Introduction
Providing a certain degree of ionization of the air environment in the working area is one of the most important factors in maintaining a good state of health and high efficiency of staff. It has been established that a significant decrease in the content of charged particles (ions) in the air coincides with the appearance of unusual sickliness in working people, fatigue complaints, depression, nausea, insomnia, irritability, respiratory disorders, and others. At the same time, the presence of people in conditions with moderately high ionization of the atmosphere, with the vast majority of negative ions - on the contrary, there is a beneficial effect on the body. The process of ionization of air consists in the transformation of neutral atoms and air molecules into electrically charged particles (ions). Ions in the air (aeroions) can be formed as a result of natural and artificial ionization.
Natural ionization occurs as a result of the influence on the air of space and solar radiation and ionizing radiation (particles) that arise during the decay of long-lived radionuclides of the earth's crust (potassium-40, uranium-238, thorium-232, etc.). Natural ionization of the air environment is everywhere and constant in time. Artificial aerionization occurs under the influence of ionizing factors, which accompany some technological processes (X-ray and ultraviolet radiation, thermo-emission, photoelectric effect, etc.); as well as the effect of special devices – ionizers. The degree of ionization of air depends on the ratio of ionization and deionization processes. The latter is due to the recombination of two ions of different polarities, adsorption of light ions on uncharged nuclei, condensation, neutralization of light and heavy ions by charges of the opposite sign, and others.
Assessment of the aeration degree of the environment is carried out by comparing the measured values with the standard ones. Artificial ionizers (high-voltage, induction, radiation, etc.) and efficient, well-organized ventilation of premises are widely used to normalize the ionic mode of the air environment, as the external clean air contains 2-5 times more ions than the air of indoor premises (50-100 ions/cm3).
Many works of domestic authors are devoted to the study of aeroionic mode. Modeling of aeroionic mode in working zones under conditions of artificial ionization is presented in the work [1]. The problem of the evaluation and the relationship between aerosol pollution and the aeroionic composition of air in the working zone is considered in the works [8–9]. The works [2, 11] are devoted to the modeling of the aeroionic mode in premises with artificial ionization using the means of numerical Modeling. The proposed program information system for the optimization of the microclimate in the premises is in [6]. The study of ways to improve the aeroionic mode of the working environment is presented in work [7]. The study of the microclimatic parameters influence of air exchange on the aeroionic composition of the air in the working premises and the modeling and prediction of the aeroionic composition dynamics of air are given in the works [4–5]. The methods for determining the concentration of aeroions and dust content are presented in the work [3]. The normalization of the aeroionic composition of air in office premises is considered in the work [15]. A large number of foreign works are devoted to the study of ionization processes for improving the health of employees [12–14, 16].
Purpose
The purpose of this study is to develop a new method for forecasting aeroionic mode in working areas at industrial sites, taking into account ionizing sources and surrounding obstacles (buildings).
Methodology
It is known that the formation of the concentration field of aeroions is influenced by a complex of physical factors: airflow, diffusion, electric field effect and others. In addition, there is the interaction of ions of different polarity and their interaction with particles of dust. To account for these processes during the Modeling of aeroions dispersion, the 3D equation of mass transfer is used. It is written for each component (positive aeroions, dust, negative aeroions). The Modeling equations have the form:
– to describe the process of dispersion of positive ions
;
(1)
– for modeling the transfer of dust
;
(2)
– to describe the process of dissipating negative ions
.
(3)
The denotations of physical parameters in these equations are as follows:
,
,
– the
concentration of
positive, negative
aeroions and
dust particles,
respectively; u,
v,
w –
components of
the velocity
vector of
the air
flow;
,
,
–
coefficients of
diffusion; t
– time;
– the rate
of recombination
of ions
with different
polarity;
–
the rate
of recombination
of ions
with dust
particles;
– the intensity of the emission of positive
ions at the corresponding coordinate points
,
,
;
– delta-function of Dirac;
b –
coefficient of ions mobility;
E –
electric field strength.
At the boundary of the air flow inlet into the calculated area is the initial condition:
, (4)
where
– the
initial concentration of aeroions.
