Real-Time Ultrasonic Measurement Technique for Monitoring Suspended. Sediment Concentration in Reservoirs

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1 Real-Time Ultraonic Meaurement Technique or Monitoring Supended Sediment Concentration in Reervoir Tetuya Sumi Univerity o Kyoto, Kyoto, Japan Yu-Jun Huang, Chia-Chi Sung, Jihn-Sung Lai, Fong-Zuo Lee, Yih-Chi Tan Hydrotech Reearch Intitute, NTU, Taipei City, Taiwan adamhuang@ntu.edu.tw ABSTRACT: During typhoon lood or raintorm eaon, river uually carry great amount o upended ediment lowing into reervoir. High concentration o ediment current pread out in all direction in the reervoir, which not only reduce reervoir' lie pan but alo create treatment problem in the water upply plant. For reervoir operation, real-time monitoring o ediment concentration in the turbidity current ha received igniicant attention rom reervoir deiltation operation in Taiwan. Ultraonic pectrocopy i highly uitable or real-time meaurement, in particular or dene particle ytem. In the preent tudy, an automatic ultraonic meaurement ytem i deigned and abricated or meauring olid upenion concentration with repect to the propagation o ultraound wave in olid-liquid mixture in ite. The meaurement obtained by ultraonic meaurement technique or ediment concentration in turbidity current during 009 typhoon lood in the reervoir how good agreement with the ampled data. It ha been demontrated that the ultraonic meaurement technique i operative and trutworthy in ite with harh working environment. In the uture, the ediment yield in the reervoir waterhed may be aected by global climate change in the long term. The ultraonic device develop ha taken the high upended ediment concentration meaurement into account. Keyword: ediment concentration, ultraonic, attenuation, real-time 1. INTRODUCTION During typhoon lood or torrential rain eaon, river uually carry great amount o upended ediment lowing into reervoir rom it waterhed. High concentration o ediment-laden may orm a turbidity current in the reervoir, which not only reduce reervoir capacity but alo create water treatment problem or the water upply plant. For intance, it wa oberved that the ediment concentration ampled near the intake entrance in the Shihmen reervoir, Taiwan, wa recorded up to.4 x 10 5 ppm during Typhoon Aere (004). Recent growing interet in ediment concentration monitoring by uing ultraonic diagnotic method i baed on attenuation pectrometry. Sound wave attenuation through dipered phae upenion o a continuou econd phae material could be ued to characterize upenion. The concentration meauring range o commercial intrument uing traditional light cattering method i uually only up to 30,000 ppm. Ultraonic method advantageouly penetrate optically opaque mixture. Spectrometer reult error, caued by particle ize, temperature, and trapped air bubble, trongly aect ultraonic ignal, but can be overcome by good meauring ytem deign. Urick irt conidered the ound aborption problem in upenion o one material or another. McClement olved ultraonic attenuation with a tre-train relation and equation o

