Search Results (111)

Extreme temperatures increasingly threaten public health, yet temperature–mortality relationships vary substantially across regions and are often obscured by average exposure–response models. This study investigates heat- and cold-related mortality in five climatically diverse Greek cities—Athens, Thessaloniki, Larissa, Patra, and Heraklion—during 1992–2024 using an event-based framework that integrates cumulative thermal stress with synoptic atmospheric conditions. Heat and cold events were defined using the Excess Heat Factor and Excess Cold Factor, combined with persistence criteria and Spatial Synoptic Classification air masses. Mortality responses were assessed through daily mortality ratios, regression analyses, and event severity categories. Dry Moderate air masses dominated across cities, accounting for more than 60% of all days in each city, indicating that extremes typically reflect departures from generally mild background conditions. Linear associations between cumulative thermal stress and mortality were weak overall, with correlation coefficients generally below |0.15| for cold events and below 0.20 for heat events. However, severe heat events produced substantial mortality increases, with mean mortality ratios reaching 1.69 in Larissa and exceeding 1.30 in all cities, despite relatively low event frequency. In contrast, cold-related mortality was often linked to frequent lower-severity events, particularly in Thessaloniki (more than 200 cold events) and Athens. These findings demonstrate that mortality risk concentrates in discrete high-impact episodes rather than increasing linearly with thermal stress, underscoring the value of event-based approaches for locally tailored adaptation and early-warning strategies. Full article

This study investigates the operation of an air source heat pump (ASHP) working with combined radiant floor (RF) and fan coil unit (FCU) heating systems in hot summer and cold winter (HSCW) regions. Intermittent heating demands and ASHP sensitivity to supply water temperature in these regions lead to insufficient steady-state assumptions, while experimental evidence on transient heating behavior, thermal comfort development, and operational limits remains limited. In this study, experiments were conducted to analyze six supply water temperatures (ranging from 35 °C to 45 °C) with respect to the system’s dynamic thermal response, vertical air temperature difference, floor surface temperature, power consumption, and coefficient of performance (COP). The results show that start-up heating is dominated by FCU convection, causing pronounced vertical temperature stratification, while radiant heat becomes dominant as the system approaches steady operation. A good vertical air temperature difference with respect to breathing zones and ankle-level temperature differences below 2 °C was achieved after sufficient operating time. Increasing the supply water temperature accelerated the heating response, where the time required for the average indoor temperature to reach 18 °C decreased from 5.5 h at 35 °C to 2.2 h at 45 °C. However, this improvement was accompanied by reduced energy efficiency, with the mean ASHP unit COP declining from 2.5 to 2.3. Excessively high supply temperatures further induced premature indoor overheating and the frequent start–stop cycling of the heat pump, thereby limiting thermal benefits and increasing power demand. These findings provide experimentally grounded insight into the operation and performance limits of ASHP RF–FCU heating systems. Full article

Rapid urbanization has intensified the mismatch between urban green space (UGS) and urban spatial vitality (USV), hindering sustainable development. To address this, we developed the Urban Green Space Vitality Adaptation Model (UGSVAM) and analyzed 64 subdistricts in central Nanjing. Specifically, this study asks: Does the mismatch exist? What are its spatiotemporal patterns? What factors drive it? Methodologically, we use the Gini coefficient and Lorenz curve to assess overall UGS-USV adaptation, then construct the Urban Green Space Vitality Density (UGVD) indicator to quantify the match level, classifying units as overloaded, underloaded, or balanced. OLS and GWR reveal global and local influencing mechanisms, while quadrant analysis supports differentiated planning. Results show: (1) UGS-USV adaptation in Nanjing is weak, with Gini coefficients of 0.466 (weekday) and 0.456 (weekend). UGVD exhibits a spatial pattern of a primary overload core in the central city, a secondary core in the southwest, and peripheral decline, with the southeast underloaded. Overloaded units also show notable temporal variation. (2) Globally POI density and intersection density promote UGVD, while excessive transport facilities, air pollution, and high temperatures inhibit it—ecological factors have stronger weekend effects. (3) Locally, the northeast is more sensitive to POI density, the southwest to transport and heat, and the Jiangbei New Area could enhance green space carrying capacity through transport optimization and spatial integration. The UGSVAM integrates spatial diagnosis, mechanism analysis, and planning response, offering a transferable framework for refining green space governance in high-density cities. Full article

