Measurement System of Bubbly Flow Using Ultrasonic Velocity Profile Monitor and Video Data Processing Unit, (II)

Transcription

1 Journal of Nulear Siene and Tehnology SSN: (Print) (Online) Journal homepage: Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor and Video Data Proessing Unit, () Masanori ARTOM, Shirong ZHOU, Makoto NAKAJMA, Yasushi TAKEDA & Mihitsugu MOR To ite this artile: Masanori ARTOM, Shirong ZHOU, Makoto NAKAJMA, Yasushi TAKEDA & Mihitsugu MOR (1997) Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor and Video Data Proessing Unit, (), Journal of Nulear Siene and Tehnology, 34:8, , DO: 1.18/ To link to this artile: Published online: 15 Mar 212. Submit your artile to this journal Artile views: 17 View related artiles Citing artiles: 4 View iting artiles Full Terms & Conditions of aess and use an be found at

2 Journal of NUCLEAR SCENCE and TECHNOLOGY, Vol. 34, No. 8, p (August 1997) Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor and Video Data Proessing Unit, () Flow Charateristis of Bubbly Counterurrent Flow Masanori ARTOM*t, Shirong ZHOU*, Makoto NAKAJMA**, Yasushi TAKEDA:* and Mihitsugu Moru:: * Researh Laboratory for Nulear Reators, Tokyo nstitute of Tehnology ** Mitsubishi Heavy ndustry Company!*Paul Sherrer nstitute!! Tokyo Eletri Power Company (Reeived Deember 25, 1996) The authors have developed a measurement system whih is omposed of an ultrasoni veloity profile monitor and a video data proessing unit in order to larify its multi-dimensional flow harateristis in bubbly flows and to offer a data base to validate numerial odes for multi-dimensional two-phase flow. n this paper, the measurement system was applied for bubbly ounterurrent flows in a vertial retangular hannel. At first, both bubble and water veloity profiles and void fration profiles in the hannel were investigated statistially. Next, turbulene intensity in a ontinuous liquid phase was defined as a standard deviation of veloity flutuation, and the two-phase multiplier profile of turbulene intensity in the hannel was larified as a ratio of the standard deviation of flow flutuation in a bubbly ounterurrent flow to that in a water single phase flow. Finally, the distribution parameter and drift veloity used in the drift flux model for bubbly ounterurrent flows were alulated from the obtained veloity profiles of both phases and void fration profile, and were ompared with the orrelation proposed for bubbly ounterurrent flows. KEYWORDS: two-phase ftow, measurement system, multi-dimensional ftow, ultrasoni veloity profile monitor, video data proessing unit, bubbly ounterurrent ftow, veloity profile, void fration, two-phase multiplier, turbulene intensity, probability density funtion, drift ftux model, omparative evaluations. NTRODUCTON n the study of two-phase flow, the knowledge of bubbly and liquid veloities is required for better understanding of transport phenomena in two-phase flow systems. The void fration is the most important parameter for engineering use, e.g. for the design of nulear reators, steam boilers, evaporating equipment, refrigerating equipment, et. Reently, many onepts of future light water reators (LWRs), in whih passive and simplified safety funtions are positively introdued into their safety features, have been proposed suh as the AP- 6 design(!) and the SBWR design( 2 ) in order to redue their onstrution ost, to improve their reliability and maintainability and so on. However, sine passive safety features are funtioned by the law of nature, the driving fore indued by them is muh smaller than that indued by ative ones. Multi-dimensional two-phase * Ohokayam.a, Meguro-ku, Tokyo 152. ** Wadasaki-m.ahi, Hyogo-ku, Kobe 652.!* Wurenlingen and Villigen, CH-5232, Villigen, SWTZERLAND. :: Uhisaiwai-ho, Chiyoda-ku, Tokyo 1. t Corresponding author, Tel , Fax , maritomi@nr.titeh.a.jp flow may, therefore, appear after their safety features are ativated. Consequently, it is neessary with regard to passive safety features to be able to simulate multidimensional harateristis even for the two-phase flow whih an be regarded as one dimensional flow for ative ones. The two-phase flow shows essentially multi-dimensional harateristis even in a simple hannel. The safety analysis odes suh as the TRAC( 3 ) and RELAP5( 4 l treat the flow basially as one dimensional flow and introdue multi-dimensional onvetion effets in a marosopi way due to a lak of a fundamental data base for establishing the model