Papers by Keyword: Thermal Analysis

Abstract: The successful implementation of fused filament fabrication (FFF) 3D printing using recycled plastics requires a deep understanding of the thermal behavior of the plastics throughout the printing process. This study investigated the influence of wall thickness of the printed sample, nozzle temperature, and cooling fan speed during 3D printing on the cooling rate, crystallinity, and tensile properties of recycled polyethylene terephthalate (rPET). The experimental process commenced with the collection of discarded rPET bottles, followed by thorough cleaning and washing to remove any adhesives and contaminants. Afterward, the bottles were cut and ground into flakes and then converted into filaments using a single-screw filament extrusion process. In-situ thermal analysis was conducted by integrating an infrared (IR) thermal camera into the 3D printing setup to monitor real-time temperature changes during the printing process. Results revealed that cooling rates increased markedly with reduced wall thickness, rising from 17.53 °C/min for the 3.6 mm wall thickness to 62.92 °C/min for the 1.2 mm wall thickness. Nozzle temperature exhibited a non-linear influence, with the highest cooling rate of 65.47 °C/min recorded at 240 °C, while enhanced cooling fan speed (100%) further accelerated cooling to 45.00 °C/min. Differential scanning calorimetry (DSC) and Raman spectroscopy confirmed that a slower cooling rate generally promoted crystallinity, which was observed in thick-walled and low-cooling speed prints. Tensile testing demonstrated a strong correlation between crystallinity and tensile performance, with ultimate tensile strength (UTS) reaching 55 MPa at 240 °C and 54.8 MPa at 25% cooling fan speed, outperforming previously reported rPET values. The use of rPET in FFF and the findings of this study contribute to the further exploration of rPET's potential in sustainable additive manufacturing practices.

Abstract: The dendritic microstructure formed during solidification plays a critical role in determining the mechanical properties of aluminum castings. In particular, secondary dendrite arm spacing (SDAS) is strongly influenced by the cooling rate and is closely related to yield strength, ultimate tensile strength, and elongation. However, experimental validation of these relationships requires a consistent methodology for defining cooling rate and linking it to microstructural and mechanical measurements. In this study, an experimental framework was established to investigate the relationships among cooling rate, SDAS, and mechanical properties in aluminum castings. Casting blocks with different thicknesses were fabricated to obtain a wide range of cooling rates. Cooling curves were measured during solidification, and cooling rates were determined using the second derivatives of the cooling curves. SDAS measurements and tensile tests were conducted on specimens extracted from symmetric positions within the casting blocks to ensure equivalent thermal histories. The results showed that the cooling rate–SDAS relationship exhibited a linear trend on a logarithmic scale, consistent with previously reported correlations. Smaller SDAS values were associated with increased yield strength, ultimate tensile strength, and elongation. The agreement between the present results and literature data confirms the validity of the proposed experimental framework for correlating solidification conditions, microstructure, and mechanical properties of aluminum castings.

Abstract: Poly (ethylene 2,5-furandicarboxylate) (PEF) is a bio-based polyester that is the subject of growing interest as a potential alternative to Poly (ethylene terephthalate) (PET) for sustainable packaging. Its excellent gas-barrier properties and reduced carbon footprint make it a promising candidate, but its use at industrial scale requires a solid understanding of how temperature and thermal history affect its mechanical and viscoelastic behavior. In this study, Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMA), and optical microscopy were used to characterize the thermal transitions and crystallization behavior of PEF, compared with PET and recycled PET (rPET). DSC results show that thermal crystallization of PEF proceeds very slowly, a result confirmed by in-situ microscopy. DMA measurements provide complementary information on the evolution of both storage and loss moduli with temperature, highlighting its dependence on crystallinity and thermal history. Together, these thermal and mechanical analyses clarify how PEF’s crystallization behavior affects its thermo-mechanical response. From a processing perspective, the very slow thermal crystallization of PEF is advantageous for stretch blow molding (SBM) process of bottles, as the polymer remains essentially amorphous during heating and crystallizes predominantly under deformation during the fast forming stage.

Abstract: This work presents the numerical analysis of the thermal behavior of a new model of a flat solar collector. The computational model integrates embedded piping configured in a Rhomboid Tessellation Pattern (RTP), with scaling governed by allometric and fractal principles, constrained within a 3 × 3-branched fractal tree structure. The numerical analysis was performed using Computational Fluid Dynamics (CFD) with Autodesk CFD software. The operation of the collector was estimated with water mass flows ranging from 0.01 to 0.06 kg/s, with the water inlet temperature set at 20°C, and analyzed under two simulated solar radiation conditions, 850 and 650 W/m². The studied collector exhibits superior performance compared to traditional collectors. Specifically, it achieves higher fluid temperatures with similar mass flows, even under lower solar radiation conditions. The collector demonstrates thermal performance with efficiencies reaching up to 84.3% for small mass flows. On average, the collector efficiency was 78.1%. The higher thermal efficiency compared to conventional flat plate solar collectors and the reduction in pressure drop by up to 90% compared to traditional collectors make the collector model analyzed in this study a promising option for systems employing solar collectors or collector-evaporators.

Abstract: Recently, there has been a growing interest in replacing synthetic fibres with natural fibres in polymer composites due to environmental concerns. This study examined the fibres from the Newbouldia laevis plant for their potential use in lightweight polymer composites, particularly in applications sensitive to strength and temperature. The fibres were extracted from the plant's stem, and various properties such as density, moisture content, moisture regain, and diameter were measured. Chemical analysis revealed the percentages of cellulose, hemicellulose, lignin, extractives, and ash present in the fibres. Furthermore, Fourier transform infrared analysis confirmed the presence of these essential components. Scanning electron microscopy images showed the rough surfaces of the fibres, which enhance the adhesion between the fibre and matrix during the production of polymer composites. Energy dispersive X-ray analysis identified carbon and oxygen as the main elements in the fibres. Thermal analysis provided insights into the thermal stability and maximum degradation temperatures of the fibres. Lastly, a single fibre tensile test was performed to evaluate the tensile strength, elastic modulus, and elongation at break of the fibres using Weibull distribution statistical analysis. The results of this study indicate that Newbouldia laevis fibres could be a promising reinforcement for lightweight polymer composites in strength and temperature-sensitive applications.