2 tate uing a boundary condition erie expanion at the ingle particle urace, reviewed by Allegra and Hawley. The Harker and Temple coupled-phae upenion model calculated ultraonic attenuation in upenion. All ultraonic method intended or liquid low meaurement include everal procee: tranmiion, propagation and reception o ultraonic wave, ignal conditioning, and data proceing. During the procee, determining ultraonic velocity in a movable liquid i the ultimate goal. Relative velocity i motly meaured. Ultraonic method can be ucceully implemented in a liquid low meaurement becaue they have atiactory tability, a wide dynamic range, and allow velocity meaurement o electrical conductive and nonconductive liquid both in clean and impure liquid. Although an ultraonic ytem ha a concentration meaurement advantage, it provide only tranmitting and receiving ignal. In the preent tudy, a novel portable ultraonic device wa deigned and manuactured or real-time ediment concentration and low velocity meaurement in the ield. A erie o experiment were conducted uing kaolin and reervoir ediment within a wide range o concentration up to 300,000 ppm at variou temperature. The experimental data were compared with the numerical reult calculated by the coupled-phae model propoed by Harker and Templeto examine the eect o the particle ize ditribution. Regreed relationhip o concentration were alo contructed a a unction o attenuation and temperature. Through laboratory tet or calibration and validation and had been ucceully employed to meaure ediment concentration and low velocity (timedierence method by ultraonic probe) along water column during typhoon lood in the Shihmen reervoir, Taiwan. model aume no gravitational ield, nor heat or ma traner between phae. For brevity, we deine /, in which δ i the vicou kin depth, η i vicoity, ω i the angular requency o the ocillation, and u denote luid local velocity. In a olid particle upenion, each particle o denity i aumed to be uniorm, pherical, and o radiu a. The continuity equation are written a ( ) ( u ) 0 (1) t z [( 1 ) ] [(1 ) u ] 0 () t z Equating the um o related orce to the particle momentum change rate give ( u ) u t 9 [ ] u 4 a a [(1 ) u t 9 [ 4 a a 1 9 dur ( u ) ( ) z (1 ) 4a dt r ] u p ( ) z ] u r [(1 ) u z p ( )( 1) z (3) 1 9 dur ] ( ) (1 ) 4a dt (4) where u i the moving particle velocity, i the luid denity, and u r = u - u denote relative velocity i the particle volume raction, and p denote luid preure. We aume variation only in the z direction, and a upenion uiciently dene to be treated a a volumeaveraged continuum. Equation 1 to 4 can be olved uing a wave-like olution. The complex ultraonic wave number k derived i expreed a ollow [7]:. THEORY k [(1 ) [ (1 S) S(1 )] ]{ } (1 ) [ S (1 )] The coupled-phae model wa propoed by Harker and Temple [7] to analyze wave propagation in a two-phae mixture. The model i contructed by our governing dierential equation in a ytem coniting o two continuity equation, Eq. 1 and, the drag on one phae by the other in Eq. 3, and the momentum equation conervation or a olid-liquid mixture in Eq. 4. The (5) Where i luid phae compreibility, and i olid phae compreibility. S i a complex quantity given by S ( ) i ( ) (6) 1 4a 4 a a

3 Once the complex wave number k i obtained, attenuation α and velocity c can be calculated rom k i. c Apparently, attenuation depend on the particle volume raction, the luid vicoity, the particle radiu a and the requency. The coupled-phae model in Eq. 1 to 4 i idealized in a orm containing only particle o a ingle ize in the olid-liquid mixture. Experimental veriication o thi theory require monodipere ediment that are diicult to ue commercial product in preparation procee. Additionally, ediment ampled rom the ield contain naturally varying ize o particle. Thereore, it i neceary to extend the applicability o thi model by taking the ditribution o particle ize into account. Thu, attenuation or ediment with variou particle ize obtained by the laer ize analyzer (Materizer 000, Malvern Intrument Limited, UK) i approximated by dividing equally the ize ditribution into i raction, and obtaining it correponding percentage o weight rom the ditribution curve. The reulting attenuation with variou particle ize i expreed a izi (7) i where index i denote the et o particle radiu by the ize analyzer, αi i the attenuation o et i, and Zi i the weight percentage o et i. The weight percentage or i et i deined a mi Zi (8) W where mi i the particle weight o et i, and W i the total weight o the mixture. The particle weight and volume o et i are written, repectively, a 4 mi a 3 mi i ni vi ai ni ; 3 (9) where a i the ize o et i, and ni i the particle i number o et i. Finally, we obtain the modiied expreion or attenuation a ollow. ni 3 iwmi i i N i 4Na 3 i (10) where N i the total number o particle in the olid upenion. 3. MEASUREMENT SYSTEMS AND EXPERIMENTS Two meaurement ytem, a model-typed device and a portable ultraonic device (PUD), are introduced in thi ection. The model-typed device deigned or concentration meaurement in the laboratory, while the PUD i a prototype deigned or meauring both concentration and velocity in the ield. For meauring concentration, both o them have the ame deigned ytem keeping the ame ditance between probe. The model-typed device i deigned or real-time meaurement o olid upenion concentration in the laboratory. Figure 1 illutrate the main part o a tandard piezoelectric tranducer or generating longitudinal ultraound. When it i being ued a a tranmitter, a uitably varying voltage caue the piezoelectric dic to behave a a piton radiator and generate a ound wave in the load, i.e., the medium in the ront o the ace o the tranducer. The model-typed device i baically ued or calibrating the temperature and preure enor, etimating the eect o air bubble, regulating the peed o the tirring machine, teting the perormance o the piezoelectric tranducer, and obtaining the regreion unction or peciic ediment in the laboratory. With a probe holder keeping the ditance o 0.16m between probe, the model-typed device hown in Fig. 3 i calibrated by uing variou concentration ample to obtain the regreion unction or dierent ediment. The operating concentration range i rom 1,000 to 300,000 ppm with reolution o 00 ppm. Meaurement accuracy i ±% and ±5% at concentration range le than 50,000 ppm and greater than 50,000 ppm, repectively. The prototype device, wa deigned and manuactured or real-time monitoring o olid upenion concentration and low velocity in the ield. All the electronic circuit and tranducer in the portable ultraonic device have the ame element a thoe in the model-typed device. A hown in Fig. 3, the PUD i 0.75 m in length and 0.5 m in diameter with two pair o probe. The ditance between probe are 0.16 m (i.e. ame a that o the model-typed device) and 0.46m or concentration and low velocity meaurement, repectively. The low velocity meaurement range i ±3

