Microwaves are produced inside the oven by an electron tube called a magnetron. The microwaves are reflected within the metal interior of the oven where they are absorbed by food. Microwaves cause water molecules in food to vibrate, producing heat that cooks the food.MW are electromagnetic waves generated by magnetrons and klystrons. Frequency 300MHz and 300GHz Wavelength from 1mm to 1m industrial heating purposes the available frequencies are 915 and 2450MHz MW giving up their energy to the material, with a consequential rise in temperature Two imp mechanisms are: Ionic polarization: conversion of kinetic energy of the moving ions into thermal energy Dipole rotation: rotation of polar molecules leads friction with surrounding medium and heat is generated ENERGY EFFICIENCY: During microwave heating, electrical energy is first converted into microwave energy The microwave then interacts with foods and is converted into heat TWO EFFICIENCIES: Microwave generation efficiency Microwave absorption efficiency ENERGY CONSUMPTION Specific energy consumption was defined as the total energy supplied divided by the amount of water removed during drying Overheating could increase the energy consumption due to high moisture loss from the overheated region CONVERSION OF MICROWAVE ENERGY INTO HEAT MW Heating is a consequence of the interactions between microwave energy and a dielectric material PD= 55.61 X 10-14 f’ E2 ἐ tanᵹ where, PD Power dissipation W/cm3 f ‘ frequency in Hz E electric field in v/cm (V/m) ἐ relative dielectric constant tanᵹ: loss tangent MICROWAVE OVEN GENERALLY CONSISTS OF THE FOLLOWING BASIC COMPONENTS (i) power supply and control: it controls the power to be fed to the magnetron as well as the cooking time (ii) magnetron: it is a vacuum tube in which electrical energy is converted to an oscillating electromagnetic field. Frequency of 2450 MHz has been set aside for microwave oven for home use Conti….. (iii) waveguide: it is a rectangular metal tube which directs the microwaves generated from the magnetron to the cooking cavity (iv) stirrer: it is commonly used to distribute microwaves from the waveguide and allow more uniform heating of food (v) cooking cavity: it is a space inside which the food is heated when exposed to microwaves Conti…. (vi) turntable: it rotates the food products through the fixed hot and cold spots inside the cooking cavity and allows the food products to be evenly exposed to microwaves (vii) door and choke: it allows the food to the cooking cavity. they prevent microwaves from leaking through the gap between the door and the cooking cavity FACTORS AFFECTING MICROWAVE HEATING Dielectric properties Temperature and frequency Shape and size of food items DIELECTRIC PROPERTIES Penetration of microwave energy inside a material is a function of its dielectric properties.