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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. 

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. 

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 the 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 at 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. 

Thermoelectric generators are being used as a successful power sources for space applications since 1960's in radioisotope-thermoelectric generators (RTGs) to supply power to space systems in deep space. RTG’s are capable of directly converting heat energy to uninterrupted electric power with no moving parts involved. The ability of thermoelectric materials to convert heat energy to electrical energy is defined by a dimensionless value known as the thermoelectric figure of merit (ZT) 1. This value quantifies the maximum thermoelectric efficiency of a thermoelectric generator (TEG) and is calculated by ZT= S2σT/κ, where S, σ, T, and κ represent Seebeck coefficient, electrical conductivity, temperature, and thermal conductivity, respectively. Among all of the thermoelectric materials, Bi2Te3 and its alloys have been reported to have high ZT values for low temperature energy harvesting and are highly suitable for powering wearables and self-powering sensors2, 3.