4 m/ec with a reolution o 0.01 m/ec, and it accuracy i ±0.01 m/ec and ±% or velocity range < 0.5 m/ec and 0.5 ~ 3 m/ec, repectively. Cable Cae Backing (damping) Piezoelectric dic Front ace (impedance matching layer) Electrode on ace o piezoelectric dic Figure 1. The deign o a tandard probe. rpm to enure well-mixed upenion without depoition. It wa ound that there wa no dierence in attenuation meaurement by operating the tirrer at variou peed, and thi wa alo reported by Jame and Richard (1999). The temperature wa decreaed rom ambient to 15 o C (the lowet temperature recorded during typhoon lood in the Shihmen reervoir) by circulating Freon through a coil intalled near the cell bottom. A 1 MHz and 30- cycle tone burt wa generated a an ultraonic ignal. The energy lo between tranmitter and receiver wa meaured to obtain ultraonic attenuation. Cooling ytem Meaurement ytem Stirrer Stirrer 0.16m Figure. The model-typed device and it probe holder or concentration meaurement in the laboratory. Flowmeter probe Rear in Tranmitter Receiver Figure 4. Experimental etup Laptop 0.46m 0.75m 0.16m Cable Concentration probe Figure 3. The PUD or both concentration and low velocity meaurement in the ield. The layout o the experimental etup i hown in Fig. 4. The central requency o probe wa 1MHz, and the ditance between tranmitter and receiver wa 0.16m. The experiment were conducted in a 0.6 m long, 0.5 m wide and 0.5 m tall plexigla cell equipped with two variable-peed mechanical tirrer to maintain a homogeneou particle upenion in the liquid. A ourblade propeller (45 pitch) o 0. m diameter provided agitation and wa placed at 0.05 m above the cell bottom. The tirrer rotation rate wa operated rom 500 to SELF-CONFIRMATION TESTS FOR MEASUREMENT SYSTEM The entire component o meauring concentration in the PUD are the ame a there in the model-type device, except the packing. In order to veriy the accuracy o concentration meaurement by adopting the regreion unction in the PUD, a circular tank with a high power tirrer wa et up. Figure 5 how the experimental coniguration and the ampling poition in the tank. The PUD wa placed at the location between pt. A and pt. B during experiment. 1. m 0.m 0.m 1.5 m 0.m 0.m 0.m (a) B1 A1 B A B3 A3 B A Stirrer (b)

