Search Results (744)

This research was conducted on mountain summits in South Yakutia, Russia. The findings indicate that within the goltsy altitudinal belt (comparable to the alpine zone), the weathering intensity of rocks above 1400 m depends on the development of snow-ice formations, particularly snowpatches. Snowpatches promote physical rock weathering along their edges by up to 1.5–4 times more intensely compared to baseline levels. The ground temperature at the edges was examined in relation to air temperatures. The conditions that facilitate rock weathering at the snowpatch edge during the summer months are characterized by diurnal air temperatures below 10–15 °C, with minimum temperatures below 5 °C. Nivation processes in the goltsy altitudinal belt of South Yakutia are considered as one of the dominant geomorphic agents. However, future changes are expected in the existing nival-glacial belts, as snowpatches respond rapidly to climate change, with the mean annual air temperature in South Yakutia exhibiting a rising trend. Full article

The present research, using finite element method simulation, studies the heat dissipation of a fin-type passive cooling system installed on monocrystalline photovoltaic panels under different environmental conditions associated with altitude. For this purpose, three scenarios at different altitudes were analyzed: Manta (14 m.a.s.l.), Puyo (926 m.a.s.l.), and Ambato (2724 m.a.s.l.). A model simulated using the finite element method, validated in a previous investigation, was used to simulate these three cases. The model was meshed, and the boundary conditions used were obtained from meteorological data averaged over one year. The variables used in this stage were irradiance, ambient temperature, and wind speed in the time range from 08:00 to 17:00. The numerical model used in the simulation considered the mechanisms of conduction in the panel layers, mixed convection toward the surrounding air, and thermal radiation from the exposed surfaces. The results show that, in the city of Ambato, the heat sink presents its best thermal performance. Under conditions of minimum ambient temperature and solar irradiance, a maximum percentage reduction of 3.11% in the photovoltaic panel temperature was obtained, while under conditions of maximum ambient temperature and solar irradiance, the reduction reached 11.11%. This reveals that, when higher panel temperatures occur, the heat sink exhibits better performance. In general, the results showed a reduction in temperature when this heat dissipation mechanism was used. It is evident that the effectiveness of these systems depends not only on geometry or materials, but also on the atmospheric conditions associated with altitude. It is concluded that the heat dissipation capacity of passive cooling mechanisms is influenced by the meteorological conditions of the area, such as ambient temperature, solar irradiance, and wind speed, which may vary according to the altitude at which the system is located. Full article

Exhaust piping in diesel engines is subject to severe thermal stress arising from high-temperature, high-pressure gas flows, and spray cooling with atomizing nozzles has become a widely adopted method to safeguard structural reliability. However, at present, the understanding of the spray fragmentation mechanism of two-phase flow under low inlet pressure is still not comprehensive. This study establishes a three-dimensional model of a gas–liquid impinging-jet nozzle and applies a coupled Volume-of-Fluid to Discrete-Phase-Model (VOF–DPM) approach to resolve the liquid breakup process in detail. High-speed imaging experiments were carried out to validate the numerical results. Orthogonal tests were conducted at five pressure levels for both gas and water—0.28, 0.24, 0.20, 0.16, and 0.12 MPa—producing 25 data pairs of spray cone angle and Sauter Mean Diameter (SMD). Within the 0–0.3 MPa air inlet pressure range explored here, raising the pressure consistently reduced the SMD and widened the cone angle, although both trends weakened as the pressure increased. Water inlet pressure exhibited a nonlinear influence, with local extrema appearing in the higher-pressure region. The overall SMD reached a minimum of 34.12 μm and a maximum of 149.04 μm. Using these 25 data points, a genetic algorithm was employed to optimize the pressure ratio under the constraint of total hydraulic power, yielding optimization strategies for different power budgets. An additional outcome of the simulation was the identification of a structural weakness: by reshaping the original flat impingement surface into a full conical surface, atomization quality improved by 29.36% under identical boundary conditions. These findings clarify the atomization mechanism of gas–liquid impinging jets under low inlet pressure and offer practical guidance for nozzle optimization. Full article

