Urban canyons, integral components of the built environment, significantly influence microclimatic conditions and thermal comfort. This review investigates their combined effects with green infrastructure on thermal comfort, offering a comprehensive framework for optimizing urban design and greening strategies. Urban canyon orientation determines solar exposure and its interaction with prevailing wind patterns, affecting ventilation and heat dissipation. The urban canyon aspect ratio influences shading and airflow regulation, while their sky view factor moderates radiative cooling and daylight availability. Urban greening—encompassing street trees, green roofs, and vertical green walls—complements urban geometry by reducing air temperatures, enhancing evapotranspiration, and modifying local wind dynamics. Tree shading can reduce the physiological equivalent temperature in urban canyons, mitigating extreme heat stress. Key vegetative parameters, such as leaf area index and canopy density, are critical for quantifying cooling contributions. Key findings underscore the role of higher aspect ratios in enhancing shading and ventilation while they emphasize the critical influence of street orientation and sky view factor on microclimatic regulation. Vegetation emerges as a vital component, with tree shading contributing substantially to cooling effects and reducing physiological equivalent temperature. The beneficial synergistic interaction between urban geometry and vegetation optimizes thermal comfort. Tailored strategies based on urban canyon typologies balance urban development with environmental sustainability. The proposed framework provides actionable strategies for designing resilient and thermally optimized urban spaces, promoting climate-adaptive urban planning by addressing the dual challenges of the urban heat island and thermal discomfort in cities.

Conventional photovoltaic performance indicators provide useful benchmarking but do not determine whether production deficits arise from expected weather and module effects or from unresolved plant-side behaviour. This study develops a residual performance diagnostic framework for data-limited grid-connected photovoltaic plants and applies it to two adjacent fixed-tilt crystalline-silicon systems, each rated at 99.36 kWp, in South Corfu, Greece, over 2016–2023. An expected-energy baseline was constructed using hourly irradiance and meteorological data from the Photovoltaic Geographical Information System after explicit correction for incidence-angle effects, irradiance-level response, module temperature, and first-order air-mass and spectral effects. Measured alternating-current energy delivered to the grid, obtained from the Hellenic Electricity Distribution Network Operator, was then compared with the corrected expected energy through a weather-adjusted system-efficiency indicator and its complementary residual-loss coefficient. The explicit module and weather loss envelope remained close to 9.01%, with temperature as the largest modelled component. Residual losses increased from 10.76% to 14.53% in Plant 1 and from 10.51% to 16.26% in Plant 2. The fitted apparent annual declines were 0.453 percentage points per year for Plant 1 and 0.609 percentage points per year for Plant 2. A generation-hour uncertainty analysis based on independent observations from the Hellenic National Meteorological Service gave expanded uncertainties of ±5.80% for expected energy and ±5.89% for the system-efficiency indicator. The framework is therefore presented as an uncertainty-bounded screening method for prioritizing inspection and maintenance, not as a root-cause diagnostic or a formal performance-loss-rate assessment.

Power electronics convert and control electrical power in applications ranging from electric motors to telecommunications and computing. Ongoing efforts to miniaturize these systems and boost power density demand advanced thermal management solutions to maintain optimal cooling and temperature control. Spray cooling offers an effective means of removing high heat fluxes and keeping power electronics within safe operating temperatures. This study presents an experimental investigation of flash spray cooling in a closed-loop system using R410A refrigerant. In particular, two nozzles with different spraying angles are used to study the effects of the distance between the spray nozzle and a heated flat surface, as well as the mass flow rate of the coolant. Results indicate that three key flow-pattern factors—surface coverage, impingement intensity, and liquid film dynamics—govern the heat transfer mechanisms and determine cooling efficiency. Flash spray cooling using refrigerants like R410A demonstrates strong potential as a high-performance thermal management strategy for next-generation power electronics.

