Page - 1 - in Adaptive and Intelligent Temperature Control of Microwave Heating Systems with Multiple Sources

1. Introduction Heating is one of the most common processes in the manufacturing industry for a wide range of applications, including sintering, curing anddrying. Itplaysanessentialrole inpromotingchemicalandphys- icalreactions,andimprovingtheprocessabilityofmaterials. Thequal- ity of heating directly determines the final quality of industrial prod- ucts. Inconventional industrialheatingequipments, suchasfurnaces, kilns and autoclaves, heat is generated by the combustion of fuels or using electric currents, and transferred to the heated material by ei- ther thermal conduction, convection, radiation, or a combination of all three. In conventional heating, all the heating energy required will be firstly generated on the surface by the thermal radiation or convection, and then transmitted through the body into the core by the thermal con- duction. The rate of the heat flow from outside to inside is entirely determined by the physical properties of the material, such as its con- ductivity, specific heat capacity and mass density. There is no way to accelerate the heating flow rate or influence the internal temperature distribution. Withthesamematerial, thethickertheheatedproduct is, the longer it takes to transfer theheat to the internalcore. Meanwhile, a large temperature deviation would occur between the surface and internalcore,whichcouldbringqualityproblems[Mer98]. Duringthe whole heating process, a huge amount of energy is lost in heating the intermediate medium (e.g. hot air), and the corresponding time con- sumption is also large. Although many proper improvements have beendoneregardingtoequipmentsizesandoperations, conventional heating has various problems unsolved. Heating still remains as one of themostchallengingprocesses tobepreciselycontrolled. 1