Slow Heating Research Articles

Microwave assisted heating of plastic waste: Effect of plastic/susceptor (SiC) contacting patterns

Plastic accumulation is a growing sustainability challenge. Most plastics are thermally inert at room temperature, requiring high temperatures for depolymerization. In the quest for developing sustainable plastic upcycling, we investigate silicon carbide (SiC) as microwave absorbing susceptors for reaching depolymerization temperatures. We utilize three SiC topologies – particles, hot-pressed plastic films containing SiC particles, and monoliths. SiC particles of >0.5 mm in diameter can provide heating rates approaching ∼200 °C/min at modest powers. Still, physically mixed plastic-susceptor beds suffer from density differences, causing non-uniform contact during plastic softening and melting. Hot-pressed plastic films containing SiC particles allow uniform plastic-susceptor contact but suffer from slow heating as only a single layer of susceptors exists between polymer layers. SiC monoliths mitigate these challenges by preferentially dissipating the microwaves and rapidly heating the plastics independently of polymeric properties.

Exploring the thermal behavior of nitrocellulose used for lacquers by slow heating experiments

Exploring the thermal behavior of nitrocellulose used for lacquers by slow heating experiments

Research on temperature field during the hot pressing process of UHMWPE-based water-lubricated bearing

This paper aimed at the problem of uneven heating of ultra-high molecular weight polyethylene (UHMWPE) bearing in the process of UHMWPE was made into water-lubricated bearing, and have used ICEPAK software to study the temperature distribution of the UHMWPE during hot pressing. Research indicated that hot pressing UHMWPE was an unsteady heat transfer in the process of heating and holding. Air convection had little effect on the overall process. During processing, the slow heating method to process smaller UHMWPE water-lubricated bearing could effectively reduce the temperature difference. It made the inner heating of UHMWPE uniform and equated to the temperature of the shaft sleeve. This research can provide data support for temperature control and process optimization for the UHMWPE-based water-lubricated bearing hot pressing process.

Effect of Heat Dissipation Rate on Microstructure and Mechanical Properties of Al0.5FeCoCrNi High-Entropy Alloy Wall Fabricated by Laser Melting Deposition

High-entropy alloys (HEAs) are a new type of multi-component alloy. The design of the compositions breaks the design ideas of traditional alloys and shows many excellent properties. Therefore, an Al0.5FeCoCrNi HEA with face-centered cubic (FCC) and body-centered cubic (BCC) dual-phase structure was used in this paper. During the additive manufacturing process, the heat dissipation rate gradually changes with the increase in wall height. As a result, the composition of the phases changes, resulting in differences in mechanical properties. Here, we designed laser melting deposition (LMD) on T-beams of different heights to change the heat dissipation rate of the wall, and the effects of the heat dissipation rate on the microstructure and mechanical properties of Al0.5FeCoCrNi HEAs were studied. The experimental results showed that increasing the height of the T-beam would gradually slow down the heat dissipation rate of the wall. The above phenomena not only led to a gradual reduction of the BCC phase under the influence of heat accumulation but also increased the length of columnar crystals in the wall with the slowing of heat dissipation. Heat accumulation hindered the nucleation during solidification and eventually led to the growth of grains across the deposition layer. Furthermore, the slow heat dissipation rate changed the grain number and BCC phase content, which gradually decreased the strength and hardness, while the ductility of the samples improved.

Computational assessment of the thermal response of a Li-ion battery module to transient loads

This paper provides a methodology to assess the average surface temperature of battery cells under realistic transient scenarios. Computational fluid dynamics modelling of battery cooling is conducted for the cases exposed to the ramps of internal heat generation inferred from the standard driving cycles. The results are then post-processed to determine the effectiveness of air and water as the coolant fluids. A quantitative measure of the maximum overshoot, dimensionless settling (DST), heating (DHT), and cooling (DCT) time is subsequently presented. It is shown that, compared to water, air produces a considerably delayed response to temporal changes in the internal heat generation and is slower at reaching the new steady state condition. Cooling battery cells by using water almost always ensures remaining within the safe operating range. Nonetheless, regardless of the coolant type, the long period ramps tend to produce smaller values of DST. The primary origin of the delay is the slow heat conduction within the battery cells. In addition, it is shown that water responds to changes in the internal heat generation far quicker during the heating and the cooling phases. The study highlights the importance of transient analyses for characterising the thermal behaviour of battery packs.

