Modeling Of Microwave Heating Research Articles

A Fully Coupled Electromagnetic Irradiation, Heat and Mass Transfer Model of Microwave Heating on Concrete

Due to the potential for significant process benefit, microwave assisted concrete recycling is highlighted by many scholars and engineers over the world recently. In this paper, a multi-field model is established to simulate the microwave heating process of concrete specimen with single-particle aggregate by using of COMSOL Multiphysics. The validation of this model is verified by comparison with temperature from experiment. Mechanical properties of aggregate-mortar interface during microwave heating process was experimentally investigated. Electric, temperature, stress field evolution and moisture transformation during microwave heating process are discussed in detail. Temperature and stress gradient at mortar-aggregate interface influenced by microwave heating power, frequency and duration are analyzed and graphically presented, which are the dominant factors to achieve the interface debonding. Based on the comparison between concrete absorbed energy and temperature variation, energy efficiency for microwave heating concrete is also briefly discussed. Results of this investigation could provide a multi-field understanding for the microwave treatment on concrete.

Design of Microwave Directional Heating System Based on Phased-Array Antenna

Microwave selective/localized heating has been widely used in special areas, e.g., medical treatment and food processing, but the control of selective/localized heating in restricted space, e.g., microwave ovens, is difficult to accomplish. In this article, a Giuseppe Peano fractal phased-array antenna is designed, and the phase of each radiator is derived to achieve the arbitrary spatial division of the electromagnetic field in a cavity based on the superposition principle of waves. Then, a multiphysics model of microwave heating is established by coupling the electromagnetic field and heat transfer to simulate the directional control of microwave heating in a cavity. An experimental system is built, and the heating results are measured using an infrared thermal imager to verify the temperature distribution in different spatial regions. Finally, the feasibility of the model for different heating targets is discussed.

Numerical modelling and investigation of microwave heating and boiling phenomena in binary liquid mixtures using OpenFOAM

To understand Microwave (MW) heating and boiling of binary liquid mixtures, a new multiphysics model was developed. The new model solves Maxwell's equations for the electromagnetic field distribution. Concerning the coupled dispersed and segregated vapor-liquid flow during MW boiling, it was modelled based on a hybrid Two-Fluid-Volume-of-Fluid method. As for the modelling of heat and mass transfer, Two-fluid energy and species conservation equations were solved, with new dispersed and segregated interphase heat and mass transfer closures formulated using appropriate interface jump conditions combined with vapor-liquid equilibrium relations. The new model showed reasonably good agreement with the experimental data. The capability of the model to simulate MW heating, superheating, superboiling, and interphase transfer phenomena in methanol-water mixture (heated in a multi-mode MW cavity) was demonstrated, and the associated physics was investigated. The simulation results revealed three underlying mechanisms that lead to superheating (up to 9.5°C at 300 W) in binary mixtures, namely limited bubble nucleation, inefficient mixing, and higher interfacial saturation temperature compared to that in bulk liquid (about 2°Chigher). Besides, the results also showed that the increase of heating time mainly increases the amount of superheat rather than the superheat temperature. It was also found that MW superheating tends to reduce the mass fraction of the lighter component in the released vapor (by up to 2%). In the subsequent study, the effects of several operating conditions were examined. The simulation results generally showed that higher liquid methanol concentration, higher MW power, rectangular sample geometry, and smaller sample volume lead to higher superheat intensity, but poorer methanol concentration in the vapor released. The new model and findings could open up new avenues for the design and improvement of processes such as MW-assisted synthesis, extraction, biodiesel production, and distillation.

Multiscale modeling of microwave-heated multiphase systems

Modeling of microwave heating of multiphase systems requires resolving the electromagnetic field from the single particle to the entire cavity. We introduce a multiscale methodology for computationally affordable simulations of microwave heating of multiphase systems consisting of one phase dispersed in a continuum phase. The methodology homogenizes the original multiphase system, by taking advantage of the large separation of length scales, to calculate the effective permittivity, effective thermal conductivity, and volumetric power absorbed in each phase. The methodology is rigorously assessed against particle-resolved detailed numerical simulations of model systems. We demonstrate a significant reduction in computational cost while retaining the accuracy of detailed simulations. The present methodology enables high throughput exploration of novel multiphase system designs utilizing microwave heating.

