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Drying characteristics of Saskatoon berries under microwave and combined microwave-convection heatingReddy, Lakshminarayana 20 March 2006
The study on dehydration of frozen saskatoon berries and the need for dried fruits has been strategically identified in the prairies. Our motivation was to find a suitable method for dehydration in order to extend saskatoon berry shelf life for preservation. Microwave, convection and microwave-convection combination drying processes were identified to finish-dry saskatoon berries after osmotic dehydration using sucrose and high fructose corn syrup (HFCS) sugar solutions. Osmotic dehydration removes moisture in small quantities and also introduces solutes into the fruit that acts as a preservative and also reduces the total drying time. <p>Due to the very short harvesting season of saskatoon berries, an accelerated process like microwave combination drying can bring down the moisture to safe storage level, immediately after harvest. Untreated and osmotically dehydrated berries were subjected to convection (control), microwave and microwave-convection combination drying conditions at different product drying temperatures (60, 70 and 80C) until final moisture content was 25% dry basis. A laboratory-scale microwave combination dryer was developed, built with temperature and moisture loss data acquisition systems using LabView 6i software. Thin-layer cross flow dryer was used for convection-only drying and for comparison. <p>Drying kinetics of the drying processes were studied and curve fitting with five empirical equations including Page equation, was carried to determine drying constant, R2 and standard error values. The microwave-combination drying method proved to be the best for drying saskatoon berries. Dehydrated product quality analysis by means of color changes, rehydration ratio measurements and observed structural changes with scanning electron microscope technique were the factors in drying method selection for saskatoon berries.<p> This research was instrumental in the modification and development of a novel drying system for high-moisture agricultural materials. Microwave-convection combination drying at 70oC, yields good results with higher drying rates and better end-product quality.
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Design of a Cylindrical Cavity Resonator for Measurements of Electrical Properties of Dielectric MaterialsLi, Xiang, Jiang, Yan January 2010 (has links)
In microwave communications, the main aspects for affecting the dielectric losses in the materials are relating to the dielectric properties and the radiation frequencies. Normally, the different dielectric materials will lead to the different losses and reflections for microwave frequencies. To evaluate the dielectric properties from the different materials plays an essential role in the microwave engineering. There are many approaches can be used to measure the dielectric materials, e.g. capacitor methods, transmission line methods, cavity resonator methods, open cavity methods and so on. The cavity resonator method is one of the most popular ways for measuring the dielectric materials. In this thesis, some of the techniques will be reviewed, and the TM010 mode cylindrical cavity resonator with perturbation technique will be used for determining the dielectric properties. The design and measurements will be presented in both simulations and practice. With 1.2GHz cavity resonator, in the simulations, the dielectric permittivity for Teflon is measured as 2.09-0.0023i and 2.12-0.0116 in copper cavity and ferromagnetic cavity. Finally the sample is measured as 3.83-0.12i in practice.
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Drying characteristics of Saskatoon berries under microwave and combined microwave-convection heatingReddy, Lakshminarayana 20 March 2006 (has links)
The study on dehydration of frozen saskatoon berries and the need for dried fruits has been strategically identified in the prairies. Our motivation was to find a suitable method for dehydration in order to extend saskatoon berry shelf life for preservation. Microwave, convection and microwave-convection combination drying processes were identified to finish-dry saskatoon berries after osmotic dehydration using sucrose and high fructose corn syrup (HFCS) sugar solutions. Osmotic dehydration removes moisture in small quantities and also introduces solutes into the fruit that acts as a preservative and also reduces the total drying time. <p>Due to the very short harvesting season of saskatoon berries, an accelerated process like microwave combination drying can bring down the moisture to safe storage level, immediately after harvest. Untreated and osmotically dehydrated berries were subjected to convection (control), microwave and microwave-convection combination drying conditions at different product drying temperatures (60, 70 and 80C) until final moisture content was 25% dry basis. A laboratory-scale microwave combination dryer was developed, built with temperature and moisture loss data acquisition systems using LabView 6i software. Thin-layer cross flow dryer was used for convection-only drying and for comparison. <p>Drying kinetics of the drying processes were studied and curve fitting with five empirical equations including Page equation, was carried to determine drying constant, R2 and standard error values. The microwave-combination drying method proved to be the best for drying saskatoon berries. Dehydrated product quality analysis by means of color changes, rehydration ratio measurements and observed structural changes with scanning electron microscope technique were the factors in drying method selection for saskatoon berries.<p> This research was instrumental in the modification and development of a novel drying system for high-moisture agricultural materials. Microwave-convection combination drying at 70oC, yields good results with higher drying rates and better end-product quality.
