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Journal of Thermal Analysis and Calorimetry
Journal Prestige (SJR): 0.587  Citation Impact (citeScore): 2 Number of Followers: 27  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1388-6150 - ISSN (Online) 1588-2926 Published by Springer-Verlag  [2468 journals]
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- Preparation and characterization of hybrid polymeric coating films of
chitosan–clay loaded with açaí extract (Euterpe oleracea) for
application in food and pharmaceutical areas-
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Abstract: Abstract This study aimed to study the interaction between two different açaí extracts used in synthesis of hybrid polymeric films based on chitosan–clay and evaluate its morphological and physical–chemical properties, indeed antibacterial and antioxidant activities. Films with acidified açai extract (FEAA) and non-acidified açai extract (FEBANA) were prepared using the casting method. It was possible to observe a surface with a rough appearance, varying according to the added extract concentration using SEM photomicrographs. The reflection peaks were similar to the Chit–Clay film (2θ = 14° and 16.8°) and the reduction in the degree of chitosan crystallinity for the FEBANA films in relation to FEAA films. The TG data also show that the FEBANA films have a higher percentage of water of hydration than the FEAA films, corroborating this state of anhydrous films for FEAA and state of hydrated films for FEBANA. The FEBANA films were two stretches in the region between 842 and 962 cm−1, and a shoulder 1095 cm−1 covered by bands 1025 cm−1 (Si–O–Si) and can attributed to the PEG plasticizer. This greater detection of PEG stretches in the FEBANA films suggests a greater concentration of PEG on the surface of the FEBANA film. MIC microbiology demonstrated that both types of extracts were capable of inhibiting Gram (−) strains, Escherichia coli and Pseudomonas aeruginosa, and Gram ( +) strains, Staphylococcus aureus and Staphylococcus epidermidis. In disk diffusion, the acidified extract showed inhibition activity for Edwardsiella tarda, Enterococcus faecium and Streptococcus pyogenes. Both extracts are effective in inhibiting the growth of both Gram (−) and Gram ( +) bacteria. The FEAA polymeric films showed a higher degree of recovery, reversible chemical bonding with the matrices and consequently greater DPPH free radical scavenging capacity compared to the FEBANA polymeric films. The FEAA and FEBANA films present characteristics of releasing active ingredients from the hybrid polymeric film and can be applied in edible packaging or use in biodegradable smart packaging or as food biopreservative; or even, in pharmaceutical release systems for releasing active ingredients onto the skin, as organic active ingredient release membranes for skin health and beauty, wound healing or even as adjuvants in tissue bioengineering for skin reconstruction after burns and in plastic skin surgery as biodegradable films.
PubDate: 2024-08-27
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- Synergistic enhancement of properties in copper oxide-reinforced
polystyrene nanocomposites via in situ polymerization-
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Abstract: Abstract The study primarily focuses on the in situ synthesis of polystyrene (PS) and copper oxide (CuO) nanocomposites. An extensive analysis was conducted on the optical, thermal, mechanical, and electrical properties of PS with different CuO concentrations. The effective inclusion of CuO into PS was characterized by Fourier-transform infrared spectroscopy (FTIR), UV–visible spectroscopy, filed emission scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD), differential scanning calorimetric analysis (DSC) and thermal gravimetric analysis (TGA). The reinforcement of CuO into the PS was established through FTIR. The optical bandgap energy deduced from UV–visible spectra decreases with CuO addition, whereas the refractive index rises significantly with the addition of CuO nanoparticles up to 7 mass%. The XRD analysis revealed the amorphous to crystalline transformation of PS with the homogeneous dispersion of nanoparticles. The SEM–EDX analysis revealed the uniform distribution of CuO nanofillers in the PS matrix. The CuO addition considerably increased the glass transition temperature and thermal stability of PS. The tensile strength, impact resistance and hardness of nanocomposite were significantly increased with the loading of CuO in the polymer matrix. The AC conductivity and dielectric constant of the PS was improved with the addition of CuO nanoparticles. The effect of temperature on conductivity, activation energy, and pre-exponential factor was determined using the universal power law and the Arrhenius equation. The highest electrical and mechanical properties were observed for 7 mass% nanocomposite. The synthesized PS/CuO nanocomposites with excellent optical characteristics, thermal stability, electrical conductivity, dielectric constant and mechanical strength can be used in supercapacitors and flexible nano-electronic devices.
