How should the layout and design of ventilation ducts be considered to ensure uniform airflow in the workshop?

The layout and design of ventilation duct should ensure the uniform airflow in the workshop, and it is necessary to comprehensively consider the spatial structure of the workshop, the distribution of dust production points, the principle of airflow dynamics and the performance of equipment. The following are key design points and optimization strategies:

First, the core principles of duct layout

1. The principle of priority coverage of dust producing points.

Positioning dust source: Set suction hood (such as umbrella hood and side suction hood) directly above or on the side of grinding and polishing station to ensure that dust is directly sucked into the air duct when it is generated, so as to reduce diffusion.

Example: For the wheel hub polisher, a fixed enclosure can be designed to seal the equipment on three sides, leaving only the operating surface, forming negative pressure inside to quickly extract dust.

Angle of connection between branch pipe and main pipe: When connecting branch pipe and main pipe, adopt 30-45 oblique connection to avoid airflow impact and resistance loss caused by right-angle connection and ensure uniform air distribution of each branch pipe.

2. Symmetrical distribution and balanced design

Symmetric pipe network layout: adopt ring pipe network or symmetrical dendritic pipe network, so that the distance, pipe diameter and resistance of each branch pipe to the fan are similar, and avoid excessive near-end air volume and insufficient far-end air volume.

Case: When the dust production points on both sides of the workshop are symmetrical, the air ducts can be symmetrically arranged along the central axis, and the branch pipes are connected to the main pipe at equal intervals.

Resistance balance calculation: hydraulic calculation (such as assumed velocity method) can ensure that the resistance difference of each branch pipe is ≤10%, which can be realized by adjusting the pipe diameter, setting regulating valves (such as butterfly valves) or changing the pipe length.

Second, the optimization of key parameters of duct design

1. Matching of pipe diameter and wind speed

Wind speed control:

Metal dust (such as aluminum and magnesium) is easy to settle, and the wind speed of the air duct should be ≥18-25m/s (the larger the particle size, the higher the wind speed) to avoid dust accumulation and blockage in the pipeline.

The wind speed of the branch pipe can be slightly higher than that of the main pipe (for example, the branch pipe is 20-25m/s and the main pipe is 15-20m/s), and the airflow stability can be maintained by using the velocity difference.

Pipe diameter calculation:

D=

πv

4Q

(

D

Is the pipe diameter,

Q

For the air volume,

v

For wind speed), ensure that the air volume of each pipe section matches the pipe diameter, and avoid insufficient wind speed caused by "large pipe with small air volume" or increasing resistance caused by "small pipe with large air volume".

2. Pipe curvature and component design

Radius of elbow: the radius of curvature of elbow is ≥1.5 times the pipe diameter (for example, the pipe diameter is 200mm, and the radius of curvature is ≥300mm), so as to reduce airflow vortex and pressure loss. If space is limited, guide vanes can be used to improve airflow smoothness.

Tee design: The included angle of tee is controlled at 30-60. When the velocity of branch pipe is close to that of main pipe, an equal-diameter tee is used, and when the velocity difference is large, a variable-diameter tee is used to avoid "backward flow" or uneven distribution of airflow.

Three, air distribution mode and equipment selection

1. Air distribution mode

Total ventilation vs local ventilation:

Local exhaust (such as suction hood) is preferred to directly control the dust source, supplemented by comprehensive air supply and exhaust (such as top air supply and bottom air exhaust in the workshop) to form directional airflow to avoid dust circulation.

Recommended mode: supply air from clean area (such as office) to polluted area (grinding area) to form positive pressure gradient to prevent dust from spreading to non-production area.

Air flow direction design: the air supply outlet and the air exhaust outlet are diagonally arranged to make the air flow through the whole workshop and avoid the formation of air flow dead angle. For example, the air supply outlet is set on the ceiling and the air exhaust outlet is set on the wall side near the ground, and the dust gravity is used to assist the settlement.

2. The fan is matched with the filtering equipment.

Calculation of wind pressure of fan: The total wind pressure needs to overcome the resistance along the pipeline (such as friction resistance) and local resistance (such as elbows and valves), and can be calculated by the formula

P=∑(λ

d

l

2g

v

2

+ξ

2g

v

2

)

Calculate (

λ

Is the coefficient of friction,

ξ

Is the local drag coefficient).

Application of variable frequency fan: it is equipped with variable frequency fan to automatically adjust the air volume according to the real-time dust concentration in the workshop, which not only ensures uniform airflow, but also saves energy and reduces consumption.

Pre-installation of filtering equipment: a primary filter (such as cyclone dust collector) is installed before the air duct is connected to the fan, so as to reduce the abrasion of dust on the fan impeller and avoid uneven attenuation of air volume caused by equipment loss.

Four, workshop space and installation details

1. Pipeline installation height and direction

Overhead laying: the air duct is installed overhead along the top of the workshop or the wall, with a distance of ≥2m from the ground, so as to avoid affecting the operation of equipment and the passage of personnel, and at the same time, the siphon effect of air flow is enhanced by the height difference.

Avoid long and straight horizontal pipes: when the length of horizontal pipes is more than ＞10m, set a gradient of ≥ 3, and slope to the dust collector or ash outlet to prevent dust accumulation.

2. Verification of airflow uniformity

Wind speed measurement: After installation, use a hot-bulb anemometer or pitot tube to measure the wind speed of each branch pipe, and adjust the regulating valve to make the deviation ≤5%.

Smoke test: release smoke (such as smoke generator) in the workshop, observe whether the airflow direction meets the design expectation, mark the dead angle of airflow and optimize the layout of air duct (such as adding auxiliary exhaust points).

V. Examples of Typical Layout Schemes

Scene: rectangular workshop, single-sided multi-station grinding

Duct layout:

Main air duct (pipe diameter 300-400mm) is set along the length direction of the workshop, which is located at the top center.

A branch pipe (with a diameter of 150-200mm) is set above each station, which is connected to the main pipe at an angle of 45, and the length of the branch pipe is as consistent as possible.

Explosion-proof fan and bag dust collector are set at the end, and the air volume of the fan is calculated according to the total dust production (for example, a single station needs 2000 m/h, and the total air volume of 10 stations is ≥ 20000 m/h).

Air flow effect: the air speed of the suction hood at each station is uniform, and the workshop as a whole forms a directional air flow of "top air supply → station dust suction → end purification", and the dust concentration is ≤ 8 mg/m (better than the national standard limit).

summary

The core of airflow uniformity is to accurately control the balance of air volume, wind speed and pressure in each area, which needs to be realized through the systematic scheme of "directional control of dust production point+symmetrical design of pipe network+quantitative calculation of parameters+dynamic adjustment of equipment". In the actual project, it is suggested to combine CAD drawing to simulate the airflow path, and finally ensure that the dust concentration, temperature and humidity in every corner of the workshop meet the production and safety standards through iterative optimization of field testing.