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 hole of the furnace is designed to catch the flow of gases escaping from the hole under the influence of excess pressure in the furnace. 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 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 tg=1150 0C, the air temperature in the working area =25 0C

1. Let us determine the average speed at which gases are knocked out of the furnace opening by first calculating:

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

cross-sectional area of ​​the pipe:

0.7850.52=0.196 m2

Air speed in the pipe m/s

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

An air shower is a flow of air directed at a limited workplace or directly to the worker.

The use of air showers is especially effective when a worker is exposed to heat. In such cases, an air shower is installed at the place where a person spends the longest time, and if short breaks for rest are provided during work, then at the place of rest.

The upper parts of the body should be blown with air, as they are most sensitive to the effects of thermal radiation.

The speed and temperature of the air in the workplace when using air showers are prescribed depending on the intensity of a person’s thermal irradiation, the duration of his continuous stay under irradiation and the ambient temperature.

Fan unit type VA-1

1 - electric motor;
2 - shell;
3 — mesh;
4 — axial fan;
5 - confuser;
6 — fairing;
7 - pneumatic nozzle;
8 - guide vanes

Air showering should be provided in permanent workplaces with an irradiation intensity of 350 W/m2 or more. In this case, an air flow can be directed at a person at a speed o = 0.5...3.5 m/s and a temperature of 18-24 ° C, depending on the period of the year and the intensity of physical activity.

Constructive implementation of air showers.

The air coming out of the shower pipe must wash the head and body of a person at a uniform speed and have the same temperature.

The axis of the air flow can be directed to the person’s chest horizontally or from above at an angle of 45° while ensuring the specified temperatures and air speeds in the workplace, as well as to the face (breathing zone) horizontally or from above at an angle of 45° while ensuring acceptable concentrations of harmful emissions.

The distance from the shower pipe to the workplace must be at least 1 m with a minimum pipe diameter of 0.3 m. The width of the working platform is assumed to be 1 m.

Design of VA-1 units

According to their design, showering units are divided into stationary and mobile.

The fan unit type VA-1 consists of a cast iron frame on which is mounted an axial fan No. 5 type MC with an electric motor, a shell with a collector and mesh, a confuser with guide vanes and a fairing, a pneumatic nozzle type FP-1 or FP-2 and pipelines with fittings and flexible hoses for water supply and compressed air. The unit is manufactured with the fan rotated around the axis of the frame up to 60° and the barrel raised vertically by 200-600 mm.

In addition to fan units of type VA, a rotating unit PAM.-24 is used in the form of an axial fan with a diameter of 800 mm with an electric motor on one shaft. The unit's productivity is 24,000 m 3 /h with a jet range of 20 m. The unit is equipped with a pneumatic nozzle for spraying water in the air flow.

Stationary shower installations supply both untreated and treated (heated, cooled and humidified) outside air to the shower pipes. Mobile units supply room air to the workplace. Water may be sprayed into the air flow they supply. In this case, droplets of water falling on clothing and exposed parts of the human body evaporate and cause additional cooling.

Fixed workplaces can be showered with shower pipes various types. The HIP pipes have a compressed outlet section, a swivel joint for changing the direction of air flow in the vertical plane, and a rotating device for changing the direction of flow in the horizontal plane within 360°.

Regulation of the direction of the air flow in the PD nozzles is carried out in the vertical plane by turning the guide vanes, and in the horizontal plane using a rotary device. PD pipes can be used both with and without nozzles for pneumatic water spraying. The pipes should be installed at a height of 1.8-1.9 m from the floor (to the bottom edge).

Calculation of the air showering system at the metal pourer's workplace

Air showering is one of the most effective measures combating radiant heat, as well as toxic gases and vapors released during work with forging hammers and presses. Heated (in winter) and cooled (in summer) air supplied from above through special devices supplies the worker with fresh, humidified air, and by adjusting the speed of air movement, a partial decrease in the air temperature at the workplace can be achieved. Sometimes air is supplied to the workplace through flexible rubberized hoses from a mobile air shower unit. Appearance the shower installation is shown in Fig. 3.4.

Figure 3.4 - Showering installation

We will calculate the air shower using the method of B.M. Zlobinsky.

The calculation of air showers comes down to determining the diameter of the shower pipe and the parameters of the air coming out of it.

The cross-sectional diameter of the jet is calculated using formula 2:

where is the turbulence coefficient, depending on the shape of the outlet section (0.06 - 0.12). Let's take =0.12.

x is the distance from the point of exit of the jet from the nozzle to the workplace. Let's take x = 2 m.

d 0 - diameter of the outlet section of the pipe. Let's take d 0 =0.7.