PubDate: 2024-08-27
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- Lime reactivity and overburning: the case of limestones belonging to
Tuscan Nappe sequence (NW Tuscany, Italy)-
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Abstract: Abstract This study examines limestone properties and calcination process to enhance product quality. Limestone burning produces lime (CaO, calcium oxide) and carbon dioxide (CO2). Lime is a substance highly reactive and turns into slaked lime (Ca(OH)2, calcium hydroxide) when exposed to water. Six limestone samples from Tuscan Nappe sedimentary sequence, outcropping in the Monti d’Oltre Serchio area (NW Tuscany, Italy), were selected and calcined at different temperatures (800, 900, 1000 and 1100 °C). The obtained lime was slaked, and chemical, mineralogical and petrographic analyses were conducted to study its reactivity during slaking process. Key factors influencing lime reactivity were identified: calcination temperature/time and limestone characteristics (chemical and mineralogical composition). The lime reactivity was measured through the rate of lime hydration reaction. Results showed that higher reactivity in lime, lower calcination temperature. The increase in temperature and time leads to an increase of CaO grain size and, consequently, to a decrease in reactivity. Temperature increase has a more significant effect on the increasing of grain size and reactivity than time. The optimal calcination temperature was found to be 900 °C, like that of ancient limekilns. The study emphasized the close link between lime reactivity and chemistry/mineralogy of limestone. Overall, the research provides insights for improving limestone calcination processes and obtaining superior products.
PubDate: 2024-08-27
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- Synthesis, testing, and evaluation of efficiency and emissions properties
of tamarind-based biodiesel with magnetite nanoparticles-
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Abstract: Abstract The growing need for renewable and sustainable energy sources has prompted researchers to explore alternative fuels for engines traditionally powered by gasoline or diesel. Biodiesel derived from tamarind oil shows great potential as a sustainable fuel due to its renewable and eco-friendly nature. This investigation emphasizes the efficiency, emissions, and combustion characteristics of tamarind seed-based biodiesel blends with magnetite (Fe3O4) nanoparticles in a direct ignition engine. The magnetite nanoparticles in concentrations of 50 and 100 ppm are added to tamarind biodiesel blends with the help of an ultrasonicator. The prepared fuels were tested in a single-cylinder, four-stroke, vertical compression ignition engine. The experimental results revealed that the TME20M100 blend exhibits an increase in brake thermal efficiency by 5.85%, and SFC decreased by 6.18% with the maximum values of HRR and cylinder pressure are 44.5 J/°CA and 69.58 bar, respectively. Additionally, the TME20M100 blend exhibited a significant reduction of 27.32% in CO emissions, 7.93% in HC emissions, 4.05% in NOx emissions, and 3.23% in smoke emissions, as compared to the TME20. This study presents a promising approach to producing high-performance, eco-friendly biodiesel, contributing to the broader adoption of renewable energy sources.
PubDate: 2024-08-26
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- A thermodynamic investigation into protein–excipient interactions
involving different grades of polysorbate 20 and 80-
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Abstract: Abstract Developing stable biopharmaceutical formulations is of paramount importance and is typically achieved by incorporating surfactants as stabilising agents, such as polysorbate 20 and 80. However, little is known about the effect surfactant grade has on formulation stability. This study evaluates the effect of regular grade and Super-refined™ polysorbates 20 and 80 and their interaction with model proteins, namely β-lactoglobulin (β-Ig), human serum albumin (HSA) and immunoglobulin gamma (IgG), using isothermal titration calorimetry (ITC) and differential scanning calorimetry (DSC). ITC results indicated that all four polysorbates underwent binding interactions with β-Ig and HSA, yet no interaction was observed with IgG this is postulated to be a consequence of differences in secondary structure composition. Surfactant binding to β-Ig occurred at ratios of ~ 3:2 regardless of the surfactant used with dissociation constants ranging from 284 to 388 µM, whereas HSA bound at ratios of ~ 3:1 and dissociation constants ranging from 429 to 653 µM. Changes in enthalpy were larger for the surfactant interactions with HSA compared with β-Ig implying the former produced a greater binding interaction than the latter. DSC facilitated measurement of the temperature of unfolding of each protein with the presence of each polysorbate where results further confirmed interactions had occurred for β-Ig and HSA with an increased unfolding temperature between 4 and 6 K implying improved protein stability, yet again, no interaction was observed with IgG. This study thermodynamically characterised the role of polysorbates in protein stabilisation for biopharmaceutical formulations.
