An Investigation on the Use of Venturi Weirs as an Aerator

Transcription

1 Wter Qul. Res. J. Cnd, 2003 Volume 38, No. 4, Copyright 2003, CAWQ An Investigtion on the Use of Venturi Weirs s n Aertor AHMET BAYLAR* Civil Engineering Deprtment, Firt University, 23279, Elzig, Turkey The most clssic exmple of hydrulic structure where gs trnsfer occurs is weir. Trnsfer of gses etween the tmosphere nd river wter cn occur in free overfll jet from weir. A free overfll jet from weir plunging into downstrem wter cuses entrinment of ir ules if the free overfll jet velocity exceeds the criticl vlue where ertion occurs. This pper investigtes the free overfll jets from Venturi nd rectngulr notch weirs nd their effect on ir entrinment rte. A Venturi weir ws plced t the upstrem chnnel end in order to increse the flow velocity of the free overfll jet nd, in turn, to increse ir entrinment. It ws demonstrted tht the ir entrinment rte of the Venturi weir is significntly etter thn the rectngulr notch weir, nd this dvntge ecomes more pronounced s the throt width of the Venturi weir is decresed. These results demonstrted tht Venturi weirs cn e used s highly effective ertors in strems, rivers, constructed chnnels, fish htcheries, wter tretment plnts, etc. Moreover, regression eqution ws otined for the Venturi weirs, relting ir entrinment rte to unit dischrge, weir crest width, drop height nd throt width of Venturi weir. There ws good greement etween the mesured ir entrinment rtes nd the vlues computed from the predictive eqution. Key words: ir entrinment rte, ertion, jet expnsion, Venturi, weir Introduction As wter flows over weir or spillwy (or rpids or wterfll), tmospheric gses (minly nitrogen nd oxygen) cn dissolve into it. Likewise, dissolved gses in the wter cn come out of solution t these structures, in effect degssing the wter. The process hs environmentl importnce long ll rivers. For exmple, if there is too little dissolved oxygen in river, then qutic life such s fish cn die, nd the river my hve odour prolems. At the other end of the spectrum, too much dissolved nitrogen cn lso e hrmful to orgnisms such s fish. Thus, there is rnge of dissolved gs concentrtions tht define n cceptle level of wter qulity. Recent reserch hs focused on developing mesurement nd predictive techniques for gs trnsfer t hydrulic structures to help mintin nd enhnce wter qulity. Before reking up into drops, the flow over weir or wterfll would e clssified s free overfll jet, s shown in Fig. 1. The weir er- * ylr@firt.edu.tr

2 754 BAYLAR Fig. 1. Free overfll jet over Venturi weir: () pln view, () elevtion view. tion is cused y ir eing crried y the free overfll jet into the receiving pool. The mechnisms y which ir is entrined nd trnsferred into wter ecuse of the free overfll jet re extremely complex nd vry with free overfll jet velocity nd geometry. The free overfll jet chrcteristics nd receiving pool geometry lso dictte the hydrodynmics nd turulent mixing within the receiving pool nd the movement of the ir ules. Therefore, the chrcteristics of the free overfll jet nd the geometry of the receiving pool ultimtely determine the volume of ir entrined, V, its contct re with the wter, A, nd the time it remins in the receiving pool or contct time, t c (Wormleton nd Tsng 2000). The ertion effect of weirs hs een studied experimentlly y numer of investigtors. Gmeson (1957) ws the first to report on the ertion potentil of weirs in rivers. Since then, numer of lortory investigtions into weir ertion hve een crried out, notly Vn der Kroon nd Schrm (1969,), Apted nd Novk (1973), Avery nd Novk (1978), nd Nksone (1987). These investigtors hve produced empiricl reltionships relting ertion efficiency. The reltionships were developed sed on dt otined from smll flumes with stright weirs or from field oservtions. Wormleton nd Soufini (1998) nd Wormleton nd Tsng (2000) studied tringulr nd rectngulr plnform lyrinth weirs nd their effect on ertion performnce. Investigtions lso hve een reported on the ertion performnce of existing hydrulic structures nd these re reviewed y Wilhelms et l. (1993), Chnson (1995), Gulliver et l. (1998), nd Ervine (1998). Bylr nd Bgtur (2000) nd Bylr et l. (2001) demonstrted tht ertion performnce of weirs chnged depending on weir shpes. Bylr nd Emiroglu (2002) investi-

