CN111719272A - A method for improving the air uniformity of wide-width multi-nozzle air ducts - Google Patents

Abstract

The present invention relates to a method for improving the uniformity of air blowing from a wide-width multi-nozzle air duct, comprising the following steps: (1), target analysis; (2), calculating frictional resistance: calculating the frictional resistance of the first air duct; (3) ), calculate the local resistance: look up the fluid local resistance coefficient table, obtain the corresponding local resistance coefficient, and calculate the local resistance of the first stage from the dynamic pressure drop; (4), calculate the flow conservation equation: calculate by steps (2) and (3) The obtained friction resistance and local resistance, calculate the dynamic pressure drop of the next section; (5), calculate the section height: Calculate the dynamic pressure drop obtained in step (4), calculate the speed of the next section, and calculate the flow rate and wind speed. The height of the second section is calculated from the width of the track; (6), a specific structure is generated. The invention can better keep the air flow rate flowing through each nozzle basically the same, improve the quality of the processed products in the heat setting process, and reduce the energy consumption of the system.

Description

A method for improving the air uniformity of wide-width multi-nozzle air ducts

【Technical field】

The invention relates to a method for improving the air spray uniformity of wide-width multi-nozzle air ducts, and is especially suitable for air ducts with high requirements on the uniformity of air spray volume of each nozzle within a wide width range, belonging to the technical field of fabric printing and dyeing heat-setting.

【Background technique】

As the world's largest textile printing and dyeing country, my country ranks first in the world in terms of output and export volume of printing and dyeing textiles. However, as a big country in printing and dyeing, my country still has many deficiencies in printing and dyeing equipment and technical capabilities, such as high emissions and high energy consumption.

Taking printing and dyeing heat-setting processing as an example, it is one of the most critical processing procedures in dyeing and finishing. The heat setting is generally completed in the drying room. During the heat setting process, the hot air in the drying room is acted by the circulating fan, flows through the air duct, flows out from the nozzles of the air duct, and acts on the surface of the fabric at a certain speed in both directions, so as to realize the drying effect of the fabric. ironing. The uniformity of the air volume of each nozzle affects and determines the energy consumption level of the heat setting process to a large extent and the quality stability of the heat setting processed products.

In the prior art, for example, in the air duct structures of the shaping machines published by CN108589136A, CN204455593U, CN203807779U, etc., the cross-sections of the air ducts are all trapezoidal structures. Under this structure, after the gas input by the self-circulating fan is subjected to the pressure loss of the nozzle and the pressure loss along the way, the air flow rate ejected by each nozzle is not uniform, which seriously causes the drying unevenness of the fabric in the width range. , affecting the quality of processed fabrics and causing serious waste of process energy.

In order to solve the above-mentioned technical problems, it is indeed necessary to provide an innovative method for improving the uniformity of the air spray from the wide-width multi-nozzle air duct, so as to overcome the defects in the prior art.

[Content of the invention]

In order to solve the above-mentioned problems, the purpose of the present invention is to provide a method for improving the uniformity of the air spray of the wide-width multi-nozzle air duct, which can make the air flow rate flowing through each nozzle basically consistent, and improve the quality of the processed products in the heat setting process. Reduce system power consumption.

In order to achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a method for improving the uniformity of air spray from a wide-width multi-nozzle air duct, which comprises the following steps:

(1), target analysis: to ensure that the static pressure drop upstream and downstream of each nozzle remains constant;

(2) Calculate the frictional resistance: the frictional resistance coefficient is obtained from the empirical formula, the hydraulic diameter is obtained from the width and height of the air duct of the first section, the Reynolds number is obtained from the hydraulic diameter and dynamic viscosity, and then the first section is calculated by the above three formulas The frictional resistance of the air duct;

(3), calculate the local resistance: find the fluid local resistance coefficient table, obtain the corresponding local resistance coefficient, and calculate the local resistance of the first stage from the dynamic pressure drop;

(4), calculate the flow conservation equation: the sufficient condition to keep the static pressure of each nozzle constant is that the dynamic pressure drop is equal to the total pressure loss between adjacent nozzles; the frictional resistance calculated in steps (2) and (3) is related to the local resistance, calculate the dynamic pressure drop of the next section;

(5), calculate the height of the section: calculate the dynamic pressure drop obtained by step (4), calculate the speed of the next section, and calculate the height of the second section from the flow rate and the width of the air duct;

(6), generate a specific structure: the height of each section calculated in step (5) constitutes a data set, and then a numerical fitting technique is used to obtain a fitting curve with the smallest error, and the surface manifold and specific parameters of the air duct are obtained. Air duct structure.

