CN1392391A - Multiple air channel air amount measuring method and device in large air channel - Google Patents

Abstract

The invention discloses a method and a device for measuring the air volume of multiple air ducts in a large air duct. The measurement method is to divide the large air duct into n parts, use n wind measuring devices to measure the total pressure and static pressure difference in each air duct, transmit the pressure difference to the signal collector through the pressure sensor, and complete the air volume calculation of the air duct by the system host and display. The invention has the following advantages: ①Grilles are installed in front of the wind measuring device to rectify the gas entering the wind measuring device, eliminating eddy currents caused by elbows or dampers, and improving measurement accuracy. ② After the separation, the equivalent diameter of each small air duct is reduced, and the size of the airfoil or Venturi measuring device is correspondingly reduced, which reduces the requirements for the space position of the wind measuring device. ③Using this technology can reduce the equivalent diameter of the sub-air duct and reduce the absolute length of the straight pipe section required before the wind measuring device, which meets the requirements of the wind measuring device for the straight pipe section when the space of the large air duct is relatively narrow.

Description

Multi-duct air volume measurement method and device in large air duct

Technical field

The invention relates to a method and device for measuring the air volume of multiple air ducts in a large air duct.

Background technique

For a long time, the online measurement of air volume in large-section air ducts has been a difficult problem. The air flow in large air ducts is often affected by external factors such as dampers, flow channel turning, diversion and confluence, and expansion and reduction of pipe cross-sections, making the flow of large air ducts develop into Flows with complex velocity distributions.

The influencing factors of flow measurement are various, because there are: 1. The diversity of fluid properties, such as the difference of fluid viscosity, single-phase and multi-phase, compressible and incompressible, the level of pressure and density parameters, The cleanliness of the fluid, etc.; 2. The diversity of the piping system, such as the circular or non-circular cross section of the pipe, the smoothness and roughness of the inner wall, whether it is curved, diversion and confluence, the size of the flow, etc.; 3. The diversity of flow states, Such as laminar flow and turbulent flow, rotating flow and pulsating flow, whether the flow is fully developed, etc. At the same time, it is also influenced by the working principle of the measuring device and whether it meets its technical regulations.

At present, the main wind measuring devices used for air volume measurement in large air ducts include wing, duct-type Venturi, flute-type pipe and double Venturi, etc., each with its own advantages. The measurement principle of the large air duct air volume measurement device uses the concept of average flow velocity. If the output signal can represent the corresponding average flow velocity, it is necessary to ensure that the flow velocity distribution during measurement reaches a relatively uniform flow velocity distribution, which is necessary to ensure accurate measurement. condition. Generally, it is considered according to the fully developed flow velocity distribution, and a certain length of straight pipe section is required before the measuring device.

The measurement of air volume requires a stable or similar flow field, but it is impossible to stabilize the flow in the air duct during the operation adjustment process, and sometimes the flow velocity distribution is also not similar. To measure accurately, it is necessary to stabilize the rectification to meet the requirements of the measuring device, but sometimes the site conditions and spatial location cannot meet the measurement requirements

Contents of the invention

The purpose of the present invention is to provide a method and device for measuring the air volume of multiple air ducts in a large air duct.

The measurement method is to divide the large air duct into n parts, use n wind measuring devices to measure the total pressure and static pressure difference in each air duct, transmit the pressure difference to the signal collector through the pressure sensor, and complete the air volume calculation of the air duct by the system host and display.

The measuring device is sequentially provided with a rectifying device, an air measuring device, and an air duct dividing plate in the air duct.

The present invention has the following advantages:

① A grille is installed in front of the wind measuring device to rectify the gas entering the wind measuring device, eliminating the eddy current caused by elbows or dampers, and improving the measurement accuracy.

② After the separation, the equivalent diameter of each small air duct is reduced, and the size of the airfoil or Venturi measuring device is correspondingly reduced, which reduces the requirements for the space position of the wind measuring device.

③Using this technology can reduce the equivalent diameter of the air duct, and reduce the absolute length of the straight pipe required before the wind measuring device (the size of the shortest straight pipe required by the wind measuring device is generally proportional to the equivalent diameter of the air duct, such as airfoil air volume The measurement device requires at least 0.6 times the equivalent diameter of the straight pipe section in front of the device), which meets the requirements of the wind measurement device for the straight pipe section when the space of the large air duct is relatively narrow.

④ When the size of the wind measuring device and the length of the straight pipe section in front of the wind measuring device are barely met, the large wind duct is divided. The length of the pipe section is relatively increased, and the measurement accuracy of the air flow measuring device is greatly improved.

⑤ When the air volume deviation of each sub-air duct is large, the air volume of each sub-air duct is measured separately and then summed to reduce the air volume measurement error.

⑥Because the resistance coefficients of the air volume measuring devices in each air duct are consistent, when the wind speed distribution in each air duct is uneven, the air duct with high wind speed has high resistance, while the air duct with low wind speed has small resistance, and the air duct with large resistance will force some The air flow turns to the air channel with less resistance to pass through, and automatically reaches a balanced state, so the wind speed distribution is more uniform after passing through the divided air channel.

Description of drawings

Fig. 1 is a structural schematic diagram of a multi-air volume measuring device in a large air duct;

Figure 2 is a schematic diagram of differential pressure signal output wiring.

Detailed ways

The method of measuring the air volume of the large-section air duct is to transmit the pressure difference to the signal collector through the pressure sensor, and use the pressure difference of each wind measuring device in parallel to generate a pressure difference for transmission, or use the pressure difference of each wind measuring device to transmit separately.

