Search Results (43)

This paper addresses the need for an integrated approach to develop an improved clam dredge system. Current designs often rely on empirical methods, resulting in a disconnect between theoretical models, computational simulations, and experimental validation. To bridge this gap, the study integrates computational fluid dynamics (CFD), experimental tests, and analytical methods to develop a clam dredge system. Firstly, the paper introduces an analytical tool that facilitates decision making by evaluating pump parameters, and to determine the operating point for various hose and nozzle parameters. This guides the parameter selection of pump, hose and jets for maximum performance. Secondly, CFD is utilized to analyze flow behavior, enabling the design of internal nozzle geometries that minimize head losses and maximize the scouring effect. A full-scale experimental measurement was conducted to validate computational results. Furthermore, a replica manifold is constructed using 3D printing and tested, demonstrating improvements in jet speed with both original and new nozzle designs. Analytical results indicate that increasing hose length reduces BHP, flow rate, and jet velocity, while increasing hose or jet diameter boosts BHP and flow but reduces jet speed due to pressure drops. Switching pumps reduced power consumption by 10.5% with minimal speed loss. The CFD analysis optimized nozzle design, reducing jet loss and enhancing efficiency. The proposed slit nozzle design reduces the loss coefficient by 85.24% in small-scale runs and by 83% in full-scale runs compared to the original circular jet design. The experiments confirmed the pressure differences between the CFD and experimental tests are within 10%, and demonstrated that rectangular jets increase speed by 9% and seafloor force by 19%. This paper improved the hydrodynamic design of the clam dredge system, and provides a framework for future dredge system designs. Full article

Wide-beam laser direct energy deposition (LDED) has been widely used due to its superior deposition efficiency. To achieve optimal laser-powder coupling, this technique typically employs rectangular powder nozzles. This study establishes a simulation model to systematically investigate the powder flow field characteristics of rectangular symmetric nozzles. Through parametric analysis of powder feeding rate, carrier gas flow rate, and shielding gas flow rate, the effects on powder stream convergence behavior are quantitatively evaluated to maximize powder utilization efficiency. Key findings reveal that, while the powder focal plane position is predominantly determined by nozzle geometry, powder feeding parameters exhibit negligible influence on flow field intersections. The resulting powder spot demonstrates a rectangular profile slightly exceeding the laser spot dimensions, and the powder concentration exhibits a distinctive flat-top distribution along the laser’s slow axis, contrasting with a Gaussian distribution along the scanning direction. Experimental validation through powder collection tests confirms strong agreement with the simulation results. Furthermore, a mathematical model was developed to accurately describe the powder concentration distribution at the focal plane. These findings provide fundamental theoretical guidance for optimizing powder feeding systems in wide-beam LDED applications. Full article

Fused Deposition Modeling (FDM) is widely used for custom manufacturing but has limitations in strength for load-bearing applications. This study explores the optimization of mechanical properties for lightweight, cost-effective components using continuous fiber reinforcement. ONYX polymer, reinforced with continuous fiberglass, was printed using the Markforged^® Mark Two dual nozzle 3D printer. A Design of Experimentation (DoE) based on a Taguchi L9 array was used, varying fiberglass content (10%, 20%, 30%), infill densities (30%, 40%, 50%), and pattern types (hexagonal, rectangular, Triangular). The results show that increasing fiberglass content, infill density, and using a rectangular pattern enhanced mechanical properties, with a 30% fiberglass addition achieving a 4.743-fold increase in Izod impact energy. The highest mechanical performance was obtained with 30% fiberglass, 50% infill density, and a rectangular pattern, yielding an impact energy of 1576.778 J/m, compressive strength of 29.486 MPa, and Shore D hardness of 68.135 HD. Full article

Ejectors, as widely utilized devices in the field of industrial energy conservation, exhibit a performance that is significantly affected by their structural parameters. However, the study of the influence of nozzle geometry parameters on asymmetric ejector performance is still limited. In this paper, the effect of the nozzle upper divergent angle on the operating characteristics of an asymmetric rectangular section ejector was comprehensively investigated. The results indicated that the entrainment ratio gradually decreased with an increase in the nozzle upper divergent angle, and the maximum decrease could be 20%. At the same time, the relationship between the upper and lower divergent angles was closely linked to the trend of change in the secondary fluid mass flow rate. The analysis of flow characteristics found that the deflection of the central jet was caused by the pressure difference between the walls of the upper and lower divergent sections of the nozzle. Additionally, quantitative analysis of the development of the mixing layer showed that the mass flow rate of the secondary fluid inlet was related to the development of the mixing boundary. Shock wave analysis demonstrated that the deterioration in ejector performance was due to the reduction in the shock wave strength caused by Mach reflection and the increase in the Mach stem height. Full article

