There are always employees who apply showering. Air showering

1700 W/m2. Air temperature in the working area = 25 0C. According to table. 4.23 average temperature =19 0C, air mobility in the workplace

2.3 m/s. Distance from the shower pipe to the working pipe X = 1.8 m.

During the adiabatic cooling process, the air temperature at the outlet of the nozzle chamber is 18.5 0C.

We accept the PDN-4 shower pipe

Dimensions 630 mm h1=1540 mm l1=1260 mm

Estimated area 0.23 m2

Coefficient m=4.5 n=3.1 =3.2 =00-200

Determine the thermal cross-sectional area of ​​the pipe:

Table value =0.23 m2

Find the air speed at the outlet of the pipe:

We set the air flow supplied by the shower pipe:

During the cold season and in transitional conditions, the temperature and air speed in the workplace should be within the following limits:

18...19 0С =2.0...2.5 m/s =16 0С

We leave unchanged those adopted for the warm period, determine the air temperature at the outlet of the shower pipe at =16 0C and =19 0C using the formula:

Ventilation of crane operator's cabins

Ventilation system for crane operator cabins with outside air supply. Ventilation should provide a back-up of 10-15 Pa.

The cabin ventilation system with outside air supply is carried out according to the diagram shown in Fig. 1. The structure contains a manifold located along the path of movement of the crane, an intake device moving in the slot of the manifold and rigidly connected to the crane operator’s cabin. A rubber band or hydraulic seal is used as a sealing device for the manifold gap.

Rice. 1 - Ventilation of the crane cabin with air supply through the collector: 1 - collector, 2 - fan, 3 - crane cabin, 4 - muffler, 5 - rubber sealing tube

Local exhaust ventilation

Local suction from equipment emitting vapors, gases, bad odors

Calculation of the umbrella - canopy over the loading hole of the heating furnace

An umbrella - a canopy over the loading opening of the furnace is designed to catch the flow of gases emerging from the opening under the influence of overpressure in the oven. The dimensions of the suction opening of the umbrella must correspond to the dimensions of the suction jet, taking into account its curvature under the influence of gravitational forces (Fig. 2.)

Rice. 2

Let us determine the volume of air removed and the dimensions of the umbrella - canopy for a thermal furnace that has a loading hole of size h?b=0.5?0.5 m. The gas temperature in the furnace is maintained at tg=1150 0C, the air temperature in the working area =25 0C

1. Let's define average speed, with which gases are knocked out of the furnace opening, having previously calculated:

where - flow coefficient 0.65

Excess pressure in the furnace, Pa

h0 - half the height of the loading opening, m

and - density of air, respectively working area and gases leaving the furnace, kg/m3

2. Volume of gases leaving the working opening of the furnace, m3/s

where is the area of ​​the furnace working opening, m2

2.78(0.5?0.5)=0.69 m3/s

0.690.25=0.17 kg/s

3. Calculate Archimedes' criterion

where is the equivalent area diameter of the working opening, m

and - temperature, respectively, of gases in the furnace and air in the working area, K

Archimedes criterion at m

4. The distance at which the axis of the gas flow, curved under the pressure of gravitational forces, reaches the plane of the suction opening of the zone, m

where m, n are the coefficients of change in speed and temperature at the ratio of the height of the loading opening h to its width and in the range of 0.5...1, which are applied equal to 5 and 4.2, respectively. Let's determine the distance x at h0=0.25 m=5 n=4.2

5. Diameter of gas flow at a distance x at

0.565+0.440.653=0.852 m

6. Find the reach and width of the umbrella

B=b+(150...200)=b+0.2=0.5+0.2=0.7 m

7. Determine the flow rate of the sucked mixture of gases and air:

8. Air consumption drawn from the room:

0.727-0.69=0.037 m3/s

0.0371.18=0.044 kg/s

9. Temperature of gas mixture and mixture, 0C

Which is unacceptably high for natural (< 300 0С) и для механической (< 80 0С). Принимаем =300 0C, когда расход подсасываемого воздуха м/с, увеличивается до значения:

Total volume:

Let's determine the height chimney to remove the found mass of air. Let's take the pipe diameter dTP=500 mm

square cross section pipes:

0.7850.52=0.196 m2

Air speed in the pipe m/s

We preliminarily set the pipe height htr = 6 m. At the pipe head we install a deflector with a diameter ddef = 500 mm, deflector height hdef = 1.7 ddef = 1.70.5 = 0.85 m

Deflector local resistance coefficient

Umbrella local resistance coefficient

The pressure loss in the exhaust pipe together with the deflector, taking into account contamination of the walls, is determined by the formula:

Let us clarify the approximate height of the exhaust pipe from the equation:

Outside air temperature tн=21.2 0С, then:

Umbrella height:

Let's substitute the calculated values ​​into the formula:

5.73 m close to previously applicable

To create the required meteorological conditions at workplaces, air showers are used. The installation of air showers is necessary: ​​when workers are exposed to thermal radiation with an intensity of 350 W/m2 or more, when the air in the work area is heated above the set temperature, when it is impossible to use local shelters for sources of harmful emissions gases and vapors.

The use of air showers is advisable for thermal irradiation of workers in industrial furnaces, molten metal, heated ingots and workpieces. Intensity of thermal irradiation of the workplace, W/m 2 , 5.67 – black body emissivity coefficient, W/(m 2 K 4); – coefficient taking into account the distance from the radiation source to the workplace (Fig. 11.9, A); – irradiance coefficient for radiation from the hole (Fig. 4.3);

– temperature of the irradiation source, ºС.

Stationary shower. Air showers trace. Arranged after measures have been taken to reduce exposure to radiation from the application protective screens or water curtains. In hot shops it is necessary. provide thermal insulation of air ducts supplying air to the shower pipes.

When calculating outdoor air shower systems. accept design parameters A - for the warm and B - for the cold periods of the year. These systems cannot be combined with systems supply ventilation, they must be separate. Supply chambers or air conditioners are used to process and supply outside air to showers.

The direction of the air flow can be horizontal or from top to bottom at an angle of 45º. When combating harmful gas emissions, the air flow of the shower is directed into the person’s face. The width of the permanent workplace platform in the calculations is taken to be 1 m, and the minimum area of ​​the outlet section of the shower pipe is 0.1 m2 (or diameter 0.3 m).

Air showers can supply: 1) outside air that is humidified, cooled or heated and cleaned from dust; 2) outside air after cleaning from dust; 3) indoor air after cooling and 4) indoor air without treatment.

By design, air showers are stationary (Fig. 11.9, b) and mobile (Fig. 11.9, V).

Mobile units supply indoor air to workplaces without processing it. Sometimes they add to the air flow they create mist water, which enhances the cooling effect due to the evaporation of water droplets.

To cool and humidify the outside air supplied to the showers, it is processed in nozzle chambers, since the process using artificial cold requires significant costs.

The VA-1 fan unit and the PAM-24 unit were used as mobile showering units.

VA-1 has a cast iron frame 1 carrying an axial fan 3, a shell 4 with a mesh 5, a confuser 6 with guide vanes 7 and a fairing 8, a pneumatic nozzle 9 of type FP-1 or FP-2 and pipelines with flexible hoses 10 for supply compressed air and water. The fan can rotate around its axis at an angle of up to 60º, and rise vertically on the telescope 11 by 200-600 mm. The unit's productivity is 6 thousand m 3 /h. Fan units VA-2 and VA-3 develop productivity of two and three times, respectively.

Topic 2 Design of air showering of workplaces to improve microclimate parameters and air composition

When a worker is exposed to thermal radiation with an intensity of 0.14 kW/m2 or more (according to GOST 12.1.005-88), air showering is used (supply of supply air in the form of an air stream aimed at workplace). When the irradiation intensity is higher than 2.1 kW/m2, the air shower cannot provide the necessary cooling. In this case, radiation exposure should be reduced by providing thermal insulation, shielding and other measures. Or design devices for periodic cooling of workers (cabins, rest rooms, control stations).

The cooling effect of air showering depends on the temperature difference between the body of the worker and the air flow, as well as on the speed of air flow around the cooled body. To ensure specified temperatures and air velocities in the workplace, the air flow axis is directed towards the person’s chest horizontally or at an angle of 45. The distance from the edge of the shower pipe to the workplace must be at least 1 m. The minimum diameter of the pipe is taken to be 0.3 m. For fixed workplaces, the estimated width of the working platform is taken to be 1 m.

