Lithium alumino-silicate (LAS) glass-ceramics are commonly used in household applications, particularly in cooktops. However, managing their end-of-life remains a substantial technological challenge. This study presents an innovative, energy-efficient upcycling strategy for LAS glass-ceramic waste that avoids remelting by leveraging previous research on mild alkali activation of glass powders. Fine LAS powders were treated with a diluted alkaline solution (3 M NaOH) for 3 h and hardened at 75 degrees C for 72 h. Unlike conventional alkali-activated systems, this method fosters interparticle bonding through surface activation without extensive dissolution of the crystalline phase, preserving the material's intrinsic properties. The formation of strong interparticle bonds, maintaining the integrity of the (3-eucryptite phase, was confirmed through stability tests after boiling-water immersion and analyzed via SEM, FTIR, and XRD. Both unfired and fired (700 degrees C) materials demonstrated a favorable combination of compressive strength and density comparable to commercial lightweight construction materials. Additionally, incorporating sodium perborate and sodium dodecyl sulfate enabled the production of highly porous foams with low thermal conductivity (lambda = 0.114 +/- 0.001 W m- 1 K-1). This method is the first demonstration of mild alkali activation applied to highly crystalline LAS glass-ceramics for creating structural and insulating components, paving new paths for the circular valorization of cooktop waste.

Condensation process inside small diameter channels is nowadays of considerable interest in refrigeration, heat pumps and cooling applications. The reduced cross-sectional area of the channels enables compact heat exchangers design but it makes local heat transfer coefficient measurements more difficult during condensation. High-quality data collection is essential for developing and validating predictive models for heat exchangers' design. To address this challenge, a novel test section having a 2.76 mm inner diameter channel was built by additive manufacturing for accurate local heat transfer coefficient measurements with refrigerants and using water as secondary fluid for heat rejection. The design, optimized by computational fluid dynamics (CFD) simulations, resulted in a complex finned geometry of the water side. The fabrication of the test section was achieved using laser powder bed fusion with AlSi10Mg alloy. Given the limited number of experimental data available for the low-GWP (Global Warming Potential) refrigerants in small-diameter channels, condensation tests were performed with R1234ze(E) and R1233zd(E) at 40 degrees C saturation temperature and mass flux ranging from 30 to 350 kg m-2 s-1. Results at 0.5 vapour quality show that, R1233zd(E) achieves 62 % higher heat transfer coefficients than R1234ze(E) at high mass flux (330-350 kg m-2 s-1) and 18 % higher at low mass flux (60 kg m-2 s-1). High-speed videos revealed distinct flow patterns that can be linked to the heat transfer coefficient trends. Finally, the accuracy of selected heat transfer coefficient correlations was assessed, showing good predictive capability for R1234ze(E) but lower accuracy in the case of R1233zd(E).

Exposure to hot environments can induce physiological thermal strain in the human body, leading to reduced working endurance, impaired performance, and an elevated risk of heat-related illnesses. Activities such as sports, military training, and physically demanding work like firefighting can worsen these conditions. The increasing demand for energy-efficient solutions and diverse application requirements has driven the development of wearable cooling systems. These systems offer a localized and efficient alternative to conditioning entire environments, especially for individuals working outdoors or in settings where traditional air conditioning is impractical. This review provides a comprehensive overview of wearable cooling systems, covering their operating principles, designs, testing methodologies, applications, benefits, challenges, and classifications. Wearable cooling systems have been categorized into active, passive, and hybrid types, employing various cooling mechanisms, including air cooling, liquid cooling, vapor-compression cycle cooling, thermoelectric cooling, gas cooling, vacuum desiccant cooling, evaporative cooling, phase change materials, and conductive and radiative textile-based cooling. The review assesses these technologies based on cooling capacity, weight, and operating time, offering a rationale for their selection. Additionally, insights into future research opportunities in wearable cooling systems are discussed, emphasizing the need for continued innovation to enhance thermal comfort and safety.

This study investigated the thermal behavior of various sands types from different geographical locations and compositions. The thermal conductivity and heat capacity per unit volume were measured, and correlations with the bulk density, color, chemical composition, grain size, and solar reflectance were explored. The experimental data were compared with those of theoretical models, providing insights into the factors influencing the sand temperature under solar radiation. The results indicate that sand color and solar reflectance strongly influence temperature variations, where thermal conductivity is correlated with density. Microstructural analysis revealed differences between coral and non-coral sands. Chemical composition analysis suggested that the silica content may affect the thermal conductivity.

