Search Results (257)

Photovoltaic–thermal (PVT) technology has attracted considerable attention for its ability to significantly improve solar energy conversion efficiency by simultaneously providing electricity and heat during the day. PVT technology serves a purpose in condensers and subcoolers for passive cooling in refrigeration systems at night. In our previous work, we proposed a switchable film-insulated photovoltaic–thermal–passive cooling (PVT-PC) module to address the structural incompatibility between diurnal and nocturnal modes. However, the performance of the proposed module strongly depends on two key design parameters: the structural height and the vacuum level of the air cushion. In this study, a numerical model of the proposed module is developed to examine the impact of design and meteorological parameters on its all-day performance. The results show that diurnal performance remains stable across different structural heights, while nocturnal passive cooling power shows strong dependence on vacuum level and structural height, achieving up to 103.73 W/m² at 10 mm height and 1500 Pa vacuum, which is comparable to unglazed PVT modules. Convective heat transfer enhancement, induced by changes in air cushion shape, is identified as the primary contributor to improved nocturnal cooling performance. Wind speed has minimal impact on electrical output but significantly enhances thermal efficiency and nocturnal convective cooling power, with a passive cooling power increase of up to 31.61%. In contrast, higher sky temperatures degrade nocturnal cooling performance due to diminished radiative exchange, despite improving diurnal thermal efficiency. These findings provide fundamental insights for optimizing the structural design and operational strategies of PVT-PC systems under varying environmental conditions. Full article

Maintaining the required relative humidity values in the vehicle cabin is an important HVAC task, along with considerations related to the temperature, velocity, air pressure and noise. Deviation from the optimal values worsens the psycho-physiological state of the driver and affects the energy efficiency of the train. In this study, a model of liquid film formation on and removal from various cabin surfaces was constructed using the fundamental Navier–Stokes hydrodynamic equations. A special transport model based on the liquid vapor diffusion equation was used to simulate the air environment inside the cabin. The evaporation and condensation of surface films were simulated using the Euler film model, which directly considers liquid–gas and gas–liquid transitions. Numerical results were obtained using the RANS equations and a turbulence model by means of the finite volume method in Ansys CFD. Conjugate fields of temperature, velocity and moisture concentration were constructed for various time intervals, and the dependence values for the film thicknesses on various surfaces relative to time were determined. The verification was conducted in comparison with the experimental data, based on the protocol for measuring the microclimate indicators in workplaces, as applied to the train cabin: the average ranges encompassed temperature changes from 11% to 18%, and relative humidity ranges from 16% to 26%. Comparison with the results of other studies, without considering the phase transition and condensation, shows that, for the warm mode, the average air temperature in the cabin with condensation is 12.5% lower than without condensation, which is related to the process of liquid evaporation from the heated walls. The difference in temperature values for the model with and without condensation ranged from −12.5% to +4.9%. We demonstrate that, with an effective mode of removing condensate film from the window surface, including recirculation modes, the energy consumption of the climate control system improves significantly, but this requires a more accurate consideration of thermodynamic parameters and relative humidity. Thus, considering the moisture condensation model reveals that this variable can significantly affect other parameters of the microclimate in cabins: in particular, the temperature. This means that it should be considered in the numerical modeling, along with the basic heat transfer equations. Full article

Increased market demand for plant herbs has prompted growers to ensure a continuous and assured supply of superior nutritional quality over the years. Apart from the nutritional value, culinary herbs contain phytochemical benefits that can improve human health. However, a significant amount of research has focused on enhancing yield, frequently overlooking the impact of production practices on the antioxidant and phytonutritional content of the produce. Thus, the study aimed to evaluate the yield, phytonutrients, and essential mineral profiling in selected aromatic herbs and their intricate role in nutritional quality when grown under different production systems. Five selected aromatic herbs (coriander, rocket, fennel, basil, and moss-curled parsley) were evaluated at harvest when grown under three production systems: in a gravel-film technique (GFT) hydroponic system and in soil, both under the 40% white shade-net structure, as well as in a soilless medium using sawdust under a non-temperature-controlled plastic tunnel (NTC). The phytonutritional quality properties (total phenolic, flavonoids, β-carotene-linoleic acid, and condensed tannins contents) as well as 1,1-diphenyl-2-picrylhydrazyl (DPPH) were assessed using spectrophotometry, while vitamin C and β-carotene were analyzed using HPLC-PDA, and leaf mineral content was evaluated using ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry). The results show that the health benefits vary greatly owing to the particular culinary herb. The fresh leaf mass (yield) of coriander, parsley, and rocket was not significantly affected by the production system, whereas basil was high in soil cultivation, followed by GFT. Fennel had a high yield in the GFT system compared to in-soil and in-soilless cultivation. The highest levels of vitamin C were found in basil leaves grown in GFT and in soil compared to the soilless medium. The amount of total phenolic and flavonoid compounds, β-carotene, β-carotene-linoleic acid, and DPPH, were considerably high in soil cultivation, except on condensed tannins compared to the GFT and soilless medium, which could be a result of Photosynthetic Active Radiation (PAR) values (683 μmol/m²/s) and not favoring the accumulation of tannins. Overall, the mineral content was greatly influenced by the production system. Leaf calcium and magnesium contents were highly accumulated in rockets grown in the soilless medium and the GFT hydroponic system. The results have highlighted that growing environmental conditions significantly impact the accumulation of health-promoting phytonutrients in aromatic herbs. Some have positive ramifications, while others have negative ramifications. As a result, growers should prioritize in-soil production systems over GFT (under the shade-net) and soilless cultivation (under NTC) to produce aromatic herbs to improve the functional benefits and customer health. Full article

