Thermal Process Research Articles

From circular to square‐based section spouted beds: Scale‐up and design overview of a multistage thermal unit

AbstractThis work summarizes the results of several research projects to demonstrate the possibility of scaling‐up spouted beds by assembling a number of square‐based jet units. Cylindrical vessels with a bottom cone and parallelepiped ones with a frustum base do not differ to a large extent in terms of hydrodynamic features. The existing correlations can be used to predict these square‐based spouted beds. Spouted beds can be very reasonably described as well‐mixed reactors. By assembling several units, it is possible to approach a plug flow state for solids residence time distribution (RTD) in continuous processes. Spouting stability is fully reached when the modules do not interfere each other: this goal is obtained by positioning the downstream units at a certain lower level and having the solids move by overflow; placing internal vertical baffles between contiguous units is the solution. Two hydrodynamical models are proposed to describe single and multiple spouted beds; their predictions help in choosing the best geometrical configuration for the assemblage. A possible application of a multiple spouted bed reactor was envisaged for gasifying pelletized textile residues to generate syngas which can be directly used in situ as a co‐fuel. Two units were built: a single 0.2 m side square‐based spouted bed furnace and the consequent dual stage scale‐up apparatus suitable for an auto thermal process. In the bottom stage, four units work independently to run combustion/gasification of low‐quality solid residues, while the upper stage had a cascade of four modules to run pyrolysis/gasification of selected biomass and obtain valuable secondary products.

From circular to square‐based section spouted beds: Scale‐up and design overview of a multistage thermal unit

AbstractThis work summarizes the results of several research projects to demonstrate the possibility of scaling‐up spouted beds by assembling a number of square‐based jet units. Cylindrical vessels with a bottom cone and parallelepiped ones with a frustum base do not differ to a large extent in terms of hydrodynamic features. The existing correlations can be used to predict these square‐based spouted beds. Spouted beds can be very reasonably described as well‐mixed reactors. By assembling several units, it is possible to approach a plug flow state for solids residence time distribution (RTD) in continuous processes. Spouting stability is fully reached when the modules do not interfere each other: this goal is obtained by positioning the downstream units at a certain lower level and having the solids move by overflow; placing internal vertical baffles between contiguous units is the solution. Two hydrodynamical models are proposed to describe single and multiple spouted beds; their predictions help in choosing the best geometrical configuration for the assemblage. A possible application of a multiple spouted bed reactor was envisaged for gasifying pelletized textile residues to generate syngas which can be directly used in situ as a co‐fuel. Two units were built: a single 0.2 m side square‐based spouted bed furnace and the consequent dual stage scale‐up apparatus suitable for an auto thermal process. In the bottom stage, four units work independently to run combustion/gasification of low‐quality solid residues, while the upper stage had a cascade of four modules to run pyrolysis/gasification of selected biomass and obtain valuable secondary products.

Poly-ε-caprolactone-based granules with allylisothiocyanate for controlling of golden cyst potato nematode

In this study, the characteristics of extruded granules based on biodegradable poly-ε-caprolactone and montmorillonite deposited with allylisothiocyanate and their effect on Globodera rostochiensis RoI were investigated. The prepared granules were characterized using Fourier-transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. It was shown that encapsulation efficiency of allylisothiocyanate in montmorillonite depends on the conditions of complex preparation and ranges from 0.76 to 29.83%, and in poly-ε-caprolactone/montmorillonite/allylisothiocyanate granules after thermal processing it decreases down to 1.06 %. According to the results of Fourier-transform infrared spectroscopy it was found that allylisothiocyanate inclusion did not result in formation of new chemical bonds, but significantly affected the temperature of poly-ε-caprolactone degradation that decreased from 537 to 472 °С. In comparison with the thermogram of montmorillonite, the weight loss corresponding to dehydration at 100 °С decreased by 2.9 %, which probably means that part of the intramolecular water was replaced by allylisothiocyanate molecules encapsulated in montmorillonite. In the experiment with two potato varieties infested with nematode cysts it was shown that soil treatment with allylisothiocyanate solutions allows to decrease number of cysts of Globodera rostochiensis RoI compared to positive control (non-treated infested potato) in 1.5–3.0 times depending on the variety. Moreover, in contrast to allylisothiocyanate solutions, poly-ε-caprolactone/montmorillonite/allylisothiocyanate granules are more effective that makes them promising for applications in Globodera rostochiensis RoI control.

