Application Of Microwave Energy Research Articles

Microwave Encounters Ionic Liquid: Synergistic Mechanism, Synthesis and Emerging Applications.

Progress in microwave (MW) energy application technology has stimulated remarkable advances in manufacturing and high-quality applications of ionic liquids (ILs) that are generally used as novel media in chemical engineering. This Review focuses on an emerging technology via the combination of MW energy and the usage of ILs, termed microwave-assisted ionic liquid (MAIL) technology. In comparison to conventional routes that rely on heat transfer through media, the contactless and unique MW heating exploits the electromagnetic wave-ions interactions to deliver energy to IL molecules, accelerating the process of material synthesis, catalytic reactions, and so on. In addition to the inherent advantages of ILs, including outstanding solubility, and well-tuned thermophysical properties, MAIL technology has exhibited great potential in process intensification to meet the requirement of efficient, economic chemical production. Here we start with an introduction to principles of MW heating, highlighting fundamental mechanisms of MW induced process intensification based on ILs. Next, the synergies of MW energy and ILs employed in materials synthesis, as well as their merits, are documented. The emerging applications of MAIL technologies are summarized in the next sections, involving tumor therapy, organic catalysis, separations, and bioconversions. Finally, the current challenges and future opportunities of this emerging technology are discussed.

Application of Microwave Energy in Agriculture

Application of Microwave Energy in Agriculture

Design of a Microwave Heating and Permittivity Measurement System Based on Oblique Aperture Ridge Waveguide.

In this paper, an oblique aperture ridge waveguide operating at 2450 MHz is proposed, and, using the ridge waveguide, a permittivity measurement system is constructed which can measure the permittivity of materials during microwave heating. The system calculates the amplitudes of the scattering parameters by using the forward, reflected and transmitted powers of the power meters, and it reconstructs the permittivity of the material by combining the scattering parameters with an artificial neural network. The system is used to measure the complex permittivity of mixed solutions of methanol and ethanol with different ratios at room temperature, and the permittivity of methanol and ethanol with increasing temperature, from room temperature to 50 °C. The measured results are in good agreement with the reference data. The system allows simultaneous measurement of the permittivity with microwave heating and provides real-time, rapid changes in the permittivity during heating, avoiding thermal runaway and providing a reference for applications of microwave energy in the chemical industry.

Effect of metal slots on the heating uniformity of multisource cavity microwave

Microwave heating as a new type of heating has been widely used in numerous fields; however, microwave heating in multi-source cavity still poses several problems, including non-uniformity, low efficiency, restriction of the heating object, and “thermal runaway”, thus limiting the application of microwave energy. This study adopts a method to place a slotted layer in the cavity such that the energy can be radiated uniformly to improve the heating uniformity. The distribution of the electric field in the cavity is optimized by changing the arrangement and size of the slots in the slot layer. The effects of the slot arrangements are elucidated, and experiments are performed to study the real-life application of the slot arrangements. The results show that these metal slots are effective in improving the uniformity and efficiency of multisource cavity heating.

Microwave Hybrid Heating for Moulding of Sisal/Jute/HDPE Composites

ABSTRACT Microwave processing of polymer composites is gaining attention as a viable alternative to traditional thermal processing techniques owing to several reasons, including faster and environment-friendly processing. In the present study, High-density polyethylene (HDPE) reinforced with jute and sisal fibers (10 wt.%) composites were fabricated using microwave energy at 2.45 GHz frequency. The mechanism of microwave molding of the composites has been explained. To understand and compare the performance of the fabricated composites, mechanical (tensile and flexural), thermogravimetric (TGA), and X-ray diffraction (XRD) analyses were employed to evaluate the performance of the composites. The composites exhibited significant improvement in tensile strength (29.25% and 48.69%), flexural strength (19.22% and 27.47%), and crystallinity (6.41% and 13.02%) for HDPE/Jute and HDPE/Sisal, respectively while compared to pure HDPE. The fractography confirmed that the fiber pull-out was the major mechanism of failure of the composites under mechanical loading. The processing data show that the application of microwave energy is a potential method to process natural fiber-based polymeric composites in a relatively low processing time.

