Measuring Gas Velocity with the D-FL 100 Differential Pressure Bar

D−FL 100 Seite 11. ApplicationOne of the most popular and reliable methods of measuring the differential pressure in a duct or stack isby means of a mechanical device such as a venturi or a differential pressure bar.The differential pressure bar is useful in measuring the velocity of exhaust gases that are not saturatedwith steam or water vapors. These gases may be generated by burning fossil fuels; e.g., in currentplants, waste incinerators and cement kilns. The differential pressure bar is designed to measurebetween 0 and 2,000,000 m 3 /h, depending on velocity and on the inner diameter of the duct/stack. Theminumum velocity should be more than 3 m/s.The DURAG D-FL 100 Velocity Measuring System has been suitability tested by TÜV Nord, Test ReportNo 128CU11650 dated 29. March 1996.2. Functional DescriptionThere are several advantages to using a differential pressure bar instead of a venturi to measure thevelocity of a gas. A venturi reduces the pressure, thus causing pressure loss, whereas a differentialpressure bar has only a marginal influence on the gas flow. Because a differential pressure bar hasminimal effect on the gas flow, it can be used in shorter ducts/stacks, where installation of a venturiwould not be as cost-effective. Finally, a differential pressure bar requires less blower force for equalgas velocity, making it less expensive in overall operating costs.The velocity of a gas in a duct/stack is derived from the difference between the total impact pressureand the reference pressure on the differential pressure bar or Pitot tube (Fig. 1). This relationship isexpressed by Bernoulli’s equation:(Eq. 1)ΔPPgesPstatρvdifferential pressuretotal impact pressure (flow side)static (reference) pressuregas densityvelocityGmbH