Improving the air environment. Ventilation systems. Report: Ventilation and air conditioning Air conditioning BZhD

One of the main means of collective protection of workers from negative impact harmful factors air environment(dust, gas contamination, increased heat and humidity) is ventilation.

Ventilation- is a complex of interconnected devices and processes designed to create organized air exchange necessary to remove contaminated or overheated (cooled) air from the production premises with the supply of clean and cooled (heated) air instead, which allows creating work area favorable conditions air environment.

The amount of air required to ensure the required air parameters in the work area is determined depending on the amount of harmful factors released in such a way as to ensure maximum permissible concentrations and levels.

Under ventilation system understand a set of ventilation units with different purposes that can serve separate room or building. The classification of the main types of ventilation is presented in Fig. P1.9.

Depending on the method of air movement in work areas, ventilation is divided into artificial (mechanical), natural and combined.

At natural ventilation air exchange is carried out in two ways:

Unorganized (ventilation and air infiltration through window, door openings, cracks and microcracks);

Organized (through aeration and using deflectors).

Natural unorganized air exchange in a room is caused by the action of two factors: thermal air movement and wind pressure. Thermal movement is created by the difference in the weight of air columns outside and inside the room. Thus, a pressure difference occurs, which causes air exchange. Wind pressure is caused by the action of the wind, due to which excess pressure occurs on the windward surfaces of the building, and rarefaction occurs on the leeward sides. The resulting pressure difference causes air to enter from the windward side of the building and exit through openings on the opposite windward side. In some cases, unorganized air exchange is not enough to remove harmful emissions from the room, so a special device is used - a deflector (see Fig. A1.10). The deflector is the end of a pipe designed to remove air from the upper zone of the room. The wind flow, hitting the deflector and flowing around it, creates a vacuum that ensures air suction from the room through the deflector channel. Aeration is organized natural air exchange, carried out in pre-calculated volumes and regulated in accordance with external meteorological conditions.

The advantage of natural ventilation is the simplicity of the devices and minimal operating costs. The disadvantage is the influence of natural factors (wind, ambient temperature) on its effectiveness, as well as the fact that air is supplied and removed from the room that has not undergone special treatment (not cleared of dust and other harmful impurities, not refrigerated or heated). Therefore, natural ventilation is used mainly where there are no significant emissions of harmful factors.

At artificial ventilation air movement is activated mechanical devices. Classification mechanical ventilation shown in Fig. P1.11.

According to the nature of the room coverage ventilation systems can be general exchange, local (local) and combined.

At general ventilation air change occurs throughout the entire volume of the room. This type of ventilation can be carried out either naturally (aeration) or mechanically.

The purpose of local ventilation is to localize harmful emissions in places of formation and remove them from the room. It can be carried out mechanically with the help of fans and naturally with the help of deflectors.

With a combined system, simultaneously with the general air exchange, the individual most intense sources of emissions are also localized.

Local ventilation can be supply or exhaust.

The supply air is provided for the purpose of supplying clean air into the work area to create a microclimate in individual places (air showers, curtains and oases). An air shower is a stream of air directed at a person. The air curtain prevents cold air from entering the industrial building through the gates. winter time. Air oases improve weather conditions for limited area room, which is separated for this purpose on all sides light partitions and is flooded with air that is colder and cleaner than the air in the room.

Exhaust ventilation they are installed in places where harmful emissions are formed in the form of cabinets, umbrellas, suction from various equipment, vacuum cleaners, dust collectors, ejection units, individual suction units, and so on.

General mechanical ventilation can be supply, exhaust, supply and exhaust, and can also be carried out using air conditioners. With forced-air general ventilation, fresh air is taken from places outside the building and distributed throughout the entire volume of the room. Polluted air is displaced by fresh air through doors, windows, lights and cracks building structures. Supply ventilation is used in the presence of heat emissions and the absence of gas emissions.

Exhaust general ventilation allows you to remove contaminated and overheated air from the entire volume of the room. To replace the removed air, clean air is sucked in from the outside through doors, windows, and cracks in building structures.

Supply and exhaust general exchange mechanical ventilation consists of two separate units. Through one, clean air is supplied, through the other, contaminated air is removed.

Air conditioning is ventilation unit, which, using automatic control devices, maintains the specified air parameters in the room.