An improved analytical model of effective thermal conductivity for hydrate-bearing sediments during elastic-plastic deformation and local thermal stimulation

As one of the crucial thermal properties controlling the dissociation of natural gas hydrate (NGH), effective thermal conductivity (ETC) should be precisely determined to improve the efficiency of NGH exploitation. But so far, most existing analytical ETC models of hydrate-bearing sediments could not accurately characterize the evolution of ETC. In this paper, an improved analytical model is derived for quantitatively revealing physical relations between ETC and various influencing factors during elastic-plastic deformation and local thermal stimulation processes, including hydrate saturation change, complex pore structures evolution, and hydrate occurrence patterns transition. The effectiveness of the proposed model is validated against available experimental data and compared with other existing models, then effects of various critical parameters on ETC are investigated. Results show that the porosity of hydrate-bearing sediments is accurately predicted during both loading and unloading processes, and the calculated ETC values under various conditions (effective stress, hydrate saturation, and temperature) are satisfactory with the test data. Contributions of elastic deformation and plastic deformation to ETC increments are quantitatively obtained. It is noteworthy that this proposed model is significant to reveal the evolution mechanisms of ETC, helping to accurately predict gas production and offer better plans for efficient NGH exploitations.

Experimental Investigation on Thermal Runaway of Lithium-Ion Batteries under Low Pressure and Low Temperature

Understanding the thermal runaway mechanism of lithium-ion batteries under low pressure and low temperature is paramount for their application and transportation in the aviation industry. This work investigated the coupling effects of ambient pressure (100 kPa, 70 kPa, 40 kPa) and ambient temperature (−15 °C, 0 °C, 25 °C) on thermal behaviors in an altitude temperature chamber. The experimental results indicate that lowering ambient pressure and temperature could attenuate the thermal runaway intensity, which is mainly attributable to the reduction in oxygen concentration and the increase in heat loss. Such a dual effect leads to the maximum temperature decreasing from 811.9 °C to 667.5 °C, and the maximum temperature rate declines up to 2.6 times. Correspondingly, the whole thermal runaway process is deferred, the total time increases from 370 s to 503 s, and the time interval, Δt, from safety venting gains by 32.3% as the ambient pressure and temperature decrease. This work delivers an in-depth understanding of the thermal characteristics under low pressure and low temperature and provides meritorious guidance for the safety of cell transportation in aviation.

Experimental Investigation on Thermal Runaway of Lithium-Ion Batteries under Low Pressure and Low Temperature

Understanding the thermal runaway mechanism of lithium-ion batteries under low pressure and low temperature is paramount for their application and transportation in the aviation industry. This work investigated the coupling effects of ambient pressure (100 kPa, 70 kPa, 40 kPa) and ambient temperature (−15 °C, 0 °C, 25 °C) on thermal behaviors in an altitude temperature chamber. The experimental results indicate that lowering ambient pressure and temperature could attenuate the thermal runaway intensity, which is mainly attributable to the reduction in oxygen concentration and the increase in heat loss. Such a dual effect leads to the maximum temperature decreasing from 811.9 °C to 667.5 °C, and the maximum temperature rate declines up to 2.6 times. Correspondingly, the whole thermal runaway process is deferred, the total time increases from 370 s to 503 s, and the time interval, Δt, from safety venting gains by 32.3% as the ambient pressure and temperature decrease. This work delivers an in-depth understanding of the thermal characteristics under low pressure and low temperature and provides meritorious guidance for the safety of cell transportation in aviation.

