Showing papers on "Nozzle published in 2019"

Helicon-type radiofrequency plasma thrusters and magnetic plasma nozzles

Abstract: Development of electrodeless radiofrequency plasma thrusters, e.g., a helicon thruster, has been one the of challenging topics for future high-power and long-lived electric propulsion systems. The concept simply has a radiofrequency plasma production/heating source and a magnetic nozzle, while it seems to include many aspects of physics and engineering issues. The plasma produced inside the source is transported along the magnetic field lines and expands in the magnetic nozzle, where the plasma is spontaneously accelerated into the axial direction along the magnetic nozzle, yielding a generation of the thrust force. Hence, the plasma transport and spontaneous acceleration phenomena in the magnetic nozzle are key issues to improve the performance of the thrusters. Since the thrust is equal in magnitude and opposite in direction to momentum flux exhausted from the system, the direct measurement of the thrust can reveal not only the thruster performance but also fundamental physical quantity of plasma momentum flux. Here studies on fundamental physics relating to the thruster development and the technology for the compact and efficient system are reviewed; the current status of the thruster performance is shown. Finally, a recently proposed future new application of the thruster is also discussed.

Influence of printing parameters on the stability of deposited beads in fused filament fabrication of poly(lactic) acid

Abstract: Fused Filament Fabrication (FFF) is one among a wide variety of processes of Additive Manufacturing. Similar to the others, FFF enables freeform fabrication and optimized structures, from. The aim of this work is to optimize the printing conditions in the FFF process based on reliable properties: printing parameters and physical properties of the polymer. The chosen polymer is poly(lactic) acid (PLA), a biodegradable thermoplastic polyester derived from corn starch and, as one of the most common polymers in the FFF process. the maximum inlet velocity of the filament in the liquefier is empirically determined according to process parameters such as the feed rate, the nozzle diameter and the dimensions of the deposited segment. Then, the rheological behavior of poly(lactic) acid including the velocity field, the shear rate and the viscosity distribution in the nozzle are determined by analytical study and numerical simulation. Our results show the variation of the shear rate according to the diameter of the nozzle and the inlet velocity. The shear rate reaches its maximum value for high inlet velocity and smaller diameters, near the internal wall. The distribution of the viscosity is obtained along the radius of the nozzle. For high inlet velocity, some defects appear at the surface of the extrudates. At highest shear rates, the extrudates undergo severe deformation microscopy. These results are valuable for choosing the printing parameters ( in order to improve the quality of the manufactured parts.

In-situ monitoring of polymer flow temperature and pressure in extrusion based additive manufacturing

Abstract: We demonstrate a novel Fused Filament Fabrication (FFF) nozzle design to enable measurements of in-situ conditions inside FFF nozzles, which is critical to ensuring that the polymer extrudate is flowing at appropriate temperature and flow rate during the part build process. Testing was performed with ABS filament using a modified Monoprice Maker Select 3D printer. In-situ measurements using the printer’s default temperature control settings showed an 11 °C decrease in temperature and significant fluctuation in pressure during printing as well as fluctuations while idle of ± 2 °C and ±14 kPa. These deviations were eliminated at lower flow rates with a properly calibrated proportional–integral–derivative (PID) system. At the highest tested flow rates, decreases in melt temperature as high as 6.5 °C were observed, even with a properly calibrated PID, providing critical insight into the significance of flow rate and PID calibration on actual polymer melt temperature inside the FFF nozzle. Pressure readings ranging from 140 to 6900 kPa were measured over a range of filament feed rates and corresponding extrusion flow rates. In-situ pressure measurements were higher than theoretical predictions using a power-law fluid model, suggesting that the assumptions used for theoretical calculations may not be completely capturing the dynamics in the FFF liquefier. Our nozzle prototype succeeded in measuring the internal conditions of FFF nozzles, thereby providing a number of important insights into the printing process which are vital for monitoring and improving FFF printed parts.

