WELCOME

A Seminar on : Induction

HeatingSpeakers:Shamim HossainGanesh Saswade

Dairy Technology DivisionNATIONAL DAIRY RESEARCH INSTITUTE

CONTENTS :

INTRODUCTIONPRINCIPLECOMPONENTSEFFECT OF ELECTROMAGNETIC PHENOMENAHEATING MODES APPLICATIONSADVANTAGESDISADVANTAGES

INTRODUCTION: Process of heating an electrically

conducting object by electromagnetic induction through heat generated in the object by eddy current.

Complex combination of electromagnetic, heat transfer, and metallurgical phenomena

The material to be heated is known as work piece and the coil wound around it is known as work coil.

Induction heating is also known as high frequency heating

Michael Faraday

Principle : When a high frequency

ac voltage is applied across the work coil, a magnetizing current flows through it. this will generate flux in the work piece and induce voltage into the work piece.

since the work piece is closed onto itself, eddy current flows into it. the work piece will be heated up due to finite resistance offered by the work piece to the flow of the eddy currents.

Components :

Power supply

Load-matching station

Induction coil

Work piece

Feedback system

Important Factors to Consider

1)The Characteristics of the Part Metal or Plastic Magnetic or Non-Magnetic Thick or Thin Resistivity

2) Induction Coil Design

3) Power Supply Capacity

4) Degree of Temperature Change Required

Effect of Electromagnetic Phenomena :

A) Skin effect : Phenomenon of non uniform

current distribution within the conductor cross-section is called the skin effect.

Maximum value of the current density will be located on the surface of the conductor.

The skin effect increases the effective resistance of the metal to passage of the large current,hence increases the heating.

B) Proximity effect :

Conductive parts located in close proximity to a current carrying conductor Own magnetic fields Interact with nearby fields Current and power density

distribution distorted

C) Ring effect :

Magnetic flux lines concentrated inside the ring and the density of the magnetic field higher inside the ring.

Appearance of the ring effect can have a positive or negative effect on the process.

1. Ring effect plays a negative role in the induction heating of internal surfaces when the induction coil is located inside the work piece.

2. When the work piece is located inside the induction coil this effect plays a positive role.

Heating Modes :

1) Static Heating : Work piece is placed into an induction heating

coil for a given period of time and set amount of power is applied the component reaches the desired heating conditions

2) Continuous Heating

Work piece is moved in a continuous motion through one or more induction heating coils.

3) Oscillating heating

Component moves back and forth (oscillates) during the process of heating inside a single-coil or multi coil induction heater with an oscillating stroke featuring a space-saving design approach.

Applications of Induction Heating

INDUCTION COOKING : The circulating

currents in the metal pan on the top of the induction coil directly heats the pan.• Copper bottomed

pans, aluminium pans and other non-ferrous pans are generally unsuitable.

INDUCTION SEALING :

Is a non-contact method of heating a metallic disk to hermetically seal the top of plastic and glass containersReasons to use induction sealing Tamper evidence Leak prevention Freshness Retention Pilferage protection Sustainability Production Speed

Milk Pasteurization: Rise milk temperature faster than traditional

method.

Destruction of total bacterial load was 99.5%.

Coliform and Escherichia counts have been one tenth to traditional method .

Fouling was not produced due to the fast heat transfer.

(Hagh Nazar et al., 2015)

STEAM GENERATION: Short interaction times to

reach the required temperature.

Several hundred degrees can achieve.

Reduced thermal distortion and damage in the processing plant.

ANNEALING:

Annealing is a process used to soften metal for improved ductility and machinability, as well as to relieve residual stress.

BRAZING:Brazing is the process of joining two or more pieces of metal or ceramic material with a molten filler metal such as silver, aluminum alloy or copper.

SOLDERING:Solering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint.

SURFACE HARDENING:It is the process of hardening the surface of a metal, often a low carbon steel, by infusing elements into the material's surface, forming a thin layer of a harder alloy.

OTHER APPLICATIONS: Induction food warmer Induction extruder Cauldrons Heating of roller Can sterilization Bio oil Production

ADVANTAGES : Heating speed linked to the possibility of

obtaining very high power density.

Exact location of the heating effect thanks to the inductor design and an operating frequency perfectly adapted to the part to be heated.

The possibility to heat at very high temperatures with an efficiency practically independent of the temperature.

A process perfectly adapted to industrial medium-sized and mass production requirements.

Continue…… Easy automation of equipment. Absence of thermal inertia (rapid start-up). Repeatability of operations carried out. Often extremely high heating efficiency. Absence of pollution from the source of

heating (cold source). Good working conditions.

LIMITATIONS : Big investment cost

High Frequency electrical power

Induction heating is preferably used for heating relatively simple shapes

Non-ferrous cookware cannot be used on an induction cook-top

Thanks!Any questions?