The use of a guide-tube and bluff-body with an advanced atmospheric pressure plasma source is investigated for the low-temperature synthesis of single-crystalline high-density plasma polymerized pyrrole (pPPy) nano-materials on glass and flexible substrates. Three process parameters, including the position of the bluff-body, Ar gas flow rate, and remoteness of the substrate from the intense and broadened plasma, are varied and examined in detail. Plus, for an in-depth understanding of the flow structure development with the guide-tube and bluff-body, various numerical simulations are also conducted using the same geometric conditions as the experiments. As a result, depending on both the position of the bluff-body and the Ar gas flow rate, an intense and broadened plasma as a glow-like discharge was produced in a large area. The production of the glow-like discharge played a significant role in increasing the plasma energy required for full cracking of the monomers in the nucleation region. Furthermore, a remote growth condition was another critical process parameter for minimizing the etching and thermal damage during the plasma polymerization, resulting in single- and poly-crystalline pPPy nanoparticles at a low temperature with the proposed atmospheric pressure plasma jet device.
This work examines analytically the effects of non-Darcian and nonuniform permeability conditions on the natural convection from a vertical plate in porous media. The non-Darcian effects, which include the no-slip and inertia effects, decrease the flow and heat transfer rate, while the nonhomogeneity effect enhances the heat transfer. For packed spheres, in particular, the nonhomogeneity in permeability due to the packing of spheres near the solid wall results in a strong flow-channeling effect that significantly increases the heat transfer. The effect of transverse thermal dispersion is also examined. This dispersion effect causes an increase in the heat transfer.
Electrostatic spraying
is a method of atomizing a fluid using a
high voltage as an atomization auxiliary device, and various spraying
modes exist according to experimental parameters and viscosity. A
maximum of 11 spray modes were identified according to the changes
in the applied voltage and flow rate. To produce fine droplets and
a uniform size, which are the advantages of electrostatic spraying,
in this experiment, the Sauter mean diameter (SMD) and SMD distribution
were evaluated in each spray mode of electrostatic spraying. By comparing
the other spray modes with the cone jet mode, it was confirmed that
the maximum difference of the SMD was less than 1.5 times and the
standard deviation of the rotated and pulsed jets was 2.5 times or
more. In the cone shape range, the SMD and SMD distribution according
to the applied voltage confirmed that the droplet size was the smallest
in the middle of the cone jet mode, and the droplet distribution was
also narrow. In the cone jet mode, the droplet size increased linearly
with the viscosity and flow rate. In addition, the droplet distribution
range was distinctive depending on the type of fluid. In the case
of the relationship between the droplet size and current, it was proven
that the higher the viscosity, the higher the current value for the
same SMD; furthermore, the difference in the current–SMD increase
rate was insignificant. Through experiments, this work presents experimental
data of SMD, SMD distribution, and current–SMD in electrostatic
spray experiments under various conditions.
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