Microwave Heating Process Research Articles

COMSOL-Based Simulation of Microwave Heating of Al2O3/SiC Composites with Parameter Variations

The process of microwave heating involves the coupling of multiple physical phenomena, specifically including the distribution of the electromagnetic field in the resonant cavity. The electromagnetic effect generates heat and encourages the transfer of heat inside the material. In this numerical study, a 3D computer model of microwave heating of Al2O3/SiC composites using a multimode microwave heating chamber was established based on the simulation software COMSOL Multiphysics 5.6, and the symmetry treatment of the model was carried out, which effectively reduced the amount of model calculations and accurately analyzed the microwave heating characteristics of the samples. The analysis of the microwave heating characteristics of the sample was mainly preformed from the perspective of the electric field distribution in the resonant cavity, the sample heating rate and the sample heating uniformity, and then it was determined how the microwave source power and sample mold selection affect the temperature and electric field parameters of the sample. After experimental verification, the error between the simulation results and the temperature parameters obtained from the actual experiments is less than 2%. This study contributes to further understanding the heating behavior of Al2O3/SiC composites in complex multimode microwave heating environments and can be used to control the dynamic parameters during microwave heating in order to improve the heating rate and heating uniformity of samples.

Dynamic dielectric properties of biomass fractionation system using ethylene glycol

The unclear interaction between microwaves and reaction systems limits the further application of microwave in biomass fractionation. This article explored the main factors and their influencing mechanisms that affect biomass fractionation system’s dielectric properties at the frequency of 915 MHz. The experimental results shown that as the temperature of the system increases from 30 to 140 °C, its dielectric constant varies between 23 and 36, while the dielectric loss ranges from 10.5 to 17. The dielectric properties of the system can be influenced by its moisture content, biomass particle content, and ion concentration, except for the intermediate products formed during the biomass fractionation process. Based on the experimental data, empirical expressions for the dielectric constant and dielectric loss factors of biomass fractionation systems as a function of temperature was constructed with the correlation coefficients of 0.9779 and 0.9902, respectively. This study introduces a novel approach to explore the changes in dielectric properties of non-equilibrium systems. The findings of this study are highly significant for the design and optimization of microwave heating processes.

Control of Thermal Uniformity in Microwave Heating Process by BPNN and Adaptive Particle Swarm Optimization

As China advances its green economy, innovative methods are being employed to enhance energy optimization and conservation within energy-intensive industries. Among these methods, microwave heating stands out due to its superior heating efficiency and lack of pollution. Nonetheless, uniform heating remains a challenge because the microwave absorption capacity of the heated medium varies with changes in heating time and temperature. To address this issue, an Adaptive Particle Swarm Optimization (APSO) neural network microwave system based on the Back Propagation Neural Network (BPNN) is proposed. This system leverages the fundamental principles of Particle Swarm Optimization (PSO), categorizing particle swarms into three types and iterating them through distinct processes to achieve optimal results. An APSO controller is designed based on system identification, adjusting the controller parameters according to the error between the real-time system output and the identification model. The feedback error is used as the fitness function in the PSO algorithm, continuously adjusting the weights and thresholds of the neural network. This intelligent control approach optimizes the microwave oven's input power to minimize the error between the actual temperature output and the identified temperature. The APSO controller is designed based on system identification, with the intelligently controlled microwave heating system adjusting its input power to minimize the error between the identified and actual temperature outputs. Unlike traditional Proportional Integral Differential (PID) and BPNN controllers, this approach calculates the output of the identified model and the error of the actual model, feeding this information back to the controller. The feedback error serves as the fitness function in the PSO algorithm, enabling continuous adjustment of the network's weights and thresholds to regulate the microwave equipment's output power, thereby ensuring the output temperature closely follows the preset temperature curve. Experimental results demonstrate that the actual output value of the system closely aligns with the original preset temperature curve, with a root mean square error of only 0.74. This designed identification and control system effectively achieves the desired outcome.

