Purpose	Basic Requirement
	Silence	Min. head loss
	Main channels	Main channels		Branches
		Inflow	Hood	Inflow	Hood
Living spaces	3	5	4	3	3
Hotels	5	7.5	6.5	6	5
Institutions	6	8	6.5	6	5
Restaurants	7	9	7	7	6
The shops	8	9	7	7	6

Based on these values, the linear parameters of the air ducts should be calculated.

Algorithm for calculating air pressure losses

The calculation must begin with drawing up a diagram of the ventilation system with the obligatory indication of the spatial location of the air ducts, the length of each section, ventilation grilles, additional equipment for air purification, technical fittings and fans. Losses are determined first for each individual line and then summed up. For a separate technological section, losses are determined using the formula P = L×R+Z, where P is the loss of air pressure in the design section, R is the loss per linear meter of the section, L is the total length of the air ducts in the section, Z is the loss in the additional fittings of the system ventilation.

To calculate pressure loss in a round duct, the formula Ptr is used. = (L/d×X) × (Y×V)/2g. X is the tabulated coefficient of air friction, depends on the material of the air duct, L is the length of the design section, d is the diameter of the air duct, V is the required air flow speed, Y is the air density taking into account temperature, g is the acceleration of fall (free). If the ventilation system has square air ducts, then table No. 2 should be used to convert round values ​​to square ones.

Table No. 2. Equivalent diameters of round air ducts for square ones

	150	200	250	300	350	400	450	500
250	210	245	275
300	230	265	300	330
350	245	285	325	355	380
400	260	305	345	370	410	440
450	275	320	365	400	435	465	490
500	290	340	380	425	455	490	520	545
550	300	350	400	440	475	515	545	575
600	310	365	415	460	495	535	565	600
650	320	380	430	475	515	555	590	625
700		390	445	490	535	575	610	645
750		400	455	505	550	590	630	665
800		415	470	520	565	610	650	685
850			480	535	580	625	670	710
900			495	550	600	645	685	725
950			505	560	615	660	705	745
1000			520	575	625	675	720	760
1200				620	680	730	780	830
1400					725	780	835	880
1600						830	885	940
1800						870	935	990

The horizontal axis indicates the height of the square duct, and the vertical axis indicates the width. Equivalent value round section is at the intersection of lines.

Air pressure losses in bends are taken from table No. 3.

Table No. 3. Pressure loss at bends

To determine pressure losses in diffusers, data from table No. 4 is used.

Table No. 4. Pressure loss in diffusers

Table No. 5 gives a general diagram of losses in a straight section.

Table No. 5. Diagram of air pressure loss in straight air ducts

All individual losses in a given section of the air duct are summed up and adjusted with table No. 6. Table. No. 6. Calculation of flow pressure reduction in ventilation systems

During design and calculations, existing regulations It is recommended that the difference in pressure loss between individual sections should not exceed 10%. The fan must be installed in the area of ​​the ventilation system with the highest resistance; the most distant air ducts must have minimal resistance. If these conditions are not met, then it is necessary to change the layout of air ducts and additional equipment, taking into account the requirements of the regulations.

Ph.D. S.B. Gorunovich, PTO engineer, Ust-Ilimskaya CHPP, branch of OJSC Irkutskenergo, Ust-Ilimsk, Irkutsk region.

Statement of a question

It is known that many enterprises that in the recent past had reserves of thermal and electrical energy paid insufficient attention to its losses during transportation. For example, various pumps were included in the project, as a rule, with a large power reserve; pressure losses in the pipelines were compensated by an increase in flow. The main steam pipelines were designed with jumpers and long lines, allowing, if necessary, to transport excess steam to neighboring turbine units. When reconstructing and repairing transportation networks, preference was given to the universality of the schemes, which led to additional tie-ins (fittings) and jumpers, installation of additional tees and, as a result, additional local losses total pressure. At the same time, it is known that in long pipelines at significant medium velocities, local losses of total pressure (local resistance) can entail significant losses in costs for consumers.

Currently, the requirements for efficiency, energy saving, and total optimization of production force us to take a fresh look at many issues and aspects of the design, reconstruction and operation of pipelines and steam lines, therefore taking into account local resistances in tees, forks and fittings in hydraulic calculations pipelines becomes an urgent task.

The purpose of this work is to describe the tees and fittings most commonly used at energy enterprises, to exchange experience in the field of ways to reduce coefficients local resistance, methods for comparative assessment of the effectiveness of such events.

To estimate local resistance in modern hydraulic calculations, they operate with the dimensionless coefficient of hydraulic resistance, which is very convenient because in dynamically similar flows, in which geometric similarity of sections and equality of Reynolds numbers are observed, it has the same value, regardless of the type of liquid (gas) , as well as on the flow speed and transverse dimensions of the calculated sections.