3D Extrusion Printing and Post-Processing of Fibre-Rich Snack from Indigenous Composite Flour

Abstract: This study focused on developing nutritious 3D-printed snacks from composite flour prepared from barnyard millet, green gram, fried gram, and ajwain seeds. The work evaluated extrusion printability of the high-fibre, high-protein composite flour. Optimised process parameters that gave best resolution and stability are nozzle diameter of 0.84 mm, nozzle height of 0.63 mm, printing speed of 2400 mm/min, extruder motor speed of 300 rpm, and movement speed of X/Y and Z axis of 6000 mm/min and 1000 mm/min, respectively. 3D-printed objects were post-processed by deep frying, hot-air drying followed by deep frying and microwave drying. With proximate analysis of the post-processed 3D-printed foods, we conclude that microwave drying could better retain nutrients, while ensuring minimal changes in colour and textural properties, as compared with other post-processing methods. All post-processed samples were acceptable in terms of sensory attributes; the developed snack has the potential to be commercialised. This work explains the successful development of nutritious 3D-printed snacks from diverse plant sources, importantly, with emphasis on the development of high-fibre foods with good consumer acceptance.

Propulsive Performance and Heating Environment of Rotating Detonation Engine with Various Nozzles

Abstract: Geometric throats are commonly applied to rocket combustors to increase pressure and specific impulse. This paper presents the results from thrust measurements of an ethylene/gas-oxygen rotating de...

Planar deposition flow modeling of fiber filled composites in large area additive manufacturing

Abstract: The rapid transition of the Fused Filament Fabrication (FFF) Additive Manufacturing (AM) process from small scale prototype models to large scale polymer deposition has been driven, in part, by the addition of short carbon fibers to the polymer feedstock. The addition of short carbon fibers improves both the mechanical and thermal properties of the printed beads. The improvements to the anisotropic mechanical and thermal properties of the polymer feedstock are dependent on the spatially varying orientation of short carbon fibers which is itself a function of the velocity gradients in the flow field throughout the nozzle and in the extrudate during deposition flow. This paper presents a computational approach for simulating the deposition flow that occurs in the Large Area Additive Manufacturing (LAAM) process and the effects on the final short fiber orientation state in the deposited polymer bead and the resulting bead mechanical and thermal properties. The finite element method is used to evaluate Stokes flow for a two-dimensional planar flow field within a Strangpresse Model 19 LAAM polymer deposition nozzle. A shape optimization method is employed to compute the shape of the polymer melt flow free surface below the nozzle exit as the bead is deposited on a moving print platform. Three nozzle configurations are considered in this study. Fiber orientation tensors are calculated throughout the fluid domain using the Folgar-Tucker fiber interaction model. The effective bulk mechanical properties, specifically the longitudinal and transverse moduli, and the coefficient of thermal expansion, are also calculated for the deposited bead based on the spatially varying fiber orientation tensors. Fiber orientation is found to be highly aligned along the deposition direction of the resulting bead and the computed properties through the thickness of the bead are found to be affected by nozzle height during deposition.

Three-dimensional numerical thrust performance analysis of hydrogen fuel mixture rotating detonation engine with aerospike nozzle

Abstract: The propulsive performance for an H2/O2 and H2/Air rotating detonation engine (RDE) with conic aerospike nozzle has been estimated using three-dimensional numerical simulation with detailed chemical reaction model. The present paper provides the evaluation of the specific impulse (Isp), pressure gain and the thrust coefficient for different micro-nozzle stagnation pressures and for two configurations of conic aerospike nozzle, open and choked aerospike. The simulations show that regardless of the nozzle, increase the micro-nozzles stagnation pressure increases the mass flow rate, the pre-detonation gases pressure and consequently the post-detonation pressure. This gain of pressure in the combustion chamber leads to a higher pressure thrust through the nozzle, improving the Isp. It was also found that the choked nozzle increases the chamber time-averaged static pressure by 50–60% compared with the open nozzle, inducing higher performance for the same reason explained before.