There are two types of air conditioners: full air conditioning units that ensure constant temperature, relative humidity, speed of movement and air purity, as well as installations of incomplete air conditioning, ensuring the constancy of only part of these parameters or one parameter, most often temperature.

Depending on the method of refrigeration supply, air conditioners are divided into autonomous and non-autonomous. In stand-alone air conditioners, the cold is produced by its own built-in refrigeration units. Non-autonomous air conditioners are supplied with coolants centrally.

According to the method of preparing and distributing air, air conditioners are divided into central and local. The design of central air conditioners provides for the preparation of air outside the serviced premises and its distribution through the air duct system. In local air conditioners, air is prepared directly in the premises served; the air is distributed concentratedly, without air ducts.

The purpose of ventilation is to ensure clean air and specified meteorological conditions in production premises.

Ventilation is achieved by removing polluted or heated air from a room and introducing fresh air into it.

Depending on the method of air movement, ventilation can be natural or mechanical. It is also possible to combine natural and mechanical ventilation (mixed ventilation) in various options.

Depending on what the ventilation system is used for - to supply (supply) or remove (exhaust) air from the room or both at the same time, it is called supply, exhaust or supply and exhaust.

Depending on the location of action, ventilation can be general and local.

The action of general ventilation is based on the dilution of excreted harmful substances fresh air up to maximum permissible concentrations or temperatures. This ventilation system is most often used in cases where harmful substances are released evenly throughout the room. With such ventilation, the necessary parameters of the air environment are maintained throughout its entire volume (Fig. 2, a).

Rice. 2. Ventilation systems:

a, b, c - general exchange; g - general exchange and local; d — organization of air exchange: 1 — control panel room; 2 - local suctions

If the room is very large, and the number of people in it is small, and their location is fixed, it does not make sense (for economic reasons) to improve the health of the entire room completely, you can limit yourself to improving the air environment only in the places where people are. An example of such an organization of ventilation can be observation and control cabins in rolling shops, in which local supply and exhaust ventilation is installed (Fig. 2, d), workplaces in hot shops equipped with air showering units, etc.

Air exchange in a room can be significantly reduced if harmful substances are captured at the points of their release, preventing them from spreading throughout the room. To this end technological equipment, which is a source of release of harmful substances, is equipped with special devices from which polluted air is sucked out. Such ventilation is called local exhaust or localization (Fig. 2, d).

Local ventilation Compared to general exchange, it requires significantly lower costs for device and operation.

In industrial premises in which large quantities of harmful vapors and gases may suddenly enter the air of the working area, emergency ventilation is provided.

In production they often arrange combined systems ventilation (general exchange with local, general exchange with emergency, etc.).

For successful work ventilation system, it is important that the following technical and sanitary-hygienic requirements are met even at the design stage.

1. The volume of air flow into the room Lnp must correspond to the exhaust volume Lext; the difference between these volumes should not exceed 10-15%.

In some cases, it is necessary to organize air exchange in such a way that one of the volumes is necessarily larger than the other. For example, when designing the ventilation of two adjacent rooms (Fig. 2, d), in one of which harmful substances are released (room I), the volume of exhaust from this room is greater than the volume of inflow, i.e. Lout > LnpI, resulting in This room creates a slight vacuum and harmless air from room II with slight overpressure LBblTII

There are also possible cases of organizing air exchange when excess pressure relative to atmospheric pressure is maintained throughout the room. For example, in electric vacuum production workshops, for which the absence of dust penetrating through various leaks in enclosures is especially important, the volume of air inflow is greater than the volume of exhaust, due to which a certain excess pressure is created (RPom > Patm).

2. Supply and exhaust systems in the room must be correctly placed.

Fresh air must be supplied to those parts of the room where the amount of harmful emissions is minimal (or none at all), and removed where the emissions are maximum (Fig. 2, b, c).