Optimization of temperature uniformity for multi microwave source alternating heating based on superpermutation planning enhanced by Harris Hawks optimization

For the optimization of material temperature distribution during multi-source microwave heating processes, we propose utilizing the Harris Hawks Optimization Algorithm to enhance the alternating heating strategy among multiple waveguides with superpermutations. Firstly, we innovatively introduce the concept of superpermutations to assign character weights, which subsequently correlates the alternating sequences of different waveguides. Besides, we employ Hamiltonian path planning to determine the optimal order of waveguide alternation. Then, we apply the Harris Hawks Optimization Algorithm and improve the algorithm based on microwave heating evaluation criteria to optimize the strategy for waveguide alternation and enhance search performance. At last, experimental validation involves heating SiC materials in a microwave reactor to verify the credibility of physical experiments against the simulation model used. This analysis includes assessing temperature uniformity and energy conversion efficiency during the heating process, thereby demonstrating the effectiveness of the proposed heating strategy. The experimental results indicate that temperature uniformity improved by 37.75% to 80.25%, and energy conversion efficiency increased by 7.72%.

Recovery of NMC-lithium battery black mass by microwave heating processes

The exceptional microwave absorption capabilities of carbon-based materials make them highly effective for facilitating various chemical reactions, such as synthesis, reduction, exfoliation, doping, and decoration. In this study, we applied microwave irradiation to the thermochemical treatment of spent nickel manganese cobalt (NMC622) lithium-ion batteries, obtained as a mix of the cathode and the anodic graphite. This approach significantly accelerated the chemical reactions, leveraging carbon's robust ability to absorb microwave energy. As a proof-of-concept, we demonstrated that within just 5 min, the carbothermic reduction reactions in the black mass facilitated the formation of water-soluble Li2O, and enhanced the solubility of Co, Mn, and Ni in a weak acid. More than 90% of Li and 87% of Mn are recovered. This method, which bypasses the need for cathodic and anodic separation, presents a promising new approach for recovering strategic metals from spent lithium-ion batteries.

The combined effect of active packaging and relative phase sweeping on microwave heating performance in a dual-port solid-state system

The combined effect of active shielding packaging and relative phase sweeping on heating performance in a dual-port solid-state microwave heating process was evaluated. Four types of heating strategies that combine two factors (passive and active packaging and fixed and sweeping relative phase) were used in heating a tray of 300 g gellan gel sample for 3 min. The temperature distributions at the top and middle layers of the heated samples were collected and analyzed for heating uniformity index (HUI) and power absorption efficiency (PAE). The results showed that both active shielding package and relative phase sweeping can individually improve the HUI while maintaining high PAE. The packaging factor and relative phase factor showed a significant interaction effect (p = 0.0021) in influencing HUI but not PAE, highlighting the necessity of considering both factors (packaging and relative phase) when optimizing the microwave heating uniformity. The combination of active packaging and sweeping relative phase is a robust heating strategy that delivers the best heating performance that is significantly better than or similar to other combinations of packaging and relative phase strategies.

Numerical simulation of continuous microwave drying of rice grains

AbstractTo comprehensively understand temperature and moisture changes in a continuous microwave rice grain drying system, this study proposes a simulation strategy that facilitates the continuous movement of rice grains. The study establishes a three‐dimensional model concerning multiple physical fields, including electromagnetism, heat, and mass transfer. It examines the effects of rice grain layer thickness and microwave intensity on the moisture and temperature of rice grains. The results indicate that the drying rate is negatively correlated with material thickness but positively correlated with temperature. The optimal thickness for the rice grain layer is 8 mm. Furthermore, both the microwave drying rate and temperature increase with microwave intensity. These findings contribute to a deeper understanding of the hydrothermal change mechanisms in rice grains during microwave drying.Practical applicationsMicrowave drying, as an emergent drying technology, has garnered widespread attention for its selective heating, efficient drying, energy savings, and environmental protection. Nevertheless, enhancing uniformity during the microwave heating process constitutes an important research topic in scientific research and technological applications. Numerical simulation methods can visually analyze electric field distribution, thereby optimizing microwave heating uniformity and improving drying effects. This article aims to accurately predict the continuous microwave drying time of paddy and maximize energy usage by optimizing drying thickness and microwave power parameters establishing a mathematical model for the process. The study not only provides a solid theoretical basis for microwave dryer design but also scientifically guides the continuous microwave drying of rice and other food crops.

