Solid state RF generator for dielectric heating of food

products

By Kadeval Hina N.

M.E (D.C) ,PIET

Introduction

Radio frequency:It is spectrum within range of 3khz to 300Ghz.

This field can be used for wireless broadcasting and communication over some significant portion of spectrum.

Radio frequency Heating:

In RF heating system ,RF generator creates an alternating electric field betn two electrodes .

Material to be heated is conveyed betn electrodes , where polar molecules are to be reoriented continuously to the face opposite to electrodes.

RF heating is different,it heats at molecular level so heats on entire mass.

R

Radio frequency drying:

Conventional dried product is hot outside and wet inside.

With RF drying product is dry inside and wet outside.

If material has high loss factor ,it absorbs energy quickly and heat quickly.

RF V/S Microwave heating: Faster heating and drying times. More even heating and drying . Self limiting during drying. Moisture leveling and profiling. Selective heating. Instant start and stop. Energy efficiency. Speed and uniformity. Some environment issues. Moisture equilibration. Space saving,Physical contact,Efficiency,Precise

control.

Heating types : Ohmic heating: Require electrical current to pass th. Conducting material to be heated. Does not uniformly heat the entire portion of material. Induction heating: Apply rapidly alternating magnetic field to induce electrical current to flow . Does not work well with non metallic material.

Microwave heating: do not penetrate deeply into material to be heated.Cause localized overheating .

Dielectric heating :

It is instantaneous and does not require direct contact betn hot surface and material.

So material need not to be electrically conductive need to be capacitive lossy

This heaters operate on tens of MHz It is used in food processing industry, can be backed , dryed,

pasteurized . Moisture content can be controlled precisely. Conventional dielectric heater uses vaccum tubes to produce

KW RF energy. but they r bulky,less lifespan, expensive. So reliable ,affordable and efficient means and way is

needed to generate RF power for dielectric heating.

Basic pattern concept

Food processing sys.

Storage container

Product to be heated

Heating module Heating stage Heating

pipe

Heating module

Heating pipe

sensor

Status indicator

Heating stage

Heating module

RF shielding

Capa.plate Capa.plate Product

1

2

8

3

4

5

6

7

10

9

Heating stage

Heating pipe

plate plate

conductorconductor

310

RF power source

Cross sectional diagram

Capacitive plateCapacitive plate

Heating pipe

Single heating stage with RF power source

RF power source

Air core inductor

Solid state Rf generating

DC-DC converter

Bridge rectifier

Fault signal

Feedback signal

Computer interface

Grounded RF shielding

Heating stage

Rf power source

RF generating ckt card

Heat exchanger

Cooling fan

Inductor coil

200

Heating stage

Embedded solid state RF generator

controller Buck converter

conductor

High voltage air core inductor

Coil tuning capacitor RF generating

ckt card

oscillator

Solid state RF generator

Oscillator segment

RF chokeoscillator

RF generating ckt card

Coil segment

Driver cell

Driver cell (self biasing)

Driver cell device

Gate driver transformer

Heating system/120kw

1 Heating module/

20kw

4 Heating module/

20kw

2 Heating module/

20kw

3 Heating module/

20kw

5 Heating module/

20kw

6 Heating module/

20kw

1

2kw 2kw

3

2kw

4

2kw

5

2kw

6

2kw

7

2kw

8

2kw

9

2kw

10

2kw

1 2 3 4 5 6 7 8

12.5wx10 12.5x10

Heating stage

Rf generating stage each of 250w

Heating module

12.5w x 20=250w

Thank you