The coefficient of hydraulic resistance is the ratio of the total energy (power) lost in a given section to the kinetic energy (power) in the accepted section or the ratio of the total pressure lost in the same section to the dynamic pressure in the accepted section:

where  p total is the total pressure lost (in a given area); p - density of liquid (gas); w, - speed in the i-th section.

The value of the drag coefficient depends on what design speed and, therefore, what section it is reduced to.

Exhaust and supply tees

It is known that a significant part of local losses in branched pipelines consists of local resistance in tees. As an object representing local resistance, the tee is characterized by the branch angle a and the ratios of the cross-sectional areas of the branches (lateral and direct) F b /F q, Fh/Fq and F B /Fn. In the tee, the flow ratios Q b /Q q, Q n /Q c and, accordingly, the speed ratios w B /w Q, w n /w Q can change. Tees can be installed both in the suction sections (exhaust tee) and in the discharge sections (supply tees) when dividing the flow (Fig. 1).

The resistance coefficients of exhaust tees depend on the parameters listed above, and those of conventionally shaped supply tees depend almost only on the branch angle and the speed ratios w n /w Q and w n /w Q, respectively.

The resistance coefficients of conventionally shaped exhaust tees (without rounding and widening or narrowing of a side branch or straight passage) can be calculated from the following formulas.

Resistance in the side branch (in section B):

where Q B =F B w B, Q q =F q w q - volumetric flow rates in section B and C, respectively.

For tees of type F n =F c and for all a, the values ​​of A are given in table. 1.

When the ratio Q b /Q q changes from 0 to 1, the resistance coefficient changes from -0.9 to 1.1 (F q =F b, a = 90 O). Negative values are explained by the suction effect in the line at low Q B .

From the structure of formula (1) it follows that the resistance coefficient will quickly increase with a decrease in the cross-sectional area of ​​the nozzle (with an increase in F c /F b). For example, with Q b /Q c =1, F q/F b =2, a = 90 O, the coefficient is 2.75.

Obviously, a reduction in resistance can be achieved by reducing the angle of the side branch (nozzle). For example, when F c =F b , α = 45 O, when the ratio Q b /Q c changes from 0 to 1, the coefficient changes from -0.9 to 0.322, i.e. his positive values are reduced by almost 3 times.

Resistance in direct passage should be determined by the formula:

For tees of type Fn=F c, the KP values ​​are given in table. 2.

It is easy to verify that the range of change in the resistance coefficient in the direct passage

where, when the ratio Q b /Q c changes from 0 to 1, it is in the range from 0 to 0.6 (F c =F b, α = 90 O).

Reducing the angle of the side branch (nozzle) also leads to a significant reduction in resistance. For example, when F c =F b, α =45 O, when the ratio Q b /Q c changes from 0 to 1, the coefficient changes from 0 to -0.414, i.e. As Q B increases, “suction” appears in the forward passage, further reducing resistance. It should be noted that dependence (2) has a pronounced maximum, i.e. the maximum value of the resistance coefficient falls on the value Q b /Q c = 0.41 and is equal to 0.244 (at F c = F b, α = 45 O).

The resistance coefficients of inlet tees of normal shape in turbulent flow can be calculated using the formulas.

Side branch resistance:

where K B is the flow compression ratio.

For tees of type Fn=F c the values ​​of A 1 are given in table. 3, K B =0.

If we take F c =F b , a = 90 O, then when the ratio Q b /Q c changes from 0 to 1, we obtain coefficient values ​​in the range from 1 to 1.2.

It should be noted that the source provides other data for the coefficient A 1 . According to the data, you should take A 1 =1 at w B /w c<0,8 и А 1 =0,9 при w B /w c >0.8. If we use data from , then when the ratio Q B /Q C changes from 0 to 1, we obtain coefficient values ​​in the range from 1 to 1.8 (F c = F b). In general, we will obtain slightly higher values ​​for the resistance coefficients in all ranges.

The decisive influence on the growth of the resistance coefficient, as in formula (1), is exerted by the cross-sectional area B (nozzle) - with increasing F g /F b, the resistance coefficient increases rapidly.

Resistance in direct passage for supply tees of type Fn=Fc within

The values ​​of t P are indicated in the table. 4.

When the ratio Q B /Qc(3) changes from 0 to 1 (Fc=F B, α=90 O), we obtain coefficient values ​​in the range from 0 to 0.3.

The resistance of conventionally shaped tees can also be noticeably reduced by rounding the junction of the side branch with the prefabricated sleeve. In this case, for exhaust tees, the angle of rotation of the flow should be rounded (R 1 in Fig. 16). For supply tees, rounding should also be performed on the dividing edge (R 2 in Fig. 16); it makes the flow more stable and reduces the possibility of it being separated from this edge.

In practice, rounding the edges of the junction of the generatrices of the side branch and the main pipeline is sufficient at R/D(3=0.2-0.3.

