Search Results (2,094)

In many developing African countries, milk safety is often managed through traditional methods such as fermentation or boiling over firewood. While these approaches reduce some microbial risks, they present critical limitations. Firewood dependency contributes to deforestation, depletion of agricultural residues, and loss of soil fertility, which, in turn, compromise environmental health and food security. Solar pasteurization provides a reliable and sustainable method for thermally inactivating pathogenic microorganisms in milk and other perishable foods at sub-boiling temperatures, preserving its nutritional quality. This study aimed to evaluate the thermal and microbial performance of a low-cost solar milk pasteurization system, hypothesized to effectively reduce microbial contaminants and retain milk quality under natural sunlight. The system was constructed using locally available materials and tailored to the climatic conditions of the Savanna ecological zone in West Africa. A flat-plate glass solar collector was integrated with a 0.15 cm thick stainless steel cylindrical milk vat, featuring a 2.2 cm hot water jacket and 0.5 cm thick aluminum foil insulation. The system was tested in Navrongo, Ghana, under ambient temperatures ranging from 30 °C to 43 °C. The pasteurizer successfully processed up to 8 L of milk per batch, achieving a maximum milk temperature of 74 °C by 14:00 GMT. Microbial analysis revealed a significant reduction in bacterial load, from 6.6 × 10⁶ CFU/mL to 1.0 × 10² CFU/mL, with complete elimination of coliforms. These results confirmed the device’s effectiveness in achieving safe pasteurization levels. The findings demonstrate that this locally built solar pasteurization system is a viable and cost-effective solution for improving milk safety in arid, electricity-limited regions. Its potential scalability also opens avenues for rural entrepreneurship in solar-powered food and water treatment technologies. Full article

The photon spin Hall effect (PSHE) arises from the spin–orbit interaction of light. Metasurfaces enable precise control over the PSHE through their influence. Using electromagnetic simulations as its foundation, this work engineers a metal–insulator–metal (MIM) metasurface for generating vortex beams in the near-infrared band, targeting enhanced modulation of the PSHE. Electromagnetic simulations embed vanadium dioxide (VO₂)—a thermally responsive phase-change material—within the MIM metasurface architecture. Numerical evidence confirms that harnessing VO₂’s insulator–metal-transition-mediated optical switching dynamically tailors spin-dependent splitting in the illuminated MIM-VO₂ hybrid, thereby achieving a significant amplification of the PSHE displacement. Electromagnetic simulations determine the reflection coefficients for both VO₂ phase states in the MIM-VO₂ structure. Computed spin displacements under vortex beam incidence reveal that VO₂’s phase transition couples to the MIM’s top metal and dielectric layers, modifying reflection coefficients and producing phase-dependent PSHE displacements. The simulation results show that the displacement change of the PSHE before and after the phase transition of VO₂ reaches 954.7 µm, achieving a significant improvement compared with the traditional layered structure. The dynamic modulation mechanism of the PSHE based on the thermal–optical effect has been successfully verified. Full article

With the rapid development of information technology and semiconductor technology, the iteration speed of electronic devices has accelerated in an unprecedented manner, and the market demand for miniaturized, highly integrated, and highly intelligent devices continues to rise. But when these electronic devices operate at high power, the electronic components generate a large amount of integrated heat. Due to the limitations of existing heat dissipation channels, the current heat dissipation performance of electronic packaging materials is struggling to meet practical needs, resulting in heat accumulation and high temperatures inside the equipment, seriously affecting operational stability. For electronic devices that require high energy density and fast signal transmission, improving the heat dissipation capability of electronic packaging materials can significantly enhance their application prospects. In order to improve the thermal conductivity of composite materials, hexagonal boron nitride (h-BN) was selected as the thermal filling material in this paper. The BMI resin was structurally modified through molecular structure design. The results showed that the micro-branched structure and h-BN synergistically improved the thermal conductivity and insulation performance of the composite material, with a thermal conductivity coefficient of 1.51 W/(m·K) and a significant improvement in insulation performance. The core mechanism is the optimization of the dispersion state of h-BN filler in the matrix resin through the free volume in the micro-branched structure, which improves the thermal conductivity of the composite material while maintaining high insulation. Full article

