Characteristic Melting Temperatures Research Articles

Experimental and numerical analysis of the thermal performance of PCM-impregnated reticular structures obtained by additive manufacturing

This paper proposes a combined experimental and numerical analysis of the melting of three different paraffin waxes embedded in reticular structures fabricated by additive manufacturing. The parent material of the reticular structures is AlSi10Mg. Metal structures, having a 100 mm square base and a thickness of 20 mm, were printed between two 10 mm thick plates. Samples were positioned in an upright position and laterally heated applying different heat fluxes. Three different paraffins were tested, with different characteristic melting temperatures (42 °C, 55 °C, and 64 °C), which are suitable for electronics cooling applications. Four different structures were tested, having a cell length of 5 mm and 10 mm, and porosities of 0.87 and 0.93. Besides the experimental tests, numerical simulations of the melting phenomenon were carried out using a purely conductive model implemented in ANSYS Fluent. The discretized numerical domains represented just small repetitive portions of the test modules, thus allowing substantial computational time savings. This simplified method has been proven to yield results that are in good agreement with the experimental data. The main outcome of this work is the setup of the simplified numerical procedure, which was then validated and used to investigate the effectiveness of the considered structures in diffusing heat into the low thermal conductivity phase change materials. It was concluded that the best overall thermal performance can be obtained with low porosity and low cell size since this enables faster melting processes and better surface temperature control.

Lipid-membranes interaction, structural assessment, and sustainable production of polyhydroxyalkanoate by Priestia filamentosa AZU-A6 from sugarcane molasses

This study presented for the first time the PHA-lipid interactions by circular dichroism (CD) spectroscopy, besides a sustainable PHA production strategy using a cost-effective microbial isolate. About 48 bacterial isolates were selected from multifarious Egyptian sites and screened for PHAs production. The Fe(AZU-A6) was the most potent isolate, and identified genetically as Priestia filamentosa AZU-A6, while the intracellular PHA granules were visualized by TEM. Sugarcane molasses (SCM) was used an inexpensive carbon source and the production conditions were optimized through a Factor-By-Factor strategy and a Plackett-Burman statistical model. The highest production (6.84 g L−1) was achieved at 8.0 % SCM, pH 8.0, 35 °C, 250 rpm, and 0.5 g L−1 ammonium chloride after 72 h. The complementary physicochemical techniques (e.g., FTIR, NMR, GC–MS, DSC, and TGA) have ascertained the structural identity as poly-3-hydroxybutyrate (P3HB) with a characteristic melting temperature of 174.5 °C. The circular dichroism analysis investigated the existence of interactions between the PHB and the different lipids, particularly 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The ATR technique for the lipid-PHB films suggested that both the hydrophobic and electrostatic forces control the lipid-PHB interactions that might induce changes in the structuration of PHB.

Numerical analysis of the thermal energy storage in cellular structures filled with phase-change material

This paper reports the results of a numerical study on the thermal performance of metal cellular structures that can be obtained by additive manufacturing (selective laser melting) when they are impregnated with phase change material (PCM) for possible applications in electronic cooling. Two body-centered cubic (BCC) periodic structures with cell sizes of 5 mm and 10 mm and a porosity of 87%, made of two solid materials (aluminum alloy and copper), and two paraffins with characteristic melting temperatures of 55 and 64 °C were considered. The numerical simulations are carried out using the commercial code ANSYS Fluent and are based on a previously validated purely conductive heat transfer model. The computational domains include just small repetitive portions of the considered composite structures, thus allowing substantial savings of computational time. Computed results show that, with both paraffins, the copper made finer BCC structure (5 mm) yields the best thermal performances, i.e, the shortest PCM melting time and the highest rate of thermal energy storage during transients.

Syngas composition and ash characteristics of corn straw under a CO2 atmosphere

Corn straw is one of the most common materials utilized as biomass. The effects of temperature and residence time on the syngas composition and ash characteristics of corn straw prepared in a CO2 atmosphere in a tubular furnace were studied. The results showed that CO was the dominant component of the syngas. With increasing temperature, the volume fraction of CO first decreased and then increased. When the temperature increased to 800 °C, CH4, CnHm and H2 participated in the gas-phase reaction, which promoted the generation of CO. At high temperature, longer residence times before the corn straw reacted completely resulted in greater CO production. Analysis of the ash characteristics showed that the higher the temperature and the longer the residence time were, the lower the ash mass. When the temperature was below 800 °C, the inorganic crystals in the residual ash were KCl and SiO2. When the temperature increased to 800 °C, the inorganic materials in the ash melted and slagged, resulting in low-melting-point salts such as CaMgSi2O3 and KAlSi3O8. The presence of carbon residue hindered the slagging of ash. At 800 °C, ash with a high K content exhibited obvious melting, while ash with a high Al content remained solid. With increasing temperature, the characteristic melting temperatures of ash also increased.