In the present work, the turbulent wake of a circular cylinder in a confined flow environment at a blockage ratio of 14% is experimentally investigated in a wind tunnel consisting of a parallel test section followed by a constant-area distorting duct, under subcritical Re inlet conditions. The initial stage of wake development, extending from the bluff body to the end of the parallel section, is analyzed, with the use of hot-wire anemometry and laser-sheet visualization. The near field reveals partial similarity to unbounded wakes, with the principal difference being a modification of the Kármán vortex street topology, attributed to altered vortex dynamics under confinement. Further downstream, the mean and fluctuating velocity distributions of the confined wake gradually evolve toward channel-flow characteristics. To elucidate this transition, wake measurements are systematically compared with channel flow data obtained in the same configuration under identical inlet conditions and with reference channel-flow datasets from the literature. Experimental results show that a vortex-transportation mechanism exists due to confinement effect, resulting in the progressive crossing and realignment of counter-rotating vortices toward the tunnel centerline. Although wake flow characteristics are preserved, suppression of classical periodic shedding is clearly depicted. Furthermore, it is shown that the confined near-wake spectral peak persists up to x1/d~60 as in the free case and then vanishes as the spectra broadens. Coincidentally, the confined wake exhibits a narrower halfwidth than its free wake counterpart, while a centerline shift of the shed vortices is observed. Farfield wake-flow maintains strong anisotropy, while a weaker downstream growth of the streamwise integral scale is observed when compared to channel flow. Together, these findings explain how confinement reforms the nearfield topology and reorganizes momentum transport as the flow evolves to channel-like flow.

Indoor Air Quality (IAQ) in educational environments is a critical determinant of students’ health, well-being, and learning performance, with inadequate ventilation and pollutant accumulation consistently associated with respiratory symptoms, fatigue, and impaired cognitive outcomes. Conventional monitoring approaches—based on periodic inspections or subjective perception—provide only fragmented insights and often underestimate exposure risks. Artificial intelligence (AI) offers a transformative framework to overcome these limitations through sensor calibration, anomaly detection, pollutant forecasting, and the adaptive control of ventilation systems. This review critically synthesizes the state of AI applications for IAQ management in educational environments, drawing on twenty real-world case studies from North America, Europe, Asia, and Oceania. The evidence highlights methodological innovations ranging from decision tree models integrated into large-scale sensor networks in Boston to hybrid deep learning architectures in New Zealand, and regression-based calibration techniques applied in Greece. Collectively, these studies demonstrate that AI can substantially improve predictive accuracy, reduce pollutant exposure, and enable proactive, data-driven ventilation management. At the same time, cross-case comparisons reveal systemic challenges—including sensor reliability and calibration drift, high installation and maintenance costs, limited interoperability with legacy building management systems, and enduring concerns over privacy and trust. Addressing these barriers will be essential for moving beyond localized pilots. The review concludes that AI holds transformative potential to shift school IAQ management from reactive practices toward continuous, adaptive, and health-oriented strategies. Realizing this potential will require transparent, equitable, and cost-effective deployment, positioning AI not only as a technological solution but also as a public health and educational priority.

Buildings are responsible for nearly 40% of primary energy consumption. Over the recent decades, numerous methods have been proposed to model, predict, and optimize the heating and cooling energy consumption in buildings, prioritizing efficiency, accuracy, simplicity, and speed. From basic deterministic formulations to advanced machine learning techniques, various methods have been proposed to improve the thermal performance of existing structures and optimize the design of new ones. This manuscript reviews statistical and machine learning approaches in building energy performance simulation, presenting and discussing theoretical considerations and a review of published research studies, covering input, output, distinctive modeling features, and main results. Statistical learning techniques include linear prediction models, generalized linear models, linear mixed-effects models, Bayesian approaches, and time series analysis. Machine learning techniques include deep learning approaches, such as deep feed-forward, recurrent, and convolutional artificial neural networks. Support-vector machines and ensemble machine learning are also discussed, each with a review of relevant research studies, respectively. The application of machine learning approaches in building design and control include both model predictive and reinforcement learning-based control, and building retrofit. The goal is to provide a detailed overview of historical and contemporary developments in data-driven methodologies, encompassing various scientific approaches and algorithms shedding light on the complexities and trends in the dynamic field of energy-efficient building design and operation.

In this research work, the hemodynamic field of an occluded artery with anastomosis by means of computational simulation has been studied. The main objective of the current study is the investigation of 3D flow field phenomena in the by-pass region and the effect of the bypass graft to stenosis volume flow ratio on their formation. The anastomosis type was end-to-side with a 45° angle, while stenosis imposed a 75% area blockage of the aorta vessel and the total volume flow was 220 lt/h. The computational study of the flow field was utilized via a laminar flow model and three turbulence models (k—ε RNG, standard k—ω, and k—ω SST). Numerical results were compared qualitatively with experimental visualizations carried out under four different flow conditions, varying according to the flow ratio between the stenosis and the anastomotic graft. Comparison between computational results and experimental visualization findings exhibited a good agreement. Results showed that SST k—ω turbulence models reproduce better visually obtained flow patterns. Furthermore, cross-sectional velocity distributions demonstrated two distinct flow patterns down the bypass graft, depending on the flow ratio. Low values of flow ratio are characterized by fluid rolling up, whereas for high values fluid volume twisting was observed. Finally, areas with low wall shear stresses were mapped, as these are more prone to postoperative degradation of the bypass graft due to the development of subendothelial hyperplasia.

