Fully coupled CEM/CFD modelling of microwave heating in a porous medium

Computational results for the microwave heating of a porous material are presented in this paper. Coupled finite difference time domain and finite volume methods are used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. These equations are nonlinearly coupled through the dielectric properties which depend both on temperature and moisture content. By investigating the resonant behaviour in two-dimensional microwave cavities, the FD-TD scheme is validated. Validation of the microwave power distribution in 3-D microwave enclosures is compared with other numerical results available. 3-D temperature distribution in a biomaterial is validated against experimental results. Results using the proposed fully coupled approach are discussed and analyzed. The model is able to reflect the evolution of both temperature and moisture fields as well as energy penetration as the moisture in the porous medium evaporates. Moisture movement results from internal pressure gradients produced by the internal heating and phase change. The model is validated by comparison to some published results for simpler problems

A constrained pressure-temperature residual (CPTR) method for non-isothermal multiphase flow in porous media

For both isothermal and thermal petroleum reservoir simulation, the Constrained Pressure Residual (CPR) method is the industry-standard preconditioner. This method is a two-stage process involving the solution of a restricted pressure system. While initially designed for the isothermal case, CPR is also the standard for thermal cases. However, its treatment of the energy conservation equation does not incorporate heat diffusion, which is often dominant in thermal cases. In this paper, we present an extension of CPR: the Constrained Pressure-Temperature Residual (CPTR) method, where a restricted pressure-temperature system is solved in the first stage. In previous work, we introduced a block preconditioner with an efficient Schur complement approximation for a pressure-temperature system. Here, we extend this method for multiphase flow as the first stage of CPTR. The algorithmic performance of different two-stage preconditioners is evaluated for reservoir simulation test cases.Comment: 28 pages, 2 figures. Sources/sinks description in arXiv:1902.0009

Macroscopic Modeling of Microwave-enabled Solution-processable Graphene

Microwave-assisted chemical reactions offer many attractive benefits. A new technique for microwave-enabled production of graphene demonstrates a very short reaction time and the potential for low-cost mass production. Further development of this technique requires inefficient and expensive trial-and-error experiments. This MQP aims to facilitate the mass production of graphene through dedicated modeling. The introduced models: predict 3D temperature inside high viscosity reactant by solving electromagnetic-thermal coupled problem by FDTD technique; estimate average temperature of well-stirred liquids; and study the selective heating effect through modeling temperatures of two components of the reactant. The models can be used to guide microwave-assisted production of new nanomaterials

Thermal ablation of biological tissues in disease treatment: A review of computational models and future directions

Percutaneous thermal ablation has proved to be an effective modality for treating both benign and malignant tumors in various tissues. Among these modalities, radiofrequency ablation (RFA) is the most promising and widely adopted approach that has been extensively studied in the past decades. Microwave ablation (MWA) is a newly emerging modality that is gaining rapid momentum due to its capability of inducing rapid heating and attaining larger ablation volumes, and its lesser susceptibility to the heat sink effects as compared to RFA. Although the goal of both these therapies is to attain cell death in the target tissue by virtue of heating above 50 oC, their underlying mechanism of action and principles greatly differs. Computational modelling is a powerful tool for studying the effect of electromagnetic interactions within the biological tissues and predicting the treatment outcomes during thermal ablative therapies. Such a priori estimation can assist the clinical practitioners during treatment planning with the goal of attaining successful tumor destruction and preservation of the surrounding healthy tissue and critical structures. This review provides current state-of- the-art developments and associated challenges in the computational modelling of thermal ablative techniques, viz., RFA and MWA, as well as touch upon several promising avenues in the modelling of laser ablation, nanoparticles assisted magnetic hyperthermia and non- invasive RFA. The application of RFA in pain relief has been extensively reviewed from modelling point of view. Additionally, future directions have also been provided to improve these models for their successful translation and integration into the hospital work flow

Modelling volume change and deformation in food products/processes: An overview

Volume change and large deformation occur in different solid and semi-solid foods during processing, e.g., shrinkage of fruits and vegetables during drying and of meat during cooking, swelling of grains during hydration, and expansion of dough during baking and of snacks during extrusion and puffing. In addition, food is broken down during oral processing. Such phenomena are the result of complex and dynamic relationships between composition and structure of foods, and driving forces established by processes and operating conditions. In particular, water plays a key role as plasticizer, strongly influencing the state of amorphous materials via the glass transition and, thus, their mechanical properties. Therefore, it is important to improve the understanding about these complex phenomena and to develop useful prediction tools. For this aim, different modelling approaches have been applied in the food engineering field. The objective of this article is to provide a general (non-systematic) review of recent (2005–2021) and relevant works regarding the modelling and simulation of volume change and large deformation in various food products/processes. Empirical-and physics-based models are considered, as well as different driving forces for deformation, in order to identify common bottlenecks and challenges in food engineering applications.Fil: Purlis, Emmanuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; ArgentinaFil: Cevoli, Chiara. Università di Bologna; ItaliaFil: Fabbri, Angelo. Università di Bologna; Itali

