ria

hi

Volute casing

conuded and, raditirs s

2011 Elsevier Ltd. All rights reserved.

rbomae is reqw, forolute cly use

to restrict the ow against the given head without incurring signif-icant losses.

The total ow of the impeller discharge passes through the vo-lute throat area and only a part of the impeller capacity passesthrough any other section. There were ve geometrical parametersin volute design. The most important parameter was the volutethroat area [6]. If the volute throat area is too small in comparison

The design objective is to achieve a uniform ow at volute inlet.This is usually attained at the design ow rate only; at off designconditions the volute is either too small or too large and a pressuredistortion develops circumferentially around the volute passage.The pressure distortions reduce the stage performance and havea direct impact on diffuser and impeller ow stability. The stableoperating range of the compressor is also decreased [1]. The pres-sure distribution in any cross section is mostly determined by thevertical nature of the ow. The strong vortex ow induces acentrifugal effect, which results in an increasing pressure gradienttowards radially outward direction [3].

Corresponding and presenting author. Tel.: +91 261 2201994.

Applied Energy 90 (2012) 335343

Contents lists availab

lseE-mail address: pbr@med.svnit.ac.in (B.D. Baloni).the centrifugal blower. The blower of this type is used to provideforced draft to boiler and general industry due to their simplestructure, small size and low production cost. In this type ofblower, an impeller forces the gas from the impeller and leads itaway at a high pressure. Before the gas leaves the stator i.e. volute,its kinetic energy is reduced and partially converted into pressureby diffusing action. The stator takes no part in the head generationhence consequently all theoretical consideration in casing designdeals with losses. But the casing plays an important part in locatingbest efciency point by virtue of its hydraulic losses and its ability

volute having an equal width [15,17]. To avoid shock and separa-tion loss at the volute tongue, the volute angle av is made to corre-spond to the direction of the absolute velocity vector at theimpeller discharge ow angle. At higher specic speeds, besidesthe volute angle, the length and shape of the tongue become moreimportant [4,15,16] Removal of a portion of the tongue reduces theefciency from 85% to 81% while restoring the tongue to the origi-nal shape the efciency can be brought back to 85% [15]. Depend-ing upon casing, the tongue may be sharp or blunt but it must bealong the streamline [16].Backward curved blade impellerThree-dimensional probeFull throttle

1. Introduction

To improve the design of any Tustanding of the ow of such machinwith an experimental study of the ovolute of a centrifugal blower. The vthan the impeller exit width is wide0306-2619/$ - see front matter 2011 Elsevier Ltd. Adoi:10.1016/j.apenergy.2011.02.016chine, a better under-uired. This paper dealsthe different designs ofasing with width largerd without a diffuser in

with the optimum value, the peak efciency will decrease slightlyand move towards a lower capacity [15]. If volute area is too large,the peak efciency may increase but will move towards a highercapacity, efciency at partial capacity will be lower in this case[15]. The volute exit to inlet area ratio has a signicant effect onthe diffusion and losses into the volute ow processes [2]. A volutewith width exceeding the impeller width is more efcient than aKeywords:Turbomachine

the experimental data, analyzed results were presented for the pressure recovery coefcient and losscoefcient.Pressure recovery and loss coefcient vacentrifugal blower volute designs

Beena D. Baloni a,, S.A. Channiwala a, V.K. MayavansaDepartment of Mechanical Engineering, SVNIT Surat, IndiabDepartment of Mechanical Engineering, MSU -Vadodara, India

a r t i c l e i n f o

Article history:Received 8 July 2010Received in revised form 28 January 2011Accepted 12 February 2011Available online 5 March 2011

a b s t r a c t

An experimental study waswith backward blade shrostant angular momentumstudied at various angularwith full throttle open conwhich gave ow paramete

Applied

journal homepage: www.ell rights reserved.tions in the two different

b

ducted using two different designs of volute casing of a centrifugal blowerimpeller. The volute casing designs were based on the principle of con-constant mean velocity. For both design of volute the ow elds were

dial and axial locations in the volutes. The experiments were conductedon at inlet. Analysis was done with the help of three-dimensional probe,uch as stagnation pressure, static pressure and ow directions. Based on

le at ScienceDirect

Energy

vier .com/locate /apenergy

The outline of this paper is as follows. First, the experimentalset-up and instrumentation is described, followed by details oftwo different designs of volute casing. Finally results of both thecasing, based on analysis of experimental data at various angular,radial and axial locations is discussed for the pressure recoverycoefcient and loss coefcient. Also the ow condition aroundthe impeller is analyzed at immediate exit.