ЭЛЕКТРОМАГНИТНАЯ СУШКА ВЛАЖНЫХ МАТЕРИАЛОВ С МАЛОЙ ГЛУБИНОЙ ПРОНИКНОВЕНИЯ СВЧ-ИЗЛУЧЕНИЯ В УСЛОВИЯХ ТЕПЛОСБРОСА РАДИАЦИЕЙ И КОНВЕКЦИЕЙ. III. СТАДИЯ ПАДАЮЩЕЙ СКОРОСТИ СУШКИ

Актуальность исследованияпродиктована необходимостью разработки математических моделей СВЧ-нагрева и МВ-сушки влажных материалов для получения технологически оптимальных и экономически выгодных режимов. Настоящая публикация является продолжением статей тех же авторов в «Известия Томского политехнического университета. Инжиниринг георесурсов», в которой с помощью математического моделирования подробно был изучен процесс на первой и второй стадиях сушки – стадии прогрева, когда теплообмен между поверхностью влажного тела и окружающей средой осуществляется за счет радиации и конвекции, а СВЧ-энергия поглощается поверхностным слоем из-за малой её глубины проникновения, а также стадии постоянной скорости сушки. Построены асимптотические решения этой нелинейной задачи для малых и больших значений безразмерного времени, востребованные инженерной практикой, как для параметрического анализа, так и для проведения оперативных расчетов. Подход, связанный с рассмотрением третьей стадии – стадии падающей скорости сушки, основан на установлении базового уравнения сушки, которое обеспечивает взаимосвязь между теплообменом и влагообменом с помощью критерия Ребиндера. Цель: постановка задачитретьего этапа СВЧ-сушки влажного материала – этапа падающей скорости сушки– и реализация теоретического решения по определению распределения температурного поля по толщине слоя ивеличины скорости сушки. Объектом исследования является плоский слойвлажного материала – уголь, песок,древесина и др. капиллярно-пористые массивы, на которые воздействует СВЧ-излучение. Такие материалы обладают высокой диэлектрической проницаемостью и как следствие весьма эффективно поглощают СВЧ-излучение, которое почти на 100 % преобразуется в тепловую энергию. Методы исследованиясвязаны с математическим моделированием, в основе которых лежат уравнения электродинамики Максвелла и тепловлагопереноса А.В. Лыкова. В данной статье при оценке параметров тепловлагопереноса учет теплообмена ведется более детально, нежели массообмена. Также одной из особенностей данной задачи электромагнитной сушкиявляется рассмотрение материалов с малой глубиной поглощения, в силу чего в системе уравнений для нагрева источниковый член находится в граничном условии. В результате исследованийбыли определены температура и влагосодержание подсушиваемого тела в режиме падающей скорости сушки, получены расчетные соотношения аналитического характера для малых и больших параметров времени.

ЭЛЕКТРОМАГНИТНАЯ СУШКА ВЛАЖНЫХ МАТЕРИАЛОВ С МАЛОЙ ГЛУБИНОЙ ПРОНИКНОВЕНИЯ СВЧ-ИЗЛУЧЕНИЯ В УСЛОВИЯХ ТЕПЛОСБРОСА РАДИАЦИЕЙ И КОНВЕКЦИЕЙ. I. СТАДИЯ ПРОГРЕВА

Актуальность исследования продиктована необходимостью разработки математических моделей СВЧ-нагрева и МВ-сушки влажных материалов для получения технологически оптимальных и экономически выгодных режимов. В силу сложности и нелинейности протекающих процессов внутри влажных материалов при СВЧ-обработке чрезвычайно важно построение моделей, которые давали бы возможность построения аналитически приближенных решений с целью нахождения на их основе главных закономерностей и характерных особенностей рассматриваемых процессов. Цель: постановка первого этапа задачи СВЧ-сушки влажного материала – этапа прогрева. Поиск аналитического решения для температуры слоя в разные моменты времени позволяет определить начало следующего этапа – сушки. Объектом исследования является плоский слой влажного материала – уголь, песок, древесина и др. капиллярно-пористые массивы, на которые воздействует СВЧ-излучение. Такие материалы обладают высокой диэлектрической проницаемостью и как следствие весьма эффективно поглощают СВЧ-излучение, которое почти на 100 % преобразуется в тепловую энергию. Методы исследования связаны с математическим моделированием, в основе которого лежат уравнения электродинамики Максвелла и тепловлагопереноса А.В. Лыкова. В данной статье задача Максвелла решена независимо от задачи тепломассопереноса, поэтому плотность потока поглощенного СВЧ-излучения считается известной. Также одной из особенностей данной задачи является рассмотрение материалов с малой глубиной поглощения, в силу чего в системе уравнений для нагрева источниковый член находится в граничном условии. В результате исследования с помощью асимптотических процедур решена задача тепловлагопереноса при заданной мощности источника тепла. Получены приближенно-аналитические решения для первой из трех характерных стадий СВЧ-сушки в условиях малой глубины проникновения микроволн: стадии прогрева влажного материала. Выполнен анализ построенных решений.