Abstract: Paper investigates the possibility of producing silicon from silica contained in Shoda-Kedela (Oni-Gebi district, Georgia) quartz deposition. Characterization of silica from Shoda-Kedela quartz rock is carried by its crushing, grinding, thermal analysis, studying composition and density. Metallurgical grade silicon (MG-Si) is obtained by reducing Shoda-Kedela quartz in its reaction with coke in an electric arc furnace at temperature of ~1800°C. The obtained in this way material reveals that Shoda-Kedela silica containing of 99.58% SiO₂ would be useful for developing the silicon high-technology production.

Abstract: This study investigates the impact of chemical and thermal activation on the sorption capacity of Transcarpathian clinoptilolite from the Sokyrnytsky deposit. The chemical activation of natural clinoptilolite was performed using aqueous solutions of 5% HCl and 25% H₂SO₄ at a solid-to-liquid phase ratio of 1:10. Thermal activation was conducted at a temperature of 300°C. The sorption capacity of both natural and activated clinoptilolite was evaluated for water vapor in this thermal analysis. The ability of activated clinoptilolite to absorb direct blue dye was determined through spectrophotometric analysis. The partial degradation of clinoptilolite due to acid modification was confirmed by X-ray phase analysis and electron microscopy. The sorption isotherms of direct blue dye were modeled using the Langmuir equation, and the corresponding constants were determined. Clinoptilolite activated with a 25% aqueous H₂SO₄ solution is recommended for use in sorption technologies for wastewater treatment from direct dyes.

Abstract: In a hot and dry climate country, performance of a gas turbine power cycle is low. Incorporation of a regenerator in the cycle and a spray cooler before compression of inlet air enhances its performance. Accordingly, this study focuses on the effect of regeneration and cooling of the inlet air on performance of an open cycle gas turbine plant, which mainly includes improvement in its thermal efficiency and reduction in specific fuel consumption. In this context, a suitable mathematical model is developed on the basis of fundamental understanding of thermodynamics and gas turbine relations. This model is then used in simulations by developing a code on Java platform where ambient temperature, pressure ratio and regenerator effectiveness are considered as major system parameters. In the simulation, a comparison among a simple Brayton cycle, a regenerative cycle and a regenerative cycle with spray cooler is considered under different system parameters. It is predicted that there is a significant increase in thermal efficiency and a significant decrease in specific fuel consumption on incorporation of regenerator and spray cooler to the cycle. However, addition of a spray cooler is applicable above an optimal pressure ratio (≈6) and in the high temperature environmental condition. As an example, 12.89% increase in thermal efficiency is found at a regenerator effectiveness of 0.85 on addition of spray cooler before compression of inlet air at an ambient temperature of 328K, and subsequent reduction in specific fuel consumption is found as 2.85% at pressure ratio of 10.

Abstract: The object of the study was the Ukrainian bentonite clays of the Cherkasy deposit (layer II of the Dashukivska area) and the Ilnytske deposit of the Transcarpathian region. Enrichment of clays with montmorillonite was carried out by the method of sedimentation of the coarsely dispersed phase. The natural type of montmorillonite and the nature of isomorphic substitutions in its structure were confirmed by X-ray diffractometric and complex thermal analyses. Activation of bentonite clay enriched with montmorillonite was carried out by the action of ultrasonic waves. The sorption capacity of activated and montmorillonite-enriched clays with respect to Cu²⁺ ions was assessed by the results of energy dispersive X-ray analysis. The ion exchange mechanism of sorption of Cu²⁺ ions was confirmed by the data of diffractometric X-ray analysis. The prospects for the use of enriched bentonite clays activated by ultrasonic waves are outlined.

Abstract: In a coupled analysis of steel-concrete composite structural elements, radiative heat flux is the main component of the heat transfer. The majority of the available methods to model the radiative heat flux are based on prescriptive values of the surface thermal properties of the participating medium, which do not take into account the specific geometry of the system and the effective values of the thermal properties of the participating medium. The prescriptive method assumes that the terminal properties of the participating medium are independent of the temperature and the wavelength of the electromagnetic radiation. The mentioned assumptions improve the formulation of the mathematical model which describes the physical phenomena, yet considering the number of parameters that influence the physical phenomenon, for example, the gray body assumption, or neglecting the local geometric conditions may cause the supraevaluation of the real situation. The present study assumes to establish on a quantitative and qualitative level the radiative heat flux for two situations. The first situation involves the radiative heat transfer between the flame and a solid surface, one of the first steps in the thermal analysis of composite structural elements. The evaluation of the thermal properties of the fame involves the influence of soot, which may enhance on a quantitative scale the radiative heat flux up to 42 [%]. The second case deals with the radiative heat transfer between two parallel solid surfaces, a particular case if one desires to model the thermal discontinuity between steel and concrete. The present study assumes to evaluate the thermal and geometric parameters that influence the radiative heat flux for a wide range of temperatures and compares the different approaches with the standard formulation. The local geometric conditions and the blackbody fraction introduced in the model enhance the value of the radiative heat flux by approximately 2 [%], for temperatures indicated by the ISO-834 standard fire curve, up to 1300 [K].