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Measuring the dielectric properties of crushed copper oreGroenewald, Nico Albert 12 1900 (has links)
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Previous work has shown that microwave heating of mineral ores induces micro cracks within the ore
structure, which can be attributed to the difference in the adsorption of microwaves amongst the different
mineral phases. This reduces the energy required during subsequent grinding and enhances the liberation
of valuable minerals. In order to design microwave applicators for this purpose, knowledge of the
effective dielectric properties of the crushed ore is required. Of particular interest is the effective complex
permittivity of the bulk crushed ore. The measurement of the effective permittivity of a large volume of
crushed ore is most readily accomplished using the waveguide measurement technique. In this method a
representative sample of the material is placed in a defined and fixed volume in a standard size
rectangular section metallic waveguide. The magnitude and phase angle of the transmitted and reflected
low power microwaves through and from the sample are measured. The complex permittivity can be
extracted from these so-called scattering, or Sij parameters.
In this study the effective complex permittivities for two porphyry copper ores and a copper carbonatite
ore were determined as a function of particle size distribution (-26.5+2mm) using two sizes of waveguide
(WR284 and WR340). The sample holders incorporate dielectric windows for the location of the material
under test. The extraction of dielectric properties from Sij parameter measurements is problematic using
standard algorithms in such cases. Accordingly a new Database Extraction (DBE) Algorithm has been
developed. In this method, a database of scattering parameters is established through electromagnetic
modelling of the measurement system. A search algorithm is used to determine the effective complex
permittivity of the modelled load whose scattering parameters provide the best fit to the experimental
data. The goodness of the experimental fit of the simulated to the measured Sij parameters is determined
by a root mean squared deviation minimisation metric. Results show that the method can be used successfully to determine an effective complex permittivity for a
bulk volume of the crushed material. It is concluded that the dielectric property extraction over the full
operational frequency interval (2.3-3 GHz) is preferred as it has a larger degree of extraction confidence
and hence reliability.
Results show that with increasing particle size, the experimental fit between the simulated and measured
Sij parameters becomes increasingly poor, as wall effect become more prominent. The effect is most
prominent for the smaller WR284 waveguide size. It is shown that for a waveguide size of similar size to
the particle size, the Sij parameter fitting is poorer compared to when a larger waveguide size is used. The
extracted complex permittivity reproducibility between repeated dielectric property measurements is
improved for the WR340 waveguide size, as the extractions in the WR284 waveguide is dominated by the
combined particle size and wall-effects of the sample holder.
Ore mineralogy is identified as a key parameter that influences the dielectric properties of the crushed
ore. For ores with a dominant microwave absorbent mineral phase, the dielectric constant and loss factor
is found to be larger, compared with ores with a more dominant microwave transparent gangue mineral
phase. / AFRIKAANSE OPSOMMING: Navorsing toon dat die verhitting van mineraal erts, met mikrogolwe, mikroskaal frakture in die
mineraalstruktuur teweeg bring weens die verskil in die adsorpsie van mikrogolwe in die verskillende
mineraalfases. Gevolglik verminder die energievereiste vir die vergruising van die erts en verbeter die
vrystelling van waardevolle minerale wat vasgevang is in die mineraalmatriks. Vir die ontwerp van
mikrogolfapplikators vir dié doel, word die effektiewe diëlektriese eienskappe van die vergruisde erts
benodig. Van spesifieke belang is die effektiewe komplekse permittiwiteit van die erts. Die effektiewe
permittiwiteit van `n vergruisde materiaal monster word met behulp van die golfgeleier tegniek gemeet.
Vir dié tegniek word `n verteenwoordigende monster van die materiaal in `n rigiede volume in `n
standaard grootte reghoekige golfgeleier geplaas. Die grootte en fasehoek komponente van die
deurgelate en weerkaatste mikrogolwe deur en van die oppervlak van die materiaal word gemeet. Die
komplekse permittiwiteit van die vergruisde materiaal kan geëkstrakteer word vanaf hierdie sogenaamde
verspreide, of Sij parameters.