of multi-dimensional two-phase flow dynamis. Therefore, it is one of the important problems to establish analytial methods of multi-dimensional twophase flow to verify analytially the effetiveness of passive safety features. t is also one of the most important subjets in the researh of two-phase flow dynamis to larify its multi-dimensional flow harateristis. Measurement methods of two-phase flow harateristis were reviewed in our previous paper( 5 ). The authors have developed a new measurement system omposed of an Ultrasoni Veloity Profile Monitor (UVP) and a Video Data Proessing Unit (VDP)( 5 ), whih an measure simultaneously the multi-dimensional flow hara- 783

3 784 M. ARTOM et al. teristis of bubbly flows suh as veloity profiles of both gas and liquid phases and a void fration profile in a hannel, an average bubble diameter and an average void fration. n this work, the proposed measurement system was applied to fully developed bubbly ounterurrent flows in a vertial retangular hannel in order to verify its apability and to understand multi-dimensional flow harateristis in bubbly ounterurrent flows. At first, both bubble and water veloity profiles and void fration profiles in the hannel were investigated statistially under various onditions of both gas and liquid phase flow rates. n addition, turbulene intensity in a ontinuous liquid phase was defined as a standard deviation of veloity flutuation, and the two-phase multiplier profile of turbulene intensity in the hannel was larified as a ratio of the standard deviation of flow flutuation in a bubbly ounterurrent flow to that in a water single phase flow. Finally, onerning the drift flux model, the distribution parameter and the drift veloity were alulated diretly from these measured profiles.. EXPERMENTAL APPARATUS AND DATA PROCESSNG METHOD 1. Experimental Apparatus Figure 1 shows a shemati diagram of an experimental apparatus. Air and water were used as working fluids. The experimental apparatus was omposed of a water irulation system, an air supply system, a test setion and a measurement system. The test setion was a vertial retangular hannel of 1 mm in width, 1 mm in deep and 5 mm in height made of Plexiglas as shown in Fig. 2. The measurement system onsisted of the UVP, the VDP and a personal omputer to reord and treat data. Water was fed into the upper tank and flowed downward in the test setion. The water level in an upper tank was kept onstant with an overflow nozzle whih was onneted to a lower feedwater tank. The flow rate was measured by an orifie flowmeter and regulated by a flow ontrol valve whih was installed at the downstream Fig. 1 :.... :: to feed water tank.".".: Test setion A shemati diagram of experimental apparatus A B C DE i o; ; ;! US : Ultrasoni Measuring line US transduer A-E : Measuring points 1 unit: mm Fig. 2 Test setion end of the test setion. Adopting this flow ontrol system, the water flow rate ould be kept onstant for hours. Miro partiles of Nylon powder were suspended in water to reflet ultrasoni pulses. Water temperature was kept onstant by a subooler. The air supply system onsisted of a ompressor and a pressure regulation valve. Bubbles were injeted from three needles loated near the bottom of the hannel. The air flow rate was measured by a float flowmeter and regulated by another flow ontrol valve. As a result, the air flow rate ould be kept onstant for hours. Pressure transduers and thermoouples were installed at several points in the loop to monitor the flow ondition. A personal omputer aquired the readings from these sensors for an on-line ontrol of the experimental ondition. An ultrasoni transduer was installed on the outside surfae of the front wall of the hannel with a ontat angle (9) of 45 and a gap between the transduer and the wall was filled with a jelly to prevent a refletion of ultrasoni pulses on the wall surfae as shown in Fig. 2. After both air and water flow rates were set up at the desired values, 9,216 (1,24x9) veloity profiles along a measured line were measured by the UVP under one experimental ondition to treat them statistially. t takes about 3 minutes to get them. The hydrostati head was simultaneously measured as a pressure drop between the pressure taps installed on the side wall using a differential pressure transduer to get an averaged void fration. A video amera equipment onsists of an 8 mm video amera, a light soure and a transluent sheet to unify the luminane brightness. The