The formulas proposed above for calculating the resistance coefficients of tees and the corresponding tabular data refer to carefully manufactured (turned) tees. Manufacturing defects in tees made during their manufacture (“dips” of the side branch and “overlapping” of its cross-section with an incorrect wall cut in the straight section - the main pipeline) become a source of a sharp increase in hydraulic resistance. In practice, this happens when the fitting is inserted into the main pipeline poorly, which happens quite often, because "factory" tees are relatively expensive.

The gradual expansion (diffuser) of the side branch effectively reduces the resistance of both exhaust and supply tees. The combination of fillet, bevel and side branch extension further reduces tee resistance. The resistance coefficients of improved tees can be determined using the formulas and diagrams given in the source. Tees with side branches in the form of smooth bends also have the lowest resistance, and where practical, tees with small branch angles (up to 60°) should be used.

In turbulent flow (Re>4.10 3), the resistance coefficients of the tees depend little on the Reynolds numbers. During the transition from turbulent to laminar, there is a sudden increase in the resistance coefficient of the side branch in both exhaust and supply tees (about 2-3 times).

In calculations, it is important to take into account in what section it is reduced to average speed. In the source there is a link about this before each formula. The sources provide general formula, where the reduction speed is indicated with the corresponding index.

Symmetrical tee for merging and dividing

The resistance coefficient of each branch of a symmetrical tee when merging (Fig. 2a) can be calculated using the formula:

When the ratio Q b /Q c changes from 0 to 0.5, the coefficient changes from 2 to 1.25, and then as Q b /Q c increases from 0.5 to 1, the coefficient acquires values ​​from 1.25 to 2 (for the case F c =F b). It is obvious that dependence (5) has the form of an inverted parabola with a minimum at the point Q b /Q c =0.5.

The resistance coefficient of a symmetrical tee (Fig. 2a) located in the injection (separation) section can also be calculated using the formula:

where K 1 =0.3 - for welded tees.

When the ratio w B /w c changes from 0 to 1, the coefficient changes from 1 to 1.3 (F c =F b).

By analyzing the structure of formulas (5, 6) (as well as (1) and (3)), one can be convinced that reducing the cross-section (diameter) of the side branches (sections B) negatively affects the resistance of the tee.

Flow resistance can be reduced by 2-3 times when using fork tees (Fig. 26, 2c).

The resistance coefficient of the fork tee when dividing the flow (Fig. 2b) can be calculated using the formulas:

When the ratio Q 2 /Q 1 changes from 0 to 1, the coefficient changes from 0.32 to 0.6.

The resistance coefficient of the tee-fork during merging (Fig. 2b) can be calculated using the formulas:

When the ratio Q 2 /Q 1 changes from 0 to 1, the coefficient changes from 0.33 to -0.4.

A symmetrical tee can be made with smooth bends (Fig. 2c), then its resistance can be further reduced.

Manufacturing. Standards

Industry energy standards require thermal power plant piping low pressure(at working pressure P slave.<22 кгс/см 2 и температуре среды t<425 О С) использовать тройники сварные по ОСТ34-42-762

OST34-42-765-85. For higher environmental parameters (P rab.<40 кгс/см 2) изготавливают тройники из углеродистых и кремнемарганцовистых сталей: штампованные по ОСТ108.720.01, ОСТ108.720.02-82; сварные по ОСТ108.104.01 - ОСТ108.104.03-82; с обжатием (с вытянутой горловиной) по ОСТ108.104.04, ОСТ108.104.05-82. Из хромомолибденованадиевых сталей изготавливают тройники: штампованные по ОСТ108.720.05, ОСТ108.720.06-82; сварные по ОСТ108.104.10 - ОСТ108.104.12-82; с обжатием (с вытянутой горловиной) по ОСТ108.104.13 - ОСТ108.104.15-82 для паропроводов высокого давления (с параметрами Р раб. до 255 кгс/см 2 и температурой t до 560 О С). Существуют соответствующие нормативы и для штуцеров.

The design of tees manufactured according to existing (listed above) standards is not always optimal from the point of view of hydraulic losses. The reduction in the coefficient of local resistance is facilitated only by the shape of stamped tees with an elongated neck, where a radius of rounding is provided in the side branch according to the type shown in Fig. 1b and fig. 3c, as well as with compression of the ends, when the diameter of the main pipeline is slightly smaller than the diameter of the tee (according to the type shown in Fig. 3b). The fork tees are obviously made to a separate order according to “factory” standards. In RD 10-249-98 there is a paragraph devoted to strength calculations of tees-forks and fittings.

