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sustainability
Article
Research of Modified Atomizers and Their
Application for Moistening of Air-Cleaning
Device Charges
Pranas Baltr˙
enas and Edita Baltr˙
enait˙
e-Gedien˙
e *
Institute of Environmental Protection, Vilnius Gediminas Technical University, Saul˙
etekio al. 11,
Vilnius LT-10223, Lithuania; pranas.baltrenas@vgtu.lt
*Correspondence: baltrenaite@aol.com or gediene@vgtu.lt
Received: 13 September 2019; Accepted: 1 October 2019; Published: 6 October 2019
Abstract:
The size of sprayed droplets is a very important parameter that influences the operational
efficiency of air-cleaning device charges. It is desirable for atomizers to spray droplets that are
dispersed as much as technically and economically reasonable and possible. Fine dispersion spraying
ensures effective moistening of the air-cleaning device charges, as well as an optimal consumption of
water or other liquids. Three modifications of special atomizers were used for experimental analysis.
The atomization of liquid and spraying in the special atomizer occurs when two frontal streams
confront each other. Frontal streams are formed by an inner shield located in the special atomizer.
The experiment was conducted using different spraying pressures, namely: 6 bar, 4 bar, 2 bar. The
evaluation (performed using a microscope) of the size of sprayed droplets shows that the best (finest)
spraying was by the special atomizer of modification 3. The depth of the channel of the inner shield
is the parameter that has the biggest influence on the size of sprayed droplets. The special atomizer
of modification 3 produces droplets with the following size distribution and rates:
≤
0.05 mm—63.2
vol%; 0.2–0.6 mm—28.3 vol%; 0.6–1.0 mm—8.1 vol%; ≥1.0 mm—0.4 vol%.
Keywords: atomizer; air cleaning; modification; moisture
1. Introduction
Industry began cleaning air by a wet method using absorption as the key physical parameter from
1900 onwards [
1
]. Absorbers as waste air cleaning devices may be categorized as physical, chemical,
and biological absorbers, and are mainly used for the abatement of polar compounds. Biological
processes may be further categorized according to the amounts of water used for bioscrubbers (for polar
compounds; big amounts of water [
2
]), biotrickling filters (both for polar and lipophilic compounds;
moderate amounts of water [
3
]), and biofilters (mainly for lipophilic compounds and odor; low
amounts of water [
4
]). The biological processes underline the relevance of optimal spraying conditions,
both to the size of spray droplets to avoid an insufficient dispersion of the water phase as well as the
volume of the water phase sprayed in total. The efficiencies of (biological) waste air treatment may
severely depend on the techniques and the corresponding irrigation densities used [
5
,
6
]. Furthermore,
spraying technologies are commonly used to stabilize biomass in trickling filter processes [7].
Air-cleaning devices (or their charges) must be moistened constantly; namely, they must be
designed together with hydraulic systems [
8
]. The atomizer is one of the fundamental elements of
the hydraulic system. The atomizer is equipment that facilitates and enables spraying; namely, it is a
device that atomizes liquid by means of the peculiarities of its form [
9
]. The spraying—i.e., formation
of the initial droplets and their abruption—normally is regulated by the flow in the interior of the
atomizer [
10
,
11
]. The following actual droplet diameters (sizes) are predominant in the industrial area:
Sustainability 2019,11, 5522; doi:10.3390/su11195522 www.mdpi.com/journal/sustainability
Sustainability 2019,11, 5522 2 of 14
500
µ
m, 1200
µ
m, and 5500
µ
m [
12
]. Spraying, in case of insufficient dispersion, wastes the water, so it
is important to support optimal spraying. For the optimal moistening of charges used in air-cleaning
devices, it fully suffices to spray droplets of the middle size, i.e., with the diameter of 1200
µ
m. The
character of the spraying type depends on the sort of energy that is used for atomization of the liquid.
Such energy might be in the liquid itself: atomizers that are running by pressure or a.k.a. hydraulic
atomizers. In addition, energy might be mechanical (rotating or disk atomizers), electrical, or acoustic.
The six main types of the atomizers are described below. Pressure or hydraulic atomizers are such a
type of atomizers that are mostly used [
13
]. Pneumatic (or air) atomizers are pneumatic atomizers
(twin-fluid atomizers) that typically use the kinetic energy of pressurized gas that interacts with the
liquid surface to disintegrate the liquid. If the diameter of the air vent and tag angle of the atomizer
are increased [
14
], the rate of spraying will decrease. In twin-fluid atomizers, their spray is even. The
operating principle of rotary (or disk) atomizers is based on the interaction of a quickly rotating disk or
wheel with liquid, which is affected by the centrifugal force. Although the distribution of the sizes of
droplets that are sprayed by rotary atomizers are more equal than those by hydraulic atomizers [
15
], the
dependence on the energy of the rotary atomizers for one kilogram of liquid is repeatedly major [
16
].
Ultrasonic atomizers either directly use the acoustic energy in a gaseous atmosphere or indirectly use
the vibrational energy of an ultrasonic excitated surface. Within an electrostatic atomizer, an electrically
charged liquid is accelerated in an electric field, thereby forming an accelerating tiny liquid jet that
finally breaks down into fine droplets at the tip [
17
]. The main failing of spraying of such a type is that
mini fraction droplets might be received only in small quantities [
18
]. Monosize droplet generation
is developed in some fields of the industry, where sprayed droplets must be of equal size [
19
]. The
disturbance generates waves of uniform size that lead to the continuous breakup of the liquid jet into
identical droplets [20].
The emphasis in this article is on a hydraulic special atomizer and its spraying performance.
Droplets produced by this atomizer are made by the collision of two frontal streams. The said atomizer
must be called “special” by the reason that the usage of two advanced streams is to be regarded as a
new method to obtain spraying. Moreover, Lawrence and Wang together with other scientists [
21
]
abstracted on the following types of atomizers that are used in biotechnology: Berlin, Sacrament,
New York, and Dresden atomizers. According to the qualification of the atomizers made by the
scientists, this special atomizer will be called the Vilnius atomizer. In the process of selecting an
atomizer type, it is important to know what type of spraying is optimal, i.e., how the greatest effect can
be achieved with minimal consumption. The need to assess droplet size distribution is critical [
22
].
The types of spraying should be abstracted based on their specific parameters as follows: (1) hollow
cone, (2) double cone, and (3) plane spraying [
23
]. The hollow cone spraying is used where small
droplets and high efficiency are required. During double cone spraying, the surface is fully covered
with droplets of normal or of extensive size. Plane spraying is usually used as a “knife” of a plane,
strong, or tight stream—for example, in situations when paper mass is cut in paper plants. Spraying
velocity is very important for such a type of spraying [23].
