Search Results (276)

Transient increments of X-ray radiation and extreme ultraviolet (EUV) during solar flares are strong drivers of thermospheric dynamics on Mars, yet their class-dependent impacts remain poorly measured. This work provides the first direct, side-by-side study of Martian thermospheric reactions to flares X8.2 on 10 September 2017 and M6.0 on 17 September 2017. This study shows nonlinear, class-dependent effects, compositional changes, and recovery processes not recorded in previous investigations. Species-specific responses deviated significantly from irradiance proportionality, even though the soft X-ray flux in the X8.2 flare was 13 times greater. Argon (Ar) concentrations rose 3.28× (compared to 1.13× for M6.0), and radiative cooling led CO₂ heating to approach a halt at ΔT = +40 K (X8.2) against +19 K (M6.0) at exobase altitudes (196–259 km). N₂ showed the largest class difference, where temperatures rose by +126 K (X8.2) instead of +19 K (M6.0), therefore displaying flare-magnitude dependent thermal sensitivity. The 1.95× increase in O concentrations during X8.2 and the subsequent decrease following M6.0 (−39 K cooling) illustrate the contradiction between photochemical production and radiative loss. The O/CO₂ ratio at 225 km dropped 46% during X8.2, revealing compositional gradients boosted by flares. Recovery timeframes varied by class; CO₂ quickly re-equilibrated because of effective cooling, whereas inert species (Ar, N₂) stabilized within 1–2 orbits after M6.0 but needed >10 orbits of the MAVEN satellite after the X8.2 flare. The observations of the X8.2 flare came from the western limb of the Sun, but the M6.0 flare happened on the far side. The CME shock was the primary driver of Mars’ EUV reaction. These findings provide additional information on atmospheric loss and planetary habitability by indicating that Mars’ thermosphere has a saturation threshold where strong flares induce nonlinear energy partitioning that encourages the departure of lighter species. Full article

The construction sector presently consumes about 40% of global energy and generates 36% of CO₂ emissions, making facade retrofits a priority for decarbonising buildings. This review clarifies how ventilated facades (VFs), wall assemblies that interpose a ventilated air cavity between outer cladding and the insulated structure, address that challenge. First, the paper categorises VFs by structural configuration, ventilation strategy and functional control into four principal families: double-skin, rainscreen, hybrid/adaptive and active–passive systems, with further extensions such as BIPV, PCM and green-wall integrations that couple energy generation or storage with envelope performance. Heat-transfer analysis shows that the cavity interrupts conductive paths, promotes buoyancy- or wind-driven convection, and curtails radiative exchange. Key design parameters, including cavity depth, vent-area ratio, airflow velocity and surface emissivity, govern this balance, while hybrid ventilation offers the most excellent peak-load mitigation with modest energy input. A synthesis of simulation and field studies indicates that properly detailed VFs reduce envelope cooling loads by 20–55% across diverse climates and cut winter heating demand by 10–20% when vents are seasonally managed or coupled with heat-recovery devices. These thermal benefits translate into steadier interior surface temperatures, lower radiant asymmetry and fewer drafts, thereby expanding the hours occupants remain within comfort bands without mechanical conditioning. Climate-responsive guidance emerges in tropical and arid regions, favouring highly ventilated, low-absorptance cladding; temperate and continental zones gain from adaptive vents, movable insulation or PCM layers; multi-skin adaptive facades promise balanced year-round savings by re-configuring in real time. Overall, the review demonstrates that VFs constitute a versatile, passive-plus platform for low-carbon buildings, simultaneously enhancing energy efficiency, durability and indoor comfort. Future advances in smart controls, bio-based materials and integrated energy-recovery systems are poised to unlock further performance gains and accelerate the sector’s transition to net-zero. Emerging multifunctional materials such as phase-change composites, nanostructured coatings, and perovskite-integrated systems also show promise in enhancing facade adaptability and energy responsiveness. Full article