Combining biobutanol and oxyhydrogen in an SI engine can reduce fossil-fuel use and improve power, but oxyhydrogen increases NOx. Without sacrificing combustion stability, this work investigates lean–burn coupled with exhaust gas recirculation for a gasoline port injection + biobutanol direct injection + oxyhydrogen in-cylinder negative pressure indraft engine, across five oxyhydrogen flow levels, four exhaust gas recirculation ratios, and three excess air ratios. Results show that with lean–burn + exhaust gas recirculation, oxyhydrogen more effectively lowers the coefficient of variation of indicated mean effective pressure and increases indicated mean effective pressure, peak cylinder pressure, and peak heat release rate. With 16 L/min oxyhydrogen, the negative effects of 6–12% exhaust gas recirculation on CA 0–10 and CA 10–90 are mitigated for all excess air ratios, and the crank angle corresponding to peak pressure remains optimal under lean conditions when 6% ≤ exhaust gas recirculation ≤ 12%. Oxyhydrogen reduces CO and HC after exhaust gas recirculation, while lean–burn dominates CO reduction. Exhaust gas recirculation suppresses NO more than lean–burn. At 1.1 ≤ excess air ratios ≤ 1.2, the optimal exhaust gas recirculation is 12%, ensuring favorable in-cylinder conditions. Overall, lean–burn + exhaust gas recirculation effectively controls NO and maximizes thermal efficiency and renewable-fuel substitution. The optimal strategy is “oxyhydrogen = 16 L/min, exhaust gas recirculation = 12%, 1.1 ≤ excess air ratios ≤ 1.2”. Full article

To advance the engineering application of the fusion decoupling combustion technology previously proposed by our research group, this work focuses on its second stage—the high-temperature syngas combustion stage—and specifically addresses the critical issue of whether high-temperature gasified syngas can achieve direct and stable ignition when mixed with ambient air. For this purpose, a high-temperature syngas combustion experimental system was established, utilizing syngas that simulates the composition of biomass gasification products as the research subject. A systematic investigation was carried out to explore the influence patterns of syngas temperature and key components on the ignition limits, which are characterized by the lower and upper limits of the excess air coefficient (λ_min and λ_max). The results indicate that increasing the syngas temperature significantly broadens the ignition limits: λ_min decreased from 0.73 to 0.59, while λ_max increased simultaneously, primarily due to accelerated reaction kinetics and the contribution of high-temperature sensible heat. An increase in H₂ content significantly expands the ignition range, whereas an increase in CO content narrows the limits, reflecting the opposing roles of these two components in terms of reactivity. Both diluent components, CO₂ and N₂, increase λ_min; however, N₂ exhibits a more pronounced inhibitory effect due to its higher volumetric heat capacity and greater thermal inertia. This study confirms the feasibility of direct ignition between high-temperature gasification syngas and ambient air, providing important experimental evidence for the engineering application of the fusion decoupling combustion process. Full article