When designing and reconstructing networks, it is important to take into account the direction of movement of media and possible ranges of changes in flow rates in tees. If the direction of the transported medium is clearly defined, it is advisable to use inclined fittings (side branches) and fork tees. However, the problem of significant hydraulic losses remains in the case of a universal tee, which combines the properties of supply and exhaust, in which both merging and dividing the flow is possible in operating modes associated with significant changes in flow rates. The above-mentioned qualities are characteristic, for example, of switching units for feedwater pipelines or main steam pipelines at thermal power plants with “jumpers”.

It should be taken into account that for steam and hot water pipelines, the design and geometric dimensions of welded pipe tees, as well as fittings (pipes, branch pipes) welded on straight sections of pipelines, must meet the requirements of industry standards, normals and technical specifications. In other words, for critical pipelines it is necessary to order tees made in accordance with technical specifications from certified manufacturers. In practice, due to the relative high cost of “factory” tees, tapping of fittings is often carried out by local contractors using industry or factory standards.

In general, it is advisable to make the final decision on the insertion method after a comparative technical and economic analysis. If the decision is made to carry out the tapping “on their own”, engineering and technical personnel need to prepare a fitting template, perform strength calculations (if necessary), control the quality of the tapping (avoid “failures” of the fitting and “overlapping” its cross-section with an incorrect wall cut in a straight section) . It is advisable to make the internal joint between the metal of the fitting and the main pipeline with a rounding (Fig. 3c).

There are a number of design solutions for reducing hydraulic resistance in standard tees and line switching units. One of the simplest is to increase the size of the tees themselves to reduce the relative velocities of the medium in them (Fig. 3a, 3b). In this case, the tees must be equipped with transitions, the expansion (constriction) angles of which are also advisable to be selected from a number of hydraulically optimal ones. As a universal tee with reduced hydraulic losses, you can also use a fork tee with a jumper (Fig. 3d). The use of tee-forks for main switching units will also slightly complicate the design of the unit, but will have a positive effect on hydraulic losses (Fig. 3d, 3f).

It is important to note that with a relatively close location of local (L=(10-20)d) resistances of various types, the phenomenon of interference of local resistances occurs. According to some researchers, with the maximum approach of local resistances, it is possible to reduce their sum, while at a certain distance (L = (5-7)d), the total resistance has a maximum (3-7% higher than the simple sum) . The reduction effect could be of interest to large manufacturers who are ready to manufacture and supply switching units with reduced local resistances, but to achieve a good result, applied laboratory research is necessary.

Feasibility study

When making one or another constructive decision, it is important to pay attention to the economic side of the problem. As mentioned above, “factory” tees of a conventional design, and even more so those made to special order (hydraulically optimal), will cost much more than inserting a fitting. At the same time, it is important to roughly estimate the benefits in case of reducing hydraulic losses in the new tee and its payback period.

It is known that pressure losses in station pipelines with normal fluid speeds (for Re>2.10 5) can be estimated by the following formula:

where p - pressure loss, kgf/cm 2; w - medium speed, m/s; L - expanded length of the pipeline, m; g - free fall acceleration, m/s 2 ; d - design diameter of the pipeline, m; k - friction resistance coefficient; ∑ἐ m – sum of local resistance coefficients; v - specific volume of the medium, m 3 /kg

Dependence (7) is usually called the hydraulic characteristic of the pipeline.

If we take into account the dependence: w=10Gv/9nd 2, where G is the flow rate, t/h.

Then (7) can be represented as:

If it is possible to reduce local resistance (tee, fitting, switching unit), then, obviously, formula (9) can be presented as:

Here ∑ἐ m is the difference between the local resistance coefficients of the old and new nodes.

Let us assume that the hydraulic pump-pipeline system operates in nominal mode (or in a mode close to nominal). Then:

where Р n - nominal pressure (according to the flow characteristics of the pump/boiler), kgf/cm 2 ; G h - nominal flow rate (according to the flow characteristics of the pump/boiler), t/h.

If we assume that after replacing the old resistances, the “pump-pipeline” system will remain operational (Р«Рн), then from (10), using (12), we can determine the new flow rate (after reducing the resistance):

The operation of the “pump-pipeline” system and changes in its characteristics can be clearly represented in Fig. 4.

It is obvious that G 1 >G M . If we are talking about the main steam pipeline transporting steam from the boiler to the turbine, then by the difference in flow rates LG = G 1 -G n one can determine the gain in the amount of heat (from the turbine extraction) and/or in the amount of generated electrical energy according to the operating characteristics of a given turbine.

By comparing the cost of a new unit and the amount of heat (electricity), you can roughly estimate the profitability of its installation.

Calculation example

For example, it is necessary to evaluate the cost-effectiveness of replacing an equal-bore tee of the main steam pipeline at the confluence of flows (Fig. 2a) with a fork tee with a jumper of the type shown in Fig. 3g. The steam consumer is a heating turbine produced by TMZ, type T-100/120-130. Steam enters through one thread of the steam pipeline (through a tee, sections B, C).