3 THE USE OF VENTURI WEIRS AS AN AERATOR 755 gted shrp-crested weirs hving different cross-sectionl geometry nd their effect on the ir entrinment rte. Much of these works hve delt with oxygen trnsfer efficiency in rectngulr notch weirs nd none hs concentrted specificlly on the ir entrinment rte (Q A ) of Venturi weirs. This pper descries n experimentl investigtion into Q A of the Venturi weirs, nd in prticulr, the effect of vrying the throt widths of the Venturi weirs. A Venturi weir consists of converging level inlet section with verticl sidewlls nd diverging level outlet section lso with verticl sidewlls. There is the shrp connection etween the converging section nd the diverging section. A Venturi weir does not hve ny prllel wlls forming stright throt. The nrrow throt produces differentil hed which under the proper conditions is proportionl to flow rte (Fig. 2). Bule Genertion Mechnisms y Free Overll Jets Gmeson (1957) demonstrted three phses of oxygen trnsfer for free overfll jet plunging into receiving pool. These re: (1) in the free overfll jet itself during fll this is regrded s smll; (2) vi the free surfce of the receiving wter this depends on the intensity of surfce gittion in the receiving pool; nd (3) in the ir-wter iphsic flow tht exists within the receiving pool ecuse of ir entrinment this phse is governed y the ir entrinment rte nd the ule contct time in the wter. Gmeson oserved tht the lst phse ws the most significnt contriutor to the oxygention process. The mechnisms y which ir is entrined nd trnsferred into wter ecuse of free overfll jet re severl nd complex. Ervine et l. (1980) descried four sic ir entrinment mechnisms with reference to circulr wter jets. Tsng (1987) dpted these to the current oservtions of free overfll jets from norml nd prllel weirs. Tsng (1987) clssified mechnisms of ir entrinment s: 1 smooth, 2 rough, 3 oscillting, nd 4 disintegrted. A description of these stges is given elow. c Fig. 2. Venturi weir: () side view, () pln view, (c) elevtion view.

4 756 BAYLAR Type 1 Type 1 results lrgely from smooth, solid jets (Fig. 3). The mjor source of ir supply is visulized s thin lyer surrounding the jet nd crried into the wter upon impct, nd therefore ir entrinment cpcity is limited. The wter surfce in the receiving pool is reltively undistured. Type 2 Type 2 results from rough, solid jets (Fig. 3). The ir supply cn e considered s coming lrgely from smll ir pockets entrpped etween the jet surfce roughness nd the receiving wter. At impct, the jet produces ripples on the receiving pool surfce. Compred to the Type 1 mechnism under similr conditions, this results in shllower ule penetrtion depth ut incresed entrinment rte, ecuse the ules re more densely pcked in the iphsic zone. Type 3 Type 3 results from oscillting jets nd those pproching disintegrtion (Fig. 3c). The primry ir source origintes from lrge ir pockets entrpped etween the undulting jet nd the receiving pool surfce. The receiving pool surfce is considerly gitted, nd ir my lso e entrined y surfce roller nd splshing. Lrge ir pockets re trnsported from the surfce into the wter nd roken down due to turulence. Type 4 Type 4 results from disintegrted jets (Fig. 3d). The receiving pool surfce is intensely gitted, nd ir is entrined y the ction of surfce rollers nd y engulfing ir pockets s jet frgments hit the receiving pool surfce. The ules re generlly only trnsported to reltively shllow depths. Disintegrted jets hve the dvntge over solid jets of greter surfce re; however, Q A nd ule penetrtion re significntly reduced ecuse of energy loss to the surrounding tmosphere during fll (Wormleton nd Tsng 2000). Experimentl Aertion experiments were conducted using n experimentl pprtus in the Hydrulic Lortory t the Engineering Fculty of Firt University, Elzig, Turkey. The free overfll jets from the weirs plunged into receiving pool, whose height could e djusted using pulley rrngement. The wter depth in the receiving pool ws controlled y n djustle weir. The pln-view dimensions of the receiving pool were m. The upstrem chnnel used in this study ws 3.40 m long, 0.60 m wide nd 0.50 m deep. The wter in the upstrem chnnel ws circulted y wter pump. The flow rte, Q, ws mesured using wter flow meter (Fig. 4). The flow rte over the weirs vried from to

