Pressure measurements in air flows using a micromanometer and Pitot (Prandtl) tubes

Abstract

Until recently, the micromanometer and Pitot tube were used only by a few, relatively few research institutes dealing with ventilation issues, but now these instruments are finding increasing application in mines and pits of the Soviet Union for solving various practical problems, such as: identifying ventilation "bottlenecks" by measuring the static pressure drop along a section of a working where a large pressure loss occurs; determining the total and static head of mine fans; determining friction coefficients or local resistances of particular mine workings of interest to the mine. The author has set himself the task, in a brief article, of providing a sufficiently detailed analysis of the operation of the micromanometer in conjunction with the Pitot tube for various cases encountered in practice. In conclusion, the consequences of measuring total vacuum instead of static vacuum when testing fans should be pointed out. When designing mine ventilation, the fan delivery and the (static) depression of the mine are determined. Then a fan type is selected based on individual fan characteristics. If the static head is measured incorrectly during fan testing, its characteristic will show an increased static head by the amount of the velocity head at the Pitot tube location, and instead of the required fan with capacity Q at static head h, we will select a fan with capacity Q at static head h – a, where a is the velocity head, which can reach 15–20 mm. Consequently, the fan we select will give a delivery at a lower depression.

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