5 Figure 5. Coniguration o the circular tank and ampling poition een a (a) ide view (b) top view Table 1 how the reult o concentration meaurement by PUD in the circular tank, compared with ampling reult ater extraction and oven drying. For each run, the data obtained rom dierent ampling poition by extraction uing a iphon were very cloe. It indicate that the olution wa well-mixed in the tank. The averaged error between meaurement and extraction reult wa 5%, which would be attributable to the ytem error and could be oet. Table 1. Concentration meaurement by PUD compared with thoe o extraction ample at 5 o C Run No Sampling Poition Extraction ample (ppm) Meaurement by PUD (ppm) Error A % A % A % B % B % B % A % A % A % B % B % B % A % A % A % B % B % B % A % A % A % B % B % B % Figure 6 how the photo o the 150 m long, 10 m wide and 6 m deep towing tank with a carriage. In the experiment, the peed o the carriage wa controlled a the tandard peed and varied rom 0 to 3 m/ec in tep o 0.5 m/ec. The PUD wa mounted on the carriage and immered in water, 1 m deep, to meaure low velocity. Table lit the comparion o low velocity by PUD and the tandard peed by carriage to preent very good agreement. The error in all tet run are le than %. Figure 6. Photo o the (a) PUD mounted on the carriage (b) the towing tank Table. Flow velocity meaurement by PUD, compared with tandard peed Run No Standard peed (m/ec) Meaurement (m/ec) Error 0.0% -.0% 1.0% 0.0% -.0% -0.8% -1.0% 5. FIELD MEASUREMENT RESULTS Due to dangerou working condition, it i uually impoible to conduct meaurement on hip during typhoon lood in a reervoir. Fortunately, we had the opportunity to perorm real-time ield meaurement by PUD in the Shihmen reervoir during Typhoon Jangmi on September 30 in 008, while wind and low were relatively low. The Shihmen reervoir i one o the two major multipurpoe reervoir in northern Taiwan, which erve purpoe including lood control, water upply, immigration and power generation. Figure 7 how that the PUD wa operated by a motor-driven crane mounted on the hip. The PUD wa irt lowered into the water and near to the bottom; aterward, the PUD wa lited gradually. A the PUD wa continuouly lited up rom bottom to urace, the ample o reervoir ediment olution were collected at everal peciic poition or

6 validation o the meaured data. The ampling time o the PUD wa ec to obtain time-averaged concentration and velocity, while the preure (in term o depth) and temperature were imultaneouly recorded with concentration. The ediment olution ample were taken by a ediment ampler controlled by an electromagnetic valve, and the concentration o each ample wa obtained later by oven drying in laboratory. Figure 8. Meaured data (008/9/8/1pm) by PUD and ampled data at the loating barrier in the Shihmen reervoir Figure 7. Operation o PUD in the Shihmen reervoir The data taken were collected by PUD at Lungchu Bay and the loating barrier, located 4 km and 7 km rom the dam, repectively, in the Shihmen reervoir during Typhoon Jangmi. A hown in Fig. 8, the meaured ediment concentration how very good agreement with ampled one. The vertical proile o ediment concentration indicate that the turbidity current body (inner region) had about 5 m deep above the bottom and the highet concentration wa recorded near the bottom o the reervoir. The low velocitie meaured are plotted together with the data taken by a D electronic current meter (ACM-RS, ALEC CO., LTD.). In Fig. 9, the vertical velocity proile o turbidity current ha a maximum velocity in it inner region (inide the body o the turbidity current), directed downtream; in the outer region the uptream velocity relect the backlow o ambient luid in till reervoir water. Figure 9. Velocity proile data (008/9/8/1pm) by PUD at the loating barrier in the Shihmen reervoir 6. CONCLUSIONS In ummary, the modiied coupled phae model (ultraound propagation in particulate mixture model) i ued in thi reearch. The theoretical attenuation by weight percentage ha better conitency with experiment reult. The particle ize radiu dominate the attenuation lope, cauing a light dierence between prediction reult and meaurement reult. Attenuation or both theoretical reult increae with increaing concentration and decreaing particle ize.the good experimental reult were ound by employing PUD or ediment concentration and low velocity meaurement in turbidity current during Typhoon Sinlaku and Jangmi lood in Shihmen reervoir, which demontrate that the PUD i operative and trutworthy on ite.

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