Thermal Homogenization Research Articles

Investigating the Effects of Induction Heating on a Submerged Hollow Cylindrical Element

ABSTRACTThis article proposes an induction heating element that addresses heat transfer and thermal homogenization while being fully submerged in a liquid, specifically focusing on heating of water as a case study. The design calculations, fabrication, and realization of a resonant induction heating system that heats the proposed heating element are presented. The geometric shape of proposed heating element is a hollow cylinder that maintains structural strength while delivering required thermal energy because of an external time‐varying magnetic field. Detailed mathematical modeling of the proposed heating element's equivalent electric circuit has been presented while considering physical parameters including diameter, thickness, height, material properties, magnetic field frequency, and skin effect. A laboratory scale prototype of the induction heating system including the proposed heating element has been built, and experiments have been demonstrated. The experimental results of the working induction heating resonant inverter and RLC resonant circuit inductance and capacitance with induction load are presented. Additionally, the results of thermographic images and temperature–time profile of the water sample, which was heated using the proposed heating element, are provided to demonstrate the heating element's reliability and practicality. This research contributes to the field of induction heating technology by investigating a heating element that is submerged in a liquid medium, resulting in a uniform temperature distribution throughout the liquid. The conventional method of heating water in a stainless steel cup‐shaped container is an inefficient heat transfer process. In stainless steel cup‐shaped containers, a portion of the energy input used to boil the water is lost to the environment through the surface area of the container that is not in direct contact with the water. This heat loss occurs due to the container's design, which exposes a large surface area to the surrounding environment, allowing thermal energy to dissipate through conduction, convection, and radiation.

Imposing Dirichlet boundary conditions directly for FFT-based computational micromechanics

We discuss how Dirichlet boundary conditions can be directly imposed for the Moulinec–Suquet discretization on the boundary of rectangular domains in iterative schemes based on the fast Fourier transform (FFT) and computational homogenization problems in mechanics. Classically, computational homogenization methods based on the fast Fourier transform work with periodic boundary conditions. There are applications, however, when Dirichlet (or Neumann) boundary conditions are required. For thermal homogenization problems, it is straightforward to impose such boundary conditions by using discrete sine (and cosine) transforms instead of the FFT. This approach, however, is not readily extended to mechanical problems due to the appearance of mixed derivatives in the Lamé operator of elasticity. Thus, Dirichlet boundary conditions are typically imposed either by using Lagrange multipliers or a “buffer zone” with a high stiffness. Both strategies lead to formulations which do not share the computational advantages of the original FFT-based schemes. The work at hand introduces a technique for imposing Dirichlet boundary conditions directly without the need for indefinite systems. We use a formulation on the deformation gradient—also at small strains—and employ the Green’s operator associated to the vector Laplacian. Then, we develop the Moulinec–Suquet discretization for Dirichlet boundary conditions—requiring carefully selected weights at boundary points—and discuss the seamless integration into existing FFT-based computational homogenization codes based on dedicated discrete sine/cosine transforms. The article culminates with a series of well-chosen numerical examples demonstrating the capabilities of the introduced technology.

Geometry-induced process and part characteristics in support-free powder bed fusion of polypropylene at room temperature

Laser-based powder bed fusion (LPBF) of semi-crystalline polymers enables the support-free layer-wise manufacturing of geometrically diverse, complex components. In contrast to the established quasi-isothermal powder bed fusion of polymers at elevated temperatures, non-isothermal, cold processing strategies allow to significantly extend the range of applicable material systems. Relying on the superposition of discretized, fractal exposure strategies and the implicit mesoscopic compensation of crystallization shrinkage, the support-free LPBF of polypropylene at room temperature is demonstrated. The present paper displays the temporally and spatially discrete exposure of superposed fractal, space-filling curves that enable the support-free LPBF of polypropylene through combining the mesoscopic compensation of crystallization shrinkage and the laser-induced minimization of thermal shrinkage through the implementation of pre-exposure scans. The non-isothermal processing regime was observed to exhibit an intrinsic robustness towards the influence of processing parameters on emerging peak temperatures while showing a significant extent of accumulated heat within manufactured parts. Complementary mechanical characterizations showed an orientation-dependent influence of the applied energy density on emerging mechanical properties, correlated with geometry-dependent temporal process characteristics that implicitly influence the available coalescence time and the timespan available for the thermal homogenization.

