Search Results (6,408)

Unmanaged waste can cause environmental pollution, as well as hygiene and health problems. Sitimulyo Piyungan Bantul at the coordinates of −7.86409, 110.42888 was established in 1994 and is the final waste repository area in Yogyakarta, and it is now completely closed; consequently, causing joblessness in the surrounding community. There are activities that can be undertaken to recycle waste such as managing rubbish. Waste can be divided into four categories scrapping, composting, and producing maggot food. However, unmanaged and useful waste, namely, inorganic and hazardous waste, remains a big problem. This research work aims to solve the problem by re-engineering and making an initial simulation using computational fluid dynamics of an incinerator to complete unmanaged inorganic and hazardous rubbish. The incinerator was produced to process non-organic solid and medical waste, which should be combusted at temperatures higher than 800 °C to reduce combustible rubbish that can no longer be recycled, and toxic chemicals, to kill bacteria and viruses. The main incinerator frame is made of an iron elbow. Construction of the incinerator is divided into the chamber, recirculation zone, and chimneys. The wall of the incinerator machine is made of refractory stone and insulators. To measure and control the temperature, thermocouples and a thermocontrol are placed at the inner wall of the incinerator machine. The function of the incinerator machine was tested, and it ran normally. Initial operation of an incinerator for solid hazardous waste such as infusion bottles, pets, glass bottles, pampers, and expired medicines was undertaken. The performance showed that the achieved temperature was 705 °C during the process of the operation, and all of the hazardous waste became ash and the recycled material became a paving block that is economically worthwhile. Hence, the incinerator can be operated as a household industrial tool for a solid medical waste processing apparatus. An initial computational study of the incinerator was also carried out briefly using the student version of commercial software. Full article

The energy consumption pattern in the world, and in Indonesia today, is still dominated by fossil energy in oil, gas, and coal. It contradicts the reduced production of fossil energy, especially petroleum. Therefore, the government is trying to increase the role of new and renewable energy. One of the renewable energy sources that can be developed is wind energy. Indonesia has the potential for wind energy of 60.6 GW with an average wind velocity of 3–6 m/s. Given these conditions, it is expected that the installation of vertical axis wind turbines (VAWT) in buildings in urban areas and remote islands will be able to take advantage of the wind speed flowing above or beside buildings or skyscrapers, where the wind conditions do not have obstacles such as trees, houses, and so on. As a result, analysis and experimentation are required to design a wind turbine with good performance that can be used in cities or remote islands at relatively low wind speeds. The method used in this study is numerical analysis with computational fluid dynamics (CFD) with poly-hexacore meshing type, and the geometry sample is an H-Darrieus turbine. The input parameter is wind speed, which ranges from 2.5 to 9 m/s. The final goal of this study is to determine whether the CFD simulation modeling used is credible or valid. Full article

When a submarine moves near the free surface, the lift and drag characteristics that act on it are different compared to when in deep water; for example, waves on the free surface cause submarine motions that are not seen in deep water conditions and lead to changes in speed, fuel efficiency, safety, and maneuverability. To accurately predict the maneuverability of a submarine, it is necessary to consider how both maneuvering and seakeeping performance are affected by free-surface effects during the design stage. In this study, the unified maneuvering and seakeeping dynamic model is proposed. In the maneuvering performance analysis, hydrodynamic forces in the horizontal plane were calculated using STAR-CCM+. In the seakeeping performance analysis, the 6-DOF motions of the submarine and the mean wave drift forces in the horizontal plane were calculated using Ansys AQWA. Since the maneuvering motion component has a relatively long period and the seakeeping motion component has a relatively short period, the unified maneuvering and seakeeping dynamic model for a submarine moving near the surface was established using a two-time-scale approach. Using the established unified maneuvering and seakeeping dynamic model, turning circle simulations were performed in both calm water and in waves. In calm water, there were no significant differences as depth was varied. However, in irregular waves, significant differences were found in the trajectories and motion variables as depth varied. These findings underscore the necessity of accounting for sea surface conditions when operating near the free surface to ensure safety and avoid potentially hazardous scenarios during submarine operations. Full article