The Yarlung Zangbo River Basin (YZRB) stores abundant solid water resources. These components are highly sensitive to climate warming and play a critical role in regulating downstream water availability. However, the spatiotemporal responses of the thermal state to ongoing climate change and its potential atmospheric forcing remain poorly understood. Here, we use satellite-based land surface temperature (LST) to characterize the thermal dynamics of the YZRB during 2000–2024. Further, a machine learning model combined with Shapley Additive Explanations (SHAP) is applied to quantify the pixel-level statistical contributions of meteorological variables to LST trends. The climatological LST exhibits pronounced spatial and seasonal heterogeneity, with lower temperatures in the northwestern and northeastern regions and higher temperatures in the central and southeastern regions. The intra-annual cycle follows a unimodal pattern, peaking in early summer, while downstream sub-basins show a delay in peaking times. Mean LST increases at a rate of 0.18 °C decade⁻¹, while maximum LST warms at nearly twice this rate (0.40 °C decade⁻¹) with widespread warming across the basin. However, minimum LST shows no significant long-term trend, mainly due to the polarization trend within the year. The warming signal shows strong season dependence, with the largest monthly warming trend exceeding 0.80 °C decade⁻¹ for all three LST metrics. Attribution analysis identifies precipitation as the primary meteorological factor statistically associated with basin-scale LST trends. Wind speed may largely represent a response to increasing LST rather than a direct driving factor. Downward shortwave radiation, air temperature and specific humidity exhibit stronger influences in specific regions rather than at the basin scale. The dominant control of precipitation reflects strong monsoon influence on LST dynamics along the southern margin of the Tibetan Plateau. Full article

With the sustained industrial development, air pollution remains a prominent environmental challenge in North China. As a key atmospheric contaminant, nitrogen dioxide (NO₂) is closely associated with significant adverse impacts on both ecological systems and public health. However, existing research regarding the factors related to NO₂ column concentration and the comparative strength of these associations remains limited. To address this research gap, this study employs TROPOMI satellite-based NO₂ data and six categories of influencing factors (meteorology, population density, vegetation coverage, etc.) to characterize the spatiotemporal patterns and the statistical relationships between NO₂ column concentrations and various influencing factors in North China from 2019 to 2023. The results indicate that elevated NO₂ column concentrations are primarily concentrated in central North China, including northern Henan, southern Hebei, and central–western Shandong. During 2019–2023, the regional NO₂ column concentration displayed an overall decreasing trend, accompanied by distinct seasonal variations: peaking in winter, moderate in autumn, and reaching the minimum in summer. Among the evaluated factors, temperature exhibited the strongest correlation with NO₂ variations, followed by surface net solar radiation and Normalized Difference Vegetation Index (NDVI). The relationship between wind and NO₂ was found to vary according to direction, speed, and regional topography. In addition, population density showed a prominent positive association with NO₂ vertical column density. This study identifies key factors linked to NO₂ variability, thereby providing methodological and empirical support for relevant studies in other regions. Full article

This study analysed climate change in the eu-Mediterranean and sub-Mediterranean areas of the Istrian Peninsula, Croatia, and examined the influence of climatic conditions on crown defoliation in pubescent oak and Aleppo pine. Climate data from representative meteorological stations for the period 1980–2022 and crown defoliation data for 2000–2023 were analysed. Drought conditions were assessed using potential evapotranspiration, rainfall anomaly indices, and the number of dry months. The results indicated a significant increase in mean annual air temperature and potential evapotranspiration throughout the Istrian region, with temperatures rising by 0.8–1.2 °C compared to the reference period. Southern Istria experienced three dry months, characteristic of the steno-Mediterranean vegetation zone, indicating increasing aridity. The highest proportion of trees was recorded in the 26–60% defoliation class, including 54% of Aleppo pine and 59% of pubescent oak trees. Crown defoliation showed significant correlations with precipitation, rainfall anomaly index, and air temperature. Higher temperatures were associated with moderate defoliation levels, while lower minimum temperatures negatively affected severely defoliated Aleppo pine trees. No statistically significant differences in crown defoliation were found between pubescent oak and Aleppo pine. Full article