Fig. 4.3. Air supply diagrams: diagrams a - from top to bottom; b - from top to top; c - from bottom to top; g - from bottom to bottom Rice. 4.2. Pressure distribution in a building Rice. 4.4. Scheme supply ventilation: 1 - device in the form of a channel or shaft; 2 - filter for air purification; 3 - bypass channel; 4 - air heater; 5 - air duct network; 6 - fan; 7 - supply pipes with nozzles Rice. 4.5. Schemes of supply nozzles: a, b - for vertical supply; c, d - for one-sided feeding at different angles; d - for concentrated inclined feed; f, g - for scattered horizontal feed Rice. 4.6. Exhaust ventilation diagram: 1 - air purification device; 2 - fan; 3 - central air duct; 4 - suction air ducts Rice. 4.7. Supply and exhaust ventilation: 1 - shaft; 2 - filter for air purification; 3 - bypass channel; 4 - air heater; 5 - air ducts; 6 - fan; 7 - supply pipes with nozzles Rice. 4.8. Supply and exhaust ventilation with recirculation: 1 - shaft; 2 - filter for air purification; 3 - bypass channel; 4 - air heater; 5 - air ducts; 6 - fan; 7 - supply pipes with nozzles; 8 - exhaust pipes with nozzles; 9 - valve Rice. 4.9. Air curtains: a - with bottom air supply; b - with lateral two-way air supply; c - with one-way air supply; d - detail of the slot; H, B - height and width of gates (doors), respectively; b - slot width Rice. 4.11. Fume hoods: a - with top suction; b - with lower suction; c, d - with combined suction Rice. 4.10. Local suctions: a - umbrella; b - overturned umbrella; c - suction panel Rice. 4.12. Onboard suction: a - to remove volatile vapors; b - to remove heavy vapors Rice. 4.13. Cyclone TsN-15 NIIOGAZ: 1 - bunker; 2 - metal cylinder; 3 - pipe; 4 - pipe

Per condition human body big influence influence meteorological conditions (microclimate) in production premises.

In accordance with GOST 12.1.005-88 microclimate production premises is determined by the combinations of temperature, humidity and air speed acting in them on the human body, as well as the temperature of the surrounding surfaces.

If work is carried out in open areas, then meteorological conditions are determined climatic conditions and season of the year.

Air temperature- a parameter characterizing its thermal state, i.e. kinetic energy molecules of gases included in its composition. Temperature is measured in degrees Celsius or Kelvin.

The temperature regime of the room depends on the formula "src="http://hi-edu.ru/e-books/xbook908/files/tp, these two factors determine the convective and radiative heat exchange between humans and the environment. To assess the influence of temperatures of heated surfaces, the concept of radiation temperature is introduced. Roughly it can be defined as follows:

Gif" border="0" align="absmiddle" alt=".

Joint influence formula" src="http://hi-edu.ru/e-books/xbook908/files/tp.gif" border="0" align="absmiddle" alt=".gif" border="0" align="absmiddle" alt="

In most cases, for ordinary premises the formula" src="http://hi-edu.ru/e-books/xbook908/files/tp.gif" border="0" align="absmiddle" alt=".gif" border="0" align="absmiddle" alt=".

Under atmospheric pressure refers to a quantity characterized by column pressure atmospheric air per single surface. Normal pressure is considered to be 1013.25 hPa (hectopascal, very rarely used in practice) or 760 mm. rt. Art. (1 hPa =
= 100 Pa = 3/4 mm. rt. Art.).

Atmospheric air consists of a mixture of dry gases and water vapor, i.e. we always deal with moist air or a steam-air mixture. Moreover, water vapor can be either in a superheated or saturated state. To characterize the moisture content in the air, the concepts of absolute and relative humidity are used.

Absolute air humidity is the mass of water vapor contained in 1 mark"> Air mobility. A person begins to feel the movement of air at a speed of approximately 0.1 m/s. At normal temperatures, light air movement, blowing away the steam-saturated and superheated layer of air enveloping a person, promotes good health. At the same time, in conditions low temperatures, high air speed causes an increase in heat loss by convection and evaporation and leads to severe cooling of the body.

All life processes in the human body are accompanied by the formation of heat, the amount of which varies from 80 J/s (at rest) to 700 J/s (when performing heavy physical work).

Despite the fact that the factors that determine the indoor microclimate can vary greatly within wide limits, the human body temperature remains, as a rule, at a constant level (36.6 mark "> Weather conditions, in which there are no unpleasant sensations and tension in the thermoregulatory system are called comfortable (optimal) conditions.

