INCREASING THE EFFICIENCY OF THE INERTIA AIR CLEANER OF LOCOMOTIVES

ABSTRACT

The fact that the air surrounding locomotives contains dust and foreign matter is obvious to everyone. Therefore, the operation of locomotives occurs in conditions of greater or lesser dust content of atmospheric air. Currently, in the scientific and technical literature, two methods of industrial air purification for refrigeration and air conditioning are distinguished - dry and wet. On diesel locomotives, ventilation air cleaners of various designs can be used. Air filters are compared according to a number of indicators, of which the following are most important: 1) automation of the filter; 2) the strength of the filter element; 3) high cleaning efficiency and low hydraulic resistance. The article considers the efficiency of the inertial air cleaner of locomotives.

АННОТАЦИЯ

То, что воздух, окружающий локомотивов, содержит пыль и посторонние включения, очевидно для всех. Поэтому эксплуатация локомотивов происходит в условиях большей или меньшей запыленности атмосферного воздуха. В настоящее время в научной и технической литературе различают два метода промышленной очистки воздуха для охлаждения и кондиционирования - это сухой и мокрый. На тепловозах могут применяться очистители вентилирующего воздуха различных конструкций Воздушные фильтры сравнивают по ряду показателей, из которых наиболее важны следующие: 1) автоматизация работы фильтра; 2)прочность фильтрующего элемента; 3) высокая эффективность очистки и низкое гидравлическое сопротивление. В статье рассмотрена эффективность инерционного воздухоочистителя локомотивов.

Keywords: inertial air cleaner, air flow, air filters, efficiency, dust.

Ключевые слова: Инерционный воздухоочиститель, воздушного потока, воздушные фильтры, эффективность, пыль.

The inertial louvered air cleaner, consisting of a set of parallel operating devices, is an aerodynamic system with a number of features. The principle of operation of inertial air cleaners is based on the inertia of dust particles in the air [1,2].

In this paper, we consider the problem of dust separation in a channel of a rectangular cross section of an air cleaner, the design scheme of which is shown in Fig.1. Depending on the nature of the flow around the grid, the elastic properties and shape of dust particles, the angle of inclination and shape of the blades, the state of the surface and the coefficient of friction, the particle reflected by the blade can either enter the suction zone or the clean air path, or participate in repeated interaction with the following along the flow of the blades [3].

Figure 1. Scheme of dust separation in an inertial air cleaner

The momentum component of the particle along the surface of the blade changes after impact depending on the friction coefficient of the particle, and the normal surface - depending on the Poisson's ratio [4]. In the first approximation, particles and blades can be considered absolutely elastic, and the angle of incidence is equal to the angle of reflection.

When solving it, it is assumed that with a uniform distribution of each dust fraction in the inlet section of the channel, the ratio of the amount of captured dust of given sizes to the amount that enters the channel is equal to the ratio:

,                                                             (1)

Where  - the path in the radial direction traversed by particles of a given size during separation in a curved section of the channel with a width .

Irregularities in the field of air flow velocities in the section of the suction channel behind the louvre

,                                                  (2)

Where  - respectively, the maximum and minimum air velocity in a given section.

The value of the coefficient of unevenness  changed from 0, When , before 2, When . In the first case, the air velocity distribution field is uniform, and in the second case, it is the most uneven.

In view of this, in order to determine  we use the expression obtained in (11)

,                                        (3)

Where  и  - constant coefficients.

Locomotive air cleaners operate in dusty conditions with fine dust, therefore the value  can be neglected, since at particle sizes  мкм , therefore, the efficiency in relation to a certain fraction will be expressed

.                                                (4)

It can be seen from Fig. 1 that the efficiency of an inertial air cleaner is determined by the free path of a particle before it hits an obstacle (the particle trajectory is shown by a dotted line), it mainly depends on the geometric dimensions of individual particles. If the free path of individual particles , then they are captured completely, i.e. . Otherwise, individual particles enter the clean air chamber and, respectively . Meaning  determined from (4).

Denote

                                                (5)

values  are substituted in мкм. Then we rewrite expression (3) in the form

                                   (6)

From (55)   is defined as

 .                                   (7)

From (7) one can get four values , however, computational checks show, that for the cases under consideration, in fact, only one value corresponds , which should be calculated from the expression

 .                                       (8)

Obviously, in trapping fractions of 70...1000 мкм, an important role is played by the reflection of particles by the grating blades into the volume and their abrupt movement along the blades.

To derive formulas for the overall efficiency of dust collection in a curvilinear channel, we use the particle size distribution density function [5].

,                                                (9)

Where  - constant coefficients depending on the fractional composition of dust (for dust in the railway area of the North-West region  = 4.703, = 0.0543).

The dust collection efficiency with particle sizes from to   can be expressed as

.                                                 (10)

Since the efficiency of trapping dust particles with dimensions  is equal to one, then

                                          (11)

Let us substitute into (11) the expressions for from (4) and   from (9). Let us preliminarily transform (4) to the form:

.                                           (12)

Then

 +

+ .                                   (13)

Formula (13) is correct provided that   is sufficiently small compared to unity.

When deriving (13), it was assumed that a dust particle with a free path equal to or less than the lattice spacing  would be captured. This assumption is usually made when determining the efficiency of dry wall dust separators.

Analysis of the results confirmed the obvious assumption about the determining influence of the degree of air suction on the efficiency of the cleaner (Fig. 2).

Figure 2. The efficiency of air purification from the degree of air suction

At the same time, an excessive increase in the degree of suction reduces the air flow through the cooled electric machines, which can lead to an increase in their temperature, and also increases the power consumption for the fan drive of the cooling system of traction electric machines [6].

With an increase in the pitch of the louvre grille, the turbulence index of the air flow decreases and, ultimately, with a pitch of   > 10 mm, it can be considered laminar. On the one hand, this improves the quality of air purification due to a greater velocity impulse transmitted to the particle by a uniform flow of the medium, but on the other hand, the length of the inertial path of particles with a diameter of less than 20 мкм is slightly less than the lattice pitch. As a result, after reflection from the obstacle, the particle is carried away by the secondary flow into the cavity of clean air - the cleaning efficiency decreases.

It is the different intensity of reflection of particles from the blades that explains the great influence of the opening angle of the air cleaner gratings on the cleaning efficiency. The calculated curves showing this effect are shown in Fig.3.

Figure 3. Efficiency of air purification from the opening angle of the gratings

At constant values of the main design parameters of the air cleaner (the pitch of the louvre grille , the angle of inclination of the louvre , the opening angle of the louvre , as well as the length of the louvre grille  and the air suction coefficient), the cleaning efficiency depends to a very large extent on the composition of the dust (Fig. 4) .

It is especially difficult to provide highly efficient cleaning in inertial air cleaners in the case of light (<2000 кг/м³) fine dust [7]. Here an efficiency of 90% is not achieved with  = 4 mm even at an air speed of  24 m/s and a suction of 0.15. In this case, to improve efficiency, you should further reduce . However, with a decrease in , the coefficient of hydraulic resistance  increases accordingly, and the efficiency decreases when working on fine sticky dust. Comparison of the obtained results with the experimental data shows that the calculation gives somewhat overestimated values of the degree of air purification.

Figure 4. The efficiency of air purification from the fractional composition of dust This is explained by the nature of the assumptions made in solving the problem

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