The Pin Structure Design of LaVAi-1.5-1400 Microwave Vertical Tubular Furnace Based on COMSOL

The microwave heating process will involve a variety of physical phenomena, including the distribution of the electromagnetic field in the heating cavity, the heat generated by electromagnetic loss, and the transfer of heat inside the material during heating. In this paper, the simulation software COMSOL Multiphysics 5.6 based on the finite element analysis method is used to establish the microwave heating model of Al2O3/SiC composites and design the pinning structure of the experimental furnace for multi-mode microwave heating. From the uniformity of microwave heating of the sample and the coupling with microwave, the heating characteristics of the sample with different pin spacing, pin radius, and pin insertion depth were simulated and analyzed. This pin structure design can be used to control the heating conditions of Al2O3/SiC composites in microwave heating ovens to meet industrial requirements.

Optimization of heating temperature uniformity for multi-microwave source group based on dynamic switching topology

Aiming at the mutual coupling of multiple physical fields in the microwave heating process and the generation of thermal runaway phenomenon, in this paper, a cooperative variable power heating strategy with multi-microwave source clusters under dynamic switching topology is proposed in order to improve the temperature uniformity. Firstly, an algebraic graph theory is used to establish a communication topology for complete information transfer, which is used to construct a distributed structure among multiple microwave source intelligences. Secondly, the dynamic topology switching algorithm under event triggering is introduced, and the real-time temperature distribution of the heated materials is considered to achieve the dynamic switching of the topology connection mode between microwave source clusters in order to synchronously coordinate the power consistency output between different clusters. On this basis, a numerical calculation model is constructed to solve the mixed optimization of integer and continuum variables by means of the finite element method. Finally, the effectiveness of the heating strategy to improve temperature uniformity is verified by microwave heating SiC media simulation calculation. The numerical calculation results show that the temperature uniformity indexes are improved by 34.1%–50.4% and 28.1%–55.2% in each horizontal and vertical section for single materials, and by 59.1%–59.7% and 46.5%–63.4% in each horizontal and vertical section for multi-materials, respectively, in comparison with the general heating method. This strategy effectively avoids the residence of hot and cold spots in the material, which in turn optimizes the temperature distribution.

Analysis of microwave heating of copper powder compacts

The influence of the native oxide films, which is essential for the understanding of the microwave heating of metal powder, is analyzed numerically based on the experimental data on temperature, dilatation and resistance of compacted copper powder samples. The indicative thickness of the oxide films, determined from the resistivity data using an effective medium approximation, is shown to decrease from ≥1 μm to below 1 nm. The effective complex dielectric permittivity and magnetic permeability of the copper powder with oxide films on the particles are calculated within the recently developed models. The dielectric permittivity exhibits a percolation behavior in the temperature range of the oxide decomposition, viz. 210–250 °C when microwave heating is carried out in nitrogen and 330–375 °C – in argon. The efficiency of absorption of the incident 30 GHz microwave radiation in a slab of powder is assessed separately for the electric and magnetic-type losses, the contribution of the latter being predominant until the percolation transition. The energy flux density of the incident microwave radiation required to sustain the prescribed heating rate is shown to increase during the microwave heating process from ∼20 W/cm2 to >1 kW/cm2 due to increasing reflection. The additional microwave energy input required for the completion of the endothermic oxide decomposition reaction is shown to be significant at the initial stage of the process (below 200 °C).