5 THE USE OF VENTURI WEIRS AS AN AERATOR 757 c d Fig. 3. Bule genertion mechnisms y free overfll jets hving different mounts of turulence m 3 in m 3 steps. Drop height, h, defined s the difference etween the wter levels upstrem nd downstrem of the weir, ws vried etween 0.20 to 1.00 m in 0.20-m steps. In the experiments, Venturi nd rectngulr notch weirs, mde of metl, were used s ertors. Venturi weirs were plced t the upstrem chnnel end in order to increse flow velocity of the free overfll jet nd hence to increse the ir entrinment. The Venturi weirs hd converging Fig. 4. Sketch of experimentl pprtus.

6 758 BAYLAR level inlet section with verticl sidewlls nd diverging level outlet section lso with verticl sidewlls. There ws the shrp connection etween the converging section nd the diverging section. The Venturi weirs didn t hve ny prllel wlls forming stright throt. The throt width of the Venturi weir ws vried from 5 to 15 cm in 5-cm steps. The lengths of the converging section, L 1, nd the diverging section, L 2, were 25 nd 30 cm, respectively. The Venturi weirs hd verticl sidewll height, L 3, of 15 cm. The crest widths of the Venturi nd the rectngulr notch weirs were kept constnt t 20 cm in ll experiments (Fig. 5). The depth of the receiving pool cn ffect ertion efficiency of free overfll jet, ecuse oxygen mss trnsfer is to some degree dependent upon the residence time of the oxygen ules in the wter. If the receiving pool depth is less thn the ule penetrtion depth, the ules flow pth through the wter will e curtiled y the ed of the receiving pool nd residence time, nd hence ertion efficiency will e limited. This is confirmed y Jrvis (1970), Apted (1975), Avery (1976), nd Avery nd Novk (1978) who defined the receiving pool depth s optimum when it equled the ule penetrtion depth. At receiving pool depths greter thn the optimum vlue, the effect of receiving pool depth upon ertion ws very much reduced. Nksone (1987) dvised tht the receiving pool depth, D p, ceses to ffect ertion efficiency when it exceeds two-thirds of the drop height (i.e., D p 2/3 h), nd Avery nd Novk (1978) gve the reltionship s D p 7.5 h 0.58 F j -0.53, where h is drop height nd F j is jet Froude numer. Wormleton nd Tsng (2000) crried out series of experiments to scertin the penetrtion depth nd determine the effect of reltive receiving pool depth. They confirmed tht the ertion efficiency is reltively unffected y the receiving pool depth when it is greter thn the ule penetrtion depth. For consistency, ll tests reported in this pper were crried out under these conditions. In ll of the experiments for ll weirs, flow pths of entrined ir ules in the receiving pool Fig. 5. Venturi weir used in experiments.

7 THE USE OF VENTURI WEIRS AS AN AERATOR 759 were uninterrupted, i.e., the receiving pool depth ws greter thn the ule penetrtion depth. Since ir entrinment y wter jets occurs s loclized phenomenon t the plunging point, siclly two groups of methods of entrined ir flow rte mesurements were developed: 1) ctching ir fter it hs een entrined into the receiving pool wter; nd 2) mesuring the removl of ir from gseous spce ove the receiving pool surfce round the plunging point. To the first group elong experiments with free overfll jets from weirs, inclined plunging wter jets from nozzles, nd those in which ule trps hve een used. The second group is used in experiments with verticl plunging wter jets from nozzles nd orifices. The gseous spce ove the receiving pool in the vicinity of the plunging point is in this cse seprted from the mient, nd supplementry ir is let into this spce through n pproprite flow rte device (orifice, rotmeter, nemometer or from volumetric nd time redings). Trps or ir removl rrngements my interfere with the fluid flow in the receiving pool. However, since the ir entrinment phenomenon depends minly on the flow in the direct neighourhood of the plunging point, n pproprite sumergence nd geometry of the trp would not gretly ffect the mount of entrined ir. In this study, ule trp for which the pln-view dimensions were m, ws used to otin the vlues of Q A using n ir rotmeter instlled on its surfce. Experimentl Results The prime purpose of this study is to compre the ir entrinment rte of the Venturi weirs with the rectngulr notch weir under similr opertion conditions. The vlues of the ir entrinment rte were otined depending on drop height, h, unit dischrge, q, nd weir type. The following sections present nd discuss the free overfll jet expnsion t impct point, j, nd the ir entrinment rte results, Q A. The chnge in the free overfll jet expnsion, j, ws mesured s function of drop height, h, nd unit dischrge, q, s illustrted in Fig. 6 nd 7. It ws oserved from Fig. 6 nd 7 tht vrition in j is closely relted to drop height, unit dischrge, nd weir type. j incresed s unit dischrge incresed in ll experiments, s shown in Fig. 6. The Venturi weir with the throt width of 5 cm hd the gretest vlues of j. The vlues of j decresed s drop height incresed in the rectngulr notch weir nd the Venturi weirs with the throt width of 10 nd 15 cm. For the Venturi weir with the throt width of 5 cm, t low unit dischrges, nd m 3, j decresed s drop height incresed (Fig. 7 to 7) ut t high unit dischrges, nd m 3 /s m, j incresed s drop height incresed (Fig. 7c to 7d). The rectngulr notch weir showed the lowest vlues of j mong ll weir types tested. The primry reson for the increse in the free overfll jet expnsion with decresing the throt width of the Venturi weir cn e found y the increse in flow velocity over the Venturi weir nd the increse in the divergent ngle of the Venturi weir.

