Axial Flow Fans

Necessary Equations for Fan Design Total Pressure, Air Horse Power, Brake Horse Power, Efficiencies

Total Total Pressure = Static Pressure + Velocity Pressure

TP = SP + VP   Fan outlet velocity

Vo

=

cfm

[ fpm]

 Ao

Velocity Pressure (Dynamic Pressure)

 V    VP =  o ÷  4005 

2

[in WC ]  

Poer out!ut o" t#e "an ($ir %orse Poer)

ahp =

( cfm ) ( TP ) &'5&

[hp ]

ec#anical ""iciency (Total (Total ""iciency)

 ME

= TE  =

ahp bhp

[*]

 #!= motor out!ut = "an in!ut otor ""iciency (lectrical ""iciency)

 EE  =

( 0,-4& ) ( bhp ) kW 

[*]

""iciency o" t#e set

Set Eff , = ME × EE  

[*]

Axial Flow Fans Propeller Fan Pro!eller "an is .esi/ne. to o!erate in t#e ran/e near "ree .elivery to move lar/e air volumes a/ainst lo static !ressure,

T#e motor is usually on t#e inlet si.e ut in s!ecial a!!lications it can e on t#e outlet si.e,

Pro!eller "ans

1ar/esi3e !ro!eller"an #eels run at lo s!ee.s an. t#ere"ore are elt .riven, " t#e motor #orse!oer is lar/e /oo. e""iciency is .esire. an. to accom!lis# t#is t#e "an #eel #as a 20* to 40* #uti! ratio an. air"oil  la.es it# a tist resultin/ in la.e an/les eteen '0 to 50 .e/rees at t#e #u an. eteen 0 to 25 .e/rees at ti!, Small !ro!eller "ans can e uilt it# eit#er .irect .rive or elt .rive, %ere t#e motor #orse!oer is small an. "an e""iciency t#ere"ore is o"  minor im!ortance, Tube axial Fans Tue a6ial "an is a /lori"ie. !ro!eller "an it# a cylin.rical #ousin/ aout one .iameter lon/,

 Tue $6ial "lo "an

T#e u!stream motor #as t#e .isa.vanta/e t#at some turulence ill e  !ro.uce. y t#e motor su!!ort a#ea. o" t#e "an #eel, T#is may a""ect t#e e""iciency an. ill result in some#at increase. noise level, n /eneral a la.e o!eratin/ in turulent air"lo ill not "unction  !ro!erly, Turulence !ast t#e "an #eel t#ere"ore is not too #arm"ul, t  7ust increases t#e resistance o" t#e system an. t#ere"ore t#e static !ressure a/ainst #ic# t#e "an ill o!erate, Turulent a#ea. o" t#e "an #eel is #arm"ul, t not only increases t#e static !ressure re8uire. ut it also results n t#e la.es o!eratin/ in turulent air"lo an. t#ere"ore it# loer e""iciency an. a #i/#er noise level, T#e "an #eel o" tue a6ial "an can e similar to t#at o" a !ro!eller "an, t o"ten #as a me.ium si3e. #u .iameter aout '0* to 50* o" t#e la.e outsi.e .iameter in case o" .irect .rive !re"eraly not too muc# .i""erent "rom t#e motor .iameter "or streamline "lo con.itions, ane!Axial Fan Hub Dia"eter of ane!Axial Fans 9sually eteen 50* to :0* o" #eel .iameter, t is .esi/ne. to o!erate in t#e ran/e o" "airly #i/# static !ressures an. t#is re8uires a lar/e #u .iameter,

 ;000  = ÷  rpm    '022&  d min =  ÷  rpm   d min

SP

[ inch ]

Pa

[ mm ]

Smaller #u .iameter mi/#t result in an ina.e8uate !er"ormance o" t#e inner la.e !ortion i,e, turulence an. !ossile reverse air "lo near t#e #u, T#is is calle. stallin/,

 Vane $6ial "lo "an

T#e SP !ro.uce. y vanea6ial "an (outlet vanes) SP = ( ','4 × 0−; ) ( rpm ) ( z B ) ( CL ) ( l ×W )  < 2

W

 = Va2 +  VB − Vr   ÷  2   

 2π r rpm V B =  ) ÷( 2  

< Vr

<

 2,'' × 05  SP  = ÷  ÷  rpm   r

<

 V = cfm a Aa  

(  D − d  ) π  2

< Aa

=

2

5-&

For /oo. e""iciency t#e static !ressure !ro.uce. s#oul. e t#e same "or  any ra.ius "rom #u to ti!, #$eel Dia"eter of ane!Axial Fans

 cfm   D min = d + & ÷ rpm     Q&  2  D min = d + ;  ÷ rpm    2

[ inch ] [ mm ]