3D numerical modelling of microwave heating of SiC susceptor

Microwave processing has been gaining popularity owing to its energy saving characteristics which is majorly assisted by using susceptors like SiC. It is imperative to simulate the heating of SiC susceptor to understand its role in the microwave heating process. In this work, finite element simulations are used to predict and analyse microwave heating of SiC cylinders. The effects of varying microwave power and dimension of SiC on heating of SiC are investigated. The value of temperature of SiC observed through COMSOL simulation is validated with experimental results.

The Regularity of Solution for Weakly Coupled System Derived by Microwave Heating Model

In this paper, we study the regularity of the weak solution of the coupled system derived from the microwave heating model with frequency variable. We first show that the weak solution E of the system is Hölder continuous near the boundary of S = ∂ Ω . The main idea of the proof is based on the estimation of linear degenerate system in Campanato space. Then we show that the solution u of the heat conduction equation is Hölder continuous with exponent α 2 . Finally, under the appropriate conditions we show that the coupled system with microwave heating has a weak solution. Moreover the regularity of the weak solution is studied.

Existence of solution of a microwave heating model and associated optimal frequency control problems

Microwave heating has been widely used in various fields during recent years. However, it also has a common problem of uneven heating. In this paper, optimal frequency control problem for microwave heating process is considered. The cost function is defined such that the temperature profile at the final stage has a relative uniform distribution in the field. The controlled system is a coupled by Maxwell equations with nonlinear heating equation. The existence of a weak solution for coupled system is proved. The weak continuity of the solution operator is also shown. Moreover, the existence of a global minimizer of the optimal frequency control problems is proved.

Numerical analysis and optimization of the microwave inductive heating performance of water film

This paper focuses on the influence of various design parameters on microwave heating performance by coupling of the electromagnetic and the heat transfer equations by COMSOL Multiphysics software. The coupled model of microwave heating is numerically implemented using a finite element method and validated by comparison with previous experimental results. Results indicate that samples with different permittivities show different temperature rise. With some design parametric variations such as cavity shape, waveguide location, loading sample position and so on, the heating effects which are the energy utilization and temperature distribution exhibit sensitively. The results show that with the waveguide location changing with axial direction of cavity, the heating performance will fluctuate not monotonically while repeating, which means the optimal waveguide location is not unique. Furthermore, when the loading samples situate off the center of cavity, the heating effect is even better. Since previous studies barely paid attention to the structure design of cavity and inside vessel, this work concentrates on specific cavity and heating equipment which in turn fills design rules of microwave heating process and offers guidance for the design and scaling-up of microwave applicator.

Study of microwave heating of reference liquids in a coaxial waveguide reactor using the experimental, semi-analytical and numerical means

In this work, a new application of coaxial waveguides for microwave heating of individual liquid substances and reaction mixtures is considered. The studied reactor is a small hollow coaxial waveguide in which liquids (methanol or ethanol) are exposed to microwaves generated by a miniature semiconductor source of 2.45-GHz frequency. The temperature of a liquid in the coaxial chamber is measured using an IR temperature sensor, thermocouple and optic fiber probes through non-radiating (in microwave range) openings in the thick copper reactor's wall, with the satisfactory accord between their readings at the medium-level power (10 W). The dynamics of microwave heating is studied using the semi-analytical and numerical simulations, which prove to be in good agreement with the experimental data. Two semi-analytical models of microwave heating in the coaxial waveguide as particular cases of the general electromagnetic-thermal problem are developed. One of them is the lumped system model in which uniformity of the temperature field is assumed. It gives good agreement with the measurements and is physically justified at late heating times. Another one is a simplified non-uniform heating model which is based on consideration of a convective turbulent boundary layer in a short horizontal coaxial waveguide. This model furnishes a quantitative explanation of the measured temperature difference at opposite ends of this waveguide over the entire heating period. The results of this study are interesting for development of miniature reactors for on-demand chemistry and pharmacy.