The size of sprayed droplets is very important when selecting an atomizer [
22
]. The size of the
sprayed droplets depends on the characteristics of the liquid, the effectiveness of the atomizer, the
spraying pressure, and the spraying angle. The lesser the spraying pressure, the bigger the sprayed
droplets, and vice versa. The higher spraying pressure generates smaller droplets [12].
One of the important problems with the hydraulic atomizers spraying water is the wear and tear
of these atomizers (characteristic of abrasiveness) [
24
]. A typical symptom of the wear and tear of the
atomizer is the unacceptable growth of ineffectiveness caused by the erosion of the atomizer’s inner
structure [
25
]. The material of which the atomizer is made is very important for the functioning of the
atomizers. Nevertheless, the environment also greatly affects the development of corrosion [
26
]. Water
(liquid) that flows also contains various sediments and microorganisms; it may be the reason for the
stoppage of atomizers or pulling of the film, which worsens the effectiveness of the spraying [27].
Sustainability 2019,11, 5522 3 of 14
Air-cleaning equipment for which watering is required includes physical scrubbers (e.g.,
non-biological scrubbers) and biochemical reactors (e.g., biofilters, biotrickling filters, and bioscrubbers).
In the physical scrubbers, the liquid (water) gets into interaction with gas to absorb gas and solid
particles to increase their sedimentation [
8
,
28
]. Biofiltration uses microorganisms fixed to a porous
medium to break down the pollutants present in an air stream. Some form of water addition is used
to control the moisture content and add nutrients [
29
]. In biotrickling filters and bioscrubbers, gas
contaminants are absorbed in a free liquid phase prior to biodegradation by either suspended or
immobilized microorganisms [
30
]. The chemical effect (chemical reaction) and biochemical effect
(reaction catalyzed by enzymes) are favored by the presence of moisture.
In a biofilter during the air-cleaning process, the molecules of the supplied pollutant slowly move
across the charge. After the pollutants have migrated from the gaseous to the watery stage, they are
involved in fermentation, and are disrupted by microorganisms that are located inside the biofilter
charge [
31
]. The charge that is irrigated increases the aerodynamic resistance of the layers of the
biofilter. This reduces the time of the interaction between the pollutants and the microorganisms,
resulting in a reduction of cleaning efficiency [32].
It is evident that watering highly influences the effectiveness of cleaning in the process of using
air-cleaning technologies [
33
–
35
]. For this reason, research and analysis of the special atomizer, aimed
at decreasing the droplet size and increasing the distribution of the sprayed liquid, is described in
this paper.
The aim of this article is to examine the effectiveness of the atomizers of special structure and to
assess the suitability of the atomizers of the above-mentioned structure for watering the equipment for
clearing of the air.
2. The Research Methodology
The experiments for assessing the sizes of the droplets were performed in the Institute of
Environmental Protection at Vilnius Gediminas Technical University (Lithuania). The system of the
experiment included the experimental atomizer, which was connected to the water supply pipe by a
fenestrated hose. The highest pressure inside the water supply pipe was 6 bar. After the fenestrated
hose was connected, the pressure was changed with a connected manual valve (Figure 1).
Sustainability 2019, 11, x FOR PEER REVIEW 3 of 14
particles to increase their sedimentation [8,28]. Biofiltration uses microorganisms fixed to a porous
medium to break down the pollutants present in an air stream. Some form of water addition is used
to control the moisture content and add nutrients [29]. In biotrickling filters and bioscrubbers, gas
contaminants are absorbed in a free liquid phase prior to biodegradation by either suspended or
immobilized microorganisms [30]. The chemical effect (chemical reaction) and biochemical effect
(reaction catalyzed by enzymes) are favored by the presence of moisture.
In a biofilter during the air-cleaning process, the molecules of the supplied pollutant slowly
move across the charge. After the pollutants have migrated from the gaseous to the watery stage,
they are involved in fermentation, and are disrupted by microorganisms that are located inside the
biofilter charge [31]. The charge that is irrigated increases the aerodynamic resistance of the layers of
the biofilter. This reduces the time of the interaction between the pollutants and the microorganisms,
resulting in a reduction of cleaning efficiency [32].
It is evident that watering highly influences the effectiveness of cleaning in the process of using
air-cleaning technologies [33–35]. For this reason, research and analysis of the special atomizer, aimed
at decreasing the droplet size and increasing the distribution of the sprayed liquid, is described in
this paper.
The aim of this article is to examine the effectiveness of the atomizers of special structure and to
assess the suitability of the atomizers of the above-mentioned structure for watering the equipment
for clearing of the air.
2. The Research Methodology
The experiments for assessing the sizes of the droplets were performed in the Institute of
Environmental Protection at Vilnius Gediminas Technical University (Lithuania). The system of the
experiment included the experimental atomizer, which was connected to the water supply pipe by a
fenestrated hose. The highest pressure inside the water supply pipe was 6 bar. After the fenestrated
hose was connected, the pressure was changed with a connected manual valve (Figure 1).
Figure 1. Scheme of the experiment: 1—the arm of the water supply system; 2—fenestrated hose; 3—
manometer; 4—manual valve; 5—experimental atomizer; 6—atomization (spraying); 7—the affected
surface.
The water was sprayed upon a square with dimensions of 3 cm × 3 cm (Figure 2); additionally,
it was divided into nine smaller squares of 1 × 1 cm in order to determine the sizes of droplets more
accurately. A smaller square that was made of plastic of blue color was used for insulation of the live
wires. Such material was selected because it is waterproof. Moreover, its surface was matted and
nonslip, so when the droplets fall on such a surface, they do not change their form. The atomizer was
removed from the affected surface at a distance of 60 cm.
Figure 1.
Scheme of the experiment: 1—the arm of the water supply system; 2—fenestrated hose;
3—manometer; 4—manual valve; 5—experimental atomizer; 6—atomization (spraying); 7—the
affected surface.
The water was sprayed upon a square with dimensions of 3 cm
×
3 cm (Figure 2); additionally,
it was divided into nine smaller squares of 1
×
1 cm in order to determine the sizes of droplets more
accurately. A smaller square that was made of plastic of blue color was used for insulation of the live
wires. Such material was selected because it is waterproof. Moreover, its surface was matted and
nonslip, so when the droplets fall on such a surface, they do not change their form. The atomizer was
removed from the affected surface at a distance of 60 cm.
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Figure 2. Positions of sheets (sizes in cm).
The affected surface (Figures 1–7) was a sheet of organic glass with dimensions of 100 × 100 cm,
onto which water was sprayed. Organic glass does not absorb water; consequently, the sizes of the
droplets do not change after spraying.
2.1. The Course of the Experiment
The affected surface that was a sheet of organic glass (the size of 100 × 100 cm) was prepared.
