D.D. Dinčov, K.A. Parrott and K.A. Pericleous
Computational results for the microwave heating of a porous material are presented in this paper. Combined finite difference time domain and finite volume methods were used to…
Abstract
Computational results for the microwave heating of a porous material are presented in this paper. Combined finite difference time domain and finite volume methods were used to solve equations that describe the electromagnetic field and heat and mass transfer in porous media. The coupling between the two schemes is through a change in dielectric properties which were assumed to be dependent on both temperature and moisture content. The model was 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.
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T. Tilford, K.I. Sinclair, C. Bailey, M.P.Y. Desmulliez, G. Goussettis, A.K. Parrott and A.J. Sangster
This paper aims to present an open‐ended microwave curing system for microelectronics components and a numerical analysis framework for virtual testing and prototyping of the…
Abstract
Purpose
This paper aims to present an open‐ended microwave curing system for microelectronics components and a numerical analysis framework for virtual testing and prototyping of the system, enabling design of physical prototypes to be optimized, expediting the development process.
Design/methodology/approach
An open‐ended microwave oven system able to enhance the cure process for thermosetting polymer materials utilised in microelectronics applications is presented. The system is designed to be mounted on a precision placement machine enabling curing of individual components on a circuit board. The design of the system allows the heating pattern and heating rate to be carefully controlled optimising cure rate and cure quality. A multi‐physics analysis approach has been adopted to form a numerical model capable of capturing the complex coupling that exists between physical processes. Electromagnetic analysis has been performed using a Yee finite‐difference time‐domain scheme, while an unstructured finite volume method has been utilized to perform thermophysical analysis. The two solvers are coupled using a sampling‐based cross‐mapping algorithm.
Findings
The numerical results obtained demonstrate that the numerical model is able to obtain solutions for distribution of temperature, rate of cure, degree of cure and thermally induced stresses within an idealised polymer load heated by the proposed microwave system.
Research limitations/implications
The work is limited by the absence of experimentally derived material property data and comparative experimental results. However, the model demonstrates that the proposed microwave system would seem to be a feasible method of expediting the cure rate of polymer materials.
Originality/value
The findings of this paper will help to provide an understanding of the behaviour of thermosetting polymer materials during microwave cure processing.
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Fernando Camelli and Rainald Löhner
The combined use of damage criteria, genetic algorithms and advanced CFD solvers provides an effective strategy to identify locations of releases that produce maximum damage. The…
Abstract
The combined use of damage criteria, genetic algorithms and advanced CFD solvers provides an effective strategy to identify locations of releases that produce maximum damage. The implementation is simple and does not require any change to flow solvers. A rather general criterion has been formulated to determine the damage inflicted by the intentional or unintentional release of contaminants. Results of two typical cases show that damage can vary considerably as a function of release location, implying that genetic algorithms are perhaps the only techniques suited for this type of optimization problem.
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This paper aims to investigate the thermal performance involving larger heating rate, targeted heating, heating with least non-uniformity of the spatial distribution of…
Abstract
Purpose
This paper aims to investigate the thermal performance involving larger heating rate, targeted heating, heating with least non-uniformity of the spatial distribution of temperature and larger penetration of heating within samples vs shapes of samples (circle, square and triangular).
Design/methodology/approach
Galerkin finite element method (GFEM) with adaptive meshing in a composite domain (free space and sample) is used in an in-house computer code. The finite element meshing is done in a composite domain involving triangle embedded within a semicircular hypothetical domain. The comparison of heating pattern is done for various shapes of samples involving identical cross-sectional area. Test cases reveal that triangular samples can induce larger penetration of heat and multiple heating fronts. A representative material (beef) with high dielectric loss corresponding to larger microwave power or heat absorption in contrast to low lossy samples is considered for the current study. The average power absorption within lossy samples has been computed using the spatial distribution and finite element basis sets. Four regimes have been selected based on various local maxima of the average power for detailed investigation. These regimes are selected based on thin, thick and intermediate limits of the sample size corresponding to the constant area of cross section, Ac involving circle or square or triangle.
