Application Of Microwave Heating Research Articles

Comparison of Chemically Treated, Pasteurized, and Microwave-Treated (at Different Time Durations) Chia Seeds Added To Mango-Whey Beverage, during Different Storage Periods, for Physicochemical and Sensory Parameters

Foods that are widely consumed and accepted have had a lot of ingredients added to them which may enhance consumer’s health. Whey is a byproduct in the manufacture of cheese or curd and is widely used in different beverage formulations, due to its nutritional importance. In this context, a mango-based functional whey drink, added with omega-3-rich chia seeds, was de veloped. Different treatments of beverage were as follows: untreated control beverage (T0), application of chemicals (T1), pasteurization (T2), and microwave heating (at 4 different time lengths: T3, T4, T5, and T6). Beverages were analyzed for physiochemical, microbiological, and sensorial changes, during the 90 days of storage. Chemical analysis of chia seeds before incorporation in beverages revealed a high nutritional profile of chia seeds, especially the presence of essential fatty acids. Significant variation in color parameters of the beverage was observed as a result of treatments and storage, with optimum values observed for T3. A decrease in pH and an increase in acidity during storage for all treatments were evident, with the most significant results for microwave treatment for longer time periods. The total plate count of the beverage was the highest (2.36 ± 0.1 CFU/ml) for control, followed by chemically treated (2.17 ± 0.1 CFU/ml) and lowest in microwave-treated (0.98 ± 0.1 CFU/ml) at the start of the experiment, and this total plate count was found to be increasing in all treatments during storage. Total solids were increased and soluble solids were decreased during longer microwave treatments and also during storage of all treatments. The most acceptable treatment T3 (85 ml whey, 2 g chia seed, and microwave heating for 30 sec) was further subjected to a storage study and it was observed that the sensory scores gradually decreased during the 90 days of storage. From the outcomes of the study, it was concluded that microwave treatment of the beverage for 30 sec, as compared to longer durations and chemical preservatives, was proved helpful for optimum quality retention of the formulated beverage, with minimum deteriorating effects. Thus, proper treatments of different beverage formulations, following the necessary protocols, could provide the consumers safe, healthy, and nutritious beverages.

Chemical recycling of polymer composites induced by selective variable frequency microwave heating

AbstractThe application of variable frequency microwave (VFM) heating to achieve rapid thermal depolymerization of polymer composites is reported for the first time. The thermal and chemical influence of composite additives on polymer decomposition has been studied for a set of chemically recyclable polymers, including polyphthalaldehyde, polypropylene carbonate, two polyhydroxyalkanoates, and nylon 6. Carbon‐based additives, specifically nanocarbon particles, were used as effective microwave absorbers to controllably degrade the surrounding polymer matrix into valuable, monomeric compounds. Depolymerization and byproduct confirmation were quantified by gel permeation chromatography and nuclear magnetic resonance spectroscopy. Synergistic effects can be leveraged from pre‐treating composite samples to further reduce the total microwave energy required to depolymerize composite samples. This study establishes the use of VFM heating for chemical recycling of polymer composites that can be leveraged toward a plastic circular economy.

High-efficiency and compact microwave heating system for liquid in a mug

The demand for efficient and compact heating for dynamic dielectric liquid has grown significantly. Compared with traditional heating, microwave heating has the advantages of being fast and efficient. Moreover, the demand for outdoor portable heating and industrial compact heating is increasing. To address this limitation, this study proposes a compact heating system based on a metamaterial-based circular waveguide. First, asymmetric propagation theory is introduced, and an asymmetric propagation circular waveguide is designed in detail according to the discretisation of the relative permittivity. Then, a multi-physics model using a circular waveguide and a mug for high heating efficiency is developed by coupling Maxwell's equations and the heat transfer equation. Furthermore, heating experiments are performed for liquids with different relative permittivity and the experimental results consistently validated an efficiency rate of over 88 %, which agrees with the simulation results. Finally, the effects of the dielectric properties of the material and mug on the heating efficiency are discussed to highlight the robustness of the proposed heating system, with heating efficiency consistently maintained at 75 % or higher. In summary, the proposed design features a compact structure that is suitable for practical microwave heating applications.

