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1. Investigation of Virtual Impactor Design Parameters in Aerosol Jet Printing Using Computational Fluid Dynamics

   https://doi.org/10.1115/1.4068128  

   Sareen, Akashita; Hill, Curtis W; Salary, Roozbeh “Ross” (April 2025, Journal of Micro and Nano Science and Engineering)

   Dimov, Stefan; Zhang, TieJun (Ed.)

   Abstract Aerosol jet printing (AJP) is a direct-write additive manufacturing technique used to fabricate electronics, such as sensors, capacitors, and optoelectronic devices. It has gained significant attention in being able to utilize aerodynamic principles to deposit conductive inks (such as silver nanoparticle-based inks) onto rigid and flexible substrates. The aerosol jet printing system consists of three main components to execute the printing process: (i) the pneumatic atomizer, (ii) the virtual impactor, and (iii) the deposition head. The virtual impactor (VI) lies between the pneumatic atomizer and the deposition head, accepting the accelerated flow of differently sized aerosol particles from the pneumatic atomizer while acting as an “aerodynamic separator.” With the challenges associated with efficiency as well as resulting quality of the AJP process, the virtual impactor presents a unique opportunity to gain a deeper understanding of the component itself, aerosol particle flow behavior, and how it contributes to overall printing inefficiencies, poor repeatability, and resulting print quality. Broadly, this effort enables the expedited adoption of AJP in the electronics industry and beyond large scales. The challenges mentioned are addressed in this work by conducting a computational fluid dynamics (CFD) study of the virtual impactor to visualize fluid transportation and deposition under specific conditions. The objective of this study is to observe and characterize a single-phase, compressible, turbulent flow through the virtual impactor in AJP. The virtual impactor geometry is modeled in the ANSYS FLUENT environment based on the design by Optomec. The virtual impactor is assembled using a housing, collector, jet, stem, O-rings, and a retaining nut. Subsequently, a mesh structure is generated to discretize the flow domain. In addition, material properties, boundary conditions, and the relevant governing equations (based on the Navier–Stokes equations) are utilized to, ultimately, generate an accurate steady-state solution. The fluid flow is examined with respect to mass flow rates set at boundary conditions. The aerosol particles' interactions with the inner walls of the virtual impactor are observed. Particularly, an insight into the characteristics of aerosol particles entering the virtual impactor and their transition into a smoother flow before entering the deposition head is gained. Furthermore, the analysis provides an opportunity to observe fluid flow separation based on the design of the virtual impactor, one of its main functions in the AJP process. This exposes probable causes for inaccurate print quality, flow blockages, inconsistent outputs, process instability, and other material transport inefficiencies. Overall, this research work lays the foundation for improvements in the knowledge and performance of aerosol jet printing's virtual impactor toward optimal fabrication of printed electronics. 

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2. A Computational Fluid Dynamics Approach to Analyze the Virtual Impactor in Pneumatic Aerosol Jet Printing

   Sareen, Akashita (May 2025, Marshall Digital Scholar (https://mds.marshall.edu/etd/1940))

   Aerosol jet printing (AJP) is a 3D printing, advanced manufacturing process that generates an aerosol mist appropriate for fine printing small, low-volume electronic parts. The pneumatic aerosol jet printing technology’s virtual impactor is the focus of this study. In this technology, high velocity nitrogen gas aerosolizes various inks in the atomizer. The aerosolized stream of ink is then transported to a virtual impactor (VI) to become dense and concentrated as it begins to enter the deposition head for high precision electronics printing. AJP faces challenges in large-scale adoption due to challenges related to overspray, instability, ink clogging etc. There is discrepancy in the knowledge of the sources that cause such issues. Computationally simulating the pneumatic aerosol jet printing environment provides insights into unapparent ink flow behavior that may contribute to printing inefficiencies in the system. While the pneumatic atomizer and deposition head are sufficiently simulated and analyzed, the VI lacks the same focus. Therefore, simulating the VI environment provides a comprehensive understanding of the pneumatic AJP technology. This is accomplished by 3D computational fluid dynamics (CFD) modeling and simulation of the VI system in ANSYS Fluent. First, an initial characterization of the system is completed by creating a 3D CAD model based on x-ray images of the VI by Optomec and a subsequent CFD analysis using a turbulent k-epsilon model. Second, design investigations and corresponding CFD simulations are conducted by altering critical design parameters in the system such as the impactor and collector lengths, impactor to collector diameter ratio, and aerodynamic transport channels (ATC) count and diameter. The initial characterization study revealed that the VI experiences non-uniform flow removal, flow circulation, and increased EGF port velocity. 