8 760 BAYLAR c d Fig. 6. Vrition in free overfll jet expnsion t impct point with drop height nd unit dischrge for () Venturi weir with B = 5 cm, () Venturi weir with B = 10 cm, (c) Venturi weir with B = 15 cm, nd (d) rectngulr notch weir. Figure 8 shows the vrition in the ir entrinment rte, Q A, of the Venturi nd the rectngulr notch weirs with the rtio of free overfll jet expnsion t impct point to drop height j /h for four unit dischrges, 5, 10, 15, nd m 3 /s m. For ll weir types tested, Q A incresed with decresing the j /h rtio. As unit dischrge incresed, the j /h rtio nd Q A incresed in the Venturi nd the rectngulr notch weirs. Moreover, Q A incresed with decresing the throt width of the Venturi weir. The rectngulr notch weir showed the lowest vlues of Q A mong ll weir types tested, s shown in Fig. 8. Figure 9 shows the vrition in the ir entrinment rte, Q A, of the Venturi nd the rectngulr notch weirs with drop height, h, nd unit dischrge, q. Figure 10 lso shows the vrition in the ir entrinment rte, Q A, of the Venturi nd rectngulr notch weirs with drop height while unit dischrge is constnt. All of these grphs show n increse in Q A s unit dischrge nd drop height incresed over the whole rnge of weir types tested. The results of experiments involving differing dischrges were fr less explicit thn those involving drop height. The increse in Q A with incres-

9 THE USE OF VENTURI WEIRS AS AN AERATOR 761 c d Fig. 7. Free overfll jet expnsion t impct point s function of drop height for Venturi nd rectngulr notch weirs; () q = m 3 /s m, () q = m 3 /s m, (c) q = m 3 /s m, nd (d) q = m 3 /s m. es in unit dischrge nd drop height cn e explined with the incresed momentum of the jet flow nd the incresed jet surfce roughness. The Venturi weirs hd the greter vlues of ir entrinment rte, Q A, thn the rectngulr notch weir, s illustrted in Fig. 10. The gretest vlues of Q A were oserved in the Venturi weir with the throt width of 5 cm. Q A decresed s the throt width of the Venturi weir incresed. As shown in Fig. 10, the rectngulr notch weir ws found to hve the lowest vlues of Q A mong ll weir types tested. The reson for this increse in the ir entrinment rte, Q A, of the Venturi weirs cn e found y the incresed flow velocity over the Venturi weirs nd the incresed contcting perimeter etween the jet flow nd the wter surfce due to the increse in free overfll jet expnsion. Regression nlyses were performed using the nonliner regression module. An empiricl correltion predicting ir entrinment rte, Q A, ws developed for the Venturi weirs. The resulting correltion is given in eqution 1. The correltion coefficient (R 2 ) for eqution 1 is 0.99 for the 60 dt points used. No reltionship for predicting the ir entrinment rte,