A fully coupled electromagnetic, heat transfer and multiphase porous media model for microwave heating of coal

Microwave heating has gained widespread popularity in coal processing. Numerical simulation is a promising tool to visualize and quantize microwave-coal interactions. However, coal is always assumed as a solid continuum in the current models, which cannot accurately predict the thermodynamic behavior. In this study, a fully coupled electromagnetic, heat transfer and multiphase porous media model was developed to investigate microwave heating of coal. Results show that microwave absorption by coal induces significant redistribution of the electromagnetic field in the cavity, forming high- and low-energy regions. The nonuniform electromagnetic distribution and microwave selective heating generate hot and cold spots, whereas heat convection tends to homogenize the thermal field. The temperature rise during microwave heating is characterized by “fast-slow-fast”. In addition, water evaporation and surface heat convection can exert profound impacts on the thermal evolution of coal. When water evaporation is included in the model, the temperature increases nonlinearly because the dielectric property of coal is constantly changing during microwave heating. Outcomes of this study can be used to identify the heating behaviors of coal during microwave processing and thereby help to optimize the microwave applicators.

Laboratory and Numerical Investigation of Microwave Heating Properties of Asphalt Mixture.

Microwave heating is an encouraging heating technology for the maintenance, recycling, and deicing of asphalt pavement. To investigate the microwave heating properties of asphalt mixture, laboratory tests and numerical simulations were done and compared. Two types of Stone Mastic Asphalt (SMA) mixture samples (with basalt aggregates and steel slag aggregates) were heated using a microwave oven for different times. Numerical simulation models of microwave heating of asphalt mixture were developed with finite element software COMSOL Multiphysics. The main thermal and electromagnetic properties of asphalt mixture, served as the model input parameters, were measured through a series of laboratory tests. Both laboratory-measured and numerical simulated surface temperatures were recorded and analyzed. Results show that the replacement of basalt aggregates with steel slag aggregates can significantly increase the microwave heating efficiency of asphalt mixture. Numerical simulation results have a good correlation with laboratory test results. It is feasible to use the developed model coupling electromagnetic waves with heat transfer to simulate the microwave heating process of asphalt mixture.

Numerical modelling of microwave heating of a porous catalyst bed

A Multiphysics numerical model was developed using COMSOL Multiphysics to study the effect of size, shape and position of catalyst bed within the microwave reactor (2450 MHz). The dielectric properties of HZSM-5 catalyst were measured at different frequencies and nine different temperatures ranging from 25 °C to 370 °C. The heat transfer in porous media was coupled with RF electromagnetics module and flow-through porous media by extracting the heat source term Q for the heat transfer problem from the electromagnetics. A solid-fluid thermal non-equilibrium condition was modelled as the heat is generated within the catalyst. It was observed that sample position, shape and size of the sample, all significantly affect the heating profile and temperature gradient inside the porous media. The experimental results and the predicted temperatures were in good agreement. Microwave heating had higher total internal energy but conventional heating had lower temperature gradient after reaching steady state. Brick-shaped sample heats more uniformly compared to cylindrical sample. If the radius of the sample is decreased, while maintaining the volume of the sample, microwaves penetrate deeper inside the sample, and more uniform temperature distribution is observed throughout the length of the sample.

Comparison between Lambert and Maxwell Approaches in the Modelling of Microwave Heating of Liquid Foods

Microwave heating of liquid foods in laminar flow through a circular tube has been modeled. In particular, skim milk as a Newtonian fluid and apple sauce and tomato sauce as non-Newtonian fluids have been considered. The temperature profiles have been obtained solving the motion and energy equations in transient regime and Maxwell’s equations in the frequency domain. Numerical resolution of Finite Element Method has been implemented in Comsol Multiphysics. The generation term due to the microwave heating has been evaluated according both to Lambert’s law and Poynting theorem. Finally, a comparison between the two methods has been made in order to check to what extent the results obtained with the simpler Lambert’s law approximation are comparable with those deriving from the exact solution of Maxwell equations. Dielectric properties are considered to be temperature dependent.

Numerical Estimation of Agricultural Raised Bed Microwave Disinfection

AbstractThe use of electromagnetic fields to solve issues related to agriculture is an interesting, cost‐effective, and eco‐friendly possibility to be explored. One of the most promising applications is the disinfection of soils obtained by microwave‐induced heating. This work deals with the nonlinear computational modeling of such microwave heating of soils in metal raised bed cultivations within a greenhouse. By modeling the dielectric properties of soil, in terms of composition, moisture content, and actual temperature, and accounting for the exact thermal and electromagnetic conditions in raised beds inside the greenhouse, several realistic and nonlinear multiphysics simulations were carried out. The disinfection is directed to fungi, such as Sclerotium rolfsii, and weeds, for example, ryegrass and fleabane. The effectiveness of the proposed procedure is quantified and critically discussed exploiting analytical thermal death kinetics of soilborne plant pathogens and compared to the solarization technique.