speed of 6 frames per seond an be obtained. After the proess was videotaped, the video digital data were reorded in a personal omputer through an image onverter. The piture elements are 64x24 dots, the olor is monotone, and the brightness resolution is 1/256. Sine the detailed information about the data-handling method of the VDP was reported in our previous paper< 5 l, its outline is desribed in this paper. To modify uneven brightness in the whole piture, the piture in a liquid single phase flow was taken as a standard one, and the differential piture of a bubbly flow was made by subtrating a brightness value obtained from the standard one. The data of the differential piture 1 JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

4 Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor 785 were onverted into two-valued variables, and 1, by a threshold value: means a liquid phase and 1 does the interfae. Variables at every point in the inside surrounded by the interfae were replaed with 1. For a narrow hannel and a low void fration, assuming that bubbles were not overlapped in the measured line and that the horizontal ross setion of eah bubble was a irle, the number of bubbles in a ontrol volume was ounted, eah bubble volume was alulated and the average void fration in the hannel was obtained by summing them. Assuming that a bubble was spherial, an average bubble diameter was obtained from the number of bubbles and the sum of the bubble volume in the ontrol volume. n this work, 5 measuring points were adopted and the results showed that the veloity profiles of the bubbly ounterurrent flow in entral 3 measuring points were almost same, the veloities near the wall 2 measuring points were a little lower than those in entral 3 measuring points. Therefore, the veloity profiles of 5 measuring points were measured to alulate loal void fration profiles. The experimental onditions are tabulated in Table Data Proessing Method Sine the detailed information of the proposed measurement system was also reported in our previous work< 5 l, its measurement priniple is not desribed and data proessing method will be further illustrated in this paper. As the sound speed of the longitudinal wave is the most fundamental parameter for this method, it is not possible to treat a two-phase medium as a homogeneous single phase medium. Figure 3 shows typial patterns of veloity profiles, Fig. 3( a) displays a typial result of Table 1 System pressure Water superfiial veloity Air superfiial veloity Experimental onditions Atmospheri pressure -.6, -.12m/s m/s a measuring ultrasoni beam without bubbles. Fig. 3(b) shows a typial result of a measuring ultrasoni beam with single bubble and Fig. 3( ) indiates a typial result of a measuring ultrasoni beam with multiple refletion. Sine the eho of the ultrasoni pulse from the partile suspended in water is very weak intensity, multiple refletion does not appear among the partiles. This fat is onfirmed from measurement of veloity profiles in a water single phase flow. However, the eho from the bubble surfae is not weak. Therefore, if the pulse intensity is strong, multiple refletion ours between the bubble surfae and the partiles. At first, we tried to optimize the pulse intensity as the lower value whose the eho from the partile an be deteted. For this optimized pulse intensity, multiple refletion is not indued between the bubble surfae and the partiles. This optimization was onfirmed from measurement in bubbly ounterurrent flows as shown in Fig. 3(b). As a rule, beause a sound wave experienes multiple refletion among bubbles and its path returning to the transduer annot be straight as shown in Fig. 4. t is however possible to obtain veloity profiles of liquid phase until the position of the nearest bubble from the transduer. Therefore, the authors attempted to derive information from eah individual profiles by analyzing their shapes. Sine the veloity information is derived from Doppler shift frequeny, no data must be available for the wall whih is at rest. The diameter of an ultrasoni pulse beam is 5 mm and an UVP transduer must be inlined to the wall in order to measure veloities in the flow diretion. Figure 5 shows a typial result of frequeny of data existene in different setting angles of transduer to the wall. t is diffiult to determine the wall position D Fig. 4 A multiple refletion pattern Cii. E :::l <: Cii. E :::l <: Cii. E :::l <: Qi > Position number Position number Position number (a) Without bubbles (b) Single bubble () Multiple refletion 4 Fig. 3 A typial pattern of veloity profiles VOL. 34, NO. 8, AUGUST 1997