Findings
The thin sample limit (Regime 1) corresponds to samples with spatially invariant power absorption, whereas power absorption attenuates from exposed to unexposed faces for thick samples (Regime 4). In Regimes 2 and 3, the average power absorption non-monotonically varies with sample size or area of cross section (Ac) and a few maxima of average power occur for fixed values of Ac involving various shapes. The spatial characteristics of power and temperature have been critically analyzed for all cross sections at each regime for lossy samples. Triangular samples are found to exhibit occurrence of multiple heating fronts for large samples (Regimes 3 and 4).
Practical implications
Length scales of samples of various shapes (circle, square and triangle) can be represented via Regimes 1-4. Regime 1 exhibits the identical heating rate for lateral and radial irradiations for any shapes of lossy samples. Regime 2 depicts that a larger heating rate with larger temperature non-uniformity can occur for square and triangular-Type 1 lossy sample during lateral irradiation. Regime 3 depicts that the penetration of heat at the core is larger for triangular samples compared to circle or square samples for lateral or radial irradiation. Regime 4 depicts that the penetration of heat is still larger for triangular samples compared to circular or square samples. Regimes 3 and 4 depict the occurrence of multiple heating fronts in triangular samples. In general, current analysis recommends the triangular samples which is also associated with larger values of temperature variation within samples.
Originality/value
GFEM with generalized mesh generation for all geometries has been implemented. The dielectric samples of any shape are surrounded by the circular shaped air medium. The unified mesh generation within the sample connected with circular air medium has been demonstrated. The algorithm also demonstrates the implementation of various complex boundary conditions in residuals. The numerical results compare the heating patterns for all geometries involving identical areas. The thermal characteristics are shown with a few generalized trends on enhanced heating or targeted heating. The circle or square or triangle (Type 1 or Type 2) can be selected based on specific heating objectives for length scales within various regimes.
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Akash K. Gupta, Rahul Yadav, Malay K. Das and Pradipta K. Panigrahi
This paper aims to present the implementation of a multi-layer radiation propagation model in simulations of multi-phase flow and heat transfer, for a dissociating methane hydrate…
Abstract
Purpose
This paper aims to present the implementation of a multi-layer radiation propagation model in simulations of multi-phase flow and heat transfer, for a dissociating methane hydrate reservoir subjected to microwave heating.
Design/methodology/approach
To model the induced heterogeneity due to dissociation of hydrates in the reservoir, a multiple homogeneous layer approach, used in food processes modelling, is suggested. The multi-layer model is incorporated in an in-house, multi-phase, multi-component hydrate dissociation simulator based on the finite volume method. The modified simulator is validated with standard experimental results in the literature and subsequently applied to a hydrate reservoir to study the effect of water content and sand dielectric nature on radiation propagation and hydrate dissociation.
Findings
The comparison of the multi-layer model with experimental results show a maximum difference in temperature estimation to be less than 2.5 K. For reservoir scale simulations, three homogeneous layers are observed to be sufficient to model the induced heterogeneity. There is a significant contribution of dielectric properties of sediments and water content of the reservoir in microwave radiation attenuation and overall hydrate dissociation. A high saturation reservoir may not always provide high gas recovery by dissociation of hydrates in the case of microwave heating.
Originality/value
The multi-layer approach to model microwave radiation propagation is introduced and tested for the first time in dissociating hydrate reservoirs. The multi-layer model provides better control over reservoir heterogeneity and interface conditions compared to existing homogeneous models.
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The purpose of this paper is to develop a general numerical solution for the wetting fluid spread into porous media that can be used in solving of droplet spread into soils…
Abstract
Purpose
The purpose of this paper is to develop a general numerical solution for the wetting fluid spread into porous media that can be used in solving of droplet spread into soils, printing applications, fuel cells, composite processing.
Design/methodology/approach
A discrete capillary network model based on micro‐force balance is numerically implemented and the flow for an arbitrary capillary number can be solved. At the fluid interface, the boundary condition that accounts for the capillary pressure jump is used.
Findings
The wetting fluid spread into porous medium starts as a single‐phase flow, and after some particular number of the porous medium characteristic length scales, the multi‐phase flow pattern occurs. Hence, in the principal flow direction, the phase content (saturation) decreases, and in the lower limit for the capillary number sufficiently small, the saturation should become constant. This qualitative saturation behavior is observed irrespective of the flow dimensionality, whereas the quantitative results vary for different flow systems.
