1. 1 Department of Technical Education Andhra Pradesh Name: V. Narsimha Reddy Designation: Lecturer in EEE Branch : D.E.C.E. Institute : GMR. Polytechnic Gajwel Year / Sem.: VI Semester Subject : Electrical Utilization & Automation Subject Code : EE605A Topic: Electric Heating Duration: 50 Minutes Sub topic: Direct & Indirect Resistance Heating Teaching Aids : PPT, Diagrams, Animation Revised By : K. Chandra Sekhar, L/EEE, GPT, HYD 9EE605A.12

2. 2 Recap In the last class you have learnt about Advantages of Electric Heating Requirements of Good Heating Material Materials employed for Heating Element 9EE605A.12

3. 3 Objectives On completion of this topic you would be able to know Resistance Heating Methods of Resistance Heating Applications of Resistance Heating 9EE605A.12

4. 4 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 = I 2 Rt Power loss = I 2 R watts = VI Watts = V 2 /R watt 9EE605A.12

5. 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 9EE605A.125

6. Types of Resistance Heating 9EE605A.126 The resistance heating is further classified into three types Direct resistance heating Indirect resistance heating. Infra red or Radiant heating.

7. 7 Direct Resistance Heating Fig. 1 9EE605A.12 A.C.or D.C High resistance powder charge furnace

8. 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 9EE605A.128 A.C.or D.C High resistance powder charge furnace

9. Direct Resistance Heating The resistance offered by the charge to the flow of current causes power loss I 2 R and it results in the heating of the charge The charge may be in the form of solid pieces, powder or liquid 9EE605A.129 A.C.or D.C High resistance powder charge furnace

10. 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 9EE605A.1210 A.C.or D.C High resistance powder charge furnace

11. 11 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 9EE605A.12

12. 12 Indirect Resistance Heating Fig. 2 9EE605A.12 A.C or D.C Chamber Heating element Charge Furnace

13. 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 9EE605A.1213 A.C or D.C Chamber Heating element Charge Furnace

14. Indirect Resistance Heating Charge will enclose the heating element for efficient heat transfer The heat produced in the element is transferred to the charge by radiation or convection methods 9EE605A.1214 A.C or D.C Chamber Heating element Charge Furnace

15. 15 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 9EE605A.12

16. 16 Summary In this class we have discussed about Resistance Heating Direct and Indirect Resistance Heating Applications of Resistance Heating 9EE605A.12

17. 17 Quiz 1.Which type of heating is used in resistance welding a)Direct resistance heating b)Indirect resistance heating c)Infrared heating d)None 9EE605A.12

18. 18 2.Which type of heating is used in immersion water heaters a)Direct resistance heating b)Indirect resistance heating c)Infrared heating d)None Quiz 9EE605A.12

19. 19 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 ? 9EE605A.12

20. 20 THANK YOU