5 786 M. ARTOM et al. diretly from the UVP data. The enter of the hannel is determined from measurement of a veloity profile in water laminar flows. The wall position was evaluated from the sound speed of water. t is therefore possible to identify the wall position in the profile themselves. n pratie, the wall position is defined as a loation where the probability of data existene is 5% in liquid single phase flow as shown in Fig. 5. Sine the diameter of an ultrasoni pulse is 5 mm, the measuring ross setion of an ultrasoni pulse is a irular one in main flow region as shown in Fig. 6 and the eho of the ultrasoni pulse an be ompletely measured in the form of the irulru: ross setion. However, the measuring ross setion of the ultrasoni pulse was not a irular one near the wall region as shown in Fig. 6 and the eho of the ultrasoni pulse annot be ompletely measured in the form of the irular ross setion. Consequently, the measured position information near the wall region should be orreted. Figure 6 shows the measuring ross setion of the ultrasoni beam in B-B position. Sine the statistial average position of the measuring ross setion of an ultrasoni pulse is not the enter of the ultrasoni pulse near the wall region beause the ultrasoni beam annot be ompletely refleted in the form of the irular ross setion. Assuming that the statistial average position C-C of the measuring ross setion of an ultrasoni pulse divide the measuring ross setion up two equal part. The statistial average position C-C is determined by and S 8 = 1rR 2 - ((3R 2 - R 2 sin(3os(3), S = 1R 2 - S = Sa/2, R 2 sin 1 os/, where S 8 is the measuring ross setion area of an ultrasoni beam in B-B position, R is the radius of ultrasoni beam, and S, (3 and 1 are shown in Fig. 6. From Eqs. (1), (2) and (3), (3 and 1 are alulated numerially by the Newton's method. Thus, an aurate statistial average position C-C an be obtained. The data at the position where measuring ross setion area is less than (1) (2) (3) Fig. 6 -f L _ ' "' 'Measuring line -- The measuring ross setion of the ultrasoni beam 5% of the whole ultrasoni beam one are omitted. The measurement error of the wall position is estimated as ±.1 mm and the measurement error of the loation is estimated as ±.6 mm. A probability density funtion inludes the veloity information of both phases. t is assumed that eah probability density funtion of both phases an be expressed by a normal distribution as follows: N[u, a 2 ](u) = exp [ (u- ) 2 ]. V27ra2 2a The probability density funtion of mixture veloity is given by (4) o Single phase flow Two phase flow o Single phase flow Two phase flow o Single phase flow Two phase flow Position Number Position Number Position Number 8= 45' Fig. 5 8= 6' 8= 75' Definition of the wall position JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

6 Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor 787 Pu(Y, u) = (y)n[ua(y), o};(y)](u) + (1- (y))n[ul(y), ai,{y)](u). (5) where iia, U, aa and " are average veloities and standard deviations of both phases respetively, is the probability of bubble existene. These five variables, ua, ill, aa, O" and. are alulated numerially by the least squares method. An example of the probability density funtion obtained from the UVP data is representatively shown in Fig. 7. t is diffiult to derive the genuine information under high void fration onditions beause the multiple refletion of ultrasoni pulse is indued by bubbles. Moreover, very little information on bubble veloities an be obtained at very low void frations. To solve these problems, several data proessing programs were developed in this work< 5 l. These programs are desribed below: Sine bubbly ounterurrent flows are dealt with in this work, positive veloity data means bubble upflow veloity and negative veloity data does water downward one. The PROC1 ode is a program whih selets positive veloity data before the position where the maximum bubble veloity appears and uts off them behind the position in order to eliminate wrong data indued by a multiple refletion under onditions of high void frations. Treating the data shown in Fig. 7 with this program, the results are given in Fig. 8(a). The PROC2 ode is another program to pik out only the maximum bubble veloity in one profile as bubble veloity data and uts off other