PubDate: 2024-08-25
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- Evaluation of the effect of biodiesel content in diesel/biodiesel fuel
blends on sediments and gums formation during storage-
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Abstract: The oxidation process of fuels during storage affects their quality and has been a recurring problem in the use of neat biodiesel or diesel/biodiesel blends. One of the most significant and undesirable change that occurs due to deterioration is the formation of sediments and gums (SG’s). SG’s are degradation products resulting from oxidation process of fuels and have a negative effect on the fuel atomization process, reducing its calorific value and ignition quality (cetane number). Diesel fuel sold in Brazil is a diesel/biodiesel blend containing 14% by volume of biodiesel (B14), which increases fuel degradation during storage time. The main aim of this study was to evaluate the effect of the biodiesel content in diesel/biodiesel fuel blends on the SG content formed after storage period using thermogravimetric analysis (TGA). Blends were prepared using methyl soybean biodiesel (B100) and S10 diesel with different volumetric biodiesel percentage, from 10% (B10) to 50% (B50). The samples were stored in amber glass bottles (similar to ASTM D4625), at room temperature and protected from light. Every 30 days, bottles of each mixture were opened and a sample collected for analysis. This procedure was repeated for six consecutive months. Blends oxidized and not oxidized (immediate age) were analyzed using thermogravimetry (TG) and derivative thermogravimetry (DTG). The physicochemical properties of blends were also evaluated, such oxidation stability, kinematic viscosity at 40 °C and specific mass a 20 °C. Size exclusion chromatography analyses (SEC) were also performed. Thermogravimetry shows that, as the B100 content increases regarding diesel, the interactions between the two fuels are distinct, which result in changes in the TG/DTG curve profile. It is also observed that the increase in B100 promotes the retardation of the mass loss steps of the blends to higher temperatures. The final (Tendset) and the maximum (Tonset) degradation temperatures are affected as well. The TG/DTG curves of the sample showed that increasing biodiesel content in the blend, the percentage of SG formed for the same aging age increases. Moreover, the formation of SG is correlated with the proportion of the blend constituents. The profiles of TG/DTG curves for each blend are a function of the added percentages of biodiesel in the mixture. The experimental results obtained showed that the degradation products formed during the storage of fuels, sediments/gums (SG’s), can be quantified using thermogravimetric techniques. Graphical abstract
PubDate: 2024-08-25
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- Thermophysical properties of magnetic nanofluids under effects of magnetic
field-a review on mechanisms and studies-
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Abstract: Abstract Magnetic nanofluids play a crucial role in enhancing thermal properties, providing a promising pathway for optimizing energy supply systems and improving heat transfer efficiency. Beyond advanced thermal management, these innovative fluids showcase potential applications in the medical field, underscoring their versatility in addressing challenges across various industries. In this review, emphasis is placed on the nature and philosophy of magnetic field effects on the thermophysical properties, explaining basic mechanisms and investigating implications across applications. Under magnetic influence, particles align, forming clusters and chains, influencing thermal conductivity, viscosity, and specific heat capacity. Temperature variations serve a vital function, impacting the fluid’s response to magnetic fields. Brownian motion, affected by these fields, contributes to controlled particle motion, while agglomeration tendencies under magnetic conditions further shape thermal properties. In this review, several key findings about the behavior of magnetic nanofluids are revealed. For example, it is found that by increasing the magnetic field intensity at a constant shear rate, the viscosity first reaches a plateau and then decreases with further increases in field intensity. Furthermore, below/above the Curie temperature, the alignment of magnetic nanoparticles increases/decreases, influencing thermal expansion coefficient. This review presents two novel aspects that have not yet been compiled coherently elsewhere: firstly, an in-depth description of the nature and mechanisms of the magnetic field’s effect on thermophysical properties, and secondly, an examination of the rarely investigated properties of thermal expansion coefficient and specific heat capacity.