Synthesis of Metal Nanoparticles under Microwave Irradiation: Get Much with Less Energy

Microwave irradiation is widely used to intensify various chemical processes, including in the synthesis of nanomaterials. The purpose of this review is to present recent trends in the application of microwave heating for the preparation of monometallic, bimetallic, and more complicated metal nanoparticles. The advantages and drawbacks behind the use of microwave irradiation in the synthesis of unsupported and supported metal nanoparticles are summarized. Such metals as Ag, Au, Pt, Pd, Rh, Ir, Cu, Ni, Co, etc. are considered. Illustrative examples have been presented of the positive effects of microwave treatments, including the preparation of particles of different shapes and particles of immiscible metals.

Microwave assisted glycerol esterification using CeO2, ZrO2, mixed metal oxide catalyst

Present study focuses on the up-cycling of glycerol by esterification reaction using acetic acid to produce acetins. Heterogeneous catalysts such as CeO2, ZrO2 (commercially procured) and CeO2-ZrO2 mixed metal oxide catalysts synthesized using solution combustion method were used to synthesize acetins. The reactions were performed in a microwave reactor at a power level of 900 W, which rendered the reactions faster and simpler compared to the conventional heating method. The effect of temperature (80 °C, 90 °C, 100 °C), the initial molar ratio of glycerol: acetic acid (1:5, 1:10, 1:15) and the amount of catalyst (3 wt%,5 wt%,7 wt%) were studied for all the three catalysts. The study showed a rapid phase of reaction for up to 30 min and then the reaction proceeded at a constant rate. The conversion was higher at 100˚C. Rate constants determined from kinetic model was increasing with temperature. The kinetic data was observed to best fit the pseudo-first-order kinetic model. The study has demonstrated an efficient way of synthesizing acetins in presence of metal oxides by the application of microwave heating as process intensification technology.

Effects of susceptor thickness on microwave heating of raw meat

The susceptor and susceptor thickness significantly influence the microwave heating process. This work theoretically investigates the effects of two different susceptors with various thicknesses on microwave heating of raw meat. A susceptor with low dielectric loss (alumina) and a susceptor with high dielectric loss (SiC) are used for present study to investigate the effect of dielectric loss during microwave heating. The addition of the alumina susceptor either enhances or diminishes the heating rate of resonating samples depending on thickness, while the addition of the SiC susceptor improves the heating uniformity of resonating samples. The addition of susceptors on thick samples shows different characteristics from resonating samples. High heating rate and heating uniformity are the two major criteria for several microwave heating applications. Hence, the optimum susceptor thicknesses for specific sample dimensions are determined based on either high heating rate or heating uniformity.

Review of the Application of Microwave Heating Technology in Asphalt Pavement Self-Healing and De-icing

In the past decades, a large amount of research was conducted to investigate the application prospect of microwave heating technology in improving the efficiency of asphalt pavement self-healing and de-icing. This paper reviewed the achievements in this area. Firstly, the properties of asphalt concrete after microwave heating were summarized, including microwave sensitivity and heating uniformity. Then, the evaluation indicators and influence factors of the self-healing properties of the asphalt mixtures heated by microwave were reviewed. Finally, the application of microwave heating in asphalt pavement de-icing was explored. In addition, asphalt pavement aging due to microwave heating was also reviewed. It was found that microwave heating technology has good prospects in promoting asphalt pavement self-healing and de-icing. There are also some problems that should be studied in depth, such as the cost-effectiveness of microwave-sensitive additives (MSAs), the performance of the pavement with MSAs, mechanism-based self-healing performance indicators, and the aging of asphalt pavements under cycling microwave heating.

Lead-acid batteries (LABs) and the thermogravimetric analysis of Pb metal reduction from PbO2 via microwave heating at 2.45 GHz

The lead (Pb) in lead-acid batteries (LABs) accounts for up to 60% of their total weight and 80% of the metallic Pb produced worldwide. As a toxic substance but sought-after resource, developing a method to reclaim Pb from spent batteries, both safely and efficiently, is highly desirable. To this end, this paper explores the application of microwave heating to reduce Pb from PbO2, a component of LAB pastes, using a carbon (C) reductant. Various experiments were conducted between 200 and 1000 W to determine mass loss kinetics using a homemade thermogravimetric apparatus. The mechanisms and kinetics of the reactions, and their resultant phases, are discussed in comparison to differential thermal analyses (TG-DTA) of the same samples. Microwave heating was found to be highly effective, resulting in up to a 97% recovery of Pb metal at < 300 °C; however, complete reduction was unrealized due to crucible interference, microwave penetration depth, and the reflection of microwaves as Pb metal formed. The reduction and decomposition reactions were evaluated using X-ray diffraction (XRD).