The construction sector accounts for approximately 36% of global final energy consumption and close to 40% of total CO₂ emissions, making it a primary target of international climate policy. Despite this growing attention, the indigenous building traditions of the Ecuadorian Andes remain virtually absent from the international scientific literature on vernacular sustainability. This study presents a systematic field documentation and bioclimatic assessment of vernacular bahareque dwellings in the Kichwa-Saraguro community of Ilincho, canton of Saraguro, province of Loja, Ecuador (2700 m a.s.l.). A field survey of 30 dwellings identified five morphological typologies—I-1P, I-2P, 2B, L, and C—with typology C, a compact C-shaped block with a three-sided portal, accounting for 53.3% of the sample. A structured multi-criteria framework of 48 bioclimatic indicators distributed across eight categories, adapted to the cold-temperate mountain climate of the study area, was applied to quantify each typology’s bioclimatic performance. All typologies exceeded 75% overall compliance on the global Bioclimatic Performance Index (BPI), with typology C achieving the highest value (88.5%). Categories F (Materials and construction) and H (Cultural and social aspects) scored 100% across all typologies, reflecting system-level properties of the bahareque constructive system rather than morphological differences between typological variants; a supplementary morphological BPI restricted to Categories A–E and G is reported. An exploratory, uncalibrated energy simulation of typology C provided indicative evidence consistent with the expected thermal behavior of a high-thermal-mass bahareque envelope, with simulated minimum temperatures in the sleeping area within the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) 55-2013 comfort range (T-min 18.80 °C). Collectively, these findings contribute quantified bioclimatic documentation of vernacular bahareque architecture in Ilincho, identifying attributes—encompassing solar control, spatial compactness, high-thermal-mass envelope performance, and use of locally sourced low-embodied-energy materials—that may inform sustainable rural housing discussions in the Ecuadorian Andes and comparable high-altitude mountain contexts. Its documentation in the indexed scientific literature constitutes a step toward recognizing this constructive heritage as a practical resource for low-carbon building policy. Full article

The fuel and operation efficiency of combustion engines and power plants as a whole depends essentially on the in-cycle air temperature and drops when the temperature increases. Thermally stabilized, fuel-efficient engine operation at lower air temperatures is possible due to cooling. This can be conducted by heat recovery chillers (HRC) consuming the heat removed from the engine. Such combined production of power, heat, and refrigeration, applied for cooling engine in-cycle air, is considered to be a promising trend in integrated energy systems (IES) and energetics as a whole. The in-cycle trigeneration ensures a sustainable, thermally stabilized, and highly fuel-efficient operation of power plants. Starting from the strong influence of cyclic air temperature, the rate of in-cycle air cooling is considered as the rate of engine thermal stabilization (RS) and calculated as a ratio of the real drop in cyclic air temperatures to their target values when cooling air to the desired temperatures. Such a novel approach allows for assessing the effectiveness of cooling air issuing based on both aspects: fuel efficiency and engine thermal stabilization quantitatively by RS as a unified primary criterion indicator to synthesize a cooling system with heightened RS. A case study of an IES with in-cycle trigeneration confirmed that the developed an innovative gas engine cyclic air cooling system provided increased annual average weighted values of RS_avr of about 0.44 with an enlarged duration of engine thermally stabilized operation against 0.24 for a basic typical system. Furthermore, the engine’s thermally stabilized operation due to in-cycle air cooling ensures minimum thermal load fluctuations, caused by air temperature variation. As a result, the concept of sustainable fuel-efficient operation of IES due to in-cycle air cooling and the general approaches, hypotheses, and criteria at its core have been developed. Full article