positive veloity data. Figure 8(b) illustl ates the results treated with this program. The PROC3 ode is another program to selet only profiles inluding bubble veloities and is effetive under onditions of very low void frations. The results obtained by this program is shown in Fig. 8(). t is seen from Figs. 7 and 8(a), (b) and () that the mixture veloity of both phases in the probability density funtion does not hange even if the original data are treated with the PROC1, PROC2 and PROC3 odes. Therefore, these programs were used only Fig. 7 2 "iii Ql 'C 1 : _gj e a.. Veloity (m/s) A typial experimental result of the probability density funtion to get the average veloity of gas phase and the standard deviation of gas phase in the probability density funtion of bubble veloity. The FREQUENCY ode is a program whih analyzes pulse height of measured veloities to give a veloity probability distribution at eah point from the results for a measured profile. Sine zero veloity annot be distinguished from the data when the refletion wave is not reeived, the probability of the veloity number of is substituted by averaging the values for the veloity numbers of -1 and 1. The SUM ode sums every probability distribution alulated by the FREQUENCY ode through one experimental ondition. The VELOC TY ode piks up a probability distribution at one point from the data obtained by the SUM ode and onverts the loation and veloity numbers into the real position and veloity as shown in Fig. 7. The SEPARATE ode is used to alulate those variables in the probability density funtion. Those variables are alulated numerially and iteratively by the least squares method< 5 l. :fl 2.;:! (/) Ql u 1 :a.. :fl 2.;:! :. - (/) Q) u 1 :a!. '.. o.j s... " :fl 2 2 "iii Q) u Veloity (m/s) Veloity {m/s) Veloity (m/s) :a!... (a) The PROCl ode (b) The PROC2 ode () The PROC3 ode Fig. 8 The probability density funtion treated by the data proessing odes VOL. 34, NO. 8, AUGUST 1997

7 788 M. ARTOM et al.. RESULTS AND DSCUSSON 1. Veloity Profiles of Both Phases Veloity profiles of both phases in the hannel were measured with the UVP. The experimental results are shown in Fig. 9. Sine it is neessary to orret the positions near the wall with signifiant auray due to an ultrasoni beam diameter of 5 mm, they are orreted in the figure. Water veloities beome higher toward the enter of the hannel from the wall in the same tendeny as a water single phase flow. n ontrast with this, bubble veloities are higher near the wall than those in the ore. Relative veloity, whih means a differene between bubble and water veloities, are shown in Fig. 1. t an be seen from Fig. 9 that the flow harateristis of bubbly ounterurrent flows is strongly dependent on the water veloity whih is a ontinuous phase and that a bubble rising veloity is indued by the differene between the buoyany and interfaial drag fore. As a result, in fully developed bubbly ounterurrent flow, it an be regarded statistially that bubble diameters are almost same so that the relative veloities are nearly equal in the whole hannel. Sine air flow rates are muh lower than water ones under the present onditions, the veloity profiles.2.1 g g a; >-.1 Air Water li'l ltl!ll ll ll ltl ig(m/s) jl(m/s).327 (> -.6 (> Distane from a wall (mm) Fig. 9 Veloity profiles of both phases of both phases are sarely varied even if an air flow rate inreases. With an inrease in a water flow rate, water veloities beome higher but their profiles are hardly influened. n addition, the relative veloities are almost onstant in the whole hannel and are sarely varied with hanges in both water and air flow rates. 2. Void Fration Profiles The hydrostati head is obtained from the measured differential pressure and average void fration is alulated by (LlP/LlZ)Head = P(a)g + pl(l- (a))g, (6) beause frition loss is negligibly small due to low water flow rates. Sine it was larified in our previous workc 5 l that the threshold brightness, whih identifies the bubble surfae, influenes evaluation of the average bubble diameter and void fration even though it does not affet the number of bubbles, the threshold brightness was alibrated. A omparison of average void frations obtained by the hydrostati head and by the VDP is shown in Fig. 11. The void frations obtained by the VDP agree well with those obtained by the hydrostati head within ±5% error. A bubble diameter is alulated from its volume by assuming that it is spherial. The relationship between