At the boundary
of the area outlet from the calculated we set a «soft» boundary
condition:
,
where
–
unit
vector of the external normal to the solid surface.
For numerical implementation such a boundary condition is recorded:
, (5)
where
– the
values of ions in the last boundary cell,
– the
value of ions in the penultimate difference cell.
On the ground surface and all solid surfaces, the boundary condition for non-permeability is set:
. (6)
This condition physically means that the flow of ions at these boundaries is zero.
Using
the Modeling
equations (1)
– (3)
speed components
,
,
must satisfy the equation of continuity:
. (7)
To fulfill this condition one should solve an aerodynamic problem for determining the velocity field. To determine the components of the air velocity vector, a three-dimensional model of the potential flow is used, where the Laplace equation for the velocity potential serves as the simulating equation:
,
(8)
where P – speed potential.
Components of the velocity vector of the air are related to the velocity potential by the following relationships:
,
,
. (9)
For the Laplace equation, the following boundary conditions are set:
– on
firm boundaries the condition of non-permeability is set
;
– on
the boundary of the flow outlet from the calculated region the
Dirichlet boundary condition is set
;
– at
the boundary of the air flow inlet into the calculated area, the
boundary condition is set
,
where
–
known velocity of the inflow.
When simulating the propagation of aeroions, it is necessary to take into account the influence of the electric field on this process. Since the aeroions have a charge, they generate an electric field E. For the Modeling of the electric field, the following equation is used [2, 12]:
, (10)
where
– dielectric
permeability;
– volumetric
charge density.
From equation (5.7) we can go to the scalar potential, if we take into account such dependence:
,
,
. (11)
Then we obtain the Poisson equation:
, (12)
where
,
– concentration
of
positive
aeroions;
– scalar
potential;
– elementary
charge.
On
the basis of this equation electric field Modeling is carried out.
As the boundary condition, the condition of electrical insulation is used:
,
where
–
unit
vector of the external normal to the solid surface.
For numerical
integration of the mass transfer equations, a difference scheme is
used based on the geometric and physical splitting of the simulating
equations (1) – (3). In each of the four
fractional steps, only one direction of perturbation transfer is
taken into account; the fifth split step takes into account the
change in the concentration of aeroions due to the action of the
emission source. The calculation is performed on a rectangular
difference grid. Concentration
of quantities
,
,
is determined in the centers of the
difference cells, whereas the components of the velocity vector of
the air are set at the boundaries of the difference cells
[2, 11–12].
Findings
To estimate the aeroionic mode in the working zones, based on the developed method, it is necessary to determine the aeroions emission intensity from the specific sources. As already noted, one of these sources is the worker, who exhales positive aeroions. Physical experiment was conducted to obtain scientifically substantiated information regarding the magnitude of such emission.
For the
experiment, a group of people of dif-ferent ages was selected: 16
people in each age group. The
mouth area
was measured
S=9.5
cm2,
the rate
of air
flow when
exhaled was
on average
V=0.4
m/s,
flow rate
m3/s,
the intensity of the emission of positive
aeroions when exhaled
ions/s, where
– concentration of positive aeroions at
exhalation. The results of measuring the average concentration of
positive aeroions when exhaling for each age group are given in
Table 1.
Experiment to measure the concentration of aeroions from human exhalation was carried out using the KT-401 AIRION TESTER.
Table 1
The
value of the concentration of positive
aeroions when person
exhales
|
Age of a person, years |
Concentration of positive aeroions, ions/cm3, |
|
8–9 |
166–176 |
|
18–19 |
232–349 |
|
40 |
277–329 |
|
78 |
210–256 |
The data
obtained on the basis of the conducted physical experiment, were
used during computational experiments. During the experiments it was
taken into account that the source of positive aeroion emission
during exhalation had a periodic action, namely, exhalation for 1 s
in quantity
,
the inhalation – emission is absent and
after 2 s again exhalation with the same emission.
That is, the source of periodic emission
is known.
Verification of the developed forecast method was carried out. A test task was solved to calculate the emission of positive aeroions with exhaust gases of vehicles.
