Технические науки/13. Охрана труда

G.S. Bekturgаnova

Kazakh National Technical University named after K.I. Satpayev,

Republic of Kazakhstan.

STUDYING OF REGULARITY OF RANGES OF ABSORPTION OF THE EXHAUST DEVICE

Abstract. This article discusses the suction side suction, applied to the conditions of work table welder, in particular, the angle of inclination of the visor, visor for horizontal mounting, and provided set at the edges of the side panel plates.

Key words: purification of gases, filtration, protection of atmospheric air.

Distribution and intensity of speeds in a zone of absorption of the exhaust device in big degree define efficiency of catching of dust particles and gases. Dribble of air to the soaking-up opening is carried out due to the depression created by the fan in a local suction or an exhaust air duct. As the air consumption in an absorption zone in all sections is constant, speeds of air are inversely proportional to the areas of surfaces through which there is an air dribble.

If diameter of d₀ to consider a branch pipe with a round opening as a dot drain, surfaces with equal speeds of the movement of air will represent spheres. The size of speeds of air at some distance from the local suction executed in the form of a cylindrical pipe can be determined by a formula

(1)

where L₀ – a consumption of the air deleted by a branch pipe, m3/s; F – a sphere surface the radius of, gram/m².

Having designated the average speed of air in the plane of an exhaust opening of a branch pipe of v0 and having considered that

(2)

we, will receive approximate expression for determination of relative speed of air in a zone of absorption of a cylindrical branch pipe at distance x:

(3)

As appears from a formula (3), air speed in a range of absorption decreases in inverse proportion to a distance square to the considered point, and at the distance equal to one diameter, decreases approximately by 16 times, and at distance of two diameters – by 64 times (figure 1).

Figure 1 – Air speeds in a zone of absorption of a round opening:

I – a field of speeds of air in an absorption range without screen; II – a range absorptions of a round opening with the flat screen; III – the flat screen (figures on curves – speed percent in an absorption range from initial speed of v₀).

The long soaking-up crack can be considered as a linear drain l₀ length. Surfaces of equal speeds in a zone of absorption will be cylindrical. Therefore,

(4)

Having designated width of the soaking-up crack 2b₀ and considering that L₀ = 2b₀l₀v₀, we will receive expression for determination of relative speeds in a zone of absorption of a crack

(5)

According to the obtained experimental data, speed in an absorption range at a slot-hole suction at distance of half-width of a crack of b₀ is about 6 times less than v₀ speed, and at the distance equal to crack width (2b₀), decreases by 12 times.

For the rectangular soaking-up openings it is convenient to use a formula

(6)

where k – the proportionality coefficient depending on conditions of dribble of air and a ratio of the parties of an opening. On formulas (3) and (5) it is possible to receive rather exact result at sizes х > 0,5d₀ for round and square openings and at х > b₀ for squared exhaust openings.

The limiting planes located near the soaking-up openings have a great influence on the size of speeds in ranges of absorption. If the limiting planes are established directly near the soaking-up opening perpendicular to its axis, they will have essential impact at the values of their width exceeding d₀ (for round branch pipes) or equal to the size of the smaller party 2b₀ (for rectangular openings). So, at an arrangement of the soaking-up opening in a flat wall the zone of absorption decreases twice and respectively the size of speeds of air in ranges increases (see figure 1) twice. If the limiting plane is established not in the plane of an exhaust opening, and at some distance from it, its influence on intensity of speeds decreases, and during removal more than on 1/4∙d₀ (or 1/2∙b₀) becomes almost insignificant. At an arrangement of the limiting plane parallel to an axis of an exhaust branch pipe there is a considerable change of the directions of the leaking air. Owing to braking by the plane of an air stream directly on an axis of an exhaust branch pipe of speed of air decrease, and at edges of a branch pipe increase.

The analysis of ranges of absorption of openings of the final sizes shows that the maximum speeds are observed on an axis of an exhaust branch pipe (see figure 1). In process of movement of the considered range point to edges of speed of air decrease as to extreme openings of a lattice air leaks not only in front, but also from surrounding space. Therefore for ensuring effective work of a local suction it is necessary to do extreme cracks of the soaking-up lattices approximately twice wider, than averages. When developing suctions for tables of the welder such constructive decision yielded good result.

It is important to note that at the turbulent mode of a current ranges of absorption become automated model, i.e. ranges of absorption are identical to geometrically similar designs of suctions and don't depend on a consumption of the deleted air. It allows to use data of experiment for the solution of a number of practical problems of local ventilation, helping to determine sizes of effective expenses of speeds of the deleted air.

So far questions of absorption of a lateral suction, in relation to operating conditions of a table of the welder, in particular, change of a tilt angle of a peak aren't rather studied, at horizontal installation of a peak and on condition of installation at the edges of the panel of lateral guards.

Measurements of fields of speeds of a lateral suction of a table of the welder (figure 2) are moved.

Figure 2 – Ranges of absorption of a lateral suction of a table of the welder:

a – a range at installation of a peak at an angle 45 ° (L = 1600 m³/h); and in – ranges at horizontally established peak: L = 1200 m3/h and L = 1600 m³/h respectively; (φ = 3/4π); – a range at installation on to edges of the panel of lateral guards (L = 1000 m³/h).

From comparison of figures 2, and 2, in it is visible that at change of a tilt angle of a peak φ (reduction of a zone of absorption) speeds in a range of absorption increase, especially in the zone located under a peak. Increase of speeds precisely corresponds to increase in amount of the deleted air (figure 2, and 2, c). Significantly sizes of speeds of air increase in an area of coverage of the lateral panel at installation of the limiting planes at the edges of a table (approximately twice) (figure 2, d).

Literature

1. Батурин В.В. Основы промышленной вентиляции. –М.: Стройиздат, 1986. –322 с.

2. Гринберг А.А., Топольская И.М. Вытяжной зонт с конической вставкой/Водоснабжение и санитарная техника. 1996. №8. –С. 25-29.

3. Абрамович Г.М. Теория турбулентных струй. –М.: Физматгиз, 1990. –405 с.