Design, microwave-assisted synthesis, biological evaluation, molecular docking and ADME studies of pyrrole-based hydrazide-hydrazones as potential antioxidant agents

In this study, one novel N-pyrrolyl carboxylic acid (3), the corresponding N-pyrrolyl hydrazide (5), and four new hydrazide-hydrazones (5a-d) bearing electron donating moieties were designed, synthesized, and fully elucidated by 1H NMR, FT-IR, and HRMS. The hydrazide-hydrazones were produced in five steps, which were optimized by applying microwave heating. The microwave-assisted synthesis significantly decreased the reaction times and increased the yields of the title molecules. In addition, all novel compounds were assessed for their radical scavenging properties by employing DPPH and ABTS assays. The most promising agent was obtained after condensation of the title hydrazide (5) with a 3,5-dimetoxy-4-hydroxybenzaldehyde (5d). The latter compound showed better antioxidant properties than Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) and could serve as a prominent lead structure for future optimization as an antioxidant agent. A possible binding conformation of 5d in the active site of NADPH oxidase was also identified through molecular docking simulations. Analysis of the major interactions showed the importance of the hydroxyl moiety for the antioxidant activity. Finally, the virtual calculations of the ADME properties of the synthesized compounds displayed good drug-like properties. Overall, an optimized synthetic protocol through MW irradiation was employed. The newly synthesized ethyl (E)-5-(4-bromophenyl)-1-(1-(2-(4-hydroxy-3,5-dimethoxybenzylidene)hydrazineyl)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-2-methyl-1H-pyrrole-3-carboxylate (5d) was found to possess the most prominent radical-scavenging capacity, which identifies it as a promising lead compound for the development of novel antioxidants.

Characteristics and mechanism of microwave-induced discharge of spherical bio-char with graphite addition

The enhancement of efficiency converting microwave energy into heat has become great concern on industrial application of microwave heating. Microwave discharge can generate more hot spots, exhibiting more intense thermal effect than microwave heating alone. Microwave discharge can be achieved by a variety of carbon-based dielectrics like bio-char, whose performances are highly dependent on graphite degree of the carbon-based dielectrics. Therefore, graphite addition into bio-char by mechanical mixing is promising to improve the discharge performance. However, there are few studies on characteristics of microwave-induced discharge by spherical bio-char with graphite addition, and kinetic analysis of microwave discharge is lacking. Moreover, the mechanism of microwave-induced discharge of spherical carbon-based dielectrics has not been fully clarified. As a result, the work firstly studied characteristics of microwave-induced discharge of spherical bio-char with graphite addition. The other focus of this work was to explore mechanism of microwave-induced discharge through electric field simulation. The results revealed the average discharge intensity of spherical graphite in the first 20 min was 38.2 % higher than that of spherical bio-char. Microwave-induced discharge of bio-char with graphite addition had synergistic effect at the initial stage. It was obtained apparent activation energies of microwave-induced discharge of bio-char and graphite were 237.08 W·g−1 and 48.42 W·g−1, respectively. The formation of electric field polarization focuses offered active sites for microwave discharge. The work is of significance for fundamental research about microwave-induced discharge of carbon-based dielectrics.

Reaction kinetics of lithium extraction and a recycling process for lithium meta-titanate pebbles

ABSTRACT Fusion reactors require large amounts of lithium meta-titanate (Li2TiO3) pebbles as tritium breeding materials for Japanese water-cooled solid breeder blanket. The development of a recycling process for tritium-breeding materials is essential for the early realization of fusion reactors. This study was proposed to understand the kinetics of Li extraction from Li2TiO3 by inducing chemical reactions and applying microwave heating and establish a highly efficient recycling process for spent Li2TiO3 pebbles. The results of Li extraction experiments performed under various conditions clarified that this extraction reaction could be applied via a surface chemical reaction with kct = 1 − (1 − f)1/3. The apparent activation energy associated with this extraction reaction was evaluated to be 52.78 kJ/mol, which is in agreement with that of the chemical reaction-controlled mechanism. Additionally, the reaction order for the dissolution of Li2TiO3 in the HCl solution was first-order. The highly efficient recycling process of Li2TiO3 pebbles was suggested.