Numerical solution of coupled mass and energy balances during osmotic microwave dehydration

The mass and energy transfer during osmotic microwave drying (OD-MWD) process was studied theoretically by modeling and numerical simulation. With the aim to describe the transport phenomena that occurs during the combined dehydration process, the mass and energy microscopic balances were solved. An osmotic-diffusional model was used for osmotic dehydration (OD). On the other hand, the microwave drying (MWD) was modeled solving the mass and heat balances, using properties as function of temperature, moisture and soluble solids content. The obtained balances form highly coupled non-linear differential equations that were solved applying numerical methods. For osmotic dehydration, the mass balances formed coupled ordinary differential equations that were solved using the Fourth-order Runge Kutta method. In the case of microwave drying, the balances constituted partial differential equations, which were solved through Crank-Nicolson implicit finite differences method. The numerical methods were coded in Matlab 7.2 (Mathworks, Natick, MA). The developed mathematical model allows predict the temperature and moisture evolution through the combined dehydration process.Facultad de Ingenierí

Numerical analysis of microwave heating cavity: Combining electromagnetic energy, heat transfer and fluid dynamics for a NaY zeolite fixed-bed

[EN] Three-dimensional mathematical model was developed for a rectangular TE10n microwave heating cavity system, working at 2.45 GHz. Energy/heat, momentum equations were solved together with Maxwell's electromagnetic field equations using comm. MULTIPHYSICS (R) simulation environment. The dielectric properties, epsilon' and epsilon '', of NaY zeolite (Si/Al = 2.5) were evaluated as a function of temperature. Considering these values, the microwave heating of a porous fixed-bed made of dry NaY zeolite was simulated. Electric field distribution, axial and radial temperature profiles and temperature evolution with time were obtained. The zeolite fixed bed was heated up to 180 degrees C in 5 min, with 30 W power. The fixed-bed temperature evolution under non-steady state conditions showed the same trend as the one observed experimentally with only an average deviation of 10.3%. The model was used to predict microwave heating of other materials improving energy efficiency of the microwave cavity. Furthermore, the developed model was able to predict thermal runaway for zeolites.Financial support from the European Research Council ERC-Advanced Grant HECTOR-267626 is gratefully acknowledged. Hakan Nigar acknowledges financial support from the Spanish Ministry of Education for the FPU grant (Formacion del Profesorado Universitario - FPU12/06864), and also for the academic short stay grant (Estancia Breve - FPU2016) at the Delft University of Technology, Delft, The Netherlands.Nigar, H.; Sturm, GSJ.; García-Baños, B.; Penaranda-Foix, FL.; Catalá Civera, JM.; Mallada, R.; Stankiewicz, A.... (2019). Numerical analysis of microwave heating cavity: Combining electromagnetic energy, heat transfer and fluid dynamics for a NaY zeolite fixed-bed. Applied Thermal Engineering. 155:226-238. https://doi.org/10.1016/j.applthermaleng.2019.03.117S22623815

Development of Synthetic Coal Char Simulant for Microwave Conversion Studies: A Computationally-Driven Approach

Recent experimental demonstration of new reaction windows for coal char/methane reactions that are less energy-intensive, provides innovation for modular reactors. However, the correlation of the exact mechanism for the enhancement of these reaction windows is not certain. This study investigates the simplification of these experimental studies by developing a well-characterized coal char simulant. The approach involves using a computational approach to screen macroscopic composition to replicate the dielectric and compositional response of actual char. This study is focused on PRB coal char. A discrete element method (DEM) technique was used to simulate the packing of coal chars to give the precise distribution of particle sizes. Micro-CT images of actual coal char were taken and the Feret diameter and particle count were used in DEM simulation. Using the packed DEM geometry, a finite element analysis (FEA) using COMSOL was utilized to solve Maxwell’s equations to match the experimental dielectric properties. Once the required volume fraction and constituents were known, the coal char simulate was synthesized. The comparison of simulation dielectric and actual char dielectric was within 5\% error. The synthetic char was experimentally synthesized and the density of the synthetic dielectric was determined to be 0.5 g/cc and the actual char had a density of 0.4 g/cc. It was determined that the imaginary part of the synthetic char was much larger than the actual char. This was reasoned to be due to the larger electrical conductivity associated with the synthetic char material. Further investigation of the actual char through both optical and scanning tunneling microscopy revealed significant amount of ash content surrounding the char. It is hypothesized that this ash layer coating the char as a result of pyrolysis process is leading to decreased electrical conductivity. A similar FEA approach was used to investigate the particle morphology of a magnetite (Fe$_{3}$O$_{4}$) catalyst embedding on a coal char substrate to understand the localized temperature and electric field enhancements. It was determined that a particle shape significantly influences electric field and localized temperatures. In the absence of the shaped particle the peak electric field strength and subsequently, the volumetric heat flux was two orders of magnitude lower. An optimal geometry and volume fraction to enhance these localized field effects were found during the study