Calculation method for uniform pressure-control constant-speed jet flow of exhaust duct

Abstract

The invention provides an exhaust duct uniform pressure control constant-speed jet flow calculation method which comprises the following steps: calculating the average jet flow speed of a slot type nozzle on a plenum chamber and the total air supply quantity of the plenum chamber according to the exhaust air quantity of an underground exhaust duct; selecting typical points in the static pressure box according to the pressure characteristics of the air pipe, and respectively calculating the pressure condition at each typical point; and rechecking the static pressure value of each typical point, and modifying the height, width or thickness of the static pressure box according to a static pressure restoration method for the points with large difference, so as to ensure that the static pressures of all the points are similar. According to the scheme, the average jet air speed and the total air supply amount of the slot type nozzle are calculated, the size of the static pressure box is adjusted in combination with a static pressure recovery method, and static pressure fluctuation of all typical points inside is controlled within 5%, so that the jet air speed of the nozzle is uniform and consistent, and a continuous and stable air film is formed between exhaust air of an air duct and a wall surface; and meanwhile, the problem of poor hiding effect caused by non-uniform jet flow of a traditional static pressure box is solved by carrying out segmented pressure calculation and size parameter correction on the static pressure box.

Description

Technical Field

[0001] The present invention relates to the technical field of calculation methods for uniform pressure control and isokinetic jet in exhaust ducts, and particularly to a calculation method for uniform pressure control and isokinetic jet in exhaust ducts. Background Art

[0002] Special projects require concealed exhaust, and it is required to control the temperature difference between the wall surface of the exhaust duct opening and the environment within a specified range. The exhaust temperature in the underground duct is usually relatively stable and higher than the external air temperature. Due to the heat transfer of the exhaust heat to the wall surface of the opening, the wall surface temperature of the exhaust duct opening is higher than the external air temperature, resulting in certain infrared signatures.

[0003] To ensure that the wall surface temperature of the exhaust duct opening is not affected by the exhaust air temperature, outdoor air is introduced through a static pressure box and the outdoor air is attached and jetted onto the wall surface of the exhaust duct using a slotted nozzle, forming a uniform air film between the exhaust air in the duct and the wall surface to prevent heat exchange between the exhaust air and the wall surface. However, using an ordinary static pressure box will cause the jet velocities of the slotted nozzles to be different, resulting in a non-uniform air film formed between the exhaust air in the duct and the wall surface. In this way, some areas of the wall surface will come into contact with the exhaust air in the duct and generate heat exchange, affecting the concealed exhaust effect of the duct. Therefore, there is an urgent need to design a calculation method for a static pressure box with uniform pressure control and isokinetic jet to solve the problems existing in the above-mentioned prior art. Summary of the Invention

[0004] The purpose of the present invention is to provide a calculation method for uniform pressure control and isokinetic jet in an exhaust duct, to achieve similar static pressures at various locations inside the static pressure box, maintain a constant jet velocity of the slotted nozzle and generate a uniform air film, and improve the concealed exhaust effect of the duct.

[0005] Based on the purpose of the present invention, the technical solution provides a calculation method for uniform pressure control and isokinetic jet in an exhaust duct, including the following steps:

[0006] S1: According to the exhaust air volume of the underground exhaust duct, calculate the average jet velocity of the slotted nozzles on the static pressure box and the total air supply volume of the static pressure box;

[0007] S2: Based on the pressure characteristics of the air duct, select typical points inside the static pressure box and calculate the pressure conditions at each typical point respectively;

[0008] S3: Recheck the static pressure values of each typical point. For points with a large difference, modify the size of the static pressure box according to the static pressure recovery method to ensure that the static pressures at each point are similar.

[0009] Further, the calculation process of the average jet velocity of the slotted nozzles on the static pressure box in step S1 includes:

[0010] S101: Calculate the cross-sectional velocity V when the maximum exhaust air volume of the exhaust duct is L as:

[0011] V=L / 3600(A×B+πA 2 / 8)m / s;

[0012] S102: Calculate the average jet velocity V0 of the slot nozzle on the static pressure box:

[0013] V0=αV m / s;

[0014] Where: A is the exhaust duct span, unit: m; B is the arch height, unit: m; α is the optimal wind speed ratio between the jet nozzle wind speed and the duct exhaust wind speed obtained based on engineering practice and CFD technology simulation.

