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This paper focuses on the modeling and analysis of a high-voltage layer heater (HVLH) designed for environmentally friendly vehicles, including electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs), through multiphysics simulations that cover electrical, thermal, and fluid dynamics aspects. Due to the significant expenses and extensive time needed for producing and experimentally characterizing HVLHs, simulation and physical modeling methods are favored in the development stage. This research pioneers the separate modeling of thermal boundary conditions for the heating element (TFE) within the electrical domain, enabling the calculation of Joule heating and the analysis of transient conjugate heat transfer. Moreover, this research initiates the application of transfer function modeling for the HVLH component, expanding its use to the broader context of heating, ventilation, and air conditioning (HVAC) systems. The simulation results, which include calculations for Joule heating and temperature fields based on input voltage and flow conditions, closely follow experimental data. The derived transfer function, along with the regression parameters, precisely predicts the dynamic behavior of the system. The simulation-based modeling approach presented in this study significantly advances the design and control of environmentally friendly electric heating systems, providing a sustainable and cost-effective solution.

We demonstrated conformal Al2O3 passivation via atomic layer deposition (ALD) of a flexible Ag network electrode possessing a high aspect ratio. The Ag network electrode passivated by the ALD-grown Al2O3 film demonstrated constant optical transmittance and mechanical flexibility relative to the bare Ag network electrode. Owing to the conformal deposition of the Al2O3 layer on the high aspect ratio Ag network electrode, the electrode exhibited more favorable stability than its bare Ag-network counterpart. To demonstrate the feasibility of Al2O3 passivation via ALD on a flexible Ag network, the performances of flexible and transparent thin-film heaters (TFHs) with both a bare Ag network and that passivated by ALD-grown Al2O3 were compared. The performance of Al2O3/Ag network-based TFHs was minimally altered even after harsh environmental tests at 85% relative humidity and a temperature of 85 °C, while the performance of bare electrode-based TFHs significantly deteriorated. The improved stability and reliability of the Al2O3/Ag network-based TFHs indicate that the ALD-grown Al2O3 film effectively prevents the introduction of moisture and impurities into the Ag network with a high aspect ratio. The improvement in the stability of the Ag network through Al2O3 passivation implies that the ALD-grown Al2O3 film represents a promising transparent and flexible thin film passivation material for high quality Ag network electrodes with high aspect ratios.

Nanocomposite multi-layer TiO2/V2O5/TiO2 thin films were prepared via electron-beam evaporation using high-purity targets (TiO2 and V2O5 purity > 99.9%) at substrate temperatures of 270 °C (TiO2) and 25 °C (V2O5) under a partial pressure of oxygen of 2 × 10−4 mbar to maintain the stoichiometry. Rutherford backscattering spectrometry was used to confirm the layer structure and the optimal stoichiometry of the thin films, with a particle size of 20 to 40 nm. The thin films showed an optical transmittance of ~78% in the visible region and a reflectance of ~90% in the infrared. A decrease in transmittance was observed due to the greater cumulative thickness of the three layers and multiple reflections at the interface of the layers. The optical bandgap of the TiO2 mono-layer was ~3.49 eV, whereas that of the multi-layer TiO2/V2O5/TiO2 reached ~3.51 eV. The increase in the optical bandgap was due to the inter-diffusion of the layers at an elevated substrate temperature during the deposition. The intrinsic, structural, and morphological features of the TiO2/V2O5/TiO2 thin films suggest their efficient use as a solar water heater system.

Solar water heaters (SWHs) are widely used in HVAC industries as well as in households for different heating purposes. The present numerical simulation focuses on the investigation of the thermo-hydraulic performance of novel semi-arc-rib SWHs. Semi-arc-shaped ribs in the square channel of the absorber plates with different pitch and height ratios are investigated in this study. The present novel modification disturbs the boundary layers by generating vortices, and thus, enhanced fluid mixing takes place. Water with a Reynolds number (Re) ranging from 4000 to 25,000 is used as a working fluid, and a 1.0 kW/m2 heat flux is imposed on the tube wall. The results demonstrate a significant increase in the Nusselt number (Nu) as the fluid layers localize behind each rib near the absorber plates, and at the same time, the number of swirls generated inside the tube and the frictional losses both increased noticeably. To ensure the effectivity of the present novel SWH geometry, the thermo-hydraulic performance (η) for each case was calculated, and it was found that in all the cases, it was greater than unity, which signifies that the present semi-arc-rib SWH is promising and can be used in HVAC industrial and household applications.