Comment on “The effects of radio-frequency bias on electron density in an inductively coupled plasma reactor” [J. Appl. hys. 102, 113302 (2007)

Sobolewski et al. [J. Appl. Phys. 102, 113302 (2007)] obtained the complex responses of electron density to the long-pulsed RF bias and proposed the gas composition effect as a key underlying factor. In this Comment, the consistent explanations on the complex responses indicate that the ignored slow wall heating should be taken into account.

Results of simulations of atmosphere-lake interactions using numerical model

Lakes influence the regional atmosphere through modifying thermodynamic characteristics. This study examines the effects of the Baikal lake on meteorological parameters in summertime using the numerical model. Diurnal variations in the lakes’ impact on the atmosphere are found through changing the surface energy budget, which includes changes in sensible and latent heat fluxes. The changes in heat fluxes cause relatively lower surface temperature which leads to a shallow boundary layer over the lake surfaces. Greater heat capacity in water bodies compared to grasslands causes slower heating and cooling rates in the lakes. The amplitude of air temperature over the lake surfaces is smaller than that over the grasslands. Lakes promote diverging winds near the ground, furthermore, tend to stabilize the overlying atmosphere in the summertime.

Adsorbent Coatings for Adsorption Heat Transformation: From Synthesis to Application

In recent years, growing energy demands and environmental pollution caused by the extensive use of fossil fuels have inspired considerable research interest in adsorptive heat transformation (AHT). This technology offers effective utilization of low-grade solar or waste thermal energy for cooling and heating with low environmental impact. Increasing the AHT power is a keystone for further development and dissemination of this emerging technology. The AHT power is mainly determined by ad/desorption dynamics, which is significantly hindered by slow heat transfer between the adsorbent and heat exchanger. Shaping the adsorbent bed as a coating on the heat exchanger surface is considered an effective route to enhance heat transfer and increase the AHT power. In this review, the technology of adsorbent coating for AHT is comprehensively surveyed, including coating synthesis, adsorption dynamics, and use in real AHT devices. The advantages of the coated bed configuration are considered, and its challenges are outlined. Finally, recommendations for better organization of the coating’s structure for rational control of the relative contributions of heat and mass transfer are considered.

Temporal scale-bridging of chemistry in a multiscale model: Application to reactivity of an energetic material

A heterogeneous multiscale method (HMM) to evolve chemistry across disparate temporal scales is presented. The method directly couples a particle-based, microscale coarse-grain chemistry model to a macroscale continuum finite element model of deformation. The macroscale model obtains both the material equation-of-state and instantaneous chemical reaction rates through evaluation of the microscale model subject to distinct boundary conditions. The approach is demonstrated through several simulations of the energetic material 1,3,5-trinitrohexahydro-s-triazine (RDX) subject to slow heating, including a simulation inspired by the scaled thermal explosion (STEX) experiment.

Effect of heating rate and feedstock nature on electrical conductivity of biochar and biochar-based composites

