A detailed analysis has been carried out to study efficient heating processes due to microwaves for one dimensional food samples placed on ceramic plates with various distributions of microwave incidence. The enhanced heating effects due to microwave propagation within samples have been illustrated via average power within a sample vs sample thickness diagram. The maxima in power, also termed as 'resonances' is observed for specific sample thicknesses. The spatial temperature distributions illustrate the presence of local thermal heating effects for various cases. Either one side incidence or both sides incidence with suitable distribution of microwave incidence may be preferred for various food materials attached with ceramic plates. One side incidence may cause overall larger heating rates for beef samples and the heating rates for oil samples would remain invariant irrespective of various distributions of microwave incidence. It is observed that beef samples would exhibit greater thermal runaway specially with SiC plate in presence of both sides distributed microwave incidence whereas oil sample would exhibit smaller thermal runaway effects with both sides equi-distributed microwave incidence irrespective of any ceramic plates. Current analysis has been illustrated for low and high dielectric food materials (beef and oil) and based on our analysis, a generalized heating strategy for any materials due to uniform plane waves may be derived. © 2006 Elsevier Ltd. All rights reserved.

Tanmay Basak

Department Of Chemical Engineering

A. Meenakshi

Ceramic materials

Food products

Meats

Oils and fats

Resonance

Ceramic plates

DISTRIBUTED SOURCE

FOOD SLABS

THERMAL HEATING

Microwave heating

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Food Research International

A detailed theoretical analysis has been carried out to investigate the effect of the shape of the sample on the microwave heating dynamics of food materials. The food materials are divided into four groups based on the microwave propagation parameters and the heating dynamics of each group of materials have been simulated for one representative material involving semiinfinite cylindrical samples of circular and square shapes. The selection of the two shapes (circular and square) is to investigate the influence of the presence of sharp corners in the square samples on the microwave propagation dynamics within the food materials. The detailed study reveals that the presence of the corner can have a pronounced effect (either beneficial or detrimental) on the spatial heating dynamics for the intermediate and thick samples based on the propagation parameters and orientation of microwave sources with respect to the corner. Industrial relevance Microwave processing of food materials strongly depends on shapes of the materials as microwave propagation within food materials can be altered based on various incidence and reflected waves which are largely dependent on the structure of food materials. In general, spatial non-uniformities of heating patterns occur during microwave processing and there are no generalized guidelines available for industrial food processing. The entire spectrum of food materials can be categorized in four groups and generalized heating patterns can be deduced apriori for each group of food materials. Numerical simulation results predict that the shapes or cross section of food materials (squares, circular etc.) play important roles as the square shape exhibits interesting corner heating patterns and a trivial circular sample may not be a recommended food sample for efficient industrial microwave processing. © 2016 Elsevier Ltd

Innovative Food Science and Emerging Technologies

A comprehensive analysis on the effect of shape on the microwave heating dynamics of food materials

Numerical studies have been carried out for microwave heating of food samples. It has been shown that the food materials can be divided into four groups based on the values of fp and fw and the microwave heating characteristics remain same for the materials in each group. The heating characteristics of each group of materials have been presented based on the heating front, heating rate and heating nonuniformity (thermal runaway). These characteristics are shown to be strongly dependent on sample size, which can be classified as thin (uniform heating), intermediate (localized heating fronts driven be resonances of microwave power absorption) and thick (exponential attenuation of heating rate from the exposed surface). The analysis shows that the localized heating in intermediate and thick samples can lead to significant thermal runaway, which can be efficiently avoided by selecting radial irradiation over lateral irradiation but at the expense of higher processing time. © 2015 Elsevier Ltd. All rights reserved.

A generalized approach on microwave processing for the lateral and radial irradiations of various Groups of food materials

Microwave heating has vast applications in the field of food processing such as cooking, drying, pasteurization and preservation of food materials. In this article, various applications of microwave food processing such as microwave cooking, microwave pasteurization and microwave assisted drying were extensively reviewed. The advantages and the factors affecting the microwave cooking of food materials have been reviewed. Microwave pasteurization of fresh juices, milk and various food products has been elaborately discussed. Microwave pasteurization has the ability to achieve destruction of microorganisms at temperatures lesser than that of conventional pasteurization due to significant enhancement or magnification of thermal effects. Applications of microwave drying include microwave assisted hot air drying, microwave vacuum drying and microwave freeze drying. Microwave drying combined with other conventional methods of drying enhances the drying characteristics of the sole effect of microwave drying. Modeling of microwave heating of food materials based on Maxwell's equations and Lambert's law equations have been reviewed along with their applications. Microwave modeling can be used to predict the temperature and moisture distributions during microwave heating of food materials. © 2013 Elsevier Ltd.

