In the chemical and electroplating industries, the production process often produces various gases with strong corrosive properties, such as sulfuric acid, hydrochloric acid, sodium hydroxide, etc. PP ducts can easily cope with these “acid and alkali attacks” by virtue of their excellent chemical resistance. In the sulfuric acid plant, PP ducts are used to transport high concentration of sulfuric acid vapor, and after a long time of use, the inner wall of the ducts is still smooth as before, without the slightest trace of corrosion. While the traditional metal duct, in the same environment, may be just a few months will appear serious corrosion, resulting in pipe leakage, not only affect the production, but also may bring potential safety hazards. According to relevant data, in the chemical industry, the use of PP duct equipment maintenance frequency than the use of metal duct equipment reduced by more than 50%, greatly improving production efficiency.

(ii) Sealing: “zero air leakage” guarantee

PP ducts are connected by heat fusion connection, flange connection and many other advanced connection methods. These connection methods can ensure that the ducts are tightly bonded to each other and realize “zero leakage” of air. In hospital operating rooms, good sealing is crucial. If there is leakage in the ventilation system, it will not only affect the air quality in the room, but may also lead to an increased risk of surgical infections. the excellent sealing of PP ducts can effectively prevent the leakage of harmful gases, providing a safe and clean environment for patients and healthcare workers. In industrial production, for some processes that require high gas purity, such as electronic chip manufacturing, the sealing of PP air ducts can ensure that the production environment is not interfered by external impurities, ensuring the stability of product quality.

(iii) Low noise: quiet ventilation system

PP material has good damping properties, which is the key to its noise reduction. As air flows through the duct, the PP material absorbs and attenuates sound waves, thus reducing the transmission of noise. Compared with metal ducts, PP ducts are significantly quieter in operation. According to professional tests, under the same conditions of air speed and air volume, the operation noise of metal ducts can be over 60 dB, while the noise of PP ducts can be controlled at about 40 dB, which is about 30% lower. In hospital wards, school classrooms and other noise-sensitive places, PP ducts can provide a quiet and comfortable environment, which is conducive to the recovery of patients and students’ learning.

(iv) Thermal insulation: energy saving and comfort

PP ducts can be equipped with specialized insulation, which effectively reduces heat loss. This feature is especially important in HVAC systems. In winter, PP square ducts with insulation can better retain heat in the room and reduce the energy consumption of heating equipment; in summer, it can prevent cold air from escaping and reduce the power consumption of air conditioning. Comparisons of real-world examples show that buildings with insulated PP ducts use 15% – 20% less energy for their HVAC systems than buildings with ordinary ducts. This not only saves energy costs for users, but also helps to reduce carbon emissions and realize green environmental protection.

(v) Long life: durable

PP material ages slowly, mainly due to its stable molecular structure and good chemical stability. Under normal operating conditions, PP ducts have a practical service life of 30 – 50 years. In some large industrial plants, PP ducts have been in continuous use for more than 30 years and are still performing well and do not need to be replaced. From a long-term cost perspective, although the initial investment in PP ducts may be slightly higher than some common ducts, the overall cost is lower due to their long service life and low maintenance costs. For example, while metal ducts require regular anti-corrosion treatment and repairs during use, PP ducts require little or no such additional costs, greatly reducing the operating costs of the enterprise.

Wind speed plays a key role in the determination of duct size, and there is a clear inverse relationship between it and the duct size. According to the formula for duct sizing (duct size = air volume / air velocity / 3600), the larger the air velocity, the smaller the calculated cross-sectional area of the duct for a fixed air volume of 20,000 m³/h; conversely, the smaller the air velocity, the larger the cross-sectional area of the duct.
The choice of different air velocities can affect the ventilation system in many ways. In terms of noise, a higher wind speed will lead to greater noise when the fan is running, and at the same time, the air flows at high speed in the duct, and when it passes through elbows, valves and other components, it is easy to generate airflow noise. For example, in some places with extremely high noise requirements, such as recording studios, libraries, etc., if a higher wind speed is used, the noise problem will seriously affect their normal use. Analyzing from the perspective of energy consumption, the higher the wind speed, the greater the resistance of the wind flowing in the duct, and in order to overcome these resistances, the fan needs to consume more electricity, thus increasing the operating cost of the system. In large commercial buildings, the ventilation system runs all day long, and if the wind speed is unreasonable leading to high energy consumption, it will generate a considerable amount of money in the long run. In addition, the wind speed will also affect the uniformity of ventilation, too high wind speed may lead to uneven distribution of air in the room, localized areas of under-ventilation or over-ventilation .

