Influence Of Microwave Power Research Articles

Microwave-assisted pyrolysis of plastic waste for liquid oil production

In this work, the article presents the results of the production of fuel oil from plastic waste using microwave-assisted pyrolysis. Under the influence of microwave power, microwave absorption material, time, catalyst, polyethylene (PE), polypropylene (PP), polystyrene (PS) and mixture (34% PE + 33% PP + 33 wt% PS) were pyrolyzed to liquid oil. The results showed that with 500 g of raw plastic, 500 W microwave power, and 120 minutes, the carbon absorber accounted for 10 wt% (compared to plastic), catalysts accounted for 20 wt%, fuel efficiency reached 84% with PS and PP, 83% with PE, and 83.5% with mixed plastics. The oil obtained qualified the standards of FO No. 1 TCVN 6239:2019. The gas chromatography/mass spectroscopy GC/MS analysis (GC-MS) showed that the composition of the pyrolysis oil is mainly hydrocarbon from C7-C12.

Impedance Analysis and Dielectric Performance of Microwave-Assisted Synthesized MWCNT/Polystyrene Nanocomposites: Influence of Microwave Power

Impedance Analysis and Dielectric Performance of Microwave-Assisted Synthesized MWCNT/Polystyrene Nanocomposites: Influence of Microwave Power

Integrating Microwave Heating with Foam-Mat Drying: Drying Kinetics and Optimization for Thick Foamed Mango Pulp

This study addresses the challenge of processing undersized or overripe mangoes by integrating microwave heating with traditional foam-mat drying technique. The study aims at investigating drying kinetics coupled with thin-layer drying modeling and influences of microwave power (300 - 600 W) and hot-air temperature (55 - 75 °C). Among ten drying models, the so-called Midilli equation fitted well with experimental data. Results showed enhanced drying process associated with microwave heating, providing reduced drying time from 600 - 700 min (for conventional hot-air mode) to 30 - 100 min (for microwave-assisted mode). Standard deviations of moisture content and dried foam thickness measured at various points revealed uneven heat distribution when using high microwave energy, evidenced by burnt spots at 600 W. Additionally, foam collapse was observed under the mild process with low microwave powers, possibly due to prolonged drying periods. Response surface methodology demonstrated that microwave power was more important factor, positively affecting effective diffusivity coefficient (Deff) while inversely influencing specific energy consumption (SEC) and color difference (DE). Deff value increased from 5.41´10-6 m²×s-1 at 300 W and 55 °C to 18.43´10-6 m²×s-1 at 600 W and 75 °C, confirming enhance drying performance. As assisted with microwave heating, drying foamed mango sample consumed less energy up to 92 %. Optimal drying parameters were determined based on balancing the enhancement of drying performance and color alteration, suggesting drying the thick foamed mango pulp at temperature of 55 °C combined with microwave heating at 520 W, which can be served as a basis for further industrial scale-up. HIGHLIGHTS Novel method for thick mango pulp snacks. Reduced drying time from 600 - 700 to 30 - 100 min. Lowered energy use to 5.83 kWh×kg-1. Optimal conditions at 520 W, 55 °C, desirability 0.669. Applied Midilli model with 99 % accuracy. GRAPHICAL ABSTRACT

Experimental analysis and multi-criteria optimization of process parameters in microwave drilling of kenaf-reinforced polypropylene composites

The present work utilizes the CNC-controlled microwave drilling technique to produce the holes in kenaf-reinforced polypropylene composites. The influence of microwave power and feed rate on the hole characteristics, namely, circularity, overcut, taper angle, and surface roughness was investigated. Stereo microscopic images of the hole entrance and exit were used to evaluate the circularity, overcut and taper angle. Optical profilometer was used to acquire the surface roughness of drilled holes. The TOPSIS, GRA, and MOORA multi-criteria decision making techniques were implemented to optimize the microwave drilling process parameters. The 180 W of microwave power and 145 mm/min of the feed rate were the optimum process parameters to yield the best quality holes in kenaf-reinforced polypropylene composites.