Rational development of semiconductor-based electrocatalyst and its electrochemical activity for ethanol oxidation as an assisted reaction for water splitting

Implementation of semiconductor-based nanocomposites for emerging technologies has been gaining exponential interest due to their unique physical, chemical, and electrochemical properties. Nonetheless, challenges still exist in developing active and stable materials to produce high-value-added electrocatalytic platforms for energy conversion applications. This work proposes the synthesis of a composite material comprising ZnO and Cu2O modified with SrSO4 by using the fast and versatile microwave heating process as feasible electrocatalysts for ethanol-assisted water electrolysis. The obtained composite was characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (FESEM-EDS), Thermogravimetric Analysis (TGA), Fourier Transform Infrared (FTIR), and Raman spectroscopies. Electrochemical features were assessed by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The XRD results clearly show that composite material has reflections corresponding to the ZnO, Cu2O, and SrSO4, while the FESEM-EDS analysis reveals the presence of the desired chemical elements. The fabricated ZnO–SrSO4–Cu2O composite was electrochemically characterized to determine its potential as a catalyst for the ethanol oxidation reaction (EOR). The results unveil that the electroactivity of the composite is mainly attributed to the presence of Cu species and the synergistic effect of ZnO and SrSO4 compounds. In this way, this work proposes a novel via of fabricating active semiconductive electrocatalysts for the hybrid water electrolysis in the presence of the EOR. However, we believe this kind of material can be adopted in other applications such as sensors and energy storage devices.

Study on the properties of nano-Fe3O4 modified asphalt materials based on molecular dynamics

Asphalt possesses the inherent ability to self-heal microcracks, with enhanced healing observed under active heating conditions. Nanomaterials have the capacity to alter the microstructure of asphalt blends, offering certain advantages in terms of asphalt performance. In this study, models of nano-Fe3O4 clusters and nano-Fe3O4/asphalt blending systems with varying particle sizes were established. Molecular dynamics simulations were employed to investigate the physical properties of nano-Fe3O4 and asphalt molecules at different temperatures, simulating the microwave heating process within a temperature range of 303 K to 373 K. The findings revealed that the diffusion coefficient of Fe3O4 clusters decreased with increasing particle size. Nonbonding interaction energy predominantly governed the binding between Fe3O4 clusters and asphalt molecules. The incorporation of nano-Fe3O4 was found to enhance the physical properties of asphalt. Peak values of the radius of gyration for asphaltene and aromatics indicated increased density, while asphaltene, colloids, and aromatics exhibited greater extensibility with the addition of nano-Fe3O4.

Identification of turntable function in a solid-state microwave heating process with diverse frequency-shifting strategies applied

The turntable has been used in conventional magnetron-based microwave ovens to improve the heating uniformity. Meanwhile, with the emerging solid-state technique, well-designed frequency-shifting strategies also show promise in achieving improved microwave outcomes without a rotating turntable. This study used modeling tools to comprehensively assess the turntable function under various conditions, where the affecting factors included vertical and horizontal positions of food, rotation status of the turntable, frequency-shifting strategy, and food configurations. Results illustrated that the elevation of food by the turntable is more critical to power efficiency and heating uniformity, while rotation mainly works to narrow the temperature difference between hot and cold spots. Moreover, the complementary-shifting strategy lessened the rotation function of the turntable. Hence, in a solid-state microwave system embedded with a proper frequency-shifting strategy, a simpler supporting component shall replace the current rotating turntable, streamlining the oven design without compromising the microwave performance. Industrial relevanceThis study comprehensively evaluated functions of the turntable, a conventional component, inside a novel microwave system design utilizing solid-state instead of the magnetron as its power source. Based on the evaluation, the well-implemented frequency strategies hold promise to achieve improved microwave performance with a simpler supporting component to elevate the food, rather than relying on a rotating turntable. These findings provide novel insights for designing the next-generation microwave ovens.