Melting of phase change materials inside periodic cellular structures fabricated by additive manufacturing: Experimental results and numerical simulations

• The melting of paraffin waxes inside periodic cellular structures is studied. • The effects of heat flux, melting temperature, and cell size are discussed. • The simplified numerical model of the melting process matches the experimental data. • An analytical model previously developed for foams is applied. An experimental and numerical study of the solid–liquid phase change process of three paraffin waxes, having different characteristic melting temperatures (42, 55, and 64 °C) embedded in two different cellular periodic aluminium structures fabricated by additive manufacturing, thought of as passive heat sinks, is reported. The aluminium solid media are composed of repeating elementary cells derived from the body-centred cubic (BCC) model and have a porosity of 87%. The samples were tested in an upright position and laterally heated by applying three different heat fluxes (10, 15, and 20 kW m −2 ). The experimental results showed the effects of the heat flux, melting temperature, and size of the metal cells on the temperature of the heated surface. Numerical simulations were performed to validate a simplified model for the thermal analysis of the test modules using reduced domains. Owing to the characteristics of the experimental melting front, which is almost parallel to the heated side, suggesting a negligible effect of natural convection, the numerical simulations performed with ANSYS Fluent could be conducted on computational domains that represent only small repetitive portions of the test modules, thus allowing substantial savings in the computational time. This simplified method has been proven to yield results that are in good agreement with the experimental data. Based on the numerical results, when the metal structure is finer, the evolution is faster, and the time required to completely melt the phase change material (PCM) is shorter. This numerical model may be confidently used by thermal engineers to design PCM-based heat sinks for electronics cooling. Finally, an empirical model previously developed for paraffin embedded in metal foams was applied to the present paraffin-BCC composite structures.

Investigation of biomass, RDF and coal ash-related problems: Impact on metallic heat exchanger surfaces of boilers

The goal of this work was to study the corrosion resistance of boiler steel and protective alloy coatings. Four ashes obtained from wood biomass, straw, refused-derived fuel and coal were analysed. The aggressive components of ash, such as potassium, sodium, sulphur and chlorine, can accelerate the operating problems of heat exchanging surfaces in power boilers, leading to enhanced slagging, fouling, agglomeration of ash, and corrosion. Four boiler steels were chosen for detailed investigation: 16Mo3, P265GH, Inconel 625 and 686. They were covered with ashes, placed in a furnace and heated through 4 months at 750 °C under oxidizing conditions. Multifaceted ash analysis (chemical composition, thermal behaviour, phase composition, and characteristic melting temperatures) was performed. Additionally, both slagging and fouling indices were calculated to predict the sintering properties of the studied ashes. The surfaces of studied steels after the exposure of ash presence were analysed using SEM-EDS technique. The results showed that the corrosive impact of the ashes depended on the aggressive components present in the ash. Furthermore, FactSage thermochemical equilibrium calculations were used to predict the amount of liquid slag and solid phases under the studied conditions and to determine the transformation of the mineral phases of the ash.

Multicomponent crystalline solid forms of aripiprazole produced via hot melt extrusion techniques: An exploratory study

Multicomponent crystalline solid forms (salts, cocrystals and eutectics) are a promising means of enhancing the dissolution behavior of poorly soluble drugs. The present study demonstrates the development of multicomponent solid forms of aripiprazole (ARP) prepared with succinic acid (SA) and nicotinamide (NA) as coformers using the hot melt extrusion (HME) technique. The HME-processed samples were characterized and analyzed using differential scanning calorimetry (DSC), hot stage microscopy (HSM), Fourier transform infrared (FTIR) spectroscopy, powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM). The DSC and HSM analyses revealed a characteristic single melting temperature in the solid forms, which differed from the melting points of the individual components. The discernible changes in the FTIR (amide CO stretching) and PXRD results for ARP-SA confirm the formation of new crystalline solid forms. In the case of ARP-NA, these changes were less prominent, without the appearance or disappearance of peaks, suggesting no change in the crystal lattice. The SEM images demonstrated morphological differences between the HME-processed samples and the individual parent components. The in vitro dissolution and microenvironment pH measurement studies revealed that ARP-SA showed a higher dissolution rate, which could be due to the acidic microenvironment pH imparted by the coformer. The observations of the present study demonstrate the applicability of the HME technique for the development of ARP multicomponent solid forms.