Sustainability of microwave heating in materials processing technologies

In this cutting-edge technology, industrial and competitive era, the sustainability of any manufacturing processes needs utmost attention. Sustainability itself is a broad term which can be related to the number of parameters of any process may be its efficiency, product quality, power and time consumptions, suitability of a variety of materials etc. Such parameters of sustainability can only be achieved by finding novel routes of manufacturing or materials processing technologies. The conventional systems are going out of trends due to higher energy demands and higher time consumption to achieve the desired goals instead of using conventional processes. A lot of research is going in this direction for developing processes which are clean and green methods. Microwave Processing (MWP) of materials and heating technology is one such novel route which can be used for processing of ceramics, metal matrix composites (MMC), fibre reinforced plastics (FRP), alloys, metals, material joining, coating, cladding, materials synthesis etc. The present work reports the various applications of microwave energy in various materials processing technologies, its advantages and sustainability issues. The microwave heating started with the food industry and now has penetrated its presence in the domain of metals. The microwaves are now used for processing of a variety of materials, including bulk metals in the area of cladding, joining, melting and casting. The broad perspectives of using MWP are highlighted and recent innovative contributions in this area are highlighted. Focus is on the recent trends and techniques used in microwave materials processing and its effective utilization can be compared to conventional processes. Some parameters for comparison to sustainability of various manufacturing/processing technologies are discussed in the present work.

Investigations of electrical conductivity and damage healing of graphite nano-platelet (GNP)-taconite modified asphalt materials

This proof of concept study investigates the electrical conductivity and damage healing capability of graphite nano-platelet (GNP)-taconite modified asphalt materials. Different combinations of GNP and taconite concentrate are added to an asphalt binder, and the electrical conductivity is measured by a four-probe conductivity test. Similar combinations of GNP and taconite concentrate are used to prepare asphalt mixture specimens to investigate the healing capability. Semi-circular bend (SCB) tests are performed at low temperature in two stages. First, specimens are damaged by loading them into the post peak region using crack mouth opening displacement (CMOD) control. The specimens are then subjected to microwave heating, after which they reloaded to measure the strength capacity. It is shown that the addition of GNP and taconite concentrate could effectively enhance the electrical conductivity of asphalt binders. The results also demonstrate the influence of humidity on the measured conductivity. The SCB fracture tests show that the application of microwave energy to the pre-damaged specimens restores their original load capacity, a clear indication of damage healing.

An approach towards enhancing the role of microwave heating in low-level radioactive waste management

Nuclear industries, medical industries, and nuclear research establishments generate a considerable amount of low-level radioactive waste (LLW). The paper presents the application of microwave energy for the processing of low-level radioactive wastes (volume reduction). A temperature-based study of these kinds of wastes has been performed using the COMSOL multiphysics software package. The simulated results agree well with experiments performed on a commercially available microwave oven at a frequency of 2.450 GHz. The main focus of this paper involves a detailed study of the effectiveness of microwave heating for treatment of LLW based on their dielectric loss tangent data. The study is carried out by recording the temperature rise in the corresponding waste materials, which is basically representation of the conversion of the applied electromagnetic energy into heat. Various shapes such as cubical, cylindrical, and cuboid of low-level radioactive test objects have been incorporated in the treating environment (Oven). Further, measurement of electromagnetic and heat transfer properties of the test objects has been performed to improve the accuracy of the simulation and experimental results. Many combinations of test objects with different shapes and dielectric properties have been studied for microwave heat treatment. The study suggests that radioactive waste treatment using microwave heating will be more effective after categorizing the wastes concerning their dielectric loss tangent.

