2010Experimental Validation of Particle Flow Through Conveyor Transfer

Mechanics of Materials 42 (2010) 383–394

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Mechanics of Materials

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Experimental validation of particle flow through conveyor transferhoods via continuum and discrete element methods

D.B. Hastie *, P.W. WypychCentre for Bulk Solids and Particulate Solids, Faculty of Engineering, University of Wollongong, Northfields Avenue, Wollongong, 2522 New South Wales, Australia

a r t i c l e i n f o

Article history:Received 31 July 2008Received in revised form 26 July 2009

Keywords:Conveyor transferVelocity analysisParticle flowContinuum methodDiscrete element method

0167-6636/$ - see front matter � 2009 Elsevier Ltddoi:10.1016/j.mechmat.2009.11.007

* Corresponding author. Tel./fax: +61 2 4221 439E-mail address: [email protected] (D.B. Hastie

a b s t r a c t

A critical factor in the design of hood-spoon type conveyor transfers is to match the exit veloc-ity of the material through a conveyor transfer to that of the conveyor belt receiving the mate-rial. If particle velocity increases too much issues such as particle attrition, dust generation,chute and belt wear and excessive noise can arise, whereas if particle velocity decreases, stag-nation zones can develop, resulting in issues such as spillage or chute blockage. Numerousmethods are available to analyse particle flow through a conveyor transfer, including; contin-uum-based analytical methods, the discrete element method (DEM) and experimental anal-ysis.

This paper details the findings for these three methods for granular cohesionless materials.The experimental investigations were performed on a conveyor transfer research facilitylocated at the University of Wollongong, using high-speed video to capture the flow and sub-sequently analysed with Image Pro Plus. Two continuum-based analytical analyses were thenused to predict the flow through the conveyor transfers. Lastly, the use of DEM provided a thirdmeans of quantification and prediction of the particle velocity through the transfer hood withthe data further processed using Matlab. These methods were then compared to determinewhether continuum or discrete methods allow for accurate prediction of chute flow.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

Discrete element modelling (DEM) is becoming increas-ingly popular in the analysis and visualisation of materialflow through conveyor transfer points. DEM validation isnot novel as Gröger and Katterfeld (2007) have previouslysimulated material flow at transfer stations and verifiedthe results experimentally. They primarily investigatedthe forces generated at an impact plate and the mass flowrates through the transfer station, however DEM validationof the particle velocity through a conveyor transfer is no-vel. Ilic et al. (2007) have presented comparisons betweena continuum method and DEM focussing on a slewingstacker transfer chute, however there was no comparisonmade to experimental results. Even though there was some

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7.).

agreement between the continuum method and the DEM,there is no certainty that these methods accurately predictreality.

The design of conveyor transfers has often relied on trialand error to achieve the desired outcome and has beenseen as a ‘black art’ rather than a science for many years.The development of continuum-based chute flow models,such as that of Roberts (1999, 2003) and Korzen (1988),has helped to better understand the flow behaviour of bulkmaterials. With the advent of DEM comes the possibilitythat expensive test chutes may no longer need to be con-structed to test various designs, with the design processoccurring solely on computer workstations. At presentthere is still some hesitance to rely on DEM alone as it isstill considered to be in its infancy with much more valida-tion required before designers put their full trust in it.

The presented research examines the inverted chuteflow model of Roberts (2003), the continuum method of

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Nomenclature

Ap cross-sectional area of flow stream, m2

B average width of stream through transfer hood,m

c cohesion, kN/m2

FD drag force, Ng gravity, m/s2

H0 initial height of stream at impact with transferhood, m

Kv pressure ratio, –ms material feed rate, t/hN normal force, NR transfer hood radius, mVa stream velocity after impact with transfer hood,

m/sVb belt speed, m/sVp stream velocity before impact with transfer

hood, m/s

v stream velocity, m/sv0 initial stream velocity, m/sX horizontal positioning of transfer hood, mY vertical positioning of transfer hood, mDm mass element. kgap impact angle, �c specific weight, kN/m3

h angular position around hood (measured fromhorizontal), �

he angular position of product exiting hood, �hi angular position of product impact point with

hood, �/w wall friction angle, �le equivalent friction, –lw coefficient of wall friction, –u arbitrary angle, �

384 D.B. Hastie, P.W. Wypych / Mechanics of Materials 42 (2010) 383–394

Korzen (1988) for non-cohesive materials and DEM simu-lations which are then compared to the results obtainedfrom an experimental conveyor transfer research facility.

