Seite - 16 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

2. IntroductionofHEPHAISTOS whereR is the electrical resistance of the object andV is the voltage across it. Ohmic heating is widely implemented in various industrial applications, includingfoodprocessing[DAF90]andequipmentman- ufacture (electric stove,electricheater) [WCJ+12]. 2.1.2. Inductionheating Induction heating is used for heating conducting materials (mostly metals). A conventional induction heating system is shown in fig- ure 2.1. An alternating current passes through the induction coil and generates a time-variant magnetic field surrounding the coil. The magnetic field has the same frequency as the alternating current and it will induce eddy currents [RLCB02] within the conducting mate- rial that is inserted in the coil. Heat is generated by the eddy cur- rents due to the ohmic heating effect (such as in equation 2.1). The frequency of AC power supply of induction heating is selected de- pending on the size of the workpiece to be heated. Heating smaller workpiecesrequireshigheroperatingfrequencies. Largerpartscanbe processed with lower operating frequencies. Normally the frequency ranges from5kHzto500kHz. Detailsabout inductionheatingcanbe foundin[Mer98] [RLCB02]and[RP06]. Coil Current in the coil Induced current Magnetic field Figure2.1. Inductionheatingsystem[RLCB02]. 16