With high critical heat flux (CHF) and heat transfer coefficient (HTC), spray cooling is considered as one of the most promising thermal management technologies for high-power electronic devices. To increase its cooling performance, a closed-loop experimental rig was constructed to study the effects of spray and system parameters on heat transfer enhancement by R410A. The best cooling performance can be achieved under optimal subcooling degree of 17 degrees C and nozzle diameter of 0.56 mm. When the compressor frequency reaches the upper limit of 90 Hz, maximum CHF and HTC on flat surface are 301.6 W/cm2 and 91.7 kW/(m2.K). To further improve CHF, mechanism of heat transfer enhancement by square pin finned surface was revealed in terms of droplet splashing. With fin width of 0.5 mm and height of 3 mm, CHF as high as 522.1 W/cm2 and peak HTC of 407.0 kW/(m2.K) are reached, while maintaining the cooling surface temperature lower than 55.6 degrees C. Compared to flat surface, CHF and HTC are enhanced by around 73.4% and 3.5 times, respectively. Based on the experimental data, CHF correlation applicable to pin finned surface was obtained with precision of +/- 12.4% by introducing fin height and width.

Dynamic thermal management of electronic equipment is of practical importance to adapt to the quickly changed heat load at local spot. A closed-loop experimental system was constructed to study the heat transfer mechanism and cooling performance of flashing spray cooling by R410A on a smooth flat copper surface in steady-state and varying operating conditions, especially the effect of frequency conversion of compressor. The results indicated that the superheat of 4 degrees C and 22 degrees C can be regarded as the transition points between three heat transfer stages of steady R410A flashing spray cooling: single-phase heat transfer, nucleate boiling, and transition boiling. To achieve the best cooling performance, superheat should be between 4 degrees C and 22 degrees C to keep heat transfer in stage II. The increase of compressor frequency can improve the cooling performance of spray system effectively. When the compressor frequencies are 10 Hz, 15 Hz and 20 Hz, CHF can reach 162.9, 168.3 and 175.0 W/cm2, and the maximum heat transfer coefficient is around 60.5, 80.6, and 90.4 kW/(m2.K), separately, with surface temper-ature below 35 degrees C, 30 degrees C and 25 degrees C. At the same heat flux, the power consumptions for the system to reach steady-state at 15 Hz and 20 Hz are 12.2% lower but 5.9% higher than that at 10 Hz, which provides a feasible energy-saving strategy for spray cooling system in the practical thermal management of electronic equipment.

Flashing spray occurs when the saturated liquid is discharged into a gaseous environment at an ambient pressure lower than its saturation pressure. Internal flow is a primary determinant on the behavior of external flashing spray, so its transient effect was investigated with iso-pentane as working medium. The coupled effect of superheat level and injection pressure was comprehensively explored with initial temperature from 30 degrees C to 70 degrees C and injection pressure from 1.2 MPa to 2.4 MPa. Under different injection pressure, the stable spray patterns can still be categorized as non-shattering, partially shattering, completely shattering and flare flashing separated by the shattering index X center dot(P-inj/P-a)(0.5) of 0.21, 0.39 and 0.76, which represents the product of homogeneous nucleation rate and the ratio of injection pressure over ambient pressure. A strong correlation between the spray cone angle and the shattering index is proposed as a piecewise function separated by X center dot(P-inj/P-a)(0.5) = 0.39. High-void -fraction internal two-phase flow is easier to be formed in partially shattering or completely shattering pattern, which would lead to a hysteretic flashing spray with a significant increase of spray cone angle and droplets concentration. Low X center dot(P-inj/P-a)(0.5) yields slower response of external morphological changes but larger enhance-ment of radial expansion.

This research investigated potential fire hazards originating in hidden areas of pressurized sections of aircrafts. The objective was to establish a laboratory-scale flammability test method to predict the behavior of fire propagation under real fire conditions. A confined fire apparatus (CFA) was designed and constructed, and several tests were conducted to better understand the involved mechanisms and their consequences and to estimate flame spreading in hidden-zone fires. The experimental facility and flame-spreading results obtained for a typical material involved in hidden fires, specifically a ceiling panel, were presented and discussed. The experimental facility consisted of a narrow passage where a fire was initiated using a burner on a specimen exposed to a controlled heat flux. Experiments were conducted in the absence of forced airflow. Flame spreading was estimated through visual monitoring of fire development or temperature measurements at specific locations in the specimen. Both methods yielded similar results. The flame spread velocity in relation to the imposed heat flux allowed for the estimation of the critical heat flux for spreading q˙sp,cr″ and for ignition q˙ig,cr″; the corresponding temperatures, Ts,min and Tig; and the flame spread parameter Φ.