Three small squares the size of 3 × 3 cm were placed on the sheet: (1) at the center of the sheet; (2) at
the periphery of the sheet that was 25 cm from the center; and (3) at the periphery of the sheet that
was 35 cm from the center. Figure 2 represents the scheme of the position of the sheets. Such a pattern
of locating was selected because the dispersion and concentration of the droplets change when
receding from the center. Then, the valve of the water supply pipe was opened. The desirable
pressure was established by positioning the valve. The experiments were performed at the following
three different pressures: 6 bar, 4 bar, and 2 bar.
The valve that was located before the atomizer (Figure 1) was checked for control purposes, and
then whether the pressure inside the fenestrated hose was proper was checked as well. It was also
checked whether everything was hermetic, and if not, whether everything was clamped with clips.
Control spraying was performed into a plastic pail of 12 L. After we were sure that everything was
operating acceptably (everything was hermetic and proper pressure was established), the valve was
closed (Figures 1–4), and the conclusion was that we were ready for the experiment.
The distance (60 cm) from the prepared affected surface was measured by use of a belt ruler. The
atomizer was kept above the center of a sheet of organic glass of 100 × 100 cm. Three small plastic
squares the size of 3 × 3 cm were placed onto the organic glass in such an arrangement as in Figure 2.
After the position of the atomizer above the affected surface (at the center) was fixed, the manual
valve was opened and closed by a sudden movement (see Figure 1); the jet released in this way was
sprayed and reached the affected surface. After the jet was sprayed, we used tweezers to take each of
the samples, i.e., small squares (size of 3 × 3 cm). We took pictures of them and then carried them to
the laboratory for microscope testing.
Then, we entered the number of droplets into a table, grouping droplets by size into four sizes:
0.05 mm, 0.2 mm, 0.6 mm, and 1 mm. The size of the droplets was established using the scaled ruler
located in the spyglass of the microscope.
The experiment was repeated n times. In this case, we repeated the experiment three times when
at least one of the parameters (pressure, peculiarity of structure, etc.) changed. Then, we calculated a
part of the droplets of the respective fraction during each experiment according to Equation (1):
𝑁𝑞𝑝,% =𝑛𝑞𝑝
∑𝑛𝑞𝑝
×100, %
(1)
where Nqp,% is the part of qp droplets of the respective fraction in percent as compared to the number
of all droplets, vol%; qp is the droplets fraction at the corresponding pressure; nqp is the number of qp
Figure 2. Positions of sheets (sizes in cm).
The affected surface (Figures 1–7) was a sheet of organic glass with dimensions of 100
×
100 cm,
onto which water was sprayed. Organic glass does not absorb water; consequently, the sizes of the
droplets do not change after spraying.
2.1. The Course of the Experiment
The affected surface that was a sheet of organic glass (the size of 100
×
100 cm) was prepared.
Three small squares the size of 3
×
3 cm were placed on the sheet: (1) at the center of the sheet; (2) at the
periphery of the sheet that was 25 cm from the center; and (3) at the periphery of the sheet that was
35 cm from the center. Figure 2represents the scheme of the position of the sheets. Such a pattern of
locating was selected because the dispersion and concentration of the droplets change when receding
from the center. Then, the valve of the water supply pipe was opened. The desirable pressure was
established by positioning the valve. The experiments were performed at the following three different
pressures: 6 bar, 4 bar, and 2 bar.
The valve that was located before the atomizer (Figure 1) was checked for control purposes, and
then whether the pressure inside the fenestrated hose was proper was checked as well. It was also
checked whether everything was hermetic, and if not, whether everything was clamped with clips.
Control spraying was performed into a plastic pail of 12 L. After we were sure that everything was
operating acceptably (everything was hermetic and proper pressure was established), the valve was
closed (Figures 1–4), and the conclusion was that we were ready for the experiment.
The distance (60 cm) from the prepared affected surface was measured by use of a belt ruler.
The atomizer was kept above the center of a sheet of organic glass of 100
×
100 cm. Three small plastic
squares the size of 3
×
3 cm were placed onto the organic glass in such an arrangement as in Figure 2.
After the position of the atomizer above the affected surface (at the center) was fixed, the manual valve
was opened and closed by a sudden movement (see Figure 1); the jet released in this way was sprayed
and reached the affected surface. After the jet was sprayed, we used tweezers to take each of the
samples, i.e., small squares (size of 3
×
3 cm). We took pictures of them and then carried them to the
laboratory for microscope testing.
Then, we entered the number of droplets into a table, grouping droplets by size into four sizes:
0.05 mm, 0.2 mm, 0.6 mm, and 1 mm. The size of the droplets was established using the scaled ruler
located in the spyglass of the microscope.
The experiment was repeated n times. In this case, we repeated the experiment three times when
at least one of the parameters (pressure, peculiarity of structure, etc.) changed. Then, we calculated a
part of the droplets of the respective fraction during each experiment according to Equation (1):
Nqp,% =
nqp
Pnqp
×100, % (1)
Sustainability 2019,11, 5522 5 of 14
where N
qp,%
is the part of qp droplets of the respective fraction in percent as compared to the number
of all droplets, vol%;
qp
is the droplets fraction at the corresponding pressure; n
qp
is the number of qp
droplets of the respective fraction in units;
Σ
n
qp
is the number of all droplets during the experiment
irrespective of the fraction in units.
After n experiments were performed, we calculated the average of the part of droplets of the
particular fraction according to Equation (2):
Nvid.qp,% =
Pnqp,i
n×100, % (2)
where N
vid.qp,%
is the average of the part of qp droplets of the particular fraction, vol%; qp is the droplets
fraction at the corresponding pressure;
Σ
n
qp,i
is the number of all droplets during the ith experiment in
units; and nis the number of performed experiments in units. We must note that the results reflected
the number of droplets; however, they did not reflect the area of the surface covered with them.
2.2. Types of Special Atomizers
During the experiments, special atomizers of three modifications were tested: with diameters
of 12 mm, 14 mm, and 16 mm. The main detail that influences the spraying characteristics of special
atomizers is namely the inner shield (Figure 3a), which resolves the integral stream of water into two
frontal streams, and when they confront, they form fine spraying. This detail was glued at the cap near
the opening (Figure 3).
Sustainability 2019, 11, x FOR PEER REVIEW 5 of 14
droplets of the respective fraction in units; Σnqp is the number of all droplets during the experiment
irrespective of the fraction in units.
After n experiments were performed, we calculated the average of the part of droplets of the
particular fraction according to Equation (2):
𝑁𝑣𝑖𝑑.𝑞𝑝,% =∑𝑛𝑞𝑝,𝑖
𝑛×100, %
(2)
where Nvid.qp,% is the average of the part of qp droplets of the particular fraction, vol%; qp is the
droplets fraction at the corresponding pressure; Σnqp,i is the number of all droplets during the ith
experiment in units; and n is the number of performed experiments in units. We must note that the
results reflected the number of droplets; however, they did not reflect the area of the surface covered
with them.
