Flow Measurement Lab Report.docx

August 8, 2018 | Author: interestingese | Category: Flow Measurement, Pressure Measurement, Magnetic Field, Accuracy And Precision, Density
Share Embed Donate


Short Description

Download Flow Measurement Lab Report.docx...

Description

Comparison of Diff Different erent Flow Measurement Devices CHEG 2810 - Experiment 1

Danielle Valdivia, Travis Garlock, and Alex Maldonado October 22th, 2015

AB!"AC!

!he purpose of this e#periment was to calculate volumetric flow rates usin$ various flow measurement %evices an% compare their accurac& an% precision' !he three flow measurement %evices were( rotameter, orifice plate, an% ma$netic flow meter' As it turns out the most accurate an% precise flow meter was the ma$netic flow meter' !he ma$netic flow meter ha% an avera$e of  2'1) error while the orifice plate an% rotameter ha% a 1*'+) an% 2'*) error respectivel&' !he ma$netic flow meter an% rotameter were both accurate an% precise, but the orifice plate was neither' !his error was more than liel& to be cause% b& inefficienc& in the water collecte% from the output an% for the orifice plate the constant -umpin$ of pressures %i% not allow accurate rea%in$s' !hese results show that when precision is essential the rotameter or ma$netic flow meter shoul% be use%' Of these two when the flowrate nee%s to be imme%iatel& nown an% eas& to see chan$es the rotameter is the best choice'./!"ODC!.O/ an% BAC"O/D ./FO"MA!.O/ !he rotameter is a versatile process control %evice that can %emonstrate chan$es in flow of various materials3 in both $as an% li4ui% phases' !he %esi$n of the rotameter is %esi$ne% to e#ploit the opposition between the %ownwar% force of $ravit& an% the opposin$ force of the flowin$ flui%' !his force of the flowin$ flui% mainl& comes from the pressure %ifference the  bottom of the rotameter an% the si%es of the rotameter Basics of "otameters, 20026' 7hen the flui% approaches the bottom of the bob, the velocit& increases %ue to the contraction of the -et streams' 7hen there is a volumetric flow passin$ throu$h the meter, the velocit& of the -et is $iven b& the e4uation

u=

q C c a x

where 4 is the flow rate, Cc is the ratio narrowest part of the -et to the area of the area of the tube' .f we substitute Bernoulli8s law we $et  P1− P2=

 ρ 2

( ) q C c a x

Example

of the bob, an% a# as this in to

2

 which %emonstrates that the pressure

%ifference

cause% b& the -et stream contraction causes the buo&ant force' 7hen the flow rate is increase% an% the flui% an% rotameter sta& the same6 the pressure %ifference becomes $reater thus increasin$ the buo&ant force Di-stelber$en, 1+*96' 7hen the buo&ant force is the same as the $ravitational force of the bob ne$lectin$ the $ravitational force of the flui%6 the Rotameter in lab  bob reaches e4uilibrium' !his e4uilibrium stabili:es the hei$ht of the bob relative to the tube an% the velocit& of the flui% can be calculate% usin$ the e4uation u=



2 g V b

7here,

C Ab

(



 ρb− ρ f   ρf 

)

• • • • • • •

u; ; volumetric flow rate Cm ; variable that contains constants from previous e4uation

!hese e4uations an% theor& show the useful an% versatile the rotameter is to measure flow rate' "otameters are still ver& popular amon$ in%ustrial applications because of cost effectiveness' !he& are relativel& ine#pensive an% provi%e a simple wa& to control flow for a wi%e variet& of substances' 7ith more comple# flowmeters the accurac& an% precision is $reatl& increase% but comes with a heft& price ta$' Overall rotameters are viable options when simplicit& an% cost effectiveness are priorities, an% when precision is top priorit& %ifferent flow meters are better options' Another wi%el& use% flow meter is calle% the orifice meter an% measures the flow of a li4ui% similar to that of a venturi meter, b& restriction' !he fi#e%?area flow is %ue to a finel& machine% concentric hole within a plate mounte%  perpen%icularl& between two flan$es' @ressure taps are place% before an% after the machine% plate an% connecte% to a manometer an%or a %ifferential pressure transmitter' !he cross sectional area of the pipe %iameter is re%uce%, increasin$ the velocit& hea% while %ecreasin$ the pressure hea% McCabe, 226'  !his re%uction in pressure hea% is what the connecte% %evice measures an% is correlate% to the li4ui% flow rate'

As the li4ui% approaches the orifice plate, a vena contracta forms' !his is where the flui% stream separates itself from the %ownstream si%e of the orifice plate an% forms a -et in the %ownstream li4ui% an% where the li4ui% is as its minimum cross section' !his is a $oo% location for the tap to  be place% so that the meter ma& measure the %ownstream velocit&' !his st&le of tap is calle% the vena contracta tap an% will have a static hole one?half to two pipe %iameters from the orifice  plate an% the other locate% at the vena contracta @err&, ?96' !hese t&pe of taps $ive the lar$est %ifferential hea% for a $iven flow rate' !he flow rate e4uation is $iven below' Q=

C d  A 2

√ ( ) 1−

 A 2  A1

2



2

( p

1

 p2 )



 ρ

7here • • • • •

p1?p26 ; the pressure %rop = ; the %ensit& A1 ; the pipe cross?sectional area A2 ; the orifice cross?sectional area C% ; the %ischar$e coefficient