Application of low-cost Fe-based catalysts in the microwave-assisted pyrolysis of macroalgae and lignocellulosic biomass for the upgradation of bio-oil

The combined application of microwave energy and special catalysts holds the potential for the selective conversion of biomass during the pyrolysis process. In this work, steel slag (SS) and biochar-based Fe (RHC/Fe) were adopted as both low-cost Fe-based catalysts and microwave absorbers in the microwave-heating pyrolysis system for the upgradation of bio-oil from macroalgae (Sargassum) and lignocellulosic biomass (pine sawdust). The catalysts all showed strong microwave adsorption performance, exhibiting higher heating rates than that of SiC. SS with a high content of iron oxides plays a catalytic role in biomass decomposition, while RHC/Fe with a highly porous structure not only promotes biomass decomposition but also enhances the secondary reaction of volatiles. The presence of SS significantly improved the content of lighter compounds (<C10 compounds) in Sargassum-derived bio-oil, leading to an improvement in the yield of potential chemicals such as phenols and furans; the formation of phenols was also significantly enhanced by SS during pine sawdust pyrolysis with a high phenols content of 55.8% in the obtained bio-oil. RHC/Fe exhibited remarkable selectivity on Sargassum pyrolysis and the obtained bio-oil contained only 13 compounds including 33.8% of <C10 compounds and 66.2% of >C20 compounds without any C10–C20 compounds. The N-containing compounds in Sargassum-derived bio-oil were successfully removed using RHC/Fe. RHC/Fe also showed a significant catalytic effect on the production of combustible gases from the pyrolysis of Sargassum and pine sawdust, with significant improvement in the total gas yields and combustible gas concentrations.

Applications of Microwave Energy in Medicine.

Microwaves are a highly utilized electromagnetic wave, used across a range of industries including food processing, communications, in the development of novel medical treatments and biosensor diagnostics. Microwaves have known thermal interactions and theorized non-thermal interactions with living matter; however, there is significant debate as to the mechanisms of action behind these interactions and the potential benefits and limitations of their use. This review summarizes the current knowledge surrounding the implementation of microwave technologies within the medical industry.

Increasing the impregnability of Oriental spruce wood via microwave pretreatment

Microwave (MW) pretreatment was used to increase the impregnability of Oriental spruce sapwood (Picea orientalis (L.) Link.). Wood samples with moisture contents of 55% and 83% were subjected to different MW energy treatments (1156 MJ/m3 and 1542 MJ/m3). Additionally, the mechanical properties of the treated wood samples were tested to determine the degradation caused by exposure to the MW radiation. According to the test results, the average preservative material retention rates increased by 47.5% and 70% for the samples with initial moisture contents of 55% and 83%, respectively, compared to the reference samples. The mechanical properties of the MW pretreated wood samples decreased within the range of 1.7% to 2.9% in the case of the compression strength; changed within the range of (+)1.9% to (-)6.1% in case of the bending strength; and changed within the range of (+)0.9% to (-)6.2% in case of the modulus of elasticity (MOE). The application of MW energy at different power settings on the samples with similar moisture levels was determined to have no impact on the mechanical properties of treated wood.

Microwave energy for gold ore processing

Quite a few studies have been carried out that look at the application of microwave energy for material processing in various spheres. Microwaves can selectively and quickly heat the target bulk material thanks to its dielectric properties. Gold ores have a complex mineral composition and the effect of microwaves is different on different minerals. This enables to heat selected areas of the rock causing a strong thermal stress. This leads to microcracks occurring at the mineral boundaries resulting in weaker grains and hence better grinding performance. Refractory gold concentrates contain a lot of sulphides, which get hot instantly when exposed to microwave radiation. Thus, microwave energy can be efficiently used to roast sulphide gold concentrates. During microwave roasting, heat conversion takes place directly in the sulphides and the reaction starts immediately. That’s why microwave roasting is a much faster process compared with convection roasting. This paper provides a brief overview of microwave energy used for gold ore and concentrate processing and describes the behaviour of minerals in the microwave field, as well as the results of a number of studies that looked at using microwave energy to destroy rocks, roast refractory sulphide gold concentrates and regenerate charcoals. The key advantages of microwave radiation include an easy process control, the possibility to quickly and selectively heat the product and low energy costs.