2. Conveyor transfer research facility

The experimental component of this research is per-formed on the conveyor transfer research facility locatedat the University of Wollongong, consisting of three Aero-beltTM conveyors arranged to allow steady-state flow ofmaterial, as shown in Fig. 1.

The feed bin supplies material to the first conveyor, in-clined at 5�, while the other two conveyors are inclined at23�. The conveyor transfer being investigated consists of ahood and spoon and is located directly after the first con-veyor, however the focus here will only be on the transferhood, detailed in Fig. 2. It is important to note at this point

Fig. 1. Conveyor transfer research facility.

that the design of a transfer hood generally compliments agiven conveyor belt speed and that varying the belt speedcan result in less than ideal results, this fact will be pre-sented in the results. The hood is lined with 6 mm Poly-stone Ultra to minimise chute wear and frictional losses.From the horizontal (he = 0�), 5� increments have beenmarked around the hood, indicating the locations wherethe velocity will be analysed. This allows for accuratedetermination of the point of impact of the trajectorystream, h, coming from the feed conveyor. Polyethylenepellets have been selected as the test material, due to theirgranular sphero-cylindrical shape as well as robustness.Some particle and wall characteristics are listed in Table 1.

The particle friction is also required for the DEM simu-lations, however there was some conjecture over the best

Fig. 2. Detail of conveyor transfer hood.

Table 1Particle and bulk properties of polyethylene pellets.

Loose-poured bulk density 515 kg/m3

Particle density 919 kg/m3

Particle size distribution (2.36–3.35 mm) 2.90%Particle size distribution (3.35–4.00 mm) 11.73%Particle size distribution (4.00–4.75 mm) 85.37%Particle sphericity 0.873 tan /w

Wall friction angle (3 mm Aerobelt) 25.7� 0.481Wall friction angle (4.5 mm Acrylic) 21.5� 0.394Wall friction angle (6 mm Acrylic) 19.1� 0.346Wall friction angle (6 mm Polystone Ultra) 15.75� 0.282Wall friction angle (Polyethylene sheet) 12.5� 0.222Coefficient of restitution (average) 0.65

Table 2Product feed rates used in experimental tests.

Belt speed, Vb (m/s) Low feed rate (t/h) High feed rate (t/h)

2 2 313 (position A) 2 383 (position B) 10 38

D.B. Hastie, P.W. Wypych / Mechanics of Materials 42 (2010) 383–394 385

method to use. The direct shear test to measure the instan-taneous yield loci (IYL) was deemed unsuitable due to thematerial forming a relatively non-consolidated streamwhen fed onto the conveyor. Ideally the particle frictionwould be measured by shearing two pellets against eachother under various loads, however there was no readilyavailable test equipment to allow this. The decision wasmade to perform a wall yield loci test (WYL) on the poly-ethylene pellets by also using a sheet of polyethylene asthe wall material to obtain an estimate.

2.1. Experimental analysis of particle flow

One of the key features of the conveyor transfer researchfacility is that the transfer enclosure and hood and spoon havebeen constructed of acrylic. This provides the ability to recorda variety of material flow characteristics with both high-speed video and digital still cameras. A Redlake X3 MotionProhigh-speed video camera has been used to capture the parti-cle flow through the hood at between 1000 and 1500 framesper second. The video footage will be captured from the sideof the transfer hood and as such will be capturing particles atthe extremities of the flow stream. These particles will also bein direct contact with the side wings of the hood, where wallfriction effects may have an influence on the particle velocity.The fact that the particle stream is not consolidated shouldkeep these effects to a minimum.

Two conveyor belt speeds, Vb, have been investigated,Vb = 2 m/s and Vb = 3 m/s. These both result in high-speedconveying conditions, with the material discharging fromthe point of tangency between the conveyor belt and thehead pulley. Initially, a conveyor belt speed of Vb = 1 m/swas also to be investigated but the geometry of the con-veyor resulted in slow-speed conditions. The productachieved a substantial angle of wrap around the head pul-ley before discharge and as a consequence the material hadvery little horizontal displacement, meaning the use of atransfer hood was not required.