Conventional fuels can contribute to negative environmental repercussions, including climate change and destruction of the ozone layer. Solar energy-based water heating is one of the most sophisticated and cost-effective renewable energy systems. Despite their extensive use, flat plate solar collectors (FPSCs) have restricted thermal performance due to the inadequate thermal transfer properties of water as an operating fluid. This research addresses a significant gap in the experimental evaluation of uniformly shaped perforated wavy tapes integrated into flat plate solar collectors (FPSCs), which is a configuration that has been largely overlooked in the literature. The novelty of the present work is the comprehensive assessment of the system’s performance across six key metrics (6E)—energy, exergy, economic, environmental, exergoeconomic, and exergoenviroeconomic—through the integration of wavy tapes and three distinct novel tapes with different perforations of equilateral size (6, 9, and 12 mm). The experimental findings revealed that the heat transfer rates (Nu) of the FPSC with a PWT of 6 were greater than those of the WT, plain WT, 12 PWT, and 9 PWT by ratios of 21.32, 15.35, 9.35, and 6.25%, respectively. The average energy efficiency of the FPSC with a PWT of 6 is 47.5, 30.20, 18.93, and 10.87% greater than that without a WT, plain WT, 12 PWT, and 9 PWT, respectively. The average exergy efficiency was also greater by 67.31, 34.86, 17.49, and 24.49%, respectively. Moreover, the hot water production cost decreased by 26%, and CO₂ mitigation reached 27.62 tons/year on an energy basis—the highest among all the tested configurations. The exergoeconomic efficiency peaked at 13.2 kWh/$, underscoring the economic viability of the proposed design. This study not only demonstrates the thermoeconomic superiority of integrating 6 mm PWTs into FPSCs but also validates their potential to support sustainable energy policies through reduced carbon emissions and improved system efficiency. Graphical abstract Highlights A comprehensive 6E (energy, exergy, economic, environmental, exergoeconomic, and exergoenviroeconomic) analysis of a flat plate solar water heating system is conducted. The study investigates the effect of integrating wavy tapes and three different sizes of perforated wavy tapes (6, 9, and 12 mm) into the solar collector system. Daily energy efficiency increased by 47.5, 30.20, 18.93, and 10.87% in the 6 mm PWT system compared to other configurations. The average exergy efficiency of the system with 6 mm PWT was found to be 67.31, 34.86, 17.49, and 24.49% higher than the other studied cases. Economic analysis indicated that using 6 mm PWT reduces the cost per liter of hot water by 26, 14, and 7.62% compared to FPSC without tape, with plain WT, and with 9 mm PWT, respectively. Exergoeconomic analysis showed that FPSC with 6 mm PWT offers the highest performance with 13.2 KWh/$ compared to other configurations. Environmental analysis confirmed that FPSC with 6 mm PWT leads to the maximum reduction of CO₂ emissions over its operational life.

The study investigates the determination of selected fire properties of spruce wood, specifically the charring rate, using a modified testing method described and registered at the Industrial Property Office of the Slovak Republic PUV 50121-2020, utility model no. 9373. The samples were exposed to a square ceramic infrared heater, FTE-750W, with a power output of 750 W, using which we determined the heat flux as a function of voltage (V). Spruce wood specimens with dimensions of 75 mm × 75 mm × 50 mm (l × w × h) were subjected to thermal exposure under heat fluxes of 10, 15, 20, and 25 kW∙m−2. The charring rate was evaluated using two distinct approaches: the first method measured the thickness of the char layer formed after a duration of 1800 s, while the second method was based on reaching a temperature threshold of 300 °C. The findings demonstrated a positive correlation between the thermal load and the charring rate. The charring rates obtained using the first method ranged from 0.2397 to 0.6933 mm∙min−1, whereas those derived from the second method varied from 0 to 1.0344 mm∙min−1. This suggests that the 300 °C temperature criterion may not be a reliable parameter for calculating the charring rate. The precision of the results was corroborated through numerical simulations.