Thermal processing of wheat bran: Effect on the bioactive compounds and dietary fiber

In the current study bran from six wheat cultivars were subjected to different heat treatments and the effect of heat treatments on the bioactive composition, dietry fibre content and structure of wheat bran was evaluated. The findings indicated that thermally treated wheat bran contains higher soluble dietary fiber, but lower insoluble and total dietary fiber than untreated wheat bran samples. Microwave heat treatment caused highest increase in the soluble dietary fiber content and highest soluble dietary fiber content was observed in bran of WH-1105 wheat variety. The presence of six different phenolic acids evaluated were gallic acid, p-hydroxybenzoic acid, ferulic acid, syringic acid, vanillic acid, and p-coumeric. Heat treatment caused significant increase in all the six phenolic acids. The bran sample obtained from wheat variety WH-1105 showed highest level of all phenolic acid among the all-bran sample obtained from other wheat varieties. Among the all heat treatments, microwave heat treatment caused highest increase in the phenolic acids. Among all phenolic acid evaluated highest increase was observed for syringic acid after microwave heat treatment in the bran of WH-1105 wheat variety. Further it was observed that crystallinity index significantly increased after thermal treatment and microwave heating caused higher increase in crystallinity than other heat treatments.

Optimization of Torrefaction Parameters Using Metaheuristic Approach

The probabilistic technique was used to optimize the torrefaction parameters that indirectly influence the yield of end-products obtained through the pyrolysis of biomass. In the same pursuit, pine cones underwent thermal pre-treatment at 210 °C, 220 °C, 230 °C, 240 °C, and 250 °C in the presence of N2 gas with a flowing rate of 0.7 L∙s−1, whereas the duration of the pre-treatment process was 5 min, 10 min, and 15 min at each. To facilitate the processing of pine waste, a muffle furnace was improvised for pilot-scale testing. The thermal process used to carry out torrefaction was quasi-static. The average dynamic head of volatile gases inside the chamber was 1.04 m. The criteria for determining the optimal solution were based on calorific value, solid yield, energy consumption during the pre-treatment process, and ash handling. In absolute terms, time and temperature did not influence the statistical deviation in cellulose and hemicellulose decomposition after thermal pre-treatment. While considering ash content as a primal factor, thermal processing should be conducted for 5 min at 210 °C for the bounded operating conditions, which are similar to the operating conditions obtained experimentally. The optimal solid yield would be obtained if the thermal pre-treatment is performed at 250 °C for 5 min. The solution derived through a simulated annealing technique provided a better convergence with the experimental dataset.

Co-Treatment of Food Waste and Municipal Sewage Sludge: Technical and Environmental Review of Biological and Thermal Technologies

To face the ongoing issues related to global warming, a circular economy approach should be pursued, rethinking the waste management system and the recovery of organic waste. The main organic waste streams are Food Waste (FW) and municipal Sewage Sludge (SS). In the spirit of circularity, a commingled treatment of FW and SS could be a viable solution. To this end, the present work aims to review the technical and environmental aspects of the co-treatment of FW and SS through biological and thermal processes. Firstly, a detailed characterization of the two substrates is presented as well as the current and future treatment technologies. Then, the technical feasibility and the environmental impacts of conventional biological co-treatments of FW and SS (i.e., composting, anaerobic digestion, and a combination of them), as well as innovative thermal ones (i.e., incineration, gasification, pyrolysis, and hydrothermal carbonization), is summarized. The outcomes of this work could contribute to achieving a more sustainable way to approach organic waste treatment and to help policy-making authorities move toward sustainable planning.

Thermal Decomposition of Bio-Based Plastic Materials.

This research delves into a detailed exploration of the thermal decomposition behavior of bio-based polymers, specifically thermoplastic starch (TPS) and polylactic acid (PLA), under varying heating rates in a nitrogen atmosphere. This study employs thermogravimetry (TG) to investigate, providing comprehensive insights into the thermal stability of these eco-friendly polymers. In particular, the TPS kinetic model is examined, encompassing the decomposition of three distinct fractions. In contrast, PLA exhibits a simplified kinetic behavior requiring only a fraction described by a zero-order model. The kinetic study involves a systematic investigation into the individual contributions of key components within TPS, including starch, glycerin, and polyvinyl alcohol (PVA). This detailed analysis contributes to a comprehensive understanding of the thermal degradation process of TPS and PLA, enabling the optimization of processing conditions and the prediction of material behavior across varying thermal environments. Furthermore, the incorporation of different starch sources and calcium carbonate additives in TPS enhances our understanding of the polymer's thermal stability, offering insights into potential applications in diverse industries.

