In this study, a multifunctional air filtration material was developed by coating polypropylene (PP) nonwoven fabric with a chitosan/TiO₂ (P25) composite. The aim was to enhance air filtration efficiency. The chitosan–P25 composite was applied onto the PP nonwoven via a solution spray method followed by drying. Scanning electron microscopy (SEM) analysis revealed a uniform coating layer with good adherence to the PP fiber surface. X-ray diffraction (XRD) analysis confirmed the presence of crystalline TiO₂ in the P25 phases, as well as the semi-crystalline nature of the PP substrate. Air permeability tests showed a moderate reduction in air flow rate due to surface coating, while maintaining acceptable breathability for filter applications.

Fossil fuels continue to dominate energy use, despite growing environmental concerns, underscoring the need for renewable energy solutions. Photovoltaic cells convert sunlight but lose efficiency from heat, requiring cooling methods such as photovoltaic thermal systems. Tthis study evaluated a PVT system with three serpentine tubes under varied conditions using computational fluid dynamics simulations. Testing involved water coolant flow rates of 0.001, 0.005, and 0.009 kg/s, radiation intensities of 200, 400, and 600 W/m², and tube diameters of 15 mm and 17 mm. Increasing the mass flow rate significantly reduced temperature and improved thermal efficiency, while electrical efficiency remained stable as the PV panel temperature mainly influenced it. The optimal cooling performance was achieved with a 0.009 kg/s mass flow rate and a 15 mm tube diameter at 600 W/m² radiation intensity. These findings suggest water-based cooling may increase PV system performance and reliability, especially in high solar locations.

This study presents a new mathematical model for determining the specific growth rate of biomass in biotechnological production processes, which aims to optimize the production of biotechnological products such as the advanced material polyhydroxyalkanoates. The specific growth rate is classified by the FDA as a critical process parameter that affects product quality and quantity, but is difficult for laboratory personnel to determine. Therefore, a simple and robust method for real-time monitoring and control is crucial. According to the current state of the art, the established Luedeking-Piret model for determining the specific growth rate requires the determination of the biomass as an absolute value to initialize the model and to determine two further model parameters. However, determining the biomass is time-consuming and error-prone. The new relative model replaces this value with the relative change in biomass, which can be easily recorded using standard laboratory methods such as optical density measurement. This eliminates the need for time-consuming and resource-intensive preliminary work. Despite this simplification, simulation tests have shown that the new model delivers identical results to the established model. It represents an independent, precise alternative and offers advantages in terms of handling. The results underline the model's potential to make bioprocesses more sustainable and efficient. Especially in research, material consumption, laboratory time and costs can be reduced compared to the established model. Future experiments will further investigate the performance of the new approach compared to the established model.

This study presents an in-depth analysis of heat loss mechanisms in a rotary kiln system used for biomass torrefaction, with briquetted biomass fuel serving as the primary thermal energy source. The study evaluates five principal heat loss pathways: wall heat loss, exhaust gas heat loss, hydrogen-related heat loss, moisture evaporation, and heat loss due to incomplete combustion. Experimental tests were conducted at three torrefaction temperatures (230°C, 250°C, and 270°C), and thermal energy losses were quantified through temperature measurements, energy balance equations, and gas composition analysis. Results indicate that while absolute heat loss values increased with higher torrefaction temperatures due to elevated energy input and system load, the percentage of heat loss relative to total input decreased, improving net thermal efficiency. Wall heat loss was the dominant component across all conditions but declined in percentage terms from 80.5% to 30.9% as temperature increased. The reuse of exhaust gas for drying briquetted biomass was also investigated, demonstrating that waste heat recovery significantly reduces drying time—from 19 hours at 230°C to 13 hours at 270°C—without compromising fuel integrity. These findings confirm that integrating exhaust gas utilization into the torrefaction process enhances energy efficiency, supports continuous operation, and reduces external energy demand, offering a viable strategy for sustainable biomass fuel processing at an industrial scale. The findings provide design guidance for integrating heat recovery into industrial-scale biomass torrefaction systems.

