通風管道內(nèi)壓力的測定方法？

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測量通風管道中氣體的壓力應在氣流比較平穩(wěn)的管段進行。測試中需測定氣體的靜壓、動壓和全壓。測氣體全壓的孔口應迎著風道中氣流的方向，測靜壓的孔口應垂直于氣流的方向。

The measurement of gas pressure in the ventilation pipe should be carried out in the pipe section with stable air flow. The static pressure, dynamic pressure and total pressure of the gas should be measured in the test. The orifice for measuring the total pressure of the gas should face the direction of the air flow in the air duct, and the orifice for measuring the static pressure should be perpendicular to the direction of the air flow.

用U形壓力計測全壓和靜壓時，另一端應與大氣相通(用傾斜微壓計在正壓管段測壓時，管的一端應與大氣相通，在負壓管段測壓時，容器開口端應與大氣相通)。因此壓力計上讀出的壓力，實際上是風道內(nèi)氣體壓力與大氣壓力之間的壓差(即氣體相對壓力)。大氣壓力一般用大氣壓力表測定。由于全壓等于動壓與靜壓的代數(shù)和，可只測其中兩個值，另一值通過計算求得。

When U-shaped manometer is used to measure the total pressure and static pressure, the other end should be connected with the atmosphere (when inclining micro manometer is used to measure the pressure in positive pressure pipe section, one end of the pipe should be connected with the atmosphere; when measuring the pressure in negative pressure pipe section, the open end of the container should be connected with the atmosphere). Therefore, the pressure read on the pressure gauge is actually the pressure difference between the gas pressure in the air duct and the atmospheric pressure (i.e. the relative gas pressure). Atmospheric pressure is generally measured with an atmospheric pressure gauge. Since the total pressure is equal to the algebraic sum of dynamic pressure and static pressure, only two values can be measured, and the other value can be obtained by calculation.

測定儀器

Measuring instrument

氣體壓力(靜壓、動壓和全壓)的測量通常是用插入風道中的測壓管將壓力信號取出，在與之連接的壓力計上讀出，常用的儀器有畢托管和壓力計。

Gas pressure (static pressure, dynamic pressure and total pressure) is usually measured by taking out the pressure signal from the pressure measuring tube inserted into the air duct and reading it on the pressure gauge connected with it. The commonly used instruments are pitot tube and pressure gauge.

1 畢托管

1. Trusteeship

(1)標準畢托管

(1) Standard pitot

它是一個彎成90°的雙層同心圓管，其開口端同內(nèi)管相通，用來測定全壓;在靠近管頭的外壁上開有一圈小孔，用來測定靜壓，按標準尺寸加工的畢托管校正系數(shù)近似等于1。標準畢托管測孔很小，通風管道內(nèi)易被粉塵堵塞，因此這種畢托管只適用于比較清潔的管道中測定。

It is a double-layer concentric tube bent into 90 ° and its open end is connected with the inner tube to measure the total pressure; a circle of small holes are opened on the outer wall near the tube head to measure the static pressure, and the pitot tube correction coefficient processed according to the standard size is approximately equal to 1. The measuring hole of standard pitot tube is very small, and the ventilation pipe is easy to be blocked by dust, so this kind of pitot tube is only suitable for measuring in relatively clean pipe.

(2)S型畢托管

(2) S-type pitot tube

它是由兩根相同的金屬管并聯(lián)組成，測量時有方向相反的兩個開口，測定時，面向氣流的開口測得的相當于全壓，背向氣流的開口測得的相當于靜壓。由于測頭對氣流的影響，測得的壓力與實際值有較大誤差，特別是靜壓。因此，S型畢托管在使用前須用標準畢托管進行校正，S型畢托管的動壓校正系數(shù)一般在0.82～0.85之間。S型畢托管測孔較大，通風管道內(nèi)不易被粉塵堵塞，這種畢托管在含塵污染源監(jiān)測中得到廣泛應用。

It is composed of two identical metal tubes in parallel. When measuring, there are two openings in opposite directions. When measuring, the opening facing the air flow is equivalent to the total pressure, and the opening facing the air flow is equivalent to the static pressure. Due to the influence of the probe on the air flow, there is a big error between the measured pressure and the actual value, especially the static pressure. Therefore, S-type pitot tube must be calibrated with standard pitot tube before use, and the dynamic pressure correction coefficient of S-type pitot tube is generally between 0.82 and 0.85. The S-type pitot tube has a large measuring hole and is not easy to be blocked by dust in the ventilation pipe. This kind of pitot tube is widely used in the monitoring of dust pollution sources.

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