Reverse osmosis (RO) water purifiers produce a large volume of reject water, which is typically discarded, leading to water wastage and resource inefficiency. This work proposes a novel approach to reusing RO effluent as a cooling medium in a water-cooled condenser integrated into a residential hot-and-cold water purifier. The system replaces a conventional air-cooled condenser with a water-cooled unit and was evaluated under controlled laboratory conditions (ambient temperature 25 °C). Experiments were conducted at various RO effluent flow rates ranging from 0.5 to 2.5 L per minute (LPM). Key performance metrics, including the coefficient of performance (COP), cooling time, and energy consumption, were measured and compared. Results showed that replacing a conventional air-cooled condenser with a water-cooled condenser configuration reduces energy consumption by up to 37.5% and shortens cooling times by up to 33%. Performance was maintained under intermittent RO effluent supply. However, an excessive flow rate (2.0 LPM) caused evaporator frosting and efficiency loss, indicating the importance of flow control. These findings demonstrate that internally reusing an RO effluent offers a sustainable, compact, and energy-efficient solution for next-generation water purifiers. Full article

This study investigates the influence of crushed plum stones and rosin (colophony) as additives in the pelletisation of pine sawdust, with a focus on energy consumption, pellet quality, and combustion performance. The addition of crushed plum stones combined with 10% rosin reduced the energy demand of the process. Incorporating 10–20% plum stones with 10% rosin decreased the pelletiser power demand by 18% and 25%, respectively, compared to pure sawdust. Plum stone addition significantly improved the energetic parameters of pellets. At a 20% share, the calorific value increased to 18.02 MJ·kg⁻¹ and the heat of combustion to 20.04 MJ·kg⁻¹, while 10% rosin further enhanced these values by 1.67 MJ·kg⁻¹ (8.4%). Although bulk and particle density slightly decreased, a 10% plum stone share raised the kinetic strength to 97.24%, indicating improved mechanical durability. Combustion tests confirmed favourable properties of the modified pellets, including lower air excess coefficients (λ) and reduced emissions of CO, NO, and SO₂. However, a 10% rosin content slightly exceeded CO emission limits set by the Ecodesign Directive, suggesting that its share should be reduced to ~5%. The results confirm that crushed plum stones and rosin are effective modifiers in sawdust pelletisation, enhancing both process efficiency and fuel quality. This approach supports circular economy principles by converting plant-based residues into high-quality biofuels. Full article

The paper presents the application of high-speed flame imaging combined with convolutional neural networks (CNNs) for determining different states of biomass–coal co-combustion in terms of thermal power and excess air coefficient. The experimental setup and methodology used in a laboratory-scale co-combustion system are described, highlighting tests conducted across nine defined operational variants. The performance of several state-of-the-art CNN architectures was examined, focusing particularly on those achieving the highest classification metrics and exploring the dependence of input image resolution and applying a transfer learning paradigm. By benchmarking various CNNs on a large, diverse image dataset without preprocessing, the research advances intelligent, automated control systems for improved stability, efficiency, and emissions control, bridging advanced visual diagnostics with real-time industrial applications. The summary includes recommendations and potential directions for further research related to the use of image data and machine learning techniques in industry. Full article

This study aims to create environmentally comfortable building designs in hot and dry steppe climates using more effective approaches. The purpose of this study is to assess the relationship between mean radiant temperature (MRT) and indoor air temperature (Tia), taking into account the orientation of buildings, for better building thermal performance. For this purpose, residential buildings with different orientations were selected in the study region ‘Garmian—northern Iraq’, and their thermal performance was evaluated. The results show how MRT contributes to the buildings’ thermal comfort. The outcomes of this research provide innovative empirical quantification of the correlation of MRT-Tia, as the regression coefficient (β) represents the rate of change in Tia per unit increase in MRT and ranges by orientation in the study area. The findings demonstrate that north-facing buildings buffer radiant heat gain (β~0.52), resulting in a 0.5 °C increase in indoor air temperature for each 1 °C rise in MRT. Moreover, west orientation delivers promising winter passive heating (MRT up to 22 °C and indoor air temperature up to 22.8 °C with a β of ~0.82). However, south-facing buildings perform poorly in the winter, with low MRT and a weak β (~0.44), contrasting with passive solar design strategies that favor south-facing buildings in the northern hemisphere. Furthermore, in the summer, the MRT is always higher than Tia, while it is lower in winter, indicating poor envelope and fenestration thermal insulation properties, which lead to excessive energy usage to maintain thermal comfort. Finally, the study suggests the novel quantified MRT-Tia mathematical correlation responds to the orientations for such climates, offering both diagnostic and predictive tools for thermal comfort performance optimization. This study is the first to empirically quantify orientation-specific MRT–Tia relationships in BSh climates, offering a novel diagnostic tool for sustainable building design. This study involved field observations in 36 residential row houses across four orientations. Key environmental and personal variables measured included mean radiant temperature (MRT), indoor air temperature (Tia), air velocity, relative humidity, metabolic rate, and clothing insulation. Full article