Thermal management at a high heat flux is crucial for electronic devices, and jet impingement cooling is a promising solution. The heat transfer properties of a rectangular-finned heat sink are investigated under angled and multi-impingement jet configurations in this study. Experiments were conducted with three different nozzle diameters, three different heat sink angles, three dimensionless nozzle-to-heat sink distance ratios, and five different velocity values. As a result, the obtained data are presented as Nu-Re graphs, and the impacts of the parameters on heat transfer (HT) are analyzed. It is concluded that the Nusselt number increases with the increasing nozzle diameter and Reynolds number, whereas it decreases with increasing distance between the nozzle and the heat sink. When comparing the angle values under an identical flow velocity, nozzle diameter, and dimensionless h/d distance experimental conditions, it was found that the Nusselt numbers were very close to each other. Under constant heat flux and for all investigated angles, the highest Nusselt number for the rectangular-finned inclined heat sink was observed at a 10° heat sink inclination, a nozzle diameter of D = 40 mm, a dimensionless distance of h/d = 6, and a flow velocity of 9 m/s. This study deepens the understanding of the heat transfer mechanism of impinging jets and provides an efficient method framework for practical applications. Full article

This work explores a potential methodology for rectangular jet noise reduction that employs nozzle unsteady microjet excitation. Using high-fidelity computational studies and spectral analyses, major jet noise sources impacted by the applied actuation are identified. A heated supersonic rectangular jet is considered with a nozzle aspect ratio of 2:1 at a Mach number of 1.5. The current study essentially validates the hypothesis of a previous reduced-order analysis that predicted jet noise reduction through jet excitation at the harmonic or subharmonic of the dominant frequency associated with jets’ large-scale structures. Such noise reduction was attributed to the excitation-induced nonlinear energy exchange between the coherent modes. In the current study, the synthetic microjet actuation of the jet plume shear layer using $1\%$ of the jet mass flow rate is implemented at the excitation ports located at the nozzle lip and directed along the jet axis. A resulting jet noise reduction of up to 4 dB at the peak radiation angle is predicted. An analysis of the near-field Spectral Proper Orthogonal Decomposition (SPOD) results provides further insights into the impact of jet actuation on the modification of jet flow structures, thus addressing the effectiveness of the proposed noise control methodology. Full article

The current study explores the flowfield and noise characteristics of an ideally expanded supersonic (Mach 1.44) rectangular jet impinging on a flat surface. The existing literature is primarily concentrated on axisymmetric jets, known for their resonance dominance, pronounced unsteadiness, and acoustic signatures. In contrast, non-axisymmetric jets remain relatively less understood, particularly those impinging on a ground surface. By employing Schlieren imaging, high-frequency pressure measurements using high-bandwidth transducers, and particle image velocimetry (PIV), this research comprehensively examines the flow-acoustic phenomena. Schlieren imaging revealed distinct, coherent structures and strong acoustic waves, while pressure measurements at the impingement surface exhibited high-amplitude fluctuations, peaking at approximately 186 dB. Acoustic analysis identified multiple high-amplitude tones with unique directional characteristics, suggesting the potential for multiple simultaneous modes in rectangular jets. Furthermore, the PIV data elucidated differences in the jet shear layer and wall jet development attributed to the nozzle orientation. These findings contribute to a deeper understanding of non-axisymmetric jet behavior, offering insights relevant to fundamental flow physics and practical applications such as vertical takeoff and landing aircraft. Full article

