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

D−FL 100 Seite 4010.1. Explanation of the calculation sheet D-FL 100Page 1First entry box: „Parameters of the gas channel“In this box the main data of the application is requested. In the first three lines only oneparameter has to be known: either the standard flow [Nm³/h] or the flow under workingconditions [m³/h] or the velocity [m/s].The inner diameter D and the flange length are used for the construction of the differentialpressure bar. The parameter n states the number of ring zones. In the flow probe 2*nmeasuring points are used. The probe number indicates the type of flow probe: Type 1 is usedfor a duct up to 2 m diameter, flow probe 2 is used for diameters between 2 and 4 m and flowprobe 3 is used for diameters between 4 and 8 m. If the dust-concentration is higher than 30mg/Nm³ flow probe 1 is not used. In that case flow probe 2 replaces the type 1.The parameters temperature t, absolute pressure P (static pressure inside the stack), thestandard density ρ n are used to calculate the range of the differential pressure transmitter.Second box: „Results of calculation“In this box the correspondent values for the standard flow, the flow under working conditionsand the velocity are calculated. Additionally the density under working conditions and thedifferential pressure are calculated.Third box: „The following transmitters are recommended“The span of the differential pressure transmitter normally is programmed a little bit greater thanthe calculated differential pressure from the data of the application (standard dP / 0.81; this isequal to 90% of the flow range). The advantage is that the transmitter has not to berecalibrated if the flow is a little bit greater than the data given from the application.The span of the absolute pressure transmitter is by default 900-1100 hPa.The span of the temperature measurement is based on the data given from the customer.Fourth box: „Calculation formula (standard flow)“This formula is based on the equation 5 (V n ) in the manual:VThis can be rearanged like:Vn2ΔP T + 273,15 Pn= A· k · ··ρ T+27315 , PΠ 273.15 3600 · 100= · 2 · ·4 1013 1000n 2n2D · k P· ·ρ T + 273,15nn·ΔPwhereby: T n 0°C D inner diameterP n 1013 hPa ρn standard density at 0°C3600 seconds per hour 100 100Pa per mbar or hPa1000 mm per mGmbH