The speed at which air leaves the nozzle is calculated by the formula:

where area is the average air speed at the work site. This speed should not exceed 0.3 m/s. Let's take area =0.3 m/s;

b is a coefficient varying from 0.05 to 1 depending on the ratio. Let us accept d r.pl. =2 m, then:

Let us substitute the obtained values ​​into (3) and obtain that

The required temperature at the outlet of the nozzle is determined by the formula:

where t o.c. - ambient temperature, it is 20-25 0 C. Let’s take 22.5 0 C.

t cp is the average required air temperature at the smelting site. According to SanPiN 2.2.4.548-96, the permissible temperature on the site is 19-21 0 C, let’s take 20 0 C.

C is a coefficient that, like coefficient b, depends on the ratio and varies from 0.345 to 0.22. Let's take C=0.25.

Thus, in order for the temperature at the melting site to be equal to 20 0 C, an air stream d = 2.05 m is provided at t patr = 19.3 0 C, which is supplied to the melting site by a fan at a speed of 0.15 m/s and productivity 1800 m 3 /h.

Calculation of the economic efficiency of installing an air shower system of type VD-1800 at the metal pourer’s workplace will be carried out in the organizational and economic section of the diploma project.

Diseases caused by exposure to the heating microclimate of foundries (hot shops) and their prevention

Heating microclimate is a combination of parameters in which there is a change in heat exchange between a person and the environment, manifested in the accumulation of heat in the body (> 2 W) and/or in an increase in the proportion of heat loss by evaporation of moisture (> 30%). Exposure to a heating microclimate also causes health problems, decreased performance and productivity.

Working in such conditions can lead to uncomfortable sensations of heat, significant stress on thermoregulation processes, and, with a large thermal load, to health problems (overheating).

This kind of microclimate is created in rooms where the technology is associated with significant heat releases into the environment, that is, when production processes take place at high temperatures (roasting, calcination, sintering, melting, cooking, drying). Heat sources are heated to high temperature surfaces of equipment, fences, processed materials, cooling products, hot vapors and gases escaping through equipment leaks. The release of heat is also determined by the operation of machines, as a result of which mechanical and electrical energy is converted into thermal energy.

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 directed at the 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, pipes with an upper air supply of type PD V (series 4.904-36) or pipes with a bottom air supply of type PD n (series 4.904-36) should be used.

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. In this case, to ensure acceptable concentrations of 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 are given 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 of 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 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 decisions 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 harmful substances are released into production premises. 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 according to 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.

References

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)

Table 2.2 – Initial data for task No. 2

Air showering is the most effective measure for creating the required meteorological conditions (temperature, humidity and air speed) at permanent workplaces. The use of air showers is especially effective when there is significant heat radiation or in open production processes, if technological equipment, highlighting harmful substances, has no shelters or local exhaust ventilation. Air showering is a stream of air directed at a limited workplace or directly at a worker.

Air mobility in the workplace during air showering reaches from 1 to 3.5 m/s. Douching is carried out with special nozzles, and the jet is directed to the irradiated areas of the body: head, chest. The size of the blown area is m. Dusting can be carried out with external untreated air, adiabatically cooled air or isohumidity cooling. In some cases, it is permissible to use recirculated air, but there should be little thermal radiation and no harmful emissions.

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. When the jet coming out of the hole mixes with the surrounding air, the speed, temperature difference and concentration of impurities in the cross section of the free jet change. The jet should be directed so that, if possible, it prevents it from sucking in hot or gas-contaminated air. For example, if there is a fixed workplace near an open furnace opening, you should not place a showering device near the opening with the jet directed towards the worker, since in this case it is impossible to avoid the suction of hot gases, as a result of which superheated air will flow to the worker. When calculating air shower systems, design parameters A should be taken for warm periods and design parameters B for cold periods of the year. To calculate year-round air showering, the warm period is taken as the calculation period, and for the cold period only the supply air temperature is determined.

Systems supplying air to air shower nozzles are designed separately from systems for other purposes. The distance from the air outlet to the workplace should be at least 1 m. Calculation procedure

1. Set the air parameters at the workplace, mark the installation location of the pipe, the distance from the pipe to the workplace, and also set the type of shower pipe. 2. We determine the air speed at the outlet of the nozzle depending on the normalized air mobility in the room, where is the normalized air mobility, is the distance from the nozzle to the workplace, m, is the coefficient of change in speed, is the cross-section of the selected nozzle. 3. We determine the minimum temperature at the outlet of the pipe, where is the standardized temperature and is the coefficient of temperature change. 4. Determine the air flow required to supply to the nozzle.