(二) Impact of system pressure

System pressure is another important factor that governs duct sizing. In a ventilation system, pressure is divided into static and dynamic pressure, with static pressure used to overcome the resistance of the duct and dynamic pressure related to the flow rate of the air . When the system pressure is high, it means that the duct needs to withstand a greater pressure load, which requires the duct to have enough strength and sealing to prevent the duct from rupturing or leaking .
In general, ducts in high-pressure systems require thicker, stronger materials. For example, in industrial ventilation, some air ducts conveying high-temperature and high-pressure gases may be made of steel plates of greater thickness and more stringent in terms of the connection parts of the air ducts and reinforcement measures . For low-pressure systems, the strength requirements of air ducts are relatively low, and thinner materials can be used, so as to meet the operational requirements of the system and reduce costs. If air ducts that do not meet the pressure requirements are used in high-pressure systems, it may lead to deformation and rupture of air ducts, which not only affects the ventilation effect, but also may cause safety accidents.

(三) Impact of usage scenarios and demand

Different scenarios and needs have different requirements for the size of the 20000 air volume ducts. In industrial plants, due to the large space and relatively low sensitivity to noise, in order to save cost and space, a higher air velocity is usually used, and the corresponding duct size can be smaller. For example, in some large-scale machinery processing plants, the air velocity of the main duct of the ventilation system may reach 10m/s or even higher, so that the cross-sectional area of the duct can be designed to be relatively small under the circumstance of meeting the 20,000 air volume.
Commercial buildings such as shopping malls and supermarkets are densely populated and have high requirements for indoor air quality and comfort, and also need to consider the impact of noise on the shopping experience of customers. Therefore, the air velocity of the ventilation system in such places is generally controlled in a moderate range, such as 6 – 8m/s, and the size of the air ducts will be designed according to the specific layout and air volume distribution. Moreover, commercial buildings usually have decorative structures such as suspended ceilings, and the installation of air ducts needs to be coordinated with the building structure, which also affects the selection of air duct sizes.
Residential ventilation systems are relatively small, but the requirements for noise are more stringent, because noise can directly affect the quality of life of residents. In residential houses, even if the airflow reaches 20,000 (which is relatively rare, and generally the airflow of residential houses is small, but assuming special circumstances), a lower air velocity, such as 4 – 6m/s, will be used to ensure a quiet living environment . In this case, in order to meet the demand for airflow, the size of the ducts may be relatively large, but the space of the house is limited, which requires full consideration of the layout and installation location of the ducts in the design, to minimize the occupation of indoor space.

1.Metal ducts: common metal ducts include galvanized steel ducts, stainless steel ducts and aluminum ducts. Galvanized steel duct price is relatively low, has good mechanical strength and fire performance, the most widely used, in general industrial and civil building ventilation system can see its figure. Stainless steel ducts have excellent corrosion resistance and are suitable for chemical, food and other industries with high requirements for hygiene and corrosion resistance, such as the ventilation ducts of food processing plants, stainless steel ducts are often used to ensure the purity of the air and the durability of the ducts. Aluminum plate duct is lightweight and not easy to produce sparks when collision, so it will be used in places with explosion-proof requirements, such as coal mine underground ventilation system.

2.Composite duct: Composite duct is made of a variety of materials composite, generally including thermal insulation materials and surface materials. For example, phenolic composite duct, it is phenolic foam as the core material, the surface covered with aluminum foil and other materials, with lightweight, good thermal insulation performance, sound insulation effect, etc., commonly used in the air conditioning and ventilation system with high requirements for thermal insulation and sound insulation, such as hotels, office buildings, central air conditioning ducts. There is also glass-magnesium composite air duct, which has excellent fireproof performance and high strength, and is used more in some buildings with strict fire safety requirements, such as shopping malls, hospitals and other places.