Medium- and large-scale heat sinks are critical for thermal load management in high-performance systems. However, their high heat flux densities and limited space complicate cooling, leading to risks of overheating, performance degradation, or failure. This study employs the Cascaded Lattice Boltzmann Method (CLBM) to enhance their thermal performance. This numerical approach is known for being stable, accurate when dealing with complex boundaries, and efficient when computing in parallel. The numerical code was validated against a benchmark configuration and an experimental setup to ensure its reliability and accuracy. While previous studies have explored mixed convection in cavities or heat sinks, few have addressed configurations involving side air injection and boundary conditions periodicity in the transition-to-turbulent regime. This gap limits the understanding of realistic cooling strategies for compact systems. Focusing on mixed convection in the transition-to-turbulent regime, where buoyancy and forced convection interact, the study investigates the impact of Rayleigh number values ($5\times {10}^7$ to $5\times {10}^8$) and Reynolds number values (${10}^3$ to $3\times {10}^3$) on heat transfer. Simulations were conducted in a rectangular cavity with periodic boundary conditions on the vertical walls. Two heat sources are located on the bottom wall ($T_h$ = 50 °C). Two openings, one on each side of the two hot sources, force a jet of fresh air in from below. An opening at the level of the cavity ceiling’s axis of symmetry evacuates the hot air. Mixed convection drives the flow, exhibiting complex multicellular structures influenced by the control parameters. Calculating the average Nusselt number (Nu) across the surfaces of the heat sink reveals significant dependencies on the Reynolds number. The proposed correlation between Nu and Re, developed specifically for this configuration, fills the current gap and provides valuable insights for optimizing heat transfer efficiency in engineering applications. Full article

Compared to traditional temperature measurement methods, ultrasonic temperature measurement technology based on the principle of resonance offers advantages such as shorter section lengths, higher signal amplitude, and reduced signal attenuation. First, the type of sensor-sensitive element was determined, with a resonant design chosen to improve measurement performance; using magnetostrictive and resonant temperature measurement principles, the length, diameter, and resonator dimensions of the waveguide rod were designed, and a molybdenum–rhenium alloy (Mo-5%Re) material suitable for high-temperature environments was selected; COMSOL finite element simulation was used to simulate the propagation characteristics of acoustic signals in the waveguide rod, observing the distribution of sound pressure and energy attenuation, verifying the applicability of the model in high-temperature testing environments. Second, a resonant temperature sensor consistent with the simulation parameters was prepared using a molybdenum–rhenium alloy waveguide rod, and an ultrasonic resonant temperature-sensing system suitable for high-temperature environments up to 1800 °C was constructed using the molybdenum–rhenium alloy waveguide rod. The experiment used a tungsten–rhenium calibration furnace to perform static calibration of the sensor. The temperature range was set from room temperature to 1800 °C, with the temperature increased by 100 °C at a time, and it was maintained at each temperature point for 5 to 10 min to ensure thermal stability. This was conducted to verify the performance of the sensor and obtain the functional relationship between temperature and resonance frequency. Experimental results show that during the heating process, the average resonance frequency of the sensor decreased from 341.8 kHz to 310.37 kHz, with an average sensitivity of 17.66 Hz/°C. During the cooling process, the frequency increased from 309 kHz to 341.8 kHz, with an average sensitivity of 18.43 Hz/°C. After cooling to room temperature, the sensor’s resonant frequency returned to its initial value of 341.8 kHz, demonstrating excellent repeatability and thermal stability. This provides a reliable technical foundation for its application in actual high-temperature environments. Full article

The study investigated the sperm motility and morphometry of pre-freeze and post-thaw boar epididymal semen cooled at increasing holding times at 18 °C. A total of 50 testes of heterogeneous boars were collected (5 testes/day) from the local abattoir and transported to the laboratory at 5 °C within 30 min after slaughter. Semen was retrieved from the caudal part of the epididymis using the slicing float-up method, diluted with Beltsville Thawing Solution extender, pooled in a 50 mL centrifuge tube/5 testes/day, and cooled at 18 °C. Following each holding time (0, 3, 6, 9, 12, 24, and 48 h), the cooled semen sample was re-suspended with Fraction A extender and stored at 5 °C for an additional 45 min. A cooled resuspended semen sample was then diluted with Fraction B extender, loaded into 0.25 mL straws, and frozen using liquid nitrogen vapour. Thawing was accomplished by immersing the semen straws in warm (37 °C) water for 1 min and the samples were evaluated for sperm motility and morphometry traits using the computer-assisted sperm analyzer system. The data were analyzed using variance analysis. Descriptive statistics were used to assess sperm morphometry, establishing the minimum and maximum values. Boar epididymal sperm survived for up to 48 h when held at 18 °C. Furthermore, the highest post-thawed sperm motility rates were observed in semen frozen after 3 h of holding time, with a sperm total motility of 85.9%, a progressive motility of 60.3%, and a rapid motility of 33.2%, as compared to other holding times (p < 0.05). The acceptable ranges for pre-freeze and post-thawed sperm morphology were head length (8.4–9.1 µm), width (4.4–4.8 µm), area (29.9–38.2 µm²), perimeter (20.1–23.7 µm), midpiece width (1.1–2.8 µm), and sperm shape, were consistent regardless of the holding time. A holding time of 3 h enhances the cryoresistance of sperm cooled at 18 °C. Therefore, these findings suggest that boar epididymal sperm can be effectively conserved and can maintain fertilization capability when cooled for 3 h at 18 °C before freezing. Full article