Application of electron paramagnetic resonance spectroscopy to examine free radicals formed in indapamide and torasemide storage under UV irradiation and at the higher temperatures which appear under light exposition

Free radical formation in two diuretics: indapamide and torasemide was examined during UV irradiation and storage at higher temperatures using X-band (9.3 GHz) electron paramagnetic resonance spectroscopy (EPR). The aim of this study was to investigate the possibility of storing indapamide and torasemide under UV irradiation and at higher temperatures, which may occur during exposure to light. The diuretic samples were exposed to UVA irradiation for 15, 30 and 45 minutes, and stored at temperatures of 40 °C and 50 °C by 30 minutes. The EPR spectra were analyzed to determine the amplitudes (A), linewidths (ΔBpp), and integral intensities (I) and g factors. The concentrations of free radical (N) in the diuretic samples were also determined. The influence of microwave power on amplitudes, linewidths and the asymmetry parameter were evaluated. The result showed that the tested indapamide and torasemide samples exhibited high free radical concentrations in the range of 1018-1019 spin/g after UV irradiation and heat treatment. Therefore, due to the significant free radical formation indapamide and torasemide should not be stored under UV light and at temperatures of 40 °C and 50 °C. The complex character of free radical systems in the diuretic samples was proved as evidenced by the changes of the asymmetry parameters of the EPR lines with increasing microwave power. Fast spin-lattice relaxation processes were observed in all tested diuretic samples, regardless of the storage conditions. Electron paramagnetic resonance spectroscopy is proposed as a useful method in pharmacy to determine the appropriate storage conditions for diuretics.

MICROWAVE ASSISTED LACTIDE-GLYCOLIDE HOMO AND COPOLYMERIZATION INITIATED BY MAGNESIUM LACTATE

In this work, microwave-assisted ring opening polymerization (ROP) of lactide (LA) and glycolide (GA) initiated by magnesium lactate was investigated. The influence of microwave power, temperature, and reaction time on homopolymers and copolymer’s structure and thermal properties is discussed. Polymerization of L-lactide (LLA) initiated by the magnesium compound resulted in yields up to 78% and poly(L-lactic acid) (PLLA) with average molar mass of up to 30,600 g mol-1. Homopolymerization of glycolide generate poly(glycolic acid) (PGA) in yields up to 90% and in L-lactide/glycolide copolymerizations yields between 34-82%. PLLA prepared with the initiator presented microstructure with significant amount of stereo errors as the result of a racemization process during polymerization as well as low glass transition temperature (Tg) and melting temperature (Tm), while the PGAs presented high Tg, due to high crystallinity, and Tm in accordance with the literature. LLA and GA copolymerization result in poly(lactic acid-co-glycolic acid) (PLGA) with composition close to polymerization feed composition.

Response surface optimization and support vector regression modeling of microwave-assisted essential oil extraction from cumin seeds

The current research involved creating models using Response Surface Methodology (RSM) and Support Vector Regression (SVR) to forecast the amount of extractable essential oil that can be obtained from powdered cumin seeds. Influence of microwave power (140–280–420–560–700 W), amount of water (500–600–700–800–900 ml), duration of distillation (30–45–60–75–90 min) and soak time (15–30–45–60–75 min) on essential oil yield were investigated. Microwave Assisted Extraction (MAE) allowed higher recoveries compared to conventional Soxhlet extraction, without altering the chemical components of the extract. A five-level four FCC experimental design was developed using Minitab (15.1.20.0). A total of 31 runs were performed in microwave-assisted extraction apparatus. Experimental data obtained was then used for developing RSM and SVR models for the prediction of the yield of essential oil. The optimum conditions for maximum yield of cumin oil were given by RSM. Maximum yield of 3.4 ml (0.017 ml/g) was found at 140 W of microwave power, 500 ml of water, 90 min duration of distillation, and 15 min of soak time. In this work, epsilon SVR with RBF kernel was used. The grid search (depth-first search) methodology was applied for tuning the values of epsilon, gamma, and cost using the LIBSVM module on the MATLAB interface. The statistical parameters namely, average absolute relative error (AARE), coefficient of determination (R2), standard deviation (SD), and root mean square error (RMSE) were selected as the performance parameters. The developed SVR model was compared with the RSM model. The AARE values of 2.27% and 1.29%, R2 values of 0.86 and 0.99, SD values of 1.73 and 0.29, and RMSE values of 0.0284 and 0.0132 were obtained for RSM and SVR models respectively. It is found that SVR is more accurate and better tool for modeling of MAE process.