During the physical experiment, the positive aeroions at different distances from the Daewoo Matiz exhaust pipe were measured using the KT-401 AIRION TESTER. The velocity of wind and gas flow at the exhaust pipe outlet was measured using an anemometer PM 6252 B Digital Anemometer. The speed of the air flow was Vair=1.2–1.4 m/s, and the speed of gas flow Vgas=1.7–1.9 m/s, diameter of the exhaust pipe hole d=32 mm.
The method of
conducting the experiment was as follows: the concentration of
positive aeroions was measured at a height of 320 mm from the ground
surface at different distances from the exhaust pipe. To obtain data
on the intensity of emissions, the calculation was made according to
the ratio
,
where
– the velocity of the gas flow in the
outlet cross section of the exhaust pipe,
– area of the outlet cross section of the
exhaust pipe hole,
– the concentration of positive aeroions in
the outlet cross section. Immediately during the experiment
parameters
and
were measured at a distance of 0.5 cm from
the outlet cross section of the exhaust pipe hole.
The obtained data were used as input
information for numerical calculation on the basis of the developed
method. Using this method, the impurity concentration values at the
points of measurements were also calculated. Table 2 shows the
results of experimental measurements and the calculated data
obtained with the help of the developed numerical calculation
method.
Table 2
Concentration
of positive aeroions at different
distances from the emission
source
|
Distance
from |
Concentration
of positive aeroions, ions/cm3 |
Concentration
of aeroions, |
|
5 |
1 400–1 443 |
1 425 |
|
10 |
1 080–1 097 |
1 092 |
|
20 |
650–738 |
721 |
|
30 |
420–546 |
465 |
|
40 |
143–158 |
152 |
|
50 |
67–76 |
72 |
|
60 |
43–57 |
52 |
Data analysis shows the adequacy of the numerical calculation method. The corresponding deviation is due to the flow turbulization caused by the influence of the car body on the aerodynamics of the flow.
The source of positive aeroions on the street is primarily people, cars. During calculations, a complex of factors was taken into account, which had been overlooked in scientific publications: aeroion emission from cars; aeroion emission from humans; the influence of various obstacles in the street on the aeroionic mode formation; the influence of the uneven wind velocity field on the formation of aeroionic mode; the influence of the uneven field of atmospheric diffusion on the formation of the aeroionic mode; modeling of aeroions dispersion in a three-dimensional formulation (3D modeling).
Taking into account the listed factors extremely complicates the solving of these problems:
The task solution is based on three stages:
1. Modeling the formation of a field of concentration of positive, negative aeroions and dust under the influence of wind and atmospheric diffusion.
2. Modeling the transport of aeroions under the action of an electric field.
3. Change the field of concentration of aeroion, dust due to their interaction.
The developed method of forecasting was used to solve the task of estimating the level of pollution of working areas in the open air in the presence of a source of emissions: positive aeroions – emissions from vehicles and people; dust – traffic; sources of negative aeroions – an ionizer installed in the working zone and the screen (fence), which changes the aerodynamics of the aeroions and dust.
Fig.
1. Modeling
area (Google
Earth Image,
2019) Dnipro Oil
Extraction Plant:
1
– cargo
scales
As a research object, the Dnipro Oil Extraction Plant was chosen, namely, the territory where the cargo scales (Fig. 1) operate, where the lorries with seeds arrive. This area is a source of dust, positive aeroions, and workers responsible for unloading cars are constantly under the influence of these negative factors.
Scheme of the calculated area is presented in Fig. 2
There are the results of the computational experiment for calculating the field of positive, negative aeroion and dust concentration in the working area of the industrial site (Fig. 3, Fig. 5, Fig. 7). The speed of the air flow was set at 5 m/s, the size of the calculated area was 8x4 m, the intensity of the sources of aeroions was 1000 ions/cm3. Fig. 4, Fig. 6, Fig. 8 show the percentage distribution of negative, positive aeroions and dust concentrations in the working area at the height of 1.7 m.
Fig. 2. Scheme of the calculated area:
1
– emission source (car), 2
– emission source (dust),
3
– screen,
4
– source of positive aeroions,
5
– working area,
6
– source of negative aeroions (ionizer),
7
–
temporary building
Fig.