" t#e customer can not acce!t a lar/e #eel .iameter a tosta/e a6ial "lo "an may solve t#e !rolem,

ane!Axial Fans of arious Designs

, i.e la.e ti!s result in #i/# e""iciency an. 8uiet o!eration ut t#ey cause in consi.erale motor overloa. at t#e !oint o" no .elivery, 2, e.ium ti!s re.uce t#e ma6imum static !ressure an. t#e no .elivery overloa., ', >arro ti!s result in a nonoverloa.in/, ""iciency is sli/#tly loer an. t#e noise level is sli/#tly #i/#er, %ui&e anes T#e cross section o" t#e /ui.e vanes can e eit#er an air"oil s#a!e or a sin/le line o" !ro!er curvature, $ir"oil vanes are ma.e as aluminium castin/s or sometimes o" #ollosteel construction, T#e sin/les#eet steel construction is use. more commonly an. ill result in satis"actory  !er"ormance so e6tra e6!ense o" t#e air"oil construction is sel.om  7usti"ie.,

T#e an/le o" lea.in/ (outlet vanes) or trailin/ (inlet vanes)

tan δ  =

V r  V a

Nu"ber of Bla&es ' B T#e !ressure is !ro!ortional to t#e !ro.uct o" ( z  Bl ),

Turulence an. noise mostly !ro.uce. y t#e e./es (ot# lea.in/ an. trailin/) an. not y t#e sur"ace, T#ere"ore "eer an. i.er la.es ill result in a etter "an e""iciency an. loer noise level, " t#e numer o" la.es ecomes too small an. t#e la.e i.t# t#ere"ore too lar/e e are "acin/ to con"lictin/ re8uirements? "eer la.es "or   etter e""iciency an. less noise ut more la.es "or less ei/#t etc, $s a com!romise eteen e""iciency an. cost 5 to 2 la.es are /oo.  !ractical solutions,

5 ≤  z  B

≤ 2

$t t#e #u t#e la.es must not overla! "or to reasons? , @verla!!in/ la.es mi/#t c#ocA t#e air"lo 2, !rolem in san. castin/ 9sually overla!!in/ la.es ill e avoi.e. i"

l  ≤

',4d 

 z  B

T#is ill e t#e la.e i.t# at t#e #u, Nu"ber of %ui&e anes '  T#ere are to sim!le rules? , z V  s#oul. e lar/er t#an  z  B  ecause t#e /ui.e vanes s#oul. e close. to eac# ot#er, T#e risA o" c#ocAin/ t#e air"lo .ue to overla!!in/ is remote, 2, T#e numer o"  z V   an.  z  B s#oul. #ave no common .ivisor< ot#erise to la.es oul. !ass to vanes simultaneously increasin/ noise level, Pressure (afety "argin T#e !eaA !ressure o" t#e o!eratin/ ran/e s#oul. e '0 t0 50* #i/#er t#an t#e !ressure re8uire. "or t#e a!!lication, Typical Features of Axial!Flow Fans wit$ Direct Dri)e Type of fan

Propeller fan

Tubeaxial fan

Basin/

Cui.e vanes

ountin/ rin/ or   mountin/ !anel nlet si.e o" !anel  !re"erre. >one

S#ort cylin.rical #ousin/ nsi.e #ousin/ outlet si.e !re"erre. >one

%uti! ratio SP la.e an/le at #u la.e an/le at ti! a6, mec#, e""icen,

040* 0 '050 .e/, 025 .e/, -0*

'050* 0,5 2,5 '050 .e/, 025 .e/, -5*

otor su!!ort

aneaxial fan  (ingle!stage Bylin.rical #ousin/

nsi.e #ousin/ outlet si.e !re"erre. Past "an #eel  !re"erre. 45:0* ; '0&0 .e/, 0'5 .e/, ;0*

aneaxial fan  Two!stage Bylin.rical #ousin/ nsi.e #ousin/  eteen sta/es  >one or   eteen sta/es 50:0* 4: '0&0 .e/, 0'5 .e/, -0*

Application wit$ fluctuating syste"s n some .esi/ns t#e no.elivery #! rises consi.eraly aove t#e ma6imum #! in t#e o!eratin/ ran/e, T#is #a!!ens #enever t#e la.e i.t# at t#e ti! is muc# i.er t#an t#e la.e i.t# at t#e #u an. t#e  la.e an/les are small,

i.e ti! la.es may #ave to e avoi.e. in suc# a!!lications, $n. t#e motor s#oul. e e8ui!!e. it# overloa. !rotection,