Effects of microwave heat treatment on fungal growth, functional properties, total phenolic content, and antioxidant activity of sorghum (Sorghum bicolor L.) grain

Sorghum grains were subjected to microwave heating at different power levels 350 and 500 W for application times of 15, 30, and 45 s. The effect of microwave heating on fungal growth, protein content, in vitro digestibility, protein solubility, and functional and antioxidant properties of sorghum grain was investigated. The microwave heating at 350 and 500 W significantly reduced fungal incidence in the grain up to 26.2 and 33.4%. No significant changes were found in the crude protein and digestibility of protein, water holding capacity, and oil holding capacity of sorghum. However, application of microwave energy at 500 W for 30 & 45 s caused a sharp reduction on the protein solubility (8.2–7.6%), foaming capacity (6.47–0.98%), emulsion capacity (0.43–0.32 mL/g) and the emulsion stability (2.2–1.6%) of sorghum grain, respectively. Conversely, a significant increment of grain total phenolic content up to 47.1 and 50.8 mg GAE/g and the antioxidant activity up to 40.9 and 59.1% after microwave heat treatment at 350 and 500 W for 45 s, respectively, was observed. These findings revealed that sorghum grain should be treated with microwave at 350 and 500 W for 45 and 15 s, respectively, in order to maintained and enhanced its functional and nutritional properties. Accordingly, microwave heating, particularly at low power, may be an effective emerging method for improving the physicochemical and nutritional properties of sorghum grain.

Microwave-assisted Homogeneous Gold Catalyzed Organic Transformations

: Microwave chemistry is an emerging area of science mainly focusing on various applications of microwave energy into chemical processes. Microwave irradiation has enormous potential to provide controlled energy directly to the molecules of interest. On the other hand, homogeneous gold catalysis has emerged in the last two decades or so as one of the most promising fields in organic and organometallic chemistry. Its efficacy has been established many times for the construction of new C – X (X = O, N, S, etc.) and C – C bonds under mild reaction conditions. Although a significant number of reports have appeared in the literature regarding the homogeneous gold-catalyzed organic transformations under microwave conditions, this is the first review article which is going to appear in the literature. This mini-review is designed to give an interesting insight into various homogeneous goldcatalyzed organic reactions under microwave irradiation for the synthesis of a library of electronically and structurally diverse and biologically important organic molecules.

Vessel Sealing Device Using Microwave and High Frequency Current

In recent years, various types of medical applications of microwave energy have widely been investigated and reported. We present a surgical device which employs the thermal effect produced by microwave energy. High power microwave energy can generate a coagulated region at the surface of the biological tissue such as organs. By coagulating organs, bleeding can be stopped. However, a microwave surgical device cannot cut the tissue without any device support, such as a blade. On the other hand, radio frequency (RF) current capable of cutting tissue without any support. This study presents a combination of a forceps type microwave surgical device combined with RF current for biological tissue cutting mechanism. Furthermore, ten sealed porcine blood vessels, sealed by the device, capability to withstand pressure were measured. Sealed blood vessels can withstand up to 200 mmHg of pressure and sufficient to withstand human blood pressure.

Experimental and computational study on the microwave energy based regeneration in diesel particulate filter for exhaust emission control

The uncontrolled combustion and early-life failure of the Diesel Particulate Filter substrate during fuel-based regeneration has raised the requirement for an alternate regeneration technique. The Latest emission norms have made it a mandatory requirement to retrofit the Diesel Particulate Filtration system in the exhaust line of CI engines to bring down the Particulate emissions. In this work, a novel technique through application of microwave energy has been developed for active regeneration of soot particles accumulated in the filter channel. Modelling of soot layer formation and microwave regeneration were carried out using CFD software (COMSOL MULTIPHYSICS). Performance and emission characteristics of multi-cylinder CI engine were evaluated after retrofitting the developed after-treatment system comprising of Diesel Oxidation Catalysis (DOC) and microwave regeneration based Diesel Particulate Filtration (DPF) systems. Soot accumulation rate and regeneration rate were experimentally investigated at different engine loads and magnetron (microwave radiation source) power levels. The experimental results showed that the developed after-treatment system has an average filtration efficiency of 90% for brake specific particle number emissions and 55% for hydrocarbon emissions. The regeneration rate was observed to be a maximum of 0.21 g/min at 50% power levels owing to the non-linear behaviour of magnetron. Energy consumption pattern of other regeneration techniques has been compared with the developed microwave regeneration system. The effect of soot accumulation and regeneration on the morphology, microstructure, chemical composition and particle size of DPF substrate were examined using characterization studies like Scanning Electron Microscopy – Energy Dispersive X-Ray Spectroscopy (SEM-EDS), Fourier Transform Infra-Red spectroscopy (FTIR), Particle Size Analysis (PSA) and microscopic imaging.