When showering fixed workplaces with treated or untreated air, cylindrical nozzles or rotary shower pipes of the PPD type (series 4.904-22) should be used.

When showering areas where workers are constantly located with treated or untreated air, you should use nozzles with an upper air supply of type PD B (series 4.904-36) or nozzles with a bottom air supply of type PD n (series 4.904-36).

When showering areas with untreated air, rotary aerators PAM-24 and VA (OV-02-134 series) should be used. The PAM-24 aerator consists of an axial fan with a diameter of 800 mm with an electric motor on one shaft. The fan rotates at an angle of up to 60 eleven times per minute. Jet range 20 m.

When showering a group of permanent workplaces, it is recommended to use air distribution devices of the VGK type (series 4.904-68). Air showering is also used during production processes that emit harmful gases or vapors, if the use of local shelters and suction is not possible. At the same time, to ensure acceptable concentrations harmful substances the air stream is directed into the breathing zone horizontally or from above at an angle of 45.

Technical data of shower pipes and distribution devices shown in .

Thus, air showering is used in the following cases:

1) With increased intensity of thermal radiation and especially in cases where it is not possible to use other methods of protection (for example, heat shields).

2) At elevated air temperatures in the work area.

3) With an increased concentration of harmful substances in the work area.

Design order air showering in case of thermal excess in production premises.

1. Determine standard air temperature values t air flow standards and speeds v standards for air showering according to and depending on the following factors:

– intensity of thermal radiation in workplaces.

2. We set the air temperature at the outlet of the cooling device t cooling and heating of air in air ducts  t when air moves from the cooling device to the shower pipe.

3. Determine the air temperature t o at the outlet of the shower pipe

t o = t cool +  t, С (2.1)

4. Determine the ratio of temperature differences

Where t o – air temperature at the outlet from the shower pipe, ˚С;

t r.z. – air temperature in the working area outside the air flow, ˚С;

t normal – standard air temperature in the workplace, ˚С;

5. We select a shower pipe for installation according to and and determine its characteristics:

– type of pipe;

– angle of inclination of the guide vanes of the pipe to the horizon  , ˚;

– temperature coefficient n;

– air flow velocity attenuation coefficient m;

– coefficient of local resistance of the shower pipe K m.s.

6. According to the conditions of the workshop (room), we accept the installation height of the shower pipe above the level of the working platform h.

The installation diagram of the shower pipe above the working platform is shown in Figure 2.1.

Figure 2.1 – Installation diagram of the shower pipe above the working surface

Legend in the figure:

h– installation height of the pipe above the working platform, m;

h h – the height of a person from the floor to his chest, m;

 – the angle of inclination of the guide vanes of the pipe to the horizon;

x– distance from the shower pipe to the workplace, m;

7. Determine the distance from the shower pipe to the workplace

, (2.3)

We determine the estimated area of ​​the outlet section of the shower pipe.

At P T< 0,6

(2.4)

9. Select the nearest standard pipe according to or and determine its cross-sectional area F y from the condition

F y  F O.

10. Check the length of the initial section of the jet by air speed

(2.5)

Length of the initial section of the jet
shows that within this area the speed of air movement is constant and equal to the flow speed at the exit from the shower pipe.

11. Determine the speed of air movement from the shower pipe:

(2.6)

12. Calculate the estimated amount of air per shower pipe

(2.7)

13. Check the length of the initial section of the jet
by temperature

(2.8)

14. Determine the air temperature at the outlet of the shower pipe

(2.9)

At  We believe that the selected pipe and the operating mode of the air conditioner will provide the necessary air flow parameters.

At < it is necessary to change the adopted design solutions and repeat the calculation of the pipe area.

15. Determine the amount of air per one shower pipe, taking into account the reserve coefficient of air flow K h.

, m 3 /s (2.10)

16. Determine the cross-sectional area of ​​the supply air ducts to the shower pipe.

We take the diameter of the supply air ducts equal to the inlet diameter of the shower pipe according to or.

17. We accept, according to the workshop conditions, a diagram for supplying air to the shower pipe (see the previous topic of practical training).