Windcatchers are effective passive ventilation systems, but their inability to actively reduce and stabilize supply air temperatures reduces indoor cooling performance. This study addresses this limitation by integrating encapsulated phase-change material tubes (E-PCM-Ts) into a solar fan-assisted, multidirectional windcatcher. The novelty lies in the vertical placement of E-PCM-Ts within the windcatcher’s airstreams, enhancing heat transfer and addressing challenges related to temperature stabilization and cooling. Using computational fluid dynamics (CFD) under hot outdoor conditions, the ventilation, cooling, and PCM thermal storage performance are evaluated based on two different E-PCM-T arrangements. Results showed a maximum air temperature drop of 2.28 °C at a wind speed of 1.88 m/s and wind angle of 0°. This offers an optimal temperature reduction that achieved a 6.5% reduction for up to 7 h of air temperature stabilization. Placing E-PCM-Ts in all airstreams improved the thermal storage performance of the windcatcher. A 50% increase in hybrid ventilation efficiency was also achieved when wind angles increased from 0° to 30°. Overall, the proposed system demonstrated superior performance compared to that of traditional windcatchers, delivering improved thermal energy storage and cooling efficiency and adequate hybrid ventilation with supply air velocities of 0.37–0.60 m/s. Full article

Organic Rankine cycles (ORCs) are increasingly employed in power plants to recover waste energy and reduce environmental impacts. The radial turbine, a critical ORC component, experiences flow losses influenced by design parameters such as the rotor blade and stator vane numbers. Traditional empirical correlations developed for air often lack accuracy for ORCs due to differences in fluid properties and flow dynamics. This study uses advanced CFD models to evaluate and refine these correlations for ORC applications. For the ORC, waste heat from the Ha’il Cement Company in Saudi Arabia is used as the heat source. The CFD model was validated with experimental data and showed strong agreement, with a maximum deviation of 5.12% in mass flow rate and 3.97% in turbine outlet temperature. The results show that reducing vane numbers from 17 to 11 increased turbine power, efficiency, and thermal efficiency by 34.8%, 4.17%, and 35.16%, respectively. However, further reduction caused performance deterioration due to high Mach numbers and flow recirculation. Increasing the rotor blade number to 20 improved performance, but numbers beyond 20 caused declines. Among empirical correlations, Rohlik’s correlation with 20 blades achieved optimal outputs of 13.54 kW turbine power, 75% turbine efficiency, and 6.98% thermal efficiency. Further optimization yielded an ORC configuration with 11 vanes and 20 blades, achieving superior performance: 16 kW turbine power, 77% turbine efficiency, and 9% thermal efficiency. Full article

Lymphatic malformations (LMs) are benign, congenital vascular anomalies caused by abnormal lymphangiogenesis during embryology, often presenting as fluid-filled cystic lesions. Though LMs can affect any part of the body except the brain, they primarily manifest in the head and neck or axilla regions of children. With a prevalence of approximately 1 in 4000 births, LMs are commonly diagnosed by age two, with symptoms varying based on lesion location and size. This paper reviews the classification of LMs and discusses the de Serres staging system, which aids in assessing prognosis based on lesion site. Mutations in the (PIK3CA) gene are implicated in most cases, and LMs are also associated with syndromic conditions like Turner and Noonan syndromes. They are diagnosed by ultrasound (USS) or magnetic resonance imaging (MRI), while a histologic analysis can confirm lymphatic origin. Treatment options range from conservative approaches, such as observation, to sclerotherapy, pharmacotherapy, and surgery. Sclerotherapy, particularly with agents like OK-432, bleomycin, and doxycycline, has shown significant efficacy in reducing LM size and symptoms with minimal side effects. Pharmacological therapies, such as sirolimus, that target the mTOR pathway are also increasingly being used, with a good effect on the burden of disease. While surgical excision remains a choice for symptomatic or large lesions, minimally invasive approaches are often preferred due to lower morbidity. Emerging techniques include gravity-dependent sclerotherapy, electrosclerotherapy, alpelisib, everolimus, and Wnt/β-catenin pathway stimulators (e.g., tankyrase inhibitors, porcupine inhibitors). Computational atomistic molecular dynamics (MD) and density functional tight binding (DFTB) techniques may offer an experimental approach to future therapeutic targets. This paper highlights a multidisciplinary approach to LM management, emphasising individualised treatment based on lesion characteristics and patient needs. Full article