Investigating Milk Fat Globule Structure, Size, and Functionality after Thermal Processing and Homogenization of Human Milk.

Human milk provides bioactive compounds such as milk fat globules (MFGs), which promote brain development, modulate the immune system, and hold antimicrobial properties. To ensure microbiological safety, donor milk banks apply heat treatments. This study compares the effects of heat treatments and homogenization on MFG's physicochemical properties, bioactivity, and bioavailability. Vat pasteurization (Vat-PT), retort (RTR), and ultra-high temperature (UHT) were performed with or without homogenization. UHT, RTR, and homogenization increased the colloidal dispersion of globules, as indicated by increased zeta potential. The RTR treatment completely inactivated xanthine oxidase activity (a marker of MFG bioactivity), whereas UHT reduced its activity by 93%. Interestingly, Vat-PT resulted in less damage, with 28% activity retention. Sialic acid, an important compound for brain health, was unaffected by processing. Importantly, homogenization increased the in vitro lipolysis of MFG, suggesting that this treatment could increase the digestibility of MFG. In terms of color, homogenization led to higher L* values, indicating increased whiteness due to finer dispersion of the fat and casein micelles (and thus greater light scattering), whereas UHT and RTR increased b* values associated with Maillard reactions. This study highlights the nuanced effects of processing conditions on MFG properties, emphasizing the retention of native characteristics in Vat-PT-treated human milk.

A new winding homogenization method based on thermal resistance concept

PurposeThe aim of this paper is to provide a simple yet accurate and efficient geometric method for thermal homogenization of impregnated and non-impregnated coil winding technologies based on the concept of thermal resistance.Design/methodology/approachFor regular windings, the periodic microscopic cell in the winding space is identified. Also, for irregular windings, the average microscopic cell of the winding is determined. An approximation is used to calculate the thermal resistance of the winding cell. Based on this approximation, the winding insulation is considered as a circular ring around the wire. Mathematical equations are obtained to calculate the equivalent thermal resistance of the cell. The equivalent thermal conductivity of the winding is calculated using equivalent thermal resistance of the cell. Winding thermal homogenization is completed by determining the equivalent thermal properties of the cell.FindingsThe thermal pattern of different windings is simulated and compared with the results of different homogenization methods. The results show that the proposed method is applicable for a wide range of windings in terms of winding scheme, packing factor and winding insulation. Also, the results show that the proposed method is more accurate than other winding homogenization methods in calculating the equivalent thermal conductivity of the winding.Research limitations/implicationsIn this paper, the change of electrical resistance of the winding with temperature and thermal contact between the sub-components are ignored. Also, liquid insulators, such as oils, and rectangular wires were not investigated. Research in these topics is considered as future work.Originality/valueUnlike other homogenization methods, the proposed method can be applied to non-impregnated and irregular windings. Also, compared to other homogenization methods, the proposed method has a simpler formulation that makes it easier to program and implement. All of these indicate the efficiency of the proposed method in the thermal analysis of the winding.

Comparative numerical study of floor heating systems using parallel and spiral coil

This article presents a comparative numerical study aimed at determining the optimal pipe layout solution for the heating benches of traditional steam baths, with the goal of ensuring an optimal temperature distribution for customer comfort. This layout incorporates insulation on the lower side to direct most of the emitted heat upwards. The temperature distribution across the floor surface varies depending on the configuration of the buried pipes. Calculations were performed using the CFD software "COMSOL Multiphysics" to investigate the thermal behavior of an underfloor heating system. The results were used to discuss certain critical parameters that require control for the proper operation of the system. These parameters include the flow velocity inside the pipes, inlet temperatures, and pipe configuration. A new parameter designed to measure the thermal homogeneity of the floor was introduced and evaluated. In general, the findings demonstrated that the modulated spiral configuration is the best solution, minimizing pressure losses while ensuring optimal thermal homogenization across the entire floor surface.