10 762 BAYLAR c d Fig. 8. Air entrinment rte s function of j/h for Venturi nd rectngulr notch weirs; () q = m 3 /s m, () q = m 3 /s m, (c) q = m 3 /s m, nd (d) q = m 3 /s m. Q A, of the rectngulr notch weir is presented ecuse of the poor performnce s n ertor. Q A = 0.055q L B (1) h L where the ir entrinment rte, Q A, is in m 3 /s, the dischrge per unit width, q, is in m 2 /s, the weir crest width, L, is in metres, the drop height, h, is in metres, nd the throt width of the Venturi weir, B, is in metres. The mesured ir entrinment rtes, Q A, were compred with those predicted with eqution 1. A good greement etween the mesured ir entrinment rtes nd the vlues computed from the predictive eqution ws otined. Further confidence in the correltion is seen in Fig. 11. Conclusions Bsed on the findings of this study, the following conclusions cn e drwn.

11 THE USE OF VENTURI WEIRS AS AN AERATOR 763 c d Fig. 9. Vrition in ir entrinment rte with drop height nd unit dischrge for () Venturi weir with B = 5 cm, () Venturi weir with B = 10 cm, (c) Venturi weir with B = 15 cm, nd (d) rectngulr notch weir. The ertion of wter downstrem of weirs is cused y ir eing crried y the free overfll jets into the receiving pool. The precise mechnism y which the ir is entrined into the receiving pool is extremely complex nd vries with free overfll jet velocity nd geometry. A series of lortory experiments ws crried out to investigte the effect of the free overfll jets from the Venturi nd rectngulr notch weirs on the ir entrinment rte. An empiricl eqution ws otined for the Venturi weirs relting ir entrinment rte to unit dischrge, weir crest width, drop height nd throt width of Venturi weir. There is perfect greement etween the oserved nd the clculted vlues. The results indicte tht drop height nd unit dischrge re importnt prmeters influencing the ir entrinment rte t the Venturi nd rectngulr notch weirs. The ir entrinment rte incresed with incresing drop height nd unit dischrge in ll weir types tested. The reson for this cn e explined with the incresed momentum of the jet flow nd the incresed jet surfce roughness.

12 764 BAYLAR c d Fig. 10. Air entrinment rte s function of drop height for Venturi nd rectngulr notch weirs; () q = m 3 /s m, () q = m 3 /s m, (c) q = m 3 /s m, nd (d) q = m 3 /s m. Fig. 11. Comprison of ir entrinment rte in Venturi weirs etween oserved nd clculted vlues.

13 THE USE OF VENTURI WEIRS AS AN AERATOR 765 The free overfll jet expnsion for the Venturi weirs ecme greter thn the rectngulr notch weir. The free overfll jet expnsion incresed s the throt width of the Venturi weir ws decresed. The reson for this is due to the increse in flow velocity over the Venturi weir nd the increse in the divergent ngle of the Venturi weir with decresing the throt width of the Venturi weir. Incresing free overfll jet expnsion led to higher ir entrinment rte due to the incresed contcting perimeter of the jet flow. The Venturi weirs were shown to hve significntly etter ir entrinment rte thn the rectngulr notch weir. The ir entrinment rte incresed s the throt width of the Venturi weirs ws decresed. This increse resulted from not only the incresed contcting perimeter in impct point due to the increse in the free overfll jet expnsion, ut lso the incresed flow velocity over the Venturi weir. Therefore, using simple Venturi weir would significntly increse the ir entrinment rte. The Venturi weirs cn e used s highly effective ertors in strems, rivers, constructed chnnels, fish htcheries, wter tretment plnts, etc. For very wide chnnels, multiple Venturi weirs cn e used insted of single Venturi weir. The Venturi weir with its level floor nd simple inlet nd exit could esily e constructed nd instlled in lmost ny field sitution. Moreover, low construction, opertion nd mintennce costs of Venturi weirs would give it the cler dvntge in ertion processes. Initilly, the free overfll jet with reltively smooth surfce would issue from the Venturi weir. As the drop height increses, the surfce of the free overfll jet would first ecome roughened nd then the free overfll jet would oscillte during fll. With incresing drop height, the free overfll jet eventully would rek up into discrete droplets. The rekup lengths would e shorter for lower dischrges. The rekup of the free overfll jet would reduce its penetrtion depth into the receiving pool nd hence lso the depth of the iphsic zone. This would effectively reduce contct time etween the ules nd the surrounding wter nd hence lso ertion efficiency. In this cse, cscde Venturi weir would e dvised insted of single Venturi weir. For ny model study involving ir entrinment, the scling of ertion dt to prototype size is virtully impossile, lrgely due to the reltive invrince of ule size. The experiments descried in this pper cn cover unit dischrges tht re smller thn some prototype pplictions, lthough the drop heights re generlly similr to prototype scle. The results indicted tht the ir entrinment rte in Venturi weirs incresed t ll drop heights tested s the unit dischrge incresed. Clerly, tests t higher unit dischrges should e crried out to see if this trend extrpoltes.