As one of the most promising thermal management solutions, spray cooling has the advantages of high heat-transfer coefficient and maintaining a low temperature of the cooling surface. By summarizing the influential factors and practical applications of spray cooling, the current challenges and bottlenecks were indicated so as to prompt its potential applications in the future. Firstly, this paper reviewed the heat-transfer mechanism of spray cooling and found that spray cooling is more advantageous for heat dissipation in high-power electronic devices by comparing it with other cooling techniques. Secondly, the latest experimental studies on spray cooling were reviewed in detail, especially the effects of spray parameters, types of working fluid, surface modification, and environmental parameters on the performance of cooling system. Afterwards, the configuration and design of the spray cooling system, as well as its applications in the actual industry (data centers, hybrid electric vehicles, and so on) were enumerated and summarized. Finally, the scientific challenges and technical bottlenecks encountered in the theoretical research and industrial application of spray cooling technology were discussed, and the direction of future efforts were reasonably speculated.

The reduction of the environmental impact in the building sector is necessary in achieving global sustainability. In this context, Building Automation and Control systems provide the opportunity for efficient monitoring and control facilities’ subsystems, such as the heating and cooling system, the ventilation system, the hot water system, the lighting appliances among others, with the goal of improving thermal comfort as well as energy efficiency. This paper presents a Building Automation and Control system aiming at facilitating data-driven monitoring of complex, multi-storey facilities, by disagreggating total consumption of the different floors and rooms of the building and offering advanced insights and benchmarking indicators. The service is showcased with a use case application on a real building, where the benefits of the service for the energy manager are highlighted.

The increasing use of composite materials in aircraft cabins and structures poses significant challenges in order to maintain and improve the fire safety of aviation. In this work, the flammability characteristics of a commercial glass-fibre reinforced phenolic composite (GFRP) used for aircraft cabin partitions and furnishing are investigated experimentally. Thermogravimetric analysis under inert atmosphere at several heating rates provided information on the thermal decomposition process. The degradation process is modelled with one and two-step mechanisms using the Ozawa–Flynn–Wall iso-conversional method and the GPYRO numerical code which utilizes a genetic algorithm optimization scheme. The estimated activation energy and pre-exponential factor values, especially in the two-step case (77.18 and 104.69 kJ/mol and 2.60 × 106 and 3.19 × 106 min−1 for the first and the second step respectively), recover reasonably well the conversion degree and its derivative. Tests with a cone calorimeter (CC), performed at different incident heat fluxes, provided information on the reaction to fire characteristics of the material and the influence of the heat flux on the combustion process. In general, combustion proceeds in two stages, flaming and smoldering combustion. The CC results assisted by scanning electron microscopy photos provide information on the charring characteristics of the material. The critical heat flux for ignition and the corresponding ignition temperature are estimated, correlating heat fluxes with time to ignition. Thermally thin and thick models are considered, as well as a modified technique bridging the gap between these limit cases and therefore valid for thermally thin and thick but also intermediate conditions (more pertinent in the present case). The results for this latter approach are $$\dot{q}^{\prime\prime}_{ig,cr}$$ ~ 20 kW/m2 and Tig = 469°C, providing also complementing information on thermophysical properties, such as thermal diffusivity, α = 1.23 × 10−7 m2/s, thermal conductivity, k = 0.325 W/(m K) and specific heat capacity, c = 1.330 kJ/(kg K). This work provides information on the reaction to fire characteristics of GFRP, but also on physical and flammability properties in a form suitable to be used in numerical codes, for the prediction of fire and evacuation scenarios. The influence of the reinforcement structure on the fire behaviour of the composite is also illustrated and discussed.