We have the following initial data:

■ design diameter of the steam pipeline d=0.287 m;

■ nominal steam consumption G h =Q(3=Q^420 t/h;

■ nominal boiler pressure P n =140 kgf/cm 2 ;

■ specific volume of steam (at P pa = 140 kgf/cm 2, t = 560 O C) n = 0.026 m 3 /kg.

Let's calculate the resistance coefficient of a standard tee at the confluence of flows (Fig. 2a) using formula (5) - ^ SB1 =2.

To calculate the resistance coefficient of a tee-fork with a jumper, we assume:

■ division of flows in branches occurs in the proportion Q b /Q c “0.5;

■ the total resistance coefficient is equal to the sum of the resistances of the supply tee (with a 45 O outlet, see Fig. 1a) and the fork tee at merging (Fig. 2b), i.e. We neglect the interference.

We use formulas (11, 13) and obtain the expected increase in flow rate by  G=G 1 -G n =0.789 t/h.

According to the T-100/120-130 turbine mode diagram, a flow rate of 420 t/h can correspond to an electrical load of 100 MW and a thermal load of 400 GJ/h. The relationship between flow rate and electrical load is close to directly proportional.

The gain in electrical load can be: P e =100AG/Q n =0.188 MW.

The gain in terms of heat load can be: T e =400AG/4.19Q n =0.179 Gcal/h.

Prices for products made of chrome-molybdenum-vanadium steels (for tees-forks 377x50) can vary widely from 200 to 600 thousand rubles, therefore, the payback period can be judged only after a thorough market research at the time of decision-making.

1. This article describes various types of tees and fittings, and provides brief characteristics of tees used in power plant pipelines. Formulas are given for determining the coefficients of hydraulic resistance, and ways and means of reducing them are shown.

2. Promising designs of tees-forks and a switching unit for main pipelines with reduced local resistance coefficients have been proposed.

3. Formulas, an example are given and the feasibility of a technical and economic analysis is shown when choosing or replacing tees, when reconstructing switching units.

Literature

1. Idelchik I.E. Handbook of hydraulic resistance. M.: Mechanical Engineering, 1992.

2. Nikitina I.K. Handbook of pipelines for thermal power plants. M.: Energoatomizdat, 1983.

3. Handbook for calculations of hydraulic and ventilation systems/ Ed. A.S. Yuryeva. St. Petersburg: ANO NPO "Peace and Family", 2001.

4. Rabinovich E.Z. Hydraulics. M.: Nedra, 1978.

5. Benenson E.I., Ioffe L.S. Cogeneration steam turbines / Ed. D.P. Elder. M: Energoizdat, 1986.

Calculation of supply and exhaust air duct systems comes down to determining the dimensions of the cross-section of the channels, their resistance to air movement and pressure matching in parallel connections. Calculation of pressure losses should be carried out using the method of specific pressure losses due to friction.

Calculation method:

An axonometric diagram of the ventilation system is constructed, the system is divided into sections into which the length and flow rate are plotted. The calculation scheme is presented in Figure 1.

The main (main) direction is selected, which represents the longest chain of successively located sections.

3. The sections of the highway are numbered, starting with the section with the lowest flow rate.

4. The cross-sectional dimensions of the air ducts in the design sections of the main are determined. Determine the cross-sectional area, m2:

F p =L p /3600V p ,

where L p is the estimated air flow rate in the area, m 3 / h;

Based on the found values ​​of F p ], the dimensions of the air ducts are taken, i.e. is F f.

5. The actual speed V f, m/s is determined:

V f = L p / F f,

where L p is the estimated air flow rate in the area, m 3 / h;

F f – actual cross-sectional area of ​​the air duct, m2.

We determine the equivalent diameter using the formula:

d eq = 2·α·b/(α+b) ,

where α and b are the transverse dimensions of the air duct, m.

6. Based on the values ​​of d eq and V f, the values ​​of specific pressure loss due to friction R are determined.

The pressure loss due to friction in the calculated area will be

P t =R l β w,

where R – specific pressure loss due to friction, Pa/m;

l – length of the air duct section, m;

β sh – roughness coefficient.

7. Local resistance coefficients are determined and pressure losses in local resistances in the area are calculated:

z = ∑ζ·P d,

where P d – dynamic pressure:

Pd=ρV f 2 /2,

where ρ – air density, kg/m3;

V f – actual air speed in the area, m/s;

∑ζ – sum of CMR on the site,

8. Total losses by area are calculated:

ΔР = R l β w + z,

l – length of the section, m;

z - pressure loss in local resistance in the area, Pa.

9. Pressure loss in the system is determined:

ΔР p = ∑(R l β w + z) ,

where R is the specific pressure loss due to friction, Pa/m;

l – length of the section, m;

β sh – roughness coefficient;

z- pressure loss in local resistance in the area, Pa.