[0015] Furthermore, the calculation formula for the total air supply volume L0 of the static pressure box in step S1 is:

[0016] L0=3600V0×(A+2B+πA / 2)×W m 3 / h;

[0017] Where: W is the opening width of the slot nozzle, unit: m.

[0018] Furthermore, when selecting typical points in the static pressure box in step S2, due to the symmetry of the exhaust duct cross-section, only five typical points are selected on one side of the static pressure box, and the positions are as follows: the first typical point is located at the starting point when the fresh air enters the static pressure box; the second typical point is located at the position of the fresh air before the rising corner; the third typical point is located at the position of the fresh air after the rising corner; the fourth typical point is located at the position before the fresh air rises to the arc arch; the fifth typical point is located at the position when the fresh air is at the top of the arch.

[0019] Furthermore, the pressure calculation process at each typical point in step S2 includes:

[0020] S201: Calculate the pressure at the first typical point. The first typical point is where the fresh air just enters the static pressure box. Its pressure loss ΔP1 can be ignored. The static pressure P at the first typical point is 1j for:

[0021]

[0022] Where: P0 represents the total pressure at the entrance of the static pressure box, unit: Pa, which can be the total pressure of the static pressure box blower; P 1d represents the dynamic pressure at the first typical point, unit: Pa; ΔP1 represents the pressure loss from the first typical point to the inlet; ρ represents the air density, unit: kg / m3; V1 represents the wind speed at the first typical point, unit: m / s; H represents the height of the static pressure box bottom; C represents the width of the static pressure box;

[0023] S202: Calculate the pressure condition at the position of the second typical point. The second typical point is located before the rising corner of the fresh air, and its pressure loss ΔP2 is the frictional resistance along the path from the second typical point to the first typical point. The static pressure P at the second typical point 2j is:

[0024]

[0025] In the formula: P 2d represents the dynamic pressure at the second typical point, unit: pa; ΔP2 represents the pressure loss from the second typical point to the first typical point, unit: pa; Δp 2m represents the frictional resistance per unit length along the path from the second typical point to the first typical point, unit: pa / m; V2 represents the wind speed at the second typical point, unit: m / s; d e2 represents the equivalent diameter of the air duct at the second typical point;

[0026] S203: Calculate the pressure condition at the position of the third typical point. The third typical point is located after the rising corner of the fresh air, and its pressure loss ΔP3 is the local resistance from the third typical point to the second typical point. The static pressure P at the third typical point 3j is:

[0027]

[0028] In the formula: P 3d represents the dynamic pressure at the third typical point, unit: pa; ΔP3 represents the pressure loss from the third typical point to the second typical point, unit: pa; ξ3 represents the local resistance coefficient from the third typical point to the second typical point; V3 represents the wind speed at the third typical point, unit: m / s; W1 represents the thickness of the static pressure box at the third typical point, unit: m;

[0029] S204: Calculate the pressure condition at the position of the fourth typical point. The fourth typical point is located before the fresh air rises to the arc-shaped vault, and its pressure loss ΔP4 is the frictional resistance along the path from the fourth typical point to the third typical point. The static pressure P at the fourth typical point 4j is:

[0030]

[0031] Among them: P 4d represents the dynamic pressure at the fourth typical point, unit: pa; ΔP4 represents the pressure loss from the fourth typical point to the third typical point, unit: pa; Δp 4m represents the frictional resistance per unit length along the path from the fourth typical point to the third typical point, unit: pa / m; V4 represents the wind speed at the fourth typical point, unit: m / s; W2 represents the thickness of the static pressure box at the fourth typical point, unit: m, d e4 represents the equivalent diameter of the air duct at the fourth typical point;

[0032] S205: Calculate the pressure condition at the position of the fifth typical point. The fifth typical point is located at the top of the vault. The pressure loss ΔP5 is the sum of the frictional resistance and the local resistance along the path from the fifth typical point to the fourth typical point. The static pressure P at the fifth typical point 5j is as follows:

[0033]

[0034] Among them: P 5d represents the dynamic pressure at the fifth typical point, unit: pa; ΔP5 represents the pressure loss from the fifth typical point to the fourth typical point, unit: pa; Δp 5m represents the frictional resistance per unit length along the path from the fifth typical point to the fourth typical point, unit: pa / m; ξ5 represents the local resistance coefficient from the fifth typical point to the fourth typical point; V5 represents the wind speed at the fifth typical point, unit: m / s; W3 represents the thickness of the static pressure box at the fifth typical point, unit: m, d e5 represents the equivalent diameter of the air duct at the fifth typical point.