Inconel 718 is extensively used in various fields due to its excellent thermal and mechanical properties, combined with high resistance to corrosion and oxidation. In addition, the alloy retains these properties over a wide temperature range, up to around 750 degrees C, making it suitable for high-temperature applications. However, machining Inconel 718 is challenging as the above properties are coupled with a very low thermal conductivity, which reduces the heat dissipation in the cutting zone, resulting in significant tool wear. Ceramic tools, characterized by very high hot hardness, are being extensively used to mitigate this effect; in addition, inserts with a round geometry can alleviate the issue of the ceramics' low toughness. In this study, the wear behavior of two round advanced ceramic inserts, namely SiC whiskers-reinforced alumina and Bidemics (TM) ones, was investigated using a conventional coated carbide tool (WC) as the baseline for comparison. The inserts' characteristics were evaluated as constitutive elements, microstructure, surface topography, hot hardness, thermal conductivity, and wettability. A turning campaign was carried out to investigate the inserts' performance in terms of material removal rate, flank wear, cutting forces, and machined surface finish. The inserts' wear modes were evaluated based on their distinctive round geometry, revealing that the highest wear occurred in the central zone of the flank face regardless of the inserts' material. Notch wear and chipping were observed as the primary wear modes on the leading and trailing cutting edges of the Al2O3+SiCw and Bidemics (TM) inserts, respectively. It was found that the Bidemics (TM) inserts outperformed both the SiC whisker-reinforced alumina and the coated WC ones, demonstrating that Bidemics (TM) as insert material is an effective solution in machining Inconel 718 due to its high hot hardness and thermal conductivity.

A substantial proportion of glass waste is disposed of in landfills due to the limitations of conventional recycling methods in processing articles with specific chemical compositions or contamination, such as serigraphed glass, borosilicate glass, and glass mud residues. This study proposes an approach for managing such waste through the fabrication of highly porous, chemically stable glass foams at nearly room temperature, without the use of precious additives. Fine glass powders were homogeneously dispersed in weak alkaline suspensions, which were subsequently foamed by a combination of a limited amount of surfactant, foaming agent, and intensive mechanical stirring. The cellular structures were first stabilized through gelation and subsequently dried at 40 degrees C for 7 days. As an alternative, viscous flow sintering at 700 degrees C for 60 min was investigated as an end-of-life option for the first-generation green foams, resulting in porous glass-ceramic foams exhibiting an excellent strength-todensity ratio. The newly synthesized foams demonstrated an excellent compressive strength, ranging from 2 to 7 MPa, and a thermal conductivity of 0.13 W/m center dot degrees C, despite their high overall porosity of 68-73 %, which compares favourably to existing cement-based materials in terms of strength-to-density ratio and effective thermal conductivity.

Nickel-based superalloys, like Inconel 718, are very attractive metals for aerospace applications due to their excellent mechanical properties and thermal stability. However, these materials pose a significant challenge to the metal machining industry due to their very low machinability, especially in terms of reduced tool life because of the high heat generated during cutting. Nevertheless, it can be improved using high-performing tools that retain their hardness when exposed to high temperatures, such as ceramic tools. In this context, the study aims to compare the performance of two advanced ceramic tools, namely an alumina ceramic tool reinforced with SiC whiskers and a Bidemics™ one, when turning Inconel 718 at different cutting speeds, using as a baseline a conventional coated cemented carbide tool. First, the three inserts were characterized in terms of topography, thermal conductivity, and hot hardness to fully understand their operational behavior. Then, turning trials were conducted showing that both the ceramic tools outperform the coated carbide one in terms of tool life, with Bidemics™ demonstrating the best performance among all. This can be ascribed to its very high hardness maintained even at high temperatures, as well as its moderate thermal conductivity.

The recent advances in additive manufacturing technology have widened the choice of materials that can be printed, opening new frontiers in the field of heat transfer devices. This paper explores the use of a solid porous matrix in which paraffin waxes, having different melting temperatures (42, 55, and 64 °C), were embedded. The solid matrix is made by additive manufacturing. The parent cell of the porous matrix occupies the volume of a cube with an edge of 5 mm. The entire 3D printed matrix has a square base with an edge of 100 mm, and it has a height of 20 mm. The solid matrix was printed between two plates, each one with a thickness of 10 mm, where thermocouples were inserted, and it was tested in an upright position, laterally heated applying three different heat fluxes (10, 15, and 20 kW m−2). The experimental results are given in terms of the temperature of the heated side, as well as of the phase change material, during the heating process. The temperature reached by the heated side and the time needed to completely melt the paraffin waxes are compared at the different working conditions. Furthermore, the thermal conductivities and diffusivities of the three paraffins and of the parent material of the porous matrix were experimentally evaluated.

In this paper we report on the study of sintered ceramic composites based on a low melting glass in which ZnO nanocrystals and commercial YAG:Ce3+ phosphor are embedded. A low Tg is necessary to avoid high temperature sintering which can damage the optical properties of the embedded phosphor, while ZnO is introduced to increase the thermal conductivity of the system. The compositions have been optimized in terms of stability, sintering efficiency and thermal conductivity. Selected samples were optically characterized using a GaN high power multimode 450 nm Laser Diode, with a maximum output power of 1.6 W at 1.5 A.