2. Experimental set-up and instrumentation

Fig. 1 shows existing blower experimental set-up. The singlestage blower has backward straight blade type impeller with

Nomenclature

Cp pressure recovery coefcientP local static pressure, mm of waterPave average static pressure within the Volute, mm of waterPo local stagnation pressure, mm of waterPoav average stagnation pressure within the volute, mm of

waterr radius, mm

336 B.D. Baloni et al. / Applied Eneshroud, having decreasing width from inlet to outlet. The detailsof impeller data are provided in Table 1. To rotate the impeller,the motor of 5.5 KW (7.5 HP) at speed of 2900 r.p.m. was used.

The volute casing, stator of blower was design based on two dif-ferent approaches namely constant angular momentum andconstant mean velocity. To visualize the probe in the casing, itwas made of acrylic 8 mm thick sheet and FRP on the side of casing.To analyze the pressure, tapping were made at azimuth angle from0 to 360 at an interval of 30 as shown in Fig. 2.

Five-hole probe was used for three-dimensional ow survey,which was calibrated in a suction subsonic wind tunnel havingworking section of 50 cm 60 cm. It was calibrated for zero set-ting, dynamic pressure and pitch angle. Probe tubes were con-nected to the multi tube inclined manometer having water asFig. 1. Experimental set-up of Blower unit.

Table 1Data specication of impeller.

Inlet Outlet

Diameter (cm) 30 42.5 Number of Blade 12Blade width (cm) 17.5 13 Blade thickness (cm) 0.5Blade angle, b (deg.) 20 483.1. Constant angular momentum design

In this design concept the angular momentum of the ow isconsidered constant through out the volute casing. It is also knownas Free vortex design. The ow for a free vortex design followsthe equation,

r Vu constant 1In this design, if the ow through volute is incompressible, and

volute has constant width then the direction of streamline remainsconstant [17].uid for measurement of pressure. Flow eld was measured at fourangular positions at 180, 240, 300 and 360. At each angularlocation ve radial positions were selected for the purpose of owsurvey along each axial distance. A traversing mechanism was de-signed to provide movement to the probe in all three-directionsalong with simultaneous yawing in ow passage as shown inFig. 3. Probe traversing device controlled the position of the proberadially and circumferentially with the help of vertical lead screwwith machining nut and a guided rod assembly. The axial andyaw movement of the probe is controlled by probe holder withthe help of threaded rod with lock nut and disk as shown in Fig. 4.

3. Design aspects of volute casing

Many researches had gone into more and more systematic de-sign of centrifugal blower. Different authors have suggested differ-ent procedure although each has a slightly different method ofcalculation. The volute design process is often subject to many con-straints such as maximum casing size, location of piping to whichthe volute connect, avoiding necessary auxiliary equipment etc.,often limit the designers option [7]. Usually design methods forvolutes are based either on the assumption of constant angularmomentum [12] or on the assumption of constant mean velocity[14]. Osborne [11], Church [8], Aungier [7], and Yahya [17] amongothers have incorporated the detail design of one-dimensionalvolute.

Rc3 velocity distribution factorVm mean velocity of ow within Volute, m/sV 02 actual absolute velocity at Impeller exit, degreeVu tangential velocity of ow within volute, m/sW load coefcientav volute angle, degree

rgy 90 (2012) 3353433.2. Constant mean velocity design

The volute is designed on the basis of constant mean velocitythrough out the volute. Constant mean velocity Vm can be obtainedby multiplication of volute velocity distribution factor (Rc3) withactual absolute velocity at impeller exit (V 02).

Rc3 V 02 Vm constant 2To obtain high efciency, it is necessary to maintain constant

velocity of the uid in the volute passage at design point [17]. Thiswould give uniform static pressure distribution around theimpeller.

For both the design concepts, main parameters of volute casingare shown in Table 2.

Motor

Fig. 2. Line diagram o

Fig. 3. Probe traversing mechanism.

Fig. 4. Probe holder.

B.D. Baloni et al. / Applied EneAnalysis of ow at different angular, radial and axial positionsin both volute casing is revealed that maximum 15% variations oc-cur with the average value of r Vu in constant angular momen-tum concept whereas in constant mean velocity concept,

f existing set-up.