18. Determine pressure losses in air ducts.

19. Select a fan or air conditioner to ensure the required air flow parameters.

At P t = 0.6-1.0 calculations are carried out using the formulas:

(2.11)

(2.12)

At P t > 1.0 calculations are carried out using the formulas

(2.13)

(2.14)

It should be taken into account that when P T< 1,0 применяют адиабатичесое охлаждение воздуха. При P t  1.0 artificial air cooling is required.

Design order air showering when releasing harmful substances in the production area. Calculation is carried out according to the formulas

Where WITH r.z. And WITH o – concentration of harmful gas and dust vapors in the air of the working area and the air supplied from the shower pipe, mg/m3;

MPC – maximum permissible concentration of harmful substances in the air at the workplace, mg/m 3 (according to GOST 12.1.005-88).

At P To< 0,4 расчет ведут по формулам

At P k = 0.4-1.0 calculations are carried out using the formulas

;

;

.

When radiant heat and emissions of dust and gases enter the premises at the same time, calculations are made for each hazard separately. Further calculations are made using a large pipe made from those calculated for each type of harmful substance.

Bibliography

1. Means of protection in mechanical engineering: Calculation and design: Directory / S.V. Belov et al. – M.: Mashinostroenie, 1989. – 368 p.

2. Internal sanitary installations. In 2 parts / Ed. I.G. Staroverova // Part 2. Ventilation and air conditioning: Designer’s Handbook. – M.: Stroyizdat, 1978. – 509 p.

3. SNiP 2.04.05-86. Heating, ventilation and air conditioning / Gosstroy USSR. – M.: CITP Gosstroy USSR, 1987. – 64 p.

4. Handbook of labor protection at industrial enterprises / K.N. Tkachuk et al. – K.: Tekhnika, 1991. – 286 p.

Task No. 1 for the practical lesson "Design of air showering"

Air showering is organized in the production area. It is necessary to determine the required air exchange for one shower pipe (m 3 /h). The initial data is given in Table 2.1.

Task No. 2 for the practical lesson "Design of air showering"

Air ventilation of workplaces has been organized in the production area. Determine the pressure that the fan must develop to ensure the required air flow parameters. The initial data is given in table 2.2.

Table 2.1 – Initial data for task No. 1 (t r.z. =32˚C)

Installation height of the pipe above the working surface, m

, m

Class 36d, 1a, USSR esievznm

Iatenaa-teeeeeekav

P. V. Uchastkin

VENTILATION SHOWER UNIT FOR WORK

INSIDE HOT PRODUCTION EQUIPMENT In some cases, it becomes necessary! It is necessary to carry out work inside a hot production equipment . These include renovation work

in the furnaces of powerful electric steam boilers : stations, hot open hearth furnaces, as well as work on production operations inside heating and firing furnaces various products

These works are carried out under conditions of high temperature (up to 100), which is caused by the need to reduce downtime of the specified production equipment. These works are very difficult and cannot be carried out for a long time.

L7H To facilitate such work, a mobile ventilation showering unit is offered. The principle of operation of the installation is aimed at creating a zone of low temperature in the hot space by supplying air at a lower temperature than the temperature inside the hot equipment.

A distinctive feature of the proposed installation is the method of protecting the air shower torch from excessive new-! singing temperature when mixing the surrounding grief:.ci o Air.

Known designs of such installations do not provide protection for the suffocating 1ra kel and Ot na Grs VYa1. To address this drawback, it is proposed to install water spray nozzles on the shower nozzle. which create a curtain of finely atomized water on the periphery of the air plume. Hot air sucked from the surrounding space towards the main stream meets sprayed water on its way. Intense IIcoapeHIIe of water occurs, as a result of which the ambient air temperature decreases, which leads to a significant decrease! !o temperature in the choking torch.

To move the torch, it is proposed to use a flexible air duct, at the end of which 11PIHI Pe11.7PH d31INRU1oshi1 pump current. H!OH:Ioå can be mounted on a stand so that it can be rotated as needed! direction. No. 84128

Drawing 1 (Fig. 1) shows a diagram of a ventilation shower installation in operation; Fig. 2 – installation without hose, side view; in fig. 3 – “the same, front view.