Thermal behaviors of cement and mortar under microwave treatment and the influencing factors: An experimental study

Microwave-assisted breakage of cementitious materials has emerged as a promising green and low-carbon method for dismantling cementitious structures. To understand the mechanism of microwave-induced cracking in structures, it is essential to study the thermal behaviors of cement and mortar under microwave treatment. In this paper, the effects of mixture ratio, water content, and microwave power on the microwave heating characteristics of cement and mortar specimens were investigated through real-time temperature and mass monitoring. In particular, the influence of microwave power on the bursting effect of cement and mortar specimens was analysed, and the mechanism of specimen bursting was explained. The results show that moisture content, water-cement ratio, and microwave power significantly impact the heating rate and mass loss of cement and mortar during microwave treatment. Based on the heating rate, the heating process of cement and mortar under microwave treatment can be divided into three to four stages, depending on the moisture content. The primary reasons for variations in the heating rate are water evaporation and the decomposition of hydrolysis products. The thin-wall ball model based on steam pressure theory can explain the bursting of cement and mortar specimens. Our findings suggest that increasing microwave power and water content in mortar specimens can lead to microwave-induced cracking.

Microwave-Induced Rapid Shape Change of 4D Printed Vegetable-Based Food.

Microwave heating acts as an environmental stimulus factor to induce rapid shape changes in 4D-printed stereoscopic models over time. The influence of microwave power and model structure on the shape change behavior was explored, and the applicability of the deformed method to other vegetable-based gels was verified. The results described that the G', G″, η, and proportion of bound water of yam gels increased with the increase in yam powder content, and the yam gel with 40% content had the best printing effect. The IR thermal maps showed the microwaves first gathered in the designed gully region caused the swelling phenomenon, which induced the printed sample to undergo a bird-inspired "spreading of wings" process within 30 s. Increasing the microwave power and microwave heating time were able to increase the bending angles and dehydration rates of the printed samples, thus improving the deformed degree and deformed speed. Different model base thicknesses (4, 6, 8, and 10 mm) also had significant effects on the shape change of the printed structures. The efficiency of the shape changes of 4D-printed structures under microwave induction can be judged by studying the dielectric properties of the materials. In addition, the deformed behaviors of other vegetable gels (pumpkin and spinach) verified the applicability of the 4D deformed method. This study aimed to create 4D-printed food with personalized and rapid shape change behavior, providing a basis for the application scenarios of 4D-printed food.

Effect of ultrasound pretreatment and microwave vacuum drying in the production of dried poniol fruit

AbstractThis study suggested a combination of microwave and vacuum drying to meet the requirements of preserving the nutritional content of fresh poniol fruit, consuming lower energy, and having a faster drying rate. In this study, the influence of microwave power, vacuum level, and citric acid pretreatment level on the product quality of dried poniol was analyzed. The citric acid pretreatment was conducted in an ultrasonicator bath. The pretreated was dried by changing the microwave power () from 400 to 800 W and the vacuum level () from 300 to 600 mmHg. The quality of the dried product was analyzed in terms of total phenolic content (), antioxidant activity (), total change in color (), and rehydration ratio () of dried poniol fruit. The response range in the sequence was between 22.219–38.361 mg GAE/g, 69.037–92.578 %DPPH inhibition, 23.451–40.148, and 1.38–3.81, respectively, at various combinations of independent variables. The optimal combination of independent variables for maximal recovery of total phenolic content, antioxidant activity, rehydration ratio, and minimal color changes was obtained at 440 W power level, 600 mmHg vacuum, and pretreated with citric acid of concentration .8%. Under the optimum combination of independent variables, the total phenolic content, antioxidant activity, rehydration ratio, and total color change values were 37.904 mg GAE/g, 92.973%, 23.906, and 3.307, respectively. Because of the low temperature in the vacuum process combined with the rapid heating time of microwaves, the results indicate that microwave vacuum drying might be a viable alternative method for improving the quality of dried food products.Practical ApplicationsMicrowave vacuum drying is a technology that uses microwave radiation to generate heat in the absolute pressure range between the triple point of water and atmospheric pressure. Heat is generated in microwave vacuum drying by directly converting electromagnetic energy into kinetic molecular energy. Hence, heat is generated deep inside the product being dried. Because interior temperatures are greater than exterior temperatures, evaporating water is driven to the surface, resulting in higher partial pressure. As a result, the moisture evaporating within the product is released through the pore structure of the macro‐capillary system of the solid material, resulting in a faster drying rate. Since the superficial layer does not dry out completely, the surfaces remain porous. This method results in a superior end product that is also very nutritious with enhanced sensory properties. As a result, this approach is used in the chemical, pharmaceutical, and food industries.