PubDate: 2024-08-24
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- Characterization studies of Genipa americana extract and its granules:
phytochemical, physicochemical and thermal properties-
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Abstract: Abstract Genipa americana L. is popularly known as jenipapo and has a potential herbal medicine with various pharmacological activities. Granules is a simple and useful pharmaceutical form to obtain herbal medicines in solid-state and has advantage due to protection of the bioactive compounds herbal extract. The aim of this study was to conduct studies of characterization of Genipa americana extract and its granules to evaluate their phytochemical, physicochemical and thermal properties. The crude extract of Genipa americana leaves was obtained by maceration using ethanol. A total of four Genipa americana granules were obtained using wet granulation process. Phytochemical characterization was performed: total phenol and total flavonoid contents and DPPH, FRAP and MDA assays. Physicochemical characterization was performed using SEM, FTIR, UV–Vis, dissolution profile and UFLC-DAD/UV analysis. Thermal characterization was performed using TG technique. The crude extract of Genipa americana and its granules showed the presence of iridoids (genipin and geniposides), flavonoids and phenolic compounds and genipin derivatives after hydrolysis experiment using the UFLC-DAD/UV. The DPPH assay showed antioxidant activity with an IC50 of 207.07 µg cm−3 for the Genipa americana extract and 198.34 to 298.71 µg cm−3 for the Genipa americana granules. The FRAP assay showed a good ability to reduce the iron III–TPTZ complex to iron II–TPTZ with values between 1092 and 1532 µM ferrous sulfate. g−1 also explained by the presence of phenolic compounds and flavonoids. The maloaldehyde (MDA) assay showed acceptable levels and similar to the scientific literature. SEM analysis showed granules with morphology and particle size that characterize them as microparticles. FTIR analysis showed similarity between the identification bands of the crude Genipa americana granules with pharmaceutical excipients. The dissolution profiles of the Genipa americana granules showed characteristics of highly water-soluble pharmaceutical compositions with total release of the genipin marker between 30 and 60 min. The Genipa americana granules showed moisture content between 4.27 and 11.6% by the thermogravimetric analysis. The granules indicated greater protection and stability for the Genipa americana extract in these pharmaceutical formulations. The wet granulation process proved to be suitable and low-cost for Genipa americana extract. The moisture content of the granules can cause variability in genipin content to be stored in appropriate environment and packaging.
PubDate: 2024-08-24
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- What role does the safety valve play in the safety of lithium-ion cells'
Part II. Cells with various states of health and formats-
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Abstract: Abstract To demonstrate the role of safety valves in enhancing the safety characteristics of lithium-ion cells, this study conducts a set of abusive testing including accelerating rate calorimetry testing, overheating testing, and overcharge testing. Additionally, the influence of safety valves on cells with different states of health (100%, 90%, and 80% SOH) and formats (14,650, 18,650, and 22,650) is investigated. The results reveal that safety valves have a substantial influence on the thermal runaway behaviour of cells. They effectively mitigate the risks and hazards associated with thermal runaway during overheating and ARC conditions. Beyond that, the presence of a safety valve can prevent thermal runaway triggered by overcharge. It is observed that cells with lower SOH and/or smaller diameters are more prone to experiencing earlier thermal runaway. Furthermore, this research finds that the influence of safety valves is more pronounced in cells with less degradation and/or smaller formats.
