Article
Optimisation of a Side Inlet for H
2
Entry into an Ultrasonic
Spray Pyrolysis Device
Žiga Jelen, Domen Kandare, Luka Lešnik and Rebeka Rudolf *
Citation: Jelen, Ž.; Kandare, D.;
Lešnik, L.; Rudolf, R. Optimisation of
a Side Inlet for H
2
Entry into an
Ultrasonic Spray Pyrolysis Device.
Processes 2021, 9, 2256. https://
doi.org/10.3390/pr9122256
Academic Editors: Arkadiusz Gola,
Izabela Nielsen and Patrik Grznár
Received: 29 October 2021
Accepted: 10 December 2021
Published: 14 December 2021
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4.0/).
Faculty of Mechanical Engineering, University of Maribor, Smetanova ulica 17, 2000 Maribor, Slovenia;
z.jelen@um.si (Ž.J.); domen.kandare@gmail.com (D.K.); luka.lesnik@um.si (L.L.)
* Correspondence: rebeka.rudolf@um.si
Abstract:
An ultrasonic spray pyrolysis (USP) device consists of an evaporation and two reaction
zones of equal length, into which an aerosol with a precursor compound enters, and where nanopar-
ticles are formed in the final stage. As part of this research, we simulated the geometry of a side inlet,
where the reaction gas (H
2
) enters into the reaction tube of the device by using numerical methods.
Mixing with the carrier gas (N
2
) occurs at the entry of the H
2
. In the initial part, we performed a
theoretical calculation with a numerical simulation using ANSYS CFX, while the geometries of the
basic and studied models were prepared with Solidworks. The inlet geometry of the H
2
included a
study of the position and radius of the inlet with respect to the reaction tube of the USP device, as
well as a study of the angle and diameter of the inlet. In the simulation, we chose the typical flows of
both gases (N
2
, H
2
) in the range of 5 L/min to 15 L/min. The results show that the best geometry is
with the H
2
side inlet at the bottom, which the existing USP device does not allow for. Subsequently,
temperature was included in the numerical simulation of the basic geometry with selected gas flows;
150
◦
C was considered in the evaporation zone and 400
◦
C was considered in the other two zones—as
is the case for Au nanoparticle synthesis. In the final part, we performed an experiment on a USP
device by selecting for the input parameters those that, theoretically, were the most appropriate—a
constant flow of H
2
5 L/min and three different N
2
flows (5 L/min, 10 L/min, and 15 L/min). The
results of this study show that numerical simulations are a suitable tool for studying the H
2
flow in a
UPS device, as the obtained results are comparable to the results of experimental tests that showed
that an increased flow of N
2
can prevent the backflow of H
2
effectively, and that a redesign of the
inlet geometry is needed to ensure proper mixing. Thus, numerical simulations using the ANSYS
CFX package can be used to evaluate the optimal geometry for an H
2
side inlet properly, so as to
reconstruct the current and improve future USP devices.
Keywords:
USP device; H
2
; N
2
; gas mixing; computer fluid dynamics; fluid flow simulation;
ANSYS CFX
1. Introduction
Nanoparticles range in size from 0.1 nm to 100 nm, and gold nanoparticles have
recently been at the forefront of research. This is due to their different properties [
1
]
compared to bulk gold, which are known at the macro level. Gold nanoparticles have a
large surface area in terms of volume, so they are useful for many new applications. They
have functional properties, among which biocompatibility and catalytic activity make them
different from other metal nanoparticles [2,3].
Ultrasonic spray pyrolysis (USP) is a method of nanoparticle synthesis. Compared
to other methods (laser ablation [
4
], nanoemulsion [
5
], reduction in liquid [
3
]) it enables
the continuous synthesis of nanoparticles and represents a promising method for their
industrial production [
6
]. The existing USP device (Figure 1) [
7
], which has three tempera-
ture zones, allows for the controlled synthesis of metal nanoparticles on a laboratory scale.
They are synthesised by the transformation of the pre-prepared solution (the so-called
Processes 2021, 9, 2256. https://doi.org/10.3390/pr9122256 https://www.mdpi.com/journal/processes