In hierdie studie word die effektiewe permitiwiteit van twee porforie koper ertse en `n koper karbonatiet
erts bepaal as funksie van partikel grootte (-26.5+2 mm) deur gebruik te maak van twee standaard
grootte golfgeleiers. Die monster houers inkorporeer diëlektriese vensters om die vergruisde materiaal
monster in posisie te hou. In so `n geval is die ekstraksie van die diëlektriese eienskappe vanuit die Sij
parameter metings problematies. Gevolglik is ‘n nuwe Databasis Ekstraksie Algoritme ontwikkel wat `n
databasis van verspreide parameters opstel deur die elektromagnetiese simulasie van die metingsisteem.
`n Soek-algoritme word gebruik om die effektiewe komplekse permitiwiteit van die gesimuleerde monster
te bepaal wat die beste ooreenstem met dié van die gemete eksperimentele Sij parameter data. Die mate
van ooreenstemming tussen die parameters, word bepaal aan die hand van die minimaliserings
prosedure. Resultate toon dat dié metode geskik is vir die bepaling van die effektiewe komplekse permitiwiteit van die
vergruisde monster. Dit word vasgestel dat die betroubaarheid van die geëkstraeerde Sij parameters, en
gevolglik die diëlektriese eienskappe van die erts, toeneem indien die algoritme oor `n groter frekwensie
band uitgevoer word.
Resultate toon verder dat met toenemende partikel grootte, die mate waartoe die absolute grootte en
fasehoek komponente van die gesimuleerde en gemete Sij parameters ooreenstem, versleg. Dit word
toegeskryf aan wand-effekte. Hierdie verskynsel is veral opmerklik vir die kleiner grootte golfgeleier. Dit
word getoon dat vir metings waar die golfgeleier dieselfde orde grootte geometriese afmetings het as die
vergruisde erts self, die passing tussen die gesimuleerde en gemete Sij parameters swakker is, wanneer dit
vergelyk word met metings waar dit nie die geval is nie. Die reproduseerbaarheid van die geëkstraeerde
diëlektriese eienskap waardes verbeter vir lesings wat uitgevoer word in `n groter grootte golfgeleier.
Laasgenoemde word toegeskryf aan die meer dominante wand-effekte wat kenmerklik is vir `n kleiner
golfgeleier.
Erts mineralogie word geïdentifiseer as `n sleutel parameter wat die diëlektriese eienskappe van die
vergruisde materiaal beïnvloed. Beide die diëlektriese konstante en verliesfaktor is groter vir ertse met `n
oorheersende mikrogolf absorberende mineraalfase.
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Dielectric investigations on attograms and zeptograms of matter / Etudes diélectriques sur des attogrammes et zeptogrammes de matièreHouachtia, Afef 13 January 2016 (has links)
Les recherches sur des attogrammes (1 attogramme = 10 -18 gramme) et zeptogrammes (1 zeptogramme = 10-21 gramme) de matière offrent la possibilité de mettre en évidence la transition entre la nanoscience et la physique des molécules, ouvrant la porte à des questions fondamentales en physique de la matière molle, comme par exemple ‘’Quelle est la quantité minimale de matière nécessaire pour ‘‘définir’’ les propriétés des matériaux ?’’. Les propriétés électriques et diélectriques des matériaux, à cette échelle, sont étudiées par la spectroscopie diélectrique. Cette technique offre une large gamme de fréquence, pour mesurer les propriétés diélectriques des matériaux, couvrant plus de 10 ordres de grandeur et allant de 10-3 à 10+7 Hz. Cette technique assure une caractérisation précise d’une grande diversité des phénomènes physiques qui se déroulent à des échelles de longueur et de temps différents, tels que: les transitions des phases, les fluctuations de densité, les fluctuations moléculaires, le transport des charges, etc. Les mesures à l’échelle des attogrammes et zeptogrammes nécessitent l’utilisation des cellules ayant des dimensions nanométriques. Basé sur le concept d’utiliser des nano-conteneurs comme des cellules expérimentales, un développement expérimental a été mis en évidence, dans cette thèse, permettant d’étudier la dynamique moléculaire et les transitions des phases des matériaux polymères, allant jusqu’au zeptogrammes de matière. Cette approche permet de cristalliser des très petites quantités des matériaux sous l’application d’un champ électrique élevé, dans le but d’induire une cohérence macroscopique des fonctions moléculaires. Cela peut donner lieu à des nouvelles propriétés des matériaux, qui n’existent pas dans le cas des matériaux en masse / Dielectric investigations on attograms (1 attogram = 10 -18 gram) and zeptograms of matter (1 zeptogram = 10 -21 gram) offer the possibility of exploring the transition between nanoscience and molecule physics, opening the door for fundamental questions in soft-matter physics, such as for instance “What is the minimum amount of matter necessary to “define” the material properties?”