On processing strategy to minimize defects while drilling borosilicate glass with microwave energy

Application of microwave energy at 2.45 GHz frequency has the potential to provide thermal energy-based alternative solution to drilling of glass in the sub-millimeter domain. In this process, the concentrated microwave energy around a concentrator (tool) is utilized to melt or ablate the target material from the workpiece. The present study discusses the effect of parameters like tool shape, tool immersion depth, feed rate, and machining gap on the quality of hole in terms of thermal damage, overcut, and amount of material removed while drilling borosilicate glass using a graphite concentrator. It was found that the concentrator with a conical tip performs better compared to the concentrator with cylindrical tip due to concentration of thermal energy at the tip. Further, it was observed that the thermal damage, overcut, and amount of material removed decrease with the increase in immersion depth and feed rate. A machining gap (~ 300 μm) between the concentrator tip and the workpiece is essential as it facilitates flushing the glass residue from the machining zone. Effective flushing also reduces thermal damage and roundness error around the hole drilled. However, overcut and amount of material removed increases with increase in the machining gap due to increased plasma zone area and interaction time between plasma and the workpiece. The results of heat-affected zone obtained from this research were significantly less compared to that in published results. The approach was found to be promising while drilling borosilicate glass, though further study will be needed to improve precision.

Modelling of simultaneous heat and mass transfer considering the spatial distribution of air velocity during intermittent microwave convective drying

Drying is a complex simultaneous heat and mass transfer process where water is migrated from the sample to the drying air through continuous evaporation. The rate of evaporation can be accelerated by the intermittent application of microwave energy with convective drying, which is called intermittent microwave convective drying (IMCD). However, theoretical aspects of IMCD process is not clearly understood yet, which is required to obtain a better -quality product and for designing energy efficient IMCD drying systems. Therefore, several researchers have attempted to develop a theoretical modelling framework for IMCD. However, most of the existing models do not consider the spatial distribution of air velocity around the product, which is important as it significantly affects the heat and mass transfer coefficient throughout the sample and eventually alters the drying kinetics. This paper aims to address this research gap by developing an IMCD modelling framework through integrating a simultaneous heat and mass transfer model with a computational Fluid Dynamics (CFD) model (drying air flow) under the condition of volumetric heating. A 3D model was developed, and the simulated results were validated with the experimental results. It was found that the integration of fluid flow (CFD) with an IMCD model significantly affected the drying kinetics as heat and mass transfer coefficients spatially varied throughout the sample. Drying models may thus overpredict the drying kinetics like moisture content if the spatial distribution of air velocity is not taken into account. It was also found that the nonuniform microwave power absorption caused an inhomogeneous distribution of the sample temperature. The new findings and knowledge from this study will lead to the development of more accurate drying models.

Applications of microwave energy in gas production and tar removal during biomass gasification

Microwave heating has the potential to promote gas production and tar removal during biomass pyrolysis or gasification based on its advantageous characteristics such as rapid heating and selective heating.

Application of microwave energy for rapid fabrication of nano-hydroxyapatite reinforced polycaprolactone composite foam

This research work is aimed to utilize microwave energy for rapid fabrication of nano-hydroxyapatite (nHA) reinforced polycaprolactone (PCL) composite foam. Weight fraction of nHA and NaCl was fixed at 20% and 30%, by weight, respectively. The NaCl was acts as microwave absorber as well as the porogen agent in the composite. The interconnected porosity was induced by leaching of the NaCl particles from composite in an ultrasonicator bath. The influence of microwave process parameters such as microwave power and exposure time was studied on mechanical and microstructural feature of PCL/nHA composite foam.