Determination of optimal air supply form on sludge convective drying process: A CFD-DEM study

Convective thermal drying is usually used in sludge dryers, and the air supply forms significantly affect the sludge drying efficiency. In this work, the drying process of multi-layered sludge is numerically simulated using a coupled computational fluid dynamics-discrete element method (CFD-DEM) approach. Better than our previous work, the current CFD-DEM model further considers the dynamic process of humidity within the flow field. Firstly, the CFD-DEM model is validated based on the mechanistic experimental data. Then, extensive numerical simulations are carried out to investigate the two-layered sludge drying process in the dryer, and the effects of two conventional air supply forms (Top-to-Bottom and Bottom-to-Top) as well as a novel air supply form (Side-assist) on the two-phase flow system are discussed. The simulation results provide in detail the dynamic processes of momentum, heat and mass (moisture) in the convective drying system under different working conditions. Following recommendations are presented to facilitate the operation of the dryer: Bottom-to-Top is better for sludge drying and tends to utilize less heat from the heat source compared to the Top-to-Bottom. The drying efficiency can be further improved by supplying the Side-assist with an optimal flow ratio of side-wind to bottom-wind. Numerical results show that the optimal flow ratio is related to the total air volume, the deflection angle and the side-wind temperature. The present study reveals in depth the impact mechanism of the air supply form on the convective thermal drying process of sludge, which contributes to the design and optimization of high-efficiency dryers.

High-speed single-frame polarimeter for thermal radiation to measure the 3D geometry of hot metal surfaces

The 3D geometry of the interaction zone in laser material processing is of major importance as it defines the absorption of the laser beam and may influence the hydrodynamics of the process. With the aim of measuring this geometry, which typically changes with frequencies in the order of 10 kHz, a single-frame polarimeter with acquisition rates of up to 75 kHz is presented in this work. It simultaneously records four images of the thermal process emission, through four linear polarizers with different orientations. The formulae required for the reconstruction of the 3D geometry from these images are derived and validated on an example of a heated steel sphere. The reconstructed geometry was found to be in good agreement with the examined sphere. An experimental example is also given of the application of this technology to geometry measurement of a highly dynamic laser cutting front at a framerate of 75 kHz.

The Influence of Varying Ar/O2 Gas Ratio with Catalyst-Free Growth by Homemade Thermal Evaporation Technique

A nanostructured zinc oxide (ZnO) with different percentages of argon and oxygen gas flow rate was deposited on a silicon wafer by a simple hot tube thermal evaporation technique. The effect of different percentages of gas flow rate on the crystal structure, surface morphology and optical properties were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and RAMAN spectroscopy, respectively. The changes of morphologies from FESEM were significant where the grown ZnO nanostructures show three different shapes which are nanotripods, nanoclusters and nanorods at 5%, 10% and 25% of oxygen gas, respectively. EDX results revealed that Zn and O elements have a major percentage in the sample indicating a composition has high purity of ZnO. XRD patterns displayed the most intense diffraction peak of ZnO at (101), which exhibited a single crystalline hexagonal structure with preferred growth orientation in the c-axis. RAMAN scattering study found that synthesized ZnO shows the high intensity of E2 mode and low intensity of E1 mode attributed to all the samples having good crystal quality containing fewer structural defects. In conclusion, the E15 sample with a 25% oxygen gas flow rate was selected as an optimum result for synthesizing a homogenous surface and high crystallinity of ZnO by using a hot tube thermal evaporation process. This work can enhance the development of ZnO production in various applications.

