11. TRADITIONAL MEASUREMENT OF VOLUME FLOW RATE Volume flow rate deduced from velocity measurement data Application example

Transcription

1 11. TRADITIONAL MEASUREMENT OF VOLUME FLOW RATE Volume flow rate deduced from velocty measurement data Applcaton example Prncple and layouts = ' ' A V da v q = A da v = A da v A A n A v = 1 = = n A v 1 = = n v n A n 1 1 = v A

2 DISCRETISATION: For rectangular cross-sectons: k x k Log-ln method ISO

3 v = n = 1 n k = 1 v k weghtng

4 For crcular cross-sectons: 10-pont method ( r ) v = vmax 1 n r R s /D = 0.06; 0.08; 0.146; 0.6; 0.34; 0.658; 0.774; 0.854; 0.918; Accurate ntegraton: for nd order parabolod profle only!

5 Log-ln method ISO partal areas ( y) = A lg y + B y C v + s /D = 0.03; 0.135; 0.31; 0,679; 0.865; 0.968

6 General notes The nose of the probe s to be adjusted parallel to the wall of the duct p _dyn_ref Check of steadness ρ v ref 0 = p dyn _ ref _ 0 v ref _ = p ρ dyn _ ref _ v = ρ p dyn _ Correcton: v corr = v v v ref 0 = ref v p p dyn _ ref _ 0 dyn _ ref _ Obtanment of densty

7 Advantages and dsadvantages Quck scannng:

8 STANDARDS: the recent one, beng n effect, s to be used! Example: ISO 5801:007(E): Industral fans Performance testng usng standardzed arways

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12 Calbraton of an AMCA type probe

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15 K[-] 1,0 1, y = 0,9614x + 0,4445 R² = 0,9997 0,80 1 0,60 0,40 0,0 0, v[m/s] v Prandtl [m/s] v LDA [m/s] Velocty magntude wthn +/- 1 % at hgher veloctes; For ths uncertanty: drectonal nsenstvty wthn +/- 5 deg

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17 11.. Volume flow rate measurements usng contracton elements Applcaton example Prncple and layouts Inlet orfce plate (nlet orfce meter)

18 Assumpton of deal flud: nvscd, ncompressble flow p q 0 v p + ρ ρ ρ = v = ( p0 p) = pm = d π d π v = 4 4 ρ V p m Realty: vscous, compressble flow A/ Effect of vscosty flow coeffcent α dependence on d/d_n, Re for the nlet orfce meter: α = 0.6 B/ Effect of compressblty expanson coeffcent ε dependence on d/d_n, p, p_n, κ for the nlet orfce meter: ε = 1 q d π = α ε 4 ρ V p m

19 Through-flow orfce plate (through-flow orfce meter) Standard n effect: ISO 5167 / 003

20 Standard n effect: Measurement of flud flow by means of pressure dfferental devces nserted n crcular cross-sectons runnng full ISO 5167 (003)

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22 Geometry α, ε Installaton Examples Accuracy Examples Problems q d π = α ε 4 ρ V p m

23 Ventur meter ISO 5167

24 Inlet cone ISO (E) Re = 4q V πρdν 5 5 ( αε ) = ± 0.00 f 10 < Re < ( αε ) = ± f Re > 3 10

25 11.3. Other types of tradtonal flowmeters Example: Elbow meter

26 11.4. Comparson between volume flow rate measurement deduced from velocty data (VEL) and usng contracton elements (CON) ASPECT CON VEL 1/ Intrusveness Introduces consderable losses the operatng state may be modfed to be ncluded already n the system desgn state / Followng temporal changes n the operatonal state + Follows unsteady flow rate contnuously 3/ Requrements Strct (manufacturng, nstallaton, system s to be stopped ) + Neglgble ntrusveness (wall bores) Does not follow (surface ntegraton) ( correcton..?) + Moderate (no requrements, only recommendatons, system may run contnuously )

27 4/ Expenses Hgh (manufacturng, nstallaton, operaton: losses to be covered) 5/ Accuracy + Hgh (lmted uncertanty, guaranteed by the standard) Legally defensble! Moderate + Moderate (lmts of uncertanty are not guaranteed) Legally assalable! CON: hgh-precson, contnuous, legally defensble measurements (e.g. accountng, process control, etc.) VEL: occasonal (case study) measurements, bref estmaton (e.g. fault dagnostcs)