Effect of Microwave Power and Gas Flow Rate on the Combustion Characteristics of the ADN-based Liquid Propellant

As a new type of energy-containing material, Ammonium dinitramide based liquid propellant has the advantages of being green, having low toxicity, good stability, and high safety performance. Traditional catalytic combustion methods require preheating of the catalytic bed and deactivation of the catalytic particles at high temperatures, while microwave ignition methods can effectively solve these problems. To study the combustion characteristics of ADN-based liquid propellants during microwave ignition, the influence of microwave power and gas flow rates on the combustion process are analyzed using experimental methods. A high-speed camera was used to observe the enhanced effects of microwave power and gas flow on plasma and flame. Combined with temperature measurement, the combustion process of ADN-based liquid propellants under the action of plasma was analyzed. The combustion process in the presence of microwaves was observed by comparing parameters such as flame length, flame temperature, and radical intensity. Those results show that, with the increase in microwave power, the luminous burning area of the flame grows significantly. The microwave power is increased by 250 W each, and the flame jet length is increased by nearly 20%. The increase in microwave power also leads to an increase in propellant combustion temperature, however, this increase gradually slows down. At a gas flow rate of 20 L/min, the ADN-based liquid propellant showed the best combustion performance with a maximum jet length of 14.51 cm and an average jet length increase of approximately 85.9% compared to 14 L/min. Too much gas flow rate will hinder the development of the jet, while the high-velocity airflow will have a cooling effect on the flame temperature. The results provide a basis for the specific parameter design of microwave ignition and promote the application of ADN-based liquid propellants in the aerospace field.

Influence of microwave power and HDPE blend ratio on thermal and mechanical properties of kenaf reinforced PLLA/HDPE blended composites

Influence of microwave power and HDPE blend ratio on thermal and mechanical properties of kenaf reinforced PLLA/HDPE blended composites

The Effect of Microwave Baking Conditions on the Quality of Biscuits and the Control of Thermal Processing Hazards in the Maillard Reaction.

To reduce thermal processing hazards (TPHs), microwave baking has been extensively used in food thermal processing. In this study, the influence of microwave power and microwave time on the formation of TPHs and their precursors was explored in microwave-baked biscuits. The results indicated that the content of acrylamide, 5-hydroxymethylfurfural, methylglyoxal, and 3-deoxyglucosone increased linearly with the extension of microwave time (2, 2.5, and 3 min) and microwave power (440, 480, and 520 W). There was a significant correlation between the four TPHs. 3-Deoxyglucosone may directly or indirectly participate in the formation of the other three TPHs. The relationship between TPH levels with some heat-induced sensory characteristics was analyzed. The correlation between the sensory characteristics and the content of TPHs is L* > a* > hardness > Water activity (AW). The correlation coefficients between L* value and the four TPHs are −0.950, −0.891, −0.803, and −0.985. Furthermore, the content of TPHs produced by traditional baking and microwave baking under the same texture level was compared. Compared with traditional baking (190°C, 7 min), microwave baking at 440 W for 3 min successfully decrease methylglyoxal, 3-Deoxyglucosone, acrylamide, and 5-hydroxymethylfurfural content by 60.75, 30.19, 30.87, and 61.28%, respectively. Traditionally baked biscuits, which had a more obvious color, as characterized by lower L* value, larger a* and b* values, are more susceptible to the formation of TPHs. Therefore, microwave baking can reduce the generation of TPHs.