The flow coefficient of the wind measuring device in the sub-air duct in the calculation of the air volume of the air duct completed by the host computer of the above system is calculated according to the individual calibration value.

The large-section air duct partition air volume measuring device is provided with a rectifying device 1, an air measuring device 2, and an air duct dividing plate 3 in sequence in the air duct. The rectification device is a uniform or non-uniform grid. The wind measuring device 2 is an airfoil wind measuring device, a Venturi wind measuring device, a flute tube, a double Venturi wind measuring device, a Pitot tube, a back pipe, an annubar tube, and a thermoelectric wind measuring device. The partition plate is a partition that separates the large air duct into small air ducts.

The present invention divides an unstable and dissimilar flow field into a plurality of relatively stable or similar sinking fields according to the specific conditions of the measured large air duct flow, and performs air volume measurement respectively. This is the basis and essence of multi-air duct air volume measurement. . Although on a certain section of the air duct, due to the influence of various factors, the distribution of its velocity is unstable, but after being divided into several areas by adding partitions, a relatively stable or similar velocity distribution can be obtained in each area.

Moreover, after the air duct is divided, the equivalent diameter of the air duct is shortened, and the length of the straight pipe section where the wind measuring device is located is relatively extended, so that the purpose of stabilizing the flow field can be achieved. At the same time, the length of the air volume measuring device can be greatly shortened, and the space requirement for the straight air duct is greatly reduced. For example, if a square air duct is evenly divided into two parts, the diameter of the two parts can be shortened to 75%; after being divided into four parts, the diameter can be shortened to 50%. This is very beneficial when the site layout space is small.

The present invention divides the large air duct into n parts (n is determined according to the site conditions and the size of the air duct), uses n wind measuring devices to measure the total pressure and static pressure difference in each air duct, and transmits them to the signal collector through the pressure sensor. The system host completes the calculation and display of the air volume of the air duct. In order to eliminate the vortex that may exist at the inlet of the air duct, a rectifying device is installed in front of the partition device.

The rectification device 1 is installed before the partition plate 2, and generally adopts a rectification grille, and its purpose is to eliminate the eddy current when entering the partition air duct. The number of partitioned ducts and the length of partitions are the key parameters of this measurement technology, which should be determined according to the site conditions, pipe size and the form of the wind measuring device 3 . The wind measuring device 3 is installed in each partitioned air duct. The wind measuring device 3 can use airfoil, Venturi, flute or other probes. The specific form is determined according to the site location, measurement accuracy, and resistance requirements. The length of the straight pipe section in front of the wind measuring device 3 should meet the requirements of this type of sensing device for the straight pipe section.

The pressure signals from each wind measuring device 3 are output in parallel or separately according to the position of the air duct structure. If the flow field of each small air duct is similar and the flow rate is not much different, the total pressure and static pressure can be connected in parallel to a differential pressure transformer output. Otherwise they should be output separately, the flows calculated separately and then summed. The output signal connection is shown in Figure 2. Air volume calculations are shown below. When outputting in parallel, $Q=k\·A\·\sqrt{\frac{2\mathrm{\Δp}}{\mathrm{\ρ}}}$ In the formula, Q--the total air volume of the air duct; k--the flow coefficient of the wind measuring device; A--the area of the small air duct after separation; Δp--the total differential pressure after parallel connection; ρ--gas density; $Q=\underset{i=1,\mathrm{no}}{\mathrm{\Σ}}(k_i\&Center\; Dot;A_i\&Center\; Dot;\sqrt{\frac{2\mathrm{\Δ}{p}_i}{{\mathrm{\ρ}}_i}})$ In the formula, Q--the total air volume of the air duct; n--the number of small air ducts _{; ki} --the flow coefficient of each wind measuring device; A _i --the area of each small air duct after separation; The output differential pressure of the channel wind measuring device; the rectification device ρ _i -- the gas density in each small air channel;

Claims (7)

1. A large-section air duct separation air flow measurement method is characterized in that the large air duct is divided into n parts, and n wind measuring devices are used to measure the total pressure and the static pressure difference in each air duct, and the pressure difference is transmitted by a pressure sensor To the signal collector, the system host completes the calculation and display of the air volume of the air duct. 2. The method for measuring the air flow volume separated by large cross-section air ducts according to claim 1, characterized in that the pressure difference is transmitted to the signal collector through the pressure sensor, and the pressure difference of each wind measuring device is connected in parallel to generate a pressure difference for transmission. , or use the pressure difference of each wind measuring device to transmit separately. 3. The method for measuring the air volume of the separated air duct with large cross-section according to claim 1, characterized in that the flow coefficient of the wind measuring device in the sub-air duct in the calculation of the air volume of the air duct completed by the system host is calculated according to a separate calibration value. 4. A large cross-section air duct separation air volume measurement device, characterized in that a rectifying device (1), an air measurement device (2), and an air duct partition plate (3) are sequentially arranged in the air duct. 5. The large-section air duct separation air volume measurement device according to claim 3, characterized in that said rectifying device is a uniform or non-uniform grille. 6. The large-section air duct separation air volume measuring device according to claim 3, characterized in that said wind measuring device (2) is an airfoil type wind measuring device, a Venturi wind measuring device, a flute tube, a double Venturi wind measuring device Inside wind measuring device, Pitot tube, back tube, Annubar tube, thermoelectric wind measuring device. 7. The large-section air duct separation air volume measurement device according to claim 3, characterized in that said partition plate is a partition that divides the large air duct into small air ducts.