3.Polymer duct: Polymer duct is made of polymer material, such as polyvinyl chloride (PVC) duct, PVC duct has the characteristics of strong corrosion resistance, low price, easy installation, etc., which is widely used in some industrial places with corrosive gas emission, such as the ventilation system of electroplating workshop. However, PVC ducts have poor high temperature resistance and relatively narrow temperature range.

How to size ducts for 20000 air volume.

1.Assumed air velocity method
The assumed wind speed method is a common and relatively simple calculation method for determining the duct size required for 20,000 airflow. The core formula is: duct size (cross-sectional area) = air volume / air velocity / 3600. The principle of this formula is based on the relationship between flow rate, velocity and time. The unit of air volume is usually cubic meters per hour (m³/h), which indicates the volume of air passing through the duct in a unit of time; the unit of wind speed is meters per second (m/s), which describes the speed of air flowing through the duct; and 3600 is the conversion factor for converting hours to seconds, which gives the cross-sectional area of the duct in square meters (m²).
When applying this, it is first necessary to make reasonable assumptions about the wind speed. The choice of wind speed is not arbitrary, but to consider a variety of factors. For example, in the civil building ventilation system, if the noise control requirements are high, the wind speed should not be too large, generally the main duct wind speed can be controlled at 4 – 7m / s; in industrial plants and other relatively low noise requirements of the place, in order to reduce the size of the duct, reduce costs, the main duct wind speed can be increased appropriately, such as 6 – 12m / s . Suppose we have to determine the duct size for 20000m³/h airflow in an industrial project with general noise requirement, assuming the air velocity is 8m/s. According to the formula, the cross-sectional area of the duct = 20000÷8÷3600 ≈ 0.694m².
If a circular duct is used, we can further calculate the duct diameter according to the formula of the area of a circle S = πr² (where S is the area and r is the radius). From 0.694 = 3.14×r², we can get r² = 0.694÷3.14 ≈ 0.221, r ≈ 0.47m, then the diameter d = 2r ≈ 0.94m. If you choose rectangular duct, you also need to determine the ratio of length and width according to the actual installation space and design requirements, assuming that the ratio of length and width of 2:1, set the width of x meters, then the length of 2x meters, 2x × x = 0.694, that is, 2x ² = 0.694, can be obtained x ² = 0.347, x ≈ 0.59m, then the length of 2x ≈ 1.18m, that is, the size of the rectangular air duct can be 1180mm × 590mm.

2. Introduction to other calculation methods
In addition to the assumption of wind speed method, there are also a variety of methods to calculate the size of the duct, such as specific resistance method, area method, flow coefficient method. Specific resistance method is to calculate the friction resistance per unit length of the duct (specific resistance), combined with the total resistance of the duct and the air volume to determine the size of the duct, this method of calculation is relatively complex, you need to consider more resistance factors, such as the roughness of the duct, air viscosity, and so on. Area method is based on the known cross-sectional area of the duct and wind speed to calculate the air volume, and the assumption of wind speed method of calculation of the opposite idea, in the known air inference duct size, you need to determine the appropriate size through a number of trial calculations. Flow coefficient method is based on the flow coefficient of the inlet or outlet of the duct, combined with the wind speed and cross-sectional area to calculate the air volume, the method needs to know the flow coefficient of the duct in advance, and the flow coefficient is usually provided by the manufacturer or determined by experiments.
However, in practical engineering applications, the assumed air velocity method is most commonly used because it is relatively simple and intuitive to calculate, and can meet the accuracy requirements of most projects. In this discussion on 20000 air volume duct sizing, we also focus on the assumed air velocity method as an example to analyze and calculate, so that we can understand and grasp the basic method of duct sizing more clearly.