To investigate the influence of material flow rate on thevelocity of the particle stream, a low experimental productfeed rate was selected as well as a product feed rate whichallowed the conveyors to operate at full capacity, based onedge distance calculations (C.E.M.A, 2005). Table 2 summa-rises the feed rates used. Initially, a low feed rate of 2 t per h(t/h) was used for the 3 m/s belt speed, however this wasfound to be too low when analysing the data via Image Pro

Plus, hence the increase to 10 t/h for the subsequent hoodgeometry.

One hood position was used for the Vb = 2 m/s hoodgeometry, whereas for the Vb = 3 m/s case, two hood posi-tions were used. The initial hood position was aligned so thatthe incoming flow would cause a substantial angle of inci-dence with the hood, while the second case aligned the hoodto minimise the angle of incidence. Fig. 3 shows a snapshot ofthe steady-state flow through each of the transfer hoodgeometries for both the low and high feed rates.

A number of key observations can be made from Fig. 3:

� for each of the high feed rates, the angle of incidence isless than the low feed rate ‘‘equivalent” due to the depthof the material stream,

� Fig. 3(c) highlights a substantial amount of spray of par-ticles after impact due to the high angle of incidence,whereas in Fig. 3(d) there is no spray,

� Fig. 3(b), (d) and (e) each show the product streamspreading onto the hood wings,

� the angle of incidence in Fig. 3(f) is near ideal whencompared to that of Fig. 3(d),

� the position of the hood for Vb = 3 m/s position A(Fig. 3(c) and (d)) did not allow for any measurementat the exit point of the hood, i.e. h = 0�.

The particle velocity was determined using the soft-ware package Image Pro Plus (IPP). Calibration of the lin-ear distance was first performed to ensure IPP analysedthe video footage correctly. The linear calibration wasperformed by selecting a known measurable distanceon a frame of the video and entering the true length.The time step, see Eq. (1), was determined from thenumber of frames per second (FPS) being recorded bythe high-speed camera.

Time step ¼ 1FPS� 1

ð1Þ

Utilising the manual tracking feature, particles aretracked by selecting the particle centroid at each time stepat each five degree increment, as shown in Fig. 4. The re-sults for each particle are tabulated within IPP and then ex-ported for further analysis. In most instances, the numberof particle tracked at each angular position was between10 and 20, dependant on clarity of the video footage. Theaverage velocity was then determined for these particles,as well as the minimum and maximum velocity at eachangular position.

The averaged particle velocities at each angular positionfor the six cases shown in Fig. 3 are presented in Fig. 5. Thefollowing observations can be made from the average par-ticle velocity results:

Fig. 3. Material flow through the conveyor hood. (a) Vb = 2m/s and ms = 2 t/h, (b) Vb = 2 m/s and ms = 31 t/h, (c) Vb = 3 m/s Pos A, ms = 2 t/h, (d) Vb = 3 m/sPos A, ms = 38 t/h, (e) Vb = 3 m/s Pos B, ms = 10 t/h, (f) Vb = 3 m/s Pos B, ms = 38 t/h.


� for Vb = 2 m/s, both the low and high feed rate start withan approximate velocity of 2 m/s before increasing to avelocity of 2.75–2.9 m/s at the hood exit,

� the Vb = 3 m/s position A tests with the high angle ofincidence showed a pronounced drop in velocity soonafter impact before steadily increasing to approximately3 m/s at hood exit,

� the Vb = 3 m/s position B tests showed a more consistentaverage velocity through the hood, even more so for thehigh feed rate test. There was still, however, a slight risein overall particle velocity towards the hood exit.

3. Continuum method analysis

Predicting the flow through a conveyor hood is possiblewith the use of two continuum-based methods: the in-verted chute flow model (Roberts, 2003) and the modelfor cohesive material flow (Korzen, 1988). Each of thesemethods require parameters such as, initial particle veloc-ity, hood impact angle and the initial and average heightand width of the particle stream. If the transfer hood hadnot already been constructed, then estimates of these val-ues would have been used in order to generate a solution.

Fig. 4. Particle tracking using Image Pro Plus.

Fig. 6a. Material stream height through the hood.


However, with this research comes the added benefit thatthese values can be extracted directly from the experimen-tal test program to better compare the continuum methodswith the experimental results, refer to Figs. 6(a) and 6(b)for examples of measuring the stream height and width.