In this article, thermal investigation methods for electrically insulating and thermally conductive substrate materials will be presented. The investigations were performed in their real-world application environment, i.e., in the form of IGBT (insulated gate bipolar transistor) module substrate plates. First, the overall thermal resistance and thermal structure function of the system in a multivariable parameter space were revealed using CFD (computational fluid dynamics) simulations. Afterwards, thermal transient testing was performed on real samples, with the help of which the thermal resistance values of the modules were determined using the thermal dual interface test method. The presented tests are not intended to determine material parameters, but to rank different substrate materials based on their thermal performance. Full article

In the context of the growing need to reduce greenhouse gas emissions and to develop sustainable solutions for the construction industry, foamed geopolymers represent a promising alternative to traditional binders and insulation materials. This study investigates the thermal properties of novel low-emission, insulating geopolymer binders made from fly ash with diatomite, chalcedonite, and wood wool aiming to assess their potential for use in thermal insulation systems in energy-efficient buildings. The stability of the foamed geopolymer structure is also assessed. Measurements of thermal conductivity, specific heat, microstructure, density, and compressive strength are presented. The findings indicate that the selected geopolymer formulations exhibit low thermal conductivity, high heat capacity and low density, making them competitive with conventional insulation materials—mainly load-bearing ones such as aerated concrete and wood wool insulation boards. Additionally, incorporating waste-derived materials reduces the production carbon footprint. The best results are represented by the composite incorporating all three additives (diatomite, chalcedonite, and wood wool), which achieved the lowest thermal conductivity (0.10154 W/m·K), relatively low density (415 kg/m³), and high specific heat (1.529 kJ/kg·K). Full article

Rammed earth (RE), a traditional material aligned with circular economy (CE) principles, has been gaining renewed interest in contemporary construction due to its low environmental impact and compatibility with sustainable building strategies. Though not a modern invention, it is being reintroduced in response to the increasingly strict European Union (EU) regulations on carbon footprint, life cycle performance, and thermal efficiency. RE walls offer multiple benefits, including humidity regulation, thermal mass, plasticity, and structural strength. This study also draws attention to their often-overlooked ability to mitigate indoor overheating. To preserve these advantages while enhancing thermal performance, this study explores insulation strategies that maintain the vapor-permeable nature of RE walls. A parametric analysis using Delphin 6.1 software was conducted to simulate heat and moisture transfer in two main configurations: (a) a ventilated system insulated with mineral wool (MW), wood wool (WW), hemp shives (HS), and cellulose fiber (CF), protected by a jute mat wind barrier and finished with wooden cladding; (b) a closed system using MW and WW panels finished with lime plaster. In both cases, clay plaster was applied on the interior side. The results reveal distinct hygrothermal behavior among the insulation types and confirm the potential of natural, low-processed materials to support thermal comfort, moisture buffering, and the alignment with CE objectives in energy-efficient construction. Full article

This study aims to explore the potential of aerogel to optimise the thermal conductivity of mineralised foam materials. Experiments were conducted with (i) addition methods of aerogel, (ii) proportion of aerogels in cement slurry, and (iii) water/cement ratio as influencing parameters for mineralised foam. Additionally, mixed Ordinary Portland Cement (OPC)/Calcium Sulphoaluminate Cement (CSA) slurries were used to test whether a synergy could be achieved. In this study, the defoaming effect of the aerogel and its mitigation to a certain extent by pre-mixing the aerogel with cement slurry were confirmed. The thermal conductivity of the mineralised foams was reduced from 0.049 to 0.036 W/(m·K) when the aerogel was up to 10 wt.% of the cement. In the specimens prepared from the mixed OPC/CSA slurry, a homogeneous circular pore structure was observed under the microscope along with a reduction in the thermal conductivity. The use of aerogels and CSA cements can effectively reduce the thermal conductivity of ultra-low-density mineralised foams to levels comparable with certain plastic foams that dominate the building insulation market. Full article

To meet the European Green Deal targets, the construction sector must improve building thermal performance via advanced insulation systems. Eco-friendly sandwich panels offer a promising solution. Therefore, this work aims to develop and validate a new eco-friendly composite sandwich panel (basalt fibres and recycled extruded polystyrene) with enhanced multifunctionality for lightweight and energy-efficient building façades. Two panels were produced via vacuum infusion—a reference panel and a multifunctional panel incorporating phase change materials (PCMs) and silica aerogels (AGs). Their performance was evaluated through lab-based thermal and acoustic tests, numerical simulations, and on-site monitoring in a living laboratory. The test results from all methods were consistent. The PCM-AG panel showed 16% lower periodic thermal transmittance (0.16 W/(m²K) vs. 0.19 W/(m²K)) and a 92% longer time shift (4.26 h vs. 2.22 h), indicating improved thermal inertia. It also achieved a single-number sound insulation rating of 38 dB. These findings confirm the panel’s potential to reduce operational energy demand and support long-term climate goals. Full article