3. Distribution of negative
aeroions
concentration,
intersection у=4
м
In Fig. 3 it is evident that at the distance of 3 m from the beginning of the calculated area there are no negative aeroions, since there is no source of emission on this site, and on another section a complex picture of the distribution, which is caused by the movement of the air flow and the action of atmospheric diffusion, is observed.
The value of the concentration at the height H = 1.7 m slowly increases under the influence of the emission source and diffusion (Fig. 4).
Fig. 4. Distribution of the concentration of negative aeroions at the height H = 1.7 m, intersection у=4 м
Fig.
5. Distribution of dust concentration,
intersection
у=4 м
In Fig. 5 it is evident that the entire research area is filled with dust, due to its intensive allocation on two sites: before the screen – the emission of dust from cars; from the screen to the location of the scales – the work area of the workers. The dust is driven by wind flow and gets into the working area in the open ground. The maximum permissible concentration is MPCa.d.=0.15 mg/m3, so the dust concentration in this zone exceeds the MPCa.d.by 20%.
Fig.
6. Distribution of dust concentration
at the height H
= 1.7 m,
intersection у=4
м
The dust concentration at the height of H = 1.7 m slowly increases under the influence of the emission source (motor vehicles), then it is reduced due to the screen action and decreases at insignificant distance, but under the influence of the source of emissions (workers) increases again and decreases due to changing the flow direction near the awning of the temporary building and diffusion (Fig. 6).
Fig. 7 shows the distribution of positive aeroions.
Fig.
7. Distribution of the concentration of
positive aeroions,
intersection у=4
м
Apparently, in the working zone there is a dynamics of growth of positive aeroions, which is caused by the transport of positive aeroions from vehicles (source of emissions – cars) and the emission of positive aeroions from people in the working zone, that is, the interaction of sources of aeroion emissions takes place.
As the dust concentration values, the concentration of positive aeroions slowly increases at the height H = 1.7 m under the action of the emission source of positive aeroions (vehicles), then it is reduced by the screen action and decreases at insignificant distance, but under the influence of the source of emissions (workers) increases again and decreases due to changing the flow direction near the awning of the temporary building and diffusion (Fig. 8).
The optimal level of positive aeroions 1500-3000 ions/cm3, the maximum allowable level is 50000 ions/cm3, in the working area is observed exceeding the permissible level by 10%.
Fig.
8. Distribution of the concentration
of positive aeroions at the
height of H=1.7
m,
intersection у=4
м
Originality and practical value
1. The method of aeroionic mode forecasting in working zones is developed, which is based on three-dimensional modeling of the distribution of negative, positive ions and dust under the influence of wind and diffusion.
2. The peculiarity of the proposed method is the possibility of forecasting the aeroionic mode, taking into account almost all physical factors that significantly affect the formation of concentration fields of aeroions in working areas at industrial sites.
3. The proposed method of forecasting was used to solve the problem of aeroion assessment in open areas in industrial site in the presence of emission sources: positive aeroions – emissions of vehicles and breathing of people; dust – the movement of workers and vehicles; sources of negative aeroions – ionizer installed in the working zone and the screen, which changes the aerodynamics of aeroions and dust.
4. The regularities of the change in the concentration of aeroions and dust at the height of 1.7 m are established, which corresponds to the position of the respiratory organs of the workers.
5. The developed mathematical method of forecasting can be used to estimate the concentration of aeroions of different polarity and dust.
6. The method is implemented in the form of application program for the calculation of aeroionic mode in the working areas in the open field of industrial sites.
Findings
As a result of the conducted research the following results were obtained:
– the mathematical method of numerical calculation of the concentration of positive, negative aeroions and dust is proposed;
– the method is not tied to a specific industrial site, it allows estimating the value of the concentration of aeroions both locally and in the entire calculated area;
– a physical experiment was conducted demonstrating the adequacy of the numerical calculation method;
– the results of calculations are useful in terms of ensuring acceptable working conditions in the workplaces of industrial sites, in creating new jobs and reengineering the existing ones.
The prospect of development of this direction is to improve the established method for assessing the parameters of well-being of workers in outdoor areas of industrial sites in the established aeroionic mode.