This study proposes a machine learning framework utilizing physical feature dimensionality reduction to address the problem of predicting the maximum excess temperature beneath the tunnel ceiling under the influence of multiple factors. First, theoretical analysis is used to systematically explore the impacts of various factors on the maximum excess temperature, including the heat release rate of the fire source, tunnel height, slope, and ambient air pressure. Physical relationships are established to identify key factors, remove redundant features, and construct a simplified feature vector set. Five typical machine learning models are selected: Random Forest (RF), Support Vector Regression (SVR), Fully Connected Neural Network (FCNN), Multi-Layer Perceptron (MLP), and Bayesian Neural Network (BNN). A hybrid data collection strategy combining scale model tests and CFD numerical simulations constructs a small-sample structured dataset with physical backgrounds. The models are evaluated regarding prediction accuracy, stability, and generalization ability. Results show that the Bayesian Neural Network (BNN) optimized by random search parameter optimization and Bayesian regularization significantly outperforms other comparative models in evaluation indices such as root mean square error (RMSE), and mean absolute error (MAE), and coefficient of determination (R²), making it the optimal model and algorithm combination for such tasks. This study provides a reliable quantitative analysis method for tunnel fire safety assessment and offers a new methodological reference for the research on fire dynamics in underground spaces. Full article

As the global demand for clean and efficient energy continues to grow, the development of advanced energy storage technologies is becoming increasingly important. This study explores the influence of the dead volume coefficient and pulse-width modulation (PWM) control strategy on the performance of a piston expander in a micro-compressed air energy storage system. Simulation results showed that low dead volume values, combined with short air supply durations with PWM values between 0.1 and 0.2, led to improved energy utilization. This was achieved through complete piston strokes and stable power output. In contrast, high dead volume values and high PWM settings, such as 0.9, resulted in incomplete air expansion, excessive air consumption, and a significant reduction in overall system efficiency, even though peak power output may increase. Sensitivity analysis confirmed that PWM had a major impact on efficiency, with the highest value of 0.76 achieved for a dead volume coefficient of 0.05 and a PWM value of 0.2. Under these operating conditions, the expander delivered a generated power output of 970 W. Additionally, PWM enabled flexible control of power output, without requiring modifications to the system’s physical design. The study highlights the importance of adjusting the air admission strategy to match the internal volume characteristics. Full article

In this study, the sensitivity of operating parameters such as the hydrogen and air excess coefficient, cathode inlet pressure, intake relative humidity, and coolant inlet temperature and their effects on the performance of single proton exchange membrane fuel cells (PEMFCs) are experimentally assessed. The results revealed that the fuel cell node voltage increases as the hydrogen and air excess coefficient increases, and the impact of the hydrogen and air excess coefficient on the fuel cell node voltage gradually increases as the current density increases. However, a higher hydrogen and air excess coefficient is not always better. The node voltage increases as the intake pressure increases. However, it is not that a higher intake pressure is always better, but rather that there is an optimal intake pressure value to achieve the best overall performance of the fuel cell. The node voltage increases as the coolant inlet temperature increases at most fuel cell current densities. However, the optimum fuel cell operating inlet temperature is not necessarily higher, as the coolant inlet temperature may have a strong coupling relationship with other operating conditions that will also affect the fuel cell performance. The fuel cell operating inlet temperature may have a strong coupling relationship with the intake relative humidity, and both of these parameters must be well-matched to achieve better fuel cell performance. Full article