Noise *e)el T#e noise level !ro.uce. y ell.esi/ne. a6ial "lo "ans is loer t#an t#at o" centri"u/al "ans o" t#e same ti! s!ee. ut it is more sensitive to t#e e""ect o" turulent air"lo,

Pro.uce. noise can e .ue to? , o!eratin/ in t#e stallin/ ran/e 2, #i/# ti! s!ee. ', lacA o" an inlet ell 4, ostructions in t#e air stream close. to t#e la.es 5, elos close to t#e "an &, viration .ue to !oor alance or .uo to a resonance con.ition -, sin/let#icAness la.es as o!!ose. to air"oil la.es :, inlet /ui.e vanes as o!!ose. to outlet /ui.e vanes ;, many narro la.es as o!!ose. to "eer an. i.er la.es +utlet &iffuser an& outlet tail piece $ .i""user an. tail !iece ill increase t#e "an e""iciency y aout 4* .ue to a sli/#t increase in air volume an. static !ressure, T#is may !ermit a sli/#t la.e an/le re.uction an. conse8uently a sli/#t re.uction in #!, n lar/e units suc# as t#ose use. "or mine ventilation t#is #! re.uction may e consi.erale,

n very lar/e units #ere elt .rive is use. an. t#e motor is locate. outsi.e t#e #ousin/ t#e outlet .i""user an. tail !iece are usually inclu.e.,

@utlet .i""user an. tail !iece

(election of axial!flow fans T#e or.erline eteen tuea6ial an. vanea6ial "ans is 8uite "le6ile,

T#e ran/e "or centri"u/al "ans i.ely overla!s it# t#e ran/e "or to sta/e a6ial "ans an. even it# t#e ran/e "or sin/lesta/e vanea6ial "ans, Bertain air volume an. static !ressure are re8uire. "or certain system,

$s a rule e can otain same air volume an. static !ressure it# a smaller "an at #i/#er s!ee. an. it# a lar/er "an at loer s!ee., T#e a.vanta/es o" usin/ lar/er "ans? , t ill #ave loer !oer consum!tion (#!) an. t#ere"ore a loer  o!eratin/ cost, 2, t ill #ave a loer ti! s!ee. an. t#ere"ore a loer noise level, T#e a.vanta/es o" usin/ smaller "ans? , t ill e more com!act, 2, t ill #ave loer "irst cost, +)erlapping perfor"ance ranges Ee8uirement "or air volume an. static !ressure o"ten .etermine #at ty!e o" "an s#oul. e use. "or a s!eci"ic a!!lication?

SP ≤  2

≤

' 4

inWC  →

SP ≤ ' inWC  →

Pro!eller "an Tue$6ialFan i" "an s#oul. e6#aust "rom a .uct Vane$6ialFan i" "an s#oul. lo into a .uct

high η and SP ≥ ,5 inWC   → Vane$6ialFan re/ar.less o" "an los e6#austs SP ≥ & inWC   → Tosta/e$6ialFan ut e""iciency ill e lo Bentri"u/alFan  !ro.uces etter e""iciency $.vanta/es o" vanea6ial "an over centri"u/al"an? , Creater com!actness 2, 1oer "irst cost ', strai/#tline installation 4, loer soun. level at t#e same ti! s!ee. $.vanta/es o" centri"u/al"an over vanea6ial "an? , >atural a.a!taility to installation re8uirin/ ;0 .e/, turn o" t#e air  stream 2, etter accessiility o" t#e motor com!are. it# .irect.rive vane a6ial "ans ', etter !rotection o" t#e motor a/ainst #ot or contaminate. /ases 4, Creater assurance "or o!eration in t#e e""icient an. 8uite  !er"ormance ran/e !articularly "or systems it# "luctuatin/ "lo resistance

(a"ple &esign calculation for )ane!axial fan  !!, 4,&2 an. Tale 4,: Axial!flow fans &ri)en by t$ree &ifferent "et$o&s T#ere are t#ree met#o.s "or .rivin/ a "an? , .riven y an en/ine 2, .riven y a turine? #ic# are use. in locations o" #a3ar.ous atmos!#ere or #ere electric !oer is not availale, $ ty!ical a!!lication oul. e a marine ventilator use. to e6#aust t#e /as "rom t#e insi.e o" an oil tanAer  ', .riven y reaction to com!resse.air 7ets? t#ey are !articularly ell suite. "or t#e ventilation o" con"ine. s!aces "or t#e removal o"  #a3ar.ous "umes or o" contaminate. air "rom el.in/ an. san.lastin/ o!erations an. "or locations #ere com!resse. air is availale ut electric !oer is not,

T#e .elivery ratio is t#e volume .elivere. .ivi.e. y t#e volume o" t#e com!resse. air consume.