The method for improving the air uniformity of wide-width multi-nozzle air ducts of the present invention is further as follows: in the step (1), in order to ensure that the upstream and downstream static pressure drop of each nozzle remains constant, the mass flow rate of each nozzle is the same; The formula for calculating the mass flow rate is as follows:

Where Q _total represents the total volume ratio of the air duct inlet, and n represents the total number of nozzles in the air duct.

The method for improving the air spray uniformity of wide-width multi-nozzle air ducts of the present invention is further as follows: in the step (2), the calculation formula of friction resistance is as follows:

Among them, P _f(i-(i+1)) represents the frictional resistance of the air ducts from i to i+1, L represents the length of the i and i+1 air ducts, f represents the frictional resistance coefficient, D represents the hydraulic diameter, e represents the roughness, Re represents the Reynolds number, μ represents the dynamic viscosity, w represents the width of the cross-sectional air duct, and h represents the height of the cross-sectional air duct.

The method for improving the air uniformity of wide-width multi-nozzle air ducts of the present invention is further as follows: in the step (3), the calculation formula of the local resistance is as follows:

P _l(i-(i+1)) =P _d *δ

Among them, P _l(i-(i+1)) represents the local resistance of the air duct from section i to section i+1, and δ represents the local resistance coefficient.

The method for improving the air uniformity of wide-width multi-nozzle air ducts of the present invention is further as follows: in the step (4), the flow conservation equation is as follows:

P _d(i) +P _s(i) =P _d(i+1) +P _s(i+1) +P _f(i-(i+1 ))+P _{l(i-(i+1) )}

P _s(i) =P _s(i+1)

P _d(i) -P _d(i+1) =P _f(i-(i+1)) +P _l(i-(i+1))

where P _d(i) represents the dynamic pressure of the i-th air duct, and P _s(i) represents the static pressure of the i-th air duct.

The method for improving the air spray uniformity of the wide-width multi-nozzle air duct of the present invention is further: in the step (5), the calculation formula of the section height is as follows:

Where S _i+1 represents the cross-sectional area of the i+1th section, Q _(i-i+1) represents the air flow from the section i to the section i+1, and h _i+1 represents the height of the i+1th section.

Compared with the prior art, the present invention has the following beneficial effects: the method for improving the air spray uniformity of wide-width multi-nozzle air ducts of the present invention can better keep the air flow rate flowing through each nozzle basically the same, and improve the heat setting process. Improve the quality of processed products and reduce system energy consumption.

【Description of drawings】

FIG. 1 is a flow chart of the method of the present invention for improving the uniformity of the spray of the wide-width multi-nozzle air duct.

FIG. 2 is a diagram showing the direction of airflow velocity.

Figure 3 is a schematic diagram of the flow conservation equation.

Figure 4 is a schematic diagram of the optimized structure and flow field of the air duct.

【Detailed ways】

Please refer to the accompanying drawings 1 to 4 of the description, the present invention is a method for improving the uniformity of air spray from a wide-width multi-nozzle air duct, which includes the following steps:

Step 10, target analysis: under the condition of low flow rate, the flow rate of the nozzle is determined by the pressure difference between the upstream and downstream of the nozzle. In order to ensure the uniformity of the spray of each nozzle, the static pressure drop between the upstream and downstream of each nozzle is kept constant.

Specifically, due to the static pressure difference between the inner and outer walls of the nozzle, if there is a nozzle in the air duct, airflow will be generated. Therefore, the outlet airflow velocity direction is perpendicular to the air duct wall. However, the flow velocity in the air duct also affects the actual flow velocity direction of the airflow outside the nozzle. The relationship between the speed driven by static pressure drop and the speed driven by dynamic pressure drop and air density is as follows:

Where V _s represents the speed driven by static pressure drop, V _d represents the speed driven by dynamic pressure drop, P _s represents static pressure drop, P _d represents dynamic pressure drop, and ρ represents air density.