Meteorological conditions are perceived by a person as comfortable only when the amount of heat generated by the body is equal to the total heat transfer to the environment, i.e. while maintaining thermal balance.

Heat exchange body with environment may happen in various ways: convective transfer of heat to the surrounding air (in normal conditions up to 5% of all heat removed); radiant heat exchange with surrounding surfaces (40%); contact thermal conductivity through contacting surfaces (30%); evaporation of moisture from the surface of the skin (20%); due to heating of exhaled air (5%).

When the air temperature drops, to reduce heat transfer, the body reduces the temperature of the skin, reduces the moisture content of the skin, thereby reducing heat transfer. When the air temperature rises blood vessels the skin expands, there is an increased blood flow to the surface of the body, and heat transfer to the environment increases significantly..gif" border="0" align="absmiddle" alt="With significant thermal radiation from heated surfaces, the body's thermoregulation is disrupted. This can lead to overheating, especially if moisture loss approaches 5 liters per shift. In this case, there is increasing weakness, headache, tinnitus, distortion of color perception (everything turns red or green), nausea, vomiting, and increased body temperature. Breathing and pulse quicken, blood pressure first increases, then falls. In severe cases, heat stroke occurs. A convulsive disease is possible, which is a consequence of a violation of the water-salt balance and is characterized by weakness, headache, and sudden cramps of the limbs.

But further, if such painful conditions do not occur, overheating of the body greatly affects the state of the nervous system and human performance. It has been established that with a 5-hour stay in an area with an air temperature of 31 hint ">, neuritis, radiculitis, etc., as well as colds. Any degree of cooling is characterized by a decrease in heart rate and the development of inhibition processes in the cerebral cortex, which leads to a decrease In particularly severe cases, exposure to low temperatures can lead to frostbite and even death.

Different combinations of microclimate parameters, having a complex effect on a person, can cause the same thermal sensations. This is the basis for the introduction of the so-called effective and effective-equivalent temperatures. Effective temperature characterizes a person's sensations when exposed to temperature and air movement simultaneously. The effective equivalent temperature also takes into account air humidity. The effective temperature and comfort zone can be determined using a nomogram constructed empirically(Fig. 4.1 ).

Excess heat, moisture release, thermal radiation, and high air mobility worsen the microclimate of industrial premises, complicate thermoregulation, adversely affect the body of workers and contribute to a decrease in productivity and quality of work.

Air contaminated with harmful gases, vapors and dust poses a risk of poisoning or occupational diseases, causes increased fatigue, and, as a consequence, increases the risk of injury.

From a physiological point of view, air should be considered from two positions: as air inhaled by a person, and as a medium surrounding a person. The role of air, accordingly, is to supply the body with oxygen, remove moisture during exhalation and ensure heat exchange between a person and the environment. Air is also a working agent that removes dust, moisture, and harmful emissions from the room.

Sanitary standards establish the values ​​of optimal microclimate parameters in workplaces (Table 4.1).

Table 4.1

Optimal parameters microclimate 5 at workplaces
(SanPiN 2.2.4.548-96)

5 Relative air humidity for all seasons and categories

MINISTRY OF EDUCATION AND SCIENCE OF UKRAINE

KRASNODON MINING TECHNIQUE

Abstract on the subject “SAFETY

TECHNOLOGICAL

PROCESSES AND PRODUCTION"

on the topic: “INDUSTRIAL VENTILATION »

Student of group 1EP-06

Uryupov Oleg

Checked by: Drokina T.M.

Krasnodon 2010

Ventilation is a complex of interconnected devices and processes for creating the required air exchange in industrial premises. The main purpose of ventilation is to remove contaminated or overheated air from the working area and supply clean air, as a result of which the necessary favorable air conditions are created in the working area. One of the main tasks that arises when installing ventilation is determining the air exchange, i.e. the amount ventilation air necessary to ensure an optimal sanitary and hygienic level of the indoor air environment.

Depending on the method of air movement in industrial premises, ventilation is divided into natural and artificial (mechanical).

The use of ventilation must be justified by calculations that take into account temperature, air humidity, release of harmful substances, and excess heat generation. If there are no harmful emissions in the room, then ventilation should provide an air exchange of at least 30 m3 / h for each worker (for rooms with a volume of up to 20 m3 per worker). When harmful substances are released into the air of the working area, the necessary air exchange is determined based on the conditions of their dilution to the maximum permissible concentration, and in the presence of thermal excess - from the conditions of maintaining permissible temperature in the work area.