The Sulige Gas Field is a typical low-permeability, low-pressure tight gas field, where pneumatic jetting is crucial for production. However, existing gas jet pumps have low efficiency, limiting field production and overall development. This paper explores the effect of adding water, at specific volume fractions, to the driving gas on pneumatic jet pump performance. Using Volume of Fluid (VOF) and Computational Fluid Dynamics (CFD) simulations, a three-dimensional fluid domain model was developed to analyze the flow field, turbulent kinetic energy, and energy conversion in the pump. Results show that the water volume fraction significantly impacts pump efficiency, with performance improving over natural gas as the driving medium. The optimal performance occurs at a 0.5 water volume fraction, with efficiency exceeding 40% and a dimensionless mass flow ratio of approximately 2.0. As the volumetric fraction of water increases, the optimal working point of the jet pump (the dimensionless mass flow ratio corresponding to the peak pump efficiency) gradually decreases. It drops from 2.0 at water volumetric fractions of 0.1 and 0.5, to 1.8 at 0.8, and further to 1.5 at 1.0. These findings provide valuable insights for optimizing pneumatic jet performance in the Sulige Gas Field. Full article

Nanofluids, with their enhanced thermal properties, provide innovative solutions for improving heat transfer efficiency in renewable energy systems. This study investigates a numerical simulation of bioconvective flow and heat transfer in a Williamson nanofluid over a stretching wedge, incorporating the effects of chemical reactions and hydrogen diffusion. The system also includes motile microorganisms, which induce bioconvection, a phenomenon where microorganisms’ collective motion creates a convective flow that enhances mass and heat transport processes. This mechanism is crucial for improving the distribution of nanoparticles and maintaining the stability of the nanofluid. The unique rheological behavior of Williamson fluid, extensively utilized in hydrometallurgical and chemical processing industries, significantly influences thermal and mass transport characteristics. The governing nonlinear partial differential equations (PDEs), derived from conservation laws and boundary conditions, are converted into dimensionless ordinary differential equations (ODEs) using similarity transformations. MATLAB’s bvp4c solver is employed to numerically analyze these equations. The outcomes highlight the complex interplay between fluid parameters and flow characteristics. An increase in the Williamson nanofluid parameters leads to a reduction in fluid velocity, with solutions observed for the skin friction coefficient. Higher thermophoresis and Williamson nanofluid parameters elevate the fluid temperature, enhancing heat transfer efficiency. Conversely, a larger Schmidt number boosts fluid concentration, while stronger chemical reaction effects reduce it. These results are generated by fixing parametric values as 0.1<ϖ<1.5, 0.1<Nr<3.0, 0.2<Pr<0.5, 0.1<Sc<0.4, and 0.1<Pe<1.5. This work provides valuable insights into the dynamics of Williamson nanofluids and their potential for thermal management in renewable energy systems. The combined impact of bioconvection, chemical reactions, and advanced rheological properties underscores the suitability of these nanofluids for applications in solar thermal, geothermal, and other energy technologies requiring precise heat and mass transfer control. This paper is also focused on their applications in solar thermal collectors, geothermal systems, and thermal energy storage, highlighting advanced experimental and computational approaches to address key challenges in renewable energy technologies. Full article