2.2. Types of Special Atomizers
During the experiments, special atomizers of three modifications were tested: with diameters of
12 mm, 14 mm, and 16 mm. The main detail that influences the spraying characteristics of special
atomizers is namely the inner shield (Figure 3a), which resolves the integral stream of water into two
frontal streams, and when they confront, they form fine spraying. This detail was glued at the cap
near the opening (Figure 3).
(a)
(b)
Figure 3. Scheme of the special atomizer inner shield (a) and the body and cap (b).
As the aim is to establish what combination of the parameters ensures good spraying, the outer
bodies of the atomizers of various parameters were manufactured, as Figure 3b shows. The inner
shield that is demonstrated in Figure 3a was mounted at the cap with the help of glue, as presented
in Figure 3b. These bodies were manufactured of brass bars.
During the performance of the experiments, the following parameters were changed (Figure 3):
B—width of the inner shield, b—width of the channel, l—length of the channel, h—depth (height) of
the channel. The length of the inner plates was 20–25 mm; however, it is not marked, because it does
not affect the characteristic of spraying. The following additional parameters are demonstrated by
the scheme (Figure 3b): L—length of the body of the special atomizer, k—width of the chamber of the
outer cap, d—inner diameter of the atomizer, D—outer diameter of the atomizer.
Table 1 presents the values of the modification parameters of all the special atomizers that were
tested.
Table 1. Parameters of special atomizers of different kinds.
No.
Parameters, mm
l
B
b
h
d
D
L
k
Figure 3. Scheme of the special atomizer inner shield (a) and the body and cap (b).
As the aim is to establish what combination of the parameters ensures good spraying, the outer
bodies of the atomizers of various parameters were manufactured, as Figure 3b shows. The inner
shield that is demonstrated in Figure 3a was mounted at the cap with the help of glue, as presented in
Figure 3b. These bodies were manufactured of brass bars.
During the performance of the experiments, the following parameters were changed (Figure 3):
B—width of the inner shield, b—width of the channel, l—length of the channel, h—depth (height) of
the channel. The length of the inner plates was 20–25 mm; however, it is not marked, because it does
not affect the characteristic of spraying. The following additional parameters are demonstrated by the
scheme (Figure 3b): L—length of the body of the special atomizer, k—width of the chamber of the
outer cap, d—inner diameter of the atomizer, D—outer diameter of the atomizer.
Table 1presents the values of the modification parameters of all the special atomizers that
were tested.
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Table 1. Parameters of special atomizers of different kinds.
No. Parameters, mm
l B b h d D L k
1 4.0 7.0 7.0 2.7 6.0 16.0 135.0 4.0
2 3.4 6.8 4.5 1.6 6.0 14.0 135.0 4.0
3 3.2 6.7 4.3 1.4 6.0 12.0 135.0 4.0
3. Results and Discussion
3.1. Special Atomizer: Modification No. 1
Table 1presents the parameters of this modification of the special atomizer. Spraying results
were achieved under different pressures (namely 6 bar, 4 bar, and 2 bar). It was observed that on
average, 41.7 vol% of the sprayed droplets under the pressure of 6 bar are of fine dispersion: 0.05 mm
in diameter and smaller. Droplets between 0.05–0.2 mm have formed 1/3 of the sprayed droplets.
More massive droplets the size (diameter) of 0.2–0.6 mm have formed 14.3 vol% of the number of the
droplets. The most hefty droplets (
≥
1.0 mm) form at most 9 vol% of the total number of droplets, but
it is necessary to consider the fact that the area of the surface that is covered with these droplets is
the biggest. Therefore, although they are few, they cover a comparatively large area of the surface.
Figure 4presents the dependence of frequencies on the size of the droplets under the conditions of
different pressure. Figure 5represents the spraying results under the pressure of 6 bar. The view of the
small square that is located at the center is represented by part aof Figure 5. It becomes evident that
spraying has succeeded in being fine there, but with some large droplets, that might appear because of
the merging of some fine droplets. In parts band cof Figure 5, the spraying is somewhat hefty, because
there are more droplets of moderate size (0.2–0.6 mm).
Sustainability 2019, 11, x FOR PEER REVIEW 6 of 14
1
4.0
7.0
7.0
2.7
6.0
16.0
135.0
4.0
2
3.4
6.8
4.5
1.6
6.0
14.0
135.0
4.0
3
3.2
6.7
4.3
1.4
6.0
12.0
135.0
4.0
3. Results and Discussion
3.1. Special Atomizer: Modification No. 1
Table 1 presents the parameters of this modification of the special atomizer. Spraying results
were achieved under different pressures (namely 6 bar, 4 bar, and 2 bar). It was observed that on
average, 41.7 vol% of the sprayed droplets under the pressure of 6 bar are of fine dispersion: 0.05 mm
in diameter and smaller. Droplets between 0.05–0.2 mm have formed 1/3 of the sprayed droplets.
More massive droplets the size (diameter) of 0.2–0.6 mm have formed 14.3 vol% of the number of the
droplets. The most hefty droplets (≥1.0 mm) form at most 9 vol% of the total number of droplets, but
it is necessary to consider the fact that the area of the surface that is covered with these droplets is the
biggest. Therefore, although they are few, they cover a comparatively large area of the surface. Figure
4 presents the dependence of frequencies on the size of the droplets under the conditions of different
pressure. Figure 5 represents the spraying results under the pressure of 6 bar. The view of the small
square that is located at the center is represented by part a of Figure 5. It becomes evident that
spraying has succeeded in being fine there, but with some large droplets, that might appear because
of the merging of some fine droplets. In parts b and c of Figure 5, the spraying is somewhat hefty,
because there are more droplets of moderate size (0.2–0.6 mm).
Figure 4. Efficiency of spraying under different pressure, modification No 1.
(a)
(b)
(c)
Figure 5. Sprayed droplets (modification No. 1, pressure—6 bar) (a) at the center of the sheet; (b) at
periphery of the sheet, 25 cm from the center; (c) at periphery of the sheet, 35 cm from the center.
Figure 4. Efficiency of spraying under different pressure, modification No 1.
Sustainability 2019,11, 5522 7 of 14
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1
4.0
7.0
7.0
2.7
6.0
16.0
135.0
4.0
2
3.4
6.8
4.5
1.6
6.0
14.0
135.0
4.0
3
3.2
6.7
4.3
1.4
6.0
12.0
135.0
4.0
3. Results and Discussion
3.1. Special Atomizer: Modification No. 1
Table 1 presents the parameters of this modification of the special atomizer. Spraying results
were achieved under different pressures (namely 6 bar, 4 bar, and 2 bar). It was observed that on
average, 41.7 vol% of the sprayed droplets under the pressure of 6 bar are of fine dispersion: 0.05 mm
in diameter and smaller. Droplets between 0.05–0.2 mm have formed 1/3 of the sprayed droplets.