In this paper, we present an experimental study on the influence of low-emissivity aluminium shields on the thermal properties of low-density expanded polystyrene. As radiation is significantly influenced by the presence of shields only on low-density materials, experimental work has been done on low-density expanded polystyrene, of which the density was about 9,5 kg m−3. Expanded polystyrene panels have been measured by the Heat Flow Meter apparatus in our laboratory. Nine sets of measurements have been done. Every panel was cut horizontally, and aluminium foils were inserted between the slices as shields. As expected, the thermal conductivity decreased considerably with the number of slices in which the material was cut and the number of aluminium shields. We found a decrease in the thermal conductivity that can even reach 25 % if we cut the panel in 8 slices with 7 aluminium foils interposed between them. We compared the experimental results with our model, which considers the presence of shields in insulating materials, and this proposed model fits the experimental results with a good accuracy. This is because almost all experimental results are situated in a zone, which represents ±2 % of error.

Long-term sustainability of dropwise condensation (DWC) on treated surfaces is a key point for the exploitation of this heat transfer mechanism in industrial applications. A viable solution to achieve DWC, consisting of hybrid organic-inorganic sol-gel silica coatings containing hydrophobic moieties (methyl or phenyl group) is here presented. Different sol-gel coatings for DWC promotion were tested during condensation of steam in saturated conditions exhibiting heat transfer coefficient (HTC) around 100 kW m(-2) K-1 in the heat flux range 100-500 kW m(-2). Endurance tests have been performed at 400 kW m(-2); an optimized sol-gel coating deposited on an aluminum substrate is shown to sustain DWC for more than 100 h without transition to filmwise condensation (FWC), which is an excellent result among those achieved on aluminum substrates. A comparison between the different coatings is done by surface characterization (contact angles measurements and Scanning Electron Microscopy) performed before and after condensation tests. Video analyses are carried out looking at droplet departing radius, droplets population and surface time renewal using a home-made software to detect the dimensions of the droplets. The present data are used to assess the expression proposed by Le Fevre and Rose (1966) for the droplet population, the equation by Kim and Kim (2011) for the departing radius and the model proposed by Chavan et al. (2016) for the heat transfer coefficient.

The condensation heat transfer coefficient and two-phase frictional pressure drop of ternary zeotropic mixtures R455A (R32, R1234yf and R744 at 21.5/75.5/3.0% by mass composition) and R452B (R32, R1234yf and R125 at 67.0/26.0/7.0% by mass composition) have been measured inside a minichannel (0.96 mm diameter) and a conventional tube (8.0 mm diameter). The effects of tube diameter, mass velocity, vapor quality and saturation-to-wall temperature difference have been investigated. A comparison between the experimental data of the tested mixtures and the condensation heat transfer of the pure components R32 and R1234yf has been performed. The two-phase pressure drop and condensation heat transfer data are compared to predictions of correlations available in the literature. In the prediction of the heat transfer coefficient, the models are adapted to account for the additional mass transfer resistance occurring during condensation of zeotropic mixtures. (C) 2019 Elsevier Ltd and IIR. All rights reserved.

Thermosyphon solar collectors are popular in warm climates since their initial and operating costs are lower compared to forced-circulation units. Recently new types of thermosyphon collector with integrated storage, without any external tank, to meet law requirements about solar applications in restricted areas (e.g. old town of particular architectural significance) are put in the market. Such a collector is modelled in this paper using the software MATLAB Simulink. This model is able to describe the transient behavior of the natural circulation phenomenon and it requires a much lower computational effort compared to CFD codes. The present mathematical model has been validated using ad-hoc experimental tests and numerical simulations. The validated model has been run varying the tilt angle, the geometry and the working conditions to analyze the solar thermosyphon performance. It can predict the minimum inclination and solar radiation that is needed to promote the flow circulation.

The average cooling demand of a refrigerated vehicle depends on the external conditions and on the journey's profile, such as ambient temperature, air velocity, vehicle speed etc. In order to understand the dynamic heat load on the system and predict the peak of cooling demand, a fully dynamic model of the insulated box of a refrigerated vehicle was developed and experimentally validated. Experimental data was collected during test of a vehicle following the International Agreement for the Transport of Perishable (ATP) test. The model validation demonstrates the capability of the model to correctly predict the evolution of the internal box air temperature in both transient and steady-state conditions. The trend of dynamic load, peak of cooling demand, influence of the solar absorption coefficient and influence of the walls thermal mass on the cooling energy demand during a typical mission are also simulated.