average bubble diameters and average void frations is shown in Fig. 12. With an inrease in a water flow rate, an impat pressure at bubble generation nozzles beomes larger and a bubble rising veloity dereases as shown in Fig. 9, so that the average bubble diameter beomes larger. n addition, as an air flow rate inreases, the average bubble diameter inreases beause the air pressure in the bubble generation needles is enlarged. Figure 13 shows the experimental results of void fration profile in referene to air flow rates and water flow rates, respetively. t an be seen from the figure that void fration profile is almost flat in bubbly ounterurrent flows exept for those near the wall. Sine air flow rates are muh lower than water ones under the :::; p.2.1 ig(m/s) (>.418 jl(m/s) (> o Distane from a wall (mm) Fig. 1 Relative veloity profiles 5 Fig. 11 A omparison of average void frations measured by hydrostati head with those by the VDP JOURNAL OF NUCLEAR SCENCE AND TECHi\'OLOGY

8 Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor 789 E'.s E ttl u Q) :.. ::J.. Q) Cl Q) oo j L (m/s) Average void fration ( - ) Fig. 12 Average bubble diameter.4 &.3 if.2.1 il =-.6m/s ig=.195m/s o Single phase flow Bubbly ounterurrent flow o Distane from a wall (mm) Fig. 14 Typial standard deviation profiles of veloity flutuation in both phases.8.6 u ' ;g.4.2 ig(m/s} [;,.418 jl(m/s} [;, Distane from a wall (mm) Fig. 13 Void fration profiles present experimental onditions, water veloity profiles are sarely varied even with a hange in air flow rates. Moreover, bubble veloity is dependent on the water veloity profile as shown in Fig. 9. The void fration is, therefore, enlarged with an inrease in air flow rates. As the water flow rate inreases, the bubble rising veloity is dereased, so that void fration beomes larger. 3. Turbulene ntensity Profile n general, turbulene intensity in a bubbly flow is larger than that in a liquid single phase flow beause bubbles agitate the flow. n this work, turbulene intensity is defined as a standard deviation of water veloity flutuation in a ontinuous phase, a L. The standard deviation profile in the hannel an be alulated from the equation of the probability density funtion of mixture veloity defined by Eqs. (4) and (5). Typial results of a water single phase flow and a bubbly ounterurrent flow are shown in Fig. 14, respetively. n a water downward flow, the turbulene intensity has the maximum value near the wall and beomes lower with going toward the enter of the hannel beause the gradient of longitudinal veloities is higher near the wall. On the other hand, in a bubbly ounterurrent flow, the turbulene intensity be- omes higher with going toward the enter of the hannel and has the maximum value in the enter of the hannel. Flutuation of bubble upflow in the ore is larger than that near the wall beause the restrition of the boundary is weakened. This fat indiates that bubbles agitate the flow in a ontinuous phase. Sine loal veloities were measured not at a point but on the area beause of an ultrasoni beam diameter of 5 mm, the absolute value of the standard deviation in a water phase is not signifiant. Hene, the standard deviation ratio of a bubbly ounterurrent flow to a water single phase flow is seleted as two-phase multiplier of turbulene intensity, <7LTPF <7LSPF The results are shown in Fig. 15. The two-phase multiplier of turbulene intensity beomes larger with going toward the enter of the hannel t an be seen from Fig. 15 that altpf <7LSPF is enhaned with an inrease in air or water flow rates. 4. Distribution Parameter and Drift Veloity The drift flux model proposed by Zuber and Findlay< 6 l is applied widely to two-phase flow analysis odes. The following notations are introdued: Fig. 15 u. a. 8 6 li a. 4 2 ig(m/s) [;,.418 jl(m/s} [;, a o [;, ill Distane from a wall (mm) Turbulent intensity multiplier profiles in bubbly ounterurrent flow VOL. 34, NO. 8, AUGUST 1997