PubDate: 2024-08-24
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- Synthesis, thermal, and mechanical characterisation of metakaolin-based
geopolymers coloured with grape marc extract-
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Abstract: Over the years, several materials have been used for restoration purposes, with different types of dyes and colour hues. Recently, some researchers have proposed geopolymers (GPs) or amorphous aluminosilicate polymers for these purposes. In this work, an alcohol-based grape marc extract (GME, obtained via dark maceration assisted with ultrasound) was used as a natural dyeing agent for metakaolin-based GPs. The geopolymerisation occurrence was assessed by Fourier-transform infrared (FT-IR) spectroscopy and X-ray diffraction analysis, while the colour of the resulting material was determined through the colorimetric analysis in the L*a*b* colour space. Additionally, the thermal stability of GME and GPs was investigated by thermogravimetry coupled with FT-IR spectroscopy. The microstructure, the reticulation stability, and the antimicrobial activity of GPs were examined through the scanning electron microscopy, the pH and ionic conductivity measurements, integrity, and mass loss tests. Overall, a coloured geopolymer with suitable thermal, antimicrobial, and mechanical properties was obtained, justifying its potential use in restoration or, more generally, in the construction field. Graphical abstract
PubDate: 2024-08-24
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- Optimizing convective heat transfer in a magnetized couple stress fluid
over a stretched tube-
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Abstract: Abstract The purpose of this proposed research is to examine the two-dimensional couple stress fluid flow over an extensible cylinder. The flow rate was determined by convective boundary layer constraints and the presence of a magnetic field. A nonlinear convective expression is used to study the heat transfer process in the vicinity of the cylindrical surface, which has widespread applications in engineering and industrial sectors. Incorporating a thermal radiation source into the heat transfer process increases the effect of dissipative heat. The behavior of the flow is determined by its mathematical structure, which is then translated into ordinary differential equations by making suitable assumptions about similarity variables and stream function. The findings indicate that as the dimensionless couple stress parameter increases, fluid movement intensifies. Conversely, an increase in the Hartmann number (M) leads to a decrease in velocity. Additionally, varying the curvature parameter results in higher values for both temperature and fluid velocity profiles. The coefficient of skin friction rises with the curvature parameter but decreases with the Grashof number. Furthermore, the heat transfer rate increases with higher curvature and decreases with the Grashof number, respectively. The present study includes a comparison with existing research to reinforce the proposed model.
PubDate: 2024-08-24
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- A comparative study on the application of solar thermal collector and
photovoltaic combinations to assist an air source heat pump-
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Abstract: Abstract This study investigates the usage of photovoltaic (PV) and thermal collectors separately to assist a heat pump for supplying domestic hot water (DHW). Usage of PV and thermal collectors together to assist a heat pump and experimentally validated simulation of an air source heat pump can be considered as novelty of this study. Firstly, experimental tests were performed in a climatic room to validate the developed simulation model. Four experimental parameters, namely the coefficient of performance of the air source heat pump, average tank temperature, and heat pump inlet and outlet temperatures have been used for the validation and the highest obtained deviation was 4.5%. Simulations were carried out by adding thermal collectors and photovoltaic panels in different combinations, with a maximum of three collectors to assist the heat pump that provides DHW. For scenarios with one and two solar components (PV or thermal), applying only thermal collectors was more efficient and economical for both with a payback of 3.9 years and 4.3 years, respectively. For the scenario with three solar components, although the system supported by one thermal and two photovoltaic collectors was the most efficient option, the system supported by three photovoltaic collectors was the most economical scenario with a payback period of 4.6 years. The study found that combining thermal and photovoltaic collectors can significantly reduce energy consumption for DHW.
PubDate: 2024-08-23
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- Derivation of appropriate temperature change for application of phase
change materials in building walls for energy reduction in Korean climatic
conditions-
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Abstract: Abstract Studies are underway to apply phase change materials (PCMs) to buildings to reduce energy consumption. PCMs can be expected to achieve energy savings by exploiting their high latent heat capacity and time-lag phenomenon, slowing down the heat transfer within the structure, and accumulating and releasing latent heat. This study analyzed the appropriate melting point and energy-saving effects based on changes in external climate conditions, attachment location, and PCM properties (thickness and thermal conductivity) through building energy simulations. Climate data were quantitatively categorized into climate zones based on heating degree hours, cooling degree hours, and insolation, and a total of 14 climate zones were proposed. The appropriate melting point based on climate was evidently more effective for cooling than for heating, and external attachment was proved to be more advantageous. As the thickness increased, the appropriate melting point decreased, and the energy-saving effect remained effective. The thermal conductivity increased with the graphite content by 0.90–2.37%, and the appropriate melting point also changed by 0.72–0.91 °C. As the thermal conductivity increased, heat was rapidly transferred within the PCM, altering its energy-saving effect by 0.18–3.35%.