Cost-effective strategies for integrating bio-oil production with biochar utilization in new sustainable platforms are needed to improve the economic viability of pyrolysis for energy applications. Recently, the use of biochar as filler in the preparation of polymer based composites received a great attention due to its ability to improve polymers mechanical, electrical and thermal properties.This work aims to expand knowledge on the effect of the heating rate and feedstock chemical composition on the on the biochar structural and chemical characteristics affecting electrical properties of the biochar at different pyrolysis temperatures. Biochars were produced from three feedstocks, namely walnut shells (WS), the lignin rich residue from bio-ethanol production (LRR) and sewage sludge (SS), under slow and fast heating rate at 500, 600 and 700°C. The three feedstock differ for both the organic components (i.e. high lignin content in WS and LRR and presence of proteins in SS) and ash content which is highest in SS.The produced biochars were characterized and the observed differences in their chemical and structural properties were discussed in relation to their effect on the measured electrical conductivity.The severity of the pyrolysis treatment improved biochars electrical conductivity. Heating rate and feedstock type affected the electrical conductivity only marginally at 500 and 600°C, whereas at 700°C any relevant effect was observed. WS biochars produced at 500 and 600°C exhibited the lowest electrical conductivity regardless of the heating rate of the production process.The biochars produced at 700°C were used to prepare epoxy resins composites. Despite their comparable conductive performance, the biochars lent different electrical conductivity to the composites depending on the biomass type and the heating rate experienced by the biomass samples during the pyrolytic treatment. The composite prepared with WS biochar produced under fast heating rate exhibited the highest electrical conductivity.

Heating Rate during Shell Egg Thermal Treatment Elicits Stress Responses and Alters Virulence of Salmonella enterica Serovar Enteritidis; Implications for Shell Egg Pasteurization.

Thermal pasteurization of shell eggs, at various time-temperature combinations, has been proposed previously and implemented industrially. This study was conducted to determine if shell egg heating rate, which varies with different pasteurization implementations, alters the Salmonella enterica serovar Enteritidis response to different stresses or expression of virulence. Shell eggs, containing Salmonella Enteritidis in yolk, were subjected to a low (2.4°C/min) or a high (3.5°C/min) heating rate during treatments that mimicked the pasteurization temperature come-up stage. The low heating rate protected Salmonella from the following processes: (i) lethal heat at the holding stage, (ii) loss of viability during 8-h cooling after heating, and (iii) sequential antimicrobial ozone treatment. Transcriptional analysis using Salmonella reporter strains revealed that the heat stress response gene grpE was transcribed at 3-fold-higher levels (P = 0.0009) at the low than at the high heating rate. Slow heating also significantly increased the transcription of the Salmonella virulence-related genes sopB (P = 0.0012) and sseA (P = 0.0006) in comparison to fast heating. Salmonella virulence was determined experimentally as 50% lethal dose (LD50) values in an in vivo model. The slow heat treatment mildly increased Salmonella Enteritidis virulence in mice (LD50 of 3.3 log CFU), compared to that in nontreated yolk (LD50 of 3.9 log CFU). However, when ozone application followed the slow heat treatment, Salmonella virulence decreased (LD50 of 4.2 log CFU) compared to that for heat-treated or nontreated yolk. In conclusion, heating shell eggs at a low rate can trigger hazardous responses that may compromise the safety of the final pasteurized products but following the thermal treatment with ozone application may help alleviate these concerns. IMPORTANCE Pasteurization of shell eggs is an important technology designed to protect consumers against Salmonella Enteritidis that contaminates this commodity. A low heating rate is preferred over a high rate during shell egg thermal pasteurization due to product quality concern. However, it is not known whether raising the temperature at different rates, during pasteurizing, would potentially affect product safety determinants. The current study demonstrated that slow heating during the pasteurization come-up stage increased the following risks: (i) resistance of Salmonella to pasteurization holding stage or to subsequent ozone treatment, (ii) recovery of Salmonella during the cooling that followed pasteurization, and (iii) Salmonella's ability to cause disease (i.e., virulence). Our findings inform food processors about potential safety risks to consumers resulting from improper use of processing parameters during shell egg pasteurization. Additionally, treating shell eggs with ozone after heat treatment could alleviate these hazards and protect consumers from natural Salmonella Enteritidis contaminants in shell eggs.