3.1. Continuum method of roberts

The inverted chute flow method of Roberts (2003) is awidely accepted approach to predicting the stream velocitythrough a transfer hood for granular cohesionless materi-als, the force diagram is presented in Fig. 7.

An equivalent friction, le, is used, which incorporatesthe particle wall friction, the stream cross-section andthe internal shear of the bulk solid, see Eq. (2), and is as-sumed to be an averaged constant for all angular positionsanalysed through the hood, as the stream thickness is com-paratively low. The ratio of the pressure acting on the sidesof the chute to the pressure acting on the bottom of the

Fig. 5. Average particle velocity at each an

chute, Kv, is generally assumed to be a value between 0.4and 0.6 according to Roberts (1999, 2003). There was nomeans of directly measuring these pressures and as such,an estimate of 0.4 has been used based on the fact thatthe height of the material stream is substantially less thanthe width of the stream.

The particle velocity at any given angular positionthrough the hood can then be found using Eq. (3), by firstdetermining the constant of integration, K, by substitutionof the initial conditions, v = v0 and h = h0. The initial veloc-ity used in this analysis can be assumed to be the beltspeed of the feeding conveyor if the transfer hood is lo-cated close to the belt, or can be approximated from trajec-tory models. For the experimental work in this testprogram the actual velocity of the product stream was

gular position around transfer hood.

Fig. 6b. Material stream width through the hood.

Fig. 7. Force diagram for the inverted curved chute.


measured just before impact with the hood and has beenapplied directly.

lE ¼ lw 1þ Kvv0H0

vB

� �ð2Þ

v ¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

2gR4l2

E þ 1ð2l2

E � 1Þ sin hþ 3lE cos h� �

þ Ke2lEh

sð3Þ

Applying the experimental impact angle as the startingpoint for the analysis for each belt speed and hood posi-tion, the results of the Roberts continuum analysis are pre-sented in Fig. 8. The data presented shows a significant

Fig. 8. Predicted stream velocity thro

increase in stream velocity through the hood for both thelow and high feed rates for the 2 m/s belt speed, whereasfor both 3 m/s belt speed cases there is a relatively smallincrease in stream velocity through the transfer hood.

3.2. Continuum method of korzen

Korzen (1988) investigated the dynamics of materialflow on impact plates for both cohesive and non-cohesivematerials. Fig. 9 is a representation of the stream behaviourthrough this flow zone. This cohesive material model wasoriginally intended to have a zone of built up stationarymaterial attached to the impact plate which the main flowstream passed over. Korzen assumed this curved surfacewas of constant radius and the subsequent velocity analy-sis in Eq. (4) used the internal friction coefficient, l, due tothe flow stream shearing against the stationary material.

ugh hood by Roberts method.

Fig. 9. Flow representation for analysis by Korzen.


As the material used in this research is non-cohesive andfree flowing, it has been assumed that the curved shearingsurface can be replaced by a curved chute of constant ra-dius, resulting in the coefficient of wall friction, lw, beingused in the velocity analysis of Eq. (4).

The velocity of the material stream at an arbitrary angle,u, can be expressed by Eq. (4) and the constant of integra-tion, K, can be solved using v(u) = vp, u = ap and A(u) = Ap asthe initial conditions.

vðuÞ2 ¼ Ke�4lwu þ 2gRð1þ 16l2

wÞ5lw sin uþ ð4l2

w � 1Þ cos u� �

� cBgR2lwcAðuÞ

ð4Þ

Fig. 10. Predicted stream velocity thr

This method requires the cross-sectional area of thematerial profile at each angular position as a function ofmass flow rate, stream velocity and bulk density. As previ-ously mentioned, the experimental testing has providedthe direct measurement of the height and width of theproduct stream, thus the true cross-sectional area of theproduct stream at each angular position through theresulting flow can be determined. It should also be notedthat for this experimental test program, the material cho-sen is non-cohesive, therefore c = 0 and the right most partof Eq. (4) equals zero, negating the need to determine thestream cross-sectional area. As a result, the Korzen contin-uum method takes on a similar form to that presented bythe Roberts method.