10. Linking of branches is carried out. Linking is done starting with the longest branches. It is similar to the calculation of the main direction. The resistances in all parallel sections must be equal: the discrepancy is no more than 10%:

where Δр 1 and Δр 2 are losses in branches with higher and lower pressure losses, Pa. If the discrepancy exceeds the specified value, then a throttle valve is installed.

Figure 1 – Design diagram supply system P1.

Sequence of calculation of the supply system P1

Section 1-2, 12-13, 14-15,2-2',3-3',4-4',5-5',6-6',13-13',15-15',16- 16':

Section 2 -3, 7-13, 15-16:

Section 3-4, 8-16:

Section 4-5:

Section 5-6:

Section 6-7:

Section 7-8:

Section 8-9:

Local resistance

Section 1-2:

a) to the output: ξ = 1.4

b) 90° bend: ξ = 0.17

c) tee for straight passage:

Section 2-2’:

a) branch tee

Section 2-3:

a) 90° bend: ξ = 0.17

b) tee for straight passage:

ξ = 0,25

Section 3-3’:

a) branch tee

Section 3-4:

a) 90° bend: ξ = 0.17

b) tee for straight passage:

Section 4-4’:

a) branch tee

Section 4-5:

a) tee for straight passage:

Section 5-5’:

a) branch tee

Section 5-6:

a) 90° bend: ξ = 0.17

b) tee for straight passage:

Section 6-6’:

a) branch tee

Section 6-7:

a) tee for straight passage:

ξ = 0,15

Section 7-8:

a) tee for straight passage:

ξ = 0,25

Section 8-9:

a) 2 bends 90°: ξ = 0.17

b) tee for straight passage:

Section 10-11:

a) 90° bend: ξ = 0.17

b) to the output: ξ = 1.4

Section 12-13:

a) to the output: ξ = 1.4

b) 90° bend: ξ = 0.17

c) tee for straight passage:

Section 13-13’

a) branch tee

Section 7-13:

a) 90° bend: ξ = 0.17

b) tee for straight passage:

ξ = 0,25

c) branch tee:

ξ = 0,8

Section 14-15:

a) to the output: ξ = 1.4

b) 90° bend: ξ = 0.17

c) tee for straight passage:

Section 15-15’:

a) branch tee

Section 15-16:

a) 2 bends 90°: ξ = 0.17

b) tee for straight passage:

ξ = 0,25

Section 16-16’:

a) branch tee

Section 8-16:

a) tee for straight passage:

ξ = 0,25

b) branch tee:

Aerodynamic calculation of the supply system P1

Flow, L, m³/h

Length, l, m

Duct dimensions

Air speed V, m/s

Losses per 1 m of section length R, Pa

Coeff. roughness m

Friction losses Rlm, Pa

Amount of KMS, Σξ

Dynamic pressure Рд, Pa

Local resistance losses, Z

Pressure loss in the area, ΔР, Pa

Sectional area F, m²

Equivalent diameter

Let us make a discrepancy in the supply system P1, which should be no more than 10%.

Since the discrepancy exceeds the permissible 10%, it is necessary to install a diaphragm.

I install the diaphragm in the area 7-13, V = 8.1 m/s, R C = 20.58 Pa

Therefore, for an air duct with a diameter of 450, I install a diaphragm with a diameter of 309.

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A program for calculating the thermodynamic parameters of moist air or a mixture of two streams. Convenient and intuitive interface; the program does not require installation.

The program converts values ​​from one measurement scale to another. The "Transformer" knows the most commonly used, less common and outdated measures. In total, the program database contains information about 800 measures, many of which have brief information. There are possibilities to search the database, sort and filter records.

The Vent-Calc program was created for the calculation and design of ventilation systems. The program is based on the method of hydraulic calculation of air ducts using the Altschul formulas given in

A program for converting various units of measurement. Program language - Russian/English.

The program algorithm is based on the use of an approximate analytical method for calculating changes in air condition. The calculation error is no more than 3%

Creating comfortable living conditions in premises is impossible without aerodynamic calculation of air ducts. Based on the data obtained, the cross-sectional diameter of the pipes, the power of the fans, the number and features of the branches are determined. Additionally, the power of heaters and the parameters of inlet and outlet openings can be calculated. Depending on the specific purpose of the rooms, the maximum permissible noise level, air exchange rate, direction and speed of flows in the room are taken into account.

Modern requirements are specified in the Code of Rules SP 60.13330.2012. Normalized parameters of microclimate indicators in premises for various purposes are given in GOST 30494, SanPiN 2.1.3.2630, SanPiN 2.4.1.1249 and SanPiN 2.1.2.2645. When calculating the performance of ventilation systems, all provisions must be taken into account.