Formation of imperfect crystals in poly(ε-caprolactone) at high melt-supercooling

• Fast scanning calorimetry permits homogeneous crystal nucleation in PCL. • Crystallization of PCL near the glass transition yields non-lamellar, imperfect crystals. • Low-temperature crystallization of PCL suppresses spherulitic crystal growth. Poly(ε-caprolactone) (PCL) was crystallized at high melt-supercooling in a fast scanning chip calorimeter, with this instrumentation needed to reach the temperature range of homogenous crystal nucleation by fast cooling the melt. Subsequently, after slow heating the polymer to ambient temperature, the semicrystalline morphology and X-ray structure were evaluated. Nucleation and crystallization at low temperature yields a featureless structure at the micrometer-length scale, indicating non-spherulitic crystal growth. Images of the nanometer-scale structure suggest presence of irregular grown short lamellae or particle-like domains, and the absence of sharp peaks in the X-ray scattering pattern indicates formation of small or defective crystals. In conclusion, due to the high nuclei density, crystallization of PCL near the glass transition leads to formation of imperfect crystals, and slow heating to ambient temperature does not allow their reorganization to yield long-range orthorhombic order, typically observed on crystallization at low melt-supercooling.

Enhanced mechanical properties in metastable β titanium alloy via ω-assisted nucleation

In this study, we performed heat treatment with different solution cooling routes and aging heating rates were performed on the TB18 alloy (Ti-5.3Cr-4.9Mo-4.9V-4.3Al-0.9Nb-0.3Fe) to enhance its mechanical properties via ω-assisted nucleation. The results showed that the intragranular α plates that precipitated during aging appeared finer under slow heating than under fast heating because the ωiso particles formed during the slow heating process provide abundant ω/β interfaces, which can serve as heterogeneous nucleation sites for α precipitates and reduce the nucleation driving force. The corresponding phase transformation sequence is expected to be β + ωath → β + ωath + ωiso → β + ωiso + α → β + α during continuous heating. Further comparing the microstructures, we found that a faster solution cooling rate is more conducive to ω-assisted nucleation. During ω-assisted nucleation, the three-phase orientation relationship holds for: (112‾0)ω//(0001)α//(110)β, and [0001]ω//[112‾0]α//[11‾1]β. At the atomic scale, the ω/α interface appeared as a relatively straight atomic plane, whereas more defects, termed as disconnections, were observed at the α/β interface. Moreover, appropriate ω-assisted nucleation could enhance the ductility of the TB18 alloy without reducing its strength to obtain the optimal comprehensive mechanical properties, and the corresponding fracture mechanism was a mixed mode dominated by ductile fracture. Excessive ω-assisted nucleation could considerably strengthen the alloy but significantly deteriorated its ductility, and the mixed fracture mode was more inclined to brittle fracture.

Fire hazard analysis of Mediterranean Genista Salzmannii: Pyrolysis and kinetic characterization

The present article aims to enhance the understanding of the solid-state thermal degradation behavior and pyrolysis kinetics of Mediterranean Genista Salzmannii Needles (GSN) to support wildland fire research. In fact, proximate, ultimate and microstructural analyses were performed to characterize forest fuel-based material. In addition, a thermogravimetric system coupled with Fourier Transform Infrared spectrometry (TG-FTIR) was used to analyze the pyrolytic behavior and the evolved gaseous products. Experiments included testing both grinded and intact (cut GSN) forms of GSN, which can provide reliable information for pyrolysis models. Slow (20 and 40 °C/min) and quasi-fast (60, 80 and 100 °C/min) heating rates were applied for the TG-FTIR experiments, in order to get close from the actual conditions of wildland fires (preheating/smoldering and flame region, respectively). Furthermore, the kinetic triplet was determined at five heating rates by means of two iso-conversional methods (Flynn–Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) coupled with one model fitting method (Coats Redfern). A numerical simulation was applied to adequately estimates these parameters. The analysis findings revealed that GSN has a high content of volatile and carbon. The rapid pyrolysis zone (200–600 °C) was considered as the main stage of mass loss. The cut GSN was characterized by a higher mass loss rate compared to the grinded GSN. The dominant gases released during pyrolysis were CO2, CO bond, CC bond, CH and/or CO bond, aliphatic C-H (existence of CH4) and H2O. Moreover, kinetic analysis between 180 and 650 °C revealed that the average apparent activation energy (Eα) derived from FWO and KAS of the cut GSN (206.7, 242.2 and 376.6 kJ/mol for stage 1, 2 and 3, respectively) was slightly higher than those of grinded GSN (176.9, 203.7 and 360.1 kJ/mol for stage 1, 2 and 3, respectively). The different Eα distribution was mainly due to the compact physical structure of the cut GSN. The thermal decomposition of hemicellulose (0.05 < α < 0.35) and cellulose (0.35 < α < 0.75) were best described by the random nucleation and nuclei growth mechanisms (A1/3 and A1/2, respectively). Char formation (α > 0.75) was the most complex process and was found to be consistent with the high-order reaction model. Finally, the simulated data of conversion based on the obtained kinetic triplet exhibited a good agreement with the experimental data.