Statistical Model for Prediction of Ash Fusion Temperatures from Additive Doped Biomass

The prediction of phase transformation of biomass ashes is challenging due to the highly variable composition of these fuels as well as the complex processes accompanying phase transformations. The AFT (Ash Fusion Temperature) model was performed in Statistica 13.1 software. This model was divided into three separate submodels, which were designed to predict the characteristic ash melting temperatures for raw and modified biomass. It is based on the chemical composition of fuel and ash as obtained using ash analysis standards. For the discussed models, several coefficients describing multiple regression parameters are presented. The AFT model discussed in this article is suitable for predicting ash fusion temperatures for biomass and allows for the prediction of the temperature with an average error of <±70.05 °C for IDT; <±51.98 °C for HT; <±47.52 °C for FT for raw biomass. For some of the additionally tested biomass, a value higher than the average difference between the measured temperature and the designated model was observed (<90 °C). Moreover, morphological analyses of the structure SEM-EDS for ash samples with and without additive were performed.

Influence of pressure and CO2 in fluidized bed gasification of waste biomasses

An autothermal fluidized bed reactor was used to research the influence of pressure (0–2 barg) on the gasification process of different types of biomasses. The tested feedstocks were bark and lignin while softwood pellet was used as a reference fuel. A mixture of O2/CO2/H2O was used as a gasification agent. The impact of the application of CO2 on the yield of H2 in product gas was determined. Resulting product gas was characterized by a high content of CO which makes its use for applications based on chemical synthesis very difficult without extensive upgrading or supply of H2 from external sources. CO2 proved to improve carbon conversion efficiency (CCE) of the gasification process and to be an option for its chemical sequestration (negative carbon footprint). A slight modification of conventional indices used to evaluate efficiencies of gasification systems (CCE and water/carbon ratio) was proposed, to take into account the impact of the additional source of carbon fed into the reactor. The increase of system pressure led to changes in the composition of the product gas in line with predictions of Le Chatelier’s principle. The influence was predominantly visible in higher yields of CH4 and lower overall production of product gas. For higher hydrocarbons (CxHy), the trend was unclear. A set of stable gasification parameters were achieved for each pressure level and a standard gasification temperature of 850 °C, except for gasification of lignin performed at 2 barg. A proposed explanation for the problem is the combined effect of the increasing concentration of ash in the fluidized bed and its low characteristic melting temperatures. Due to the obtained experimental findings, a new ash agglomeration index was formulated.

Influence of Sodium Oxide on the Fusion of Solid Municipal Waste Ash

The model composition of municipal solid waste (MSW) and its ash chemical composition are characterized. Mineral compounds and melting points are studied using a variety of analytical methods, including XRD, FTIR, and AFT. The main parameters of slag formation are calculated: base-to-acid ratio, slag viscosity index, and fouling coefficient. Solid municipal waste ash contains significant amounts of CaO, SiO2 and Al2O3. Using the Terra program, thermodynamic calculations of the chemical equilibria of the CaO–SiO2–Al2O3–Na2O systems containing from 5 to 25% sodium oxide are performed. It is experimentally shown that each 5 wt % increase in the Na2O content reduces the characteristic melting temperatures of MSW ash by 30–50°С.

Single-tube, dual channel pentaplexing for the identification of Candida strains associated with human infection

Invasive candidiasis is one of the most common nosocomial fungal infections worldwide. Delayed implementation of effective antifungal treatment caused by inefficient Candida diagnosis contributes to its notoriously high mortality rates. The availability of better Candida diagnostic tools would positively impact patient outcomes. Here, we report on the development of a single-tube, dual channel pentaplex molecular diagnostic assay based on Multiplex Probe Amplification (MPA) technology. It allows simultaneous identification of C. auris, C. glabrata and C. krusei, at species-level as well as of six additional albicans and non-albicans pathogenic Candida at genus level. The assay overcomes the one-channel one-biomarker limitation of qPCR-based assays. Assay specificities are conferred by unique biomarker probe pairs with characteristic melting temperatures; post-amplification melting curve analysis allows simple identification of the infectious agent. Alerting for the presence of C. auris, the well-characterised multi-drug resistant outbreak strain, will facilitate informed therapy decisions and aid antifungal stewardship. The MPA-Candida assay can also be coupled to a pan-Fungal assay when differentiation between fungal and bacterial infections might be desirable. Its multiplexing capacity, detection range, specificity and sensitivity suggest the potential use of this novel MPA-Candida assay in clinical diagnosis and in the control and management of hospital outbreaks.