PubDate: 2024-08-23
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- Exergetic analysis of a domestic refrigerator with an innovative
mini-channel flat tube condenser-
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Abstract: Abstract In this study, the energetic and exergetic performance of a household refrigerator with a unique compact heat exchanger composed of a mini-channel flat tube condenser and offset strip fins (OSF) is investigated experimentally by considering varying amounts of R600a (48–64 g) and capillary tube lengths (2800, 3300, and 3800 mm). The experiments have been performed for two refrigerators involving two different innovative condensers composed of mini-channel flat tube and offset strip fins which have varying orientations instead of conventional wire-on-tube condensers. The experiments were conducted in a climatic chamber at a temperature of 25 ± 0.5°C. According to the standard of IEC 62552:2015, the target temperatures of the fresh food and freezer compartments are set at 4°C and −18°C, respectively. Specific and relative exergy destructions of each component, total exergy destruction, the coefficient of performance, and second-law efficiency of the overall system with two different mini-channel condensers are reported for varying amounts of refrigerant and capillary tube lengths. The major concern of the investigation is to reveal the key components contributing to the degradation of the overall performance of the unique design. It is observed that the evaporator, which has a ratio of 52–69% in total exergy destruction within all investigated cases, is the most exergy destructive component and the exergy destruction of the evaporator decreases when the amount of R600a increases. The mini-channel condensers are the second exergy destructive components with a ratio of 19–22%. As an important outcome of this unique design’s investigation, exergy destruction of the condenser and compressor does not show a monotonic change with respect to the refrigerant amount and capillary length. Besides, the highest coefficient of performance and second-law efficiency are obtained when the amount of R600a is 48–50 g in all three capillary tube lengths.
PubDate: 2024-08-22
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- Improving single-slope passive solar still efficiency through integration
of phase change materials and Al2O3 nanoparticles-
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Abstract: Abstract This research explores the enhancement of single-slope solar still performance using phase change material (PCM), specifically paraffin, incorporating Al2O3 nanoparticles. The application of paraffin, a PCM, improves energy storage density and maintains a consistent temperature during the phase transition. Adding Al2O3 nanoparticles to the PCM improves its thermal properties, increasing production rates. Three scenarios were tested for comparison: (1) a standalone solar still, (2) a solar still with PCM, and (3) a solar still with PCM containing Al2O3 nanoparticles. The productivity yields for these systems were 0.837 kg, 0.924 kg, and 1.145 kg, respectively. The results indicate a significant improvement in the solar still’s performance upon adding PCM and Al2O3 nanoparticles, yielding a 10.38% increase in daily output and a 36.77% increase in daily distillate compared to the standalone solar still. Optimizing the temperature difference between the water and the glass surface through ideal water spraying conditions also bolstered the distillate production rate. The outcomes from this research suggest that solar distillation plants, which provide an efficient source of clean drinking water, can significantly improve performance and productivity by leveraging the benefits of innovative materials such as nanoparticles.
PubDate: 2024-08-22
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- Investigation on effect of water on oxidation behaviors and kinetics of
heavy crude oil using STA and ARC-
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Abstract: Abstract In situ combustion has already been applied in reservoirs which were adopted steam recovery. It is essential to investigate the effect of water on oxidation behaviors, especially in high water content. Simultaneous thermal analysis (STA) and accelerating rate calorimeter (ARC) were used to study the impacts of water on heavy oil oxidation characteristics at atmosphere pressure (0.1 MPa) and reservoir pressure (7.2 MPa). It was found from STA data at atmosphere pressure that water in a vapor state could promote the process of heavy crude oil oxidation. Besides, the exothermicity of low-temperature oxidation (LTO) would decrease due to evaporative heat absorption of liquid water at high water saturation, resulting in lower peak temperatures, peak pressures, and self-heating rate. It is indicated that water in a liquid state would inhibit the LTO reaction. High-pressure ARC curves suggested that self-ignition technology is not advisable under the reservoir pressure (7.2 MPa) and temperature (100 °C) after steam recovery. Subsequently, the iso-conversational methods were used to calculate the kinetic parameters. Steam could increase the oxidation activity of heavy oil evident in the decreased activation energy with elevated steam fraction. This work can assist the development and application of air injection in reservoirs after steam recovery and co-injection of steam and air technology.
PubDate: 2024-08-22
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- Reactivity of precursors for geopolymerization studied by isothermal
calorimetry-
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Abstract: Abstract The paper deals with analyzes of Isothermal Conduction Calorimetry response obtained during the alkaline activation of four types of precursors (metakaolin, slag and two kinds of waste ceramic powders) to geopolymers. The first two precursors are traditionally used, while the latter two are emerging materials and knowledge of their alkaline activation might have high importance in the recycling of Construction and Demolition Waste. The studied precursors differ each to other not only in the chemical composition, but also in the phase composition—the waste ceramic precursors are highly crystalline. It was found that the total reaction heat evolved in the geopolymerization is directly proportional to the amorphous matter content as well as to the compressive strength of the activated product. This finding can be used as fast evaluation tool in searching of new potential geopolymer precursors. The dissolution and polycondensation steps were observed in all experiments and their kinetics was described by Jander’s equation. While the rate of dissolution step is not dependent on temperature, the polycondensation has been accelerated by the higher temperature. The level of the rate acceleration was described by apparent activation energy; these findings can be useful in tuning of geopolymers curing procedure.