Spatial powder flow measurement and efficiency prediction for laser direct metal deposition

Abstract: Powder deposition is a critical element for coating and additive processes such as laser direct metal deposition. The flow rate and distribution of the powder affect the size of the deposited tracks and the total efficiency of the process. Therefore, knowledge of the three-dimensional shape of the powder flow and its relative position to the melt pool is crucial for any process modeling and enables an assessment of the nozzle design. Herein, a robust, industry-oriented method is proposed to measure and evaluate the 3D powder flow density from a nozzle, considering the effect of the base material. A setup was developed to measure the flow with high spatial and temporal resolution and to determine the position of the stream focus, laser beam, and tool axis. An algorithm correlates time-dependent measurement data with the spatial position of the stream, derives a volumetric distribution plot and predicts the catchment efficiency of the process considering any misalignment. The analysis of two nozzle designs reveals the influence of the powder distribution on the process capability to perform multi-layer additive manufacturing. A comparison between the predicted and actual powder catchment efficiency shows good correlation for varying standoff distances and melt pool sizes. The prediction was applied successfully by building a multi-layer structure with high geometric accuracy.

Nozzle external geometry as a boundary condition for the azimuthal mode selection in an impinging underexpanded jet

Abstract: The role of the external boundary conditions of the nozzle surface on the azimuthal mode selection of impinging supersonic jets is demonstrated for the first time. Jets emanating from thin- and infinite-lipped nozzles at a nozzle pressure ratio of is the nozzle exit diameter, are investigated using high resolution particle image velocimetry (PIV) and acoustic measurements. Proper orthogonal decomposition is applied to the PIV fields and a difference in dominant instability mode is found. To investigate possible explanations for the change in instability mode, additional nozzle external boundary conditions are investigated, including the addition of acoustic dampening foam. A difference in acoustic feedback path is suggested to be the cause for the change in dominant azimuthal modes between the flows. This is due to the thin-lip case containing a feedback path that is concluded to be closed exclusively by a reflection from the nozzle base surface, rather than directly to the nozzle lip. The ability of the flow to form a feedback path that maximises the impingement tone gain is discussed with consideration of the numerous acoustic feedback paths possible for the given nozzle external boundary conditions.

A dynamic model for current-based nozzle condition monitoring in fused deposition modelling

Abstract: 3D printing and particularly fused deposition modelling (FDM) is widely used for prototyping and fabricating low-cost customised parts. However, present fused deposition modelling 3D printers have limited nozzle condition monitoring techniques to minimize nozzle clogging errors. Nozzle clogging is one of the significant process errors in fused deposition modelling 3D printers, and it affects the quality of prototyped parts in terms of mechanical properties and geometrical accuracy. This paper proposes a dynamic model for current-based nozzle condition monitoring in fused deposition modelling, which is briefly described as follows. First, all the process forces in filament extrusion of the fused deposition modelling were identified and derived theoretically, and theoretical equations of the feed rolling forces and flow-through-nozzle forces were derived. In addition, the effect of the nozzle clogging on the current of extruding motor were identified. Second, based on the proposed dynamic model, current-based nozzle condition monitoring method was proposed. Next, sets of experiments on FDM machine using polylactic acid (PLA) material were carried out to verify the proposed theoretical model, and the results were analysed and evaluated. Findings of the present study indicate that nozzle clogging in FDM 3D printing can be monitored by sensing the current of the filament extruding motor. The proposed model can be used efficiently for monitoring nozzle clogging conditions in fused deposition modelling 3D printers as it is based on the fundamental process modelling.