Research and Manufacture of Stretch Films using LLDPE blends

New linear low-density polyethylene (LLDPE) blends were investigated to use as stretch and breathable films. In our investigation different types of LLDPE blends were prepared by extrusion. The characteristic melting and crystallization temperatures of these LLDPE blends were determined. Specimens were injection moulded and their tensile properties were measured. The LLDPE blends with the best thermal and mechanical results were chosen to prepare film by film blowing in laboratory conditions. Tearing properties of the films were also investigated. Our aim was to determine the most appropriate LLDPE blend for stretch film usable under industrial conditions.

A Study of Thermal Stability And Crystallization Kinetics of SbSeGe Glassy Alloys

Alloys of Sb10Se90-xGex (x = 0, 19, 21, 23, 25, 27) have been prepared using melt quenching technique. Differential thermal analysis has been used to determine the three characteristic temperatures, glass transition (Tg ), glass crystallization (Tc ) and melting temperature (Tm ), at four heating rates 5, 10, 15 and 20 K/min. The thermal stability and ease of glass formation have been evaluated in terms of Hruby parameter and reduced glass transition temperature respectively. The activation energy for glass crystallization (Ec ) has been calculated using Kissinger's method and Marseglia theory. The composition dependence of Tg and Ec has also been discussed.

Modification of the characteristic melting temperatures of sawdust ashes

This research was focused on one aspect of the use of biomass in energy plants, namely, the problems associated with low melting temperatures of ashes formed after sawdust combustion, which causes serious operational problems associated with agglomeration, slagging, and corrosion. For this research, the selected methodology was evaluated by CEN (European Committee for Standardization), based on the determination of four parameters: shrinkage temperature, deformation temperature, hemisphere temperature, and flow temperature. The above mentioned temperatures were determined for ash samples of sawdust burned in an oxidizing and reducing atmosphere.

A Phase Space Approach to Supercooled Liquids and a Universal Collapse of Their Viscosity

A broad fundamental understanding of the mechanisms underlying the phenomenology of supercooled liquids has remained elusive, despite decades of intense exploration. When supercooled beneath its characteristic melting temperature, a liquid sees a sharp rise in its viscosity over a narrow temperature range, eventually becoming frozen on laboratory timescales. Explaining this immense increase in viscosity is one of the principle goals of condensed matter physicists. To that end, numerous theoretical frameworks have been proposed which explain and reproduce the temperature dependence of the viscosity of supercooled liquids. Each of these frameworks appears only applicable to specific classes of glassformers and each possess a number of variable parameters. Here we describe a classical framework for explaining the dynamical behavior of supercooled liquids based on statistical mechanical considerations, and possessing only a single variable parameter. This parameter varies weakly from liquid to liquid. Furthermore, as predicted by this new classical theory and its earlier quantum counterpart, we find with the aid of a small dimensionless constant that varies in size from $\sim 0.05-0.12$, a universal (16 decade) collapse of the viscosity data as a function of temperature. The collapse appears in all known types of glass forming supercooled liquids (silicates, metallic alloys, organic systems, chalcogenide, sugars, and water).

Development of Mold Flux for Heat-Resistant Alloy Containing Al and Ti

When continuous casting was used to replace electro-slag remelting for the production of heat-resistant alloy Incoloy 800 containing Al and Ti, there were a number of quality problems associated with the cast product which were attributed to the use of an inappropriate mold flux. The aim of the current investigation was to develop and evaluate an improved mold flux by combining data derived from laboratory experiments with results obtained from plant-trials. The effects of composition on viscosity and heat transfer properties were investigated and a new mold flux was designed with improved casting behavior. By decreasing the characteristic melting temperatures, selecting an appropriate viscosity and enhancing the heat transfer properties, slab quality was improved. Chemical analysis combined with X-ray diffraction (XRD) and scanning electron microscopy (SEM) evaluation of liquid flux and flux film samples indicated that changes in composition, characteristic temperatures, and viscosity during the casting operation were negligibly small. The flux film with a thickness of 1.1 mm, a crystalline ratio of 30%, and cuspidine as the main crystalline phase was beneficial for improving heat transfer thus strengthening the initial shell and improving the quality of the cast product.