Influence of blanching-freezing pre-treatment on moisture removal characteristics of microwave-dried potatoes

The aim of present work was mainly to study the influence of blanching-freezing pre-treatment on moisture removal characteristics of potato during microwave drying process. The influence of microwave power and the samples thickness was also assessed. For this purpose, microwave powers of 100, 350 and 550 W were practiced to dry discoid shape samples of fresh and blanched-frozen potatoes with a constant diameter of 20 mm and different thicknesses of 5, 10 and 15 mm. The obtained results revealed that time required to dehydrate treated potatoes was significantly (P < 0.05) shorter than the fresh ones. The moisture diffusivity of the fresh and blanched-frozen potatoes was determined to be in the range of 9.13 × 10−9‒7.93 × 10−8 and 9.89 × 10−9‒9.36 × 10−8 m2 s−1, respectively where enhanced with the both increasing power level and samples thickness. The average energy required to instigate water diffusion inside the treated samples with 5, 10 and 15 mm thickness was obtained to be 0.463, 0.379 and 0.331 W g−1, respectively while the values for fresh samples were 0.505, 0.466 and 0.413 W g−1, respectively.

Enhancement of fuel and physicochemical properties of canola residues via microwave torrefaction

Conversion of low value agricultural residues to better-quality products e.g. biofuel, bioproducts can solve the issues related to energy crisis as well as environmental challenges. Torrefaction, a thermochemical pretreatment was employed on canola residue (CR) to augment the physicochemical properties of biomass for heat and energy applications. In the present study, the effects of microwave torrefaction on canola residue have been investigated for the following operating parameters: microwave power (250–450 W), residence time (10–20 min), and feeding load (70–110 g). Box Behnken design method was used to design the experiments and find the interaction between process parameters. Both mass and energy yields diminished with rise in microwave power and torrefaction reaction time. The results show that the carbon content significantly increased with degree of torrefaction while oxygen content had a reverse trend, therefore the atomic ratio of torrefied biomass reduced remarkably. Torrefied biomass shows higher carbon percentages than that for the bituminous coal. In addition, a noticeable decrease in volatile matter was observed with growth in torrefaction severity and thus increased fixed carbon content. The higher heating value (HHV) was boosted up by 26% (promoted from 17.8 MJ/kg to 22.4 MJ/kg). HHV of highly torrefied canola residue is very close to bituminous coal. Fourier transform infrared spectroscopy (FTIR) analysis showed that surface functional groups for example OH, CH, and CO decreased with torrefaction severity indicating the improvement of hydrophobicity of torrefied biomass. Scanning electron microscopy (SEM) results represent a more porous structure at highest torrefaction conditions which happened due to thermal cracking and decomposition of lignin and decreased the grinding energy by 89% compared to that for raw biomass. Moreover, inductively coupled plasma-mass spectrometry (ICP) analysis data showed that concentrations of minerals, alkaline and other essential element amplified with degree of torrefaction. The influence of microwave power was the highest on properties of torrefied biomass, followed by residence time and feeding load. The optimum torrefaction conditions were found at 450W with 90 g feeding load for residence time of 20 min.

Mathematical modeling and analysis of microwave-assisted freeze-drying in biopharmaceutical applications

Freeze drying is an essential unit operation for the storage of biopharmaceuticals, with its main weakness being the very long primary drying times required to sublimate all of the ice formed in the initial freezing step. This study investigates the use of microwave irradiation to reduce drying times. Mechanistic models are derived in a proposed freeze-drying process in which two energy transfer mechanisms – microwave irradiation and heat conduction – occur simultaneously. For this design, a mechanistic model derived in this article predicts an 83% reduction in primary drying time compared to conventional freeze drying. The influence of microwave power and design parameters associated with heat conduction parameters on the primary drying time are investigated and discussed. The model is implemented as open-source software in Julia and is available for engineers to use for designing such equipment.