Applying the experimental impact angle as the startingpoint for the analysis for each belt speed and hood posi-tion, the results of the Korzen continuum analysis are pre-sented in Fig. 10. The data presented shows a significantincrease in stream velocity through the hood for both thelow and high feed rates for the 2 m/s belt speed in thesame way as the Roberts method, whereas for both 3 m/sbelt speed cases there is nearly no change in stream veloc-ity through the transfer hood.

4. Discrete element method simulation of particle flow

The programming code behind discrete element model-ling can vary greatly in terms of interaction laws and timeintegration. The commercial software Chute MavenTM hasbeen utilised for this simulation research which uses thelinear spring-dashpot contact model. As with all DEM,the contact model comprises normal and shear force com-ponents. The normal force component comprises linearelastic and viscous damping components and an equiva-lent coefficient of restitution is used to define the normalviscous damper coefficient. The explicit central differencescheme is used for the time integration (Hustrulid, 1997).

ough hood by Korzen method.

Fig. 11. (a) simulation using 50% restrain and (b) simulation using 100% restrain.

Table 3DEM simulation parameters.

Test Beltspeed(m/s)

Feedrate(t/h)

Coefficientof particlefriction

Coefficientof wallfriction

% Restrain

1 2 5 0.222 0.282 802 2 5 0.966 0.282 80


Chute MavenTM focuses on the simulation of particleflow through conveyor transfers. A three dimensionalCAD model is imported into the software defining the var-ious conveyor components, including; conveyor belt(s),head pulley, skirts, injection box(es) and transfer chute(s).Particle and system parameters are of course required andthe measured parameters supplied in Table 1 are used. TheChute MavenTM software only allows for the simulation ofspherical particles, which could lead to an over-predictionof the velocity through the transfer hood as the simulatedspherical particles should be more ‘‘free-flowing”.

The degree to which particles roll or slide during a simu-lation is quantified by a restrain parameter. The restrain ofthe particles is defined as 100% for fully sliding and 0% forfully rotating particles, other percentages refer to combina-tions of the two. On inspection of the particle output data, itwas found that particles are set as either sliding or rotatingfor the duration of the simulation based on the percentagerestrain initially chosen. In an attempt to quantify a repre-sentative restrain value, the high-speed video footage fromthe experimental tests was reviewed. It was concluded thatthe percentage of particles which fully rotate on the surfaceof the Polystone Ultra liner was dependant on stream thick-ness. In regions of substantial stream thickness with mini-mal voidage, the percentage of particles able to rotate waslow, visually around 10%. However, the number of particlesable to fully rotate or roll is even lower due to the compac-tion of the particles. In regions of low stream thickness, itwas observed that approximately 30% of particles could rollas the stream was less constrained. To assume that all parti-cles are fully restrained, especially for a free flowing mate-rial, is not ideal, thus a restraint of 80% was selected for theDEM simulations, based on experimental observation.

As a validation of this assumption, a selection of beltspeeds and material feed rates were selected and DEM simu-

lations performed as a sensitivity analysis, focusing on varia-tion of restrain, while leaving all other parameters constant.Three particle restrains were investigated, 100%, 80% and50%. On review of the outputs it was found that as the particlerestrain was reduced, there was an increase in the number ofparticles which would diverge from the main flow stream,see Fig. 11. However, analysis of the main steady-state flowstream found no change in the average stream velocity atthe exit of the hood for a given belt speed regardless of mate-rial feed rate. This finding indicates that the assumption touse 80% restrain for the DEM simulations is acceptable. Addi-tionally, a particle restrain of 0% was simulated, correspond-ing to 100% of the particles rolling. No quantifiable resultscould be obtained from this simulation as the particles failedto convey along the conveyor belt due to the extremely highslip present between the particles and the belt.

Further validation was performed to investigate the is-sue of particle friction, raised in Section 2. Two DEM simu-lations were completed, as shown in Table 3, where onlythe coefficient of particle friction was modified in each test.The value for coefficient of particle friction used in test 1was based on the wall yield loci test on a sheet of Polyeth-ylene and test 2 was based on the result of an instanta-neous yield loci test. The resulting average streamvelocities at each 5� angular position around the hoodare presented in Table 4. At the point of discharge from

Table 4Average stream velocity (m/s) from particle friction validation.