This paper presents an analysis of the dynamic characteristics observed and studied during the startup process of a gas foil radial bearing. It utilizes a comparison of both experimental data and three-dimensional fluid–solid interaction computational fluid dynamics simulations to investigate a gas foil bearing with three bump-type pads. The analytical model employs the fluid–structure interaction finite element method to examine the relationship between the components and the thin working fluid film within the bearing. This analysis was conducted under various operational conditions, including ambient pressure and temperature, shaft rotational speed, and the load applied to the shaft within the bearing. The foil structure of the bearing was modeled by representing the top and bump foils as a series of linear springs that are interconnected with the rigid housing. Meanwhile, the hydrodynamic pressure distribution acting on the top foil was modeled as a gas film operating under steady-state lubrication conditions. The comprehensive three-dimensional multi-physics model was developed using a commercial computer-aided engineering package, enabling independent finite element calculations for both fluid and solid domains. Following these calculations, the model exchanged analysis results across the interface between domains, allowing simulations to continue until the system achieved a quasi-steady state. An in-house experimental system was designed to evaluate the performance of the gas foil bearing under different working conditions, including the load applied to the shaft and the rotational speed. The experiment investigated the operational state of a gas foil radial bearing under ambient pressure (1 bar), ambient temperature (303 K), rotational speeds ranging from 1.5 to 9.5 krpm, and a load of 0.5602 kgw. Some operational conditions of the bearing were defined as boundary condition inputs for the simulation model. The model’s results, notably the predicted lift-off rotational speed of the bearing, show strong alignment with results from in-house experiments. Full article

The precision of simulation plays a pivotal role in determining the design parameters of the pressure pipe and distributor in a pneumatic centralized seeding system. This study adopted the discrete element method (DEM) to investigate wheat seed models and their motion characteristics within a pneumatic precision seed-metering device. Using Xinchun No. 6 wheat as the experimental subject, multi-sphere combination models (5, 7, 9, and 11 balls) were employed to describe the seed particle morphology. Moreover, by utilizing the coupling method of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD), along with bench tests, the air suspension velocity of seeds and the motion characteristics of the seed-supplying device were analyzed under different particle models. The physical properties of the wheat seeds were measured during the experiments. The simulation results indicated that, as the seed supply rate increased, the airflow velocity distribution within the model became more uniform, enhancing the stability of the suspension velocity. Comparisons between experiments and simulations validated the reliability of the particle models, with the minimum relative error in the suspension velocity determined as 0.21% for the 9-balls model. In addition, compared to the other models, the 9- and 5-balls models more accurately simulated the dynamic behavior of seeds within the seed-supplying device. For the 9-balls model, the relative error of particle velocity in the seed-supplying device is 1.39%, and, in the simulation of displacements in the X and Y directions of the seed-supplying device, the average error is 9.51%. The effectiveness of the multi-sphere combination models was verified, indicating their ability to accurately reflect the dynamic behavior of wheat seeds and improve the design and optimization efficiency of pneumatic precision seed-metering devices. Full article

Air pollution in urban street canyons presents a serious health risk, especially in densely populated areas. While previous research has explored airflow characteristics in these canyons, it often lacks detailed data on pollutant dispersion and the effects of wind speed on airflow patterns and vortex formation. This study uses Computational Fluid Dynamics (CFD) to deliver quantitative measurements of pollutant dispersion rates and qualitative insights into airflow patterns across various street canyon morphologies. The analysis examines a range of aspect ratios (ARs), from wide (AR = 0.75) to narrow (AR = 4.5), and different wind speeds to evaluate their effects on pollutant dispersion. Findings indicate that purging flow rates decline as the AR increases, with a more pronounced decrease at lower AR values. In narrower streets, airflow patterns are particularly sensitive to wind velocity, leading to unexpected vortices that hinder effective pollutant dispersion. By incorporating these insights into urban design strategies, cities can enhance street ventilation, thereby reducing pollutant concentrations and improving public health. This study also tests a specific street layout in Seville to predict pollutant accumulation under various conditions, assessing health risks based on World Health Organization guidelines. Ultimately, this research aids in developing healthier, more sustainable urban environments. Full article

Background: Numerical simulation is a technique that utilizes electronic computers to combine concepts of the discrete element method (DEM), finite element method (FEM), computational fluid dynamics (CFD), etc., and express simulated behaviors utilizing numerical computations and images. Compaction is the main process of tablet manufacturing; most of the current studies have focused on macroscopic compaction and tablet characterization, while the internal stress state and microstructure changes as a result of the compaction process are not well understood. Therefore, an in-depth understanding of the flow and compaction behavior of pharmaceutical powders is essential for the analysis and control of the compaction process. Methods: Current research shows that compaction is shifting from macroscopic behavior toward internal microscopic behavior using numerical simulation technology. Results: This review focuses on the application of various numerical simulation technologies during compaction and the contact model, or the constitutive equation commonly used in numerical simulation. In addition, the difficulties of numerical simulation technology in calibrating powder parameters and the limitations of the current research are also discussed. Conclusions: Numerical simulation research in medicine and other fields will continue to flourish as numerical simulation technology advances, attracting more and more researchers using it effectively. Full article