[0035] Furthermore, in step S3, the static pressure values of each typical point are reviewed:

[0036] S301: Review the static pressure at the second typical point. If represents that compared with the first typical point, the fluctuation range of the static pressure is within 5%. The wind speed change of the slot-type nozzle is small, and the size of the static pressure box at the second typical point meets the requirements; if indicates that the fluctuation range of the static pressure is large, and the static pressure regain method needs to be adopted to modify the height and width of the bottom static pressure box to make the fluctuation range of the static pressure within 5%;

[0037] S302: Review the static pressure at the third typical point. If represents that the static pressure at the third typical point meets the requirements. If it is necessary to modify the thickness W1 of the static pressure box at the third typical point to make the fluctuation range of the static pressure within 5%;

[0038] S303: Review the static pressure at the fourth typical point. If represents that the static pressure at the fourth typical point meets the requirements. If it is necessary to modify the thickness W2 of the static pressure box at the fourth typical point to make the fluctuation range of the static pressure within 5%;

[0039] S304: Review the static pressure at the fifth typical point. If represents that the static pressure at the fifth typical point meets the requirements. If it is necessary to modify the thickness W3 of the static pressure box at the fifth typical point to make the fluctuation range of the static pressure within 5%.

[0040] This technical solution calculates the average jet velocity of the slot nozzle and the total air supply volume, adjusts the size of the static pressure box in combination with the static pressure recovery method, ensures that the static pressure fluctuation at each typical point inside is controlled within 5%, so that the jet velocity of the nozzle is uniform, forms a continuous and stable air film between the air discharged from the air duct and the wall surface, effectively blocks heat exchange, and eliminates infrared signs; at the same time, by performing sectional pressure calculation and size parameter correction on the static pressure box, the problem of poor concealment effect caused by uneven jet flow in the traditional static pressure box is solved, and the concealment performance of the exhaust system for special projects is guaranteed. Description of the Drawings

[0041] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0042] Figure 1 It is a schematic plan view of the static pressure box of the exhaust air duct.

[0043] Figure 2 It is Figure 1 The sectional view along A-A in

[0044] Figure 3 It is Figure 1 The sectional view along B-B in

[0045] Description of the reference numerals: 1 - static pressure box, 2 - slot nozzle, 3 - first typical point, 4 - second typical point, 5 - third typical point, 6 - fourth typical point, 7 - fifth typical point. Specific Embodiments

[0046] The following will clearly and completely describe the technical solutions of the present invention in combination with the embodiments. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0047] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0048] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present invention, "a plurality" means two or more unless otherwise specifically defined. In addition, the terms "mounted", "connected", and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0049] Embodiment 1

[0050] As Figures 1 to 3 shown, the present invention provides a calculation method for uniform pressure control and isokinetic jet flow in an exhaust air duct, including the following steps:

[0051] Step 1: According to the exhaust air volume of the underground exhaust air duct, calculate the average jet flow velocity of the slot nozzles 2 on the static pressure box 1 and the total air supply volume of the static pressure box 1;

[0052] Among them: The calculation process of the average jet flow velocity of the slot nozzles 2 on the static pressure box 1 includes:

[0053] Step 1.1: Calculate the cross-sectional velocity V when the maximum exhaust air volume of the exhaust air duct is L as:

[0054] V = L / 3600(A × B + πA 2 / 8) m / s;

[0055] Step 1.2: Calculate the average jet flow velocity V0 of the slot nozzles 2 on the static pressure box 1 as:

[0056] V0 = αV m / s;

[0057] Where: A is the span of the exhaust air duct, unit: m; B is the camber height, unit: m; α is the optimal wind speed ratio of the jet nozzle wind speed to the air duct exhaust wind speed obtained from engineering practice and CFD technology simulation.

[0058] Step 1.3: The calculation formula for the total supply air volume L0 of the static pressure box 1 is:

[0059] L0 = 3600V0×(A + 2B + πA / 2)×W m 3 / h;

[0060] Where: W is the opening width of the slot-type nozzle 2, unit: m.

[0061] Step 2: According to the air duct pressure characteristics, select typical points in the static pressure box 1 and calculate the pressure conditions at each typical point respectively;

[0062] Step 2.1: Selection of typical points in the static pressure box 1.