Addressing the challenges of fluctuating renewable energy integration and stable green ammonia production, this study develops and optimizes a deeply integrated system comprising Solid Oxide Electrolysis Cells (SOEC), Liquid Air Energy Storage (LAES), Air Separation Units (ASU), and Haber–Bosch (HB) synthesis. We constructed a simulation model in Aspen Plus incorporating Ru/C catalyst kinetic parameters to analyze key subsystem parameters and optimize operating conditions based on maximized economy and efficiency. At the integrated system level, a parametric analysis of ammonia condensation temperature was further conducted to investigate the coupling characteristics. Using real power output data from Inner Mongolia, we formulated a dynamic energy scheduling strategy satisfying 24-h self-balancing constraints. Results indicate that a system producing 1415 tons of ammonia per day achieves a maximum hourly integrated profit of 69,838 CNY under optimal conditions: a hydrogen-to-nitrogen ratio of 2.98:1, operating pressure of 169 bar, reactor inlet temperature of 380 °C, and ammonia condensation temperature of −9 °C. Increasing the LAES throttle valve outlet pressure from 1 bar to 9 bar improved round-trip efficiency from 52.65% to 72.18%. The integrated-level parametric analysis reveals that the specific electricity consumption per unit mass of ammonia exhibits a non-monotonic trend with a minimum of 8.67 kWh/kg at −10 °C, reflecting the trade-off between refrigeration power consumption and cold energy recovery. In dynamic scheduling scenarios, the system maintains a maximum constant load of 45.78 MW with a steady-state liquid ammonia output of 6543 kg/h. This work optimizes both economic performance and system stability, providing a significant reference for the large-scale development of green ammonia systems. Full article

Contrail emissions are aviation’s largest non-CO₂ contribution to global climate change. According to the Schmidt–Appleman criterion, potential future aircraft propulsion systems may enhance contrail formation relative to conventional engines through three mechanisms: (1) increased overall efficiency, (2) the use of hydrogen as fuel, and (3) external cooling in low-temperature fuel cell propulsion systems, which is the most critical factor. This paper presents the thermodynamic background and a system concept for contrail prevention applicable to conventional gas turbines, hydrogen combustion, and fuel cell propulsion systems. First, it is shown that fuel cell propulsion and hydrogen combustion exhibit equivalent thermodynamic contrail propensity when fuel cell exhaust is mixed with cooling air, analogous to core–bypass mixing in a conventional turbofan engines. Second, contrail mitigation via controlled condensation of exhaust water vapor is analyzed. It is demonstrated that the required cooling for LT-PEM fuel cell systems is 3–5 times lower than for turbofan engines, due to the already extensive thermal management in fuel cells. Since contrail avoidance is only necessary in ice supersaturated regions, a control scheme is proposed that limits condensation to the minimum required amount of water, thereby significantly reducing the overall drag impact. Avoiding contrail formation could provide a substantial climate benefit for future propulsion architectures. Full article

Effective thermal management is crucial for the development of future electrified aircraft propulsion systems. One of the most challenging phases is the take-off phase, which imposes particularly high demands on cooling systems. In addition, the aerodynamic drag during cruise flight has to be kept to a minimum. This study introduces a novel experimental thermal management system using a test stand with a modular air duct (TMTmad), which is designed specifically to investigate different configurations of air supply and heat exchanger in fuel cell-based electrified propulsion systems. Given the versatility of nacelle-integrated electrified propulsion architectures, this approach offers high flexibility in the design and integration of thermal management systems. This includes aspects such as the location, orientation and geometry of an air-cooled heat exchanger (HEX), as well as the inlet and outlet configurations. Moreover, the optimization of the uniform flow guidance of the duct flow within the nacelle and the integration of additional fans to ensure airflow under critical conditions can be studied. The main heat source delivers up to 6 $\mathrm{k}\mathrm{W}$ of heating power with a temperature range from −20 °C to 200 °C. The study measures the heat flux and pressure losses within these systems and includes a thorough fluid flow analysis. Furthermore, the experimental data serves as a valuable resource for validating numerical models of cooling ducts, enhancing the accuracy and reliability of future design iterations. Full article