Natural ventilation production premises is carried out due to the temperature difference in the room from the outside air (thermal pressure) or the action of wind (wind pressure). Natural ventilation can be organized or unorganized.

With unorganized natural ventilation air exchange is carried out by displacing internal thermal air with external cold air through windows, vents, transoms and doors. Organized natural ventilation, or aeration, provides air exchange in pre-calculated volumes and adjustable in accordance with meteorological conditions. Channelless aeration is carried out using openings in the walls and ceiling and is recommended in large rooms with significant excess heat. To obtain the calculated air exchange, ventilation openings in the walls, as well as in the roof of the building (aeration skylights) are equipped with transoms that open and close from the floor of the room. By manipulating the transoms, you can regulate the air exchange when changing outside temperature air or wind speed (Fig. 4.1). The area of ​​ventilation openings and skylights is calculated depending on the required air exchange.

Rice. 4.1. Scheme of natural ventilation of the building: A- when there is no wind; b- in the wind; 1 - exhaust and supply openings; 2 - fuel generating unit

In small production premises, as well as in premises located in multi-storey buildings industrial buildings, channel aeration is used, in which contaminated air is removed through ventilation ducts in the walls. To enhance the exhaust, deflectors are installed at the exit from the ducts on the roof of the building - devices that create draft when the wind blows on them. In this case, the wind flow, hitting the deflector and flowing around it, creates a vacuum around most of its perimeter, which ensures air suction from the channel. The most widely used deflectors are the TsAGI type (Fig. 4.2), which are a cylindrical shell mounted above the exhaust pipe. To improve air suction by wind pressure, the pipe ends in a smooth expansion - a diffuser. A cap is provided to prevent rain from entering the deflector.

Rice. 4.2. TsAGI type deflector diagram: 1 - diffuser; 2 - cone; 3 - legs holding the cap and shell; 4 - shell; 5 - cap

Calculation of the deflector comes down to determining the diameter of its pipe. Approximate diameter of the pipe d TsAGI type deflector can be calculated using the formula:

Where L- ventilation air volume, m3/h; - air speed in the pipe, m/s.

The air speed (m/s) in the pipe, taking into account only the pressure created by the action of the wind, is found using the formula

where is wind speed, m/s; - the sum of the local resistance coefficients of the exhaust air duct in its absence e = 0.5 (at the entrance to the branch pipe); l- length of the branch pipe or exhaust air duct, m.

Taking into account the pressure created by the wind and thermal pressure, the air speed in the nozzle is calculated using the formula

where is thermal pressure Pa; here is the height of the deflector, m; - density, respectively, of outdoor air and indoor air, kg/m3.

The speed of air movement in the pipe is approximately 0.2...0.4 wind speed, i.e. If the deflector is installed without exhaust pipe directly in the ceiling, then the air speed is slightly higher.

Aeration is used for ventilation of large industrial premises. Natural air exchange is carried out through windows, skylights using heat and wind pressure (Fig. 4.3). Thermal pressure, as a result of which air enters and leaves the room, is formed due to the temperature difference between the external and internal air and is regulated by varying degrees of opening of the transoms and lanterns. The difference between these pressures at the same level is called internal excess pressure. It can be both positive and negative.

Rice. 4.3. Building aeration scheme

At negative value(exceeding external pressure over internal) air enters the room, and when positive value(internal pressure exceeds external pressure) air leaves the room. At = 0 there will be no air movement through the holes in the outer fence. The neutral zone in the room (where = 0) can only exist under the influence of excess heat alone; when there is wind with excess heat, it sharply shifts upward and disappears. The distances of the neutral zone from the middle of the exhaust and supply openings are inversely proportional to the squares of the areas of the openings. At, where are the areas, respectively, of the inlet and outlet openings, m2; -height of the level of equal pressures, respectively, from the inlet to the outlet, m.

Air flow G, which flows through a hole having an area F, calculated by the formula:

Where G- massive second consumption air, t/s; m is the flow coefficient depending on the outflow conditions; r - air density in the initial state, kg/m3; - pressure difference inside and outside the room in a given hole, Pa.

