Thesis (PhD)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Microwave heating technology is extensively used in households, is well-established in certain
industries and is being explored in others. lts attraction is that it is quick, energy efficient, clean
and can be used to heat materials of both high and low thermal conductivities. Successful
application of the technology requires knowledge of both material properties and microwave
equipment. Commercial fixtures for measuring dielectric properties are not widely available and
are usually created in-house. The domestic oven magnetron is easily available and can be used
in prototype microwave systems but applicators for specific applications need development.
This thesis covers three main areas, namely; dielectric measurement fixtures, microwave
applicators and chokes, and drying of wood.
The first part of the thesis presents four dielectric measurement fixtures, one commercial and the
others in-house. The design and calibration of the in-house fixtures is presented. An
intercomparison of the performance of the four fixtures is carried out by measuring the
permittivities of well characterised dielectrics: teflon and perspex. The most convenient fixture
is used to measure the dielectric properties of wood at different moisture contents.
The second part covers the design of a slotted waveguide fed microwave applicator and a choke.
The design of the slotted feed is carried out analytically with and without mutual coupling
between the slots. A semi-empirical design using a finite element package is done independent
of the analytical approach and the results are compared. The choke is rigorously characterised
using a procedure which avoids de-embedding.
The third and last section reports on the wood drying experiments carried out in the applicator,
simulated and mapped heating patterns of drying wood, and a mock-up industrial wood drying
facility. / AFRIKAANSE OPSOMMING: Mikrogolfverhittingstegnologie word wyd gebruik in huishoudings, is goed gevestig
in sekere nywerhede en moontlike gebruike daarvan op ander gebiede word gedurig
ondersoek. Die vernaamste voordele is dat dit vinnig, energiedoeltreffend en skoon is
en dat dit gebruik kan word om materiale van beide hoë en lae termiese
geleidingsvermoë te verhit. Suksesvolle toevoeging van die tegnologie vereis kennis
van beide materiale-eienskappe en mikrogolftoerusting. Kommersiële apparaat vir die
meet van diëlektriese eienskappe is nie wyd beskikbaar nie en word gewoonlik
"binnenshuis" ontwikkel. Die huishoudelike mikrogolfoond magnetron is geredelik
beskikbaar en kan in prototipe mikrogolfstelsels gebruik word, maar toevoegers
geskik vir spesifieke gebruike moet ontwikkel word.
Hierdie proefskrif dek drie hoofgebiede, naamlik: diëlektriese metingsapparaat,
mikrogolftoevoegers en smoorders, en die droging van hout.
Die eerste deel van die proefskrif handeloor vier diëlektriese metingsapparate, een
kommersiëel en die ander "binnenshuis". Die ontwerp en kalibrasie van die
"binnenshuis" apparate word aangebied. 'n Tussenvergelyking van die verrigtinge van
die vier apparate word gedoen deur die meting van baie bekende diëlektrikums: teflon
en perspex. Die mees gerieflike apparaat word gebruik vir die meet van die
diëlektriese eienskappe van hout teen verskillend voginhoude.
Die tweede deel dek die ontwerp van 'n smoorder en 'n mikrogolf toevoeger wat deur
'n gegleufde golfgeleier gevoer word. Die ontwerp van die gegleufde golfgeleier word
beide met en sonder wedersydse koppeling tussen die gleuwe, analities gedoen. 'n
Semi-empiriese ontwerp wat van 'n eindige-element pakket gebruik maak, is
onafhanklik van die analitiese benadering gedoen. Die resultate word dan vergelyk.
Die smoorder word deur 'n prosedure wat "de-embedding" vermy, streng
gekarakteriseer.
Die derde en laaste afdeling behandel die eksperimentele droging van hout binne die
toevoeger. Simulasies en verhittingspatrone van die hout wat gedroog word, sowel as
die "mock-up(model van die voorgestelde)" nywerheids houtdroogkamer, word gegee.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/50231 |
| Date | 12 1900 |
| Creators | Rimbi, Morris |
| Contributors | Reader, H. C., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 1 v. (various foliations) : ill. |
| Rights | Stellenbosch University |
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