric heating, it keeps 
surroundings cleanly. 
(iii) Pollution free 
 
As there are no flue gases in the electric heating, atmosphere around is pollution free; 
no need of providing space for their exit. 
(iv) Ease of control 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
In this heating, temperature can be controlled and regulated accurately either manually 
or automatically. 
(v) Uniform heating 
 
With electric heating, the substance can be heated uniformly, throughout whether it 
may be conducting or non-conducting material. 
(vi) High efficiency 
 
In non-electric heating, only 40–60% of heat is utilized but in electric heating 75–100% of 
heat can be successfully utilized. So, overall efficiency of electric heating is very high. 
 
(vii) Automatic protection 
 
Protection against over current and over heating can be provided by using fast 
control devices. (viii) Heating of non-conducting materials 
The heat developed in the non-conducting materials such as wood and porcelain is 
possible only through the electric heating. 
(ix) Better working conditions 
 
No irritating noise is produced with electric heating and also radiating losses are low. 
 
(x) Less floor area 
 
Due to the compactness of electric furnace, floor area required is less. 
 
(xi) High temperature 
 
High temperature can be obtained by the electric heating except the ability of the 
material to withstand the heat. 
(xii) Safety 
 
The electric heating is quite safe. 
 
MODES OF TRANSFER OF HEAT 
 
The transmission of the heat energy from one body to another because of the 
temperature gradient takes place by any of the following methods: 
1. conduction, 
 
2. convection, or 
 
3. radiation. 
Conduction 
 
In this mode, the heat transfers from one part of substance to another part without the movement in 
the molecules of substance. The rate of the conduction of heat along the substance 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
depends upon the temperature gradient. The amount of heat passed through a cubic body with 
two parallel faces with thickness ‘t’ meters, having the cross-sectional area of ‘A’ square 
meters and the temperature of its two faces T1°C and T2°C, during ‘T’ hours is given by: 
 
 
 
where k is the coefficient of the thermal conductivity for the material and it is measured 
in MJ/m3/°C/hr. 
 
Ex: Refractory heating, the heating of insulating materials, etc. 
 
Convection 
 
In this mode, the heat transfer takes place from one part to another part of substance 
or fluid due to the actual motion of the molecules. The rate of conduction of heat 
depends mainly on the difference in the fluid density at different temperatures. Ex: 
Immersion water heater. 
The mount of heat absorbed by the water from heater through convection depends 
mainly upon the temperature of heating element and also depends partly on the 
position of the heater. Heat dissipation is given by the following expression. 
H = a (T1 – T2)b W/m2, 
 
where ‘a’ and ‘b’ are the constants whose values are depend upon the heating surface and 
 
T1and T2 are the temperatures of heating element and fluid in °C, respectively. Radiation In 
 
this mode, the heat transfers from source to the substance to be heated without heating the 
 
medium in between. It is dependent on surface. 
 
Ex: Solar heaters. 
 
The rate of heat dissipation through radiation is given by Stefan's Law. 
 
 
 
 
 
where T1 is the temperature of the source in kelvin, T2 is the temperature of the 
substance to be heated in kelvin, and k is the radiant efficiency: 
= 1, for single element 
 
= 0.5–0.8, for several elements 
 
e = emissivity = 1, for black body 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
= 0.9, for resistance heating element. 
 
From Equation (4.1), the radiant heat is proportional to the difference of fourth power 
of the temperature, so it is very efficient heating at high temperature. 
 
ESSENTIAL REQUIREMENTS OF GOOD HEATING ELEMENT The 
materials used for heating element should have the following properties: 
 
o High-specific resistance 
 
Material should have high-specific resistance so that small length of wire may be 
required to provide given amount of heat. 
 
o High-melting point 
 
It should have high-melting point so that it can withstand for high temperature, a small increase 
 
in temperature will not destroy the element. 
 
o Low temperature coefficient of resistance 
 
From Equation (4.1), the radiant heat is proportional to fourth powers of the 
temperatures, it is very efficient heating at high temperature. For accurate temperature 
control, the variation of resistance with the operating temperature should be very low. 
This can be obtained only if the material has low temperature coefficient of resistance 
o Free from oxidation 
The element material should not be oxidized when it is subjected to high temperatures; 
otherwise the formation of oxidized layers will shorten its life. 
 
o High-mechanical strength 
 
The material should have high-mechanical strength and should withstand for 
mechanical vibrations. 
 
o Non-corrosive 
 
The element should not corrode when exposed to atmosphere or any other chemical fumes. 
 
o Economical 
 
The cost of material should not be so high. 
 