The shortage of freshwater resources has become the core bottleneck of global sustainable development. Traditional freshwater harvesting technologies are restricted by geographical conditions and environmental limitations, making them increasingly difficult to satisfy the growing water demand. In this study, based on the synergistic coupling mechanism of photothermal conversion and radiative cooling, a solar auto-tracking assisted selective solar absorber and radiative cooling all-weather freshwater harvesting device was innovatively developed. The prepared selective solar absorber achieved a high absorptivity of 0.91 in the solar spectrum (0.3–2.5 μm) and maintained a low emissivity of 0.12 in the mid-infrared range (2.5–20 μm), significantly enhancing the photothermal conversion efficiency. The radiative cooling film demonstrated an average cooling effect of 7.62 °C during typical daytime hours (12:00–13:00) and 7.03 °C at night (22:00–23:00), providing a stable low-temperature environment for water vapor condensation. The experimental results showed that the experimental group equipped with the solar auto-tracking system collected 0.79 kg m⁻² of freshwater in 24 h, representing a 23.4% increase compared to the control group without the solar auto-tracking system. By combining theoretical analysis with experimental validation, this study presents technical and economic advantages for emergency water and island freshwater supply, offering an innovative solution to mitigate the global freshwater crisis. Full article

Over the last decade, polymeric carbon nitrides (PCNs) have received exponentially growing attention as metal-free photocatalytic platforms for green energy generation and environmental remediation. Although PCNs can be easily synthesized from abundant precursors in a powdered form, progress in the field of photoelectrochemical applications requires effective methods for the fabrication of PCN films endowed with suitable mechanical stability and modular chemico-physical properties. In this context, as a proof-of-concept, we report herein on a simple and versatile chemical vapor infiltration (CVI) strategy for one-step PCN growth on porous Ni foam substrates, starting from melamine as a precursor compound. Interestingly, tailoring the reaction temperature enabled to control the condensation degree of PCN films from melem/melon hybrids to melon-like materials, whereas the use of different precursor amounts directly affected the mass and morphology of the obtained deposits. Altogether, such features had a remarkable influence on PCN electrochemical performances towards the oxygen evolution reaction (OER), yielding, for the best performing systems, Tafel slopes as low as ≈65 mV/dec and photocurrent density values of ≈1 mA/cm² at 1.6 V vs. the reversible hydrogen electrode (RHE). Full article

Most bioplastics are based on polysaccharides, which are either synthesized from a variously sourced monomer or extracted from some biomass waste. In many cases, some lignocellulosic fibers are then added to the obtained bioplastics to form biocomposites and extend their range of applications beyond packaging films and generically easily biodegradable materials. Plant-extracted tannins, which, as such, might also be building blocks for bioplastics, do nonetheless represent a useful complement in their production when added to polysaccharide-based plastics and biocomposites, since they offer other functions, such as bioadhesion, coloration, and biocidal effect. The variety of species used for tannin extraction and condensation is becoming very wide and is also connected with the local availability of amounts of bio-waste from other productions, such as from the food system. This work tries to summarize the evolution and recent developments in tannin extraction and their increasing centrality in the production of polysaccharide-based plastics, adhesives, and natural fiber composites. Full article