Research limitations/implications
The numerical solution has to be expanded to solve the spread of the fluid in the porous medium after there is no free fluid left at the porous medium surface.
Practical implications
It is shown that the multi‐phase flow can develop even on a small domain due to the porous medium heterogeneity. Neglecting the medium heterogeneity and flow type can lead to a large error as shown for the droplet spread time in the porous medium.
Originality/value
This is believe to be the only paper relating to solving the droplet spread into porous medium as a multi‐phase flow problem.
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Bahareh Seyyedin, Nasrin Omidvar, Bahar Bakhshi, Farid Zayeri and Arezoo Rezazadeh
The purpose of this study was to investigate the association of individual and environmental indicators with body mass-index-for-age-z-score (BAZ) of female adolescents living in…
Abstract
Purpose
The purpose of this study was to investigate the association of individual and environmental indicators with body mass-index-for-age-z-score (BAZ) of female adolescents living in the North-West of Iran.
Design/methodology/approach
In this cross-sectional study, 380 female adolescents aged 16-18 years were selected from two major ethnic groups (Azeri and Kurd) in Urmia city selected by stratified cluster sampling method. In total, 13 high schools (9 public and 4 private) were selected across all municipality zones of Urmia city. BAZ was calculated by Anthro-Plus software. Demographic and socioeconomic information of samples were collected by a questionnaire through interviews. Home environment features (including physical activity facilities, television, computer games and social media use, food consumption habits and family rules) and school environment features (including socioeconomic status [SES], physical activity facilities, food consumption habits) were evaluated by two separate self-constructed questionnaires via an interview with adolescents and schools’ deans, respectively.
Findings
Azeri adolescents had parents with higher education and job level and higher SES compared to Kurds (p = 0.000). A higher percent of Azeri adolescents were obese than their Kurd counterparts (p = 0.006). No association was found between individual factors and BAZ in each ethnic group. Considering home environment characteristics, in Kurd adolescents, the maternal occupational level was positively associated with BAZ (p = 0.02). With regard to school environmental features, accessibility of physical activity facilities in school was inversely associated with BAZ only in Kurds (p = 0.005).
Originality/value
To the best of the authors’ knowledge, this is the first study to investigate various environmental factors in association with adolescent’s overweight/obesity prevalence in different ethnical groups in northwest Iran.
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Ethan M. Moon and Vadim V. Yakovlev
This paper aims to introduce and illustrate a computational technique capable of determining the geometry and complex permittivity of a supplementary dielectric insert making…
Abstract
Purpose
This paper aims to introduce and illustrate a computational technique capable of determining the geometry and complex permittivity of a supplementary dielectric insert making distributions of microwave-induced dissipated power within the processed material as uniform as possible.
Design/methodology/approach
The proposed technique is based on a 3D electromagnetic model of the cavity containing both the processed material and the insert. Optimization problem is formulated for design variables (geometrical and material parameters of the insert) identified from computational tests and an objective function (the relative standard deviation [RSD]) introduced as a metric of the field uniformity. Numerical inversion is performed with the method of sequential quadratic programming.
Findings
Functionality of the procedure is illustrated by synthesis of a dielectric insert in an applicator for microwave fixation. Optimization is completed for four design variables (two geometrical parameters, dielectric constant and the loss factor of the insert) with 1,000 points in the database. The best three optimal solutions provide RSD approximately 20 per cent, whereas for the patterns corresponding to all 1,000 non-optimized (randomly chosen) sets of design variables this metric is in the interval from 27 to 136 per cent with the average of 78 per cent.
Research limitations/implications
As microwave thermal processing is intrinsically inhomogeneous and the heating time is not a part of the underlying model, the procedure is able to lead only to a certain degree of closeness to uniformity and is intended for applications with high heating rates. The initial phase of computational identification of design variables and their bounds is therefore very important and may pre-condition the “quality” of the optimal solution. The technique may work more efficiently in combination with advanced optimization techniques dealing with “smart” (rather than random) generation of the data; for the use with more general microwave heating processes characterized by lower heating rates, the technique has to use the metric of non-uniformity involving temperature and heating time.