PubDate: 2024-08-22
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- Prediction of the heats of combustion for food-related organic compounds.
A quantitative structure–property relationship (QSPR) study-
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Abstract: Abstract In the field of food research, the determination of the heats of combustion (ΔcH) of the nutrients is essential to estimate the amount of energy obtained by metabolizing during digestion. Here, we have developed six novel QSPR models to predict this thermodynamic property of different families of organic compounds. The models were developed using the experimental data set of 215 compounds (71 organic acids, 28 amino acids, 37 amines and amides, 31 sulfur compounds and 48 heterocyclic compounds). About 16,000 molecular descriptors were calculated to represent the molecular structure of the compounds. The QSPR models resulted to be simple MLRs with a maximum of three variables, facilitating the interpretation and comparison with existing models in the literature. The statistical parameters exhibited excellent predictive capacity and robustness of the models obtained. The correlation coefficients of the selected models were major to 0.8 and the root means square error minor to 0.1. These results suggested that the models could be utilized for the prediction of the ΔcH of other compounds that could be present in the foods.
PubDate: 2024-08-22
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- Analysis of flow and heat transfer characteristics of ethylene
glycol-based magnetite nanoparticles squeezed between parallel disks with
magnetic effect-
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Abstract: Abstract This study aims to theoretically analyse the flow and heat transfer characteristics of ethylene glycol ( \(\text{C}_{2}\text{H}_{6}\text{O}_{4}\) )-based nanofluid containing magnetite ( \(\text{Fe}_{3}\text{O}_{4}\) ) nanoparticles squeezed between two parallel disks with magnetic effect. The governing nonlinear partial differential equations are transformed into nonlinear ordinary differential equations by employing a set of suitable similarity transformations. Further, by adopting the homotopy perturbation method (HPM), an approximate solution to the considered model is obtained. The solutions are compared with the classical finite difference method (FDM) and are in good agreement. The current study mainly emphasizes the analysis of velocity profile, skin friction coefficient, temperature distribution curve, and Nusselt number for different pertinent parameters. The findings in this study highlight the role of applied magnetic field in modifying the flow and heat transfer characteristics of the nanofluid, notably showing that an increase in the concentration of magnetite nanoparticles correlates with higher skin friction at the disk surfaces and enhances the Nusselt number, reflecting improved heat transfer performance. This underscores the potential of magnetite-enhanced nanofluids in enhancing the efficiency of thermal systems.
PubDate: 2024-08-22
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- Effects of sand size on spread and heat transfer of continuous spill fires
with small leakage rates-
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Abstract: Abstract Spill fire, a kind of common fire accident, has the characteristics of strong sudden occurrence and fast spread rate, so there has been widespread concern about it. Compared with pool fire, there is limited research on spill fires now. In order to study the process of fire spread and combustion on sand substrate, a series of experiments were designed to investigate the effect of sand particle size on the spread and heat transfer of the continuous ethanol spill fire. The flame spread distance, substrate temperature, and penetrating heat radiation were measured. The resistance effect of sand, spread distance and rate, and steady linear burning rate were analyzed. Moreover, heat loss was also calculated. The results show that sand can effectively impede the development of spill fire. On the one hand, dry sand has strong capillary action, which makes most of the fuel adsorbed upward by the sand layer after entering the flow trough. Therefore, sand has obstructive capacity on the spread of liquid fuel, thereby shortening the spread distance of spill fire. On the other hand, sand has strong thermal conductivity, which can reduce the stable burning area of spill fire by increasing the total thermal feedback of spill fire and improving the steady burning rate of fuel. However, if the particle size of sand is too small, the liquid fuel will spill from the sand surface. In this case, the resistance effect of sand on the spread of liquid fuel will weaken. Therefore, sand with appropriate particle size should be selected for spill fire in practice.
PubDate: 2024-08-22
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