MATERIAL FOR HEATING ELEMENTS 
 
The selection of a material for heating element is depending upon the service conditions such 
as maximum operating temperature and the amount of charge to be heated, but no single 
element will not satisfy all the requirements of the heating elements. The materials normally 
used as heating elements are either alloys of nickel–chromium, nickel–chromium–iron, nickel– 
      Utilisation of Electrical Energy  
 
                                                                                                                                                                                                                                                                                        
 
chromium–aluminum, or nickel–copper. Nickel–chromium–iron alloy is cheaper when 
compared to simple nickel–chromium alloy. The use of iron in the alloy reduces the 
cost of final product but, reduces the life of the alloy, as it gets oxidized soon. We have 
different types of alloys for heating elements. Table 4.1 gives the relevant properties of 
some of the commercial heating elements. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Table : Properties of some heating elements 
 
The properties of some commercial heating element materials commonly employed for low 
and medium temperatures up to 1,200°C are Ni–Cr and an alloy of Ni–Cr–Fe composition 
of these alloys are given in Table 4.1. For operating temperatures above 1,200°C, the 
heating elements are made up of silicon carbide, molebdenum, tungsten, and graphite. 
(Ni–Cu alloy is frequently used for heating elements operating at low temperatures. Its 
most important property is that it has virtually zero resistance and temperature coefficient.) 
 
CAUSES OF FAILURE OF HEATING ELEMENTS 
 
Heating element may fail due to any one of the following reasons. 
 
1. Formation of hot spots. 
 
2. Oxidation of the element and intermittency of operation. 
 
3. Embrittlement caused by gain growth. 
 
4. Contamination and corrosion. 
 
Formation of hotspots 
Read More
23 videos|89 docs|42 tests

Top Courses for Electrical Engineering (EE)

FAQs on Electric Heating & Welding - Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

1. How does electric heating work?
Ans. Electric heating works by passing an electric current through a resistive element, such as a coil or wire, which generates heat. This heat is then transferred to the surrounding area for heating purposes.
2. What are the advantages of electric heating?
Ans. Some advantages of electric heating include efficiency, as it can convert almost all the energy consumed into heat, easy installation, low maintenance, and the ability to control the temperature precisely.
3. Can electric heating be used for welding?
Ans. Yes, electric heating can be used for welding. Electric resistance welding is a common welding technique where heat is generated by passing an electric current through the materials being welded, causing them to melt and bond together.
4. What are some common applications of electric heating?
Ans. Electric heating is commonly used in residential and commercial buildings for space heating, water heating, and cooking. It is also used in industrial processes such as welding, melting metals, and curing materials.
5. Is electric heating environmentally friendly?
Ans. Electric heating can be environmentally friendly if the electricity used comes from renewable sources such as solar, wind, or hydropower. It produces no emissions at the point of use, making it a cleaner heating option compared to fossil fuels.
23 videos|89 docs|42 tests
Download as PDF
Explore Courses for Electrical Engineering (EE) exam

Top Courses for Electrical Engineering (EE)

Signup for Free!
Signup to see your scores go up within 7 days! Learn & Practice with 1000+ FREE Notes, Videos & Tests.
10M+ students study on EduRev
Related Searches

practice quizzes

,

Free

,

pdf

,

Electric Heating & Welding | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

,

past year papers

,

Extra Questions

,

Electric Heating & Welding | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

,

MCQs

,

Sample Paper

,

shortcuts and tricks

,

Viva Questions

,

Semester Notes

,

Electric Heating & Welding | Electrical Engineering SSC JE (Technical) - Electrical Engineering (EE)

,

Important questions

,

Summary

,

ppt

,

mock tests for examination

,

Previous Year Questions with Solutions

,

Objective type Questions

,

study material

,

Exam

,

video lectures

;