Search Results (147)

Ice accretion from marine icing events accumulating on structures poses a significant hazard to ship and offshore operations in cold regions, being relevant for offshore activities like oil explorations, offshore wind, and shipping in arctic regions. The adhesion strength of such ice is a critical factor in predicting the build-up of ice loads on structures. While the adhesion strength of freshwater ice has been extensively studied, knowledge about sea spray ice adhesion remains limited. This study intends to bridge this gap by investigating the adhesion strength of sea spray icing under controlled laboratory conditions. In this study, we built a new in situ ice adhesion test setup and grew ice at −7 °C to −15 °C on quadratic aluminium samples of 3 cm to 12 cm edge length. The results reveal that sea spray ice adhesion strength is in a significantly lower range—5 kPa to 100 kPa—compared to fresh water ice adhesion and shows a low dependency on the temperature during the spray event, but a notable size effect and influence of the brine layer thickness on the adhesion strength. These findings provide critical insights into sea spray icing, enhancing the ability to predict and manage ice loads in marine environments. Full article

Evaporative cooling (EC) offers an energy-efficient alternative to direct expansion (DX) cooling but suffers from high water consumption. This limitation can be mitigated by pre-cooling incoming fresh air using cooler exhaust air via energy recovery. This study presents and optimizes a solar-driven EC system integrated with underfloor air distribution (UFAD) to enhance thermal comfort and minimize water use in a temporary office in Riyadh’s arid climate. A 3D CFD model was developed and validated against published data to simulate indoor airflow, providing data for thermal comfort evaluation using the predicted mean vote model in cases with and without energy recovery. A year-round hourly energy analysis revealed that the solar-driven EC-UFAD system reduces grid power consumption by 93.5% compared to DX-based UFAD under identical conditions. Energy recovery further cuts annual EC water usage by up to 31.3%. Operational costs decreased by 84% without recovery and 87% with recovery versus DX-UFAD. Full article

Atmospheric climate science lacks the capacity to integrate thermodynamics with the gravitational potential of air in a classical quantum theory. To what extent can we identify Carnot’s ideal heat engine cycle in reversible isothermal and isentropic phases between dual temperatures partitioning heat flow with coupled work processes in the atmosphere? Using statistical action mechanics to describe Carnot’s cycle, the maximum rate of work possible can be integrated for the working gases as equal to variations in the absolute Gibbs energy, estimated as sustaining field quanta consistent with Carnot’s definition of heat as caloric. His treatise of 1824 even gave equations expressing work potential as a function of differences in temperature and the logarithm of the change in density and volume. Second, Carnot’s mechanical principle of cooling caused by gas dilation or warming by compression can be applied to tropospheric heat–work cycles in anticyclones and cyclones. Third, the virial theorem of Lagrange and Clausius based on least action predicts a more accurate temperature gradient with altitude near 6.5–6.9 °C per km, requiring that the Gibbs rotational quantum energies of gas molecules exchange reversibly with gravitational potential. This predicts a diminished role for the radiative transfer of energy from the atmosphere to the surface, in contrast to the Trenberth global radiative budget of ≈330 watts per square metre as downwelling radiation. The spectral absorptivity of greenhouse gas for surface radiation into the troposphere enables thermal recycling, sustaining air masses in Lagrangian action. This obviates the current paradigm of cooling with altitude by adiabatic expansion. The virial-action theorem must also control non-reversible heat–work Carnot cycles, with turbulent friction raising the surface temperature. Dissipative surface warming raises the surface pressure by heating, sustaining the weight of the atmosphere to varying altitudes according to latitude and seasonal angles of insolation. New predictions for experimental testing are now emerging from this virial-action hypothesis for climate, linking vortical energy potential with convective and turbulent exchanges of work and heat, proposed as the efficient cause setting the thermal temperature of surface materials. Full article

In recent years, packed-bed systems have emerged as an attractive design for thermal energy storage systems due to their high thermal efficiency and economic feasibility. As integral components of numerous large-scale applications systems, packed-bed thermal energy stores can be successfully paired with renewable energy and waste heat to improve energy efficiency. An analysis of the thermal performances of two packed beds (hot and cold) during six-hour charging and discharging cycles has been conducted in this paper using COMSOL Multiphysics software, utilizing the optimal design parameters that have been determined in previous studies, including porosity (0.2), particle diameters (4 mm) for porous media, air as a heat transfer fluid, magnesia as a storage medium, mass flow rate (13.7 kg/s), and aspect ratio (1). The performance has been evaluated during both the charging and discharging cycles, in terms of the system’s capacity factor, the energy stored, and the thermal power, in order to understand the system’s performance and draw operational recommendations. Based on the results, operating the hot/cold storage in the range of 20–80% of the full charge was found to be a suitable range for the packed-bed system, ensuring that the charging/discharging power remains within 80% of the maximum. Full article