[0063] When selecting typical points in the static pressure box **********1, due to the symmetry of the exhaust air duct cross-section, only five typical points are selected on one side inside the static pressure box 1, and the positions are as follows: The first typical point 3 is located at the starting point when fresh air enters the static pressure box 1; the second typical point 4 is located at the position point before the fresh air rises at the corner; the third typical point 5 is located at the position point after the fresh air rises at the corner; the fourth typical point 6 is located at the position point before the fresh air rises to the arc-shaped vault; the fifth typical point 7 is located at the position point when the fresh air is at the top of the vault. For the specific position selection, see Figure 3 .

[0064] Step 2.2: Calculate the pressure conditions at each typical point.

[0065] Step 2.2.1: Calculate the pressure condition at the position of the first typical point 3. The first typical point 3 is the position where fresh air just enters the static pressure box 1, and its pressure loss ΔP1 can be ignored. The static pressure P 1j at the first typical point 3 is:

[0066]

[0067] Where: P0 represents the total pressure at the inlet of the static pressure box 1, unit: pa, and the total pressure of the air supply fan of the static pressure box 1 can be taken; P 1d represents the dynamic pressure at the first typical point 3, unit: pa; ΔP1 represents the pressure loss from the first typical point 3 to the inlet; ρ represents the air density, unit: kg / m 3 ; V1 represents the wind speed at the first typical point 3, unit: m / s; H represents the bottom height of the static pressure box 1; C represents the width of the static pressure box 1;

[0068] Step 2.2.2: Calculate the pressure condition at the position of the second typical point 4. The second typical point 4 is located before the rising corner of the fresh air, and its pressure loss ΔP2 is the frictional resistance along the path from the second typical point 4 to the first typical point 3. The static pressure P at the second typical point 4 2j is:

[0069]

[0070] In the formula: P 2d represents the dynamic pressure at the second typical point 4, unit: pa; ΔP2 represents the pressure loss from the second typical point 4 to the first typical point 3, unit: pa; Δp 2m represents the frictional resistance per unit length along the path from the second typical point 4 to the first typical point 3, unit: pa / m; V2 represents the wind speed at the second typical point 4, unit: m / s; d e2 represents the equivalent diameter of the air duct at the second typical point 4;

[0071] Step 2.2.3: Calculate the pressure condition at the position of the third typical point 5. The third typical point 5 is located after the rising corner of the fresh air, and its pressure loss ΔP3 is the local resistance from the third typical point 5 to the second typical point 4. The static pressure P at the third typical point 5 3j is:

[0072]

[0073] In the formula: P 3d represents the dynamic pressure at the third typical point 5, unit: pa; ΔP3 represents the pressure loss from the third typical point 5 to the second typical point 4, unit: pa; ξ3 represents the local resistance coefficient from the third typical point 5 to the second typical point 4; V3 represents the wind speed at the third typical point 5, unit: m / s; W1 represents the thickness of the static pressure box 1 at the third typical point 5, unit: m;

[0074] Step 2.2.4: Calculate the pressure condition at the position of the fourth typical point 6. The fourth typical point 6 is located before the fresh air rises to the arc-shaped vault, and its pressure loss ΔP4 is the frictional resistance along the path from the fourth typical point 6 to the third typical point 5. The static pressure P at the fourth typical point 6 4j is:

[0075]

[0076] Among them: P 4d represents the dynamic pressure at the fourth typical point 6, unit: pa; ΔP4 represents the pressure loss from the fourth typical point 6 to the third typical point 5, unit: pa; Δp 4mIt represents the frictional resistance per unit pipe length from the fourth typical point 6 to the third typical point 5, unit: pa / m; V4 represents the wind speed at the fourth typical point 6, unit: m / s; W2 represents the thickness of the static pressure box 1 at the fourth typical point 6, unit: m, d e4 It represents the equivalent diameter of the air duct at the fourth typical point 6;

[0077] Step 2.2.5: Calculate the pressure condition at the fifth typical point 7. The fifth typical point 7 is located at the top of the arch crown. Its pressure loss ΔP5 is the sum of the frictional resistance and the local resistance from the fifth typical point 7 to the fourth typical point 6. The static pressure P at the fifth typical point 7 5j is:

[0078]

[0079] Where: P 5d represents the dynamic pressure at the fifth typical point 7, unit: pa; ΔP5 represents the pressure loss from the fifth typical point 7 to the fourth typical point 6, unit: pa; Δp 5m represents the frictional resistance per unit pipe length from the fifth typical point 7 to the fourth typical point 6, unit: pa / m; ξ5 represents the local resistance coefficient from the fifth typical point 7 to the fourth typical point 6; V5 represents the wind speed at the fifth typical point 7, unit: m / s; W3 represents the thickness of the static pressure box 1 at the fifth typical point 7, unit: m, d e5 represents the equivalent diameter of the air duct at the fifth typical point 7.