A Fully Coupled Numerical Model for Microwave Heating Enhanced Shale Gas Recovery

Formation heat treatment (FHT) can be achieved by converting electromagnetic energy into heat energy (that is microwave heating or MWH). Experimental evidence shows that such FHT can significantly enhance oil and gas recovery. As relatively few research studies have been reported on microwave heating enhanced shale gas recovery (MWH-EGR), a fully coupled electromagnetic-thermo-hydro-mechanical (ETHM) model is developed for the MWH-EGR in the present study. In the ETHM model, a thermal-induced gas adsorption model is firstly proposed for shale gas adsorption and fitted by experimental data. This thermal-induced adsorption model considers the increase of matrix pore space due to the desorption of the adsorbed phase. Further, a thermal-induced fracture model in shale matrix is established and fitted by experimental data. Finally, this ETHM model is applied to a fractured shale gas reservoir to simulate gas production. Numerical results indicated that the thermal-induced fracturing and gas desorption make predominant contributions to the evolution of matrix porosity. The MWH can increase cumulative gas production by 44.9% after 31.7 years through promoting gas desorption and matrix diffusion. These outcomes can provide effective insights into shale gas recovery enhancement by microwave assistance.

A coupled electromagnetic irradiation, heat and mass transfer model for microwave heating and its numerical simulation on coal

As hydraulic fracturing as a means to enhance coal bed methane was banned in some countries due to possible negative environmental impacts, the microwave heating was proposed as an alternative approach to enhance coal permeability and thus gas productivity. One of the mechanisms on improving coal permeability using microwave irradiation is that thermal stress caused by microwave heating generates fractures. To study the influence of microwave settings to the heating effect of coal samples, a coupled mathematical model for electromagnetic, heat and mass transfer in the process of microwave heating is proposed and is numerically implemented using a finite element method. This coupled model for microwave heating have considered heat and mass transfer, and is validated by comparison with experimental results. Then it is used to simulate the influence of frequency, power and moisture capacity on microwave heating. The simulation results show that microwave heating of coal is highly sensitive to excitation frequency. Frequencies around 3.45 GHz contribute to significant thermal heterogeneity. With the same energy input, different powers do not influence the overall heating effect, but higher powers cause greater thermal heterogeneity. Moisture capacity also has great effect on microwave heating and thermal distribution pattern. Under 2.45 GHz and 1.0 kW, the coal sample with moisture capacity of 5% has the best microwave heating effect.

Experimental characterization and modeling of microwave heating of oil palm kernels, mesocarps, and empty fruit bunches

ABSTRACTThe current work investigates the microwave heating and drying behavior of oil palm fresh fruits and bunches. Dielectric, thermal, and mechanical properties of oil palm kernels (OPKs), mesocarps, and empty fruit bunches (EFBs) were determined. New empirical models of the dielectric constant, loss factor, elastic modulus, and yield stress as functions of moisture content were obtained for OPKs, mesocarps, and EFBs. The thermal conductivity of the mesocarps and EFBs was 0.458 and 0.0285 W/(m K), respectively. Thermal analyses showed that decomposition of OPKs, mesocarps, and EFBs started when the temperature exceeded 100°C. Multiphysics models that consider electromagnetic waves, moisture, and heat conservation as well as material deformation were developed for OPKs, mesocarps, and EFBs. The simulation results show that an EFB sample with high moisture content generated a high moisture gradient during heating, causing high stress that exceeded its yield stress. However, this effect occurred only during the initial heating. Our results show that microwave heating can aid the detachment of oil palm fruit from bunches before EFBs harden because of moisture loss.

Receding horizon H∞ guaranteed cost tracking control for microwave heating medium with temperature-dependent permittivity

This paper considers the temperature spectrum tracking control of microwave heating model, in the presence of asymmetrical input saturation, nonhomogeneous Neumann boundary condition and temperature-dependent permittivity. The sufficient condition for the existence of receding horizon H∞ guaranteed cost control is proposed based on the derived finite-dimensional ordinary differential equation (ODE) error model. Furthermore, by on-line updating and solving linear matrix inequalities (LMIs) optimization problem, the constrained tracking controller can be obtained in the sense of minimizing H∞ norm and satisfying the quadratic cost performance. The proposed control strategy is implemented on a one-dimensional cavity heating model and its performance is evaluated through the simulation.