Feasibility investigation of utilizing spontaneous combustion energy of abandoned coal gangue by constructing a novel artificial heat reservoir

In this paper, we present a novel artificial heat reservoir system for extracting spontaneous combustion energy of abandoned coal gangue. The construction process and operation method of the proposed artificial heat reservoir are introduced in detail. A multi-physical fields coupling model of seepage, heat transfer and oxidation of coal gangue is established. The spatio-temporal variation of temperature field, seepage field, oxygen concentration field and residual fuel amount in the oxidation process of coal gangue were numerically investigated. Sensitivity analysis of key parameters was carried out to provide reference for the optimization of artificial heat reservoir. Finally, the heat extraction performance of artificial heat reservoir was studied by using steel U-shaped tube, and its heating potential was evaluated. The results indicates that the process of spontaneous combustion of coal gangue can be divided into two stages: slow heating stage and rapid heating stage. The proposed artificial heat reservoir system presents a “low temperature zone-high temperature zone-low temperature zone” distribution from bottom to top. This alternating and layered temperature zones in vertical direction will form a thermal siphon effect and drive the air to flow upwards. In the rapid heating stage, the temperature increases faster with the increase of ventilation rate. When the porosity is greater than 0.35, it has a great influence on the spatial design of the heat extraction system. The specific heat capacity only affects the changing rate of temperature field and oxygen seepage velocity, but does not affect their final states. The thermal conductivity of coal gangue has little influence on each physical field of reservoir. The heat transfer rate of the middle part of the U-shaped tube is relatively large, the average value of which is about 150 W/m. The heat transfer of U-shaped tube only affects the area within the radius of 2 m. The research can provide a new idea for coal gangue disposal and heat utilization.

Re-examination of martensitic stabilization in Cu-based shape memory alloys Part II. Key factors determining occurrence of martensitic stabilization in Cu-based alloys

Present proposed mechanisms for ageing-induced martensitic stabilization cannot explain why the amount of martensites losing reverse transformation ability (RTA) positively depended on Ms temperatures in directly-quenched CuZnAl alloys owing to dynamic ageing during the cooling process of quenching and subsequent slow heating. We proposed and confirmed that the number of vacancies at martensites boundaries (Nvmb) was the key factor controlling the occurrence of martensitic stabilization and its resulting RTA or loss in shape memory effect, not the number of vacancies inside the martensites and their long-range diffusion. All reported results can be rationalized by the positive dependence of original Nvmb on the Ms temperature.

Reactivity of boron carbide and metal oxide mixtures

Boron-based materials have high energy density making them suitable as additives in propulsion systems. However, the lack of prompt ignition, for example, creates a challenge in harnessing the energy. In this work, mixtures of boron carbide and four common metal oxides (CuO, MnO2, Bi2O3, Fe2O3) are studied as a way to increase the reactivity of boron-based materials. Both burning rate and thermal analysis are used to determine the response of mixtures to fast and slow heating rates, respectively. Mixtures with CuO or Bi2O3 burned the fastest whereas Fe2O3 mixtures would not ignite and MnO2 samples had a burning rate approximately 15% that of the fastest mixtures. The thermal analysis determined that the gas produced from carbon oxidation was most influential on the combustion rate and not the thermal conductivity or oxygen release temperature of the oxide. Experimental observation indicates that the boron component is oxidized in the condensed phase despite the importance of gas generation. Spectroscopic evidence presented suggests gas generation aids in removing the molten boron oxide layer during combustion which can be utilized to improve the reactivity of boron-based additives in propulsion applications.