9 79 and (F)= LFdA A ((F)) = (;), where F is a variable and A is a flow hannel ross setion. n the drift flux model, loal drift veloity, Vgj, and the distribution parameter, C, are defined as follows: and v 9 j = ua- j, C = (aj)/(a)(j), (7) (8) (9) (1) where j is superfiial veloity of two-phase mi.xture and defined by j = ja + JL = aua + (1- a)il. (11) Sine it was diffiult to measure veloity profiles of both phases and void fration profile diretly, in many previous works, average void frations were measured under various onditions of (ja) and (j ), and C and V 9 j were determined by ((:/ = C (j) + ((V 9 j)) = Co(j) + V 9 j. (12) n this work, veloity profiles of both phases and void fration profile an be measured. Loal drift veloity is given by V 9 j(y) = [1- a(y)][ua(y)- ul(y)]. {13) Substituting experimental results of u (y), ill(y) and a(y) into Eqs. (1), (11) and (13), the distribution parameters and the drift veloity were alulated diretly from the measured veloity profiles of both phases and void fration profiles, and the results are shown in Figs. 16 and 17, respetively. t an be seen from Fig. 13 that a void fration profile is nearly flat in bubbly ounterurrent flows. Consequently, the distribution param-.5 / Zu.ber & Findlay.3,/.2.1 il =-.6m/s o il =-.12m/s M. ARTOM et al. Fig. 17 Drift veloity of the drift flux model in bubbly ounterurrent flow eter is almost 1.. Substituting the properties of air and water into the orrelation proposed by Zuber and Findlay<6l, V 9 j =.231 m/s. The results shown in Fig. 17 are idential to this value. V. CONCLUSONS The measurement system omposed of an Ultrasoni Veloity Profile Monitor and a Video Data Proessing Unit was applied to fully developed bubbly ounterurrent flows in a vertial retangular hannel and the following insights are larified: (1) Veloity profiles of both phases, void fration profiles and two-phase multiplier profiles of turbulene intensity in the hannel, an average bubble diameter and average void fration an be measured simultaneously with the proposed measurement system. (2) Water downward veloities beome higher with leaving the wall but bubble rising veloities derease beause of higher water veloities. The relative veloities between both phases are sarely varied in the hannel. {3) Void frations in the hannel are almost onstant exept for those near the wall. {4) For bubbly ounterurrent flows, the turbulene intensity is greater than that in liquid single phase flows and inreases with going toward the enter of the hannel from the wall. (5) Conerning the drift flux model for bubbly ounterurrent flows in a vertial retangular hannel, the distribution parameter is 1. and the drift veloity is the same value as proposed for bubbly upflows. [NOMENCLATURE] Fig. 16 il =-.6m/s o il=-.12m/s 2 3 <ig> (m/s) Distribution parameter of the drift flux model in bubbly ounterurrent flow A: Flow hannel ross setion (mm 2 ) Co: Distribution parameter in drift flux model F: Point quantity (F)= JA FdA/A: Average value ((F))= (af)/(a): Weighted mean value g: Aeleration of gravity (m/s 2 ) j: Superfiial veloity of two-phase mixture JOURNAL OF NUCLEAR SCENCE AND TECHNOLOGY

10 Measurement System of Bubbly Flow Using Ultrasoni Veloity Profile Monitor 791 (m/s) ja: Superfiial veloity of gas phase (m/s) h: Superfiial veloity of liquid phase (m/s) P: Pressure (Pa) LlP: Pressure drop between the pressure taps (Pa) R: Radius of an ultrasoni beam (mm) S B: Measuring ross setion of an ultrasoni beam (mm 2 ) S: Virtual measuring ross setion of an ultrasoni beam ( mm 2 ) u: Veloity of two-phase mixture (m/s) u: Mean veloity of two-phase mixture (m/s) ua: Mean veloity of gas phase (m/s) ill: Mean veloity of liquid phase (m/s) v gj: Loal drift veloity in drift flux model (m/s) V 9 j: Mean drift veloity in drift flux model (m/s) y: Coordinate along the deep diretion (mm) LlZ: Position differene between the pressure taps (mm) (Greek symbols) a: Loal void fration {3: Angle between the statistial average position and the enter of the ultrasoni beam 7: Angle between the virtual average position and the enter of the ultrasoni beam e: Probability of bubble existene 8: Angle of transduer to the flow diretion pa: Density of gas phase (kgjm 3 ) PL: Density of liquid phase (kg/m 3 ) ua: Standard deviation of gas phase (m/s) UL: Standard deviation of liquid phase (m/s) ULSPF: Standard deviation of water single phase flow (m/s) ULTPF: Standard deviation of liquid phase in two-phase flow (m/s) ACKNOWLEDGMENT This work was performed at the Tokyo nstitute of Tehnology in ollaboration with the Tokyo Eletri Power Company and the Paul Sherrer nstitut. -REFERENCES- (1) Tower, S. N., et al.: Nul. Eng. Des., 19, (1988). (2) Dunan, J. D.: Nul. Eng. Des., 19, (1988). (3) Liles, D. R., et al.: NUREG/CR-665, (1979). (4) Ransom, V. H., et al.: NUREG/CR-1827, (1981). (5) Aritomi, M., et al.: J. Nul. Si Tehno!., 33, (1996). (6) Zuber, N., Findlay, A.: Trans. ASME, J. Heat Transfer, 87, (1965). VOL. 34, NO. 8, AUGUST 1997