!he %ischar$e coefficient chan$es with "e&nol%8s /umber at the orifice, base% on the orifice %iameter an% velocit& @err&, 10?1*6' !his number will increase with e%$e?roun%ness of the machine% hole in the plate' /ear the orifice plate on the %ownstream si%e of li4ui%, e%%ies form in the li4ui% %ue to lar$e friction losses' !hese friction losses account for the poor pressure recover& of an orifice meter an% its lar$est %isa%vanta$e' @ower losses nee% to be supplemente% with pumpin$ e4uipment' !he ma$netic flow meter is a more a%vance% %evice use% to measure the flow rate of a flui%' 7hen usin$ this %evice, a ma$netic fiel% is sprea% throu$hout the measurin$ tube3 the ions flowin$ within the flui% create a potential %ifference to be measure% b& the flow meter' !his potential %ifference is proportional to the flow velocit& of the flui%' .n or%er to use a ma$netic flow meter to measure a flow?rate, the flui% must be con%uctin$, an% the pipe must be insulatin$' Ma$netic flow meters are most useful in that the& are a non?contact, non?movin$ flow meter, which is ver& useful when measurin$ the flow rate of a %irt& li4ui% or wastewater material that is water?base%'  Theoretical Magnetic Flow Meter (Cadillac Meters, 2013)

!he ma$netic flow meter is base% on the principle of Fara%a&8s aw' !his states that the volta$e across a con%uctor as it moves perpen%icular to the ma$netic fiel% lines is proportional to the velocit& of that con%uctor Ma$netic Flow Meters, 20156' Fara%a&8s aw is represente% b& the e4uation(

 E=V ∗B∗ D

7here, • • • •

E ; volta$e $enerate% in a con%uctor, < ; velocit& of that con%uctor, B ; ma$netic fiel% stren$th, D ; len$th of the con%uctor bein$ measure%'

Each ma$netic flow meter is fitte% to a ma#imum flow that can be measure% b& that  particular flow meter' !he in%uce% potential an% the measure% flow are compare% to the ma#imum permitte% potential an% ma#imum measurable flow, respectivel& prin$stea%, 20156' !he %ispla&e% value on the ma$netic flow meter can either be the %irect flow measurement, or a percenta$e of the ma#imum measurable flow of the flow meter' Ma$netic flow meters are one of the most common t&pes of flow meters use% in in%ustr&' !he& are use% for their relative ease an% their nown accurac&' Ma$netic flow meters are much less cost effective than other flow meters but are much more e#act in their measurement' Ma$netic flow meters also come with the caveat that onl& con%uctin$ flui%s ma& be measure%, which proves them to be ina%e4uate in man& in%ustrial situations' enerall&, ma$netic flow meters are use% when precision is necessar&, an% when con%uctive flui%s are involve%'

ME!OD@"O!OCO Rotameter

7hen there is not a flow throu$h the rotameter, the bob is at the lowest point in the tube' Mar this point on a piece of tape on the si%e of the rotameter' !his will be the initial point when tain$ hei$ht measurements' Open the valves an% allowin$ a small flow throu$h the pipes an% observe the small increase in hei$ht of the bob' Allow the s&stem to fin% e4uilibrium from turbulent flow to more of a laminar flow' !ae a ruler an% measure from the initial point to the point where the  bob is when water is flowin$ throu$h' 7hile tain$ the bob hei$ht measurement, for five secon%s fill a bucet with the output water' !hen wei$h the bucet an% recor% the mass of the water' Orifice Plate

enerall&, a manometer will measure the pressure %rop b& correlatin$ it to the hei$ht of flui% in the two le$s of the manometer' owever, the %i$ital manometer use% in this lab will correlate the %ifference between the mechanical pressures on two trans%ucers locate% at the taps' !his will $ive a similar rea%in$ to the %ifferential pressure trans%ucer which will %ispla& as mA' !he lower the flow rate, the lower the mechanical pressure an% therefore, the lower the rea%in$ on  both meters' 7hen the e#periment is starte%, there is no flow throu$h the orifice plate an% both meters will rou$hl& rea% close to :ero' As the flow rate increases throu$h the pipin$ at each step interval, so too %oes the rea%in$ on each meter' Each time the flow rate is increase%, the s&stem is allowe% to e4uilibrate before flow measurements are taen with a bucet an% a stop watch' !he amount of water in the $iven time is then measure% for mass an% recor%e%, resultin$ in a flow rate versus pressure %rop $raph' Magnetic Flow Meter

First, ensure that the ma$netic flow meter rea%s :ero when there is no flow throu$h the pipe' !hen open the appropriate valves allowin$ a small flow throu$h the pipe that the flow meter is attache% to' Also mae sure that after the water passes throu$h the flow meter, the water continues throu$h the pipes an% into the output tan without flowin$ throu$h the other two flow meters' Once the s&stem has reache% e4uilibrium, recor% the percenta$e %ispla&e% on the flow meter3 this percenta$e represents a percent of the ma#imum measurable flow of the flow meter' As the measurement is recor%e%, for five secon%s fill a bucet with output water from %irectl& from the pipe' !hen wei$h the bucet an% recor% the mass of the water collecte%' Be sure to tare the bucet before each water sample is collecte%' .ncrease the flow of the s&stem, allow it to reach e4uilibrium, an% perform another sample collection an% measurement' Do this until there are between five an% ten %ata points'

"E! Avera$e Mass of Output 7ater  $6

ei$ht of  Bob cm6

0'2 1'5* 2'09 2'59 G'12 G'* 9'92

1'G G'2 9'1 5'G *'9 ' '+

Actual
View more...

Comments

Copyright ©2017 KUPDF Inc.
SUPPORT KUPDF