The supersonic–supersonic ejector–diffuser system is employed to suck supersonic low-pressure and low-temperature flow into a high-pressure environment. A new design of a supersonic–supersonic ejector–diffuser was introduced to verify pressure control performance under different operating conditions and vacuum background pressure. A 1D analysis was used to predict the geometrical structure of an ejector–diffuser with a rectangular section based on the given operating conditions. Different numbers and types of nozzle plates were designed and installed on the ejector to study the realizability of avoiding or postponing the aerodynamic choking phenomenon in the mixing section. The effects of different geometrical parameters on the operating performance of the ejector–diffuser system were discussed in detail. Experimental investigation of the effects of different types of nozzle plates and the back pressures on the pressure control performance of the designed ejector–diffuser system were performed in a straight-flow wind tunnel. The results showed that the position, type and number of the nozzle plates have a significant impact on the beginning of the formation of aerodynamic choking. The geometry of the ejector and the operating conditions, especially the backpressure and inlet pressure of the ejecting stream, determined the entrainment ratio of the two supersonic streams. The experimental results showed that long nozzle-plate had a better performance in terms of maintaining pressure stability in the test section, while short a nozzle-plate had a better pressure matching performance and could maintain a higher entrainment ratio under high backpressure conditions. Full article

An approach for improving and maintaining a consistent weld quality of the deposited material during the FFF printing process is proposed. The approach is based on the analysis of the printing process thermal cycle and the real-time nozzle temperature control. The mathematical model of the FFF printing process has been developed with the use of real-time control in the algorithm of numerical implementation. The successful solution of the thermal conductivity problem made it possible to determine segment-wise heating settings for use during the printing process, resulting in a high and stable quality of welding. Comparison of the results of modeling with other well-known mathematical models of the FFF printing process and experimental results showed the adequacy of the proposed model. A maximum deviation of 17.7% between the simulation results and the thermography data was observed. The proposed model was verified using rectangular 3D polylactide shapes printed with and without regulation of the power of the heat source according to the previously estimated settings. The overall quality of regulation, stability of the system, and the PI coefficients of the controller were evaluated using a simulated model of the control system. The results of the experiment fully correspond with the modeling results. Full article

The determination of the critical ventilation flow rate is significant for risk control and standard development during accidental hydrogen leakage in a confined space with hydrogen-related equipment. This paper presents an analytical model for calculating the critical ventilation flow rate through the quantification and constraint solution of the ventilation effect and ventilation cost. The experimental method was used to investigate the effects of nozzle diameter and stagnation pressure on the diffusion and ventilation of horizontal hydrogen leakage in a cuboid chamber. Ventilations from 30 to 180 m³/h were carried out through the rectangular vent. It was shown that the peak concentration of the measuring point was positively correlated with the stagnation pressure and the nozzle diameter. The experimental data were used to verify the analytical model by calculating the effective ventilation time. This study demonstrates that the critical ventilation flow rate can be increased significantly at higher stagnation pressures and larger nozzle diameters. Furthermore, the discrepancy of critical ventilation flow rates under different nozzle diameters will be enhanced with the increase of stagnation pressure. For a stagnation pressure of 0.4 MPa, the critical ventilation flow rate under a 4 mm nozzle even increased by 52% relative to the 2 mm nozzle. Full article

This work examines the use of accelerometers to identify vibrational patterns that can effectively predict the state of a 3D printer, which could be useful for predictive maintenance. Prototypes using both a simple rectangular shape and a more complex Octopus shape were fabricated and evaluated. Fast Fourier Transform, Spectrogram, and machine learning models, such as Principal Component Analysis and Support Vector Machine, were employed for data analysis. The results indicate that vibrational signals can be used to predict the state of a 3D printer. However, the position of the accelerometers is crucial for vibration-based fault detection. Specifically, the sensor closest to the nozzle could predict the state of the 3D printer faster at a 71% greater sensitivity compared to sensors mounted on the frame and print bed. Therefore, the model presented in this study is appropriate for vibrational fault detection in 3D printers. Full article

Nowadays, since the air pollution problem is becoming global and denitrification is efficient to control nitrogen oxides, research and development of burners with low pollutant emissions in industries are urgent and necessary due to the increasingly severe environmental requirements. Based on the advanced CFD (computational fluid dynamics) numerical analysis technique, this work focuses on developing an industrial denitration-used burner, aiming to decrease the emission of nitrogen oxides. A burner with multiple ejectors is proposed, and the gas premixing and combustion process in the burner are systematically studied. Firstly, for the ejector, the well-known orthogonal experiment method is adopted to reveal the premixing performance under different structural parameters. Results show that the angle and number of swirl blades have significant effects on the $CO$ mixing uniformity. The $CO$ mixing uniformity first decreases and then increases with thr rising swirl blade angle, and it enhances with more swirl blades. Through comparison, a preferred ejector is determined with optimal structure parameters including the nozzle diameter of 75 mm, the ejector suction chamber diameter of 290 mm, the blade swirl angle of ${45}^{\circ }$, and the swirl blade number 16. And then, the burners installed with the confirmed ejector and two types of flues, i.e., a cylindrical and a rectangular one, are simulated and compared. The effects of ejector arrangements on the temperature distributions at the burner outlet are analyzed qualitatively and quantitatively. It is found that the temperature variances at the outlets of $R2$ and $C1$ are the smallest, respectively, $13.12$ and $23.69$, representing the optimal temperature uniformity under each type. Finally, the burner of the R2 arrangement is verified with a satisfied premixing performance and combustion temperature uniformity, meeting the denitration demands in the industry. Full article