Table 2Main parameters of volute casings.

Parameters Constant angularmomentum

Constant meanvelocity

Volute base circle diameter (cm) 46.75 46.75Volute exit diameter (cm) 100.57 125.26Volute width (cm) 26 26Throat length (cm) 26.91 39.26Volute tongue angle (deg) 15 21.84Tongue radius (cm) 24.35 25.51

rgy 90 (2012) 335343 337analyzed value of mean velocity was found 26.789 m/s instead ofdesign mean velocity 26.7387 m/s.

4. Experimental results and discussion

The ow parameters analysis was carried out after measure-ment of stagnation pressure, static pressure, Flow velocity and owdirections at 180, 240, 300 and 360 through out the radial dis-tance at various axial positions. Also from suction to exit i.e. A 7(Fig. 2) for the holes near impeller. For presentation of the owconditions, the angular locations at 180, 240, 300 and 360weredesignated as Sections 1, 3, 5 and 7 respectively. The radial loca-tions were non-dimensionalised by the radial width at a given sec-tion. They were expressed in terms of percentages i.e. from 0 to100. The ow was surveyed at ve radial positions at each section.The axial distance were non-dimensionalised by the impellerwidth at exit and expressed in terms of percentages, 0% being onhub side, 100% being on tip (shroud) side, 23% to 0% representsoverhung portion on hub side and 100188% represents overhungportion on shroud side. Thus the ow elds were presented interms of sections, non-dimensional radial and non-dimensional ax-ial distances.

The average values of stagnation pressure, static pressure andvelocity were determined based on area average at different angu-lar positions for the holes near the impeller as shown in Fig. 57.

The plot of average stagnation pressure reveals that the owdelivered by the impeller is of higher stagnation pressure on exitside compared to near tongue. The variation is almost nil towardsexit of the volute casing (210360). But two designs produce owwith different stagnation pressure. Volute designed with constantangular momentum principle delivered ow with higher stagna-tion pressure which leads to higher head.

120

140

160

180

200

0 30 60 90 120 150 180 210 240 270 300 330 360

Angular position (Degree)

Stag

natio

n Pr

essu

re(m

m o

f wat

er)

Volute based on "constant angular momentum" Volute Based on "Constant Velocity Method"

Fig. 5. Variations of average stagnation pressure of ow at the exit of impeller at various angular positions.

20

24

28

32

36

40

0 30 60 90 120 150 180 210 240 270 300 330 360 390

Angular position (degree)

Velo

city

(m/s

)

Volute basde on "Constant Angular momentum" methodVolute based on "Constant mean velocity" method

Fig. 6. Variations of average velocity of ow at the exit of impeller at various angular positions.

Average static pressure of flow at exit of impeller at various angular positions.

40

60

80

100

120

140

160

0 30 60 90 120 150 180 210 240 270 300 330 360 390

angular positions (degree)

stat

ic p

ress

ure

(mm

of w

ater

)

Volute based on "Constant angular momentum" methodVolute based on "Constant mean velocity" method

Fig. 7. Variations of average static pressure of ow, at the exit of impeller at various angular positions.

338 B.D. Baloni et al. / Applied Energy 90 (2012) 335343

recat s

EneVariations in PressureDistance

-0.2

0

0.2

0.4

0.6

0.8

Rec

over

y co

effic

ient

(Cp)

B.D. Baloni et al. / AppliedThe ow conditions delivered by impeller with both designsof volute were also compared by plotting average values ofvelocity and static pressure (Figs. 6 and 7). With both the de-signs, ow delivered by impeller near tongue region (30150)is to be of higher velocity and lower static pressure. The velocitydecreases and static pressure increases as ow moves fromtongue to exit section of the volute (towards 360), this justiesthe theory of one-dimensional isentropic ow with variable area.Like stagnation pressure, the values of average static pressureand velocity were lower with volute casing designed withconstant mean velocity principle. Thus the analysis shows thatdesign of volute inuences the ow conditions delivered by theimpeller.