The Influence of Varying Ar/O2 Gas Ratio with Catalyst-Free Growth by Homemade Thermal Evaporation Technique

A nanostructured zinc oxide (ZnO) with different percentages of argon and oxygen gas flow rate was deposited on a silicon wafer by a simple hot tube thermal evaporation technique. The effect of different percentages of gas flow rate on the crystal structure, surface morphology and optical properties were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) and RAMAN spectroscopy, respectively. The changes of morphologies from FESEM were significant where the grown ZnO nanostructures show three different shapes which are nanotripods, nanoclusters and nanorods at 5%, 10% and 25% of oxygen gas, respectively. EDX results revealed that Zn and O elements have a major percentage in the sample indicating a composition has high purity of ZnO. XRD patterns displayed the most intense diffraction peak of ZnO at (101), which exhibited a single crystalline hexagonal structure with preferred growth orientation in the c-axis. RAMAN scattering study found that synthesized ZnO shows the high intensity of E2 mode and low intensity of E1 mode attributed to all the samples having good crystal quality containing fewer structural defects. In conclusion, the E15 sample with a 25% oxygen gas flow rate was selected as an optimum result for synthesizing a homogenous surface and high crystallinity of ZnO by using a hot tube thermal evaporation process. This work can enhance the development of ZnO production in various applications.

Assessment of the Sensitivity of Foodborne Cronobacter spp. Strains and Other Enterobacteria to Temperature Stresses and Chlorine-Containing Biocides.

We examined the effects of elevated temperatures and biocides on survivability of food isolates of Cronobacter spp. (C. sakazakii) and concomitant enterobacteriaceae obtained in microbiological control of infant nutrition products. Increased resistance of certain strains of Cronobacter, Enterobacter cloacae, and Pantoea spp. to thermal processing was revealed. Salmonella, Pantoea, and Cronobacter bacteria were least sensitive to antimicrobial action of chlorine-containing agents. The above properties varied in the strains of the same species. Specifically, only two of three examined isolates of Cronobacter spp. demonstrated lower sensitivity to heat in comparison with the enterobacterial test-cultures of other species.

Effect of Heat Treatment on Mechanical Properties and Corrosion Response of HVOF Sprayed High Entropy Alloy Coatings

Surface and sub-surface related degradation of steels can be minimized using suitable surface coatings. High entropy alloys (HEA) are prominent and emerging materials among many coating materials. The current study investigates the effect of heat treatment of HEA coating on mechanical, metallurgical, and corrosion properties. The HEA coatings on SS304 steel were deposited using a High-Velocity Oxy-Fuel (HVOF) thermal spray process. The developed coatings were furnace heat treated at 700 °C, 900 °C, and 1100 °C, respectively, and their performance was benchmarked with the as-sprayed coatings. The metallurgical, mechanical, and microstructural analyses were performed using X-ray diffraction (XRD), Nanoindentation, Scratch test, and Field Emission Scanning Electron Microscope (FESEM) techniques. The corrosion response of the as sprayed and heat-treated coatings were recorded using a Potentiostat. The results indicated that as-sprayed coatings consisted of a single-phase BCC solid solution; however, the single-phase changed to a dual dual-phase system after heat treatment (BCC+FCC). The 900 °C heat-treated HEA coating exhibited superior mechanical and corrosion properties. But those characteristics started diminishing when the heat treatment temperature exceeded 900 °C. The introduction of the new FCC phase softened the coating, thereby leading to the evolution of microcracks in the coating. These micro-cracks acted as channels for electrolyte diffusion and further corroded the coatings. The current study surmised that HVOF-sprayed HEA coating should not be heat treated at above 900 °C.

Thermal and rheological properties and processability of thermoplastic lignocellulose

AbstractFossil‐free biobased materials like thermoplastic lignocellulose are gaining attention because of climate issues. However, there is a challenge to make these as thermoplastic as commonly used thermoplastics. Arboform® is one of today's commercially available thermoplastic lignocellulose materials. In this work, the processability of this material was studied in detail and the effects of plasticizers on its processability, rheological, and mechanical properties were determined. Thermal/calorimetry analysis indicated that the processing temperature window was shifted to lower temperature with the use of tributyl citrate (TBC) and poly(ethylene glycol) (PEG 400) plasticizers, thus enabling extrusion at lower temperature. TBC and PEG 400 decreased both the glass transition temperature and melting point of the polylactide component. Surprisingly, they also affected the lignin component, as observed by the decreasing lignin decomposition temperature. It is observed that TBC and PEG400 lowered the stiffness of the compression molded material in the temperature range investigated (−30–180°C), and tensile tests in the presence of TBC revealed a decrease in ductility. Notable is that, in contrast to most thermoplastics, the Arboform® melt increases in viscosity and elastic moduli when the processing temperature was increased (from 180 to 200°C) or when processing time was increased.