According to Stokes, the time required for a particle to precipitate depends on several conditions such as sphericity and laminar flow, as well as key parameters like particle size, densities (particle and fluid) and fluid viscosity. Therefore, if any of these conditions or parameters are unknown or not met, it becomes impossible to estimate the precipitation time. Additionally, when the separation under 1- g (Earth gravity) takes days or months but an estimation is needed in just minutes, the separation time at 1- g can be approximated by relating it to conditions at other values of gravity ( n - g ). For example, in a centrifuge. However, this n-g value is not reached instantaneously but require to consider the acceleration, plateau, and deacceleration phases to obtain a reliable estimation. This task has been addressed before; however, the resulting models tend to be either complex for practical laboratory use, or fail to account for the relationship between distance travelled by a particle under 1- g and the distance travelled under centrifugal forces. Moreover, even during the plateau phase, centripetal acceleration is unsteady because the radial distance of the precipitating particle is constantly changing. Thus, the aim of this study is to simplify the methodology for estimating particle separation time at 1- g by using separation time obtained under the unsteady conditions of centrifugation, even when the properties of the particle and fluid are unknown, through a numerical approach.

An inverse problem involves determining unknown physical quantities denoted as u = (u 1 , ..., u np ), which cannot be directly measured but need to be evaluated based on accessible measurements, represented as y = M(u), where M is a mathematical model. Solving such problems often requires mathematical techniques like differential equations or optimization methods such as least squares. Inverse problems can be well-posed (stable, unique solutions) or ill-posed (unstable or non-unique), with ill-posedness often resulting from poor experimental setups or measurement errors. This study addresses the identification of thermophysical parameters - specifically thermal conductivity and heat transfer coefficients—in a 2D steady-state diffusive medium. The proposed method uses a boundary element approach and an iterative descent algorithm to minimize a functional and identify the unknown parameters, validated through simulated thermograms. As a result, the use of sensitivity functions to weight the functional to be minimized makes it possible to avoid selection of the sensors according to the parameter to be identified.

The special edition offers readers a detailed overview of the modern challenges and solutions in materials science and engineering, serving as a valuable reference for researchers and engineers, and as a foundation for fostering innovation across disciplines.

Hail impact is a critical loading situation for unidirectional fiber reinforced composites in automotive and aerospace applications. Therefore, it was already analyzed frequently in literature, focusing on thin-walled structural components and panels. Discontinuous fiber reinforced materials, such as sheet molding compounds (SMCs), and their behavior under local, high velocity impact of hail, was not considered in detail so far. The current study is aimed to investigate the fracture behavior of 2 mm and 4 mm thick SMCs sheets under a high velocity ice ball impact (80 m/s) from a numerical and experimental point of view. The strain-rate dependent material modeling of ice balls is based on an elasto-plastic material model and utilizes smooth particle hydrodynamic (SPH) modeling. Each unidirectional fiber bundle of the SMC plate was modeled individually and the space between these discrete patches was filled by elements representing the matrix material. A micromechanical analysis using representative volume elements (RVEs) was conducted to determine the homogenised strain rate dependent response of the SMC fiber bundle. In addition, a 3D Maximum Stress and Hashin damage model was calibrated to simulate the fracture of the SMC sheets. The accuracy of the applied models was evaluated by comparing the numerical model to results gathered from experimental hail impact trials. Hereby, a high-speed camera system was used to record the experiment and to gain insight into the fracture behavior of the composite structures. In general, it was observed that a 2 mm thick SMC plate was not able to withstand the impact of an ice ball whereas the 4 mm thick sheet was not visually affected. Computer tomography measurements of the impacted region revealed significant damage within the 4 mm thick SMC plate.

The purpose of this study is to evaluate the accuracy of a simulation model for the Rotary Friction Welding (RFW) process of AA6061 aluminum alloy. RFW, widely used in the aerospace and automotive industries, is known for producing strong welds with minimal heat-affected zones (HAZ). Using ABAQUS software, a numerical model was developed to simulate key aspects of the process, such as heat generation, material flow, and axial shortening. The simulation results were compared with experimental data and previous studies to validate the model’s accuracy. The comparison demonstrated the model’s ability to closely replicate reality welding conditions, making it a reliable tool for optimizing welding parameters and improving the RFW process for AA6061.

The current research paper presents an investigation into the behavior of two-phase flow of liquid-vapour R134a within vertical circular channels with a 1 mm diameter, utilizing the Volume of Fluid (VOF) method. The main objective of these simulations was to create a numerical flow regime map to delineate the boundaries of different flow patterns for liquid-gas R134a. The injection of vapor was performed through an annular (concentric) nozzle configuration. To optimize computational efficiency, a two-dimensional axisymmetric assumption was made. The results of this study led to the identification of four fundamental flow patterns: bubbly flow/confined bubble flow, slug flow, churn flow, and annular flow. The accuracy of these findings was confirmed by comparing them with experimental flow visualization results, demonstrating a strong agreement. This study highlights the effectiveness of Computational Fluid Dynamics in establishing a reliable two-phase flow pattern map.