Thermal and dynamic characterization of a multi-jet system with different geometry diffusers

This paper proposed to use the impinging jets mixing process to improve the quality of residential heating and air conditioning. The main objective is to meet the requirements of occupants in terms of thermal comfort and air quality by proposing an optimal solution for the thermal homogenization improvement in the rooms by changing of the diffusers geometry and their arrangement in the ventilation and air-conditioning devices in blowing systems. This study involves both experimental and numerical studies of a three diffusers configurations composed of four peripheral jet with similar geometries and a central jet with a different geometry. All the configurations consist of four equidistant peripheral swirling jets, only the central jet that makes the difference between them. The configuration 1 includes a swirling central jet, on the other hand a circular central jet for the configuration 2 and finally a lobed central jet for configuration 3. The velocity and temperature distributions of the three configurations are investigated experimentally and numerically. Experimentally, the multifunction thermo-anemometer have been used to measure flow temperature and velocity. The dynamic and temperature features are more radially spread and get better homogeneity in configuration 3 and this is due to the energy distribution on the radial plane, which is relatively better than configuration 1 and configuration 2. The second part deals with numerical predictions of the dynamics and thermal fields of the three configurations considered. The study was realized using a RANS-based turbulence model. The numerical results are in reasonable agreement with our experiments for the three configurations. With this study, detailed information on the structure of the resulting flow is very useful to deepen the understanding of the physics of jet interaction and to validate turbulence models. The turbulence simulation is realized by the k-ω-SST model. This model gives a satisfactorily predicts the axial drop in velocity and temperature over the entire study range, demonstrating its ability to handle the interaction between swirling and lobe jets. Our results show that the geometry of the central diffuser is essential. This allows the axial velocity to decrease faster than configurations 1 and 2. This increases lateral diffusion, resulting in better homogenization.

Multi-Step Mechanical and Thermal Homogenization for the Warpage Estimation of Silicon Wafers.

In response to the increasing demand for high-performance capacitors, with a simultaneous emphasis on minimizing their physical size, a common practice involves etching deep vias and coating them with functional layers to enhance operational efficiency. However, these deep vias often cause warpages during the processing stage. This study focuses on the numerical modeling of wafer warpage that occurs during the deposition of three thin layers onto these vias. A multi-step mechanical and thermal homogenization approach is proposed to estimate the warpage of the silicon wafer. The efficiency and accuracy of this numerical homogenization strategy are validated by comparing detailed and homogenized models. The multi-step homogenization method yields more accurate results compared to the conventional direct homogenization method. Theoretical analysis is also conducted to predict the shape of the wafer warpage, and this study further explores the impact of via depth and substrate thickness.

Imposing different boundary conditions for thermal computational homogenization problems with FFT‐ and tensor‐train‐based Green's operator methods

AbstractTo compute the effective properties of random heterogeneous materials, a number of different boundary conditions are used to define the apparent properties on cells of finite size. Typically, depending on the specific boundary condition, different numerical methods are used. The article at hand provides a unified framework for Lippmann–Schwinger solvers in thermal conductivity and Dirichlet (prescribed temperature), Neumann (prescribed normal heat flux) as well as periodic boundary conditions. We focus on the explicit jump finite‐difference discretization and discuss different techniques for computing the discrete Green's operator. These include Fourier‐type methods, that is, based on discrete sine, cosine and Fourier transformations, as well as low‐rank tensor methods, that is, the tensor‐train approximation, whose computational prowess was demonstrated recently. We use the developed computational technology to investigate a number of interesting random materials and assess different microstructure‐generation techniques in terms of their compatibility with the prescribed boundary conditions.

Multiscale homogenization of aluminum honeycomb structures: Thermal analysis with orthotropic representative volume element and finite element method

This study develops a thermal homogenization model for an aluminum honeycomb panel using the representative volume element (RVE) concept, considering the orthotropic nature of the structure. The RVE thermal homogenization method is a numerical approach for analyzing heterogeneous materials. It employs a constitutive model based on RVE performance to represent thermal behavior. Effective parameters are determined through averaging techniques, and the finite element method solves the thermal problem, accounting for structure topology and material behavior. The resulting heat conduction problem is solved using the finite element method (FEM) to evaluate the effective thermal characteristics. A 3D RVE is generated based on the honeycomb panel's geometry, evaluating thermal conductivity tensor and describing the medium's thermal performance. Numerical tests validate the model by comparing it with the real honeycomb structure under sinusoidal heat flux. Results show good correlation, with maximum temperatures of 1101.9 °C in the real structure and 1096.4 °C in the medium. The homogeneous medium is further used to investigate thermal performance under convective conditions with varying panel thicknesses, achieving over 77 °C temperature reduction with the thickest panel. Natural vibration behavior is considered, demonstrating strong correlation between modal responses and natural frequencies. This modeling approach efficiently analyzes thermal behavior in large honeycomb structures, reducing computational time significantly.