Modern energy storage systems for both power and transportation are highly related to lithium-ion batteries (LIBs). However, their safety depends on a potentially hazardous failure mode known as thermal runaway (TR). Predicting and classifying TR causes can widely enhance the safety of power and transportation systems. This paper presents an advanced machine learning method for forecasting and classifying the causes of TR. A generative model for synthetic data generation was used to handle class imbalance in the dataset. Hyperparameter optimization was conducted using Optuna for four classifiers: Support Vector Machine (SVM), Multi-Layer Perceptron (MLP), tabular network (TabNet), and Extreme Gradient Boosting (XGBoost). A three-fold cross-validation approach was used to guarantee a robust evaluation. An open-source database of LIB failure events is used for model training and testing. The XGBoost model outperforms the other models across all TR categories by achieving 100% accuracy and a high recall (1.00). Model results were interpreted using SHapley Additive exPlanations analysis to investigate the most significant factors in TR predictors. The findings show that important TR indicators include energy adjusted for heat and weight loss, heater power, average cell temperature upon activation, and heater duration. These findings guide the design of safer battery systems and preventive monitoring systems for real applications. They can help experts develop more efficient battery management systems, thereby improving the performance and longevity of battery-operated devices. By enhancing the predictive knowledge of temperature-driven failure mechanisms in LIBs, the study directly advances thermal analysis and energy storage safety domains. Full article

Cryosurgery employs extremely low temperatures to destroy abnormal or cancerous tissue. Conventional systems use cryogenic fluids like liquid nitrogen or argon, which pose challenges in handling, cost, and precise temperature control. This study explores thermoelectric (TE) cooling using the Peltier effect as an efficient alternative. A numerical optimization of multi-stage TE coolers using bismuth telluride (Bi₂Te₃) is performed through finite element analysis in COMSOL Multiphysics. Results show that the optimized multi-stage TE system achieves a minimum temperature of −70 °C, a 90 K temperature difference, and 4.0 W cooling power—outperforming single-stage (SS) systems with a maximum ΔT of 73.27 K. The study also investigates the effects of material properties, current density, and geometry on performance. An optimized multi-stage (MS) configuration improves cooling efficiency by 22.8%, demonstrating the potential of TE devices as compact, energy-efficient, and precise solutions for cryosurgical applications. Future work will explore advanced nanomaterials and hybrid systems to further improve performance in biomedical cooling. Full article

Cast iron is a longtime reliable material for the production of heat-treated stressed castings, i.e., those that are long, are cyclically heated, and heat-stressed. The durability of thermally stressed castings used in practice is dependent on the choice of the optimum chemical composition, metallurgy of production, macro- and microstructures, construction, and the way of exploitation. Today, the successful solution of this problem is dominated by simulation programs. The comprehensive analysis of heat stress is very important, i.e., the impacts of various physical quantities on its rise, progress, and size. This paper provides a comprehensive analysis of thermal stress mechanisms in gray iron castings, with a particular emphasis on the relationships between the material properties, microstructural characteristics, and component performance under thermal loading conditions. The theoretical foundations are complemented by experimental data, establishing practical guidelines for optimizing cast iron compositions and processing parameters for thermal applications. Full article

Based on the First and the Second laws of Thermodynamics the energy dissipated in engineering materials and structures is calculated in a multidimensional mechanics framework. The existing practice of computing the dissipated energy by the area of the stress-strain (or force-displacement) curve is objected to. The conditions under which the area of a stress-strain diagram correctly measures the dissipated energy are derived and clearly presented. A general mathematical form for the dissipated energy when those conditions are not satisfied is provided. An internal variables formulation is employed in this work. Erroneous results from the literature calculating the dissipated energy are given. Erroneous calculations are abundant in publications, Theses and Dissertations, books, and even engineering codes. The terms hysteresis and hysteretic loss are technically explained and their wrong use in cases other than in viscoelasticity is explicated. Full article