This study combines high-speed shadowgraph imaging with numerical simulations to systematically examine the effect of the annular air gap area on the spray combustion characteristics of an alcohol-liquid-oxygen-air tripropellant coaxial direct-flow injector in an air heater operating under a low chamber pressure of 1.2 MPa. The underlying mechanisms of ignition, flame structure, injector atomization, and combustion stability are analyzed in detail. Results show that the annular air gap area has a significant impact on flame morphology and combustion performance. When the air gap area is relatively large (corresponding to an annular gap spacing of 1.95 mm), an elongated attached flame forms, and ignition is completed within 19 ms. Although the short ignition time and favorable flame stability are advantageous, the combustion efficiency is relatively low (91%), and the nozzle and throat are prone to ablation. When the air gap area is moderate (1.41 mm spacing), a conical flame develops, exhibiting the longest ignition time (997.4 ms) and a stratified structure consisting of fuel-rich combustion at the core and fuel-lean combustion at the periphery. This configuration demonstrates good stability. When the air gap area is small (1.10 mm spacing), a lifted flame forms. Although mixing and ignition occur relatively quickly (around 386.4 ms), stability is poor, with large chamber pressure fluctuations and a high risk of extinction once the air velocity exceeds the critical threshold. Reducing the air gap area effectively shortens the liquid oxygen atomization distance by 50% and significantly improves evaporation efficiency; however, excessive reduction promotes ignition-quenching-reignition cycles and worsens flame instability. Further analysis indicates that flame stability is primarily governed by the ratio of injection velocity to flame propagation velocity. When this ratio exceeds a critical value, shear-layer instability arises, increasing the amplitude of chamber pressure fluctuations by up to 200%. This research provides a theoretical foundation for optimizing injector design and improving combustion stability control in air heaters. The insights gained are essential for enhancing ignition reliability and thermal protection in hypersonic applications.

The problem of modeling a flat rectangular channel of a solar water heater filled with water during its freezing is considered to estimate the stresses arising in the channel walls. A mathematical model of the deformation of the wall of such a channel during partial freezing of water in it is developed. The theory of elastic cylindrical bending of a two-layer plate is used for modeling. Calculation relationships are obtained for determining the stresses in the channel walls depending on the thickness of the freezing ice. An example of calculating the stresses in the channel walls during water freezing is given. Based on the calculation results, the stresses arising in the metal wall of the solar water heater channel during water freezing are determined.

In this study, an experimental outdoor investigation of the thermal efficiency and outlet air temperature was conducted on an unglazed, double-pass, solar air heater with a perforated absorber plate and packing wire mesh layers as a supplemental absorbent area. This was done to observe their effects on the thermal performance of the solar air heater. The double-pass collector was constructed with a bed height of 0.05 m, and a collection area of 1.5 m2. The height of the upper channel was fixed at 0.015 m to improve the thermal efficiency, and the outlet temperature at air flow rates between 0.003 and 0.018 kg/s. The collector was mounted with a slope of 42° facing south, to maximize the intensity of solar irradiance during winter. The effects of the air flow rate, ambient temperature, inlet temperature, outlet temperature, and solar intensity were experimentally investigated. The results showed that thermal efficiency could be improved by increasing the air flow rate, where the highest thermal efficiency achieved was 86% at 0.018 kg/s. However, the temperature difference was increased to a maximum value of 38.6 °C, when the air flow rate was decreased to 0.003 kg/s. Furthermore, the results demonstrated a significant improvement in the thermal efficiency and outlet temperature; and when compared with previous research, the experimental results and the predictions for the outlet temperature using the theoretical model agreed.

We have developed an all-electronic digital microfluidic device for microscale chemical synthesis in organic solvents, operated by electrowetting-on-dielectric (EWOD). As an example of the principles, we demonstrate the multistep synthesis of [18F]FDG, the most common radiotracer for positron emission tomography (PET), with high and reliable radio-fluorination efficiency of [18F]FTAG (88 ± 7%, n = 11) and quantitative hydrolysis to [18F]FDG (> 95%, n = 11). We furthermore show that batches of purified [18F]FDG can successfully be used for PET imaging in mice and that they pass typical quality control requirements for human use (including radiochemical purity, residual solvents, Kryptofix, chemical purity, and pH). We report statistical repeatability of the radiosynthesis rather than best-case results, demonstrating the robustness of the EWOD microfluidic platform. Exhibiting high compatibility with organic solvents and the ability to carry out sophisticated actuation and sensing of reaction droplets, EWOD is a unique platform for performing diverse microscale chemical syntheses in small volumes, including multistep processes with intermediate solvent-exchange steps.