Polypropylene is a high-density, side-chain-free, high-crystalline linear polymer with excellent comprehensive properties. Common products: basins, barrels, furniture, films, woven bags, bottle caps, car bumpers, etc.

pp plastic, chemical name: polypropylene, English name: Polypropylene (abbreviated as pp) specific gravity: 0.9-0.91 g/cm3, molding shrinkage: 1.0-2.5%, molding temperature: 160-220 °CPP is a crystalline polymer, and the comprehensive performance of PP is better than that of PE material. PP products are lightweight, tough and chemically resistant. The disadvantages of PP: low dimensional accuracy, insufficient rigidity, poor weather resistance, it has the phenomenon of post-shrinkage, and after demoulding, it is easy to age, become brittle and easy to deform. In engineering projects, the commonly used air duct is made of PP material.

In the PP material inside the high-purity propylene as the main material, including a small amount of ethylene copolymer, after drying, mixing, extrusion, granulation, screening and homogenization into polypropylene particles, this particle is cylindrical particles, the particles are very smooth, without any mechanical impurities, it has good mechanical properties and heat resistance, in the temperature range of minus 30 degrees Celsius to 140 degrees Celsius is not toxic.

Mechanical properties PP has high crystallinity and regular structure, so it has excellent mechanical properties. However, at room temperature and low temperature, the impact strength is poor due to the high regularity of its molecular structure. The most outstanding performance of PP is its resistance to flexural fatigue.

Chemical stability PP has good chemical stability, in addition to being eroded by concentrated sulfuric acid and concentrated nitric acid, it is relatively stable to various other chemical reagents; However, low molecular weight aliphatic hydrocarbons, aromatic hydrocarbons and chlorinated hydrocarbons can soften and swell polypropylene, and its chemical stability is improved with the increase of crystallinity, so PP is suitable for making various chemical pipes and fittings, and the anti-corrosion effect is good.

Electrical properties PP has excellent high-frequency insulation properties, and since it hardly absorbs water, the insulation properties are not affected by humidity. It has a high dielectric coefficient, and with the increase of temperature, it can be used to make heated electrical insulation products. It also has a high breakdown voltage, making it suitable for use as an electrical accessory, etc. It has good voltage resistance and arc resistance, but has a high degree of electrostatic electricity. Due to the presence of the side methyl group in PP, tertiary carbon atoms alternately appear on the molecular chain, and the tertiary carbon atoms are very easy to oxidize when in contact with copper ions, resulting in poor oxidation resistance and radiation resistance of polypropylene. Therefore, copper inhibitors must be added in applications that come into contact with copper.

The performance can be changed through additives: PP can change its performance by adding various fillers, plasticizers, antistatic agents, etc., so that it has the characteristics of flame retardant, antistatic, antibacterial, and reinforcing. For example, adding glass fiber can enhance the rigidity and strength of PP, adding carbon black can make PP have anti-ultraviolet and antistatic properties, adding antioxidants can extend the service life of PP, etc.

Differentiation of PP flame retardant materials

• The main difference between PP flame retardant materials is whether flame retardants are added or not
• The difference between PP flame retardant material and ordinary PP material is that flame retardant PP material is added in the production process, and these flame retardants are usually composed of bromine, oxygen, phosphorus, titanium, aluminum and other elements, which are designed to provide fire and flame retardant functionsThe presence of flame retardant makes the flame retardant PP material inhibit the open flame combustion and slow down the spread of the fire when it encounters the fire source, so as to achieve the purpose of fire controlThis material has been widely used in building materials, electronic appliances and other fields, because it can significantly improve the fire safety of products
• In addition, the flame retardant effect of PP flame retardant material not only depends on the type of flame retardant added, but also affects the proportion of flame retardant addedDifferent flame retardants have different properties and costs, and the selection of suitable flame retardant PP materials needs to consider their performance and cost and other factorsFor example, the fire resistance grade of PP flame retardant board is usually B1 grade, and some can reach A2 grade, depending on its production process and the amount of flame retardant addedThe addition of flame retardant will also affect the mechanical properties and melt index of PP materials, so it is necessary to weigh their fire performance and possible environmental impact when using flame retardant PP materials
• To sum up, the difference between PP flame retardant materials and ordinary PP materials lies in whether flame retardants are added, as well as the type and amount of these flame retardants, which together determine the fire performance and safety level of the material

