Comparison of linear and non-linear sweep rate regimes in variable frequency microwave technique for uniform heating in materials processing

Antonio, Christian; Deam, Rowan

doi:10.1016/j.jmatprotec.2005.03.024

Cited by 49 publications

(26 citation statements)

References 10 publications

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“…Because of time-averaged heating processes, variable frequency microwave eliminates arcing and localized heating problems. 50,51 Applications on variable frequency microwave processing are outlined below.…”

Section: Variable Frequency Microwave Processingmentioning

confidence: 99%

Microwave material processing—a review

2011

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Microwave heating is caused by the ability of the materials to absorb microwave energy and convert it to heat. This article represents a review on fundamentals of microwave heating and their interaction with materials for various applications in a comprehensive manner. Experimental studies of single, multimode, and variable frequency microwave processing were reviewed along with their applications. Modeling of microwave heating based on Lambert's law and Maxwell's electromagnetic field equations have also been reviewed along with their applications. Modeling approaches were used to predict the effect of resonances on microwave power absorption, the role of supports for microwave heating, and to determine the nonuniformity on heating rates. Various industrial applications on thermal processing have been reviewed. There is tremendous scope for theoretical and experimental studies on the athermal effects of microwaves. Some of the unresolved problems are identified and directions for further research are also suggested.

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Section: Variable Frequency Microwave Processingmentioning

confidence: 99%

Microwave material processing—a review

2011

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“…[34,35] VFM allows a frequency bandwidth to be selected, for example 3-5 GHz, although a fixed frequency can also be selected from this range. The selected frequency range is swept around a central frequency in a specified time.…”

Section: Introductionmentioning

confidence: 99%

“…Problems such as arcing are also eliminated with this type of operation since arcing occurs in the presence of an electric field in a standing wave at a constant frequency. [31] Antonio and Deam [35] studied the VFM technique. They reported that "The technique works by sweeping through a bandwidth of frequencies which are cycled through consecutively and launched into a cavity, resulting in different standing waves with many resonant modes.…”

Section: Introductionmentioning

confidence: 99%

Microwave Synthesis of SAPO‐11 and AlPO‐11: Aspects of Reactor Engineering

et al. 2008

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AlPO-11 and SAPO-11 are synthesized using microwave heating. The effects of precursor volume, reaction temperature, reactor geometry, stirring, applicator type and frequency on the microwave synthesis of SAPO-11 and AlPO-11 are studied. The nucleation time and crystallization rate are determined from crystallization curves for SAPO-11 (and/or AlPO-11), for the various parameters investigated. Increasing volume of the reacting material decreases the reaction rate of SAPO-11 at 160 degrees C. In particular, the nucleation time increases with increase in the reaction volume. Increasing the reaction temperature increases the crystallization rate and decreases the nucleation time, however it decreases the particle size. Nucleation of SAPO-11 and AlPO-11 under microwave heating is strongly dependant on the reaction temperature. Using wider geometry vessel (33 mm compared to 11 mm diameter) enhances the reaction rate, producing larger crystals in the same reaction time, even though the crystallization rate is decreased. The crystallization rate is enhanced by applicator type in the following order CEM MARS-5 oven>CEM Discover "focused" system>monomode waveguide. Stirring the reacting solution during heating affects primarily the nucleation time. The effect of microwave frequency on the nucleation and growth of SAPO-11 shows a dependence on the applicator type more than the specific frequency, for the frequency range 2.45-10.5 GHz. The difference between the crystallization rate observed at higher frequencies and that at 2.45 GHz maybe due to the multimode nature of the waveguide at frequencies above 2.45 GHz. Sweeping the microwave frequency linearly between 8.7 and 10.5 GHz at rates of 10 min(-1) and 100 min(-1) shows an intermediate crystallization curve to that for fixed frequencies of 2.45 GHz and that for 5.8, 8.7 and 10.5 GHz.

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“…Antonio and Deam [89] focused on the sweep-rate regime used in VFM and the effect of varying this parameter. They investigated two-dimensional computer model and it was found that a more even temperature distribution could be achieved using a VFM curing method.…”

Section: Variable Frequency Microwave Curing Technologiesmentioning

confidence: 99%