Ventilation unit @4th unit of the installation consists of a medium-pressure centrifugal fan 1 and an electric motor 2. Mounted on the motor shaft Working wheel fan The fan and electric motor are mounted on a trolley 3, which has three wheels: two of them are mounted on common axis, the third is rotary. Turning the wheel Exec. 1 II cT c H Il P H Il o M o IH H P g H o B T II H . T I koso f O R vI;1 0 H H e x o I O B o l l I B c T H t e l e kkn provides it with good maneuverability. The fan inlet is covered with a mesh. To wind the rubber pad 11GYA 4, use reel b.

A starting device 6 of the electric motor, consisting of two package switches, is mounted on the trolley frame. One of the switches is used to turn the engine on or off, the other is used to switch phases, so that for any connection to the network electric current the direction of rotation of the electric motor required for the fan was ensured.

The air duct 7 is made of a flexible metal hose and has a length of 6 l. For more convenient use, it consists of two links, connected “in a row” using cuffs and locks. At one end of the duct there is a square flange for connection to the fan outlet, and at the other end there is an adapter pipe with a round flange and tightening locks for connection with the shower nozzle 8. The last one is an adapter outlet, inside of which 10 guide vanes are installed. The nozzle is articulated with a tripod 9, there is a round flange around which it can freely rotate 360. On the top of the nozzle, a tap 10, a tube for water supply and 11 water sprayers with an outlet diameter of 0.6 l1m are fixed.

To prevent clogging of water spray nozzles, a mesh filter l2 is installed on the rubber hose. The hose has inner diameter 10 mm, at one end there is a union nut for connection to the tube of the spray nozzle, and at the other end there is a nut for connection to the faucet on the water supply.

The worker must be in the area of ​​the air flow emerging from the nozzle, so that the head and upper body are in the flow.

When a worker moves, the shower flow is directed to a new location by rotating the nozzle around its axis.

The installation allows you to reduce the temperature in the workplace by

30 - 50C. If usually after 5 - 10 l1in of stay inside the furnace of a boiler or open-hearth furnace, the worker’s body temperature reached 39, then when working with the proposed installation and for 30 11 to one hour, the body temperature was 37. ,1", the essence of the invention

1. Ventilation showering installation for work inside hot production equipment, characterized by the fact that, in order to prevent an increase in the temperature of the showering air torch from mixing ambient air into it, water spray nozzles are installed on the periphery of the showering nozzle, creating water curtain around the air torch, ensuring a decrease in the temperature of the intake air. No. 84128

2. Installation according to item 1, specifically with the use of a flexible air duct, at the end of which a shower nozzle is attached, in order to bring the shower torch closer to the place of work.

3. Installation according to paragraphs. 1 and 2, characterized in that the shower nozzle is mounted on a stand with the ability to rotate it to direct the shower torch. No. 84128

11odp. to the stove 30j. (II - 61

Oum format. 70 108)i;

CBTI at the 1st (omitsts for affairs of innovations and discoveries of the prp Council of Ministers of the USSR

Moscow, Center, M. Cherkassky per., 216.

Volume It, 35 ed. l.

Price 7 kopecks.

Printing house, Sapunova Ave., 2, Editor N. I. Mosin Tskred A. A. 1 (Udryavitskaya 1 (orr. R. Rabinovich

An air shower is a local air flow directed at a person. In the area of ​​effect of the air shower, conditions are created that are different from the conditions throughout the entire room. With the help of an air shower, the following parameters of the air at a person’s location can be changed: mobility, temperature, humidity and the concentration of a particular hazard. Typically, the air shower's coverage area is: fixed workplaces, places where workers stay for the longest time, and rest areas. In Fig. Figure 3.19 schematically shows an air shower used to create the necessary conditions in the workplace.

Air showers are most often used in hot shops at workplaces exposed to thermal radiation.

Rice. 3.18. Onboard suction: a - simple; b - overturned; in - front blower

Rice. 3.19. Air shower: a - vertical; b - inclined; in - group

3.0 m/sec, temperature can vary from 16 to 24 °C. If an air shower is used to combat dust, the air speed should not be higher than 0.5-1.5 m/sec to prevent raising dust that has settled on the floor.