The approximate amount of air leaving the room through 1 m2 of opening area, taking into account only thermal pressure and provided that the areas of the holes in the walls and lanterns are equal and the flow coefficient m = 0.6, can be determined using a simplified formula:

Where L- amount of air, m3/h; N- distance between the centers of the lower and upper holes, m; - temperature difference: average (altitude) indoors and outdoor, ° C.

Aeration using wind pressure is based on the fact that excess pressure occurs on the windward surfaces of the building, and rarefaction occurs on the windward sides. Wind pressure on the surface of the fence is found by the formula:

Where k- aerodynamic coefficient, showing what proportion of the dynamic wind pressure is converted into pressure in a given section of the fence or roof. This coefficient can be taken on average equal to + 0.6 for the windward side, and -0.3 for the leeward side.

Natural ventilation is cheap and easy to operate. Its main disadvantage is that the supply air is introduced into the room without preliminary cleaning and heating, and the exhaust air is not cleaned and pollutes the atmosphere. Natural ventilation is applicable where there are no large emissions of harmful substances into the work area.

Artificial (mechanical) ventilation eliminates the shortcomings of natural ventilation. With mechanical ventilation, air exchange is carried out due to the air pressure created by fans (axial and centrifugal); The air is heated in winter, cooled in summer and is also cleaned of contaminants (dust and harmful vapors and gases). Mechanical ventilation can be supply, exhaust, supply and exhaust, and according to the place of action - general and local.

At supply ventilation system(Fig. 4.4, A) air is taken from the outside using a fan through a heater, where the air is heated and, if necessary, humidified, and then supplied to the room. The amount of air supplied is controlled by valves or dampers installed in the branches. Polluted air comes out unpurified through doors, windows, lanterns and cracks.

At exhaust system ventilation(Fig. 4.4, b) polluted and overheated air is removed from the room through a network of air ducts using a fan. Polluted air is cleaned before being released into the atmosphere. Clean air is sucked in through windows, doors, and structural leaks.

Supply and exhaust ventilation system(Fig. 4.4, V) consists of two separate systems - supply and exhaust, which simultaneously supply clean air into the room and remove polluted air from it. Supply ventilation systems also replace air removed by local suction and spent on technological needs: fire processes, compressor units, pneumatic transport, etc.

To determine the required air exchange, it is necessary to have the following initial data: the amount of harmful emissions (heat, moisture, gases and vapors) per 1 hour, the maximum permissible amount (MAC) of harmful substances in 1 m3 of air supplied to the room.

Rice. 4.4. Scheme of supply, exhaust and supply and exhaust mechanical ventilation: A- supply; 6 - exhaust; V- supply and exhaust; 1 - air intake for intake of clean air; 2 - air ducts; 3 - filter for air purification from dust; 4 - air heaters; 5 - fans; 6 - air distribution devices (nozzles); 7 - exhaust pipes for releasing exhaust air into the atmosphere; 8 - devices for cleaning exhaust air; 9 - air intake openings for exhaust air; 10 - valves for regulating the amount of fresh secondary recirculation and exhaust air; 11 - a room served by supply and exhaust ventilation; 12 - air duct for the recirculation system

For rooms with the release of harmful substances, the required air exchange L, m3 / h, is determined from the condition of the balance of harmful substances entering it and diluting them to acceptable concentrations. Balance conditions are expressed by the formula:

Where G- rate of release of harmful substances from technological installation, mg/h; G etc- rate of entry of harmful substances with air flow into the work area, mg/h; Gud- the rate of removal of harmful substances diluted to permissible concentrations from the work area, mg/h.

Replacing in expression G etc And Gud by the product and, where and are, respectively, the concentration (mg/m3) of harmful substances in the supply and removed air, a and the volume of supply and removed air in m3 per 1 hour, we obtain

To maintain normal pressure in the working area, equality must be satisfied, then

The necessary air exchange, based on the content of water vapor in the air, is determined by the formula:

where is the amount of removed or supply air indoors, m3/h; G P- mass of water vapor released in the room, g/h; - moisture content of removed air, g/kg, dry air; - moisture content of supply air, g/kg, dry air; r - density of supply air, kg/m3.

where are the masses (g) of water vapor and dry air, respectively. It must be borne in mind that the values ​​and are taken from the tables physical characteristics air depending on the value of the standardized relative humidity of the exhaust air.

