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

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, the 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 AJP process. In pursuit of this goal, the objective is to forward a 3D compressible, turbulent, multi-phase 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 and also accurate measurements, obtained from 3D X-ray computed tomography (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 upon 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-? 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 were defined based on experimental sensor data, recorded from the AJP setup. The accuracy of the model was validated using a factorial experiment, composed of AJ-deposition of silver nanoparticles on a polyimide substrate. The outcomes of this study pave the way for the implementation of physics-driven in situ control of AJP.

Efficient Focusing of Aerosol Particles in the Microchannel under Reverse External Force: A Numerical Simulation Study

“…As a result, a stronger Saffman lift force pointing to the channel center was induced in the converging channel, which enhanced the lateral migration of the aerosol particle and led to a smaller focusing bandwidth. Figure 6 D,E shows that the lateral migration of the aerosol particle was further enhanced by the reverse external force, and the particle focusing bandwidth was ~8 μm, which is much smaller than the bandwidth achieved by the existing focusing methods [ 12 , 19 , 34 ] and commercial aerosol jet printing. The best focusing of the aerosol particle could be obtained by combining the converging geometry and the reverse external force, both of which increased the velocity difference between the aerosol particle and the gas.…”

“…The focusing performance of aerosol particles in the nozzle strongly depend on the flow conditions and the channel geometry [ 10 ]. Although these passive methods have the advantages of simple structure and easy operation, harsh flow conditions are often required to induce sufficient aerodynamic force [ 11 , 12 ]. For example, a gas velocity higher than 100 m/s is often needed for the focusing of the aerosol particles in the converging nozzle [ 3 , 13 ].…”

A hybrid multi-objective optimization of functional ink composition for aerosol jet 3D printing via mixture design and response surface methodology

“…It is important to select nanoparticle functional ink with high boiling point and high viscosity co-solvent for aerosol jet printing, which helps obtain printed lines with good edge definition by reducing the coffee ring effect. Moreover, due to the equipped ultrasonic atomizer, the range of viscosity for the adopted functional ink is limited 23 . On the other hand, it is essential to adopt single-walled CNTs with a low number of wall defects, otherwise the defect can cause deformation of the CNTs along the tube axis, which could be problematic during aerosol transportation.…”

Perspective Chapter: Advanced Manufacturing for Bone Tissue Engineering and Regenerative Medicine

“…It was observed that the transport of molten PCL through the micro-capillary nozzle (under a flow pressure of 550 kPa) would be a viscous flow having a Reynolds number ( Re ) of 1  , implied from Figure 4(c). This PME material deposition regime is unlike that of the other additive manufacturing processes, such as AJP, where material deposition is intrinsically turbulent [14,16,17].…”