Therefore, the outflow angle between the actual velocity direction and the duct axis is defined as:

where θ is the outflow angle and V _r is the actual velocity.

The relationship between the nozzle area and the project area in the air outlet direction is as follows:

Among them, S represents the project area in the air outlet direction, and S ₀ represents the nozzle area.

Then the volume rate of air flow through a single nozzle can be expressed as follows:

表示喷嘴的流量系数，定义为0.8。where Q ₀ represents the volume ratio of air flow through a single nozzle, V ₀ represents the average nozzle velocity,

Indicates the flow coefficient of the nozzle, defined as 0.8.

If the nozzle area and nozzle flow coefficient are kept constant, the static pressure drop must be kept constant in order to achieve the same mass flow per nozzle according to the above equation. The formula for calculating the mass flow rate of each nozzle is as follows:

Where Q _total represents the total volume ratio of the air duct inlet, and n represents the total number of nozzles in the air duct.

Step 11, calculate the frictional resistance: obtain the frictional resistance coefficient from the empirical formula, obtain the hydraulic diameter from the width and height of the air duct of the first section, obtain the Reynolds number from the hydraulic diameter and dynamic viscosity, and then calculate the first section of the wind by the above three formulas. Road frictional resistance.

Specifically, due to the objective existence of fluid viscosity, when the airflow passes through the air duct, the phenomenon of molecular infiltration and adhesion on the surface of the object will occur, so that the airflow molecules close to the air duct surface interact with the molecular particles on the air duct surface. When friction occurs, the sum of the shear stress braking effect caused by the viscosity of the airflow is the friction resistance, and the calculation formula is as follows:

Among them, P _f(i-(i+1)) represents the frictional resistance of the air ducts from i to i+1, L represents the length of the i and i+1 air ducts, f represents the frictional resistance coefficient, D represents the hydraulic diameter, e represents the roughness, Re represents the Reynolds number, μ represents the dynamic viscosity, w represents the width of the cross-sectional air duct, and h represents the height of the cross-sectional air duct.

Step 12, calculate the local resistance: look up the fluid local resistance coefficient table, obtain the corresponding local resistance coefficient, and calculate the local resistance of the first stage from the dynamic pressure drop.

Specifically, when the airflow passes through the air duct, due to local obstacles such as changing diameter and direction, the energy loss caused by the separation of the boundary layer and the generation of vortices is the local resistance. Calculated as follows:

P _l(i-(i+1)) =P _d *δ

Among them, P _l(i-(i+1)) represents the local resistance of the air duct from section i to section i+1, and δ represents the local resistance coefficient.

Step 13, calculate the flow conservation equation: the sufficient condition to keep the static pressure of each nozzle constant is that the dynamic pressure drop is equal to the total pressure loss between adjacent nozzles; the frictional resistance and local resistance calculated in steps (2) and (3) , calculate the dynamic pressure drop of the next section.

Specifically, considering keeping the static pressure of each nozzle constant, the total pressure loss between adjacent nozzles needs to be equal to the dynamic pressure drop. Calculated as follows:

P _d(i) +P _s(i) =P _d(i+1) +P _s(i+1) +P _f(i-(i+1)) +P _{l(i-(i+1) )}

P _s(i) =P _s(i+1)

P _d(i) -P _d(i+1) =P _f(i-(i+1)) +P _l(i-(i+1))

where P _d(i) represents the dynamic pressure of the i-th air duct, and P _s(i) represents the static pressure of the i-th air duct.

Step 14: Calculate the height of the section: Calculate the velocity of the next section from the dynamic pressure drop calculated in step (4), and calculate the height of the second section from the flow rate and the width of the air duct.

Specifically, the velocity of the next section is calculated from the dynamic pressure drop obtained by the previous calculation, and the height of the section is calculated from the flow rate and the width of the air duct. Calculated as follows:

Where S _i+1 represents the cross-sectional area of the i+1th section, Q _(i-i+1) represents the air flow from the section i to the section i+1, and h _i+1 represents the height of the i+1th section.

