Development of a Semi-Empirical Model for Droplet Size Determination of a Three-Channel Spray Nozzle for Pellet Coating Based on the Optical Method Concept

The purpose of this study was to investigate the droplet size obtained with a three-channel spray nozzle typically used in fluid bed devices and to construct a semi-empirical model for prediction of droplet size. With the aid of a custom-made optical method concept, the impact of the type of polymer and solvents used through dispersion properties (viscosity, density, and surface tension), dispersion flow rate, atomization pressure, and microclimate pressure on droplet size was investigated. A semi-empirical model with adequate predictability for calculating the average droplet size (R2 = 0.90, Q2 = 0.73) and its distribution (R2 = 0.84, Q2 = 0.61) was constructed by employing dimensional analysis and design of experiments. Newtonian and non-Newtonian dispersion and process parameters on laboratory and on production scale were included, thereby enabling constant droplet size irrespective of the scale. Based on the model results, it would be possible to scale-up the atomization process (e.g., coating process) from laboratory to production scale in a systematic fashion, regardless of the type of solvent or polymer used. For the system investigated, this can be performed by understanding the dispersion properties, such as viscosity, density, and surface tension, as well as the following process parameters: dispersion flow rate, atomization, and microclimate pressure.

Identification of Buffer and Surface Traps in Fe-Doped AlGaN/GaN HEMTs Using Y21 Frequency Dispersion Properties

The buffer and surface trapping effects on low-frequency (LF) Y-parameters of Fe-doped AlGaN/GaN high-electron mobility transistors (HEMTs) are analyzed through experimental and simulation studies. The drain current transient (DCT) characterization is also carried out to complement the trapping investigation. The Y22 and DCT measurements reveal the presence of an electron trap at 0.45–0.5 eV in the HEMT structure. On the other hand, two electron trap states at 0.2 eV and 0.45 eV are identified from the LF Y21 dispersion properties of the same device. The Y-parameter simulations are performed in Sentaurus TCAD in order to detect the spatial location of the traps. As an effective approach, physics-based TCAD models are calibrated by matching the simulated I-V with the measured DC data. The effect of surface donor energy level and trap density on the two-dimensional electron gas (2DEG) density is examined. The validated Y21 simulation results indicate the existence of both acceptor-like traps at EC –0.45 eV in the GaN buffer and surface donor states at EC –0.2 eV in the GaN/nitride interface. Thus, it is shown that LF Y21 characteristics could help in differentiating the defects present in the buffer and surface region, while the DCT and Y22 are mostly sensitive to the buffer traps.

Improved wave dispersion properties in 1D and 2D bond-based peridynamic media

In this study, a novel method for improving the simulation of wave propagation in Peridynamic (PD) media is investigated. Initially, the dispersion properties of the nonlocal Bond-Based Peridynamic model are computed for 1-D and 2-D uniform grids. The optimization problem, developed through inverse analysis, is set up by comparing exact and numerical dispersion and minimizing the error. Various weighted residual techniques, i.e., point collocation, sub-domain collocation, least square approximation and the Galerkin method, are adopted and the modification of the wave dispersion is then proposed. It is found that the proposed methods are able to significantly improve the description of wave dispersion phenomena in both 1-D and 2-D PD models.