[0080] Step 3: Recheck the static pressure values at each typical point. For points with large differences, modify the size of the static pressure box 1 according to the static pressure recovery method to ensure that the static pressures at each point are similar.

[0081] The steps for rechecking the static pressure values at each typical point are as follows:

[0082] Step 3.1: Recheck the static pressure at the second typical point 4. If represents that compared with the first typical point 3, the static pressure fluctuation range at the second typical point 4 is within 5%, the wind speed change of the slot-type nozzle 2 is small, and the size of the static pressure box 1 at the second typical point 4 meets the requirements; if it indicates that the static pressure fluctuation range is large, and the static pressure recovery method needs to be used to modify the size (height H and width C) of the bottom static pressure box 1 so that the static pressure fluctuation range is within 5%;

[0083] Step 3.2: Recheck the static pressure at the third typical point 5. If represents that the static pressure at the third typical point 5 meets the requirements. If it is necessary to modify the thickness W1 of the static pressure box 1 at the third typical point 5 so that the static pressure fluctuation range is within 5%.

[0084] Step 3.3: Recheck the static pressure at the fourth typical point 6. If It indicates that the static pressure at the fourth typical point 6 meets the requirements. If it is necessary to modify the thickness W2 of the static pressure box 1 at the fourth typical point 6 so that the static pressure fluctuation amplitude is within 5%;

[0085] Step 3.4: Recheck the static pressure at the fifth typical point 7. If it indicates that the static pressure at the fifth typical point 7 meets the requirements. If it is necessary to modify the thickness W3 of the static pressure box 1 at the fifth typical point 7 so that the static pressure fluctuation amplitude is within 5%.

[0086] Embodiment 2

[0087] Based on Embodiment 1, this embodiment is illustrated by taking Embodiment 1 as an example:

[0088] For example: When the exhaust duct size is set as follows: the span is A = 2.5 m, the rise height is B = 2.5 m, 1 / 2 arch, and the maximum exhaust air volume of the exhaust duct is L = 100000 (m3 / h).

[0089] In Step 1.1: Calculate the cross-sectional wind speed when the maximum exhaust air volume of the exhaust duct is L:

[0090] V = L / 3600(A × B + πA 2 / 8) = 3.2 m / s;

[0091] In Step 1.2: Calculate the average jet wind speed of the slotted nozzles 2 on the static pressure box 1:

[0092] V0 = αV = 1.5 × 3.2 = 4.8 m / s;

[0093] Among them, the best wind speed ratio α is taken as 1.5.

[0094] In Step 1.3: Calculate the total air supply volume of the static pressure box 1:

[0095] L0 = 3600V0 × (A + 2B + πA / 2) × W = 9871.2 m3 / h;

[0096] Among them: W represents the opening width of the slotted nozzles 2, and the value is taken as 0.05 m.

[0097] Select a fresh air supply fan according to the calculation results. The air volume of the supply fan L0 is taken as 10000 m3 / h, and the total pressure of the fan is 300 Pa.

[0098] In Step 2.2: Calculate the pressure conditions at each typical point as follows:

[0099] Step 2.2.1 Calculate the pressure condition at the position of the first typical point

[0100] Wind speed at the first typical point 3

[0101] Static pressure at the first typical point 3

[0102] Step 2.2.2: Calculate the pressure condition at the second typical point 4 position.

[0103] Wind speed at the second typical point 4:

[0104] At the second typical point 4:

[0105] Static pressure at the second typical point 4:

[0106] Step 2.2.3: Calculate the pressure condition at the third typical point 5 position. The thickness W1 of the static pressure box 1 at the third typical point 5 is 0.35 m, and the local resistance coefficient ξ3 = 0.7 can be obtained from the data.

[0107] Wind speed at the third typical point 5

[0108] Static pressure at the third typical point 5:

[0109]

[0110] Step 2.2.4: Calculate the pressure condition at the fourth typical point 6 position. The thickness W2 of the static pressure box 1 at the fourth typical point 6 is 0.2 m.