Application of microwave heating in the production of homogeneous paste from the fruits of small-fruited apple trees

The paper presents data on the chemical, physical and microbiological changes during storage of paste from the fruits of small-fruited apple trees processed with microwaves. After six month of storage the content of water soluble solids increased 1.02 times (from 21.50 % to 21.93 %). The sugar-acid index decreased 1.23 times (from 10.25 % to 8.35 %); the titratable acidity increased 1.13 times (from 9.92 g/dm3 to 11.21 g/dm3). The mass fraction of pectin substances decreased 2.51 times (from 2.31 % to 0.92 %) and the content of Vitamin C decreased 1.26 times (from 24.1 mg/100 g to 19.12 mg/100 g). The number of mesophilic aerobic and facultative anaerobic microorganisms did not exceed 200 colony-forming units (CFU) per gram. The number of yeasts did not exceed 260 CFU/g and the number of filamentous fungi did not exceed 620 CFU/g. No pathogenic or facultative pathogenic bacteria were found during all the period of storage.

Design of Magnetron Cooling Method Based on Heat Exchanger System for Microwave Heating Application

Microwave heating is a novel thermal recovery technique developed for heavy oil reservoirs. Particulary in deep reservoirs, it allows more effective thermal recovery to counter heat loss.. The magnetron as a microwave generator works based on cavity resonant vibrations and it needs an appropriate cooling system to avoid damage to its cavity elements. In this paper, the design of a cooling system based on a heat exchanger as well as the investigation of the proper material and coolant to fit the microwave characteristics are proposed.

Rapid Preparation of Manganese Monoxide by Microwave-Enhanced Selective Carbothermal Reduction

Most of the manganese resources in China have existed in the form of low-grade pyrolusite which is not utilized efficiently because of the high energy consumption and environmental pollution during the reduction process. Applying microwave heating to minerals reduction endows improved production efficiency and reduced production costs. In the present work, rapid preparation of manganese monoxide (MnO) was attempted through reducing low-grade pyrolusite with coal reducing agent by microwave heating, with the samples characterized by XRD, scanning electron microscopy, XPS as well as TG/DSC. The influences of the reduction reaction parameters on the reduction process of Mn in pyrolusite were comprehensively studied. The results indicated that higher temperatures and longer holding times facilitated the reduction roasting of pyrolusite, and manganese monoxide can be fabricated with a reduction ratio of 97.7% obtained at 650°C for 50 min. The mechanism of the gradual transformation of MnO2 to MnO from the macroscopic to the molecular level was also revealed in the order of MnO2 → Mn2O3 → Mn3O4 → MnO. Compared to traditional roasting, the proposed microwave-enhanced roasting process benefits from the superior kinetic conditions provided by the synergy between microwave enhancement and compact pellets, and thus reduced the roasting temperature and roasting time.

Twenty Years’ Research on Microwave Application to Metal Production and Recycling

Ever since discovery of microwave heating in 1946, its application has been developed in various fields. Our research group has performed intensive studies on microwave heating application to metal production and recycling for these twenty years. In this article, it is intended to introduce our attempts having made for different projects. They are 1. Microwave processing of Ti bearing blast furnace slag, microstructural alteration and comminution. 2. Microwave carbo-thermic reduction of valuable metals from various oxides. 3. Microwave drying and dehydration of wet wastes. 4. Vapor de-phosphorization by microwave rapid heating. It is to be emphasized that we utilized a single mode microwave applicator for the purpose of clarification on the heating mechanisms of various metallurgical matters and compounds, and it was intended to discuss the reaction kinetics excited by microwave heating.

Occupational exposure to radiofrequency electromagnetic fields.