To determine the volume of ventilation air based on excess heat, it is necessary to know the amount of heat entering the room from various sources(heat arrival), and the amount of heat spent to compensate for losses through the building’s enclosures and other purposes, the difference expresses the amount of heat that goes to heat the air in the room and which must be taken into account when calculating air exchange.

The air exchange required to remove excess heat is calculated using the formula:

where is the excess amount of heat, J/s, is the temperature of the removed air, ° K; - supply air temperature, ° K; WITH- specific heat capacity of air, J/(kg×K); r - air density at 293° K, kg/m3.

Local ventilation Is there an exhaust or supply? Exhaust ventilation is used when pollution can be captured directly at the point of its origin. For this purpose, fume hoods, umbrellas, curtains, side suction at bathtubs, casings, suction at machine tools, etc. are used. Supply ventilation includes air showers, curtains, and oases.

Fume hoods work with natural or mechanical exhaust. To remove excess heat or harmful impurities from the cabinet naturally, a lifting force is required, which occurs when the air temperature in the cabinet exceeds the air temperature in the room. The exhaust air must have sufficient energy to overcome aerodynamic resistance on the way from the entrance to the cabinet to the point of release into the atmosphere.

Volume flow rate of air removed from fume hood with natural exhaust (Fig. 4.5), (m3 / h)

Where h- height of the open cabinet opening, m; Q- amount of heat generated in the cabinet, kcal/h; F- area of ​​the open (working) opening of the cabinet, m2.

Rice. 4.5. Scheme of a fume hood with natural exhaust: 1 - level zero pressure; 2 - diagram of pressure distribution in the working hole; T1- room air temperature; T 2 - gas temperature inside the cabinet

Required exhaust pipe height (m)

where is the sum of all resistances of a straight pipe along the path of air movement; d- straight pipe diameter, m (preset).

With mechanical extraction

Where v- average suction speed in sections of an open opening, m/s.

Onboard suctions arranged near production baths for removal of harmful vapors and gases that are released from bath solutions. For bath widths up to 0.7 m, single-sided suction units are installed on one of its longitudinal sides. When the bath width is more than 0.7 m (up to 1 m), double-sided suction is used (Fig. 4.6).

The volumetric flow rate of air sucked from hot baths by single- and double-sided suction units is found using the formula:

Where L- volumetric air flow, m3/h, k 3 - safety factor equal to 1.5...1.75, for baths with special harmful solutions 1,75...2; k T- coefficient for taking into account air leaks from the ends of the bath, depending on the ratio of the width of the bath IN to its length l; for single-sided simple suction; for double-sided - ; WITH- dimensionless characteristic equal to 0.35 for single-sided suction and 0.5 for double-sided suction; j is the angle between the suction boundaries (Fig. 4.7); (in calculations it has a value of 3.14); TV And Tp- absolute temperatures, respectively, in the bath and air in the room, °K; g=9.81 m/s2.

Exhaust hoods used when the released harmful vapors and gases are lighter than the surrounding air and its mobility in the room is insignificant. Umbrellas can be either with natural or mechanical exhaust.

Rice. 4.6. Double-sided bath suction

With natural exhaust the initial volumetric air flow rate in the thermal jet rising above the source is determined by the formula:

Where Q- amount of convective heat, W; F- horizontal projection area of ​​the heat source surface, m2; N- distance from the heat source to the edge of the umbrella, m.

With mechanical extraction the aerodynamic characteristic of the umbrella includes the speed along the axis of the umbrella, which depends on the angle of its opening; with increasing opening angle, the axial speed increases compared to the average. At an opening angle of 90°, the axial speed is l.65 v (v- average speed, m/s), with an opening angle of 60°, the speed along the axis and across the entire cross section is equal v .

In general, the flow rate of air removed by the umbrella is

Where v- average speed of air movement in the intake opening of the umbrella, m/s; when removing heat and moisture, the speed can be taken as 0.15...0.25 m/s; F- design cross-sectional area of ​​the umbrella, m2.