[0111] Wind speed at the fourth typical point 6:

[0112] At the fourth typical point 6:

[0113] Static pressure at the fourth typical point 6:

[0114]

[0115] Step 2.6. Calculate the pressure condition at the fifth typical point 7 position. The thickness W3 of the static pressure box 1 at the third typical point 5 is 0.1 m, and the local resistance coefficient ξ5 = 0.28 can be obtained from the data.

[0116] Wind speed at the fifth typical point 7:

[0117] At the fifth typical point 7:

[0118] Static pressure at the fifth typical point 7:

[0119]

[0120] Step 3: Recheck the static pressure values at each point.

[0121] Step 3.1: Recheck the static pressure at the second typical point 4, meeting the requirement that the static pressure fluctuation range is within 5%.

[0122] Step 3.2: Recheck the static pressure at the third typical point 5, meeting the requirement that the static pressure fluctuation range is within 5%.

[0123] Step 3.3: Recheck the static pressure at the fourth typical point 6, meeting the requirement that the static pressure fluctuation range is within 5%.

[0124] Step 3.4: Recheck the static pressure at the fifth typical point 7, meeting the requirement that the static pressure fluctuation range is within 5%.

[0125] Through rechecking, it is known that the dimensions H, C, W1, W2, and W3 of the static pressure box 1 can meet the calculation requirements, and the static pressure generated inside the static pressure box 1 is similar, meeting the condition for generating an equal-velocity jet.

[0126] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A calculation method for uniform pressure control and isokinetic jet flow in an exhaust air duct, characterized in that, It includes the following steps: S1: Calculate the average jet velocity of the slot nozzles on the static pressure box and the total air supply volume of the static pressure box according to the air exhaust volume of the underground exhaust duct; S2: Select typical points in the static pressure box according to the pressure characteristics of the air duct, and calculate the pressure conditions at each typical point respectively; S3: Recheck the static pressure values of each typical point. For points with large differences, modify the height, width or thickness of the static pressure box according to the static pressure recovery method to ensure that the static pressures at each point are similar.

2. The equal-velocity jet flow calculation method with uniform pressure control for the exhaust air duct according to claim 1, wherein The calculation process of the average jet velocity of the slot nozzles on the static pressure box in step S1 includes: S101: Calculate the cross-sectional velocity V when the maximum air exhaust volume of the exhaust duct is L as: V = L / 3600(A×B + πA 2 / 8) m / s; S102: Calculate the average jet velocity V0 of the slot nozzles on the static pressure box as: V0 = αV m / s; In the formula: A is the span of the exhaust duct, unit: m; B is the arch height, unit: m; α is the optimal velocity ratio of the jet nozzle velocity to the air duct exhaust velocity obtained by engineering practice and CFD technology simulation.

3. The method for calculating the uniform pressure control and equal velocity jet flow in the exhaust air duct according to claim 2, wherein The calculation formula for the total air supply volume L0 of the static pressure box in step S1 is: L0 = 3600V0×(A + 2B + πA / 2)×W m 3 / h; In the formula: W is the opening width of the slot nozzle, unit: m.

4. The method for calculating the uniform pressure control and constant velocity jet flow in the exhaust air duct according to claim 1, characterized in that, When selecting typical points in the static pressure box in step S2, due to the symmetry of the cross-section of the exhaust duct, only five typical points are selected on one side inside the static pressure box, and the positions are as follows: The first typical point is located at the starting point when the fresh air enters the static pressure box; The second typical point is located at the position point before the fresh air turns at the rising corner; The third typical point is located at the position point after the fresh air turns at the rising corner; The fourth typical point is located at the position point before the fresh air rises to the arc-shaped vault; The fifth typical point is located at the position point when the fresh air is at the top of the vault.