. The electric and dielectric properties of materials at this level are investigated by Broadband Dielectric Spectroscopy. This technique provides an extraordinary broad frequency range, for measuring dielectric properties of matter, covering more than 10 orders of magnitude, typically from 10-3 to 10+7Hz. It ensures a precise characterization of large diversity of physical phenomena taking place at different length and time scales such as: phase transitions, density fluctuations, molecular fluctuations, charge transport processes, etc. Measurements on the scale of attograms and zeptograms require sample cells having all three dimensions on the nanometric length-scale. Based on the concept of employing nanocontainers as experimental cells, a novel experimental development allowing investigations on molecular dynamics and phase transitions of polymeric materials down to the level of zeptograms is demonstrated in the present PhD study. This approach enables one to crystallize tiny amounts of matter under high electric fields with the goal of inducing a macroscopic coherence of molecular functionalities. This could give rise to new material properties, not naturally available in the case of bulk materials.
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Výzkum nových elektrokeramických struktur pro nové aplikace senzorů / An investigation of novel electroceramic structures for new sensor applicationsNan, Bo Unknown Date (has links)
Piezoelektrické keramické materiály jsou široce používány v mnoha aplikacích a průmyslových odvětvích, nicméně tradiční materiály obvykle obsahují olovo, které je toxické vůči životnímu prostředí. Většina zemí proto zavedla zákony a omezení, které postupně minimalizují spotřebu olova a podporují výzkum v oblasti bezolovnatých kompozic, které by nahradily olověné protějšky. Bezolovnatá piezoelektrická keramika se tak stala žhavým tématem v posledních letech. Nicméně výzkumy na praktické využití bezolovnatých piezoelektrických materiálů jsou jen zřídka publikovány. V této diplomové práci byl vybrán jeden z nadějných kandidátů na piezoelektrickou bezolovnatou keramiku (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 za účelem zkoumání metody snížení jeho vysoké teploty slinování pomocí dotování uhličitanem lithným, kde syntéza prášku byla připravená pomocí techniky sol-gel. Výsledky byly srovnány s konvenčním práškem syntetizovaným v pevné fázi. Vzorky vyrobené ze sol-gel prášku dopovaného 0.5% hmotn. uhličitanem lithným a slinované při 1300 °C po dobu 2 hodin vykazovaly d33 = 447 ± 9 pC N–1, teplotu Curie 98.7 °C a velikost zrn 7.0 ± 0.3 m. Další důležitou otázkou pro aplikace bezolovnatého piezoelektrického keramického materiálu je jeho výroba v různých konfiguracích. Použitím techniky odlévání pásky a aditivních výrobních postupů byla piezoelektrická keramika zpracována do tří různých konfigurací (2-2, 3-3 a 1-3), aby se překlenula mezera mezi materiálovými vědami a materiálovým inženýrstvím. Pro dolévání pásky byly použity suspenze na bázi oleje a vody. Pro přípravu neslinutých keramických fólií bez trhlin, byly pro odlévání na bázi oleje vyvinuty uhlíkové suspenze s obsahem pevných látek 25% hmotn. a BCZT suspenze s obsahem pevných látek 65% hmotn. Problém práškové hydrolýzy ve vodných suspenzích byl vyřešen povrchovou úpravou prášku Al(H2PO4)3, což umožnilo, aby byly tlusté vrstvy bez trhlin odlety v jednom kroku. Tlusté vrstvy slinované při 1500 °C vykazovaly relativní dielektrickou konstantu 1207, dielektrickou ztrátu 0.018 při 1 kHz, remanentní polarizaci 7.54 µC/cm2 a koercitivní síla intenzity pole (Ec) 0.23 kV/mm při 3 kV/mm. Pro tvarování BCZT v konfiguraci 3-3 a 1-3 byla použita přímá metoda tisknutí inkoustu. Pro správnou úpravu tiskového procesu byla použita inkoustová náplň s viskoelastickým chováním obsahující 41.6% obj. pevných látek BCZT a se zpracovatelskými přísadami (HPMC ~ 2.4% a PEI ~ 0.03%). Vzorky v konfiguraci 3-3, slinované při 1500 °C, vykazovaly nejvyšší dielektrické a piezoelektrické vlastnosti, kde Curieho teplota = 86 °C, tan = 0.021, remanentní polarizace = 4.56 µC/cm2 a d33 = 100 ± 4 pC/N. Vzorky v konfiguraci 1-3 slinované při 1500 °C, které byly smíchány s epoxidem, vykazovaly dielektrickou konstantu 144 a dielektrickou ztrátu 0.035 při 1 kHz. Tato práce popisuje tvarování bezolovnaté piezoelektrické keramiky s vynikajícími vlastnostmi v pokročilých strukturách jako krok k návrhu pro moderní senzorické a energy harvesting aplikace.