A deep material network approach for predicting the thermomechanical response of composites

Recent progress combining micromechanics and machine learning holds promise for accurately and rapidly predicting the mechanical behavior of complex composite materials. This study extends the Deep Material Network (DMN), a binary-tree network trained on linear direct-numerical-simulation data, to predict the thermo-elasto-viscoplastic behavior of composites. This extension incorporates the thermal expansion properties homogenization into the network’s building blocks and expands the online formulation to consider thermal boundary conditions. By comparing various implementations of these building blocks, we demonstrate the network’s extrapolation to thermomechanical problems. We then show how this extended DMN can be applied to uncertainty quantification and inverse design problems.

Changes in thermal niche position and breadth of bird assemblages in Spain in relation to increasing temperatures

AbstractAimAnimal communities around the world are responding to climate change by altering their taxonomic composition, mainly through an increase in the colonisation rate of warm‐dwelling species and the local extinction of cold‐dwelling ones. We assessed whether the taxonomic composition of bird assemblages in peninsular Spain has changed in accordance with the recent increase in temperature. We also evaluated the role of species thermal affinities and population dynamics on these changes.LocationPeninsular Spain.TaxonBirds.MethodsWe compared assemblages reported in the last Spanish breeding bird atlases (1998–2002 vs. 2014–2018) in 10 × 10 km squares. We described species' thermal niches by overlaying global species breeding distributions and world temperature metrics (based on mean, minimum, maximum and range), and then aggregated them to obtain a set of community thermal indices for each assemblage (CTIs and CTR for ranges). Long‐term average temperatures and local current temperatures were related to changes in CTIs using spatial GLMMs, which considered habitat change. We identified the species most responsible for variation in assemblages and regressed species' influence on thermal affinities and population dynamics.ResultsCTIs increased with temperature and warm‐dwelling species became more prevalent to the detriment of cold‐dwelling ones. However, we found a counteracting effect of temperature and habitat. Cold‐dwelling forest species were among the most influential species, mainly through colonisation, while warm‐dwelling farmland species contributed through local extinctions (both attenuated local increases in CTI). The mean thermal breadth of assemblages (CTR) decreased with temperatures.Main conclusionsThe taxonomic composition of bird assemblages shifted in line with the main expectations due to global change (thermophilisation), mainly due to local colonisation of warm‐dwelling species, although it did not show the pattern of thermal homogenisation suggested elsewhere. Our results add further evidence of the interplay between climate warming and land‐use change in the ongoing adjustment of animal communities.

Liquid immersion thermal management of lithium-ion batteries for electric vehicles: An experimental study

The thermal and electrical performance of lithium-ion batteries subjected to liquid immersion cooling conditions in a dielectric fluid has been experimentally investigated in this study. A single 26650 LiFePO4 cylindrical cell is completely immersed in Novec 7000 and charged and discharged at onerous maximum rates of up to 4C and 10C, respectively, where C can be defined as the measure of the rate at which a cell is charged or discharged relative to its rated capacity. Immersion cooling offers high rates of heat transfer from the cell's surface, in particular when the saturation temperature of the fluid is exceeded, and two-phase conditions are established. At a preheated liquid pool temperature of 33 ± 0.5 °C for discharge rates ≥ 2C, subcooled boiling conditions develop, with the cell's temperature rise limited to 3.6 °C at the end of 10C discharge. Furthermore, for 4C charging under the same preheating conditions, the cell's temperature rise does not exceed 1 °C. Superior performance is observed under two-phase immersion cooling conditions in comparison to both single phase liquid immersion and natural convection air cooling for the same charge and discharge rates. Excellent thermal homogenisation across the cell is also determined, with a maximum axial temperature difference of 0.25 °C and 1 °C for 4C charging and 10C discharging respectively.