-0.8

-0.6

-0.4

% Radi

Pres

sure

Variations of Pressure Distance a

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

% Radial

Pres

sure

reco

very

coe

ffici

ent

(Cp)

Variation of Pressure recDistance at end

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

% Radia

Pres

sure

Rec

over

y C

oeffi

cien

t(C

p)

Section 1 Sectio

Fig. 8. Pressure recovery coefcient variations near Impeller widthovery coefficient along Radial tarting of Impeller

rgy 90 (2012) 335343 339The rise in pressure on account of conversion of kinetic energyinto enthalpy is expressed in the forms of pressure recovery coef-cient (Cp) dened as,

Cp P Pave=Poav Pave 3While loss is expressed as loss coefcient (W) and dened as,

W Poav Po=Poav Pave 4where (Poav Pave) is equal to the dynamic head and also expressedas qV2. Since the values of stagnation pressure and static pressurevary along axial & angular positions of volutes, their average valueswere obtained by area average technique at various angularpositions. These average values at angular positions were used to

al Distance

recovery coefficient along Radial t mid of the Impeller

Distance

overy coefficient along Radial of the Impeller Width

l Distance

n 3 Section 5 Section 7

of volute designed on constant angular momentum concept.

recoting

EneVariation of Pressure at star

0.00

0.20

0.40

0.60

0.80

very

coe

ffici

ent

Cp)

340 B.D. Baloni et al. / Applieddetermine average value for the whole impeller. Po and P were thelocal values at a particular location of volute.

The values of pressure recovery coefcient were calculatedthroughout the volute casings. Figs. 8 and 9 represent the varia-tions in pressure recovery coefcient at starting, middle and endof Impeller width for different angular positions. It is observed thatfor both the design concept the pressure recovery coefcient islowest at Section 1 and highest at Section 7. This shows that aswe move from suction to exit the value of local static pressure in-creases due to conversion of kinetic energy into pressure energy.Which indicates that according to [9,10,13,14] casings serves its

-0.80

-0.60

-0.40

-0.20

% Rad

Pres

sure

reco (

Variations in Pressure recodistance at mid o

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

% Radi

Pres

sure

reco

very

coe

ffici

ent

(Cp)

Variations in Pressure recodiatance at en

-0.80

-0.60

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

% Radia

Pres

sure

reco

very

coe

ffici

ent

(Cp)

Section 1 Sectio

Fig. 9. Pressure recovery coefcient variations near Impeller wivery along radial distance of Impeller

rgy 90 (2012) 335343function well. Also as we move radially outward the Cp value in-creases at all angular positions except at Sections 3 and 5 in caseof Constant angular momentum design concept. At Sections 1and 3 value of Cp comes negative at hole near impeller, whichshows that the ow is delivered by the impeller at lower staticpressure than the average static pressure of the volute. It also indi-cates a pressure drop from impeller outlet to the volute.

The pressure recovery coefcient variations were also pre-sented for both design concepts in the form of contours made byMatlab software in Figs. 10 and 11. As we move from suction toexit of the volute i.e. from Sections 1 to 7, regions covered by high

ial Distance

very coefficient along radial f the impelller width

al Distance

very coefficient along radial d of the impeller

l Distance

n 3 Section 5 Section 7

dth of volute designed on constant mean velocity concept.

EneB.D. Baloni et al. / Appliedvalue of Cp, increases at radially outward position from about 10%to 60% of radial distance in case of the constant angular momen-tum design concept. And following the same about 3080% of ra-dial distance in case of the constant mean velocity designconcept. These results indicate that as we move from suction to

Fig. 10. Pressure recovery coefcient variations in volute designed on constantangular momentum concept.rgy 90 (2012) 335343 341exit of volute the conversion of kinetic energy into pressure energytakes place. In case of volute designed by constant angularmomentum, it is observed that near impeller region the value of

Fig. 11. Pressure recovery coefcient variations in volute designed on constantmean velocity concept.

Ene342 B.D. Baloni et al. / AppliedCp came negative. For another designed volute these regions arelimited up to near hub portion of the impeller region. As we movefrom suction to exit these regions of negative Cp value decreases.Compared to other, high pressure recovery regions are more incase of constant mean velocity designed volute. The gradientsare also less in case of constant mean velocity designed volute

Fig. 12. Loss coefcient variations in volute designed on constant angularmomentum concept.rgy 90 (2012) 335343which shows better uniformity of the ow compared to constantangular momentum designed volute [17].

