An official website of the United States government
Aerosol jet printing (AJP) is a direct-write additive manufacturing technique used for producing high-resolution electronic components such as sensors, capacitors, and optoelectronic devices. The increasing adoption of AJP is attributed to its ability to precisely deposit conductive inks, such as silver nanoparticle-based inks, onto both rigid and flexible substrates. The AJP system comprises three core components: (i) the atomizer, (ii) the virtual impactor (VI), and (iii) the deposition head. The VI, situated between the atomizer and the deposition head, plays a critical role by separating aerosol particles based on their size. This aerodynamic separation ensures that only appropriately sized particles continue to the deposition head, directly influencing print resolution and quality. Despite the advantages of AJP, challenges remain related to process efficiency, repeatability, and print fidelity influenced by the VI. This research work contributes to addressing these issues by establishing a computational fluid dynamics (CFD) model to analyze the internal flow dynamics of the VI. The geometry of the VI, modeled in ANSYS Fluent using design data provided by Optomec (a manufacturer of AJP systems), includes the housing, stem, impactor, collector, and exhaust outlet. In this study, a zone-adapted mesh structure was generated to discretize the internal flow domain. The boundary conditions of the CFD model were set based on experimental observations. Pressure-based CFD formulation using Navier-Stokes equations was utilized to simulate incompressible, turbulent flows under steady-state conditions. The aim of this study is to investigate the effects of several design parameters on VI performance, including: (i) impactor-to-collector diameter ratio (IDtCDR), (ii) number of aerodynamic transport channels (pores), (iii) pore diameter, (iv) impactor length, and (v) collector length. The results of this study revealed that flow behavior in the virtual impactor (VI) is highly sensitive to geometric parameters, particularly the impactor-to-collector diameter ratio (IDtCDR), impactor length (IL), and collector length (CL). An IDtCDR of 0.5 results in backflow, low pressure, and a very high level of turbulence near the collector nozzle, while IDtCDR=1.0 (i.e., when the impactor and collector have equal diameters) provides uniform flow and optimal exhaust velocity. Increasing impactor length as well as collector length raises overall turbulence and pressure. In contrast, variations in the number and diameter of aerodynamic transport channels (ATC) have minimal influence on turbulence or pressure. Overall, this study provides new insights into the influence of geometric design on flow characteristics within the VI and establishes a foundation for optimizing AJP systems. By understanding how design parameters affect flow velocity, pressure distribution, and turbulence behavior, this work supports the advancement of consistent, high-performance AJP processes for the precise fabrication of next-generation electronic devices.
more »
« less
Experimental Analysis of a Particle Separator Design with Full-Field Measurements
Particle ingestion into turbine engines is a widespread problem that can cause significant degradation in engine service life. One primary damage mechanism is deposition of particulate matter in internal cooling passages. Musgrove et al. proposed a compact particle separator that could be installed between the combustor bypass exit and turbine vane cooling passage inlet. The design had small pressure losses but provided limited particle separation, and its performance has proved difficult to replicate in subsequent experiments. Borup et al recently developed a Magnetic Resonance Imaging (MRI) based technique for making full-field, 3D measurements of the mean particle concentration distribution in complex flows. A particle separator based on the Musgrove et all design was fabricated out of plastic using 3D printing. The primary difference from earlier designs was the addition of a drain from the collector, through which 3% of the total flow was extracted. The separator efficiency was measured at two Reynolds numbers, using water as the working fluid and 33 micron titanium microspheres to represent dust particles. Particle Stokes number was shown to play the dominant role in determining efficiency across studies. MRI was used to obtain the 3D volume fraction and 3-component velocity fields. The velocity data showed that flow was poorly distributed between the separator louvers, while the collector flow followed the optimal pattern for particle retention. The particle distribution data revealed that strong swirling flow in the collector centrifuged particles toward the outer wall of the collector and intro a partitioned region of quiescent flow, where they proceeded to exit the collector.
