Flow Rate Measurements Using Obstruction Meters. Experiment No. 5

Transcription

1 MEP 365 Thermal Measuremets Flw Rate Measuremets Usig Obstructi Meters Experimet N. 5 Name Cmputer N Date f the experimet Date f submissi April 0

2 . Itrducti Obstructi meters are devices with reduced flw area whe istalled i a pipe flw. This creates pressure drp acrss the meter. Usig the basic mass cservati ad Berulli equatis e ca calculate the flw thrugh the pipe. Amg the cmm bstructi meters are: ) Orifice ) Nzzle 3) Veture tube Figure shws these three meters. Applyig the mass cservati ad Berulli equati betwee tw sectis e upstream ad the ther is just dw stream f the meter. A V A V p V p + = + ρ ρ Frm these tw equatis e ca get the vlume flw rate V & V = () () ( p p) V & = V A = A A / ρ A (3) But i drivig the abve equati, the lss betwee secti ad secti is eglected, ad usually the kw area are upstream flw area i.e. A ad the thrat area A. It is cmm t defie a discharge cefficiet C fr bstructi meter as fllws S that the actual flw rate is give by Q Q actual C = (4) ideal Q actual ( p p) = CEA (5) ρ where E is called the apprach factr, ad defied as ad A is the miimum area f the bstructi device d miimum diameter at the thrat d the up stream diameter f the pipe Smetime a flw cefficiet K is defied as the prduct f C ad E, i.e. E = (6) 4 β d d β = (7) K =CE (8)

3 Figure Obstructi meters. Apparatus The equipmet used fr this experimet is shw i Fig., frm GUNT Cmpay. The apparatus csists basically f a fa that sucks air thrugh a alg pipe. The rifice r the zzle is lcated at psiti 8 (see the figure). There is als a diaphragm flw meter called IRIS diaphragm which is as shw as item 7 i the figure. The pressure differece acrss ay f the flw meters ca be measured usig the multiple water mameters (item 9 i the figure) usig flexible hses. The mai pipe f the apparatus is als fitted with a Pitt tube (see item i figure ). the air flw directi is frm right t left. Figure () Apparatus 3

4 3. Prcedure -Ispect thrughly the equipmet fr this experimet. Ispect the fa, the IRIS diaphragm, the water mameters ad the hses used t cect pressure tabs t the mameter. -Lk it the far right ed f the pipe ad see the IRIS diaphragm flw meter. Yu ca push the IRIS valve the tp f the pipe ad twist it i rder t see hw the diaphragm peig chages as the umber the tp f the valve chages frm t 6. Let the techicia helps yu t see hw t ctrl the diaphragm peig. 3-Make sure that the istalled bstructi meter is the Nzzle. Yu ca als ispect a zzle similar t the e istalled the equipmet. Ask the lab. techicia t shw yu bth the zzle ad the rifice. 4-With the help f the Lab. techicia set the ctrl valve f the diaphragm peig t, ad tur the fa. Try t t cme very clse t the pipe ilet where the air is sucked by the fa. 5-Recrd the mameter acrss the zzle ad acrss the IRIS diaphragm meter i Table () 6-Repeat fr at least six readigs fr differet IRIS diaphragm peigs. 4. Calculatis -Calculate the pressure drp ad the vlume flw rate thrugh the IRIS diaphragm usig Pir = ρ wg( h h ) /000 (9) where ρ w is water desity, ad h ad h are the mameter readig acrss the IRIS diagram flw meter i mm The flw rate thrugh the IRIS ca be fud ce the pressure drp acrss the meter is fud usig the equati V& 3 ir = 000*0 k P ir (0) k cefficiet fr IRIS is give i Table as a fucti f IRIS peig. The abve equati gives the vlume flw rate i m 3 /s. - Calculate the pressure drp ad vlume flw rate thrugh the zzle usig P = ρ wg( h 3 h4 ) /000 () where h 3 ad h 4 are the mameter readig acrss the zzle. Agai h 3 ad h 4 are i mm. V & = K A p / ρ = CEA p / ρ () Accrdig t the equipmet maufacturer the value f K is.066, ad the miimum diameter d is 50 mm, while the upstream pipe iside diameter d is 84 mm. ρ a is the air desity. 3- Calculate the percetage differece betwee V & th ad V &. 4-O excel sheet plt the variati f V & th ad V & with IRIS diaphragm peig. 5-Assume that V & ir is mre accurate tha V & calculate the apprpriate value f K fr the zzle fr all abve cases ad draw the variati f K with Reylds umber Re d. Cmpare with text bk r stadard values. Red = ρ Vd / µ = 4m& / µπd a a 4

5 Table Summary f the results IRIS Opeig h h h ir [m] IRIS P ir [Pa] V & ir [m 3 /s] h 3 h 4 h [m] Nzzle P [Pa] V & [m 3 /s] 5

6 Table IRIS flw cefficiet k as a fucti f the diaphragm peig 5. Symbls Symbl Meaig A Crss secti area [m ] C Discharge Cefficiet E Apprach factr h Mameter readig k IRIS diaphragm flw cefficiet K Nzzle flw cefficiet p Pressure [Pa] Re d Reylds umber based d V Velcity [m/s] V & Vlume flw rate [m 3 /s] IRIS k Opeig β Diameter rati d /d ρ w Water desity [kg/m 3 ] ρ a Air desity [kg/m 3 ] Subscript ir IRIS diaphragm flw meter zzle flw meter thrat 6. Additial Data abut the apparatus d pipe iside diameter 84 mm d zzle diameter 50 mm K flw cefficiet f the zzle.066 6