This study presents a cost-effective, carbon-negative construction material for affordable housing, developed entirely from locally available agricultural wastes: rice husk ash, wood ash, and rice straw—materials often problematic to dispose of in many African regions. Rice husk ash provides high amorphous silica, acting as a strong pozzolanic agent. Wood ash contributes calcium oxide and alkalis to serve as a reactive binder, while rice straw functions as a lightweight organic filler, enhancing thermal insulation and indoor climate comfort. These materials undergo natural pozzolanic reactions with water, eliminating the need for Portland cement—a major global source of anthropogenic CO₂ emissions (~900 kg CO₂/ton cement). This process is inherently carbon-negative, not only avoiding emissions from cement production but also capturing atmospheric CO₂ during lime carbonation in the hardening phase. Field trials in Kenya confirmed the composite’s sufficient structural strength for low-cost housing, with added benefits including termite resistance and suitability for unskilled laborers. In a collaboration between the University of Tartu and Kenyatta University, a semi-automatic mixing and casting system was developed, enabling fast, low-labor construction of full-scale houses. This innovation aligns with Kenya’s Big Four development agenda and supports sustainable rural development, post-disaster reconstruction, and climate mitigation through scalable, eco-friendly building solutions. Full article

The study investigates the potential of enhancing gypsum board properties through the integration of hemp hurds and glass fibers. The investigation focuses on evaluating the composite material’s density, water absorption, flexural strength, compressive strength, and thermal performance. Experimental results demonstrate a reduction in gypsum composite density and improved thermal insulating properties with the introduction of hemp hurds. Water absorption, a significant drawback of gypsum boards, is mitigated with hemp hurds, indicating potential benefits for insulation efficiency. For mechanical tests, the gypsum ceiling board at approximately 5% by weight exhibits a flexural strength value exceeding the minimum average threshold of 1 MPa and the highest average compressive strength at 2.94 MPa. Thermal testing reveals lower temperatures and longer time lags in gypsum boards with 5% hemp hurds, suggesting enhanced heat resistance and reduced energy consumption for cooling. The study contributes valuable insights into the potential use of hemp hurds in gypsum-based building materials, presenting a sustainable and energy-efficient alternative for the construction industry. Full article

This study investigates the effect of hemp shive granulometry on the thermal conductivity and microstructure of hemp–lime composites. Three distinct particle size fractions—fine, medium, and coarse—were characterized using high-resolution image analysis to determine geometric parameters such as Feret diameters, circularity, and elongation. Composite mixtures with varying binder-to-shive and water-to-shive ratios were prepared and compacted at a consistent level to isolate the influence of aggregate granulometry on thermal performance. Results demonstrate a clear inverse relationship between particle size and thermal conductivity, with coarse fractions reducing thermal conductivity by up to 7.6% compared to fine fractions. Composite density was also affected, decreasing with increasing particle size, confirming the impact of granulometry on pore structure and packing density. However, binder content exhibited the most significant effect on thermal conductivity, with a 20% increase observed for higher binder-to-shive ratios irrespective of shive size. The study further establishes that a 15 g sample size (~2400 particles) provides sufficient statistical accuracy for granulometric characterization using image analysis. These findings provide critical insights for optimizing hemp–lime composites for enhanced thermal insulation performance, supporting sustainable construction practices by informing material formulation and processing parameters. Full article

Mycelium-based composites (MBCs) are an emerging category of cost-effective and environmentally sustainable materials that are attracting significant research and commercial interest across various industries, including construction, manufacturing, agriculture, and biomedicine. These materials harness the natural growth of fungi as a low-energy bio-fabrication method, converting abundant agricultural by-products and waste into sustainable alternatives to energy-intensive synthetic construction materials. Their affordability and eco-friendly characteristics make them attractive for both research and commercialisation. Currently, mycelium-based foams and sandwich composites are being actively developed for applications in construction. These materials offer exceptional thermal insulation, excellent acoustic absorption, and superior fire safety compared to conventional building materials like synthetic foams and engineered wood. As a result, MBCs show great potential for applications in thermal and acoustic insulation. However, their foam-like mechanical properties, high water absorption, and limited documentation of material properties restrict their use to non- or semi-structural roles, such as insulation, panelling, and furniture. This paper presents a comprehensive review of the fabrication process and the factors affecting the production and performance properties of MBCs. It addresses key elements such as fungal species selection, substrate choice, optimal growth conditions, dehydration methods, post-processing techniques, mechanical and physical properties, termite resistance, cost comparison, and life cycle assessment. Full article