Effective thermal conductivity of a gypsum mortar using harbor sediments

For sustainable use of natural resources, marine sediments areregularly dredged. One of the valorization ways of thesesediments is to reuse them as raw materials for the formulation of civil engineering products.This paper presents a thermal homogenization methodology for the optimization of heat transfer in Gypsum Plaster Boards formulation using dredged marine sediments. An up-scaling or homogenization technique that links macro- to micro thermal conductivity is given. Effective homogenized thermal conductivity formulation could be presented for a composite material on which a periodic micro-scale heat flux was subjected. For that purpose, steady state balance equations and Fourier heat law were used. Then, a thorough characterization of grain size distributions of dredged sediments were carried out. This showed that the dredged sediments are mainly sandy. Finally, ANSYS Finite Element Code is used to numerically compute the effective homogenized thermal conductivity of Gypsum-sediment composite incorporating different volume fractions of sediments. These simulations, performed on the Representative Volume Element, allowed studying the influence of the sediment grain size. The numerical simulations results, compared to classical theoretical models, have demonstrated the reuse feasibility of investigated sediment in Gypsum Plaster applications.

Preparation and Characterization of Intracellular and Exopolysaccharides during Cycle Cultivation of Spirulina platensis.

The dried cell weight (DCW) of Spirulina platensis gradually decreased from 1.52 g/L to 1.18 g/L after five cultivation cycles. Intracellular polysaccharide (IPS) and exopolysaccharide (EPS) content both increased with increased cycle number and duration. IPS content was higher than EPS content. Maximum IPS yield (60.61 mg/g) using thermal high-pressure homogenization was achieved after three homogenization cycles at 60 MPa and an S/I ratio of 1:30. IPS showed a more fibrous, porous, and looser structure, and had a higher glucose content and Mw (272.85 kDa) compared with EPS, which may be indicative of IPS's higher viscosity and water holding capacity. Although both carbohydrates were acidic, EPS had stronger acidity and thermal stability than IPS; this was accompanied by differences in monosaccharide. IPS exhibited the highest DPPH (EC50 = 1.77 mg/mL) and ABTS (EC50 = 0.12 mg/mL) radical scavenging capacity, in line with IPS's higher total phenol content, while simultaneously showing the lowest HO• scavenging and ferrous ion chelating capacities; thus characterizing IPS as a superior antioxidant and EPS as a stronger metal ion chelator.

Dean instability and thermal characteristic in sinusoidal structure

Sinusoidal structures have been widely used in various heat exchangers and micro heat sinks. In this paper, the flow and heat transfer characteristics in sinusoidal channels are numerically investigated. In particular, the unsteady fluctuation of Dean vortices has been studied in detail. It is found that a critical Reynolds number exists in sinusoidal channel. When the Reynolds number exceeds the critical Reynolds number, the flow is in an unsteady state, which is manifested by the irregular fluctuation of the Dean vortices. In addition, the POD (Proper Orthogonal Decomposition) method is used to perform mode analysis of the Dean vortices motion, and the Swirling number is used to quantify the degree of Dean instability for the first time. It is found that the fluctuations of the Dean vortices have similarity in the decomposition of modes when reaching the critical state, and the locations of the main fluctuations at 90° and 180° cross sections change. It is also found that the Dean instability has a significant effect on improving the thermal homogenization of the channel wall. In detail, 82.83% and 20.20% enhancements of thermal homogenization at the upper and lower walls at the 90° cross section are obtained, respectively. 14.06% and 14.33% enhancements of thermal homogenization are obtained at the upper and down walls at the 180° cross section, respectively.

The Effect of Interrupted Homogenization on β-Al5FeSi → α-Alx (Fe and Mn) Si Transformation in the A6063 Aluminum Alloy

The aluminum alloys corresponding to the 6000 series are mainly manufactured by mechanical forming processes. Their properties are enhanced by the homogeneous distribution of intermetallic phases such as β-Al5FeSi or α-Alx (Fe, Mn) Si. By thermal homogenization treatment, the intermetallic compound β-Al5FeSi changes its morphology from a needle type with a monoclinic structure to an acicular form known as α-Al12(Fe, Mn)3Si with an fcc structure. In the present study, samples of the 6063 alloy were subjected to different temperatures of homogenization (798, 823, and 848 K) and treatment times from 0 to 660 min (in intervals of 30 min) to evaluate their effects on the microstructures and morphologies of the intermetallic phases. For the kinetic study, the microstructures of the β and α intermetallic phases were quantified using the Image-Pro software. The results indicate that as the temperature and homogenization time increase, the percentage of phase α also increments. The results of the kinetic analysis revealed that the β → α transformation is controlled by two stages; the first corresponds to the diffusion of Mn atoms from the matrix to the interface of reaction for the formation of the intermetallic phases, while the second corresponds to the nucleation and growth of the iron- and manganese-rich intermetallic phases.