Test h – Angle from horizontal (�)

0 5 10 15 20 25 30 35 40 45

1 3.264 3.177 3.083 2.961 2.849 2.707 2.567 2.410 2.230 2.1402 3.261 3.164 3.076 2.965 2.838 2.704 2.577 2.414 2.238 2.161


the transfer hood (i.e. h = 0�), there is effectively no changein the average stream velocity between the two tests. Thisappears to indicate that the coefficient of particle friction isnot one of the primary parameters that will affect the out-come of a simulation and as such the concern raised overwhich method to use in determining the coefficient of par-ticle friction was somewhat unwarranted.

Three DEM simulations were prepared using the lowproduct feed rates shown in Table 2, to allow direct compar-isons with the experimental results. DEM simulations for thehigh material feed rates would require a substantially highernumber of particles and would see a corresponding increasein simulation time. The decision was made not to performhigh feed rate simulations but to instead look for other waysto produce comparisons. The effect of material feed rate inthe DEM simulations was investigated by preparing addi-tional tests, the full series of DEM simulations being:

� 2, 5 and 10 t/h for a belt speed of 2 m/s, and� 2, 5, 10 and 15 t/h for the 3 m/s belt speed hood

positions.

The results of these tests would hopefully presenttrends which could be applied to predict what would hap-pen at the higher feed rates. On completion of the simula-tions, an example of which can be seen in Fig. 12, thesimulated product streams were extracted and comparedwith the following observations being made;

� as product feed rate increases, so too does the height ofthe material stream, which in turn reduces the angle ofincidence at the point of impact with the transfer hood,

� hood position A for the 3 m/s belt speed shows substan-tial particles diverging from the main particle streamdue to the high angle of incidence, which is backed inFig. 3c where particles can be seen diverging in theexperimental hood,

Fig. 12. Example output from a DEM simulation.

� hood position B for the 3 m/s belt speed has a more con-trolled stream flow as a result of the optimised position-ing of the hood, minimising the angle of incidence of thematerial in-flow.

Further post processing of the simulation data focusedon the average stream velocity through the transfer hoodfor each belt speed and hood position and the results arepresented in Fig. 13. Matlab was used for this analysisand only particles with their centres within 3 mm of thePolystone Ultra liner and also within 50 mm either sideof the central flow axis were selected. In all cases therewas a transient behaviour of the average stream velocityat the point of impact with the transfer hood. It is also evi-dent that once this initial transient zone has passed, theaverage particle velocity for each group of tests falls alongthe same line, resulting in the average exit velocity of thestream being the same. This fact would seem to indicatethat regardless of the material feed rate used, the averageexit velocity of the stream will be equivalent to thoseshown in Fig. 13. This trend may or may not hold true forother products and will be investigated in future research.

5. Comparisons

The results of the three methods have been presentedabove, but to fully appreciate the comparison betweeneach method for each belt speed and transfer hood geom-etry, Figs. 14–16 are presented. Both the low and high feedrates have been plotted for the experimental, Roberts andKorzen methods while for the DEM, only the low feed ratehas been plotted, for the reasons explained in Section 4.

Transient behaviour is evident in the DEM resultsshown in Figs. 14–16, whereas this was not seen in theexperimental results. One reason for this is that the exper-imental particle velocities have been obtained from theextremities of the flow stream, whereas the velocity resultsfrom the DEM simulations have been extracted from thecentral axis of the flow stream. The experimental resultscannot therefore show the full effect of the impact of theparticle stream with the transfer hood.

There is a general over-prediction of the experimentalresults by the Roberts, Korzen and DEM methods, howeversome results do give an under-prediction. The findings aresummarised in Table 5 below.

6. Conclusion

An experimental conveyor transfer facility has beenconstructed with the fundamental aim of validating bothcontinuum-based methods and DEM simulations used topredict the particle flow through conveyor transferhoods.

Fig. 13. DEM simulation results for all material feed rates.


Experimentally, two conveyor belt speeds have beeninvestigated (2 m/s and 3 m/s) and additionally two con-veyor hood positions were investigated for the 3 m/s beltspeed, one in an optimal position to minimise the angleof incidence of the incoming particle stream and the otheroffset to induce an increased angle of incidence, conduciveof a poorly installed and/or aligned transfer hood. This wasto explore the effect of the angle of incidence on the subse-quent stream velocity through the transfer hood. As wasshown in Fig. 3, there was a noticeable change to the flowpattern of the material stream due to the differing positionof the hood for the 3 m/s belt speed.