The paper presents a numerical analysis of a tube-in-tube condenser of a small refrigeration system. One of the challenges in designing such units is to reduce their dimensions while maintaining the highest possible cooling capacity, so the research presented here focuses on the search for and impact of the appropriate flow conditions of these two fluids on condenser performance. The refrigerant is supercritical CO₂, which is cooled by water. Thermal-flow simulations were performed for eight CO₂ inlet velocities in the range of 1–8 m/s, and four cooling water velocities of 0.5–2 m/s. The main parameters of the exchanger operation were analyzed: heat transfer coefficient, Nusselt number, overall heat transfer coefficient, and friction factor, which were compared with selected correlations. The results showed that the condenser achieves the highest power for the highest water velocities (2 m/s) and CO₂ (8 m/s), i.e., over 1000 W, which corresponds to a heat flux on the tube surface of approx. 2.6 × 10⁵ W/m² and a heat transfer coefficient of approx. 4700 W/m²K. One of the most important conclusions is the discovery of a significant effect of water velocity on heat transfer from the CO₂ side—an increase in water velocity from 0.5 m/s to 2 m/s results in an increase in the heat transfer coefficient sCO₂ by over 60%, with the same Re number. The implication of this study is to show the possibility of adjusting and selecting condenser parameters over a wide range of capacities, just by changing the fluid velocity. Full article

Microelectronic technologies are progressing rapidly. As devices shrink in size, they produce a substantial heat flux that can adversely affect performance and shorten their lifespan. Conventional cooling methods, such as forced-air heat transfer and essential heat sinks, are inadequate for managing the elevated heat flux generated by these devices. Consequently, microchannel heat sinks have been developed to address this challenge. The present research is intended to study forced flow convection and heat transfer in a cone–column combined microchannel heat sink (MCHS). This study examines a regularly shaped MCHS to evaluate its heat transfer rate. The heat transfer medium employed is a graphene–water nanofluid, and the heat sink’s base is assumed to maintain a constant heat flux. The Galerkin weighted finite element method solves the nanofluid’s governing partial differential equations. This thesis investigates the impact of varying intake velocities on the Reynolds number (100 ≤ Re ≤ 900), externally applied heat flux (10⁴ ≤ q ≤ 10⁶), and the volumetric ratio of nanoparticles (0.001 ≤ φ ≤ 0.04). The study conducts a mathematical analysis to explore how these parameters affect pressure drop, friction factor, average Nusselt number, average substrate temperature, and heat transfer enhancement. The findings are compared with those of a conventional MCHS as the Re increases. The results are analyzed and visually represented through isothermal lines for temperature contours and streamlines for velocity. An increase in the inlet velocity of the water–graphene nanofluid significantly enhances heat transfer and thermal efficiency, achieving improvements of approximately 27.00% and 21.21%, respectively. The research demonstrates that utilizing water–G as a smart coolant with the cone–column combined MCHS enhances thermal efficiency by 4.05% compared to standard water. A comparison of the hydraulic performance index at the substrate reveals that the cone–column combined MCHS is significantly more effective at dissipating heat than the traditional MCHS. Full article

The continuous cooling transformation (CCT) curves of undercooled austenite serve as crucial references for obtaining desired microstructures and properties in metallic materials (particularly deformed metals) through heat treatment. In this study, static and dynamic CCT curves were constructed for experimental steels micro-doped with rare earth element Ce by combining temperature-dilatometric curves recorded after austenitization at 900 °C with microstructural characterization and microhardness measurements. Comparative analyses were conducted on the microstructures and microhardness of three experimental steels with varying Ce contents subjected to sizing (reducing) diameter deformation at 850 °C and 950 °C. The CCT experimental results revealed that the microhardness of the tested steels increased with cooling rates. Notably, dynamic CCT specimens cooled at 50 °C/s to room temperature following superheated deformation exhibited 56.7 HV5 higher microhardness than static CCT specimens, accompanied by increased martensite content. The reduction of deformation temperature from 950 °C to 850 °C resulted in the expansion of the bainitic phase region. The incorporation of trace Ce elements demonstrated a significant enhancement in the microhardness of 30MnNbRE steel. This research proposes an effective processing route for improving strength-toughness combination in microalloyed oil well tubes: introducing trace Ce additions followed by sizing (reducing) diameter deformation at 950 °C and subsequent ultra-fast cooling at 50 °C/s to room temperature. This methodology facilitates the production of high-strength/toughness steels containing abundant martensitic microstructures. Full article