More massive droplets the size (diameter) of 0.2–0.6 mm have formed 14.3 vol% of the number of the
droplets. The most hefty droplets (≥1.0 mm) form at most 9 vol% of the total number of droplets, but
it is necessary to consider the fact that the area of the surface that is covered with these droplets is the
biggest. Therefore, although they are few, they cover a comparatively large area of the surface. Figure
4 presents the dependence of frequencies on the size of the droplets under the conditions of different
pressure. Figure 5 represents the spraying results under the pressure of 6 bar. The view of the small
square that is located at the center is represented by part a of Figure 5. It becomes evident that
spraying has succeeded in being fine there, but with some large droplets, that might appear because
of the merging of some fine droplets. In parts b and c of Figure 5, the spraying is somewhat hefty,
because there are more droplets of moderate size (0.2–0.6 mm).
Figure 4. Efficiency of spraying under different pressure, modification No 1.
(a)
(b)
(c)
Figure 5. Sprayed droplets (modification No. 1, pressure—6 bar) (a) at the center of the sheet; (b) at
periphery of the sheet, 25 cm from the center; (c) at periphery of the sheet, 35 cm from the center.
Figure 5.
Sprayed droplets (modification No. 1, pressure—6 bar) (
a
) at the center of the sheet; (
b
) at
periphery of the sheet, 25 cm from the center; (c) at periphery of the sheet, 35 cm from the center.
It is evident from the results that on average, 39.4 vol% of the sprayed droplets under the pressure
of 4 bar are of fine dispersion: of 0.05-mm diameter and less. The droplets with diameters between
0.05–0.2 mm have formed a part similar to that of the fine ones, i.e., 32.9 vol%. Droplets of moderate
size between 0.2–0.6 mm (diameter) have formed 19.1 vol% of the number of droplets. The most hefty
droplets (diameter ≥1.0 mm) form 8.6 vol% of the total number of droplets.
It is evident that on average, 37.7 vol% of the sprayed droplets under the pressure of 2 bar are of
fine dispersion: 0.05-mm diameter and less. The droplets between 0.05–0.2 mm have formed a part
similar to that of fine ones, i.e. 35.8 vol%. The droplets of moderate size between 0.2–0.6 mm (diameter)
have formed 17.3 vol% of the number of droplets. The most hefty droplets (
≥
1.0 mm) form 9.2 vol%
of the total number of the droplets, but it is necessary to consider that the area of the surface that is
covered with these droplets is the biggest; therefore, although they are few, they cover a comparatively
large area of the surface.
It is seen from Figure 4provided above that the finest spraying with special atomizer (modification
No. 1), although not vividly pronounced, was under the conditions of the highest pressure, i.e.,
at pressure of 6 bar. Then, the amount of the finest droplets was approximately 42 vol%; meanwhile
under the conditions of the lesser pressures, it was 39 vol% and 38 vol%, respectively. Although the
part of the biggest droplets (size of
≥
1.0 mm) under the conditions of the different pressure was mostly
the same and equal to 9 vol%, the droplets of the size of 0.6 mm were of 5 vol%.
3.2. Special Atomizer: Modification No 2
Table 1represents the parameters of this modification of the special atomizer. It is evident from
the results that on the average, 61.9 vol% of the sprayed droplets under the pressure of 6 bar are
of fine dispersion: with diameters of 0.05 mm and less. The droplets the size of 0.05–0.2 mm have
formed 1/3 of the sprayed droplets. More massive droplets with diameters between 0.2–0.6 mm have
formed 8.9 vol% of the number of the droplets. The most hefty droplets (
≥
1.0 mm diameter) form
at most 1 vol% of the total number of the droplets, but it is necessary to consider that the area of the
surface that is covered with these droplets is the biggest; therefore, although they are few, they cover
a comparatively large area of the surface. Further, the results are represented in Figure 6, i.e., the
dependence of frequencies on the size of the droplets under the conditions of different pressure.
As seen in Figure 6, the results show that on average, 55.9 vol% of the sprayed droplets under
the pressure of 4 bar are of fine dispersion: with diameters of 0.05 mm and less. Droplets between
0.05–0.2 mm formed a smaller part than the fine ones, i.e., 30.8 vol%. The droplets of moderate size of
0.2–0.6 mm (diameter) formed 9.9 vol% of the number of droplets. The most hefty droplets (
≥
1.0 mm)
formed only 3.4 vol% of the total amount of the droplets.
Sustainability 2019,11, 5522 8 of 14
Sustainability 2019, 11, x FOR PEER REVIEW 7 of 14
It is evident from the results that on average, 39.4 vol% of the sprayed droplets under the
pressure of 4 bar are of fine dispersion: of 0.05-mm diameter and less. The droplets with diameters
between 0.05–0.2 mm have formed a part similar to that of the fine ones, i.e., 32.9 vol%. Droplets of
moderate size between 0.2–0.6 mm (diameter) have formed 19.1 vol% of the number of droplets. The
most hefty droplets (diameter ≥1.0 mm) form 8.6 vol% of the total number of droplets.
It is evident that on average, 37.7 vol% of the sprayed droplets under the pressure of 2 bar are of
fine dispersion: 0.05-mm diameter and less. The droplets between 0.05–0.2 mm have formed a part
similar to that of fine ones, i.e. 35.8 vol%. The droplets of moderate size between 0.2–0.6 mm
(diameter) have formed 17.3 vol% of the number of droplets. The most hefty droplets (≥1.0 mm) form
9.2 vol% of the total number of the droplets, but it is necessary to consider that the area of the surface
that is covered with these droplets is the biggest; therefore, although they are few, they cover a
comparatively large area of the surface.
It is seen from Figure 4 provided above that the finest spraying with special atomizer
(modification No. 1), although not vividly pronounced, was under the conditions of the highest
pressure, i.e., at pressure of 6 bar. Then, the amount of the finest droplets was approximately 42 vol%;
meanwhile under the conditions of the lesser pressures, it was 39 vol% and 38 vol%, respectively.
Although the part of the biggest droplets (size of ≥1.0 mm) under the conditions of the different
pressure was mostly the same and equal to 9 vol%, the droplets of the size of 0.6 mm were of 5 vol%.
3.2. Special Atomizer: Modification No 2
Table 1 represents the parameters of this modification of the special atomizer. It is evident from
the results that on the average, 61.9 vol% of the sprayed droplets under the pressure of 6 bar are of
fine dispersion: with diameters of 0.05 mm and less. The droplets the size of 0.05–0.2 mm have formed
1/3 of the sprayed droplets. More massive droplets with diameters between 0.2–0.6 mm have formed
8.9 vol% of the number of the droplets. The most hefty droplets (≥1.0 mm diameter) form at most 1
vol% of the total number of the droplets, but it is necessary to consider that the area of the surface
that is covered with these droplets is the biggest; therefore, although they are few, they cover a
comparatively large area of the surface. Further, the results are represented in Figure 6, i.e., the
dependence of frequencies on the size of the droplets under the conditions of different pressure.