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3. A Computational Analysis of Virtual Impactor Dynamics in Aerosol Jet Printing toward Optimal Direct-Write Fabrication of Printed Electronics

   Sareen, Akashita; Hill, Curtis W; Salary, Roozbeh “Ross” (July 2025, American Society of Mechanical Engineers (ASME) - International Mechanical Engineering Congress and Exposition (IMECE 2025))

   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. 

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4. A Computational Fluid Dynamics Investigation of Pneumatic Atomization, Aerosol Transport, and Deposition in Aerosol Jet Printing Process

   https://doi.org/10.1115/1.4049958  

   Salary, Roozbeh; Lombardi, Jack P.; Weerawarne, Darshana L.; Rao, Prahalada; Poliks, Mark D. (March 2021, Journal of Micro and Nano-Manufacturing)

   null (Ed.)

   Abstract Aerosol jet printing (AJP) is a direct-write additive manufacturing technique, which has emerged as a high-resolution method for the fabrication of a broad spectrum of electronic devices. Despite the advantages and critical applications of AJP in the printed-electronics industry, AJP process is intrinsically unstable, complex, and prone to unexpected gradual drifts, which adversely affect the morphology and consequently the functional performance of a printed electronic device. Therefore, in situ process monitoring and control in AJP is an inevitable need. In this respect, in addition to experimental characterization of the AJP process, physical models would be required to explain the underlying aerodynamic phenomena in AJP. The goal of this research work is to establish a physics-based computational platform for prediction of aerosol flow regimes and ultimately, physics-driven control of the AJP process. In pursuit of this goal, the objective is to forward a three-dimensional (3D) compressible, turbulent, multiphase computational fluid dynamics (CFD) model to investigate the aerodynamics behind: (i) aerosol generation, (ii) aerosol transport, and (iii) aerosol deposition on a moving free surface in the AJP process. The complex geometries of the deposition head as well as the pneumatic atomizer were modeled in the ansys-fluent environment, based on patented designs in addition to accurate measurements, obtained from 3D X-ray micro-computed tomography (μ-CT) imaging. The entire volume of the constructed geometries was subsequently meshed using a mixture of smooth and soft quadrilateral elements, with consideration of layers of inflation to obtain an accurate solution near the walls. A combined approach, based on the density-based and pressure-based Navier–Stokes formation, was adopted to obtain steady-state solutions and to bring the conservation imbalances below a specified linearization tolerance (i.e., 10−6). Turbulence was modeled using the realizable k-ε viscous model with scalable wall functions. A coupled two-phase flow model was, in addition, set up to track a large number of injected particles. The boundary conditions of the CFD model were defined based on experimental sensor data, recorded from the AJP control system. The accuracy of the model was validated using a factorial experiment, composed of AJ-deposition of a silver nanoparticle ink on a polyimide substrate. The outcomes of this study pave the way for the implementation of physics-driven in situ monitoring and control of AJP. 

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5. Image-Based Closed-Loop Control of Aerosol Jet Printing Using Classical Control Methods

   https://doi.org/10.1115/1.4043659  

   Lombardi, Jack P.; Salary, Roozbeh; Weerawarne, Darshana L.; Rao, Prahalada K.; Poliks, Mark D. (July 2019, Journal of Manufacturing Science and Engineering)

   Aerosol jet printing (AJP) is a complex process for additive electronics that is often unstable. To overcome this instability, observation while printing and control of the printing process using image-based monitoring is demonstrated. This monitoring is validated against images taken after the print and shown highly correlated and useful for the determination of printed linewidth. These images and the observed linewidth are used as input for closed-loop control of the printing process, with print speed changed in response to changes in the observed linewidth. Regression is used to relate these quantities and forms the basis of proportional and proportional integral control. Electrical test structures were printed with controlled and uncontrolled printing, and it was found that the control influenced their linewidth and electrical properties, giving improved uniformity in both size and electrical performance. 

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