Aerodynamic calculation of air ducts - algorithm of actions

The work includes several successive stages, each of which solves local problems. The obtained data is formatted in the form of tables, and based on them, schematic diagrams and graphs are drawn up. The work is divided into the following stages:

1. Development of an axonometric diagram of air distribution throughout the system. Based on the diagram, a specific calculation methodology is determined, taking into account the features and tasks of the ventilation system.
2. An aerodynamic calculation of air ducts is performed both along the main routes and all branches.
3. Based on the data obtained, the geometric shape and cross-sectional area of ​​the air ducts are selected, and the technical parameters of fans and air heaters are determined. Additionally, the possibility of installing fire extinguishing sensors, preventing the spread of smoke, and the possibility of automatically adjusting the ventilation power taking into account the program compiled by the users are taken into account.

Development of a ventilation system diagram

Depending on the linear parameters of the diagram, the scale is selected; the diagram indicates the spatial position of the air ducts, points of connection of additional technical devices, existing branches, places of air supply and intake.

The diagram indicates the main line, its location and parameters, connection points and technical characteristics of the branches. The location of air ducts takes into account the architectural characteristics of the premises and the building as a whole. When drawing up a supply circuit, the calculation procedure begins from the point furthest from the fan or from the room for which the maximum air exchange rate is required. When compiling exhaust ventilation, the main criterion is the maximum values ​​for air flow. During calculations, the general line is divided into separate sections, and each section must have the same cross-sections of air ducts, stable air consumption, the same manufacturing materials and pipe geometry.

The segments are numbered in sequence from the section with the lowest flow rate and in increasing order to the highest. Next, the actual length of each individual section is determined, the individual sections are summed up, and the total length of the ventilation system is determined.

When planning a ventilation scheme, they can be taken as common for the following premises:

• residential or public in any combination;
• industrial, if they belong to group A or B according to the fire safety category and are located on no more than three floors;
• one of the categories of industrial buildings categories B1 - B4;
• category industrial buildings B1 m B2 are allowed to be connected to one ventilation system in any combination.

If the ventilation systems completely lack the possibility of natural ventilation, then the diagram must provide for the mandatory connection of emergency equipment. The power and installation location of additional fans are calculated according to general rules. For rooms that have openings that are constantly open or open when necessary, the diagram can be drawn up without the possibility of a backup emergency connection.

Systems for suctioning contaminated air directly from technological or work areas must have one backup fan; turning the device into operation can be automatic or manual. The requirements apply to work areas of hazard classes 1 and 2. It is allowed not to include a backup fan in the installation diagram only in the following cases:

1. Synchronous stop of harmful production processes in case of disruption of the functionality of the ventilation system.
2. Separate emergency ventilation with its own air ducts is provided in production premises. Such ventilation parameters must remove at least 10% of the volume of air provided by stationary systems.

The ventilation scheme should provide for a separate possibility of showering a workplace with increased levels of air pollution. All sections and connection points are indicated on the diagram and included in the general calculation algorithm.

It is prohibited to place air intake devices closer than eight meters horizontally from landfills, car parking areas, roads with heavy traffic, exhaust pipes and chimneys. Air receiving devices must be protected with special devices on the windward side. The resistance values ​​of protective devices are taken into account during aerodynamic calculations of the overall ventilation system.
Calculation of air flow pressure loss Aerodynamic calculation of air ducts based on air losses is done with the aim of correctly selecting sections to meet the technical requirements of the system and selecting fan power. Losses are determined by the formula:

R yd is the value of specific pressure losses in all sections of the air duct;

P gr – gravitational air pressure in vertical channels;

Σ l – the sum of individual sections of the ventilation system.

Pressure losses are obtained in Pa, the length of sections is determined in meters. If the movement of air flows in ventilation systems occurs due to a natural pressure difference, then the calculated pressure reduction is Σ = (Rln + Z) for each individual section. To calculate the gravitational pressure you need to use the formula:

P gr – gravitational pressure, Pa;

h – height of the air column, m;

ρ n – air density outside the room, kg/m3;

ρ in – indoor air density, kg/m3.

Further calculations for natural ventilation systems are performed using the formulas:

Determining the cross-section of air ducts

Determination of the speed of movement of air masses in gas ducts

Calculation of losses based on local resistances of the ventilation system

Determination of friction loss

Determination of air flow speed in channels
The calculation begins with the longest and most remote section of the ventilation system. As a result of aerodynamic calculations of air ducts, the required ventilation mode in the room must be ensured.

The cross-sectional area is determined by the formula:

F P = L P /V T .

F P – cross-sectional area of ​​the air channel;

L P – actual air flow in the calculated section of the ventilation system;

V T – speed of air flow to ensure the required frequency of air exchange in the required volume.

Taking into account the results obtained, the pressure loss during the forced movement of air masses through the air ducts is determined.

For each air duct material, correction factors are applied, depending on the surface roughness indicators and the speed of movement of air flows. To facilitate aerodynamic calculations of air ducts, you can use tables.