The variations of Loss coefcient for both the designed volutecasings were represented in the form of contours made by Matlabsoftware in Figs. 12 and 13. It is clear from the gures that com-pared to other regions of volute casings the losses are more near

Fig. 13. Loss coefcient variations in volute designed on constant mean velocityconcept.

the tip region of the impeller. While near the hub region of theimpeller and in Section 1 at overhung portion of casing wall sidethe values of loss coefcient came negative because, the loss coef-cient compares the local stagnation pressure loss to average inletstagnation pressure. The local pressure depends upon the stagna-tion pressure on the same streamline at the impeller exit [3].Due to the circumferential pressure distortion at the volute off-design operation, stagnation pressure delivered by impeller washigher than the average stagnation pressure. As we move from suc-tion to exit of the volute casings, the higher value of colour bar isdecreased from 1 to 0.3, which indicates value of loss coefcientdecreased towards the exit of volute. In volute designed based onconstant mean velocity, the gradients were less compared toother design concept. It indicates that ow was more uniform inthis volute casing then the constant angular momentum de-signed volute [17]. The results justify the known fact that volutegeometry affects the ow delivered by the impeller [5].

5. Conclusions

An experimental analysis has been undertaken to elucidate theeffect of volute casing designs on the ow from the impeller of acentrifugal blower. The pressure recovery coefcient as well as losscoefcient variations in the casing were investigated. The follow-

Acknowledgement

The experimental work presented in this paper has been carriedout at Faculty of Technology & Engineering, The Maharaja SayajiraoUniversity. All support from faculties and the staff members isgratefully acknowledged.

References

[1] Ayder E, Van den Braembussche R, Brasz JJ. Experimental and theoreticalanalysis of the ow in a centrifugal compressor volute. ASME J Turbomach1993;115:5829.

[2] Hassan AS. Inuence of the volute design parameter on the performance of acentrifugal compressor of an aircraft turbocharger. In: Proc IMechE, vol. 221;2007. p. 695704.

[3] Hagelstein D et al. Experimental and numerical investigation of the ow in acentrifugal compressor volute. Trans ASME 2000;122:2231.

[4] Ji Chunjun, Wang Yajun, Yao Lixin. Numerical analysis and optimization of thevolute in a centrifugal compressor. ICPE-2007, October 2327, 2007,Hangzhou, China; 2007.

[5] Rutschi K. The effect of the guide apparatus on the output and efciency ofcentrifugal pumps. Schwiez Bauz 1961;79:23340.

[6] Worster RC. The ow in volutes and its effect on centrifugal pumpperformance. Porc Inst Mech Eng 1963;177:84375.

[7] Aungier RH. Centrifugal compressors: a strategy for aerodynamic design andanalysis. New York: ASME Press; 2000.

[8] Church AN. Centrifugal pumps and blowers. Joftr.witey and Sons, HemispherePublishing Corporation; 1989.

[9] Eck B. Design and operation of centrifugal, axial-ow and cross-owfans. Oxford: Pergamon Press; 1975.

[10] Karassik, Roy Carter. Centrifugal pumps. McGraw Hill Inc.; 1960.

B.D. Baloni et al. / Applied Energy 90 (2012) 335343 343ing conclusions deduced from the experimental results are:

(1) The ow within the volute casing based on constant meanvelocity design concept gives better ow conditions thanthat based on the constant angular momentum. The gradi-ent of both the ow parameters were less in case of constantmean velocity design, suggests more ow uniformity com-pared to constant angular momentum design concept.

(2) Variation in the pressure recovery is larger up to 50% ofradial distance from the impeller towards radially outwarddirection.

(3) Value of loss coefcient was decreased as ow move fromsuction to exit of volute.[11] Osborne WC. Fans. Pergomon Press; 1961.[12] Peiderer C. Centrifugal pumps for liquids and gases. Berlin,

Germany: Springer; 1948.[13] Shepherd DG. Principle of turbomachinery. New York: Macmillan Publishing

Co., Inc.; 1956.[14] Stepanoff AJ. Centrifugal & axial ow pumps: theory, design and

application. New York: Wiley; 1948.[15] Stepanoff AJ. Turbo blowers: theory, design and application of centrifugal and

axial ow compressors and fans. New York: John Wiley & Sons, Inc.; 1955.[16] Turton RK. Principles of turbomachinery. New York, London: E. & F. N. Spon

Ltd.; 1984.[17] Yahya SM. Turbine compressors and fans. New Delhi: Tata Mcgraw Hill

Publishing Company Limited; 2002.

Pressure recovery and loss coefficient variations in the two different centrifugal blower volute designsIntroductionExperimental set-up and instrumentationDesign aspects of volute casingConstant angular momentum designConstant mean velocity design

Experimental results and discussionConclusionsAcknowledgementReferences