As a bio-based polymer, polybutylene succinate (PBS) has extensive applications in plastic products and film manufacturing. However, its low melt strength results in poor spinnability, and during the forming process, it tends to form large-sized spherulites and exhibit filament adhesion phenomena. These limitations have hindered its development in the field of fiber spinning. To enhance fiber strength, this work systematically investigated the effects of spinning temperature and spinning speed on the properties and structure of PBS pre-oriented yarns (PBS-POY). The results indicated that appropriately lowering the spinning temperature and increasing the spinning speed could improve the mechanical properties of the fibers. When the spinning temperature was 195 °C and the spinning speed reached 2500 m/min, the tensile strength of pre-oriented yarns achieved 2.09 cN/dtex. Furthermore, the evolution of properties and structures of pre-oriented yarns under maximum drawing conditions across different spinning speed systems was examined. By synchronously analyzing the correlations among mechanical properties, thermal behavior and condensed state structures, the structural performance regulation mechanism under the synergistic effect of spinning–drawing processes was revealed. The results demonstrated that fibers produced at higher spinning speeds contained more numerous and smaller spherulites. After maximum drawing, these smaller spherulites split into lamellae with higher uniformity, resulting in final fibers with smaller crystal sizes, higher crystallinity and improved orientation. As the spinning speed increased, the average crystal size of the final fibers decreased; the long period of the final fibers extended from 8.55 nm to 9.99 nm, and the mechanical strength improved to 2.72 cN/dtex. Full article

As desertification intensifies, greenhouses in arid regions are increasingly challenged by severe water scarcity and low water utilization efficiency. Traditional greenhouse HVAC systems are often inadequate in efficiently recovering condensate water. This study addressed these challenges by investigating, through wind tunnel experiments, the fin angle and inlet wind speed for optimal condensation and heat transfer performance of a straight-fin heat exchanger in desert greenhouse environments. The experimental findings revealed that under low-temperature conditions, vertical fins facilitated gravity-driven droplet removal, resulting in a maximum condensate amount of 524.2 g within 120 min. Conversely, under high-temperature conditions, a fin angle of 45° optimally balanced turbulent disturbances and liquid film stability, producing a condensate amount of up to 887.1 g in the same timeframe. Additionally, wind speed tests at a 45° fin angle identified a critical wind speed of 1.5 m/s, beyond which the condensate amount significantly decreased. Furthermore, when the fin inclination reached or exceeded 60°, flow separation occurred, reducing the effective heat transfer area and negatively impacting the exchanger efficiency. Overall, the study provides significant insights into water conservation and sustainable environmental utilization by enhancing condensate recovery efficiency. Full article

To address the challenge of heat transfer enhancement in the condensation of steam with non-condensable gases on a vertical wall under natural convection conditions, an improved boundary layer model with coupled multi-physics field was proposed in this paper, and traditional theoretical limitations were broken through by innovations. The particle swarm optimization algorithm was first introduced into the solution of the condensation boundary layer, and the convergence difficulty in the laminar–turbulent transition region under infinite boundary conditions was overcome. A coupled momentum–energy–mass equation system that simultaneously considered temperature–concentration dual-driven gravity terms and liquid film drag–suction dual effects was established, and higher computational efficiency and accuracy were achieved. A new mechanism where the concentration boundary layer dominated heat transfer resistance under the coupled action of the Prandtl number (Pr) and Schmidt number (Sc) was revealed. Experimental validation demonstrated that a prediction error of less than 5% was exhibited by the model under typical operating conditions of passive containment cooling systems (pressures of 1.5–4.5 atm and subcooling temperatures of 14–36 °C), and a theoretical tool for high-precision condensation heat transfer design was provided. Full article

When the vapour–gas mixture flow heats the cold walls of a heat exchanger, condensed phase (solid and liquid) precipitation can occur on their surfaces. This study aims to improve a model of thermohydraulic processes in a heat exchanger during condensed phase precipitation on its cold surfaces. The process is considered to occur when a multi-component solid-phase layer and a liquid film are simultaneously formed on the wall. Heat is transferred to the interface surface through radiation and convection and due to the phase transition of diffusing components. The mass flow to the interphase surface is determined for each diffusing component. The developed model allows for the calculation of heat transfer parameters in both steady-state and transient conditions, taking into account the formation of a multi-component condensed phase on cold walls. Full article

Despite great research effort in recent decades, cavitation in hydrodynamic journal bearings is still a not completely understood phenomenon. In particular, it is unclear which proportions of different cavitation types are present in a bearing. Novel experimental results show a clear deviation from the predictions of hydrodynamic lubrication theory. This article presents a new approach for modeling cavitation in hydrodynamic bearings by using computational fluid dynamics with the volume of fluid method and a phase of non-condensable gas in the lubrication oil. The validation of the model is achieved through the simulation of a large Offset-Halves Bearing and a subsequent comparison of the results with various experimental data, including the fractional film content. In the results, cavitation also occurs in the convergent gap due to a pressure drop caused by inertia forces. The findings indicate that the cavitation effects in oil-lubricated hydrodynamic bearings are caused by a special form of gaseous cavitation, designated as pseudo-cavitation. The presented model with non-condensable gas is able to reproduce the observed phenomena excellently. Full article