Table No. 1. Calculation of metal air ducts of round profile.

Table No. 2. Values ​​of correction factors taking into account the material of air ducts and air flow speed.

The roughness coefficients used for calculations for each material depend not only on its physical characteristics, but also on the speed of air flow. The faster the air moves, the more resistance it experiences. This feature must be taken into account when selecting a specific coefficient.

Aerodynamic calculations for air flow in square and round air ducts show different flow rates for the same cross-sectional area of ​​the nominal bore. This is explained by differences in the nature of vortices, their meaning and ability to resist movement.

The main condition for calculations is that the speed of air movement constantly increases as the area approaches the fan. Taking this into account, requirements are imposed on the diameters of the channels. In this case, the parameters of air exchange in the premises must be taken into account. The locations of the inflow and outlet flows are selected in such a way that people staying in the room do not feel drafts. If it is not possible to achieve the regulated result using a straight section, then diaphragms with through holes are inserted into the air ducts. By changing the diameter of the holes, optimal regulation of air flow is achieved. The diaphragm resistance is calculated using the formula:

The general calculation of ventilation systems should take into account:

1. Dynamic air pressure during movement. The data is consistent with the technical specifications and serves as the main criterion when choosing a specific fan, its location and operating principle. If it is impossible to ensure the planned operating modes of the ventilation system with one unit, installation of several is provided. The specific location of their installation depends on the features of the basic design of the air ducts and the permissible parameters.
2. The volume (flow rate) of transported air masses in the context of each branch and room per unit of time. Initial data are the requirements of sanitary authorities for the cleanliness of the premises and the features of the technological process of industrial enterprises.
3. Unavoidable pressure losses resulting from vortex phenomena during the movement of air flows at various speeds. In addition to this parameter, the actual cross-section of the air duct and its geometric shape are taken into account.
4. Optimal air movement speed in the main channel and separately for each branch. The indicator influences the choice of fan power and their installation locations.

To facilitate calculations, it is allowed to use a simplified scheme; it is used for all premises with non-critical requirements. To guarantee the required parameters, the selection of fans in terms of power and quantity is done with a margin of up to 15%. Simplified aerodynamic calculations of ventilation systems are performed using the following algorithm:

1. Determination of the cross-sectional area of ​​the channel depending on the optimal speed of air flow.
2. Selecting a standard channel cross-section close to the design one. Specific indicators should always be selected upward. Air channels may have increased technical indicators; it is prohibited to reduce their capabilities. If it is impossible to select standard channels, the technical specifications provide for their manufacture according to individual sketches.
3. Checking air speed indicators taking into account the actual values ​​of the conventional cross-section of the main channel and all branches.

The task of aerodynamic calculation of air ducts is to ensure the planned ventilation rates of premises with minimal losses of financial resources. At the same time, it is necessary to strive to reduce the labor intensity and metal consumption of construction and installation work, to ensure the reliable operation of the installed equipment in various modes.

Special equipment must be installed in accessible places, with unhindered access to it for routine technical inspections and other work to maintain the system in working condition.

According to the provisions of GOST R EN 13779-2007 for calculating ventilation efficiency ε v you need to apply the formula:

with ENA– indicators of the concentration of harmful compounds and suspended substances in the removed air;

With IDA– concentration of harmful chemical compounds and suspended substances in the room or work area;

c sup– indicators of contaminants entering with the supply air.

The efficiency of ventilation systems depends not only on the power of the connected exhaust or blower devices, but also on the location of the sources of air pollution. During aerodynamic calculations, the minimum performance indicators of the system must be taken into account.

Specific power (P Sfp > W∙s / m 3) of fans is calculated using the formula:

de P – power of the electric motor installed on the fan, W;

q v – air flow rate supplied by the fans during optimal operation, m 3 /s;

∆ p – indicator of the pressure drop at the air inlet and outlet of the fan;

η tot is the total efficiency for the electric motor, air fan and air ducts.

During calculations, the following types of air flows are taken into account according to the numbering in the diagram:

Diagram 1. Types of air flows in the ventilation system.

1. External, enters the air conditioning system from the external environment.
2. Supply. Air flows entering the duct system after preliminary preparation(heating or cleaning).
3. The air in the room.
4. Flowing air currents. Air moving from one room to another.
5. Exhaust. Air exhausted from the room to the outside or into the system.
6. Recirculating. The portion of the flow returned to the system to maintain the internal temperature within the specified values.
7. Removable. Air that is removed from the premises irrevocably.
8. Secondary air. Returned back to the room after cleaning, heating, cooling, etc.
9. Air loss. Possible leaks due to leaky air duct connections.
10. Infiltration. The process of air entering indoors naturally.
11. Exfiltration. Natural air leakage from the room.
12. Air mixture. Simultaneous suppression of multiple threads.

Each type of air has its own state standards. All calculations of ventilation systems must take them into account.