In this work, measurements of the thermal properties of moist autoclaved aerated concrete specimens have been performed using both the heat flow meter apparatus (HFM) and the transient plane source technique Hot Disk (TPS). When testing moist materials, the steady-state condition can take a long time to be reached; furthermore, an additional difficulty occurs, because the temperature gradients inside the material cause a moisture transport with a moisture redistribution and a latent heat due to phase change. Therefore, for a correct determination of the thermal conductivity, it is necessary to separate these effects from the measurements. The transient plane source technique Hot Disk is a transient technique which carries out measurements in few seconds to make negligible the moisture redistribution; on the contrary, using the heat flow meter apparatus the steady-state condition is reached only when there is a total redistribution of the moisture contained in the specimen. Measurement data obtained from these two different methods (HFM and TPS) have been analyzed and compared; only in this way it was possible to perform an accurate computation of the moisture conversion coefficient \(f_\mathrm{u}\) of the thermal conductivity according to the EN 10456.

In the biomedical field the Additive Manufacturing (AM) technologies are increasingly being adopted for the production of near-net-shape products made in titanium alloys, however finishing machining operations can be necessary to obtain the required geometrical tolerances and surface characteristics. This paper aims at investigating the effects of the workpiece properties on the tool crater wear behavior in semi-finishing turning of Ti6Al4 V produced by Electron Beam Melting (EBM) and Direct Metal Laser Sintering (DMLS) AM technologies in comparison with the one of the wrought commercial alloy. Liquid nitrogen was used as a coolant to reduce the crater wear and its performances compared with dry turning. A correlation is proved between the mechanical and thermal properties of the investigated alloys and the crater wear occurrence.

This work investigates a possible application of an integrated heat recovery system with an indirect evaporative cooling section (IEC) into the air extraction and a dehumidification device into air delivery. System operation is then simulated in different climatic conditions and the energy consumptions are compared with the energy required by the same system without the IEC section.

This paper presents the results of experimental measurements of thermal conductivity and of volumetric specific heat, rho C-p, carried out at high temperature on autoclaved aerated concrete (AAC) specimens at different densities. The Knowledge of the correlation of thermal conductivity and specific heat with temperature is of fundamental importance in the study of the mechanical behaviour of building materials in presence of fire. The numerical verifications of fire resistance of structures are often carried out using computer codes that solve differential equations of thermal exchanges. For this reason a proper Knowledge of the above thermal properties as a function of temperature is required. The measurement of thermal conductivity and thermal diffusivity has been carried out using a Hot Disk Thermal Constants Analyser equipment. The experimental environment suitable to achieve high temperatures consists of a special controlled temperature oven in which measurements are made with sensors enclosed in two layers of refractory material (mica) suitable for working with acceptable accuracy in a range of temperatures between 500-1000K. The results are also compared with the directions on the material provided by national and international standards but we realized that the thermal conductivity values at high temperatures, suggested by the standard EN 12602, are significantly lower than those experimentally measured in this study and thus they are not precautionary checks for computational fire resistance. We propose to investigate on the source of the suggested data and ask a revision of the above mentioned standard.

The current methodology used for testing the thermohygrometric behaviour of building structures is proposed by the standard UNI EN ISO 13788. This Standard evaluates the risk of hygrometric damages due to: 1) critical moisture conditions of the inner surfaces of the building; 2) interstitial condensation within the structures The proposed procedures are valid in the case of steady state and are applied on a monthly basis. However, the steady state calculation is not completely correct mainly because the vapour production is not constant neither in time nor in space. For example, residential buildings are not occupied during most of the day. Therefore, in the case of a residential building, there is an intense generation of moisture mainly during a certain period of the day. Then, for a better control of the indoor values of relative humidity (and of partial vapour pressure) inside a given room, the indoor moisture production should be not considered constant and it may be appropriate to assess the importance of the hygroscopic properties the walls and furniture, able to act as a moisture buffer. In this paper, using a simplified model taking into account the interactions between the vapour concentration of the indoor air and the interior walls and furniture, the role played by the hygroscopic capacity of the indoor walls and furniture for the evaluation of indoor relative humidity is analyzed.

In recent years, the use of techniques of heating a nd space cooling with ground coupled heat pumps is spreading. This technology, also known as low energy geothermal cooling and heating, plans to use, as a heat source, the subsoi l, due to its ability to maintain its temperature constant at val ues close to the average annual temperature of the locality. The heat exchange with the ground is done by probes that generally consist of U-shaped tubes (single or doub le) made of plastic and placed in a vertical hole, drilled in t he subsoil and filled with grouting materials. For an optimal expl oitation of this technology, the use of high thermal conductivi ty grouting materials is fundamental to minimize thermal resist ance and facilitate the heat exchange between the probe and ground. This study is aimed at the thermal analysis of seal ant mortar (usually a mixtures of bentonite and cement with ad dition of sand) used in geothermal cooling and heating. In pa rticular, thermal conductivity and diffusivity measurements were performed on available materials using the so calle d Hot Disk Thermal Constants Analyser.