Static Mixers Producible by Additive Manufacturing: Novel Rapid Automatic Optimisation and Practical Evaluation.

In the extrusion of plastics, the thermal and material homogeneity of the plastic melt at the die entry are of high importance for the extrudate quality. While static mixers are widely used to improve the melt homogeneity, previous attempts at optimisation for reduced pressure loss and improved mixing had to be performed by hand and human experience, limiting the degrees of freedom and efficiency. A new automatic optimisation method based on the open source software OpenFOAM was developed. Using immersed boundary methods, new target functions in the pre-existing routine adjointShapeOptimizationFoam and an additional algorithm checking the suitability for additive manufacturing and fixing the geometry during run-time is presented. The new algorithm is used to optimise an existing static mixer based on an X-type geometry with integrated oil channels, maximising the heat exchange between oil and melt. Based on the results of these simulative optimisations, the best candidates were manufactured using selective laser melting and experimental trials were run. Experimental validation shows that with our optimisation algorithm, a pressure loss reduction of 10% could be achieved. The core melt temperature was reduced by 6 ∘C, improving the thermal homogenisation as well. While the main advantage of this method is the rapid optimisation taking the operating point into account, the trials also showed positive results in off-design operating points. This allows the low-cost design and manufacture of individualised static mixers.

Analytical and numerical analyses of RC beams exposed to fire adopting a LITS trilinear constitutive law for concrete

A trilinear compressive constitutive law for concretes exposed to fire is proposed. Concrete stress-strain relation as a function of temperature is characterized by means of only two parameters (residual values of concrete compressive strength and modulus of elasticity). The modulus of elasticity is determined through a Load Induced Thermal Strain (LITS) semi empirical model. The compressive strength is established through the design specifications. The constitutive law is implemented in finite element numerical models and in a simplified cross-sectional procedure. In the latter case, a simple methodology is proposed to estimate the residual moment capacity and the midspan deflection at any given time. The uncoupled two-step solution includes a thermal homogenization procedure followed by a sectional analysis. The deflection is estimated considering a constant equivalent stiffness for the RC beam. The case studies included the structural response under transient (hot state) condition of both a reinforced-high strength concrete (R-HSC) beam and a reinforced-ultra-high performance fiber reinforced concrete (R-UHPFRC) beam. The results are compared with experimental tests carried out in literature, showing a good approximation. Moreover, a steady state (after cooling) cross-sectional analysis of a R-HSC beam is performed. The load bearing capacity, the failure type and the midspan deflections are estimated. The analytical results approximate the experimental values, demonstrating the reliability of the proposed simplified procedures for the cases investigated.

Microalgae as a promising structure ingredient in food: Obtained by simple thermal and high-speed shearing homogenization

As a biological resource, microalgae are considered promising functional food components due to their balanced composition and various nutritional components. Its function in food is not limited to health but also plays a structural role in food. Therefore, research of the rheological properties of microalgae is vital. Thermal pre-treatment (TP) and high-speed shearing homogenization (HSH) are common processing methods in food processing. Here, we studied the effects of TP and HSH on the rheological properties, microstructure, polysaccharide content, and monosaccharide composition of Synechococcus sp. PCC 7002 and Spirulina platensis. The combined of TP and HSH treatment endowed the Spirulina platensis suspensions with shear thinning characteristics and enhanced gel characteristics (G'> G″), they also led to the breaking of Spirulina platensis cells, thus soluble polysaccharides such as polysaccharides bound to cell walls were released, which greatly increases the viscosity of the suspensions. This study provides a scientific basis for the food of microalgae and the change of food rheology containing microalgae. • A new method to improve rheological properties of microalgae. • After treatment, the viscosity was increased by 30–200 times. • Synechococcus sp. PCC 7002 has the potential as one kind of food thickener. • This study lays a foundation for the food of microalgae.