more »
« less
- Award ID(s):
- 1662422
- PAR ID:
- 10090511
- Date Published:
- Journal Name:
- ASME IGTI Turbo Expo 2019
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)To design and optimize arrays of vertical-axis wind turbines (VAWTs) for maximal power density and minimal wake losses, a careful consideration of the inherently three-dimensional structure of the wakes of these turbines in real operating conditions is needed. Accordingly, a new volumetric particle-tracking velocimetry method was developed to measure three-dimensional flow fields around full-scale VAWTs in field conditions. Experiments were conducted at the Field Laboratory for Optimized Wind Energy (FLOWE) in Lancaster, CA, using six cameras and artificial snow as tracer particles. Velocity and vorticity measurements were obtained for a 2 kW turbine with five straight blades and a 1 kW turbine with three helical blades, each at two distinct tip-speed ratios and at Reynolds numbers based on the rotor diameter $$D$$ between $$1.26 \times 10^{6}$$ and $$1.81 \times 10^{6}$$ . A tilted wake was observed to be induced by the helical-bladed turbine. By considering the dynamics of vortex lines shed from the rotating blades, the tilted wake was connected to the geometry of the helical blades. Furthermore, the effects of the tilted wake on a streamwise horseshoe vortex induced by the rotation of the turbine were quantified. Lastly, the implications of this dynamics for the recovery of the wake were examined. This study thus establishes a fluid-mechanical connection between the geometric features of a VAWT and the salient three-dimensional flow characteristics of its near-wake region, which can potentially inform both the design of turbines and the arrangement of turbines into highly efficient arrays.more » « less
-
Equilibrium theory of bidensity particle-laden suspensions in thin-film flow down a spiral separatorSpiral gravity separators are designed to separate multi-species slurry components based on differences in density and size. Previous studies [S. Lee et al., Phys. Fluids 26, 043302 (2014); D. Arnold et al., Phys. Fluids 31, 073305 (2019)] have investigated steady-state solutions for mixtures of liquids and single particle species in thin-film flows. However, these models are constrained to single-species systems and cannot describe the dynamics of multi-species separation. In contrast, our analysis extends to mixtures containing two particle species of differing densities, revealing that they undergo radial separation—an essential mechanism for practical applications in separating particles of varying densities. This work models gravity-driven bidensity slurries in a spiral trough by incorporating particle interactions, using empirically derived formulas for particle fluxes from previous bidensity studies on inclined planes [J. T. Wong and A. L. Bertozzi, Phys. D 330, 47–57 (2016)]. Specifically, we study a thin-film bidensity slurry flowing down a rectangular channel helically wound around a vertical axis. Through a thin-film approximation, we derive equilibrium profiles for the concentration of each particle species and the fluid depth. Additionally, we analyze the influence of key design parameters, such as spiral radius and channel width, on particle concentration profiles. Our findings provide valuable insights into optimizing spiral separator designs for enhanced applicability and adaptability.more » « less
-
Rotary Bell Atomizers (RBA) are extensively used as paint applicators in the automotive industry. Atomization of paint is achieved by a bell cup rotating at speeds of 40k-60k RPM in the presence of a background electric field. Automotive paint shops amount up to 70% of the total energy costs [Galitsky et. al., 2008], 50% of the electricity demand [Leven et. al., 2001] and up to 80% of the environmental concerns [Geffen et al., 2000] in an automobile manufacturing facility. The atomization process in an RBA affects droplet size and velocity distribution which subsequently control transfer efficiency and surface finish quality. Optimal spray parameters used in industry are often obtained from expensive trial-and-error methods. In this work, three-dimensional near-cup atomization (primary and secondary breakup) are simulated computationally using a high-fidelity volume-of-fluid transport scheme that includes an electrohydrodynamic effects. The influence of fluid properties (viscosity ratio, flow rate and charge density), nozzle rotation rate and bell potential on atomization are investigated by performing a parametric study. This cost-effective method of research aims to identify the ideal spray parameters to achieve maximum transfer efficiency.more » « less
-
We investigate particle acceleration in an MHD-scale system of multiple current sheets by performing 2D and 3D MHD simulations combined with a test particle simulation. The system is unstable for the tearing-mode instability, and magnetic islands are produced by magnetic reconnection. Due to the interaction of magnetic islands, the system relaxes to a turbulent state. The 2D (3D) case both yield −5/3 (− 11/3 and −7/3) power-law spectra for magnetic and velocity fluctuations. Particles are efficiently energized by the generated turbulence, and form a power-law tail with an index of −2.2 and −4.2 in the energy distribution function for the 2D and 3D case, respectively. We find more energetic particles outside magnetic islands than inside. We observe super-diffusion in the 2D (∼ t 2.27 ) and 3D (∼ t 1.2 ) case in the energy space of energetic particles.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- The DOI is not currently available.