Unveiling the heat transfer behavior of solar collectors in concentrating solar thermochemical energy storage is crucial for harnessing full-spectrum solar light. In this study, a glass Flat Tube-Shaped Heat Pipe (FT-SHP) was developed, and a visualization experimental platform was established to investigate its internal operation mechanisms and heat transfer characteristics. The results revealed that the liquid filling ratio (FR) significantly affects the heat transfer performance, with an optimal value identified as 25%. As the heat flow temperature in the evaporation section increased, both the Bubble Growing Frequency (BGF) and Droplet Condensation Reflux Period (DCRP) decreased, leading to a reduction in thermal resistance. Conversely, an increase in the cooling flow rate resulted in opposite trends in BGF and DCRP within the tube, while both the Reynolds (Re) number and thermal resistance decreased. As such, an empirical correlation between thermal resistance and Re number was derived, demonstrating a nonlinear relationship between thermal resistance, BGF, and DCRP. These findings provide important insights for the design of heat pipes, with the potential to enhance the efficiency and reliability of solar collectors. Full article

Thermal management at a high heat flux is crucial for electronic devices, and jet impingement cooling is a promising solution. The heat transfer properties of a rectangular-finned heat sink are investigated under angled and multi-impingement jet configurations in this study. Experiments were conducted with three different nozzle diameters, three different heat sink angles, three dimensionless nozzle-to-heat sink distance ratios, and five different velocity values. As a result, the obtained data are presented as Nu-Re graphs, and the impacts of the parameters on heat transfer (HT) are analyzed. It is concluded that the Nusselt number increases with the increasing nozzle diameter and Reynolds number, whereas it decreases with increasing distance between the nozzle and the heat sink. When comparing the angle values under an identical flow velocity, nozzle diameter, and dimensionless h/d distance experimental conditions, it was found that the Nusselt numbers were very close to each other. Under constant heat flux and for all investigated angles, the highest Nusselt number for the rectangular-finned inclined heat sink was observed at a 10° heat sink inclination, a nozzle diameter of D = 40 mm, a dimensionless distance of h/d = 6, and a flow velocity of 9 m/s. This study deepens the understanding of the heat transfer mechanism of impinging jets and provides an efficient method framework for practical applications. Full article

Improving user-level energy efficiency is critical for reducing the load on the power grid and addressing the challenges created by tight power balance when operating domestic air conditioning equipment under time-of-use (ToU) pricing. This paper presents a data-driven control method for HVAC (heating, ventilation, and air conditioning) systems that is based on model predictive control (MPC) and takes ToU electricity pricing into account. To describe building thermal dynamics, a multi-layer neural network is constructed using time-delayed embedding, with the rectified linear unit (ReLU) serving as the activation function for hidden layers. Using this piecewise affine approximation, an optimization model is developed within a receding horizon control framework, integrating the data-driven model and transforming it into a mixed-integer linear programming issue for efficient problem solving. Furthermore, this research suggests a hybrid optimization model for integrating air conditioning systems and battery energy storage systems. By employing a rolling time-domain control method, the proposed model minimizes the frequency of switching between charging and discharging states of the battery energy storage system, improving system reliability and efficiency. An Internet of Things (IoT)-based home energy management system is developed and validated in a real laboratory environment, complemented by a distributed integration solution for the energy management monitoring platform and other essential components. The simulation results and field measurements demonstrate the system’s effectiveness, revealing discernible pre-cooling and pre-charging behaviors prior to peak electricity pricing periods. This cooperative economic operation reduces electricity expenses by 13% compared to standalone operation. Full article

