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Microwave induced heating is mainly performed at frequencies between 915 MHz and 5.7 GHz. The frequency of 2.45 GHz is commonly used and suitable for dielectric heating of polar molecules (dipole) and ions. The dielectric loss (e´´) quantifies the energy dissipation of microwaves in materials. The main reason for this is the polarisation effect due to the interaction between electromagnetic field and the heated material.

There are two important concepts of microwave furnaces used in industry. In multimode applicators (Fig. 1) the heated material is located in a stochastic oscillating field (Fig. 2). In this case the dissipated microwave energy is stronglylinked to the loss number of the heated material. The principle is applicated to the heating of water or materials containing water as a main component. Another application field is the indirect microwave heating using susceptor materials to heat low loss materials.

In monomode applicators exist a radiation field with clearly stationary field maximum. In principle it is possible to stabilize such a field configuration by electronic control regimes. This method is particularly convenient to heat low loss materials like borosilicate, cordierite or alumosilicates. It is possible to heat such materials during seconds reaching the melting point by raising up the field intensities using resonator principles.

Hybride heating processes combine microwave energy with radiation heating. The aim is the decrease of the temperature gradients between the center and the surface of the heating sample. Usually microwave heating is more expensive than conventional heating processes. But the advantage of a heating a volume itself within shortest times and the possibility of creating new heating regimes by the use of electromagentic parameters is most attractive for heating thermal fragile materials.

GMBU e.V. has a longterm experience on the solution of such problems and possesses a powerful equipment for development and adaption of the microwave heating to the properties of specific materials.

Topics of Research and Development
  • Microwave supported regeneration of adsorbents
  • Microwave induced heterogenenous catalysis
  • Steering of phase separation in borosilicates by use of microwaves
  • Power control of microwave devices heating material with nonlinear temperature dependence of loss tangent
  • Heating of thermal non stable materials (denaturiation, phase transition, pyrolysis)
Service Panel
  • Practical investigations with monomode and multimode applicators
  • Development and adaption of furnace concepts (resonators and travelling waves, tubes) to physical properties of the heated material
  • Modelling, simulation (COMSOL Multiphysics®) and measuring of field and temperature distribution in furnace chambers
  • Investigation of porous carbons and silicates
  • Design of electronic hf-circuits for control and steering of microwave processes (electric power control, impedance matching, temperature measurement)
  • Programming of control and steering concepts using microcontroller