As global demand for energy-efficient cooling technologies grows, optimizing window air conditioners (WACs) is crucial. This study integrates computational fluid dynamics (CFD) and experimental fluid dynamics (EFD) to analyze condensate transport induced by the slinger ring in a WAC system. To investigate condensate behavior, the WAC domain is divided into six regions based on the slinger ring’s rotational direction and impact. In the initial impact zone, large liquid structures adhere to the slinger ring before breaking into ligaments. In the upward transport region, condensate films rise along the wall due to centrifugal forces, forming short ligaments. In the rebound region, condensate impacts the top surface and transitions into droplets. In the accumulation zone, droplet coalescence occurs in a confined space, leading to localized mass buildup. In the dispersion region, condensate spreads widely due to increased rotational speed. In the splash zone, splashing and wave-like structures form near the reservoir surface. A newly identified mechanism of condensate mass discharge shows that mass ejection is concentrated in four key regions near the condenser coils. These findings offer insights into optimizing a slinger ring design for improved condensate dispersion. Future research should explore airflow variations and alternative slinger ring configurations to enhance WAC performance. Full article

Polyimides (PIs), recognized for their exceptional thermal stability, are extensively employed in advanced applications, including aerospace, flexible displays, flexible solar cells, flame-retardant materials, and high-temperature filtration materials. However, with the continuous advancements in science and technology, the demand for improved thermal performance of PIs in these application areas has increased significantly. In this study, four spirobis(indene)-bis(benzoxazole) diamine monomers (5a, 5aa, 5b and 5bb) were designed and synthesized. These monomers were copolymerized with pyromellitic dianhydride (PMDA) and 4,4-diaminodiphenylmethane (ODA) to develop Kapton-type PIs. By varying the copolymerization molar ratios of the different diamines, a series of novel ultrahigh-temperature-resistant PI films were successfully prepared, and it was found that incorporating a highly rigid and twisted spirobis(indene)-bis(benzoxazole) structure into the PI matrix enhances the rigidity of the polymer chains and restricts their mobility, thereby significantly improving the thermal performance of the PI films. When 5a and ODA were copolymerized at molar ratios of 1:9 and 4:6, the glass transition temperature (T_g) of Kapton-type films significantly increased from 396 °C to 467 °C and >520 °C, respectively. These PI films also exhibit exceptional mechanical properties, with the modulus increasing from 1.6 GPa to 4.7 GPa, while demonstrating low dielectric performance, as evidenced by a decrease in the dielectric constant (D_k) from 3.51 to 3.08 under a 10 GHz high-frequency electric field. Additionally, molecular dynamics simulations were employed to further explore the relationships between polymer molecular structure, condensed states, and film properties, providing theoretical guidance for the development of polymers with ultrahigh thermal resistance and superior overall performance. Full article

Synthesis of uniform and stable electrochromic films on a conductive layer is one of the effective ways to construct high-performance electrochromic devices. The development of more convenient and feasible polymer film preparation technology is important and necessary. Herein, we demonstrated the development of a continuous in situ polymerization method to prepare electrochromic film on ITO glass through Schiff base condensation of a tetraamine Fe-based complex and organic di-/tri-aldehyde precursors. The electrochromic film was successfully coated on the surface of the ITO conductive layer and exhibited uniform morphology and excellent stability. Film P1 exhibited two reversible redox processes allowing two steps of electrochromic processes, including the oxidation of Fe(II) to Fe(III) at 1.05 V and oxidation of triphenylamine moieties to cation radicals at 1.4 V, which induced three stable color states from initial yellow to orange red and blue. The utilization of the so-formed polymer film for the fabrication of electrochromic devices gave rise to excellent electrochromic performance of fast response time of 0.4−1.2 s and high coloration efficiencies of 241.5−352.9 cm²/C at 1.9 V (at 535 nm) and 2.5 V (at 755 nm). The present work provides a new feasible strategy for constructing polymer films for high-performance electrochromic devices. Full article

Chemical sensors, relying on electrical conductance changes in a gas-sensitive material due to the surrounding gas, have the (dis-)advantage of reacting with multiple target gases and humidity. In this work, we report CMOS-integrated SnO₂ thin film-based gas sensors, which are functionalized with mono-, bi-, and trimetallic nanoparticles (NPs) to optimize the sensor performance. The spray pyrolysis technology was used to deposit the metal oxide sensing layer on top of a CMOS-fabricated micro-hotplate (µhp), and magnetron sputtering inert-gas condensation was employed to functionalize the sensing layer with metallic NPs, Ag-, Pd-, and Ru-NPs, and all combinations thereof were used as catalysts to improve the sensor response to carbon monoxide and to suppress the cross-sensitivity toward humidity. The focus of this work is the detection of toxic carbon monoxide and a specific hydrocarbon mixture (HC_mix) in a concentration range of 5–50 ppm at different temperatures and humidity levels. The use of CMOS chips ensures low-power, integrated sensors, ready to apply in cell phones, watches, etc., for air quality-monitoring purposes. Full article