A sweeping jet is commonly preferred over a steady jet owing to its ability to better cool the region away from the strong core of an impinging jet. For industrial applications, it is important to study the thermal fields of oscillating jets in a multi-jet configuration to focus on the region that falls between the two consecutive fluidic oscillators and, hence, suggest a mechanism to uniformly cool the targeted flat surface. A comparative experimental study of dual sweeping jets (DSJs), double sweeping jets (DbSJs), and double circular jets (DbCJs) was conducted at different jet-to-plate spacings, various Re numbers, and three aspect ratios. The multi-circular and sweeping jets were impinged on a flat hot surface, which was heated at a constant flux of current, and thermocouples were employed to efficiently collect the time-averaged heat transfer distribution along the sweeping and transverse directions. It was determined that heat transfer, in terms of the Nusselt number, generally increased with increasing Re number and reduced the jet-to-wall spacing for the DSJ, DbSJ, and DbCJ, with some minor exceptions. The relative performance of these fluidic devices suggested that the best performance of DSJ was at small spacing and higher Re, DbSJ at moderate spacing and lower Re, and DbCJ at moderate spacing and moderate Re. The mutual comparison showed that along the sweeping motion, in the central region, DbCJ was better than both DSJ and DbSJ; in the right region, DSJ performance was far better than DbCJ and DbSJ; in the left region, DSJ was better than DbSJ when comparing the respective centers of DSJ and DbSJ. The dominance of DSJ over DbSJ at the centers of their respective bodies even extends in the transverse direction. Finally, for higher aspect ratios, the DSJ performed better in the outer regions, while the DbSJ performed well in the central region. Similarly, for both DSJ and DbSJ unanimously, the effect of changing the aspect ratio is interesting as initially, the Nu values increase for a higher aspect ratio, but by increasing the AR further, it causes a divergence of the fluidic volume from the central region to the surrounding region. Full article

This study investigates the impact of energy, economic, and environmental policies on Türkiye’s energy dynamics and CO₂ emissions using climate models and an agent-based simulation (ABM) framework. By integrating climate projections with policy scenarios, it assesses how energy transitions and climate change affect renewable energy sources (RES), cooling demands, and CO₂ emissions from electricity generation. Methods include selecting suitable Global Climate Models (GCMs), evaluating climate change impacts on RES performance, and simulating policy effects through ABM across one base and nine policy scenarios from 2023 to 2040. The study highlights the critical role of policy interventions in influencing emissions trends and energy prices. It identifies renewable energy subsidies and low-carbon strategies, such as nuclear power support, as effective tools for reducing emissions and stabilizing energy costs. The methodologies and findings provide actionable insights for policymakers globally, emphasizing the importance of integrating climate data with policy planning. Full article

An in-depth understanding of the texture formation in melt pools allows for the modification of the surface layer microstructure and corresponding material properties, providing an opportunity to integrate laser surface re-melting into metal additive manufacturing. This study investigates crystallographic texture formation at different cooling rates in single melting tracks on the Inconel 718 (IN718) plate produced by laser surface re-melting. The cooling rate varies from 2.31 × 10⁵ °C/s to 9.56 × 10⁵ °C/s with the increase in scanning rates from 400 mm/s to 1200 mm/s, measured by recently developed real-time temperature monitoring of melt pools. Columnar grains are dominant, with distinct crystallographic textures forming in the melt pools. At a slower scanning speed, the keyhole mode shows three different textures forming at different depths (crystallographically layered structure), while, at a faster scanning speed, the conduction mode shows only random grain orientation. There are no pores/voids detected, and the columnar grain morphology and columnar grain width (8.6 μm to 12.4 μm) follow the analysis framework in terms of thermal gradient and solidification rate analysis. This implies that laser surface re-melting provides the potential to modify the surface structure from a random grain orientation to a crystallographically layered structure. Full article

Nowadays, a lot of efforts are being made to increase turbine inlet temperatures (TIT), with the aim of increasing efficiency in aircraft and power generation turbines. Due to the higher temperature level, advanced cooling solutions to preserve material durability are necessary. It is essential to avoid contact between hot gases and the temperature-sensitive components, such as the stator and rotor cavity disks. Modern gas turbine performance optimization centers on reducing leakage and refining sealing systems. The interaction between the main flow and cavity flow in stator/rotor systems has a significant role in loss generation. This study employs Unsteady Reynolds-Averaged Navier–Stokes (URANS) simulations to investigate the unsteady interactions within the stator/rotor cavity of a low-pressure turbine. Numerical results are compared and validated against experimental data obtained in the cavity rig of the University of Genova. The research focuses on the effects of stator/rotor interactions, including wake ingestion from upstream rotor bars and the blocking influence of downstream potential effects on cavity sealing effectiveness. In this paper, a comparison between the zero cooling air flow rate and cavity sealing condition is shown. Special attention is given to unsteady loss mechanisms occurring downstream of the vane row and in areas where the cavity flow re-enters the main channel, showing how cooling flow rates affect these losses. From this study, it can be seen that by increasing the cooling flow rate injected into the cavity, there is an increase in the hub’s passage vortex effect and there is a more intense interaction between the main flow and the cavity flow. These results offer valuable insights into the mechanisms of interaction between the main flow and cavity flow. Full article