In this study, a computational thermo-fluid dynamics simulation of a wide-slot jet impingement heating process is performed. The present configuration consists of a turbulent incompressible air jet impinging orthogonally on an isothermal cold plate at a Reynolds number of around 11,000. The two-dimensional mean turbulent flow field is numerically predicted by solving Reynolds-averaged Navier–Stokes (RANS) equations, where the two-equation eddy viscosity k-$\omega$ model is utilized for turbulence closure. As the commonly used shear stress transport variant overpredicts heat transfer at the plate due to excessive turbulent diffusion, the recently developed generalized k-$\omega$ (GEKO) model is considered for the present analysis, where the primary model coefficients are suitably tuned. Through a comparative analysis of the various solutions against one another, in addition to reference experimental and numerical data, the effectiveness of the generalized procedure in predicting both the jet flow characteristics and the heat transfer at the plate is thoroughly evaluated, while determining the optimal set of model parameters. By improving accuracy within the RANS framework, the importance of model adaptability and parameter tuning for this specific fluid engineering application is demonstrated. This study offers valuable insights for improving predictive capability in turbulent jet simulations with broad engineering implications, particularly for industrial heating or cooling systems relying on wide-slot jet impingement. Full article

Hydrogen is a promising fuel in the current transition to zero-net CO₂ emissions. However, most practical combustion equipment is not yet ready to burn pure hydrogen without adaptation. In the meantime, blending hydrogen with natural gas is an interesting option. This work reports a computational study of the performance of swirl-stabilized natural gas/hydrogen flames in a novel combustion chamber design. The combustor employs an air-staging strategy, introducing secondary air through a top-mounted plenum in a direction opposite to the fuel jet. The thermal load is fixed at 5 kW, and the effects of fuel composition (hydrogen molar fraction ranging from zero to one), excess air coefficient (λ = 1.3, 1.5 or 1.7), and primary air fraction (α = 50–100%) on the velocity, temperature, and emissions are analysed. The results show that secondary air changes the flow pattern, reducing the central recirculation zone and lowering the temperature in the primary reaction zone while increasing it further downstream. Secondary air improves the performance of the combustor for pure hydrogen flames, reducing NO emissions to less than 50 ppm for λ = 1.3 and 50% primary air. For natural gas/hydrogen blends, a sufficiently high excess air level is required to keep CO emissions within acceptable limits. Full article

The interior permanent magnet synchronous motors (IPMSMs) are extensively applied in the field of new energy vehicles due to their high-power density and excellent performance control. However, the iron loss has a significant impact on their performance. This study conducts an optimization analysis on the processing technology of silicon steel sheets and motor structure, targeting the reduction of iron loss and the improvement of the motor’s integrated efficiency. Firstly, the influences of two iron core processing technologies on iron loss, namely gluing and welding, are compared. Through experimental tests, it is found that the iron loss density of the gluing process is lower than that of the welding process, and as the magnetic flux density increases, the difference between the two is expanding. Therefore, the iron loss test data from the adhesive process are employed to develop a variable-coefficient iron loss model, enabling precise calculation of the motor’s iron loss. On this basis, aiming at the problem of excessive iron loss of the motor, a novel topological structure of the stator and rotor is proposed. With the optimization goal of reducing the motor iron loss and taking the connection port of the air magnetic isolation slot and the gap of the stator module as the optimization variables, the optimized design of the IPMSM with low iron loss is achieved based on the Taguchi method. After optimization, the stator iron loss decreases by 13.60%, the rotor iron loss decreases by 20.14%, and the total iron loss is reduced by 15.34%. The optimization scheme takes into account both the electromagnetic performance and the process feasibility, it offers technical backing for the high-efficiency operation of new energy vehicle drive motors. Full article