High exposures to radiofrequency electromagnetic fields (RF EMF) are possible in workplaces involving sources used for broadcasting, telecommunication, security and identification, remote sensing and the heating and drying of goods. A systematic literature review of occupational RF EMF exposure measurements could help to clarify where more attention to occupational safety may be needed. This review identifies specific sources of occupational RF EMF exposure and compares the published maximum exposures to occupational exposure limits. A systematic search for peer-reviewed publications was conducted via PubMed and Scopus. Relevant grey literature was collected via web searches. For each publication, the highest measured electric field strength, magnetic flux density or power density was extracted. Maximum exposures exceeding the limits were reported for dielectric heating, scanners for security and radiofrequency identification, plasma devices and broadcasting and telecommunication transmitters. Occupational exposure exceeding the limits was rare for microwave heating and radar applications. Some publications concerned cases studies of occupational accidents followed by a medical investigation of thermal health effects. These were found for broadcasting antennas, radar installations and a microwave oven and often involved maintenance personnel. New sources of occupational exposure such as those in fifth generation telecommunication systems or energy transition will require further assessment.

Improving the Electromagnetic Properties of Bitumen Using SiC-Fe3O4 Composites

AbstractIt is important to further improve the microwave absorption capacity of bitumen to promote the application of microwave heating in pavement maintenance. SiC-Fe3O4 composites were prepared a...

Germination of Bacillus cereus ATCC 14579 spore at various conditions and inactivation of the germinated cells with microwave heating and UVC treatment in milk samples

In this study, germination of Bacillus cereus spores under various conditions and the inactivation of germinated cells by microwave heating (MH) and 254 nm ultraviolet (UVC) treatment in milk samples were identified. A combination of germinants, ʟ-alanine and inosine, was the most effective for germination of B. cereus spores; and heat activation during the germination step increased the germination rate to 99.98% at pH 7 with 1% sodium chloride. The resistances of germinated cells by optimized conditions, inoculated in milk samples, to MH and UVC were investigated. The reduction rate was the highest in skimmed milk followed by low-fat and whole milk samples. The resistance of germinated cells was significantly higher than that of the vegetative cells regardless of the milk type. Sequential treatments exhibited a higher reduction rate than the sum of individual treatments, and resuscitation of germinated cells was not observed even after the longest treatment. Moreover, the quality aspects of milk samples were not significantly deteriorated (p > 0.05) except for the pH values which were found to be slightly decreased. These results would be used as a fundamental database for the application of UVC and MH to inactivate B. cereus spores in milk samples.

Dielectric characterisation of asphalt mortars for microwave heating applications

Microwave (MW) heating could contribute to the sustainability of the construction and maintenance of asphalt pavements. The relationship between frequency and the dielectric properties (i.e. loss factor and penetration depth) is crucial for maximising the MW heating efficiency. The paper aims to study the dielectric properties of conventional and electric arc furnace (EAF) slag asphalt mortars. Results showed that the addition of EAF slag enhanced the dielectric response of asphalt mortars. Moreover, a frequency of 5.8 GHz seems to be the best choice for deicing application and assisted-healing of surface layers up to 7 cm.

Concrete Cutting by a Solid-State, Localized Microwave-Heating Applicator

This article presents experimental results of concrete cutting by a localized microwave-heating (LMH) applicator, fed by a ~0.25-kW solid-state microwave generator. The LMH applicator is a modified microwave-drill, operating in a stepwise pecking mode. Compared to the previously-presented, magnetron-based microwave-drill for concrete, the new device operates at a lower power; it is more compact, and it enables arbitrary cutting contours. In each pecking step in this mode, a small amount of concrete is softened by LMH, and mechanically removed. These sequential pecks are accumulated to form a long deep groove along the desired cutting contour. The lower microwave power applied in the pecking mode enables a narrower LMH applicator, which reduces the total amount of concrete removed in the cutting process (the kerf), and hence improves the overall efficiency. The solid-state LMH pecking module can be remotely controlled, and it is applicable to other masonry as well. Its silent and clean operation (with no vibration or dust effusion) classifies it as an environmental-friendly technology. The article introduces the LMH pecking concept for concrete cutting, and presents its experimental results. Concrete removal rates of ~0.35 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> /min in ~0.5-cm pecking steps (accumulated to ~6-cm-long, ~6-cm-deep grooves) were obtained by applying a ~0.25-kW microwave power, in agreement with the LMH theory. The feasibility of a faster concrete cutting in practice by advanced LMH-based devices, also in array schemes, is discussed.