Microwave Processing of Materials

Abstract

By submitting this dissertation electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification. This dissertation contains eighty five original papers published in peer-reviewed journals. The development and writing of the papers (published and unpublished) was the principal responsibility of myself and, for each of the cases where this is not the case, a declaration is included in the dissertation indicating the nature and extent of the contributions of co-authors.

Numerical modelling of the microwave heating behaviour of lunar regolith

“…Similarly, the relative permeability is compounded by permeability constant (µ′) and imaginary permeability, magnetic loss factor (µ″). On the other hand, the loss tangent indicates the ability of the material to convert absorbed energy into heat (National_Research_Council 1994 Table 1). • Study setting: For the simulation, a pre-defined Microwave Heating Multiphysics with a 'Frequency-Transient' study have been used.…”

“…In this experiment, the position of the vertical tuner is optimised and fixed for the medium-size specimen to provide the same condition to each specimen size. -- -16 - Because an understanding of the microwave heating process of new material is still empirical and speculative to some degree due to its highly nonlinear character (Vriezinga et al 2002) with variables including material properties, the shape, dimension and position of a specimen in a cavity, most research in microwave processing of material is exploratory (National_Research_Council 1994). Moreover, in the case of lunar regolith we are trying to understand an extra-terrestrial material which may not be fully understood yet with respect to the laws of physics; thus, we have adopted an empirical approach in this work.…”

“…A computer-based numerical modelling is a useful way to optimise a microwave system design and conduct a realistic process simulation for given material properties, dimension and mass/volume of a sample and the ideal conditions of the system (National_Research_Council, 1994). In addition, it could also verify Taylor and Meek's hypothesis, prior to visiting the Moon for sampling resources .…”

Kinetics of nutrient change and color retention during low‐temperature microwave‐assisted drying of bitter melon ( Momordica charantia L.)

“…Based on the initial mass of 100 g, of the fresh bitter melon slices, these input power values correspond to MPWDs of 1.5, 3.0, and 4.5 W/g, respectively. The actual absorbed microwave power that is converted into heat energy (used for water evaporation) would depend on the microwave frequency, f, electric field intensity, E, and the dielectric loss factor, ε′′, according to Equation (1) for the dissipated power density, P v (W/m 3 ) (Pitchai, Birla, Subbiah, Jones, & Thippareddi, 2012;Stein et al, 1994), wherein ε 0 is the permittivity of free space.…”

The Microwave Sources for EPR Spectroscopy

“…The main limit for klystrons is the highest frequency, which can be generated at a reasonable power level (tens of watts). The ratio between the generated frequency and the output power for modern klystrons drops rapidly when working frequency reaches 100 GHz and above [18] (Fig. 2).…”