Evolution of correlated morphological and structural disorder in boehmite‐derived alumina with progressive calcination

This study explores the morphological and structural transformation of boehmite (AlOOH) into transition aluminas during calcination, a pathway crucial for diverse industrial applications. The primary focus is on the topotactic transformation of boehmite into γ‐Al2O3 and its subsequent transitions into higher temperature polymorphs, culminating in α‐Al2O3. Utilizing a combination of in situ X‐ray diffraction, in situ and ex situ transmission electron microscopy, 27Al solid‐state nuclear magnetic resonance, thermogravimetric analysis, nitrogen physisorption, and mercury porosimetry, this work provides insights into the morphological and structural reordering during the calcination process. Furthermore, the study highlights the significant impact of thermal processing on the morphological evolution of boehmite and transition aluminas, characterized by changes in pore structure sizes and shapes. These findings offer valuable insights for optimizing the properties of alumina‐based materials for specific applications.

Coupled fluid-structure-interaction simulation approach for correction of the thermal tool elongation to improve the milling precision

During milling operation, the position of the tool centre point (TCP) is affected by structural displacements, which are caused by force loads and heat input inside the machine as well as machining induced thermal loads. These thermal loads result in considerable thermal deformations of tool holder, tool, and accordingly the TCP position. They can be summed up to about tens of microns and compromise the dimensional accuracy. The objective was to develop an integrated, numerical simulation-based approach for future TCP correction for a milling process using characteristic diagrams. For this, a complex Fluid-Structure-Interaction (FSI) simulation model predicts the uni-axial displacement in the longitudinal direction of the TCP due to a specified process heat source at the tool tip. As a partial result, the simulation has reached its performance limits, under the restriction of a reasonable simulation time in order to produce characteristic diagrams for application on a milling machine. The calculated thermally induced displacement can be further processed with the aid of Design of Experiments (DoE) and response surface methodology (RSM), depending on the thermal process load and coolant volume flow rate. That results in characteristic diagrams for the displacement as a function of process parameters. In this study the calculated value for thermally induced TCP displacement covers a span from 10 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}m to 80 μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu$$\\end{document}m, with a strongly nonlinear behaviour. Subsequently, this forms the basis for a future implementation of characteristic diagrams in the machine control system for online correction of thermal tool errors.

Effect of thermal processing on the degradation of pesticides in a banana jam partially formulated with banana peel flour

Bananas are one of the most widely consumed fruits in Brazil and across the world. However, the intensive use of pesticides in these and other crops can negatively impact human and animal health due to the possibility of pesticide residues persisting in derived products, even after industrial processing. Therefore, this study evaluated the effect of thermal processing on the degradation of the pesticides azoxystrobin, bifenthrin, difenoconazole, and simazine in samples of caramelized banana jam added of banana peel flour (4% w/w) in partial replacement of the fruit pulp. QuEChERS (quick, easy, cheap, effective, rugged, and safe) method and gas chromatography coupled to mass spectrometry (GC-MS) wa used to analyze the above compounds. The method was validated following the standard procedures of the European Commission and ANVISA. Samples of banana pulp were spiked with the pesticides at different concentrations (0.1, 0.5 and 1.0 mg.Kg-1) in order to observe their degradation following thermal processing. Degradation percentages ranged between 28 and 60%, and these were potentially influenced by the physicochemical properties of each compound, as well as the characteristics of the food matrix. The thermal processing provided partial degradations of pesticide residues, some at levels below the MRLs (Maximum Residual Levels) established for bananas. Currently, there is no specific legislation in Brazil and in many other countries for controlling pesticides in processed foods, such as fruit jellies. Therefore, this research highlights the need for the creation of new food laws by government agencies to this end to ensure the provision of safe food to the wide population.