The present study investigates the effect of the passive jet control system on the performance of a vibration energy harvester system (VIVEHS). The shape of a bluff body plays a crucial role in determining the vortex shedding mechanism, while the passive jet control system influences the dynamic behavior of these vortices, either enhancing or suppressing the bluff body’s oscillatory performance. This study introduces key innovations, including the incorporation of perforations in the bluff body, variations in outlet angles, and different inlet and outlet configurations. In this regard, a two-dimensional numerical investigation has been carried out to understand and optimize the dynamic response from the bluff body and its effect on beam deflection. The validation of the numerical code has been carried out for a cylindrical shaped bluff body using ANSYS Fluent 23.2 numerical modelling software. Upon validation, the effects of a single inlet and a symmetrical dual outlet with different outlet angles are numerically analyzed under various flow conditions to assess their impact on the dynamic behavior of the system. The outlet angle varies between 30 degrees and 120 degrees with intervals of 30 degrees. The contours of vorticity and the bluff body dynamic characteristics were observed and plotted for various flow conditions ranging between 1 m/s and 8 m/s with intervals of 1 m/s. The results of this numerical study are crucial for designing passive jet control systems in practical energy harvesting applications. The optimization of outlet configurations and control strategies can significantly enhance both the efficiency and stability of energy harvesting systems. Full article

The temperature gradient inside a tundish leads to the uneven density distribution of molten steel, resulting in thermal buoyancy, which has a significant impact on the motion of inclusion particles. Based on practice data and necessary assumptions, a three-dimensional model of a tundish considering non-uniform thermal transfer was established. The flow and temperature distribution were studied, and the changes in inclusion removal rate were compared with different casting speeds and temperature reduction rates using computational fluid dynamics simulation. It was observed that, when the inlet temperature is higher, the molten steel floats up under the action of thermal buoyancy, which can form a horizontal stream behind the weir. While the inlet temperature is lower, the horizontal stream cannot be maintained, resulting in a decrease in the removal rate of inclusions. Increasing the casting speed will increase the velocity of the molten steel in the tundish, make it easier to shorten the temperature difference between the inlet and outlet, and reduce the removal rate of inclusions. When formulating production processes, the impact of thermal buoyancy on the flow field should be taken into account. Full article

Catalyst loss is a typical fault that impacts the long-term operation of the fluidized catalytic cracking (FCC) in the oil refining process. The FCC disengager is a critical place for separating the catalyst from oil gas. A fast and precise fault-cause judgment of catalyst loss is vital for avoiding catalyst loss failures. In this study, a novel fault judgment method of catalyst loss failures with quantitative criteria was established via the fault tree analysis (FTA) method, based on the relationship model between flow field signals and faults in the FCC disengager investigated by computational fluid dynamics (CFD). The FTA method defines three intermediate events: catalyst fragmentation, process fault and mechanical fault. In CFD results, it was found that the detailed fault reason can be inferred based on the changes in the characteristic parameters within the disengager. For example, when the catalyst loss rate of the FCC disengager may rapidly increase by a factor of around 200. Furthermore, the pressure drop of the cyclone separator decreases by around 35%, which indicates that the dipleg has fractured. The new fault judgment method has been applied in cases of catalyst loss in two industrial disengagers. The method accurately pinpointed the sudden reduction in inlet velocity and blockage fault at the cyclone separator as the main factors leading to catalyst loss faults, respectively. The judgment results are consistent with actual reasons, demonstrating the reliability of the method. This study could contribute to providing theoretical support and enhancing the accuracy for the diagnosis of catalyst loss faults, thereby ensuring the safe and stable operation of the FCC unit. Full article