This study investigates the effects of varying hydrogen percentages in fuel blends on combustion dynamics, engine performance, and emissions. Experimental data and analytical equations were used to evaluate combustion parameters such as equivalent lambda, in-cylinder pressure, heat release rate, and ignition timing. The findings demonstrate that hydrogen blending enhances combustion stability, shortens ignition delay, and shifts peak heat release to be closer to the top dead center (TDC). These changes improve thermal efficiency and reduce cycle-to-cycle variation. Hydrogen blending also significantly lowers carbon dioxide (CO₂) and hydrocarbon (HC) emissions, particularly at higher blend levels (H0–H5), while lower blends increase nitrogen oxides (NO_x) emissions and risk pre-ignition due to advanced start of combustion (SOC). Engine performance improved with an average hydrogen energy contribution of 12% under a constant load. However, the optimal hydrogen blending range is crucial to balancing efficiency gains and emission reductions. These results underline the potential of hydrogen as a cleaner additive fuel and the importance of optimizing blend ratios to harness its benefits effectively. Full article

A crucial stage in the post-harvest processing of cocoa beans, drying, has a direct effect on the finished product’s quality and market value. This study investigates the efficiency, quality outcomes, and environmental implications of a mixed forced convection solar dryer designed for drying cocoa beans in Ntui, Cameroon, compared to traditional open-air drying methods. The solar dryer’s design, incorporating a solar collector, forced ventilation, and thermal storage, leverages local materials and renewable energy, offering an environmentally sustainable alternative by reducing fossil fuel reliance and post-harvest losses. Experimental trials were conducted to assess key drying parameters, including the temperature, relative humidity, water removal rate, pH, and free fatty acid (FFA) content, under the equatorial climate conditions of high solar irradiation and humidity. Results demonstrate that the solar dryer significantly reduces drying time from an average of 4.83 days in open-air drying to 2.5 days, a 50% improvement, while maintaining optimal conditions for bean quality preservation. The solar-dried beans exhibited a stable pH (5.7–5.9), a low FFA content (0.282% oleic acid equivalent, well below the EU standard of 1.75%), and superior uniformity in texture and color, meeting international quality standards. In contrast, open-air drying showed greater variability in quality due to weather dependencies and contamination risks. The study highlights the dryer’s adaptability to equatorial climates and its potential to enhance cocoa yields and quality for small-scale producers. These findings underscore the viability of solar drying as a high-performance, eco-friendly solution, paving the way for its optimization and broader adoption in cocoa-producing regions. This research contributes to the growing body of knowledge on sustainable drying technologies, addressing both economic and environmental challenges in tropical agriculture. Full article

In the age of widespread renewable energy integration, coal-fired power plants are transitioning from a primary baseload role to a more flexible peak-shaving capacity. Under frequent load changes, the thermal efficiency will significantly decrease. In order to achieve efficient dynamic operation, this study proposes a comprehensive mechanical model of a 300 MW drum-type boiler. Based on the Modelica/DYMOLA platform, the multi-domain equations describing energy and mass balance are programmed and solved. A comprehensive evaluation of the energy transformation within the boiler’s heat exchange components was performed. Utilizing the principles of exergy analysis, this study investigates how fluctuating operational conditions impact the energy dynamics and exergy losses in the drum and heating surfaces. Steady-state simulation reveals that the evaporator and superheater units account for 81.3% of total exergy destruction. Dynamic process analysis shows that the thermal inertia induced by the drum wall results in a significant delay in heat transfer quantity, with a dynamic period of up to 5000 s. The water wall exhibits the highest total dynamic exergy destruction at 9.5 GJ, with a destruction rate of 7.9–8.5 times higher than other components. Full article

Thermal modelling of additive manufacturing is a key method for furthering the quality of the components produced, as it allows for analysis that is not possible via experimental methods due to the difficulties involved with in situ monitoring. The thermal gradients present during the additive manufacturing process have a large impact on the formation of defects, such as porosity, residual stress, and cracking. The thermal gradients also have a large impact on material properties by controlling the microstructure formed. Thermal modelling methods are often based on numerical solutions of the heat conduction equation. Whilst numerical methods can be more accurate, they are often very slow because of the fine mesh requirements to capture high thermal gradients and iterative solvers to approximate the real-world solution to the required thermal field equations. An analytical model was developed to provide a fast solution to the problem. The analytical model used in this research was based on the Rosenthal equation and was analysed under a range of process parameters. A temperature-dependent Rosenthal model was also created with the aim of improving the results. The analytical model was then compared with a finite element numerical model to act as verification for the results. The analytical model accurately predicted the meltpool width over a range of process conditions. The analytical model underestimated the meltpool length compared to the numerical model, especially at high velocities. When using the standard Rosenthal model, the use of room-temperature or high-temperature thermal conductivities underestimated or overestimated the cooling rates from the meltpool, respectively. A temperature-dependent Rosenthal model was shown to produce more accurate cooling rates compared to the original Rosenthal equation. Full article