A simplified phase change model and performance optimization of plate latent heat storage unit with graded porous

In this paper, a simplified phase change model with graded porous is proposed for the problems of slow heat transfer rate and low computational efficiency in the field of latent heat storage (LHS) technology. Moreover, the proposed simplified model is further combined with the genetic algorithm to optimize the structure parameters of graded porous for the optimal strengthening effect. Considering the solidification process in the plate phase change heat storage device, the prediction accuracy and prediction efficiency of the simplified model based on the quasi-stationary approximation method are first verified. The results show that the simplified model can quickly and accurately predict the thermal performance of the LHS unit. When the effective Stefan number is less than 0.1645, the solidification time deviation is about 5% and the temperature deviation is less than 0.12%. Then, the genetic algorithm is introduced to optimize the distribution of graded porous under the different metal foam materials, metal foam consumptions, and container structure parameters. The optimization results indicate that the thermal performance of the LHS unit under different parameters gradually improves with the increase of the graded layer number. But the strengthening effect is close to the best when the graded layer number is only 4. Compared with the uniform porous structure, the solidification time can be shortened by 7.62%, while the best strengthening effect is 8.25%. Therefore, the four-graded layer structure is preferred to achieve a balance between thermal performance and structure complexity. This work can provide a simple and fast optimization design method for the structural layout of the LHS unit strengthened by graded porous.

Re-examination of martensitic stabilization in Cu-based shape memory alloys Part I. Identification of occurrence stage and degree of martensitic stabilization in CuZnAl alloys

Previous work did not identify occurrence stage and degree of martensitic stabilization in Cu-based shape memory alloys due to lower heating rate. By flash heating into liquid metals, we systematically clarified contribution of static ageing and the ones of dynamic ageing during process of quenching and heating to the martensitic stabilization in directly-quenched CuZnAl alloys. We discovered that the dynamic ageing during the cooling process of quenching could instantaneously stabilize a few already formed martensites totally although it did not stabilize the overwhelming majority of martensites. The dynamic ageing during the process of subsequent slow heating was responsible for the partial and total stabilization of overwhelming majority of martensites. Both the amounts of martensites stabilized totally by the two dynamic ageing positively depended on Ms temperature. The conventional up-quenching into oil or air actually made more martensites stabilized due to the dynamic ageing during the process of slow heating. The increase in As temperature owing to the static ageing also positively depended on the Ms temperature. These dependences cannot be explained by two well-known mechanisms for the martensitic stabilization.

Single-Mode Electromagnetic Resonance Rewarming for the Cryopreservation of Samples with Large Volumes: A Numerical and Experimental Study.

Rapid and uniform rewarming has been proved to be beneficial, and sometimes indispensable for the survival of cryopreserved biomaterials, inhibiting ice-recrystallization-devitrification and thermal stress-induced fracture (especially in large samples). To date, the convective water bath remains the gold standard rewarming method for small samples in the clinical settings, but it failed in the large samples (e.g., cryopreserved tissues and organs) due to damage caused by the slow and nonuniform heating. A single-mode electromagnetic resonance (SMER) system was developed to achieve ultrafast and uniform rewarming for large samples. In this study, we investigated the heating effects of the SMER system and compared the heating performance with water bath and air warming. A numerical model was established to further analyze the temperature change and distribution at different time points during the rewarming process. Overall, the SMER system achieved rapid heating at 331.63 ± 8.59°C min-1 while limiting the maximum thermal gradient to <9°C min-1, significantly better than the other two warming methods. The experimental results were highly consistent, indicating SMER is a promising rewarming technology for the successful cryopreservation of large biosamples.