As seen in Figure 6, the results show that on average, 55.9 vol% of the sprayed droplets under
the pressure of 4 bar are of fine dispersion: with diameters of 0.05 mm and less. Droplets between
0.05–0.2 mm formed a smaller part than the fine ones, i.e., 30.8 vol%. The droplets of moderate size
of 0.2–0.6 mm (diameter) formed 9.9 vol% of the number of droplets. The most hefty droplets (≥1.0
mm) formed only 3.4 vol% of the total amount of the droplets.
Figure 6. Efficiency of spraying under different pressures, modification No 2.
Figure 6. Efficiency of spraying under different pressures, modification No 2.
It is evident in Figure 6represented above that on average, 52.6 vol% of the sprayed droplets
under the pressure of 2 bar are of fine dispersion: of 0.05-mm diameter and less. The droplets with
diameters between 0.05–0.2 mm have formed a smaller part than the fine ones, i.e., 31.4 vol%. The
droplets of moderate size (diameter) of 0.2–0.6 mm have formed 11.5 vol% of the number of droplets.
The most hefty droplets (
≥
1.0 mm) form 4.5 vol% of the total number of the droplets, but it is necessary
to consider that the area of the surface covered with these droplets is the biggest; therefore, although
they are few, they cover a comparatively large surface area.
It is seen from Figure 6provided above that the finest spraying with a special atomizer (modification
No. 2), although not vividly pronounced, was under the conditions of the highest pressure, i.e., at a
pressure of 6 bar. Then, the amount of the finest droplets was approximately 63 vol%; meanwhile,
under the conditions of the lesser pressures, it was 55 vol% and 52 vol%, respectively. The portion
made up of the biggest droplets (size of
≥
1.0 mm) under the conditions of the different pressure was
mostly the same, and equal to about 3 vol%.
3.3. Special Atomizer: Modification No 3
Table 1represents the parameters of this modification of the special atomizer. Further, the results
are represented in Figure 7, i.e., the dependence of frequencies on the size of the droplets under the
conditions of different pressure.
Sustainability 2019, 11, x FOR PEER REVIEW 8 of 14
It is evident in Figure 6 represented above that on average, 52.6 vol% of the sprayed droplets
under the pressure of 2 bar are of fine dispersion: of 0.05-mm diameter and less. The droplets with
diameters between 0.05–0.2 mm have formed a smaller part than the fine ones, i.e., 31.4 vol%. The
droplets of moderate size (diameter) of 0.2–0.6 mm have formed 11.5 vol% of the number of droplets.
The most hefty droplets (≥1.0 mm) form 4.5 vol% of the total number of the droplets, but it is
necessary to consider that the area of the surface covered with these droplets is the biggest; therefore,
although they are few, they cover a comparatively large surface area.
It is seen from Figure 6 provided above that the finest spraying with a special atomizer
(modification No. 2), although not vividly pronounced, was under the conditions of the highest
pressure, i.e., at a pressure of 6 bar. Then, the amount of the finest droplets was approximately 63
vol%; meanwhile, under the conditions of the lesser pressures, it was 55 vol% and 52 vol%,
respectively. The portion made up of the biggest droplets (size of ≥1.0 mm) under the conditions of
the different pressure was mostly the same, and equal to about 3 vol%.
3.3. Special Atomizer: Modification No 3
Table 1 represents the parameters of this modification of the special atomizer. Further, the results
are represented in Figure 7, i.e., the dependence of frequencies on the size of the droplets under the
conditions of different pressure.
Figure 7. Efficiency of spraying under different pressures, modification No. 3.
It is evident from the results that on average, 63.2 vol% of the sprayed droplets under the
pressure of 6 bar are of fine dispersion, of diameters of 0.05 mm and less. The droplets the size of
0.05–0.2 mm have formed approximately 1/3 of all the sprayed droplets. More massive droplets with
diameters between 0.2–0.6 mm have formed 8.1 vol% of the number of the droplets. The most hefty
droplets (≥1.0 mm) form only 0.4 vol% of the total number of the droplets.
As seen in Figure 7, the results show that on average, 57.3 vol% of the sprayed droplets under
the pressure of 4 bar are of fine dispersion, with diameters of 0.05 mm and less. The droplets between
0.05–0.2 mm formed a smaller part than the fine ones, i.e., 30.7 vol%. The droplets with moderate-
size diameters between 0.2–0.6 mm formed 10.7 vol% of the number of the droplets. The most hefty
droplets (≥1.0 mm) formed only 1.4vol% of the total number of the droplets.
It is evident from Figure 7 above that on average, 54.5 vol% of the sprayed droplets under the
pressure of 2 bar are of fine dispersion, with diameters of 0.05 mm and less. Droplets with diameters
between 0.05–0.2 mm formed a smaller part than the fine ones, i.e., 30.1 vol%. Droplets of moderate
size (diameter) between 0.2–0.6 mm have formed 13.0 vol% of the number of droplets. The most hefty
droplets (≥1.0 mm) form 2.3 vol% of the total of the droplets, but it is necessary to consider that the
area of the surface that is covered by these droplets is the biggest; therefore, although they are few,
they cover a comparatively large area of the surface.
Figure 7. Efficiency of spraying under different pressures, modification No. 3.
Sustainability 2019,11, 5522 9 of 14
It is evident from the results that on average, 63.2 vol% of the sprayed droplets under the pressure
of 6 bar are of fine dispersion, of diameters of 0.05 mm and less. The droplets the size of 0.05–0.2 mm
have formed approximately 1/3 of all the sprayed droplets. More massive droplets with diameters
between 0.2–0.6 mm have formed 8.1 vol% of the number of the droplets. The most hefty droplets
(≥1.0 mm) form only 0.4 vol% of the total number of the droplets.
As seen in Figure 7, the results show that on average, 57.3 vol% of the sprayed droplets under the
pressure of 4 bar are of fine dispersion, with diameters of 0.05 mm and less. The droplets between
0.05–0.2 mm formed a smaller part than the fine ones, i.e., 30.7 vol%. The droplets with moderate-size
diameters between 0.2–0.6 mm formed 10.7 vol% of the number of the droplets. The most hefty droplets
(≥1.0 mm) formed only 1.4vol% of the total number of the droplets.
It is evident from Figure 7above that on average, 54.5 vol% of the sprayed droplets under the
pressure of 2 bar are of fine dispersion, with diameters of 0.05 mm and less. Droplets with diameters
between 0.05–0.2 mm formed a smaller part than the fine ones, i.e., 30.1 vol%. Droplets of moderate
size (diameter) between 0.2–0.6 mm have formed 13.0 vol% of the number of droplets. The most hefty
droplets (
≥
1.0 mm) form 2.3 vol% of the total of the droplets, but it is necessary to consider that the
area of the surface that is covered by these droplets is the biggest; therefore, although they are few,
they cover a comparatively large area of the surface.