Heating characteristics of igneous rock-forming minerals under microwave irradiation

Microwave-assisted mechanical excavation has been considered as a promising rock breakage method and is widely studied in recent years. Heating characteristics of minerals are the basis of research on the weakening effect of microwave irradiation on rock. In this paper, 14 igneous rock-forming minerals were microwave heated. The influences of microwave power, mineral group/sub-group, element content and water on the heating characteristics of these minerals were analyzed. The results show that the microwave sensitivities of these minerals can be categorized into different levels according to their heating rates. As the microwave power increases, the microwave sensitivity of minerals remains unchanged. Mineral group has the greatest influence on their microwave sensitivities, followed by crystal structure and iron content. In addition, different kinds of water contained in minerals greatly influence their heating characteristics.

Influence of Power on Interplay of Microstructure and Erosion-Tribo Performance of Microwave Composite Clads

Abstract Metal matrix composite (MMC) clads were developed through microwave cladding technique on CA6NM substrate using different microwave power levels. The influence of microwave power was investigated on the microstructure, phase evolution, mechanical properties, and erosion-tribo performance of the clad layers. Increase in microwave power resulted in reduction of Cr7C3 phase in clad layers, which eventually decreases the fracture toughness and microhardness of the clad. Clad fabricated at 600 W exhibited highest fracture toughness (11.6 ± 0.58 MPa√m) and microhardness (949 ± 47.45 HV). All clads exhibited highest erosion at 60 deg indicating a mixed erosion mode. Clads fabricated at power levels beyond 600 W, with less Cr7C3 content exhibited severe carbide pullout, thus deteriorated the slurry erosion resistance of the clads.

Rapid microwave assisted derivatization of nitrofuran metabolites for analysis in shrimp by high performance liquid chromatography-fluorescence detector

A sensitive analytical method was proposed based on high-performance liquid chromatography with fluorescence detection coupled with microwave-assisted derivatization for the quantitative analysis of nitrofurans metabolites in shrimp samples. A novel derivatization reagent, 4-(acridone-10-yl)benzaldehyde, was synthesized and applied to the derivatization of several common nitrofurans metabolites (semicarbazide, 1-aminohydantoin, 3-amino-2-oxazolidinone, and 3-amino-morpholinomethyl-2-oxazolidinone). The influences of microwave power, irradiation time and temperature on the derivatization efficiency were investigated using Box-Behnken design. Moreover, microwave-assisted derivatization can obtain higher derivatization yields in a shorter period of time. Under the optimized conditions, the derivatization was achieved within 7.2 min. Lower limits of detection were obtained ranging from 0.20 to 0.28 μg/kg for all nitrofurans metabolites compounds. Satisfactory recoveries were obtained ranging from 90.5 to 103.6%. The developed method was successfully applied to the determination of four nitrofurans metabolites in shrimp. Furthermore, this developed method should offer great potential to the analysis of nitrofurans metabolites in foodstuffs.

Study the effect of microwave power and slices thickness on drying characteristics of potato

In the present work, the influence of microwave power and samples thickness on drying behavior, moisture diffusivity and energy consumption of potato slices was studied. The slices with thicknesses of 3.5, 5, 7 and 9 mm were dried as mono layers at four different power levels (200, 400, 600 and 800 W). The results showed that the process time was significantly (P < 0.05) decreased with increasing power and decreasing thickness. The curves of moisture removal rate included a short accelerating rate period at the beginning followed by a long falling rate period. Seven thin layer models were practiced to simulate the experimental drying kinetics and the Midilli model showed the best performance. The average values of effective moisture diffusivity were obtained to be in the range of 1.15510−8-6.654 × 10−8 m2 s−1, and increased significantly (P < 0.05) with both of the increasing microwave power and the samples thickness. The average activation energies changed from 1.423 W g−1 to 1.621 W g−1, and decreased with increasing samples thickness. Specific energy consumption for the process were ranged from 0.680 MJ kg−1water to 2.591 MJ kg−1water.