Passive solar desalination with no discharge promises great potential for sustainable desalination. Herein, we provide a comprehensive modelling scheme for the investigation of coupled heat and mass transport in passive desalination devices. Our modelling approach integrates mass, momentum, species, and energy transport models to study the coupled phenomena of wicking, solar-driven evaporation, and salt precipitation. Our numerical model can predict the impact of spatiotemporal variation in temperature, salt concentration, and wicking velocity on the evaporation flux and thermal efficiency of solar evaporators. The impact of the evaporator’s shape, solar flux, salt concentration, and light reflection by salt crystals has been studied on the evaporator’s performance. We observed a two-fold increase in evaporation flux when solar irradiance increases from 1000 W/m² to 2500 W/m². A reduction in the thermal efficiency of the evaporators is predicted at higher solar fluxes. The modelled evaporator can achieve an evaporation flux of over 0.5 kg/m²h under 1000 W/m² for 3.5 wt.% saline water. The salt concentration along the z-position of the evaporator exhibited a double arch-shaped profile, which influences its evaporation performance. These findings provide vital guidelines for the design of high-throughput solar desalination systems. Full article

Energy transition is a challenge for remote northern communities mainly relying on diesel for electricity generation and space heating. Solar-assisted ground-coupled heat pump (SAGCHP) systems represent an alternative that was investigated in this study for the Kuujjuaq Forum, a multi-activity facility in Nunavik, Canada. The energy requirements of community buildings facing a subarctic climate are poorly known. Based on energy bills, technical documents, and site visits, this study provided an opportunity to better document the energy consumption of such building, especially considering the recent solar photovoltaic (PV) system installed on part of the roof. A comprehensive model was developed to analyze the building’s heating demand and simulate the performance of a ground-source heat pump (GSHP) coupled with PV panels. The air preheating load, accounting for 268,200 kWh and 47% of the total heating demand, was identified as an interesting and realistic load that could be met by SAGCHP. The GSHP system would require a total length of at least 8000 m, with boreholes at depths between 170 and 200 m to meet this demand. Additional PV panels covering the entire roof could supply 30% of the heat pump’s annual energy demand on average, with seasonal variations from 22% in winter to 53% in spring. Economic and environmental analysis suggest potential annual savings of CAD 164,960 and 176.7 tCO₂eq emissions reduction, including benefits from exporting solar energy surplus to the local grid. This study provides valuable insights on non-residential building energy consumption in subarctic conditions and demonstrates the technical viability of SAGCHP systems for large-scale applications in remote communities. Full article

In this study, a thin film of silicon carbide (SiC) was deposited on a porous silicon (P-Si) substrate using pulsed laser deposition (PLD). The photo–electrochemical etching method with an Nd: YAG laser at 1064 nm wavelength and 900 mJ pulse energy and at a vacuum of 10⁻² mbar P-Si was utilized to create a sufficiently high amount of surface area for SiC film deposition to achieve efficient SiC film growth on the P-Si substrate. X-ray diffraction (XRD) analysis was performed on the crystalline structure of SiC and showed high-intensity peaks at the (111) and (220) planes, indicating that the substrate–film interaction is substantial. Surface roughness particle topography was examined via atomic force microscopy (AFM), and a mean diameter equal to 72.83 nm was found. Field emission scanning electron microscopy (FESEM) was used to analyze surface morphology, and the pictures show spherical nanoparticles and a mud-sponge-like shape demonstrating significant nanoscale features. Photoluminescence and UV-Vis spectroscopy were utilized to investigate the optical properties, and two emission peaks were observed for the SiC and P-Si substrates, at 590 nm and 780 nm. The SiC/P-Si heterojunction photodetector exhibited rectification behavior in its dark I–V characteristics, indicating high junction quality. The spectral responsivity of the SiC/P-Si observed a peak responsivity of 0.0096 A/W at 365 nm with detectivity of 24.5 A/W Jones, and external quantum efficiency reached 340%. The response time indicates a rise time of 0.48 s and a fall time of 0.26 s. Repeatability was assured by the tight clustering of the data points, indicating the good reproducibility and stability of the SiC/P-Si deposition process. Linearity at low light levels verifies efficient photocarrier generation and separation, whereas a reverse saturation current at high intensities points to the maximum carrier generation capability of the device. Moreover, Raman spectroscopy and energy dispersive spectroscopy (EDS) analysis confirmed the structural quality and elemental composition of the SiC/P-Si film, further attesting to the uniformity and quality of the material produced. This hybrid material’s improved optoelectronic properties, achieved by combining the stability of SiC with the quantum confinement effects of P-Si, make it useful in advanced optoelectronic applications such as UV-Vis photodetectors. Full article