The experimental investigation of a swirling jet and an annular swirling stream issuing from coaxial cylinders is presented. The objective is to contribute to the research on the combined flow field close to vortex breakdown conditions. The two swirling water streams are interacting in the extension of the outer cylinder. Swirl is generated by two rotating impellers, located in the inner tube and the annular duct, just before the merging of the two streams. Controlled flow parameters comprise the flow rates of the streams and the angular velocities of the impellers. The flow field is monitored by means of Stereoscopic 3D-PIV, providing the velocity components on an axial, central plane. Four typical test cases were investigated comprising four combinations of inlet conditions. Two dimensionless numbers were utilized to interpret the experimental results, a modified Rossby number and the velocity ratio ζ, along with the Reynolds numbers of the internal and annular stream, respectively. The most important coherent structure developed, is a recirculation region formed downstream of the exit of the internal swirl nozzle. A bubble type vortex breakdown occurs when the appropriate flow conditions are applied. The alterations of the flow field were discussed with respect to the changes of the inlet conditions. The flowrates of the two streams and the combined swirl strength applied through the rotating impellers appear to be crucial for the onset of the vortex breakdown. Comparisons were drawn with previous work.

A 2D particle image velocimetry study of a coaxial flow with inner swirl is presented. An inner swirling jet, produced by tangential injection, interacts with an annular flow generating a recirculating flow field with strong mixing attributes. The characteristics of the cross-plane velocity components of four different test cases are presented (two levels of tangential injection flow rate combined with two levels of annular flow rate) in order to study the mean and turbulent attributes of the swirling vortex. The main features of this complex flow field, which can be considered as the interaction of a typical swirling jet undergoing “vortex breakdown” with an outer annular flow with “backward facing step flow” characteristics, are investigated, focusing on the swirling jet's characteristics. The analysis of the mean and turbulent flow is based on a modified Rossby number, previously proposed by the authors, defined as the ratio of the streamwise velocity jump across the two streams over a typical tangential velocity, which is shown to represent the ratio of the pressure difference due to the streamwise velocity difference and the entrainment of the two flows to that due to the rotation of the swirling vortex. The angular momentum diffusion downstream is evaluated, to assess the mixing between the swirling vortex and the outer flow.

Purpose - The purpose of this paper is to study the structure and dynamic development of a pair of co-rotating trailing vortices, during their formation, interaction and merging, using detailed experimental measurements of the velocity and vorticity fields.Design/methodology/approach - The vortices were generated using two half wings (NACA0030) positioned at equal and opposite angles of attack at the entrance of the test section of an open-circuit, subsonic, wind tunnel. Velocity vector measurements were obtained at Re-c = 133,000, on cross-plane grids at several distances from the trailing edges of the wings, using an in-house developed four-sensor hot wire anemometer probe.Findings - The results include cross-plane contour plots of the mean and fluctuating velocity as well as mean vorticity fields. Each of these variables is affected in a different way, providing complementary information on the development of the flow field. After shedding, the two vortices are swept along the stream-wise direction and spiral around each other, thereby developing a braid of two vortices, which then deforms the external flow field. Gradually, the interaction with the external flow field links both vortices together until the final merging and the formation of a new stable linear vortex emerges.Practical implications - Trailing vortices have been rendered particularly important during the past decades, because of increasing traffic density of very heavy aircrafts and several plane "incidents", which were attributed to the action of the vortex wake.Originality/value - The presented results provide information on the evolution and merging of a pair of vortices formed by a closely spaced differential wing configuration. The vortices interact almost immediately after shedding as expected in flap-flap or flap-wing vortices interaction.

In the present work, the hemodynamic field of an occluded artery is studied experimentally. 2D D.P.I.V measurements are presented regarding the statistically mean and turbulent flow field created in an artery having a double stenosis with over 75% occlusion. In this manuscript, the steady state case is considered. Experimental results show the influence of the stenoses on the formation of recirculation zones and the effect of flow characteristics on the shear stresses developing in the artery model.

The recirculating flow field generated by a swirling jet and a coaxial annular stream entering a pipe is investigated with the use of 2D-DPIV. Parametric change of inlet flow rates (constant tangential injection with change of annular flow and vice versa) is being considered in order to study the mean and turbulent flow field. A recirculation bubble stabilized close to the swirler exit is the dominating feature of the interaction between the inner swirling jet and the annular stream. Results are discussed in terms of bubble topology and dynamics on the basis of a modified Rossby number that appears to describe the trends of the complex flow field.

The isothermal recirculating flow field generated by a swirling jet and a coaxial annular flow entering a pipe is investigated with the use of 2D-DPIV. Parametric change of flow inlet conditions (constant tangential injection with change of annular velocity and vice versa) is being considered in order to study the effect of the coaxial flow field on the recirculation bubble structure. Measurements of the mean and turbulent flow field are discussed in terms of bubble topology and dynamics in relation to a modified Rossby number. It is shown that the vortex ring structure plays an important role both on the recirculating features of the flow and the mixing process.