It is seen from Figure 7provided above that the finest spraying with a special atomizer (modification
No. 3), although not vividly pronounced, was under the conditions of the highest pressure, i.e., at a
pressure of 6 bar. Then, the amount of the finest droplets was approximately 63 vol%; meanwhile,
under the conditions of the lesser pressures, it was 58 vol% and 54 vol%, respectively. The part of the
biggest droplets (size
≥
1.0 mm) under the conditions of different pressure was mostly the same and
equal to about 2 vol%.
3.4. Comparison of the Results Using Different Modifications
The relationships of volume flux of atomized liquid (in this case, water) versus atomization pressure,
taking into account different modifications of atomizers, are represented in Figure 8. An increase in
atomization pressure results in an increase in the volume flux of atomized liquid. The atomizer of
modification 1 showed the highest volume flux due to its biggest depth of channel (parameter h).
Sustainability 2019, 11, x FOR PEER REVIEW 9 of 14
It is seen from Figure 7 provided above that the finest spraying with a special atomizer
(modification No. 3), although not vividly pronounced, was under the conditions of the highest
pressure, i.e., at a pressure of 6 bar. Then, the amount of the finest droplets was approximately 63
vol%; meanwhile, under the conditions of the lesser pressures, it was 58 vol% and 54 vol%,
respectively. The part of the biggest droplets (size ≥1.0 mm) under the conditions of different pressure
was mostly the same and equal to about 2 vol%.
3.4. Comparison of the Results Using Different Modifications
The relationships of volume flux of atomized liquid (in this case, water) versus atomization
pressure, taking into account different modifications of atomizers, are represented in Figure 8. An
increase in atomization pressure results in an increase in the volume flux of atomized liquid. The
atomizer of modification 1 showed the highest volume flux due to its biggest depth of channel
(parameter h).
Figure 8. Volume flux of atomized liquid versus atomization pressure.
Droplet spectrum classification according to ASAE Standard S572 is shown in Table 2 below,
and was used to classify the droplet size. Based on the results, the droplet size varied from fine (141
µm) atomized with a modification 3 nozzle to coarse (300 µm), atomized with a modification 1
atomizer.
Table 2. Droplets spectrum classification.
Atomizer Type
Pressure,
bar
Mean Droplet
Diameter, µm
ASAE (American Society of Agricultural
Engineers) Standard
Symbol
Category
Code
Apx.
MD
Modification 1
6
266
C
Coarse
Blue
250–375
4
300
2
295
Modification 2
6
150
M
Medium
Yellow
175–250
4
159
2
168
Modification 3
6
141
F
Fine
Orange
100–175
Figure 8. Volume flux of atomized liquid versus atomization pressure.
Droplet spectrum classification according to ASAE Standard S572 is shown in Table 2below, and
was used to classify the droplet size. Based on the results, the droplet size varied from fine (141
µ
m)
atomized with a modification 3 nozzle to coarse (300 µm), atomized with a modification 1 atomizer.
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Table 2. Droplets spectrum classification.
Atomizer Type Pressure,
bar
Mean Droplet
Diameter, µm
ASAE (American Society of Agricultural
Engineers) Standard
Symbol Category Code Apx. MD
Modification 1
6 266
C Coarse Blue 250–375
4 300
2 295
Modification 2
6 150
MMedium Yellow 175–250
4 159
2 168
Modification 3
6 141
FFine Orange 100–175
4 154
2 166
ProMax Fulljet
6 171
MMedium Yellow 175–250
4 198
2 237
The relationship of the mean diameter of droplets for an atomization spectrum and applied
atomization pressure is shown in Figure 9.
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4
154
2
166
ProMax Fulljet
6
171
M
Medium
Yellow
175–250
4
198
2
237
The relationship of the mean diameter of droplets for an atomization spectrum and applied
atomization pressure is shown in Figure 9.
Figure 9. Relationship of the mean diameter of droplets and applied atomization pressure.
As seen in Figure 9, the atomization pressure and mean droplets diameter have the opposite
dependency—the higher the pressure is, the finer the droplets that are atomized (sprayed). The finest
atomization was performed by the atomizer of modification 3, for which the mean diameter varies
from 141 µm to 166 µm at atomization pressures of 6 bar and 2 bar, respectively. A similar diameter
(around 150 µm) of the droplets was observed by Rajan and Pandit [36] when a piezoelectric
ultrasonic atomizer was used. In comparison to a pneumatic ultrasonic gas atomizer (diameter of
around 50 µm) [37], the formed droplets are bigger, but the price of the ultrasonic gas atomizer device
is higher.
The relationship of the stream angle of atomized liquid (atomization cone) versus the
atomization pressure is shown in Figure 10.
Figure 9. Relationship of the mean diameter of droplets and applied atomization pressure.
As seen in Figure 9, the atomization pressure and mean droplets diameter have the opposite
dependency—the higher the pressure is, the finer the droplets that are atomized (sprayed). The finest
atomization was performed by the atomizer of modification 3, for which the mean diameter varies from
141
µ
m to 166
µ
m at atomization pressures of 6 bar and 2 bar, respectively. A similar diameter (around
150
µ
m) of the droplets was observed by Rajan and Pandit [
36
] when a piezoelectric ultrasonic atomizer
was used. In comparison to a pneumatic ultrasonic gas atomizer (diameter of around 50
µ
m) [
37
], the
formed droplets are bigger, but the price of the ultrasonic gas atomizer device is higher.
The relationship of the stream angle of atomized liquid (atomization cone) versus the atomization
pressure is shown in Figure 10.
Sustainability 2019,11, 5522 11 of 14
Sustainability 2019, 11, x FOR PEER REVIEW 10 of 14
4
154
2
166
ProMax Fulljet
6
171
M
Medium
Yellow
175–250
4
198
2
237
The relationship of the mean diameter of droplets for an atomization spectrum and applied
atomization pressure is shown in Figure 9.
Figure 9. Relationship of the mean diameter of droplets and applied atomization pressure.
As seen in Figure 9, the atomization pressure and mean droplets diameter have the opposite
dependency—the higher the pressure is, the finer the droplets that are atomized (sprayed). The finest
atomization was performed by the atomizer of modification 3, for which the mean diameter varies
from 141 µm to 166 µm at atomization pressures of 6 bar and 2 bar, respectively. A similar diameter
(around 150 µm) of the droplets was observed by Rajan and Pandit [36] when a piezoelectric
ultrasonic atomizer was used. In comparison to a pneumatic ultrasonic gas atomizer (diameter of
around 50 µm) [37], the formed droplets are bigger, but the price of the ultrasonic gas atomizer device
is higher.
The relationship of the stream angle of atomized liquid (atomization cone) versus the
atomization pressure is shown in Figure 10.