The continuum method of Roberts has been used forprediction of chute flows for some time, however the re-

Fig. 14. Comparison of methods

sults presented here show that there are some inaccuracieswith this method compared to the results obtained exper-imentally. In the cases presented in Figs. 14–16, there wasa distinct over-prediction of the stream velocity throughthe transfer hood.

The Korzen method behaved in much the same way asthe Roberts method, however the resulting hood exitvelocity of the particle stream better approximated theexperimental hood exit velocity, matching with the 2 m/sbelt speed and 3 m/s belt speed position A cases. The Kor-zen method actually under-predicted the hood exit veloc-ity for the 3 m/s belt speed position B case, which,experimentally showed a near ideal angle of incidenceand smooth consistent flow through the hood. Although

for a belt speed of 2 m/s.

Fig. 15. Comparison of methods for a belt speed of 3 m/s with the hood in position A.

Fig. 16. Comparison of methods for a belt speed of 3 m/s with the hood in position B.

Table 5Percentage under- or over-prediction of the Roberts, Korzen and DEMmethods when compared to the experimental results.

Belt speed(m/s)

Roberts Korzen DEM

Low(%)

High(%)

Low(%)

High(%)

Low(%)

2 +9.6 +18.1 �0.1 +7.5 +11.23 Position A +13.2 +30.2 +4.1 +23.6 +6.33 Position B �1.0 +9.4 �10.1 +2.0 +2.4


the hood exit velocity was better predicted with the Kor-zen method, it cannot be overlooked that the stream veloc-ities through the transfer hood were still over-predicted.

Both the Roberts and Korzen methods are both suited torapid-flow thin-stream analyses which could account forsome of the variation between the results obtained andthose of the experimental tests. Also, there is no facilitywithin either methods to account for non-spherical parti-cles. To account for the non-spherical nature of the mate-rial being used, the sphericity factor could beincorporated into the analyses but this will need furtherinvestigation. In the conveyor trajectory model of Korzen(1989), the effects of air drag are included and perhaps thiscould also be applied to the chute flow models of both Rob-erts and Korzen. Another option of worthy consideration isthe use of other friction models rather than Coulombfriction.


The DEM simulations produced as part of this researchshowed that regardless of the material feed rate for a givenbelt speed and/or hood position, the hood exit velocity wasidentical.

The Chute MavenTM software allows for only sphericalparticles to be simulated. With the inability to simulatethe true particle shape, differences between the DEM andexperimental results will be observed, including differingparticle interaction with model boundaries and also thefact that air drag effects cannot be modelled. As with thecontinuum methods, the sphericity of the particles usedcould be applied to the resulting velocity analyses, butagain, further investigations would be required.

Visually, the experimental results shown in Fig. 3 andthe particle stream outputs of the DEM in Fig. 12 showedsimilar trends. This seems to imply that the DEM softwareis capable of simulating the behaviour of the material flowstream quite reasonably. The initial impact of the particlestream on the transfer hood results in transient behaviour,which is due to intersecting and merging flow paths. Thisaspect of the chute flow cannot be handled by the contin-uum-based methods. In contrast, the DEM simulations areable to reproduce this transient behaviour in a similar wayto that seen experimentally.

Further research will investigate the behaviour of othermaterials through the same transfer hood in an attempt toestablish trends which can be applied in a broader context.Also, as stated above, the applicability of integrating parti-cle sphericity into the continuum methods and also to theresults of the DEM simulations will be investigated.

The possibility of including impact load measurementson the experimental transfer hood is something that would

add an additional level of analysis and comparison to theresearch. The impact forces cannot be determined fromthe DEM software but other DEM software has this capabil-ity and may be sourced as part of this work.

Acknowledgements

The authors wish to acknowledge the support of theAustralian Research Council, Rio Tinto Technology andInnovation and Rio Tinto Iron Ore Expansion Projects fortheir financial and in-kind contributions to the LinkageProject which allows this research to be pursued.

References

C.E.M.A., 2005. Belt Conveyors for Bulk Materials, sixth ed. ConveyorEquipment Manufacturers Association, p. 599.

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2010Experimental Validation of Particle Flow Through Conveyor Transfer

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