The design of the air outlet pipe (supply nozzle) has a great influence on the efficiency of the air shower. It is advisable to have this device rotatable and at the same time to provide the ability to change the angle of inclination of the flow axis by introducing rotating blades. In Fig. Figure 3.20 shows the supply nozzles designed by V.V. Baturin, made taking into account these two requirements.

Classification of ventilation and air conditioning systems

Rice. 3.20. Supply nozzles designed by V.V. Baturin: a - with upper supply; b - with lower air supply

An air shower can use outside air or air taken from the room. The latter, as a rule, undergoes appropriate processing (most often cooling). Outdoor air can also be processed to give it the necessary parameters.

Shower installations can be stationary or mobile.

Mobile units use indoor air, often treated by spraying water into the exhaust air stream.

Water evaporating adiabatically allows the air temperature to decrease. In Fig. 3.21 and 3.22 show water-air showers of this type designed by the Moscow and Sverdlovsk Institutes of Labor Protection.

IN air curtains ah, just like in air showers, the main property of the supply torch is used - its relative range. Air curtains are installed to prevent air from entering through technological openings or gates from one part of the building to another or from outside air into production premises. In Fig. Figure 3.23 shows diagrams of air curtains designed to prevent or sharply reduce the penetration of cold outside air into the workshop through the gates. The air supplied to the curtain can be preheated, and then the curtains are called air-thermal.

Air curtains designed to prevent the penetration of cold air should be installed at gates that are opened more than five times or for at least 40 minutes per shift, as well as at technological openings of heated buildings located laid down in areas with a design outdoor temperature for heating system design- 15 °C and below, when the possibility of installing gateways is excluded. If a decrease in indoor air temperature(technological or sanitary- hygienic reasons) is unacceptable, curtains can be designed for any duration of opening and any design temperature of the outside air. In this case, it is necessary to- economic justification for this decision.

Rice. 3.21. Water-air shower MIOT type small model:

Rice. 3.22. Mobile fan unit SIOT-3:

Rice . 3.23. Air curtains: A - operating principle; b - various air supply methods:

I - air supply from below; II - side air supply on one side; III - same on both sides

1 - water supply pipeline

from the water supply; 2 - casing; 3 - electric motor; 4 - axial fan; 5 - drain pipe; 6 - stand 1 - axial fan; 2 - electric motor; 3 - nozzles; 4 - metal fairing; 5 - stand on wheels; 6 - pipeline for supplying water from the water supply system

In the case of a short-term (up to 10 minutes) opening of the gate, as a rule, it is allowed to reduce the air temperature in workplaces protected from air blowing through the gate by screens or partitions. The degree of reduction depends on the nature of the work performed: for light physical work - up to 14 ° C, for moderate work - up to 12 ° C, for heavy work - up to 8 ° C. If there are no permanent workplaces in the gate area, the temperature in the work zone of this area may be reduced to +5°.

Very close to air-thermal curtains in their purpose are the so-called air buffers, created by supplying warm air to the vestibules of public buildings (shops, clubs, theaters, etc.).

Currently the necessary conditions The air environment in the workplace is quite often created by installing special ventilated cabins. In such booths, conditions are maintained that are different from the conditions throughout the entire production facility. This is most often achieved by supplying specially prepared air to the cabins: cooled in hot shops, heated in cold, unheated rooms. Ventilated cabins can be classified as local ventilation systems. Naturally, their use is possible when the workplace is strictly fixed, for example at the control panel. In Fig. Figure 3.24 shows a ventilated cabin for a crane control station, developed by the Leningrad Institute of Occupational Safety and Health.

General ventilation systems can be supply and exhaust (Fig. 3.5, 3.6, 3.9). When using general exchange systems, the task is to create the necessary air conditions in the entire volume of the room or in the volume of the work area. Unlike local systems, in this case all harmful substances released in the room are distributed throughout the entire volume. Consequently, the main task that must be solved when designing the systems under consideration is to ensure that the content of one or another harmful substance in the indoor air does not exceed the maximum permissible concentration, and that the values ​​of meteorological parameters meet the relevant requirements.

Often the room is equipped with supply and exhaust general ventilation systems (Fig. 3.10).

The general exchange method of creating specified air conditions is widely used in combination with air conditioning systems.

Rice. 3.24. Ventilated cabin

In this course, very much attention is paid to this method, since it is the main one for MO objects