Incorporation of eggshell waste in the preparation of carbon quantum dot nanoprobes for the determination of COVID-19 antiviral drug; molnupiravir

New carbon quantum dots (CQDs) with multi-doped elements from eggshell biomass waste have been employed as a direct, fast, green, and selective probe for the fluorometric determination of molnupiravir, a COVID-19 antiviral drug. For the first time, the eggshell@CQDs were prepared through a simple, single-step microwave heating process that only took 90 s. Upon excitation at λex 340 nm, the resulting CQDs exhibited a maximum bluish fluorescence emission at λem 408 nm. Molnupiravir was found to quench the native fluorescence of the prepared CQDs in a quantitative manner, based on a static mechanism by forming a non-emissive complex. The spectrofluorometric method designed for molnupiravir detection was validated per the International Council for Harmonization (ICH) requirements. The proposed fluorescent probe showed good linearity for molnupiravir detection over a range of 2.5–70 µg/mL, with percent recoveries ranging from 99.53 % to 101.79 % and %RSD (relative standard deviation) less than 1 %. The eggshell@CQDs were successfully employed to determine molnupiravir levels in marketed hard capsules, yielding good percent recoveries and repeatability. The developed approach was found to be greener than the published HPLC/UV approach, as assessed by the analytical eco-scale, green analytical procedure index (GAPI), and analytical greenness metric approach (AGREE). Furthermore, this approach highlights the potential of synthesizing CQDs from natural biomass, specifically low-value biomass waste such as eggshells.

Influence of microwave irradiation and water-based cooling on the fracturing behavior and failure mode transition of CSTBD granite

Utilizing microwave heating in conjunction with water-based cooling technology can effectively reduce the fracture toughness of hard rocks. However, the fracturing characteristics and failure modes of hard rocks following microwave heating and water-based cooling remain undisclosed. Granite, being one of the most common types of hard rocks, was selected for this study, employing Cracked Straight Through Brazilian Disc (CSTBD) specimens for laboratory testing. CSTBD specimens with various crack angles (0, 30, 60, and 90°) underwent treatment with varying microwave durations (30, 60, 180, 300, and 420 s). Subsequently, Brazilian splitting tests were conducted on the damaged specimens. To simulate the entire process of microwave heating and mechanical testing of CSTBD specimens, we developed a coupled Finite Element Method – Distinct Lattice Spring Model (FEM-DLSM) approach. The results indicate that microwave heating with water-based cooling significantly influences the fracture toughness of CSTBD granite. Mode-I fracture toughness decreases with microwave heating temperature at a low crack angle (pure tensile failure and tensile–shear mixed failure) and increases at a high crack angle (compressive–shear failure and compressive failure). Mode II fracture toughness decreases with microwave heating temperature at any crack angle. Microwave heating with water-based cooling causes a decrease in the transition angles from tensile–shear failure to compressive–shear failure and from compressive–shear failure to compressive failure. Thermally induced microcracks in the rock specimen are responsible for changes in fracture toughness and failure mode transitions. After microwave heating and water-based cooling, numerous microcracks are induced in the rock interior. While macroscopic cracks predominantly control failure, growing microcracks, by weakening the rock matrix, shift the initiation position of the failure crack from the tip of the macroscopic crack to other positions, following the principle of the weakest failure path.

Microwave-assisted synthesis of Co-free Li[Li0.2Ni0.2Mn0.6]O2 cathodes with a spinel-layered coherent structure for high-power Li-ion batteries.

Li- and Mn-rich layered oxides (LMLOs) are regarded as the most promising cathode materials for Li-ion batteries (LIBs), but they suffer from poor rate capability. Herein, a promising and practical method (i.e. a hydroxide coprecipitation method in combination with a microwave heating process) is developed to controllably synthesize cobalt-free Li[Li0.2Ni0.2Mn0.6]O2 with a layered/spinel heterostructure (LLNMO-LS). The cathode made of the LLNMO-LS delivers an excellent electrochemical performance, demonstrating a discharge capacity of 147 mA h g-1 at 10C.