The growing demand for direct current transmission emphasizes the need for advanced insulation suitable for high-capacity, long-distance applications. Thermoplastics, especially polypropylene, offer several advantages over conventional materials like XLPE (cross-linked polyethylene) and EPR (ethylene propylene rubber), including higher thermal stability, recyclability, and reduced space charge accumulation. However, due to the inherent rigidity and limited flexibility of PP, its mechanical aging becomes a critical factor in assessing its long-term reliability as a cable insulation. In this study, mechanical aging characteristics, specifically declines in tensile strength and elongation, were selected as key indicators of insulation aging. Accelerated aging tests were conducted at 90 °C, 110 °C, and 130 °C for up to 5000 h. The experimental data were fitted to exponential models to derive aging coefficients, which formed the basis for the proposed aging model and the ACI (aging condition index). The ACI enables quantitative assessment of the current insulation condition and estimation of the remaining lifetime until a predefined threshold (e.g., ACI = 0.5) is reached. These findings contribute to the development of condition-based maintenance strategies and long-term asset management for power cables, offering practical insights for improving the reliability of future power grid systems. Full article

Currently, chimney technology is looking for new materials with improved thermal insulation properties and, at the same time, adequate durability. The use of concretes based on lightweight aggregates, such as expanded perlite, is capable of meeting such a challenge, provided that the composition of the concrete mixes is appropriately modified. The main research challenge when designing chimney system casing elements lies in ensuring adequate resistance to moisture penetration (maximum water absorption of 25%), while achieving the lowest possible bulk density (below 1000 kg/m³), sufficient compressive strength (minimum 3.5 MPa), and capillary water uptake not exceeding 0.6%. In the present research, laboratory tests were conducted to improve the fundamental technical properties of lightweight perlite-based concrete to meet the aforementioned requirements. Laboratory tests of perlite concrete were carried out by adding eight chemical admixtures with a hydrophobic effect and the obtained results were compared with a reference concrete (without admixtures). However, the positive results obtained under laboratory conditions were not confirmed under actual production conditions. Therefore, further tests were conducted on chimney casings taken directly from the production line. Subsequent chemical admixtures with a hydrophobic effect, based on silane/siloxane water emulsions, were applied to determine the concrete mix’s optimal composition. The results of the tests carried out on perlite concrete chimney casings from the production line confirm the effectiveness of the applied chemical admixtures with a hydrophobic effect in improving the moisture resistance. This was further supported by the outcomes of the so-called ‘drop test’ and capillary uptake test, with the suitable bulk density and compressive strength being maintained. Full article

This study presents a comprehensive mathematical model of a semiconductor structure based on vanadium dioxide (VO₂), specifically in its conductive phase. The model was developed using the finite element method (FEM), enabling detailed simulation of the formation of a conductive channel under the influence of low-frequency alternating voltage (50 Hz). The VO₂ structure under investigation exhibits pronounced electric field concentration at the surface, where the field strength reaches approximately 5 × 10⁴ V/m, while maintaining a more uniform distribution of around 2 × 10⁴ V/m within the bulk of the material. The simulation results were validated experimentally using a test circuit. Minor deviations—no greater than 8%—were observed between the simulated and measured current values, attributed to magnetic core saturation and modeling assumptions. A distinctive feature of the model is its ability to incorporate the nonlinear dependencies of VO₂’s electrical properties on frequency. Analytical expressions were derived for the magnetic permeability and resistivity of VO₂, demonstrating excellent agreement with experimental data. The coefficients of determination (R²) for the frequency dependence of magnetic permeability and resistance were found to be 0.9976 and 0.9999, respectively. The current version of the model focuses exclusively on the conductive phase and does not include the thermally induced metal–insulator phase transition characteristic of VO₂. The study confirms that VO₂-based structures exhibit high responsiveness and nonlinear switching behavior, making them suitable for applications in electronic surge protection, current limiting, and switching elements. The developed model provides a reliable and physically grounded tool for the design and optimization components based on VO₂ in power electronics and protective circuitry. Full article