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Etude des propriétés électriques et thermiques de matériaux composites à matrice époxy-anhydride pour l'isolation haute tension / Study of electrical and thermal properties of epoxy-anhydride composite materials for high voltage insulationDesmars, Loriane 02 April 2019 (has links)
L’avènement des énergies renouvelables, notamment offshore, et la nécessité de transporter l’électricité sur des distances toujours plus grandes tout en réduisant les pertes en ligne requièrent la mise en place d’un nouveau réseau électrique plus performant, le supergrid. L’amélioration des sous-stations ultra haute tension en courant alternatif (UHVAC) de type poste sous enveloppe métallique (PSEM), i.e. la réduction de leur empreinte au sol ou leur montée en tension, s’inscrit parmi les défis engendrés par le développement du supergrid. L’amélioration de la tenue aux contraintes électrothermiques des isolants solides employés dans les PSEM a été identifiée comme le principal verrou technologique pour le perfectionnement de ces appareillages, déjà pleinement maîtrisés en HVAC. Les travaux présentés dans ce manuscrit ont été motivés par la nécessité de développer un matériau isolant électrique plus performant que les matériaux existant actuellement sur le marché. L’un des matériaux couramment employés pour la fabrication d’isolants solides pour PSEM, une matrice époxy-anhydride chargée d’alumine micrométrique, a servi de référence commerciale à notre étude. Suite à une étude bibliographique, nous avons choisi de conserver la matrice époxy du système commercial de référence et de jouer sur les charges inorganiques employées pour optimiser les propriétés du matériau isolant. Les travaux présentés mettent en évidence l’influence de la nature des charges inorganiques (alumine ou nitrure de bore hexagonal), de leur facteur de forme (quasi sphérique ou lamellaire) et de leur fraction volumique sur la conductivité thermique, le coefficient d’expansion thermique, les propriétés mécaniques dynamiques, les propriétés diélectriques, la conductivité électrique à haute tension (DC) et la rigidité diélectrique (AC) des matériaux composites. L’étude expérimentale des relations structure-propriétés est complétée par un travail de modélisation des propriétés diélectriques et de la conductivité thermique des matériaux composites. / The integration of renewable energies to the power grid requires its modification in order to ensure its stability, security and efficiency. Improving ultra-high voltage alternative current (UHVAC) gas insulated substations (GIS), e.g. reducing their size or increasing their voltage, is one of the challenges induced by the development of the future power grid, the supergrid. Increasing the ability of solid insulators used in such equipment to withstand electro-thermal stress has been identified as the main obstacle to overcome. The work presented in this manuscript has been motivated by the necessity to develop more efficient electrical insulating materials compared to commercially available ones. An epoxy-anhydride matrix filled with micron sized alumina, often used to produce GIS solid insulators, has been used as a reference for this study. We decided to keep the matrix of the reference material throughout our work and to concentrate on the filler influence in order to optimize the properties of the composites. The impact of the nature of the filler (alumina or hexagonal boron nitride), its shape factor (platelets or almost spherical particles) and its volume fraction upon thermal conductivity, coefficient of thermal expansion, dynamic mechanical properties, dielectric properties, high voltage direct current (DC) conductivity and AC breakdown strength have been highlighted. The experimental study of structure-property relationships is completed by dielectric properties and thermal conductivity modelling using the effective medium theory.
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