The receiving hole of the umbrella is located above the heat source; it must correspond to the configuration of the umbrella, and the dimensions are somewhat larger than the dimensions of the heat source in plan. Umbrellas are installed at a height of 1.7...1.9 m above the floor.

To remove dust from various machines, dust collection devices are used in the form of protective and dust removal casings, funnels, etc.

Rice. 4.7. The angle between the boundaries of the suction torch at different locations baths: A- near the wall (); b- next to the bathroom without suction (); V- separately (); 1 - bath with suction; 2 - bath without suction.

In calculations, take p = 3.14

Air volume flow L(m3/h) removed from grinding, grinding and roughening machines is calculated depending on the diameter of the wheel d To p(mm), namely:

at< 250 мм L = 2,

at 250...600 mm L = 1,8 ;

at > 600 mm L = 1,6.

The air flow rate (m3/h) removed by the funnel is determined by the formula:

Where VH- initial speed of the exhaust torch (m/s), equal to speed transportation of dust in the air duct, accepted for heavy emery dust 14...16 m/s and for light mineral dust 10...12 m/s; l- working length of the exhaust torch, m; k- coefficient depending on the shape and aspect ratio of the funnel: for a round hole k= 7.7 for rectangular with aspect ratio from 1:1 to 1:3 k = 9,1; V k- the required final speed of the exhaust torch at the circle, taken equal to 2 m/s.

LITERATURE

1. Life safety/Ed. Rusaka O.N.-S.-Pb.: LTA, 1996.

2. Belov S.V. Life safety is the science of survival in the technosphere. NMS materials on the discipline “Life Safety”. - M.: MSTU, 1996.

3. All-Russian monitoring of the social and labor sphere 1995. Statistical collection. - Ministry of Labor of the Russian Federation, M.: 1996.

4. Environmental hygiene./Ed. Sidorenko G.I..- M.: Medicine, 1985.

5. Occupational hygiene when exposed to electromagnetic fields./Ed. Kovshilo V.E.- M.: Medicine, 1983.

6. Zolotnitsky N.D., Pcheliniev V.A.. Occupational safety in construction. - M.: Higher School, 1978.

7. Kukin P.P., Lapin V.L., Popov V.M., Marchevsky L.E., Serdyuk N.I. Fundamentals of radiation safety in human life. - Kursk, KSTU, 1995.

8. Lapin V.L., Popov V.M., Ryzhkov F.N., Tomakov V.I. Safe human interaction with technical systems. - Kursk, KSTU, 1995.

9. Lapin V.L., Serdyuk N.I. Occupational safety in foundry production. M.: Mechanical Engineering, 1989.

10. Lapin V.L., Serdyuk N.I. Occupational safety management at an enterprise. - M.: MIGZH MATI, 1986.

11. Levochkin N.N. Engineering calculations on labor protection. Publishing house of Krasnoyarsk University, -1986.

12. Occupational safety in mechanical engineering./Ed. Yudina B.Ya., Belova S.V. M.: Mechanical Engineering, 1983.

13. Labor protection. Information and analytical bulletin. Vol. 5.- M.: Ministry of Labor of the Russian Federation, 1996.

14. Putin V.A., Sidorov A.I., Khashkovsky A.V. Occupational safety, part 1. - Chelyabinsk, ChTU, 1983.

15. Rakhmanov B.N., Chistov E.D. Safety during operation of laser installations. - M.: Mashinostroenie, 1981.

16. Saborno R.V., Seledtsov V.F., Pechkovsky V.I. Electrical safety at work. Methodological instructions. - Kyiv: Vishcha School, 1978.

17. Reference book on labor protection/Ed. Rusaka O.N., Shaidorova A.A.- Chisinau, Publishing House “Cartea Moldovenasca”, 1978.

18. Belov S.V., Kozyakov A.F., Partolin O.F. and others. Means of protection in mechanical engineering. Calculation and design. Directory/Ed. Belova S.V.-M.: Mechanical Engineering, 1989.

19. Titova G.N. Toxicity of chemicals. - L.: LTI, 1983.

20. Tolokontsev N.A. Fundamentals of general industrial toxicology. - M.: Medicine, 1978.

21. Yurtov E.V., Leikin Yu.L. Chemical toxicology. - M.: MHTI, 1989.