Effect of Nozzle Port Angle on Transient Flow and Surface Slag Behavior During Continuous Steel-Slab Casting

Abstract: Undesirable flow variations can cause severe instabilities at the interface between liquid mold flux and molten steel across the mold top-region during continuous steel casting, resulting in surface defects in the final products. A three-dimensional Large Eddy Simulation (LES) model using the volume of fluid method for the slag and molten steel phases is validated with plant measurements, and applied to gain new insights into the effects of nozzle port angle on transient flow, top slag/steel interface movement, and slag behavior during continuous slab casting under nominally steady conditions. Upward-angled ports produce a single-roll flow pattern with lower surface velocity, due to rapid momentum dissipation of the spreading jet. However, strong jet wobbling from the port leads to greater interface variations. Severe level drops allow easy entrapment of liquid flux by the solidifying steel shell at the meniscus. Sudden level rises may also be detrimental, leading to overflow of the solidified meniscus region. Downward-angled ports produce a classic double-roll pattern with less jet turbulence and a more stable interface everywhere except near the narrow faces. Finally, the flow patterns, surface velocity, and level predicted from the validated LES model are compared with steady-state standard k-e model predictions.

Investigations on nozzle geometry in Fused Filament Fabrication

Abstract: This investigation focuses on geometric parameters of nozzles used in Fused Filament Fabrication. They are mainly responsible for the extrusion force. Therefore, the influence of the geometric parameters was investigated. Typical nozzles are made of brass and feature a decrease in diameter from an entry channel to a capillary with a conical section in between. At a fixed entry and capillary diameter, variable parameters are the angle of the conical section and the length of the capillary. Commercially available and custom nozzles with various of these parameters were investigated on a test stand using Polylactic Acid (PLA) filament. All nozzles exhibit a common behavior. The extrusion force rises linearly with increasing filament feed velocity. At a certain point the forces fluctuate and increase rapidly. Here, unmolten plastic reaches the nozzle. This characteristic is dependent on extrusion temperature and geometric parameters of the nozzles. A work envelope was defined; the lowest extrusion forces were found for a 56° conical section, but differences in force between the angles from 30° to 118° are low in comparison to the total extrusion force. Different capillary lengths were used to determine the entry pressure loss at different filament feed velocities. The material and coating of the nozzles had no significant influence on extrusion force. A higher thermal mass, two conical sections or two entry channels have a positive effect on extrusion forces and maximum filament feed velocities, thus maximal build rate.

GRCop-42 Development and Hot-fire Testing Using Additive Manufacturing Powder Bed Fusion for Channel-Cooled Combustion Chambers

Abstract: GRCop-42 is a high conductivity, high-strength dispersion strengthened copper-alloy for use in high heat flux applications such as liquid rocket engine combustion devices. This alloy is part of the family of NASA-developed GRCop, copper-chrome-niobium alloys. GRCop alloys were developed for harsh environments specific to regeneratively-cooled combustion chambers and nozzles with good oxidation resistance. Significant development was completed on the GRCop-84 and GRCop-42 alloys in the extruded wrought form demonstrating feasibility for combustion chambers. NASA has recently developed a process for additive manufacturing, specifically Powder Bed Fusion (PBF) or Selective Laser Melting (SLM), of GRCop-42 to establish parameters, characterize the material, and complete testing of components with complex internal features. This evolution of the GRCop-42 was based on the successful predecessor development work using GRCop-84 with the motivation of establishing a new copper-alloy option for use in NASA, government, and industry programs with SLM. A few advantages have been shown with the GRCop-42 that include higher conductivity and faster build speeds over the GRCop-84, and a simplified powder supply chain. Initial property development has shown that it is possible to produce high density builds with strengths equivalent to wrought GRCop-42 and a conductivity greater than GRCop-84. The GRCop-42 has completed process development and initial properties have been established. Several demonstrator combustion chambers have also been fabricated with the SLM GRCop-42 that include integral channels and closeouts. Additional test units have been fabricated and are completing substantial hot-fire testing to demonstrate performance of the material, process, and design.