PP air duct flame retardant grade classification

The flame retardant grades of PP air ducts mainly include A, B1, B2 and B3

• Grade A: Indicates non-combustible material, barely combustible
• B1 grade: It is a flame-retardant material, with a good flame retardant effect, it is not easy to spread quickly in case of fire, and it can be extinguished by itself after leaving the fire source
• Class B2: It is a combustible material with a certain flame retardant effect, but it is still a flammable material
• Class B3: It is a flammable material, has no flame retardant effect, and is extremely flammable.
• PP flame retardant ducts should generally achieve a fire rating of at least B1 to ensure that the spread of fire can be slowed down in the event of a fire, providing more time for personnel evacuation and extinguishing the fire.In addition, for the fire rating of plastics, there is also the UL-94 flame retardant plastic standard, in which the flame retardant grade is divided into HB, V2, V1, V0, 5VB, 5VA, etc., these grades are divided according to different test standards to divide the flame retardant performance of materials.For example, a V0 rating indicates that the material has high flame retardant properties, and the flame is extinguished within 30 seconds after two 10-second burn tests, and no combustibles can fallThe V2 rating indicates that the material has certain flame retardant properties, and after two 10-second burn tests, the flame is extinguished within 60 seconds, and some combustibles can fall.
• To sum up, the flame retardant grade classification of PP air duct not only considers the combustion characteristics of the material, but also covers the detailed definition and test standards of different grades to ensure that the material can play an effective flame retardant role under specific conditions

1.Product Structure:

• Round tubes are usually constructed of circular sections, which have high torsional strength and compressive strength, and are suitable for structures that bear complex loads

• The square tube is composed of four sides of a rectangular section, which has high strength and rigidity, and is suitable for supporting structures that bear large loadsThe cross-sectional shape of the square tube makes it have high torsional strength and bending resistance, and also has strong adaptability, which can adapt to various complex installation environments

2. Usage Scenarios:

• Round pipes are widely used in various fluid transportation fields, such as petroleum, chemical industry, electric power, etc., and are also used in building structures, bridges and other fields
• Square tubes are mainly used for structural support and carrying heavy objects, such as bridges, buildings, shipbuilding, etcIn addition, square tubes can also be used to manufacture various equipment brackets, frames, etc

3. Advantages and disadvantages:

• The advantages of round pipes include high strength and stiffness, good sealing performance, suitable for conveying corrosive media or high-purity liquids (gases)
• The advantage of square tube is its strong structural stability, the ability to withstand large loads, and high impact resistanceThe installation of the square tube is more complex and the cost is higher, but its cross-sectional shape makes it have high torsional strength and bending resistance, and can adapt to various complex installation environments

To sum up, the choice of PP round pipe or square pipe should be decided according to the specific use scenario and needsIf cost, ease of installation, and general requirements for conveying fluids need to be considered, round tubing may be a more appropriate choiceIf you need to bear a large load and have higher requirements for the stability and impact resistance of the structure, the square tube is more suitableIn practical applications, factors such as pipe size, wall thickness and length should also be considered to meet actual needs

Comparison of compressive resistance of PP round pipe and square pipe

• There are differences in structure and performance between square and round tubes, which directly affect their compressive performanceThe cross-section of the square tube is square, and this structure makes it have better bending resistance and stability, which is suitable for some special requirementsIn contrast, the cross-section of a round tube is round, and its bending resistance and stability are not as good as that of a square tubeIn terms of compressive performance, square tubes usually have high compressive performance, which is due to its special cross-sectional shape and structure, which makes it better able to withstand large load occasionsIn addition, the compressive performance of the square tube is also affected by the material, specification and processing technology, which further enhances its ability to withstand pressure
• In summary, the square tube is better than the round tube in terms of compressive performance, especially in the occasion of large loads, the choice of the square tube is more suitable