5. The equal-velocity jet flow calculation method with uniform pressure control for the exhaust air duct according to claim 4, characterized in that The calculation process of the pressure conditions at each typical point in step S2 includes: S201: Calculate the pressure condition at the position of the first typical point. The first typical point is the position where fresh air just enters the static pressure box, and its pressure loss ΔP1 can be ignored. The static pressure P at the first typical point is: 1j is: Where: P0 represents the total pressure at the inlet of the plenum chamber, unit: Pa, and the total pressure of the plenum chamber blower can be taken; P 1d represents the dynamic pressure at the first typical point, unit: Pa; ΔP1 represents the pressure loss from the first typical point to the inlet; ρ represents the air density, unit: kg / m 3 ; V1 represents the wind speed at the first typical point, unit: m / s; H represents the height at the bottom of the plenum chamber; C represents the width of the plenum chamber; S202: Calculate the pressure condition at the position of the second typical point. The second typical point is located before the rising corner of the fresh air, and its pressure loss ΔP2 is the frictional resistance along the path from the second typical point to the first typical point. The static pressure P at the second typical point 2j is as follows: Where: P 2d represents the dynamic pressure at the second typical point, unit: Pa; ΔP2 represents the pressure loss from the second typical point to the first typical point, unit: Pa; Δp 2m represents the frictional resistance per unit length of the duct from the second typical point to the first typical point, unit: Pa / m; V2 represents the wind speed at the second typical point, unit: m / s; d e2 represents the equivalent diameter of the air duct at the second typical point; S203: Calculate the pressure condition at the position of the third typical point. The third typical point is located after the rising corner of the fresh air, and its pressure loss ΔP3 is the local resistance from the third typical point to the second typical point. The static pressure P at the third typical point 3j is as follows: Where: P 3d represents the dynamic pressure at the third typical point, unit: Pa; ΔP3 represents the pressure loss from the third typical point to the second typical point, unit: Pa; ξ3 represents the local resistance coefficient from the third typical point to the second typical point; V3 represents the wind speed at the third typical point, unit: m / s; W1 represents the thickness of the static pressure box at the third typical point, unit: m; S204: Calculate the pressure condition at the position of the fourth typical point. The fourth typical point is located before the fresh air rises to the arc-shaped vault, and its pressure loss ΔP4 is the frictional resistance from the fourth typical point to the third typical point. The static pressure P at the fourth typical point 4j is as follows: Where: P 4d represents the dynamic pressure at the fourth typical point, unit: Pa; ΔP4 represents the pressure loss from the fourth typical point to the third typical point, unit: Pa; Δp 4m represents the frictional resistance per unit length of the duct from the fourth typical point to the third typical point, unit: Pa / m; V4 represents the wind speed at the fourth typical point, unit: m / s; W2 represents the thickness of the static pressure box at the fourth typical point, d e4 represents the equivalent diameter of the air duct at the fourth typical point; S205: Calculate the pressure condition at the position of the fifth typical point. The fifth typical point is located at the top of the vault. Its pressure loss ΔP5 is the sum of the frictional resistance and the local resistance from the fifth typical point to the fourth typical point. The static pressure P at the fifth typical point 5j is as follows: Where: P 5d represents the dynamic pressure at the fifth typical point, unit: Pa; ΔP5 represents the pressure loss from the fifth typical point to the fourth typical point, unit: Pa; Δp 5m represents the frictional resistance per unit pipe length from the fifth typical point to the fourth typical point, unit: Pa / m; ξ5 represents the local resistance coefficient from the fifth typical point to the fourth typical point; V5 represents the wind speed at the fifth typical point, unit: m / s; W3 represents the thickness of the static pressure box at the fifth typical point, unit: m, d e5 represents the equivalent diameter of the air duct at the fifth typical point.

6. The method for calculating the uniform pressure control and equal velocity jet flow of the exhaust air duct according to claim 5, characterized in that, Recheck the static pressure values of each typical point in step S3: S301: Recheck the static pressure at the second typical point. If it indicates that, compared with the first typical point, the static pressure fluctuation amplitude at the second typical point is within 5%, the air velocity change of the slot nozzle is small, and the static pressure box size at the second typical point meets the requirements; if it shows that the static pressure fluctuation amplitude is large, and the static pressure regain method needs to be adopted to modify the height and width of the bottom static pressure box so that the static pressure fluctuation amplitude is within 5%; S302: Recheck the static pressure at the third typical point. If it indicates that the static pressure at the third typical point meets the requirements. If it is necessary to modify the thickness W1 of the static pressure box at the third typical point so that the static pressure fluctuation range is within 5%. S303: Recheck the static pressure at the fourth typical point. If it indicates that the static pressure at the fourth typical point meets the requirements. If it is necessary to modify the thickness W2 of the static pressure box at the fourth typical point so that the static pressure fluctuation range is within 5%. S304: Recheck the static pressure at the fifth typical point. If it indicates that the static pressure at the fifth typical point meets the requirements. If it is necessary to modify the thickness W3 of the static pressure box at the fifth typical point so that the static pressure fluctuation range is within 5%.

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