Step 15, generating a specific structure: the heights of each section calculated in step (5) constitute a data set, and then a numerical fitting technique is used to obtain a fitting curve with the smallest error, and the surface manifold of the air duct and the specific wind speed are obtained. Road structure.

The above specific embodiments are only preferred embodiments of this creation, and are not intended to limit this creation. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of this creation shall be included in this creation. within the scope of protection.

Claims (6)

1. A method for improving the air spraying uniformity of a wide multi-nozzle air duct is characterized by comprising the following steps: the method comprises the following steps:

(1) and (3) target analysis: ensuring that the static pressure drop of the upstream and downstream of each nozzle is kept constant;

(2) calculating the frictional resistance: obtaining a friction resistance coefficient by an empirical formula, obtaining a hydraulic diameter by the width and the height of the first section of the section air duct, obtaining a Reynolds number by the hydraulic diameter and the dynamic viscosity, and calculating the friction resistance of the first section of the air duct by the three formulas;

() Calculating the local resistance: searching a fluid local resistance coefficient table to obtain a corresponding local resistance coefficient, and calculating a first section of local resistance according to dynamic pressure drop;

(4) and calculating a flow conservation equation: a sufficient condition to keep the static pressure of each nozzle constant is that the dynamic pressure drop is equal to the total pressure loss between adjacent nozzles; calculating the dynamic pressure drop of the next section according to the friction resistance and the local resistance obtained by calculation in the steps (2) and (3);

(5) calculating the height of the cross section: calculating the speed of the next section according to the dynamic pressure drop obtained by calculation in the step (4), and calculating the height of the second section of section according to the flow and the air channel width;

(6) and generating a specific structure: and (4) forming a data set by the heights and rows of the sections obtained by calculation in the step (5), and then obtaining a fitting curve with the minimum error by adopting a numerical fitting technology to obtain the surface manifold of the air duct and the specific air duct structure.

2. The method for improving the air injection uniformity of the wide multi-nozzle air duct according to claim 1, wherein: in the step (1), in order to ensure that the static pressure drop of the upstream and the downstream of each nozzle is kept constant, the mass flow of each nozzle is the same; the mass flow per nozzle is calculated as follows:

wherein Q_totalRepresenting the total volume fraction of the tunnel inlet, and n representing the total number of nozzles of the tunnel.

3. The method for improving the air injection uniformity of the wide multi-nozzle air duct according to claim 3, wherein: in the step (2), the calculation formula of the frictional resistance is as follows:

wherein P is_f(i-(i+1))The air duct structure is characterized by representing the frictional resistance of the air ducts from the section i to the section i +1, L representing the lengths of the air ducts from the section i and the section i +1, f representing the frictional resistance coefficient, D representing the hydraulic diameter, e representing the roughness, Re representing the Reynolds number, mu representing the dynamic viscosity, w representing the width of the air duct at the cross section, and h representing the height of the air duct at the cross section.

4. The method for improving the air injection uniformity of the wide multi-nozzle air duct according to claim 1, wherein: in the step (3), the local resistance calculation formula is as follows:

P_l(i-(i+1))＝P_d*

wherein P is_l(i-(i+1))The local resistance of the air duct from the section i to the section i +1 is shown, and the local resistance coefficient is shown.

5. The method for improving the air injection uniformity of the wide multi-nozzle air duct according to claim 1, wherein: in the step (4), the flow conservation equation is as follows:

P_d(i)+P_s(i)＝P_d(i+1)+P_s(i+1)+P_f(i-(i+1))+P_l(i-(i+1))

P_s(i)＝P_s(i+1)

P_d(i)-P_d(i+1)＝P_f(i-(i+1))+P_l(i-(i+1))

wherein P is_d(i)Showing the dynamic pressure, P, of the i-th duct_s(i)The static pressure of the ith duct is shown.

6. The method for improving the air injection uniformity of the wide multi-nozzle air duct according to claim 1, wherein: in the step (5), the cross-section height calculation formula is as follows:

wherein S_i+1Denotes the cross-sectional area, Q, of the i +1 th stage_(i-i+1)Represents the air flow rate, h, from section i to section i +1_i+1Indicating the height of the i +1 th segment.

Images