Figure 10. Relationship of the atomization stream angle and applied atomization pressure.
As seen from Figure 10, the atomization pressure has an influence on the stream angle. These
parameters have positive correlation—increasing atomization pressure causes the increase in the
atomized stream angle. The widest stream angle (80 degrees) atomization was observed when using
the atomizer of modification 1 at the highest pressure (6 bar). It can be explained by the biggest depth
of the channel (parameter h), causing the highest throughput at the highest pressure. It is evident that
the finest droplets have formed under the conditions of the utmost pressure, namely 6 bar (Figure 11).
It is evident that the atomizer of modification No. 1 with the depth of the inner shield of 2.6 mm has
performed the worst, because the best spraying was reached with the special atomizer of modification
No. 3, i.e., with the depth of the channel of the inner shield at 1.4 mm (see h in Figure 3). In the process
of spraying with such a special atomizer of such modification, large droplets
(of ≥1.0 mm)
were formed
the least, namely 0.4 vol%. Droplets of the moderate sizes of 0.2–0.6 mm and 0.6–1.0 mm were formed
proportionately, namely 28.3 vol% and 8.1 vol%. Such a result is highly similar to spraying with
the special atomizer of modification No. 2, but it is still the best, because the droplets of the biggest
diameter were formed the least.
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Figure 10. Relationship of the atomization stream angle and applied atomization pressure.
As seen from Figure 10, the atomization pressure has an influence on the stream angle. These
parameters have positive correlation—increasing atomization pressure causes the increase in the
atomized stream angle. The widest stream angle (80 degrees) atomization was observed when using
the atomizer of modification 1 at the highest pressure (6 bar). It can be explained by the biggest depth
of the channel (parameter h), causing the highest throughput at the highest pressure. It is evident that
the finest droplets have formed under the conditions of the utmost pressure, namely 6 bar (Figure
11).
It is evident that the atomizer of modification No. 1 with the depth of the inner shield of 2.6 mm
has performed the worst, because the best spraying was reached with the special atomizer of
modification No. 3, i.e., with the depth of the channel of the inner shield at 1.4 mm (see h in Figure
3). In the process of spraying with such a special atomizer of such modification, large droplets (of
≥1.0 mm) were formed the least, namely 0.4 vol%. Droplets of the moderate sizes of 0.2–0.6 mm and
0.6–1.0 mm were formed proportionately, namely 28.3 vol% and 8.1 vol%. Such a result is highly
similar to spraying with the special atomizer of modification No. 2, but it is still the best, because the
droplets of the biggest diameter were formed the least.
Figure 11. Spraying efficiency of different modifications of atomizers.
While spraying during the experiment, the finest droplets, the size of which was 0.05 mm and
less, formed predominantly in the case of all the tested modifications of the special atomizer and also
in case of the standard atomizer, namely 63.2 vol%. It is namely because the biggest droplets formed
the least, and on the contrary, the finest droplets were predominantly formed, and the spraying,
which was performed with the special atomizer of modification 3, is the best of the compared
modifications.
Coarser droplets (200–300 µm) produced by atomizers of modifications 1 or 2 may be beneficial
for the purpose of flue gas scrubbing due to the slower evaporation of such droplets [38]. Finer
droplets (about 50 µm) that are produced in higher portions by the atomizer of modification 3 are
better for moistening the substrate in the biofilter. In both the cases of application, the savings of
water can be achieved due to smaller water losses.
4. Conclusions
1. The maximal influence on the spraying characteristics of the atomizers of the frontal streams is
created namely by the depth of the channel of the inner shield. What strength the frontal streams
will confront and what the size of sprayed droplets will be depends on the depth of this channel.
Figure 11. Spraying efficiency of different modifications of atomizers.
While spraying during the experiment, the finest droplets, the size of which was 0.05 mm and
less, formed predominantly in the case of all the tested modifications of the special atomizer and also
in case of the standard atomizer, namely 63.2 vol%. It is namely because the biggest droplets formed
Sustainability 2019,11, 5522 12 of 14
the least, and on the contrary, the finest droplets were predominantly formed, and the spraying, which
was performed with the special atomizer of modification 3, is the best of the compared modifications.
Coarser droplets (200–300
µ
m) produced by atomizers of modifications 1 or 2 may be beneficial for
the purpose of flue gas scrubbing due to the slower evaporation of such droplets [
38
]. Finer droplets
(about 50
µ
m) that are produced in higher portions by the atomizer of modification 3 are better for
moistening the substrate in the biofilter. In both the cases of application, the savings of water can be
achieved due to smaller water losses.
4. Conclusions
1.
The maximal influence on the spraying characteristics of the atomizers of the frontal streams is
created namely by the depth of the channel of the inner shield. What strength the frontal streams
will confront and what the size of sprayed droplets will be depends on the depth of this channel.
2.
The size of only 4 vol% of the droplets, which were sprayed with the special atomizer of
modification 3, was 1.0 mm and more. The sizes of the sprayed droplets mainly varied from
0.05 mm to 1.0 mm. These sizes result in the intervals of actual sizes of the droplets that were
determined by Schick in 2008, namely 500–5500
µ
m, and their minimum (0.05 mm) does not
reach the beginning of the interval. For this reason, it can be stated that spraying with the special
atomizer has been proven to be effective.
3.
The spraying characteristics of the hydraulic atomizers depend on the pressure, i.e., the higher
the pressure was, the finer droplets that were atomized (sprayed). It is exactly for this reason that
the spraying characteristics of atomizers of different structure and different modifications are
compared under the conditions of the utmost pressure, as well as under the conditions of the best
characteristics of spraying.
4.
The tested special atomizers might be applied for watering of the charges of biofilters or for
absorbing gases/dust in physical scrubbers. Coarser droplets (200–300
µ
m) produced by atomizers
of modifications 1 or 2 may be beneficial for the purpose of flue gas scrubbing due to the slower
evaporation of such droplets. Finer droplets (about 50
µ
m) that are produced in higher portions
by the atomizer of modification 3 are better for moistening the substrate in the biofilter. In both
the cases of application, the savings of water can be achieved due to smaller water losses. In the
case of application in a biofilter, the less water usage is associated with the lower resistance
generated by the less saturated substrate. In both the cases, the efficiency of treatment is achieved.
Lower use and greater savings of water contribute to resource savings, which is an important
indicator of sustainable development.
Author Contributions:
Conceptualization, P.B.; Funding acquisition, P.B.; Investigation, E.B.-G.; Methodology,
P.B.; Project administration, P.B.; Resources, P.B.; Supervision, P.B.; Visualization, E.B.-G; Writing – original draft,
E.B.-G.
Funding: This research received no external funding.
Acknowledgments: The authors thank Justas Burokas for obtaining the experimental data.
Conflicts of Interest: The authors declare no conflict of interest.
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