In architecture and construction, it is common practice to use acrylic products with a high flammable content, ranging from lacquers designed to improve the curing of concrete and mortar to resins that provide protection, sealing, flexibility, and elasticity. The drying process of the treated surface involves the formation of vapours of volatile organic compounds (VOCs); to prevent these from creating a potentially hazardous flammable atmosphere, a procedure is presented that establishes the maximum application rate for solvent-based products, providing equations that relate the maximum application area and the minimum drying time to the available air velocity in the work area. The results are provided for both indoor and outdoor applications. A maximum application rate is established to prevent the creation of areas classified as fire or explosion hazards: 1.5 m²/h indoors and 1 m²/h outdoors. When this is carried out at an ambient temperature of 20 °C, and from 40 °C upwards, it is not possible to apply the varnishes in practice without creating a flammable atmosphere. Full article

To investigate the thermal environments of three large-span plastic tunnels with different orientations and shapes (two east–west-oriented asymmetrical tunnels, WE15-5 and WE13-7, and one north–south-oriented symmetrical tunnel, NS10-10) under summer high-temperature and winter low-temperature conditions, we continuously monitored the air and soil temperature and conducted a comparative analysis of both under typical weather conditions. Computational fluid dynamics (CFD) simulations were used to further analyze the temperature and airflow fields. The results showed that, in summer, NS10-10 exhibited a superior ventilation and cooling performance with the most uniform temperature distribution, making it more suitable for summer crop cultivation. In winter, WE13-7 demonstrated optimal insulation and heat retention, with the highest minimum air temperatures and best daylighting capacity. CFD model validation showed a good agreement with the measured data (RMSE: 0.73–0.85 °C). These findings provide structural optimization recommendations for large-span plastic tunnels in different seasons. Full article

To investigate the influence of external ambient temperature on the transmission characteristics of laser propagation in an internal channel, a simulation model of laser transmission within a closed channel is established in this study. The model comprehensively considers factors including gas density, refractive index distribution, and thermal deformation of optical components. Based on optical transmission theory, the model is used to calculate the beam drift characteristics and the variation in the Strehl ratio at different temperatures. The results indicate that ambient temperature has a significant impact on beam stability and quality. At low temperature (−30 °C), speckle structures appear in the laser spot, with minor drift along the X direction but obvious negative drift along the Y direction, mainly caused by the sinking of cold air driven by gravity and the refractive index gradient. The beam drift decreases initially with increasing temperature, reaches its minimum at around 10 °C, and then increases gradually as the temperature continues to rise. The Strehl ratio initially increases during the early stage of temperature rise, but diminishes in the high-temperature range due to intensified gas disturbances, enhanced thermal lensing effects, and aggravated mirror surface deformation. Full article

Climate change is altering the frequency, duration, and seasonality of low flows, which are critical for water availability, ecosystem functioning, and river management. Low-flow characteristics, defining the minimum, often seasonal, flow levels in rivers or streams primarily fed by groundwater, snow or glacier melt, or lake drainage, are essential for assessing hydrological droughts and water resource vulnerability. In the Upper Vistula River Basin, variable precipitation and rising air temperatures increase the risk of droughts, impacting both natural systems and human water use. This study analyzed long-term trends in annual low flows and associated parameters, including drought frequency, duration, and deficit volume, across 41 small- and medium-sized catchments. Two datasets were considered: 25 stations with 58-year daily discharge records (1961–2019) and 41 stations with 38-year records (1981–2019). Low flows were identified using the threshold level method (TLM) at 70% and 90% exceedance (FDC70 and FDC90). Trends were assessed with the Mann–Kendall test, and spatial drought patterns were mapped to evaluate regional variability. Deep and shallow low flows occurred at all analyzed cross-sections. For the period 1961–2019, deep low flows (FDC90) occurred almost annually in 18 of the 25 cross-sections since 2012. Statistically significant increasing trends in deep low-flow parameters were detected in five cross-sections for 1961–2019 and in seven cross-sections for 1981–2019. Shallow low flows (FDC70) occurred in all sections; four rivers exhibited annual shallow droughts during 1961–2019, whereas 12 rivers showed annual events in 1981–2019. Summer droughts predominated over winter events, reflecting enhanced evapotranspiration and higher seasonal water demand. These findings highlight the relevance of analyzing low-flow parameters for understanding hydrological droughts. Such information can support water resource management, planning, and ecosystem protection under variable climatic conditions. Full article