Practical implications
While the procedure can be used for computer-aided design (CAD) of microwave applicators, a related practical limitation may emerge from the fact that the material with particular complex permittivity (determined in the course of optimization) may not exist. In such cases, the procedure can be rerun for the constant values of material parameters of the available medium mostly close to the optimal ones to tune geometrical parameters of the insert. Special manufacturing techniques capable of producing a material with required complex permittivity also may be a practical option here.
Originality/value
Non-uniformity of microwave heating remains a key challenge in the design of many practical applicators. This paper suggests a concept of a practical CAD and outlines corresponding computational procedure that could be used for designing a range of applied systems with high heating rates.
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Ajantha Sisira Kumara and Vilani Sachitra
The World Health Organization issued its global action plan on physical activities 2018–2030, emphasizing the importance of context-specific evidence on the subject. Accordingly…
Abstract
Purpose
The World Health Organization issued its global action plan on physical activities 2018–2030, emphasizing the importance of context-specific evidence on the subject. Accordingly, this study aims to provide unique and important policy insights on trends and drivers of participation in physical exercises by academic community in Sri Lankan universities.
Design/methodology/approach
For this purpose, we collected cross-sectional data (n = 456) in 2020 using a survey, and first, estimated a double-hurdle model to uncover covariates influencing likelihood and intensity of physical exercises overall. Second, count-data models are estimated to capture regularity of key exercises.
Findings
The results reveal that about 50% of members do not participate in any general physical exercise. Older members (marginal effect (ME) = 3.764, p < 0.01), non-Buddhists (ME = 54.889, p < 0.01) and alcohol consumers (ME = 32.178, p < 0.05) exhibit a higher intensity of participating in exercises overall. The intensity is lower for rural members (ME = −63.807, p < 0.01) and those with health insurance covers (ME = −31.447, p < 0.05). Individuals diagnosed for chronic illnesses show a higher likelihood of exercising but, their time devotion is limited. The number of children the academic staff members have as parents reduces the likelihood, but for those who choose to exercise have higher time devotion with increased number of children. The covariates play a similar role in determining regularity of key exercises: walking, jogging and exercising on workout machines.
Research limitations/implications
The results imply a need to promote exercising in general and particularly among younger, healthy, insured and female individuals living in rural sector.
Originality/value
The study covers an under-researched professional sub-group in an under-researched developing context, examining both the likelihood and regularity of exercising as both dimensions are equally important for individuals to maintain healthy lives.
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Stoyan Stoyanov, Tim Tilford, Farid Amalou, Scott Cargill, Chris Bailey and Marc Desmulliez
Nano‐imprint forming (NIF) is a manufacturing technology capable of achieving high resolution, low‐cost and high‐throughput fabrication of fine nano‐scale structures and patterns…
Abstract
Purpose
Nano‐imprint forming (NIF) is a manufacturing technology capable of achieving high resolution, low‐cost and high‐throughput fabrication of fine nano‐scale structures and patterns. The purpose of this paper is to use modelling technologies to simulate key process steps associated with the formation of patterns with sub‐micrometer dimensions and use the results to define design rules for optimal imprint forming process.
Design/methodology/approach
The effect of a number of process and pattern‐related parameters on the quality of the fabricated nano‐structures is studied using non‐linear finite element analysis. The deformation process of the formable material during the mould pressing step is modelled using contact analysis with large deformations and temperature dependent hyperelastic material behaviour. Finite element analysis with contact interfaces between the mould and the formable material is utilised to study the formation of mechanical, thermal and friction stresses in the pattern.
Findings
The imprint pressure, temperature and the aspect ratio of grooves which define the pattern have significant effect on the quality of the formed structures. The optimal imprint pressure for the studied PMMA is identified. It is found that the degree of the mould pattern fulfilment as function of the imprint pressure is non‐linear. Critical values for thermal mismatch difference in the CTE between the mould and the substrate causing thermally induced stresses during cooling stage are evaluated. Regions of high stresses in the pattern are also identified.
Originality/value
Design rules for minimising the risk of defects such as cracks and shape imperfections commonly observed in NIF‐fabricated nano‐structures are presented. The modelling approach can be used to provide insights into the optimal imprint process control. This can help to establish further the technology as a viable route for fabrication of nano‐scale structures and patterns.