Abstract
M.Ing.
The heating and drying of products is a process which is essential to
improve the quality. This process has been around since the
beginning of the industrial age. Most industries use natural energy
sources, e.g. coal, to generate the energy that is needed. This
energy is then used to heat air and this in turn is used to dry the
products. Heat transfer is used to dry the materials and it is a
known fact that this mechanism is not effective due to huge losses.
A certain company identified this problem and decided to investigate
microwave energy as an alternative energy source. The aim of the
project was to determine if microwave energy could dry the phosphate
and to do an economic feasibility study on such a microwave oven.
The operation of microwave sources was examined and the magnetron was
found to be the most effective source. Magnetrons that operate at a
frequency of 2.45GHz, are easily obtainable and therefore also more
economical than magnetrons that operate at other frequencies.
The loss mechanisms that are associated with microwave heating as
well as the parameters associated with volumetric heating were then
investigated. It was found that the complex permittivity and
permeability of the material to be heated, are important properties
associated with microwave heating and these were not known and needed
to be determined.
After examlnlng several methods to determine these properties, the
measurements were done by means of a network analyser. From the
results it was evident that the phosphate losses were relatively high
enabling most of the microwave energy to be absorbed. These results
were confirmed after further tests were done.