Modern methods for solving partial differential equations of parabolic type and their mathematical theoretical foundations

Abstract In this paper, the existence problem of weak solutions in partial differential equations is first discussed. Secondly, the parabolic-type partial differential equation (PDE) model with non-chiral terms is used to portray the coupling principle of microwave heating dielectric medium, and the approximate models of TEM and TE10-wave microwave heating are constructed and verified by comparing with the COMSOL model in simulation. An open-loop type iterative learning control algorithm is proposed for the distributed parameter system, and the effectiveness of the control algorithm proposed in this paper is theoretically demonstrated. It is concluded that the TEM and TE10-wave microwave heating approximation models are more successful in describing the microwave heating process than the COMSOL model, and the consistency of the simulation results fully proves the correctness and effectiveness of the proposed model. The paradigm of the system output error decreases with the increase in the number of system runs, and the paradigm of the system output error tends to be close to zero.

Modulasi Kadar Pati Resisten Berbagai Pangan Karbohidrat melalui Pemanasan Microwave: Meta-Analisis

Starch is extensively utilized in food processing for various purposes. However, the use of native starch is limited due to its unsuitability with processing conditions or products characteristics. Physical modification of starch is commonly employed to enhance the properties of native starch. The physical starch modification using microwave heating is presently developed due to its more efficient energy consumption than that of traditional heating methods. The process of microwave heating followed by cooling has been found to induce the formation of type 3 resistant starch (RS3). However, the effects of microwaving heating towards the the increase of resistant starch contents varies among researchers. For this reason, a meta-analysis was conducted to evaluate the effect of microwave heating on the levels of resistant starch in carbohydrate sources such as cereals, pulses, and tubers. The objective of this study was to analyze the carbohydrate food groups that demonstrated the most significant increase in resistant starch levels due to microwave heating, and to determine the optimal microwave treatment parameters within these food groups using meta-analysis. The findings indicate that microwave heating treatment is particularly effective for cereals, with rice being the most responsive. The most favorable treatment parameters include a power range of 401-600 W, heating time of 60-99 s, and starch moisture content of 40-60%.

Investigating the efficiency of the microwave heating process for the carbothermic synthesis of cobalt/nickel alloys

High energy consumption and its associated pollution fare among the significant issues of metal production systems. Traditional furnaces currently used in the production of alloys. The microwave heating process is a novel approach with numerous advantages compared to the conventional heating processes. On the other hand, cobalt/nickel alloy, is an important alloy with extensive applications in jet engines, gas turbines, and petroleum refining. The present research addressed the efficiency of the microwave heating process for the carbothermic synthesis of cobalt/nickel alloys. Moreover, the morphology of the produced material was evaluated. The synthesis method was based on the reduction of cobalt/nickel oxides to cobalt/ nickel alloys. Two parameters of the reaction time and the composition of the granules containing cobalt/nickel oxides were investigated to assess the efficiency of the reduction process. The results showed a decrease in the oxygen content from 20 to about 10 wt% by prolonging the processing time from 10 to 20 min. XRD analysis also indicated no crystal structure related to nickel oxide in the samples processed for 20 min. The diameter of the crystals also increased by about 71 % by prolonging the reaction time from 10 to 20 min, suggesting the growth of the crystals and enhanced adhesion of the particles. The number of oxygen atoms was also decreased by about 50 % upon increasing the reaction time from 10 to 20 min, indicating a better reduction reaction. A rise in the nickel oxide content in the raw granule from 30 % to 60 %, led to a 3.8-fold enhancement in the number of oxygen atoms in the reduced product.

An integrated numerical and analytical model to understand the effect of relative phase in a dual-port solid-state microwave heating process

The utilization of multi-port solid-state microwave heating systems presents promise in improving heating performance but lacks a deep understanding of the effect of source phase difference. This study developed an integrated numerical and analytical approach that allows efficient modeling and a better understanding of multi-mode wave interactions with source phase differences. First, two numerical models simulated the complex electric fields of individual-port microwave heating processes. The simulated nodal electric fields were used as inputs in the analytical model to predict the resultant power dissipation for dual-port heating with arbitrary source phase differences. The integrated approach was validated by comparing the predicted nodal electric field and power densities with numerical modeling results. The phase-dependent nodal and volumetric average power revealed wave-like patterns with great variances. The constructive, destructive, and interference effects were influenced by the source phase differences, emphasizing the importance of proper control of source phases for efficient and uniform heating.