Low-temperature food printing technology is used in many fields, such as personalized nutrition, cooking art, food design and medical nutrition. By precisely controlling the deposition temperature of the ink, a food with a finer and more controllable structure can be produced. This paper investigates the influence of nozzle temperature on printing performance via a numerical simulation and experimental research. The results indicate that the ink gradually changed from a granular state to a fLow-characteristic deposition structure when the nozzle temperature increased from 19 °C to 27 °C. When the nozzle temperature exceeded 21 °C, the ink demonstrated excellent extrusion behavior and tended to flow. The widths of the rectangular frame deposition showed no obvious changes and were 4.07 mm, 4.05 mm and 4.20 mm, respectively. The extrusion behavior of the ink showed a structural mutation in the temperature range of 19–21 °C. Its line width changed from 3.15 mm to 3.73 mm, and its deposition structure changed from a grainy shape to a normal shape. Under the influence of different environmental control capabilities, bulk structure deposition demonstrates an ideal printing performance at 21, 23 and 25 °C, and the latter temperature is more suitable in the case of large external interference. The ink flowed violently when the nozzle temperature reached 27 °C, at which point the deposit structure flowed and deformed seriously. On the other hand, evaporation losses had a strong effect on Low-viscosity ink. To reach the full potential of this promising technology, it is necessary to determine the effect of nozzle temperature on printing performance. This article provides a method for developing and applying Low-viscosity, Low-temperature food printing. Full article

Fiber-reinforced thermoplastics are an important construction material for lightweight applications. The increasing use of especially glass fiber-reinforced plastics leads to growing amounts of not recyclable composite materials, which is commonly disposed of by landfilling. Hence, there is a need for a recycling concept for glass-fiber-reinforced plastics that enables their complete reuse over many recycling cycles. In this paper, such a recycling concept is presented, which is based on the idea of melting the whole glass-fiber-reinforced component without prior size reduction. The fiber-reinforced melt will be pressed through a nozzle in order to achieve a strand with highly oriented fibers that can then be applied in new components via a tape-like laying process. The feasibility of the recycling concept is proved in this paper. Therefore, investigations on the reorientation of fibers in the melt by pressing through a rectangular nozzle have been carried out with different nozzle diameters, shear rates and melt temperatures. The investigations result in a stable process, which enables an increase in fiber orientation of about 37% up to a mean fiber orientation of 67% in the flow direction. These findings are independent of the initial fiber orientation. Full article

High-aspect-ratio (HAR) rectangular jets have attracted attention in automobile air conditioning (A/C) systems and turbulent jet applications owing to their excellent air delivery and mixing and attractive interior design. Active flow control (AFC) of rectangular jets using plasma actuators (PAs) has proven to be a promising technique because the actuator is simple, has low energy consumption, and can create flow features without interference. This research aims to understand the interaction between PAs and flow from a HAR rectangular nozzle using hot-wire anemometry, particle image velocimetry, and theoretical studies. Understanding how PAs affect the flow is beneficial for designing air vents to fit automobile A/C systems and various engineering applications by recreating the flow features with other AFC techniques and actuators. The combination of periodic excitation and vectoring effects transfers the flow’s mean energy to organized structures—known as spanwise vortexes—as large as 6 mm. The interaction between these coherent structures and the dissipative environment compresses the vortexes, resulting in the flow converging on the spanwise–streamwise (X–Z) plane and diverging on the transverse–streamwise (X–Y) plane. HAR rectangular jet flow features controlled by PAs can be predicted for specific cases by calculating the Strouhal number based on PA operating parameters. Full article