14 766 BAYLAR Acknowledgements Finncil support for this work ws provided y Firt University Scientific Reserch Projects (FUBAP). Thnks to Ftih Ulger for his ssistnce nd dvice during the experiments. References Apted RW The mechnics of ertion t weirs with specil reference to river qulity. M.Sc. thesis, University of Newcstle upon Tyne, Newcstle upon Tyne, U.K. Apted RW, Novk P Some studies of oxygen uptke t weirs, p In Proceedings of the XV Congress, Pper B 23, Interntionl Assocition for Hydrulic Reserch, IAHR, Istnul, Turkey. Avery S The trnsfer of oxygen from ir entrined y jets entering free wter recipient. Ph.D. thesis, University of Newcstle upon Tyne, Newcstle upon Tyne, U.K. Avery S, Novk P Oxygen trnsfer t hydrulic structures. J. Hydrul. Div. 104(HY11): Bylr A, Bgtur T Aertion performnce of weirs. Wter SA 26(4): Bylr A, Bgtur T, Tun A Aertion performnce of tringulr-notch weirs. J. Chrtered Institution Wter Environ. Mnge. 15(3): Bylr A, Emiroglu ME The effect of shrp-crested weir shpe on ir entrinment. Cn. J. Civil Eng. 29(3): Chnson H Predicting oxygen content downstrem of weirs, spillwys nd wterwys, p In Proceedings of the Institution of Civil Engineers Wter, Mritime nd Energy, 112, Mrch. Ervine DA Air entrinment in hydrulic structures: review, p In Proceedings of the Institution of Civil Engineers Wter, Mritime nd Energy, 130, Septemer. Ervine DA, McKeogh EJ, Elswy EM Effect of turulence intensity on the rte of ir entrinment y plunging wter jets, p In Proceedings of the Institution of Civil Engineers, Prt 2, 69. Gmeson ALH Weirs nd ertion of rivers. J. Instit. Wter Engineers 11(5): Gulliver JS, Wilhelms SC, Prkhill KL Predictive cpilities in oxygen trnsfer t hydrulics structures. J. Hydrul. Eng. 124(7): Jrvis PJ A study of the mechnics of ertion t weirs. M.Sc. thesis, University of Newcstle upon Tyne, Newcstle upon Tyne, U.K. Nksone H Study of ertion t weirs nd cscdes. J. Environ. Eng. 113(1): Tsng CC Hydrulic nd ertion performnce of lyrinth weirs. Ph.D. thesis, University of London. Vn der Kroon GTN, Schrm AH Weir ertion - Prt I. H 2O 22: Vn der Kroon GTN, Schrm AH Weir ertion - Prt II. H 2O 22: Wilhelms SC, Gulliver JS, Prkhill K Reertion t low-hed hydrulic structures. Technicl Report No. W U.S. Army Corps of Engineers Wterwys Experiment Sttion, Vicksurg, Miss.

15 THE USE OF VENTURI WEIRS AS AN AERATOR 767 Wormleton PR, Soufini E Aertion performnce of tringulr plnform lyrinth weirs. J. Environ. Eng. 124(8): Wormleton PR, Tsng CC Aertion performnce of rectngulr plnform lyrinth weirs. J. Environ. Eng. 126(5): Received: July 5, 2002; ccepted: July 8, Nomenclture A j B D p F j h h t L L 1, L 2 L 3 q Q A t c V Are of ir-wter interfce. Free overfll jet expnsion. Throt width of Venturi weir. Bule penetrtion depth. Jet Froude numer. Drop height. Tilwter depth. Weir crest width. Converging nd diverging lengths of Venturi weir. Verticl sidewll height of Venturi weir. Dischrge per unit width. Air entrinment rte. Air-wter contct time. Volume of ir entrined.