Axial innen engl - TLT Turbo GmbH

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Am Weinberg 68 · D-36251 Bad Hersfeld/Germany Phone: +49.6621.950-0 · Fax: +49.6621.950-100 Application example for axial-flow fans The volume flow measuring system determines the operating volume flow of an axial fan installed in an air-handling installation. The system greatly facilitates the determination of fan volume flow. As a result, the cost and effort required for in-duct measurements on the system side, as often carried out during commissioning, can be significantly reduced. Moreover, adjustments are faster and easier to carry out. The measuring accuracy of the volume-flow measuring system is approx. ± 5%. Description of the measuring system The volume flow measuring system is firmly mounted on the fan to determine the volume flow in its installed condition. The reading is obtained by a simple differential-pressure measurement between the sockets of the pressure measuring lines connected to the measuring system. The calibration curve is prepared individually, taking into account fan-specific parameters. Key influencing variables include fan type, inlet density, rpm and fan design size. Being established individually with reference to the above parameters, the calibration curve is not transferable to other fan types Options Adirect automatic volume flow measurement can be implemented by means of root-extracting differential pressure transducers or suitable electronic evaluation units. The following equation may be used for this purpose: Volume flow calculation: V = k x A x � 2 x d p VOLUME FLOW MEASURING SYSTEM VDE FOR CENTRIFUGAL ROOF FANS AND AXIAL FLOW FANS and sizes. At fan operating speeds deviating from the rated rpm level, major inaccuracies will be obtained, especially when the fan is running at slower speeds. The measuring system consists of an additional casing extension made of sheet steel, pre-installed measuring lines for the pressure measurement, and a sheet aluminium hub body attached to, and rotating with, the fan impeller. The pressure measurement ring line consists of plastic hose as employed in pneumatic applications, as well as brass screw-in adapters. The four measuring points, spaced evenly over the circumference, are connected into a ring line by means of T-fittings. The connection to a pressure measuring instrument is likewise made via a T-fitting. Technical description The calibration curves can be computed for flow medium throughput conditions as habitually employed in ventilation technology, and apply to air only. The measuring system is standardized for AXN series fans in the 315 to 2000 size range. It is recommended to use the volume flow measuring device only at blade angles equal to, or exceeding, 10 degrees so as to to maximize the accuracy of the reading. At blade angles below 10 deg., the magnitude of the differential pressure indication will not suffice for an Calculation of k: Correction factor: k = f (Re, NG, n) Reynolds number: c x Dh Re = x � Hydraulic diameter: Dh = A· 4 � � Rotational Speed: n [rpm] Reference cross section: NG [mm] 022 unambiguous volume flow measurement. The accuracy of the system depends essentially on its installation conditions and on the inlet-side approach flow situation. An irregular or swirl-impaired inlet airflow will reduce the accuracy of the volume flow measuring system. The differential pressure measurement can be carried out with the aid of electronic differential pressure sensors or other standard commercial transducers, whether mechanical or hydrostatic. The measuring range of the differential pressure instrument should be 0 - 2000 Pa, at a resolution of 1 Pa. The measuring tolerance of the instrument employed should be better than ± 2.5 of the measured value. Uses: The system may be used for the following <strong>TLT</strong> axial-flow fans: Series AXN 12/56 AXN 9/56 AXN 6/56 BVAXN 12/56 BVAXN 9/56 BVAXN 6/56 Flow velocity in the annulus area: c [m/s] Kinematic viscosity: � [kg/ms] Inlet density: [kg/m3] � Reference surface area for the volume flow determination: A= [m2 ] = annulus area of the blading d P= Differential pressure [Pa] at the volume flow measuring point
Am Weinberg 68 · D-36251 Bad Hersfeld/Germany Phone: +49.6621.950-0 · Fax: +49.6621.950-100 Rating sheet for a volume flow measuring system Example given for an AXN 12/56/1000 axial-flow fan Nominal size NG 1000 Rotational speed n 1500 rpm Tip speed u2 79 m/s Density 1,2 kg/m3 Dynamic viscosity � 1,80E-05 Pa s Reference cross-section A ring 0,5391 m 2 Reference diameter Dh ref 0,8285 m Rated fan total pressure increase dpt 500 Pa Rated volume flow VA 45000 m3/h Rated flow within measuring range* VA > 32100 m3/h Correction factor at VA k 2,13 Differential pressure under rating conditions dp 71 Pa * At smaller volume flows the differential pressure values are of insufficient magnitude. The accuracy of the volume flow measuring system depends on the pressure gauge employed as well as on the flow approach situation. Under unperturbed incoming flow condition and taking into account the inlet density, the tolerance is approx. 5% of the actual volume flow value. Table of values: VOLUME FLOW MEASURING SYSTEM VME FOR AXIAL-FLOW FANS Input data Calculated data Operating limits � Item Reynolds number Correction coefficient for volume flow measurement Differential pressure Volume flow rate Rec k dpk V (-) (-) (Pa) (m3/h) 1 150 000 undefined range 2 300 000 undefined range 3 450 000 undefined range 4 600 000 10861,97 0 21 364 5 750 000 36,35 0 26 705 6 900 000 7,06 3 32 046 7 1 050 000 3,36 20 37 386 8 1 200 000 2,37 52 42 727 9 1 350 000 2,00 92 48 068 10 1 500 000 1,84 134 53 409 11 1 650 000 1,75 179 58 750 12 1 800 000 1,70 226 64 091 13 1 950 000 1,67 274 69 432 14 2 100 000 1,65 326 74 773 15 2 250 000 1,64 380 80 114 16 2 400 000 1,63 437 85 455 17 2 550 000 1,62 498 90 796 18 2 700 000 1,62 561 96 137 19 2 850 000 1,62 628 101 477 20 3 000 000 1,61 698 106 818 21 3 150 000 1,61 772 112 159 023
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