Interaction between Chromosomal Protein HMGB1 and DNA Studied by DNA-Melting Analysis

Interaction of HMGB1 nonhistone chromosomal protein with DNA was studied using circular dichroism spectroscopy and thermal denaturation of DNA. Melting DNA in the complex was shown to be a biphasic process. The characteristic melting temperatures of unbound DNA and the DNA bound to HMGB1 in 0.25 mM EDTA solutions were found to beTmI=44.0±0.5°C andTmII=62.0±1°C, respectively. It was shown that the binding of the HMGB1 molecule affects the melting of the DNA region approximately 30 b.p. long.

Droplet Array Platform for High-Resolution Melt Analysis of DNA Methylation Density

High-resolution melting (HRM) has garnered significant interest as an analytical technique for a number of applications, including DNA methylation detection, due to its inherent sensitivity and robustness. In this study, we describe a miniaturized assay platform for quantitative methylation density analysis using a microfluidic droplet array cartridge. We demonstrate that the DNA methylation level of the RASSF1A promoter can be directly analyzed using HRM. PCR products were generated by amplifying bisulfite-treated DNA with varying CpG densities using CpG island-flanking primer sets. Subsequent HRM analysis on the miniaturized droplet platform shows distinct melting curve profiles associated with methylation levels, which was verified using a conventional benchtop PCR-HRM system. The characteristic melting temperature (Tm) of the PCR products was used to directly quantify the respective levels of DNA methylation density. Our approach provides a key advantage over current gold standard methods such as methylation-specific PCR (MSP), which are incapable of providing specific information regarding the overall methylation density of the target genes. The miniaturized platform establishes a practical approach to methylation density profiling from multiple DNA samples with a potential application in point-of-care diagnostics.

Quantitative and Qualitative Analyses of the SNRPN Gene Using Real-Time PCR with Melting Curve Analysis

Prader-Willi syndrome and Angelman syndrome are distinct neurodevelopmental disorders that are associated with the deletion of the chromosomal 15q11-13 region or uniparental disomy of chromosome 15. In this article, we applied SYBR Green I-based real-time PCR and melting curve analysis assay for rapid genotyping of the small nuclear ribonucleoprotein polypeptide N (SNRPN) gene methylation status and for detecting aberrations in copy number in a single tube. A single pair of primers was designed to create a 357 bp fragment containing the cytosine phosphodiester guanine islands in the SNRPN promoter and to amplify both unmethylated and methylated sequences. Genotypes were identified based on the TC value for copy number changes and the characteristic melting temperature of methylated cytosine phosphodiester guanine. Genotyping of SNRPN was performed on blood samples of 20 individuals with Prader-Willi syndrome, 3 individuals with Angelman syndrome, and 20 unaffected individuals. The promoter methylation status and the copy number changes were successfully determined and compared with standard methylation-specific PCR, and were validated by multiplex ligation-dependent probe amplification. This single-tube, SYBR Green I, real-time PCR with melting curve assay is rapid, reliable, sensitive, and easy to perform. It is suitable for high-throughput analysis as an alternative technique for quantitative and qualitative analysis of target genes.

Effect of fluorine and chlorine on slag melting characteristics: Experimental study and simulation by neural networks

Hazardous waste from chemical factories including fluorine and chlorine has rather low fusion temperatures. During incineration in a rotary kiln incinerator, hazardous waste including fluorine and chlorine melts and turns into slag, possibly adhering to the inner wall and leading to unstable operation of the incinerator. Prediction of the melting characteristics of hazardous waste including fluorine and chlorine hence plays an important role in preventing slagging. The effect of various chemical components on fusion temperatures (deformation temperature, DT; softening temperature, ST; hemisphere temperature, HT; and flow temperature, FT) has been investigated experimentally: Na 2O and NaF are the most remarkable chemical compounds among those investigated. Correlations between fusion temperatures and chemical components have been investigated; neural networks have been used to predict four characteristic melting temperatures and are verified by tested slag samples of hazardous waste including fluorine and chlorine. Relative errors of fusion temperatures (computed vs. measured) are mostly less than 1.2%.