Microwave food processing-A review

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. © 2011 American Institute of Chemical Engineers (AIChE).

AIChE Journal

Microwave material processing-a review

A detailed theoretical analysis has been carried out to study efficient heating of one-dimensional pork meat (PLR and WP) slabs via an alumina-meat-ceramic-meatalumina composite corresponding to one side and both side microwave incidence. The ceramic (Al2O3 or SiC) layer is composited to examine processing rate and thermal runaway. Detailed analysis has been carried out for PLR and a few test cases are shown for WP. The role of an intermediate ceramic layer is examined for one side and both side microwave incidence cases. In general, the processing time decreases with the thickness of the intermediate ceramic layer for samples with thickness (Ls)≤1cm in the presence of one side incidence. On the other hand, the processing time is found to increase with the thickness of an intermediate alumina layer for both side incidence and a similar trend is also observed for larger sample thicknesses with one side incidence. It is found that the degree of the thermal runaway is reduced with the intermediate ceramic layer for samples with Ls≤1cm whereas the thermal runaway is enhanced with the inclusion of the intermediate ceramic layer for larger sample thicknesses. Further, the role of pulsing has been demonstrated for Ls=1cm. It is found that processing time with one side incidence is smaller than that with both side incidence in the absence of pulsing, but the trend is reversed in the presence of pulsing. Thus pulsed microwave heating in the presence of both side distributed incidence with an intermediate alumina layer is found to be an optimal heating strategy for processing meat samples. © 2011 Elsevier Ltd.

Role of ceramic composites and microwave pulsing on efficient microwave processing of pork meat samples

A detailed analysis on enhanced heating effects attributed to resonance of microwaves has been carried out to study the efficient heating methodologies for oil-water emulsions. Studies on heating have been carried out for samples incident with microwaves at one side and at both sides. The maxima in average power corresponding to resonances occur at various sample thicknesses for all emulsions and we consider two dominant resonance modes R1 and R 2, where the average power at R1 is larger than that at R2. During one side incidence, it is observed that processing rates are greater at the R2 mode for both oil-in-water (o/w) and water-in-oil (w/o) emulsions, whereas for both-sides incidence, the R 1 mode is favored for o/w emulsion and the R2 mode is advantageous for w/o emulsion. The greater rates in thermal processing are observed when the emulsions (o/w and w/o) are incident at both sides. Current analysis recommends on the efficient way to use microwaves in a customized plane-wave oven for greater heating effects and determines the optimal sample thicknesses vs. various oil-water contents for thermal processing. The emulsion system is a combination of materials with very low dielectric loss (oil) and high dielectric loss (water), and the effective dielectric response is highly nontrivial to predict the efficient way to heat an emulsion, either o/w or w/o. © 2004 American Institute of Chemical Engineers.

Role of resonances on microwave heating of oil-water emulsions

Resonances or maxima in power absorption due to microwaves incidence within a slab are analyzed via transmitted and reflected waves. A generalized mathematical formulation for uniform plane waves has been established to analyze traveling waves, stationary waves and microwave power absorption within a multiphase sample. Preliminary studies based on the generalized mathematical analysis in ice and water slabs illustrate that greater amplitudes of traveling and stationary waves occur within ice samples, whereas, greater intensity of spatial resonances in microwave power occurs for water samples due to a greater dielectric loss of water. Microwave thawing is studied for specific sample thicknesses which are selected based on greater power distribution within water samples. The enthalpy method is employed for modeling of thawing of ice samples where a superficial mushy region is assumed around the melting point. Depending on the sample thickness, thawing may occur from the unexposed face as well as both the faces when the sample is exposed to microwaves at one face only, whereas thawing may originate from both the center as well as the faces when the sample is exposed to microwaves at both faces. Our analysis based on the generalized mathematical formulation validates the local maxima in spatial power distribution during intermediate thawing stages obtained with the finite element based enthalpy formulation. The generalized mathematical analysis on multiple thawed regimes further illustrates the role of traveling waves on resonances in microwave power. The influence of resonance is attributed by a non-monotonic variation of thawing time with sample thicknesses either for one side incidence or both side incidence due to microwaves. Optimal thawing strategies are recommended based on greater power savings. © 2003 Elsevier Ltd. All rights reserved.

Journal	Food Research International
ISSN	09639969
Open Access	No