Applying LDV to Air and Water Flow Measurements: Research Activities & Accreditation. Matthew A. Rasmussen, Danish Technological Institute

Transcription

1 Applying LDV to Air and Water Flow Measurements: Research Activities & Accreditation Matthew A. Rasmussen, Danish Technological Institute Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 1

2 LDV: Areas of Application Water Flow: Lab & On-Site Accreditation Air Velocity: Laboratory Accreditation Water Flow: Internal/External Assignments Air Velocity: Internal/External Assignments Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 2

3 What is LDV? Laser-Doppler Velocimetry/Anemometry (LDV/LDA) measures the velocity of particles in a liquid or gas flow. 2 laser beams emitted from a probe intersect each other and create a interference zone. When a particle moves through this interference pattern, both beams are scattered. The reflected beams are detected in the photomultiplier in the probe The frequency difference between the 2 scattered beams (the Doppler frequency) is directly proportional with the velocity component of the particle perpendicular to the dissecting line of the incoming beams. By measuring over several diameters of a pipe, one can produce a 3D flow profile, which in turn can determine the volume flow. Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 3

4 EFP Project ( ): DH flow measurement & calibration with LDV Goal To develop - with the help of LDV - a robust, accurate method for on-site calibration of district heating meters, as well as investigation & optimisation of flow conditions in installations with either water or gas flow Manufacturer: Manufacturer: Manufacturer: Kamstrup A/S Dantec Dynamics A/S Danfoss A/S Project leader: Danish Technological Institute Research Institute: DTU District Heating/Supply Companies: Århus Municipal Works Esbjerg Municipal Works Copenhagen Energy Metropolitan Copenhagen Transmission Company, etc. Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 4

5 Construction of measurement pipes Measurement pipes for laboratory use Measurement pipes for field use Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 5

6 Calculating volume flow from 3D flow profiles Constant Area Model: 2 i 1 x D i 1 1 i 1, 2,3,... n 2 2 n 1 1 k Umean u u u Z k0 n m n m 0 ij m n j 1 i 1 j n n ln ln n n n 2 n Logarithmic fitting of measured velocities at pipe edges: u x A B ln x D Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 6

7 Calculating volume flow: uncertainty budget Uncertainty contribution Std. uncertainty [%] Calibration of LDV system, incl. velocity distr. over measurement volume 0.03 Drift of LDV system 0.03 Refraction index of window & medium 0.06 Velocity variation between particles and fluid 0.03 Geometrical positioning of measurement points 0.32 Applying the CA model to the 3D profile, incl. short-term fluctuation 0.23 Cross-sectional area 0.17 Long-term fluctuation in the flow 0.04 Combined standard uncertainty 0.44 Expanded uncertainty [k = 2] 0.90 Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 7

8 Verification of uncertainty budget: lab measurements Verification of measurement method - both in the lab & in the field Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 8

9 LDV measurements in the lab Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 9

10 Accredited DH meter calibration #1: L90 (Refuse Incineration Plant, Esbjerg) Pipe dimension: 500mm Calibration result: Relative correction of -0.55% 1.3% at 1,300 m 3 /h Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 10

11 Accredited DH meter calibration #2: Esbjergværket (Combined Heat & Power Plant, Esbjerg) Pipe dimension: 1000mm Calibration results: Relative correction of +0.40% at 400 m 3 /h Relative correction of +0.85% at 1,500 m 3 /h Relative correction of +0.02% at 2,900 m 3 /h Relative correction of +0.83% at 4,700 m 3 /h Expanded, relative uncertainty [k = 2]: 0.90% Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 11

12 Internal assignment #1: Energy optimisation of a freezing unit By measuring (LDV) the air flow & thereafter simulating the process (CFD), we can pinpoint the structural error in the installation that gives rise to the deformity in the flow profile, which reduces the energy efficiency of the refrigeration unit. Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 12

13 Internal assignment #2: Flow analysis of a ice-resistant surface High-pressurized gas is sprayed onto a surface to prevent condensation of ice. LDV has been used to investigate the velocity profile of the gas on the surface and around the mouth of the nozzle for varying flow settings. Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 13

14 Internal assignment #2: Flow analysis of a ice-resistant surface Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 14

15 Implementing LDV as primary reference in Anemometry Laboratory The Anemometry Laboratory contains 2 calibration set-ups: A towing rig for velocities from 0.05 m/s to 0.7 m/s & a wind tunnel for velocities from 0.3 m/s to 30 m/s The working standards in the wind tunnel are a vane anemometer [0.3 m/s m/s] and a Pitot tube with a micromanometer [2 m/s - 30 m/s] Traceability for the vane anemometer has been achieved with a Flowmaster thermoanemometer as Transfer Standard The micromanometer has been calibrated to a traceable standard, but the 3 reference Pitot tubes themselves have simply been compared with each other on an annual basis to determine aberrant drift... We have now achieved an acceptable & reliable traceability for these working standards by implementing LDV as the Primary Reference of the laboratory. The LDV equipment is itself calibrated to a traceable flywheel standard Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 15

16 LDV as primary reference: Gradient measurements Gradient measurements were performed with LDV at velocities of: [m/s] The uncertainty contribution from the velocity gradients were measured to be: v 15: u gradient = 0,030 m/s v > 15: u gradient = 0,075 m/s These measurements are currently being repeated under more beneficial conditions... Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 16

17 LDV as primary reference: Calibration of working standards The Vane anemometer has been calibrated with LDV as reference at the velocities: [m/s]. Calibration regression: v true = v Vane The Pitot tube (with micromanometer) has been calibrated with LDV as reference at the velocities: [m/s]. Calibration regression: v true = v Pitot Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 17

18 LDV as primary reference: BMC s Velocity range [m/s] BMC - lower limit [m/s] BMC - upper limit [m/s] Traceability Working standard: Vane Anemometer Primary reference: LDV Working standard: Pitot tube Primary reference: LDV Working standard: LDV Primary reference: Flywheel Euramet Flow Meeting Danish Technological Institute, Taastrup th March 2009 Slide nr. 18